The inner hole geometry of the wire powder coating die (with the core being the inlet area and the straight cylinder area) mainly affects the surface finish of the wire by controlling friction damage, powder adhesion state, and the stability of wire operation.
The specific influences are as follows:
1. Shape of the entry area: Determines the "initial contact mass" of the welding wire The entry zone is the first contact point where the welding wire enters the mold. Its shape directly affects the initial friction and powder guidance, and thus influences the surface finish.
- Entry Angle: When the Angle is too small (such as < 40°), the resistance of the welding wire entering is large, and it is prone to hard friction with the edge of the entry, resulting in scratches on the surface. When the Angle is too large (such as > 160°), if no auxiliary flow guidance is done, the powder is prone to "flanging off" or uneven distribution. The unlubricated part of the welding wire will directly contact the mold wall, causing frictional damage. The appropriate Angle (such as 60°-70°, or adjusted according to the characteristics of the powder) can allow the powder to evenly coat the welding wire, forming a "lubricating layer", reducing the direct friction between the welding wire and the mold, and avoiding scratches.
- Smoothness of the entrance edge and inner wall: If there are burrs on the entrance edge, incomplete chamfers, or the inner wall is rough (Ra > 0.8μm), it will directly scratch the surface of the welding wire, causing local protrusions or depressions. At the same time, the rough surface is prone to adsorb powder impurities. After the impurities accumulate, they will further "grind" the surface of the welding wire, reducing its smoothness.
2. Shape of the straight cylinder area: Determines the "final surface shaping" of the welding wire The straight cylinder zone is a key area for the stable passage of welding wire after powder coating, and its geometric parameters directly affect the integrity of the coating and the surface flatness.
- Diameter accuracy of the straight cylinder area: When the diameter is too large, the welding wire will shake in the area, and the powder layer that has adhered will repeatedly rub against the inner wall, causing the coating to wear and expose the base. The exposed welding wire base is prone to being scratched. When the diameter is too small, it will overly squeeze the powder layer, causing the coating to crack and fall off. The fallen powder particles will also form a "grinding agent" between the welding wire and the mold, intensifying the surface roughness.
- Length of the straight cylinder area: If the length is too short, the powder may leave the mold before it is fully set, which can easily lead to local peeling of the coating and an uneven surface of the exposed substrate. If the length is too long , the friction time between the welding wire and the wall of the straight cylinder area will increase, which will wear down the already set powder coating, causing the surface to "fuzz" or the coating to become thinner, affecting the smoothness. The inner wall roughness of the straight cylinder area: When the inner wall is rough (Ra > 0.4μ m), it will continuously rub against the powder coating, grinding away the fine parts of the coating surface, making the surface of the welding wire appear "frosted". If impurities areadsorbed on the rough surface, they will also leave indentations on the surface of the welding wire, further reducing the smoothness.
Sandra 