How to control the thickness of electrostatic powder coating

How to control the thickness of electrostatic powder coating

The sprayed profiles have various colors and are deeply loved by customers, but due to the complexity of the cross-sectional shape of aluminum profiles, it has brought certain difficulties to spray production and coating thickness inspection. Regardless of the shape of the aluminum profile, the minimum local film thickness of the decorative surface coating is ≥40um, which is a mandatory implementation clause stipulated in GB5237.4-2008, and must be strictly implemented; Insufficient coating thickness, but not exposed.

In actual production, due to the influence of the electrostatic spraying equipment and the cross-sectional shape of the aluminum profile, the precise control of the coating thickness is certain to pay attention to. The characteristics of the spraying production line can better control the coating thickness from the following aspects.

1. Hanging method

Choosing the proper hanging tool according to the shape of the aluminum profile, choosing the correct hanging method is the key to controlling the thickness of the coating, it can not only improve the quality of the aluminum profile coating, but also reduce the need for the powder room operator to replenish the gun by hand The workload, especially the spacing of the hanging material can adjust the thickness of the powder coating. The general requirement of the spacing of the hanging material is: the width of the aluminum profile = the spacing of the aluminum profile.

2. Workpiece and rack contact

Due to poor contact between the workpiece and the rack (that is, poor conductivity), it will seriously affect the coating efficiency and the quality of the coating, resulting in a low powder rate on the workpiece, resulting in a low coating thickness or even a bottoming phenomenon, and a great deal to the recycling system. The pressure makes the excess powder overflow out of the powder room before it can be recovered, which reduces the utilization rate of the powder and pollutes the environment.

For the products produced when the workpieces are in poor contact, the coating thickness measured at different points on the same material may differ by 30um-70um. In some places, due to the thick coating, there will be defects such as orange peel, pinholes, flow marks, etc. The color and gloss will also be affected, and the sand grain powder profile has obvious defects such as zebra-like shape under natural light. Therefore, it is necessary to ensure good conduction between the workpiece and the hanger.

3. Conveyor chain speed and production process

During the production, the speed of the conveyor chain and the production process play a major role in the thickness of the powder coating, such as: elevator stroke, gun distance, powder pressure, electrostatic voltage, etc. The general requirements for elevator stroke height are: stroke height = Workpiece height +200㎜. The more complicated the shape of the workpiece, the closer the distance between the spray gun and the workpiece, the smaller the powder output and the lower the voltage; conversely, the simpler the shape of the workpiece, the farther the distance between the spray gun and the workpiece, the greater the powder output, the higher the voltage.

4. How to replenish powder by hand spray gun

Due to the complexity of the cross-sectional shape of the aluminum profile, in the production process, as the internal angle of the decorative surface, the lateral grooves, grooves, etc. are places where the automatic spray gun is not easy to reach, and the hand spray gun must be supplemented. In the place to be sprayed, the transmission pressure is adjusted too much, the distance between the hand spray gun and the workpiece is too close, it is easy to cause the phenomenon of orange peel, flow marks, pinholes, gun shots, fat edge, etc. on the surface of the workpiece. In general, when the nozzle of the hand spray gun is facing the place to be sprayed on the workpiece, the transmission pressure is 1.2 to 1.8 bar, and the distance between the hand gun and the workpiece should be controlled at 80 to 150 mm.

4. Powder pump factor

The common powder unevenness in the production process is mainly caused by the dirty parts of the Venturi powder pump. Because the powder pump presses the powder suction tube, it is easy to cause powder accumulation and sticky powder to cause blockage and lead to the reception in the powder pipeline. The force is affected, which affects the coating thickness of the workpiece. Under normal circumstances, the operator of the powder room should promptly check the cleanliness of each part of the Venturi powder pump.