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What Are the Functions of Tinplate Inner Coating

2021-03-02/in Blog /by yixin

What are the functions of tinplate inner coating?

Tips for making tinplate lids

  • Coating purpose and requirements

Tinned plate, chrome plated and aluminum alloy thin plate made of cans are susceptible to corrosion and cause the contents to deteriorate. Therefore, most food cans require coatings inside the cans. Different food cans have different coating requirements.

1.Purpose of coating

  • Certain anthocyanin-containing fruits, such as strawberries, cherries, and bayberry, use general coating material to prevent anthocyanins from corroding cans and contents from fading due to tin reduction.
  • Steamed fish and luncheon meat are easy to stick to the cans. The coating containing anti-sticking agent makes the contents easy to pour out and keep the shape complete and beautiful.
  • The acidic tomato sauce and pickled cucumber adopt acid-resistant paint to prevent acid corrosion of the cans and ensure that the canned food has a certain shelf life.
  • Protein-rich aquatic products, poultry and meat cans use anti-sulfur coatings to prevent sulfidation corrosion caused by thermal decomposition of proteins, such as vulcanization spots and iron sulfide.
  • Canned beer coating material is (spraying after weaving) to eliminate pores and prevent iron ions from dissolving, which affects the flavor and transparency of beer.

2.Coating requirements

  • The coating should be non-toxic after film formation, without affecting the flavor and color of the contents.
  • The coating material has good storage stability.
  • Convenient construction, simple operation, and a good coating film can be formed after drying.
  • The coating material and solvent price are cheap.
  • After sterilization of the canned product, the coating film will not change color, soften and fall off.
  • The coating has good adhesion after film formation, has the required hardness, punch resistance and solder heat resistance, etc., which can meet the requirements of can making process.
  • After the coating film is formed, it can effectively prevent the contents from corroding the cans.

The selection of can lids making equipment should first consider product specifications, output scale, quality requirements, followed by is equipment costs, labor costs, operating costs, plant conditions and other factors.

Generally speaking, for the production of metal covers with few specifications and varieties, large output, and high quality requirements, equipment with high production efficiency and high degree of automation should be selected, such as various types of multi-function combined machines configured as automatic production lines. Due to the small specifications, it is not necessary to change molds and debugging equipment frequently, and it is easy to take advantage of the large-scale production of high-speed automatic production lines to avoid the damage caused by the handling of semi-finished products in the semi-automatic production process. At present, more advanced lid-making equipment can be provided in China, such as corrugated plate shearing machine, double-head automatic punching machine, glue injection drying combined machine, etc. For the production of special-shaped lids with quality requirements, it is best to choose a full lids curl machine to improve the sealing quality. The small size special-shaped cover can be directly selected the automatic curl & glue lining combined machine.The large-size special-shaped cover lining machine is relatively in low production speed. So, For large-size lids lining can use multi-gun semi-automatic lining machine or automatic lining machine. The dryer can be preferred to use a vertical dryer, and its drying quality is better than that of tunnel dryer. For products with many specifications and a lack of large quantity demand, and the production of metal covers with general quality requirements, you can consider choosing multiple semi-automatic stand-alone equipment.On the one hand, you can reduce the number of mold replacements and machine adjustments.On the other hand, you can also reduce the equipment. Investment costs. The rounded edge of the special-shaped cover can be considered to use half-curl or full-curl. As far as possible, the glue injection should not use the printing glue that is facing elimination. The tunnel dryer is suitable for any size and shape of metal cover, but it covers a large area and has high energy consumption. The drying quality is not as good as the vertical dryer, and it needs manual loading and unloading. The aluminum easy-open cover has fewer varieties and specifications, but the output is extremely large, so it requires a high-speed large-scale automatic production line, which is not yet available in China. The current demand for tinplate full opening is relatively small. The production capacity of domestic production lines has reached more than 80 pieces / min. The product quality also meets the requirements for use. Compared with similar foreign products, the price is low and should be preferred.

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Quality Control of Welds and Repair Coating

2021-01-28/in Blog /by yixin

1. The main factors affecting the quality of welds
Resistance welding uses the thermal effect of current, that is, when the current passes through two metal plates to be welded, they are melted due to the high heat generated by the resistance on the welding circuit, and combined by pressure and cooling. Welding resistance consists of two parts: the contact resistance between the metal plates and the bulk resistance of the metal plates themselves. Therefore, in order to obtain a good weld, the contact resistance should be reduced and the bulk resistance of the material should be increased.
To control the weld quality, the following five basic parameters should be adjusted: welding resistance, welding pressure, overlap amount, welding speed, and another variable factor-tinplate. These factors will determine the pitch of the weld, the degree of melting, the shape and microstructure of the weld. These parameters are related to each other. When a parameter changes, the welding conditions must be reset.
(1) The relationship between welding speed and welding current
When other conditions remain unchanged, in order to obtain a good weld, the set welding speed and welding current should make the iron sheet melt well and the weld joints are connected. When the welding speed increases, the current must be relatively increased. When the welding speed is too low, it is easy to cause the iron sheet to overheat. At this time, the cooling speed of the solder joint is slower than the shrinkage speed of the iron sheet, so a large hole will be formed at the welding joint. On the contrary, when the welding speed is too high, it is easy to form a phenomenon that the solder joints are not connected. And because the iron sheet is not heated enough, elongated holes or soldering are formed between the iron sheets.
(2) The relationship between welding pressure and welding current
The surface of the tinplate is a good conductive metal with low resistance, and the tin has a very low hardness and is easily deformed under pressure, which greatly reduces the welding surface resistance and is easy to weld. The welding current increases with the increase of welding pressure. The reason is that the higher the welding pressure, the larger the contact area of tinplate and the smaller the contact resistance on the surface. The current required for welding should increase accordingly. The welding pressure should be adjusted in an appropriate range. When the pressure is too low, the fillet formed by welding will be higher, which will bring difficulties in repainting; on the contrary, when the welding pressure is high. It is easy to get a flat weld.
(3) The relationship between overlap and welding current
A large amount of overlap requires more welding heat, and the welding current increases as the amount of overlap increases. Under the setting welding conditions, when the overlap amount is larger than the normal value, the area covered by the same welding pressure increases, resulting in a decrease in welding current density and a slight increase in contact resistance. As a result, the welding heat is insufficient and the cold welding is caused. on the other hand, the decrease in the amount of overlap will easily cause the phenomenon of over welding and extrusion.
(4) The charateristic of tin plate on welding
1. The amount of tin plating
The amount of tinplate has an impact on the quality of the weld. Althoughit is a good conductor,if the contact resistance of layer of tinplate is smaller, but if the amount of tin plating is too small (the amount of tin plating <0.5g/m2), the alloy layer is relatively high because the surface contact resistance of the alloy layer is large , It is not conductive to welding quality. Especially for the same batch of iron, but the alloy layer has a large variation range and the amount of alloy tin is too high, cold welding is likely to occur under the same set conditions. For tinplate with high tin plating, the solder joint pitch obtained at the same welding current is smaller than that with low tin plating. Therefore, to achieve a good weld, the welding speed must be reduced. In addition, if the welding current is too large, when the iron sheet is welded and melted, tin will infiltrate along the grain boundaries of the iron, which may cause transcrystalline corrosion for some foods after canning.

2. Thickness
The thickness of the tinplate has an influence on the adjustment of welding parameters, especially when welding with a high-speed. When the thickness of the tinplate increases, the welding current required is higher, and the upper and lower limits of the welding conditions also decrease as the iron sheet increases.
3. Hardness
The setting of the welding current is related to the hardness of the tinplate. When the hardness of the tinplate increases, the welding current should be reduced accordingly.
Under the setting welding conditions, the variation of the thickness and hardness of the tinplate within the normal range will not affect the welding. However, if the thickness and hardness of the same batch of iron vary greatly, the welding quality will be unstable, resulting in cold welding or over welding. For example, under the setting pressure, when the tinplate hardness increases too much, the surface contact resistance between the two plates increases, and the welding current should be reduced.
4. Steel base material
When the carbon content of the steel base is high, the welder current needs to be increased. In addition, if there are many inclusions in the steel base, spattering points are likely to occur due to the increase in resistance during welding.

In a word, when producing different types of empty cans, or when changing the type of tinplate. It is necessary to reset the new welding conditions.
Second, the main factors affecting the quality of the coating film
After welding, the original protective tin layer of the tinplate has been completely removed, and only the iron of the substrate is stored in this part. Therefore, it must be covered with a polymer organic coating film to avoid corrosion and discoloration of contents after filling with the contact between the iron and the contents.
(1) Paint type
coatings can be divided into liquid coatings and powder coatings. Various types of coatings have their own characteristics due to their different compositions and coating baking processes,the coating film formed also have their own characteristics.
1. Liquid paint
There are mainly epoxy phenolic, acrylic, polyester, organosol and pigmented coatings, etc. This type of coating is suitable for the weld r coating for most food and beverage cans.
Epoxy phenolic coating has few micropores, excellent chemical resistance and sterilization resistance, but it requires high request for baking heat. When the baking heat is insufficient and , it will be nadequate curing . After sterilization, the coating film will become white, which not only affects the coating performance, but also affect Food safety ; the flexibility and adhesion of the coating film will deteriorate when over-baking, making the coating film intolerant to mechanical processing and easy to crack.
Acrylic and polyester coatings have excellent adhesion, flexibility, chemical resistance, and sterilization resistance. However, acrylic coatings are easy to absorb the color of the content and are not very resistant to vulcanization.
The biggest feature of organosol coatings is the high solid content, the ability to form a thicker film on the weld, it is not easy to produce bubbles, and it has good coverage. It has excellent flexibility and resistance to mechanical processing. In addition, it baking heat request is lower than other coatings; but organosol coatings have poor permeability resistance and are easy to vulcanization corrosion, so they are not suitable for sulfur-containing foods.

Pigment-containing coatings are usually made by adding titanium dioxide or aluminum powder to organosol, epoxy or polyester coatings. The purpose is to mask the corrosion spots under the film, so it is suitable for welding of sulfur-containing foods such as luncheon meat cans’ welding. coating etc.
2. Powder coating
The powder coating can form a thick and complete coating film to provide the most complete protection for the weld. At the same time, the coating has no problems of solvent escape and environmental pollution during processing. It has been widely used in food and beverage cans with high corrosion resistance requirements.
Powder coatings can be divided into two types: thermoplastic coatings and thermosetting coatings. The main components of thermoplastic coatings are polyester powder, titanium dioxide, barium sulfate and so on. Its film formation is only a simple melting process, so when the full tank is baked after spraying, when the temperature reaches the melting point of the powder coating, the coating film will melt again. The coating is characterized by excellent flexibility and resistance to various mechanical processing; but its chemical resistance is worse than that of thermosetting coatings, and it is easy to absorb the color of food. Its adhesion to the original color is lower than that to the weld. Therefore, the shape of the coating is like the arch of a bridge. The main component of thermosetting coatings is epoxy/polyester, which is different from thermoplastic powder coatings. The pre-polymer resin is heated and cured into a film. The thickness of the coating film is thinner than that of thermoplastics. It has excellent chemical resistance, but its processability is not as good as thermoplastic coatings. .

(2) coating film thickness
The protective characteristic of the coating film is related to its pore size. The number of micropores of the same type decreases with the increase of the film thickness. For liquid coatings, the thickness of the coating film depends on the solid content (viscosity) and coating amount during construction.
1. Viscosity
The same liquid coating, the higher the viscosity, the higher the solid content, and the better the coverage of the weld. However, the thickness of the coating film requires a long baking time. If the thickness of the coating film is increased per micron, the baking time needs to be increased by 1 second. At the same time, the coating film with high viscosity is easy to produce bubbles during baking, which will affect the micropores of the coating film; on the contrary, when the coating viscosity is low, the coating film is thin and has many micropores and poor protection performance. Therefore, it is necessary to adjust the appropriate construction viscosity to make the coating film have an appropriate thickness, and at the same time prevent the overspray and splash caused by the excessively low or excessively high viscosity, resulting in insufficient baking and curing.
2. Coating amount
In order to obtain a suitable coating film thickness, the coating amount should be controlled. In addition to adjusting the construction viscosity of the coating, attention should be paid to selecting the appropriate nozzle model, adjusting the pressure of the coating pump and the temperature of the coating when spraying. When the roller coating method is adopted, the coating wheels with different surface curves and the adjustment scraper can be selected to control.
Liquid coatings can never form a thick film in the areas where the weld seam needs the most protection, generally only 4-10 microns. This is due to the surface tension effect of the coating. Due to viscosity changes during baking, the paint will flow away from the edge of the weld (fillet) to both sides. The surface of differernt type coating.There is a difference in tension effect. The viscosity of organosol coatings will always increase with the increase of temperature, so it is not easy to cause poor coverage at the edge of the weld. With the increase of temperature, the viscosity of epoxy phenolic coatings first decreases, and then It rises straight again, so when the viscosity drops to the lowest point, the coating will flow to both sides, making the coating film thickness at the edge of the weld much lower than that on both sides.

The film thickness of powder coatings is much thicker than that of liquid coatings. Thermoplastic powder coatings should generally not be less than 40 microns, because only when the thickness of the coating film is greater than 40 microns, the number of micropores drop significantly, but when it is higher than 60 microns The mechanical properties will be worse, and the coating film will be easily broken during processing. The thermosetting powder coating has good compactness, and the thickness of the coating film is generally controlled at 20-60 microns. In addition to the thickness of the film porosity of the coating, it is also related to its density. Controlling the diameter distribution of powder particles can control the thickness and density of the coating film.
(3)Coating film integrity
1. Weld quality
The integrity of the liquid coating film depends largely on the geometry of the weld. For example, the weld has splash points or severe extrusion, and the surface is not smooth. It is impossible to completely cover it with liquid paint; in addition, the thickness of the weld also effect the coating film. If The welding is thicker ,the seam is not easy to cover. Generally, the thickness of the welding seam should be less than 1.5 times the thickness of the plate. For the second cold-rolled iron or iron with high hardness, the thickness of the welding seam is 1.5 to 1.8 times the thickness of the plate. .
Welds made without nitrogen protection will cause poor adhesion of the coating film after the oxide layer, which will cause the coating film to rupture during subsequent flanging, necking, and rolling, which will affect the integrity of the coating film .
Due to the sufficient thickness of powder coating, it can perfectly solve the problem of metal exposure caused by weld defects and provide excellent protection for the weld.
2. Bubble
The unreasonable solvent formulation of the liquid coating will affect the integrity of the coating film. When the liquid coating contains a lot of low-boiling solvents, or the temperature rises too fast during baking, or the welding seam temperature is too high, a large amount of solvent volatilizes during baking, leaving strings of bubbles or micropores in the coating film. This leads to poor coverage and reduces the protective effect of the repair coating on the weld.
(4) Baking and curing
1. the curing process of the coating
The baking and curing of liquid coatings can be roughly divided into the following stages: the coating is first leverl wetted and the empty parts (about 1 to 2 seconds), and then the solvent evaporates to form a gel (should be within 3~ Complete within 5 seconds, otherwise the paint will flow away from the weld), and finally polymerization. The paint must reach the required total heat. It has a great influence on the thickness and characteristic of the coat film. As mentioned earlier, if the bake temperature rises too quickly, bubbles are likely to occur, and if the temperature rises too slow, the peak temperature maintenance time is too short and will cause insufficient curing.
Various coatings have different peak times during baking. Epoxy phenolic coatings take longer than organosols, that is, more heat is required for baking.
The thermoplastic coating in the powder coating is simply melted to form a film during baking, and it has no polymerization reaction; while the thermosetting coating needs to undergo addition polymerization and crosslinking into a polymer compound after prepolymerization without melting, so the baking heat and supplement The characteristic of the coating film is closely related.
2. The effect of curing degree on coating film performance
coatings can show their characteristics only when they are fully baked and cured. Insufficient baking results in many micropores in the coating film, and poor processing resistance. For example, if the thermoplastic powder coating is not baked well, the coating film tends to wrinkle when flanging. Excessive baking will affect adhesion. For example, if epoxy phenolic paint is over-baked, the coating film will be scorched and brittle, and it will easily cause cracking of the coating film at flanging, necking, and rolling. In addition, sufficient cooling after baking also has an important effect on the performance of the coating film. If the thermoplastic powder coating is not quickly cooled to room temperature after the coating is baked, the coating film is likely to crack during flanging. If a cooling device can be added after the oven, the problem of flanging and cracking of the coating film can be avoided.
In one word, in order to ensure the quality of the coating film, that is, less porosity and good processing resistance, the thickness and curing degree of the film must be controlled.

https://tincanmakingmachine.net/wp-content/uploads/2021/01/Quality-control-of-welds-and-repair-coating.jpg 468 1000 yixin https://tincanmakingmachine.net/wp-content/uploads/2021/01/logo.png yixin2021-01-28 16:26:142021-03-02 16:28:05Quality Control of Welds and Repair Coating

The Main Appearance Defects of Sealing and Curling and Their Causes

2021-01-28/in Blog /by yixin

1.Iron tongue: due to poor sealing, smooth tongue protruding at the lower edge of the crimping edge. It can appear at any point along the crimping edge, but usually at the seams, where the body hook and cover hook overlap badly, or the cover hook is insufficient. It is main defect when the iron tougue>1.27 mm

2.” teeth “: usually in the narrow part of the crimping, the cover hook and the body hook are not overlapped, or the overlap is insufficient, and the v shape formed is prominent at the lower edge of the crimping.

3. vertical lip (d): the iron tongue in the joint of the can body is called the vertical lip. See figure 4-28. it is allowed to exist when there is no sharp angle, the width does not exceed 20% of the crimping width, no air leakage

w- crimping width

w1- crimping width of the joint

The possible reasons for the vertical lip of the iron tongue are :(” teeth “)
(1)Long body hook
(2) the first crimping is too loose (first crimping roller shaft wear)
(3)First curling gear wear
(4) body high and low (staggered angle)
(5) Clamping contents during curling (products)
(6) Excessive or uneven amount of glue in the lid
(7) The flanging side of the lid is not suitable
4. Fake roll (fake seal): refers to the folded body hook pressed tightly by the folded cover hook, but not hooked to each other on the connected curling. See Figure 4-29. False rolls are sometimes difficult to find during external inspections, and the curling must be dissected to find them.
The possible reasons are:
(1) The flanging of the body can body is folded or knocked flat
(2) Flanging is mushroom-shaped
(3) Damaged or bent sides of the flanging of the lid
(4) Improper coordination of can body and can lid
(5) The can is not placed on the center of the pressure head

5.Large collapsed edges: The large false seals caused by the body and the lid hooks are not hooked to each other due to the can body flanging or the edge of the lid hook severely collapsing, and there is an obvious can body flanging exposed under the curling. Sometimes due to improper adjustment of the equipment and improper lid feeding, the position of the can lid and the center line of the can body is inaccurate, which can also cause a big collapse. See Figure 4-30.
6. Sharp mouth: The front mouth inside the top of the curl is called the sharp edge. See Figure 4-31. When the sharp edge reaches the level of fracture or has caused the iron sheet to break, it is said to be sharp. See Figure 4-32. At the seam or along the entire circumference of the can lid, it is mainly because the can lid part exceeds the top edge of the indenter due to the force during the rolling. It is usually easier to find by touching it by hand than by visual inspection.
The possible reasons are:
(1) Indenter edge wear
(2) The first or second curling rollers are adjusted too tightly
(3) Groove wear of curling roller
(4) Finished products (products) are clamped in the crimp
(5) Vertical movement of the indenter assembling
(6) The first curling roller and the indenter are not calibrated
(7) Excessive vertical movement of the first curling roller
(8) Too much pressure on the chassis
(9) The can body overlapping is too large
7. Hemming fracture: refers to the double hemming that generally occurs at the overlap of the can body and the outer layer of the hemming is broken. See Figure 4-33. When this happens, corrective measures must be taken immediately.
The possible reasons are:
(1) The curling is too tight
(2) Too much sealant
(3) There is a problem with the tin cover of the can
(4) There are parts worn out or improperly adjusted in the sealing machine
8. Double-line: refers to the double-line rolling mark made by the roller on the lower edge of the curl. Anything that does not affect the sealing structure and does not significantly damage the tin layer is allowed.
9. Skip seal or skip: Refers to the phenomenon that the curling edge is thick at the seam and the roller bounces when passing the seam, and the curling edge cannot be pressed tightly. After the dissection, obvious bulge can be seen in the cover hook near the seam. See Figure 4-34. When inspecting the curling, both sides of the adjacent seams should be carefully inspected, because this is the key part that causes the curling to crack.
The possible reasons are:
(1) The sealing machine runs too fast
(2) Too much overlap at the seams of the can body
(3) The buffer spring of the second curling roller is not flexible or damaged
(4) The first roller is too tight
10. Incomplete curling (slippage): refers to the phenomenon of partial curling that is not completely compressed due to slipping of the pressure mould or poor rotation of the roller during the sealing process.
The possible reasons are:
(1) Improper pressure on the support chassis (spring)
(2) The indenter does not match the can lid (the indenter is too small and the arc does not match)
(3) Indenter wear
(4) The curling roller is not flexible (cannot rotate freely)
(5) There is grease on the indenter
(6) Excessive vertical movement of the indenter shaft
(7) Improper adjustment (the distance between the indenter and the support chassis is too high)
(8) The lower edge of the first and second rollers contact the can body
11. Warping of can body (angle)
Warping of the can body is the warping or twisting of the can directly under the sealed curling. It usually occurs near the overlap of the seam, but in serious cases, it will appear along the whole circumference of the can body.
The possible reasons are:
(1) Too much pressure on the chassis
(2) Pressure mould is too low
12, the mis-angle of the can body
The can body plate is not cut at right angles and square, resulting in uneven overlap , as shown in Figure 4-37.
13. Improper body cover match
“Improper body lid match” sometimes refers to the can lids that are not aligned. The can body and bottom lid are not aligned with each other in the sealing machine and cannot match together. Therefore, the cans with the curling edge will have partial body lids that are not complete hooking.
14. countersink too deep
Too deep countersink occurs when its size exceeds the operating limit, and causes the length of the cover hook and overlap to shorten (Figure 4-38).
The possible causes are:
(1) The chassis pressure is too high
(2) The height of the pin gauge is insufficient (short), that is, the distance between the chassis and the indenter is too small
(3) The indenter is not completely embedded in the can lid
(4) The flange of the indenter is too thick.
(5) Improper adjustment of the first roller and the indenter to each other (the roller is too high).
15. Mushroom-shaped flanging Figure 4-39
The mushroom-shaped flanging is the excessive flanging of the can body and causes the hook to grow. This can only be observed by cutting the crimp into a cross section for inspection. The possible reasons are:
Poor handling of the can cover
(1) Excessive flanging.
(2) Damaged by the canning machine.

16 Indenter damage
(1) The indenter damage defect is due to a part of the indenter flange being removed, so that the damaged part loses support for the sealing roller and the curling edge is too loose. The possible reasons are:
(2) Serious damage in the can sealing machine
(3) The gear bites the indenter
(4) Metal fatigue on the flange of the indenter
(5) Pry open the indenter to eliminate the rolling can.
17. Round curling
The top of the normal curling profile is a flat surface (7-shaped), while the round curling is arc-shaped.
Circumferential curling means that the pressure between the indenter and the support chassis is insufficient during the curling process. In addition, the pressure of the first and second rollers is too small, so the gap in the curling is large and the tightness is very likely to be insufficient. If round crimps are found, vacuum and pressure leak testing should generally be conducted for further evaluation.
If the round crimping of the non-leaking can is found during the production process, the sampling frequency should be increased, the changes should be carefully observed, the cause should be traced in time, and improvements should be made.
18. Outflow of glue (rubber overflow): 1) The amount of glue applied is too much; 2) The second roll seal is too strong; 3) The position of the film is improperly coated; 4) The glue is poor and does not adapt to the contents; 5) It doesn’t dry well.
19. Foreign matter involved
20. iron sheet Cracked
21. Outer anti-rust and scratch
The above external defects can be summarized into the following types:
①Deformation of curling, such as sharp edges, sharp mouth, broken curling, vertical lips, “teeth”; ②The body cover hook is not hooked, such as: large sag, false seal (poor fit); ③Not curling Uniformity and unevenness, such as: incomplete crimping, skipping seal; ④Other bad crimping, such as: round crimping, outflow glue, broken iron sheet, external rust-proof scratches, entrapment of foreign objects, crooked cans.

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Common Problems of Weld Repaint

2021-01-28/in Blog /by yixin

Since 1978, with the development of electric resistance welding (Super-WIMA) in the can-making industry, the overlap of can welds has been reduced to 0.4-0.6mm, and lead-free resistance welding tin-plated cans have been widely used For food cans and beverage cans, this transformation greatly improves the overall quality of the can body weld lap. In order to make the can body weld perfect, it is an indispensable process to recoat the weld seam with a protective layer of non-destructive content. The protection and anti-corrosion process of the can body resistance welding seam is also widely used, so that The resistance welding can body is more safe and reliable application.
However, in different situations, different regions, different canned contents and their storage time, the protection and corrosion protection of can body welds, and the quality parameters are also different. Therefore, solving the corrosion of welds is a major issue. Corrosion occurs in different forms. In addition, the effects of the canned sterilization process and carbonated beverages, such as beer and soft drinks, have brought many technical problems to the weld coating process.
The welding seam protection and anti-corrosion process is mainly divided into two processes. The welding seam coating process and the coating drying curing process are divided into liquid coating technology and powder coating technology in the coating process, The coating thickness and protective effect are also different, see Figure 3-51, Figure 3-52 and Figure 3-53.
Figure 3-51

Figure 3-51 The coating of liquid paint, the coating is thin, especially in the area of welding seam

Figure 3-52

Figure 3-52 coating of thermosetting powder coating, thicker coating

Figure 3-53

Figure 3-53 The patch layer of thermoplastic powder coating, the thickest layer

1. Frequent questions about the drying and curing process of liquid coating strip

① Deviation of recoating strip. Due to the poor adjustment of the can conveyor belt or the poor connection between the two conveyor belts, the can body rotates on the conveyor belt, so that the nozzle or the inner roller coating wheel cannot be aligned with the welding seam, causing the recoating strip to deviate (see Figure 3-87), The coating protection effect is not good. Solution: patiently adjust the conveyor belt so that the can body moves smoothly on the conveyor belt without rotation.

Figure 3-87

Figure 3-87 Recoating strip is off-center
② There are 4 abnormal situations.

Figure 3-88

Figure 3-88 Abnormal coating film after curing
A. The coating is too thin after curing: The reason is, for example, the wet coating thickness is normal when recoating, the coating is thin after curing, and the solid content of the liquid coating is too low, so the solid content of the coating should be increased. Or increase paint viscosity. For roller coating, choose a thick repainting curve roller. For spraying, appropriately increase the pressure of the paint pump and the temperature of the paint heater, or change the nozzle to a larger size. Or slow down the speed of the can conveyor.

B The coating is porous after curing (micro-bubbles): The reason is that the drying and curing speed is too fast, the coating boils, and bubbles and blister-type micro-pores are generated. Solution: slow down the curing speed, that is, slow down the speed of the conveyor belt of the drying curing equipment, reduce the temperature of the heating oven in the front section of the heating curing device, so that the heating temperature gradually rises.

C The coating has bubbles: When the solvent has not evaporated, or when spraying, the bubbles generated by the coating, if the curing speed is too fast, the surface coating begins to cure, but the solvent continues to volatilize or the bubbles from the recoat are not eliminated. Air bubbles and small holes are left on the surface of the cured coating. In addition, if the wrong solvent is applied, such as thinner water or banana water for ordinary paint, since these solvents evaporate slowly, the liquid recoating strip will easily have bubbles when it is cured, and it is difficult to eliminate, as shown in Figure 3-89 .

Figure 3-89

Figure 3-89 Air bubbles formed on the coating surface
Sometimes bubbles are formed on the weld, as shown in Figure 3-90. The reason is that the welding seam is too hot and the viscosity of the paint is a bit high. Solution: add a cooling device after welding, or reduce the viscosity a little.

Figure 3-90

Figure 3-90 Bubbles formed on the weld

D. Poor coverage of the weld area at the edge of the tinplate: The quality of the welding has a great influence on the protection of the liquid coating. The cause and solution of this failure: i The welding seam is splashed, slightly increase the welding seam overlap amount, or reduce the welding current, so as to make the welding seam smooth, which is conducive to the welding seam coating; ii the paint is not enough in viscosity. Solution: increase the viscosity of the paint and increase the paint temperature accordingly.

③ Overspray. There are some oversprayed paints on the outside of the weld recoating strip, which will affect the appearance (see Figure 3-91 and Figure 3-92). Sometimes these coatings are not easy to cure. Reasons and solutions: i The viscosity of the liquid paint is too low, so the viscosity should be increased; ii The nozzle model is wrong, that is, the nozzle width of the selected nozzle model is too narrow, which causes the distance between the nozzle and the weld to be too far, so that the atomized paint Scattered to the rest of the tank. Choose the correct nozzle model.

Figure 3-91

Figure 3-91 Overspray

Figure 3-92

Figure 3-92 The paint has splash points in the tank

④ Splashing. The coating strip is too thin, and there are splashes at both ends (see Figure 3-93). Reasons and solutions: i The spraying pressure is too low or the pipeline is blocked, increase the pressure. Check the pipeline, ii The viscosity of the paint is too high. The viscosity should be reduced and the paint heater temperature should be increased i; ii The nozzle is too close to the can body. The nozzle should be raised.

Figure 3-93

Figure 3-93 Splashing

2. Re-coating of welded seam powder coating

To obtain the best microporous weld repair coating, a thick protective coating layer is required. However, during the drying and curing process of the liquid coating, the thick liquid coating layer is prone to air bubbles. This phenomenon can only be achieved by application Powder coating to solve.

To achieve the best quality effect of the welding seam paint protection layer, not only depends on the coating method of the paint, the welding effect also plays an important role, such as: when the welding frequency is low, or the application of low tin iron, chrome-plated iron, etc. splashing and rough surface on the weld, as well as the existence of the weld oxide layer, make the coating layer easy to be destroyed in the subsequent processes such as flanging, necking, and rolling. In addition, the thickness of the tinplate, the quality of the slitting, etc. will bring great problems to the liquid coating process.

Although the welding equipment has made many improvements to make the weld perfect, such as increasing the welding frequency, adding auxiliary welding wheels, etc., to reduce the spatter of the inner weld, and increase the weld anaerobic protection device, but the application of liquid coatings, you must think There are still some difficulties to achieve perfect protection, especially as the welding speed increases. In addition, the powder coating process has very little air pollution during the application process. Powder coatings can also cover welding spatter points (see Figure 3-94). During the application of powder coatings, the coatings between the cans can almost be completely recycled for reuse, with less waste. Therefore, in order to achieve perfect welding seam protection, the powder coating coating process has been applied by more and more Chinese manufacturers in recent years.

Figure 3-94

Figure 3-94 Welding spatter is covered by powder coating

The advantages of powder coating are well known, but it also has certain inconveniences. The powder inlet pipe and the powder return pipe of powder coating must be fixed on the welding arm of the welding machine, and the can body can still pass through the outside. Because the powder tube is relatively thick, the outer diameter is generally 6~8mm. When making D52 can type, a special welding arm is needed to fix the powder tube on the welding arm and let the D52 can type (202) pass. The cost of canning has increased.

3. Common problems of powder coating

(1) After the powder coating enters the full spraying process and curing in a large oven, the powder coating strip will be crinkle and uneven (see Figure 3-109). Generally, there is this phenomenon in thermoplastic powder coatings, that is, the melting point of thermoplastic powder coatings is low. During the curing process of full spray coatings, after the second melting, they are solidified. Because the thermal expansion coefficient is different from that of full spray coatings, When shrinking, crinkles are formed. The solution to this method can appropriately lower the oven temperature of the full spray coating, thereby reducing the secondary melting of the thermoplastic powder coating. If it still can’t be solved, only change to other types of powder coatings, that is, the coating contains thermosetting coating components to increase the melting point of the second melting of the coating.

Figure 3-109

Figure 3-109 crinkle of powder coating strip
(2) After the rolling and flanging, the powder coating strip is broken (see Figure 3-110). The reason is that the elasticity of the coating strip is not enough. The solution: If it is a thermoplastic coating, it may be over-dried. You can appropriately reduce the drying temperature or shorten the time, and accelerate the cooling after drying and curing to increase the elasticity of the coating strip. If it is a thermosetting powder coating or a coating containing more thermosetting components, the temperature should be appropriately increased to increase the adhesion of the coating strip.

Figure 3-110

Figure 3-110 The powder coating strip breaks after rolling
(3) After the thermoplastic powder coating is baked and cured, do a peeling test. If the coating peels off too much (see Figure 3-111), more than 5mm, or the adhesion test of the thermosetting coating does not work well, then Increase the baking curing temperature to improve the adhesion of the coating strip.

In addition, if after baking and curing, the adhesion of the powder coating layer is very poor, and large pieces fall off from the overlap with the primer coating (yellow printing iron), and the improvement of baking does not work, then it may be the primer (yellow iron printing) There is too much wax in the solvent of the paint. After the primer paint is baked, the wax precipitates and settles on the surface of the primer, which causes the adhesion of the powder coating to decrease. Solution: Improve the solvent of primer paint. Or before powder re-coating, use a strong organic solvent to scrub the weld re-coated area to remove the wax layer to improve adhesion.

Figure 3-111

Figure 3-111 Peel test, the coating is peeled off too much, exceeding 5mm, the curing temperature is not enough
(4) Before the powder coating is baked and cured, the powder coating strip is uneven and crinkled, especially the powder coating matched with a low-speed welding machine. This phenomenon is that the charging voltage is too high, and the powder forms a phenomenon of homosexual repulsion. It is necessary to appropriately reduce the electrostatic high voltage. In addition, this phenomenon may also occur if the powder has been stored for too long (far beyond the supplier’s shelf life).

(5) After powder coating, before baking and curing, the powder on the conveyor belt can easily fall onto the can wall. The electrostatic voltage can be appropriately adjusted to increase the powder’s adsorption capacity. At the same time, check whether the can body has collisions, jitters and jumps during the conveying process, try to make the can body move smoothly and reduce the falling of powder.

(6) After the powder is sprayed, the powder coating becomes thinner, sometimes accompanied by shaking, and the powder spraying pipe is blocked. Unblock the powder spray tube as soon as possible, or replace with a new tube. When installing the powder tube to the welding arm, pay special attention to the powder tube not to touch the copper wire guide wheel, and to keep the powder tube working at room temperature, otherwise, if the molten powder is blocked in the tube, it will be difficult to dredge.

(7) The powder coating on both ends of the can is too thick, which affects the sealing effect of the subsequent process. The thickness of the coating should be reduced, or the suction of the external powder suction port on the OHC should be increased to make both ends of the coating thinner.

(8) When powder coatings are stored for a long time or are repeatedly used during production, the performance of powder coatings will change, such as charging performance, fluidization fluidity, and some dirty dust mixed in it, so in production Attention should be paid. In addition, powder coatings generally contain a certain amount of moisture (0.6%~0.8%), so that the fluidity of powder coatings will be better. If it loses due moisture, the fluidity of the powder will become worse, and the powder coating will easily It clumps and looks like damp. Therefore, a moisture test must be carried out. If the difference is too large, add water appropriately to make it contain the normal amount of water. Then operate according to the methods and parameters provided by the powder coating supplier.

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How to Judge the Quality of Cans

2021-01-28/in Blog /by yixin

After sterilization and cooling, canned food must be inspected after heat preservation or storage to measure whether its indicators meet the standards and commodity requirements, and determine the quality and grade of finished products. There are many inspection items and methods. Here are a few.

1. Appearance inspection: the key point of appearance inspection is to check the double seaming state, observe whether the double seaming is closely combined, whether there are tongue, teeth, crinkling and broken, and check whether the can body seam is normal. The size of double seaming can be measured with special calipers for cans. If there are air leakage micropores in the double seaming, which can not be seen with naked eyes, it can be checked with warm water or with pressure leak detector. The inspection of the can bottom cover mainly depends on whether it is concave inward. The normal can has a certain degree of vacuum, so the can bottom cover should be concave inward.

2. Heat preservation inspection: if there are microorganisms remaining in canned food due to insufficient sterilization or other reasons, it will grow and propagate at a suitable temperature and make canned food deteriorate. Most spoilage bacteria, except some heat-resistant bacteria, produce gas and make cans expand. According to this principle, the method of heat preservation storage is used to create the optimum temperature for the growth and reproduction of microorganisms, to place it in sufficient time for the growth and reproduction of microorganisms, and to observe whether the bottom cover of the can expands, so as to identify whether the quality of the can is reliable and whether the sterilization is sufficient. This method is called the heat preservation inspection of the can. This is a simple and reliable method for inspection of canned products. But some high acid food, if you ensure the correct operation process, ensure the production of good sanitary conditions, ensure adequate sterilization, can not be heat preservation inspection. At present, most factories have adopted the commercial aseptic sampling heat preservation under the condition that the process hygiene is guaranteed and the sterilization conditions are sufficient, but they only use the whole heat preservation inspection for individual products.

3. Inspection: before labeling, use the inspection stick to knock the bottom cover of all cans after heat preservation or storage to identify the quality of cans. Those with clear sound are normal cans, while those with turbid sound are inflated cans. The causes of turbidity can are as follows

① Due to insufficient exhaust and low vacuum degree of can, it can produce turbid sound. The main reasons for the decrease of vacuum in the can are as follows: the exhaust temperature is low or the time is not enough to reach the specified vacuum; too much food in the can will cause the decrease of vacuum, or too little contents will cause too large top gap in the can, so that the air in the can is not easy to exhaust, which will also cause the decrease of true vacuum. The heat transfer of the can is too slow to reach the full exhaust, and the vacuum will be low If the can is not sealed in time, the temperature of the food in the can will drop and the vacuum degree will be low. For the can which is pre-sealed and then vented, because the pre-sealed curl is too tight, the exhaust channel is blocked, so that the air in the can is difficult to be exhausted; it also causes the vacuum degree to drop, or even no vacuum degree at all.

② Turbid sound caused by incomplete sealing. There are micropores in the edge seam and the can body seam, and the air outside the can invades into the can, resulting in the decrease of vacuum. This phenomenon is often found in turbid can.

③ It is a turbid sound caused by gas generated in the can with good sealing performance. There are two reasons: one is the growth and reproduction of bacteria to produce gas. Due to insufficient heating and sterilization, the growth and reproduction of bacteria remaining in the can make the meat decompose and produce gas, resulting in turbid sound; the other is the chemical action to produce gas, resulting in turbid sound. When the raw material is heated and sterilized, it is easy to be decomposed to produce gas, which reduces the vacuum degree of the can. The lower the freshness, the lower the vacuum.

④ The changes of air temperature and air pressure lead to the decrease of vacuum degree in the can and the turbidity of sound. When the air temperature rises, the vacuum of the can will drop, and when the air pressure is low, the vacuum will also drop.

It is very important to inspect the canned products when they are packaged, and the inspection is based on practical experience, so it is necessary to equip specially trained inspectors and make detailed records of the inspection results.

4. Can vacuum is one of the physical indexes of can quality. The vacuum degree of normal cans is generally 0.024 ~ 0.051mpa, and the vacuum degree of large cans can be lower.

The vacuum degree of tinplate is usually measured directly by vacuum meter. A needle tip is arranged at the lower end of the vacuum meter, and a rubber pad is arranged at the back of the needle tip for sealing. When measuring, hold the vacuum meter with the right hand, align the needle tip with the center of the can cover, press down with force, insert the needle tip into the can, and read out the vacuum meter reading, which is the vacuum degree of the can. This method can also be used for tin covered glass cans.

5. Can opening inspection: to understand the change of the state in the can, it is necessary to open the can for inspection. Here we mainly introduce the sensory inspection and weighing inspection.

(1) Sensory examination includes the following three aspects:

① Histological and morphological examination. Canned meat, poultry and aquatic products should be heated in 80-85 ℃ warm water until the soup dissolves. Canned fruits and vegetables in sugar water should be opened at room temperature. The soup should be filtered first, and then the contents should be gently poured into the white porcelain plate. The arrangement of canned fish, individual vegetables (such as cucumbers, beans, etc.) and meat (such as braised pork, etc.) should be checked before they are poured into the porcelain plate. After pouring into the porcelain plate, first observe its shape and structure, and then gently move it with a glass rod to check whether the tissue is complete, the size and number of blocks. For sugar water fruits, it is necessary to observe whether the size is uniform, and whether there are mechanical injury, shrinkage, cracking, boiling and spots. For canned fish, check whether the spine is exposed, whether the bone and meat are continuous, whether the skin is attached to the fish, and whether the can is stuck, and carefully observe whether there are impurities or inclusions.

The syrup can is heated in 70-80 ℃ warm water until the juice dissolves, and then it is taken out. After the can is opened, the contents are flat tipped into a wire sieve and left standing for 3 minutes; the juice is allowed to sink to the bottom of the sieve, and the number or pieces of the contents are gently counted with a spoon to observe whether the size is uniform and whether there are fruits such as hardening, cracking, boiling and melting.
After the canned jam is opened at room temperature (15-20 ℃), a piece of jam is extracted with a spoon and placed on a dry white porcelain plate. Within 1 minute, the jam body is inspected for dispersion, juice secretion, impurities and seeds.

② Color check. At the same time of tissue and morphology identification, the color of the content was identified, and whether it met the requirements of the standard was observed.

For canned meat and poultry, the collected soup can be injected into a measuring cylinder, and the color and clarity of the soup can be observed after standing for 3 minutes.

For jam and canned tomato paste, pour all the paste into the white porcelain plate, observe whether the color is uniform and whether it meets the standard, and stir the paste thinly with a spoon, depending on whether there are inclusions.

Syrup can can be collected in the porcelain plate to observe whether it is cloudy, whether there is jelly and whether there are a lot of fruit chips and inclusions.

The juice of canned fruits and vegetables in sugar water can be collected in a small beaker to observe whether the juice is clear and transparent, whether there are inclusions and cloudy pulp debris.

After standing in glass container for half an hour, the degree of precipitation, stratification and oil ring were observed.

③ Taste and fragrance inspection. Participants should have normal sense of taste and smell, and cough before taste evaluation.

Take the solid and soup with spoon, first smell it with nose, then smell it to check whether it has the proper flavor.
The canned meat, poultry and aquatic products shall be inspected for the flavor of cooking (such as eggplant juice, spiced pork, braised pork, fried pork, etc.) and auxiliary materials, oyster flavor and odor, and moderate meat quality.

For fruits and vegetables, check whether they have aroma similar to the original fruits and vegetables. For jam, use a spoon to hold a small amount of jam, and chew it slowly in the mouth to evaluate its flavor. For canned fruit juice, you should smell its aroma first, and then taste it (concentrated fruit juice must be flushed to the specified concentration) to evaluate whether it is sour and sweet.

The whole sensory examination time should not exceed 2 hours.

(2) Weighing inspection

① Net content, solid content, liquid content. Clean the outer wall of the tank and weigh the gross amount of the tank. The canned meat, poultry and aquatic products should be heated in 80-100 ℃ hot water for 5-15min to melt the contents (if the contents are weighed after the sealing inspection, it can not be heated any more, but the contents must be melted). Take out the canned meat, poultry and aquatic products, pour the contents onto a wire sieve of known quality, put the sieve on a funnel with a larger diameter, and connect it with a measuring cylinder to collect the juice. Let it stand for 2-5 minutes to make the liquid run out. Clean the empty can with warm water, wipe it dry and weigh it. Then weigh the sieve and the solid together, and calculate the net content, solid content and liquid content respectively.

② Weighing of meat and oil. For canned meat and poultry, the liquid (including soup and oil) leaked through the sieve hole was collected in a 50ml measuring cylinder, maintained at a suitable temperature, and allowed to stand for 5min to separate the soup and oil into two layers. Pour the obtained liquid into another 50ml measuring cylinder which is dry, clean and of known mass until the full scale. Weigh the liquid and the measuring cylinder together, and then calculate the mass of meat, soup and oil respectively.

For Canned aquatic products. For canned fish with oil, collect the liquid (including oil and water) leaked through the sieve hole into a 100ml measuring cylinder, maintain the appropriate temperature, stand for 5min, make the oil and water into two layers, and read the ml of the water layer. The total ml minus the ml of water layer is the ml of oil layer. The quality of oil is obtained by multiplying ml of oil layer by oil density of 0.9. For canned fish with tomato juice, because all the juice leaked through the sieve hole is banru juice, the net weight minus the weight of the fish on the sieve is the quality of tomato juice.

For canned fruits and vegetables, the quality of the pulp or vegetables on the sieve is the quality of all the pulp or vegetables. However, in canned vegetables with ingredients, the weight of small ingredients must be subtracted from the weight of vegetables.

(3) Inspection of tank inner wall.

After opening the tank, clean the inner wall and observe whether the tin coating on the tank body and bottom cover is eroded, peeled and exposed due to acid or other reasons; observe whether the coating layer is corroded, discolored and peeled; whether there are rust spots and iron sulfide exceeding the requirements; and whether there is rubber flow in the tank.

(4) Chemical inspection shall be carried out according to corresponding standards.

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Double Crimping Structure and the Name of Each Part

2021-01-28/in Blog /by yixin

1. The name of each part of the first curling
1. The thickness of the first curling (Tc)
The thickness of the first curling refers to the thickness of the curling section after the can lid and the body are fitted, and the first rolling wheel is crimped to complete the first curling.
The thickness (Tc) of the first curling edge is affected by the size of the can lid’s round edge, the arc shape, the first curling roller groove and the pressure factors.
Tc=3tc+2tb+G′
tc: Thickness of iron for can lid
tb: Thickness of iron for can body
G’: The total thickness of the internal gaps of the first curling (usually 0.8-1.00mm, depending on the first curling groove shape, degree of newness or CH value)
Tc is usually controlled at 1.95-2.11mm

Figure 4-20
Figure 4-20 first step rolling
2. Width of first curling (Wc)
The width of the first channel curling refers to the width of the curling section after the completion of the curling
The curling width of the first track is affected by the size, shape, thickness of the iron sheet and the width of the first curling roller groove, etc., and it is usually controlled at 2.34 to 2.77mm. If it exceeds too much, the reason must be investigated.
Two
2. The name of each part of the second hemming

Figure 4-21

Figure 4-21 Schematic diagram of double crimping structure

1. Hemming thickness (T): the measured maximum size of each layer of iron in the hemming.
The curling thickness T consists of the thickness of the three-layer can lid and the two-layer can body. It is not parallel to the can body and forms an oblique angle of about 4°. It will be affected by the oblique angle of the outer edge of the indenter.
To
The curling thickness is usually affected by the groove shape of the second roller, the pressure of the second roller, the thickness and hardness of the tinned sheet, the type of sealing film and the amount of coating and other factors. The curling thickness T can be calculated by the following formula:
T=3tc+2tb + G (g1+g2+g3 + g4)
In the formula: tc is the thickness of the iron used for the can lid and Tb is the thickness of the iron used for the can body

G=g1+g2+g3 +g4 is the sum of the gaps of the iron sheets inside the crimping, which is approximately in the range of 0.10-0.40mm. Generally, G for φ63.5-φ98.9mm diameter tanks is 0.15mm. According to the actual situation, it is generally considered that G=0.15mm for water-soluble sealant and G=0.10mm for solvent-based sealant.

Regardless of the T value standard, the most important thing is that the thickness of the crimping in the same tank should be the same. No matter which type of tank is in the same tank, except for the joints (three-piece tank), the difference between the T values ​​of any two points must not be greater than 0.08 mm.

2. Hemming width W: parallel to the measured size of the body cover hook

The hemming width is the width of the hemming section after the second seal is completed, also known as the hemming length. There are also standards for the crimping width W, which is generally based on the shape of the can lid forming part, the first track, the second roller groove shape and the crimping pressure, the pressure of the supporting chassis, the body hook and the thickness of the can body and lid, and the wear of the roller groove And other major factors.
Reference formula: W=1.1tc+BH+Lc+1.5tc
Where: tc—the thickness of the iron used for the tank cover BH—the length of the body hook Lc—the bottom gap

Usually W is 0.3-0.4mm larger than Wc, for example WC=2.6mm, W=2.9mm (reference value)
Generally, the curling width>3.05mm (except for φ153 large cans) is considered abnormal. Except for the seams in the same tank, the curling width of any two points must not be greater than 0.13mm, and the curling width must be greater than the countersunk degree C is smaller than 0.13mm, otherwise, when the two rollers are sealed, the lower edge of the curling width will be deformed due to no indenter support and the lower edge part cannot be pressed tightly.

The curling width W is regarded as one of the indexes of the tightness of the curling during the operation. Under the same conditions of the can lid, the body, and the roller, the larger W indicates the tighter the curling. During the sealing process, the usual situation W will become smaller and smaller, that is, the tightness will become looser. Generally, the variation of W can be used to evaluate the change in the tightness of the hemming.

3. Countersunk degree C
The countersunk degree is the depth measured from the top of the crimping to the shoulder blade adjacent to the inner wall of the crimping after the second round of crimping. It is also the position where the can lid and the indenter are engaged during crimping. The countersunk degree is affected by the thickness of the flange of the indenter, the countersunk degree of the can lid, the relative height of the roller and the indenter, the distance between the indenter and the supporting chassis, and the pressure of the supporting chassis. Usually the thickness of the flange of the indenter is 0.1mm deeper than the countersunk of the can lid, and the countersink of the crimping edge after rolling is 0.1mm larger than the thickness of the flange of the indenter (0.13-0.20mm)

Example: The countersunk degree of the can lid is 3.30mm
The thickness of the indenter flange should be 3.40mm
The gap between the second curling roller and the indenter is controlled within 0.10mm
The countersunk degree of the curling edge after the second volume seal C=3.50mm
The countersunk degree of most food cans is between 3.05-3.30mm;
The iron cans for carbonated beverages and beer have a depth of 3.80-4.06mm;
The vast majority of 211-diameter aluminum cans have a countersunk degree between 6.35-6.60mm;
209 iron bottom cans, 209 aluminum bottom cans, C is between 3.05-3.33mm.

There is no absolute standard value for the countersunk degree C, which is determined by the thickness of the indenter and the roller gap, but it must be 0.13mm-0.20mm larger than the crimping width W, and the countersunk degree of any two points in the same tank should not be more than 0.13. mm. …

4. Body hook length (BH)

The body hook length BH comes from the flanging of the can body. It is the length of the can body flanging. It depends on the fit between the lid and the can body, the width of the can body flanging, the radius of the can body flanging R, the pushing force and pressure of the supporting chassis. The distance between the head and the support chassis will change; if BH is too small, tank leakage is likely to occur; if BH is too large, the cover hook will become too small.

There is no absolute standard for body hook length BH. Most tank types use 1.9-2.05mm as the standard. As long as the overlap length and overlap rate can meet the safety sealing requirements, it can be accepted. Therefore, BH needs to increase with the tank type, and W increases. Big and increase. Under good rolling conditions, BH and CH are almost equal.

In the same tank, the difference between the BH values ​​of any two points must not exceed 0.10mm, and the average value of the three tanks must not exceed 0.18mm. The greater the difference between this value, it indicates that the support plate is not parallel to the indenter or there is too much distance.

5. Cover hook length CH

The length of the lid hook CH refers to the bending length of the crimped part of the can lid inside the crimping, and the size of the crimping part of the can lid round edge can be changeable suject to the factor:the first track roller groove type, the first track roller pressure, the round edge arc shape of the can lid, the thickness of the indenter and other factors.

The cover hook length CH is the same as BH. It has different requirements according to the can diameter and varies from the width of the crimping. Generally, CH is 1.80-2.00mm, and usually the cover hook length CH must not be less than 1.65mm.

6. Cover hook gap (Upper gap) Uc, body hook gap (lower gap) Lc

The cover hook gap Uc and the body hook gap Lc are expected to be smaller in general cans. This is because the sealing film located in the crimping part moves to the crimping gap due to the pressure during the crimping process. Therefore, if Uc and Lc are too large, the sealing film will move to the gap and gather, instead of being firm, compressed, and isolated between the plates, resulting in poor sealing effect.

The Uc and Lc values ​​increase mainly due to insufficient curling of the first track, excessive pressure on the second roller, and the lower jaw of the roller to cause the CH curl to sag. Compared to the hook groove of the first roller, the second roller has passed the hook groove. High, also due to the second curling rollers to make the CH curling droop, BH or CH is smaller.

7. Overlapping length OL

Crimping length refers to the length of the overlapping part of BH and CH inside the crimping
It can be approximated by the following formula:
OL=BH+CH+(1.1)tc-W
The splicing length is one of the criteria for judging the sealing performance of the can crimping. Usually, the splicing length <1.00mm is considered unacceptable (micro-sealing<0.76mm is unacceptable).

8. Overlap rate OL%

The overlap rate OL% indicates the degree of overlap between the BH and CH inside the crimp, that is, the percentage of the actual overlap length (a) to the theoretical overlap length (b). It is the most correct to calculate based on the actual measured values ​​of the two parts a and b, and it can also be calculated approximately with the following formula

The overlap rate is also one of the criteria for judging the sealing performance of the can crimping. When the overlap rate is measured with a projector, the OL% must be >55%, and the formula calculation method must be >50%.

9. Tightness TR%
Lid hook wrinkle degree WR% refers to the degree of wrinkles on the inner edge of the lid hook after the crimping is disintegrated. It is visually graded according to the proportion of the wrinkled part to the length of the entire lid hook after the crimping is disintegrated. The number has increased. Tightness TR% and wrinkle WR% are in a corresponding relationship. The smaller the wrinkle, the higher the tightness. The wrinkle adopts ten-level method, and no wrinkle is 0. The tightness TR%=100%, and the wrinkle extends to the full cover. The elder is 10, and the tightness TR%=0%. It is usually judged by combining the flatness of the cover hook section as shown in Figure 4-22.

Figure 4-22
Figure 4-22 Tightness representation

Usually the tightness can be used to judge the sealing degree of the crimping or the adjustment of the sealing machine. When judging, the residual sealant on the lid hook should be removed, and the dent marks left by the removal should be calculated by the degree of wrinkle.
Several expression methods of crimp tightness are shown in Table 4-1.

Table 4-1 Tightness and Wrinkle Degree

10. The complete rate of inner lip, joint cover hook Jr%

For the part pressed out due to poor involvement of the cover hook, the cover hook becomes shorter and droops, which is called the inner drooping lip, as shown in Figure 4-23

Figure 4-23

Figure 4-23 – visual inspection of hook integrity of seam cover
The inner drop lip usually occurs at the joint, because the thick sheet iron at the joint often prevents the curling edge of the can cover from being drawn into the corner radius of the body hook like other parts, resulting in the drop lip. Serious external sagging or too thick welding seam and poor lap joint are enough to cause internal sagging, which will lead to leakage of the tank. After the disassembly of the curling edge, the proportion of the effective cover hook of the inner lip sagging of the cover hook to the width of the whole cover hook is expressed by naked eye or magnifying glass, and each drop is 25%. Due to the reduction of the thickness of the joint, the integrity rate of the joint cover hook is not the main problem Question.
​
11. Indentation
After the edge is disassembled, there is a mark of indenter line (angle change) around the inner edge of the can body (contact part with the cover), which is called pressure mark, and appropriate indentation must be formed. Figure 4-24

Figure 4-24

Figure 4-24 body indentation

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Diagram of Measurement Method for Related Dimensions of Empty Tank

2021-01-28/in Blog /by yixin

The seaming inspection must not only observe the corrugation on the hook part of the cover and measure the external data, but also observe the shape and position of the body hook and cover hook in the seaming cross-section. According to experience, it is absolutely not necessary to take the data measured on the outside of the curling as all the basis for evaluating the quality of the empty can.

In the inspection of double seaming, some items can be evaluated by appearance; some items need to use the corresponding micrometer and measuring instrument; some items need to be dissected and destroyed according to the regulations in order to obtain comprehensive test data and make a complete evaluation.
(1) Inspection position: points 1, 2 and 3 (and lap joint) in Figure 4-40

Figure 4-40

Figure 4-40 – detection position of round can
(2) Inspection tools: seaming micrometer, vernier caliper
(3) Inspection method:

External inspection
① Can height (H)
The vernier caliper is used to make the main ruler parallel to the can body. The height of the can that is measured is accurate to 0.02mm. Generally, the height of the empty can H should be ± 0.30mm, and the height of the large can with stiffeners should be ± 1.00mm.

② Seaming thickness (T):
Place the loosened micrometer on the top of the double seam so that the seam is balanced between the measuring anvil and the measuring shaft screw. Press and hold the micrometer with the index finger instead of the end of the micrometer, so that the anvil surface of the micrometer is at the same oblique angle with the inner side of the countersink, and the fit is good. Rotate the micrometer sleeve clockwise until the seam is tightly clamped between the measuring surface and the measuring screw. The micrometer sleeve should be made to fit, not too tight, and then read correctly. Each seam shall be measured at least three times, and the measured data shall be filled in the corresponding form.

Figure 4-41

Figure 4-41 – measuring the thickness of the seam
③ Seaming width (W)
Hold the micrometer with your thumb to make it stick to the can wall smoothly, turn the micrometer sleeve clockwise until the seam width is tightly clamped between the measuring anvil and the measuring sleeve screw, then read correctly, and fill the measured data in the corresponding table.

④ Burying degree (c)

Figure 4-42

Figure 4-42 – measuring the length of seam
The correct value of C can be read out by placing the measuring instrument on the measuring position. If the curling micrometer is used for measurement, the protruding part of 5mm can be used for measurement, and the result is 5mm – the measured value is the depth of countersink (the protruding part should be placed on a hard plane to correct the error before measurement)

The first step is to put the instrument on the reference plane; the second step is to loosen the fastening screw of the dial and turn the dial knob to make the pointer point to “0”; the third step is to repeat the first step to correct the “0” reading, as shown in figure 4-43.

Measuring steps of countersink:
The first step is to place the countersink measuring instrument on the bottom of the empty can; the second step is to read out the data, that is, the dial reading plus the revolution; fill the data into the corresponding inspection report, as shown in figure 4-44

Figure 4-43

Figure 4-43 “0” point correction of countersink tester

The measuring position of the countersink is shown in figure 4-44.
Figure 4-44
Figure 4-44 – Measurement of countersink

(5) Vertical collimation D (droop of seam at joint): first measure the widest droop Part D at joint, record the value, and then measure the nearest minimum seam width W, with D / W recording ratio, generally ≤ 20%.

Figure 4-45

Fig. 4-45 measuring position of countersink measuring instrument

Internal examination (anatomical examination of seam)
For internal inspection and measurement, magnifying glass, optical projector or video measuring instrument should be used. Each can sealing machine should take samples at least once every two hours according to the regulations. First dissect the samples, and then take measurements or take samples at least four times per shift. When a machine stops running for a long time, it should start again as soon as possible (generally after running for 1-2 minutes, once the machine is hot) Destructive anatomical test was performed.

On site inspection
(1) Tools used: sanitary can opener, flat tongs, crimping micrometer or vernier caliper
(2) Anatomical examination procedure:
① Open a hole at the center of the can surface 6mm (1 / 4 “) from the curling edge with a sanitary can opener. Figure 4-46.

Figure 4-46

Figure 4-46
② Cut and dissect the curl on the opposite side of the seam with an electric rotary saw or a hand saw. See figure 4-47

figure 4-47

Figure 4-47
③ At the place 25.4mm (1 “) away from the sawing cut, use a pair of flat tongs to cut the 6mm bottom cover iron left by the cover along the inner wall of the seaming edge. See Figure 4-48

Figure 4-48

Figure 4-48
⑤ Tap gently along the edge of the can with pliers.
④ It needs skillful operation skills to hold the cover iron with a pair of flat tongs and tear the remaining bottom cover iron along the inner wall of the curling edge. Experience has proved that it is easy to tear the bottom cover iron by using a special pair of flat tongs against the upper edge of the curling edge, and continue to pull until the sawing incision. See figure 4-49

figure 4-49
Figure 4-49

⑥ In a clockwise direction, disconnect 7 / 8 of the body hook from the cover hook of the whole curling edge from the sawing incision. Be careful not to damage the hook body, so that the cover hook is connected to the curling edge and will not fall off. See Figure 4-50

Figure 4-50

Figure 4-50
(3) Visual inspection
1) Cover hook: ① joint cover hook integrity rate (JR%) – Lip drop (ID)
(2) tightness (TR%) – wrinkle (WR%)
(3) appearance defects: skipping seal, false seal, folding, quick opening

2) Body hook: ① indentation pr
② Appearance defects: overlapping width and thickness of joints, welding tailing, edge cracking

(4) Metrological Inspection
1) Body hook (BH): ① measure to 0.02mm with vernier caliper
(2) measure to 0.01mm with seam micrometer
The measured value should be within ± 0.15mm of the standard value.
2) Cover hook (CH): tear off the corrugated side of the curling edge as the cover hook. In order to measure CH accurately, attention should be paid to the tearing action, and the integrity of the cover hook should be maintained to ensure the use of the micrometer. Measure it to 0.01mm with the micrometer and 0.02mm with the vernier caliper, and the measured value should be within ± 0.15mm of the standard value.
3) Overlap length (OL): calculated by formula according to measured data
4) Overlap rate (OL%)

① According to the measured data, the overlap ratio is calculated by the following formula.
Where: BH – body hook width
Ch – hook width
Tc – thickness of iron for bottom cover
TB – thickness of iron for tank body
W-seam width

② Check the calculation table of overlap rate according to the measured data
Steps of table checking:
Before looking up the table, the thickness of iron for can cover (TC), the thickness of iron for can body (TB), the width of cover hook (CH), the width of body hook (BH) and the width of seaming (W) must be measured, and the values of TC + TB, 2TC + TB and BH + CH must be calculated respectively. Look up the table in the following order.
The first step is to find out the value of TC + TB from the top left of the table, and from this column down, find out the value of BH + CH in the column BH + ch.

The second step is to find out the 2TC + TB value from the top right of the table. From this column to the left, the W value is found in the w column. If there is no corresponding value in the table, the latest value can be taken.

Finally, according to the above two values, it extends to the right and down to the column of overlap rate, and the value listed at the intersection is the overlap rate.

For example: TC = 0.23 TB = 0.23 BH = 1.93 ch = 1.90 w = 2.92

According to TC + TB = 0.46, this number is found in the fourth column from the upper left column of the table, and BH + CH = 1.93 + 1.90 = 3.83 is found down.

According to 2TC + TB = 0.69 ≈ 0.70, find this number from the upper right column of the table, and find w = 2.95 to the left.

From the intersection of 3.83 and 2.95, that is, the overlap rate = 54%

2. Quality control: projector inspection method (arbitration method)

(1) Instruments used: ① seam saw; ② seam projector

(2) Methods: first, the opposite point of the can joint was aligned with the seam saw;
② Cut off the sawn seam cross-section;
③ It is placed in the observation port of the projector;
④ Ol (and ol%) were measured directly on the projection screen;
⑤ Tear off the cover hook and visually check the completeness (JR%) and tightness (TR%) of the joint cover hook

(3) And check the following defects
① Body hook too long
The body hook length exceeds the specified size (Fig. 4-51).

Figure 4-51

Figure 4-51 Body hook is too long
The possible reasons are as follows:
1) The tray pressure is too high.
2) Pin gauge (pin gauge adjustment) height is not correct. The position of the seaming chunk to the tray is too low (pin gage) is a gauge specially used to measure the distance between the seaming chunk and the tray during adjustment. In Japan, it is called sealing chunk height gauge (SCH)).
3) Mushroom flanging.
② The hook is too short
The body hook length is less than the specified size (Fig. 4-52).

Figure 4-52

Figure 4-52 The body hook is too short
The possible reasons are as follows
1) Insufficient tray pressure
2) Improper adjustment of pin gauge height. The position adjustment of the seaming chunk to the tray is too high.
3) The first operation roller is too tight.
4) The adjustment of the second operation roller is too loose.
5) The flanging of can body is not good (the flanging is too short).
③ Cover hook too long
The length of the cover hook is greater than the specified size (Fig. 4-53)

Figure 4-53

Figure 4-53 The cover hook is too long
The possible reasons are as follows
1) The first operation seal is adjusted too tightly.
④ Cover hook too short
The hook length is less than the specified size (Fig. 4-54).

Fig. 4-54

Fig. 4-54 – cover hook too short
The possible reasons are as follows
1) The curl edge of the can cover is not up to the requirement.
2) The adjustment of the first operation roller is too loose.
3) The tray pressure is too high.
4) The groove of the first operation roller is worn.
5) countersink is too deep.
⑤ Insufficient overlap length
When the body hook and the cover hook are hooked together, the overlapping length is insufficient when they are less than the specified size (Fig. 4-55).

Figure 4-55

Figure 4-55 – insufficient overlap length
The possible reasons are as follows
1) The flanging of can body is out of specification.
2) The curl edge of the can cover is out of specification.
3) Poor adjustment of sealing machine.
⑥ Too tight seam of the first operation
When the first operation seaming is too tight, the bottom of the seam will be slightly flat throughout the whole length, with sharp edges and bad cover hooks (Fig. 4-56).

Figure 4-56

Figure 4-56 Too tight head curling
The possible reasons are as follows
(1) Improper adjustment of the first operation rollers (too tight).
(2) The groove of the first operation roller is too narrow.
⑦ Too loose curl on the first operation seam.
When the first operation seam is too loose, the lid hook does not contact the can body, and the curling edge of the can lid cannot be fully involved to form a good lid hook and overlapping length (Fig. 4-57).

Figure 4-57

Figure 4-57 Too loose head curling
The possible reasons are as follows
(1) Improper adjustment of the first operation sealing roller.
(2) The profile of the first operation sealing roller is worn.
(3) The roller cam or stick is worn.
(4) Wear of roller pin or bearing.
(5) The groove of the first roller is too wide.

⑧ The second operation seam is too tight
If the pressure of the second operation seam is too high, it will not produce good seam, and it will make the sheet metal extend, so that the width (height or length) of the seaming will increase and the uncoupling or overlapping length will decrease (Fig. 4-58). This kind of seam is easier to crack than that formed by normal pressure seaming. If the secondary seaming is too tight, it will produce sharp edge and extrude the sealant from the seaming. The possible causes are as follows:

(1) Poor adjustment of the second operation rollers.
(2) The thickness of can body and / or cover iron is not proper (too thick).

⑨ The second seam is too loose
If the secondary seaming is too loose, the double seaming with cracks and leaks will occur, because the layers of folded iron sheet are not fully pressed together, and the sealant is not pressed to fill the gap in the curling (Fig. 4-59). The possible reasons are as follows

(1) Poor adjustment of double sealing roller.
(2) The double sealing roller is worn.
(3) The cam or inserting rod of the sealing roller is worn.
(4) The pin or bearing of sealing roller is worn.

Fig. 4-58

Fig. 4-58 – Secondary operation seam too tight

Fig. 4-59

Fig. 4-59: the second operation seam is too loose

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