To achieve the best pore-free weld seam coating on all metal cans after welding, a thick coating layer is needed to provide protection. However, liquid coatings tend to produce bubbles when drying and solidifying, especially with thick layers. This problem can only be solved by using powder coatings.

The quality of the weld seam coating layer depends not only on the coating repair method but also on the welding effect. For example, when the welding frequency is low or when using low-tin iron, chrome-plated iron, etc., spattering and surface roughness are prone to occur on the weld seam. Additionally, the presence of an oxide layer on the weld seam makes the coating layer vulnerable to damage during subsequent processes such as flanging, necking, and seaming. Furthermore, the thickness of the tinplate, the quality of the shearing, etc., can pose significant challenges to the liquid coating repair process.

Although welding equipment has undergone many improvements to achieve perfect weld seams, such as increasing the welding frequency and adding auxiliary welding wheels to reduce spattering inside the weld seam, as well as adding weld seam oxygen protection devices, achieving perfect protection with liquid coatings still presents some difficulties, especially with increasing welding speeds. Furthermore, powder coating processes result in minimal air pollution. Powder coatings can also cover welding spatter points, and almost all coating between cans can be fully recovered and reused, resulting in minimal waste. Therefore, in order to achieve perfect weld seam protection, powder coating repair processes have been increasingly used by Chinese manufacturers in recent years.

The advantages of powder coatings are well known, but they also have some inconveniences. The powder feed and reclaim pipes need to be fixed on the welding arm of the welding machine, and the can body still needs to pass through them from the outside. Since the powder pipe is relatively thick, with a general outer diameter of 6-8mm, when making D52 can types, special welding arms are required to fix the powder pipe on the welding arm and allow the D52 can type (202) to pass through. This increases the cost of can production.

Working principle of powder coating repair: Powder coating is drawn into the powder spray gun by the airflow from the repair powder box (based on the principle of the Bernoulli equation, the faster the flow rate, the lower the pressure). Then, under the transport of the airflow, it reaches the nozzle outlet of the powder spray arm and is sprayed out. There is a high-voltage needle at the outlet of the powder spray arm, which emits a high static voltage (DC high voltage generated by voltage doubling rectification). When the powder coating passes through the high-voltage zone, the powder particles are charged. Under the action of the airflow and the high-voltage electric field, the powder particles are adsorbed on the wall of the can in the weld seam area. At the nozzle outlet of the powder arm, there are lip pieces on both sides to seal and prevent the powder from spreading to the sides, forming a neat repair band. The higher the static voltage, the better the adsorption of the powder coating. However, if the static voltage is too high, the surface of the powder coating repair band will be uneven and irregular, and there will be repulsion between particles of the same charge.

Yixin Technology has been specializing in the production of can making equipment for 30 years, committed to providing turnkey projects for metal packaging. We also have very professional opinions on welding powder coating repair coatings and can provide services to all can making factories.