Briefly describe the causes of oil porosity and shrinkage in the coating process, and what aspects s

There are many reasons for shrinkage porosity, and the following is a brief description:

1.Surface porosity caused by the substrate.

2.Surface shrinkage porosity caused by pretreatment.

3.Surface cratering caused by coatings.

4.Device-induced surface shrinkage porosity.

5.Surface shrinkage porosity caused by water or oil contamination in the air.

6.Environmentally-induced surface craters.

7.Surface craters caused by poor management.

1. When spraying manually, you can't just spray one thickly to save trouble. If it is possible, it will form defects such as sagging and biting the bottom. Instead, it should be sprayed dry first and then wet, which can cover the paint layer well and bring brilliance.

2. Whether it is electrostatic spraying or manual spraying, we must pay attention to the condition of tightening and degreasing and removing water, drain the water in the filter frequently, pay attention to whether the pressure can be stable, and the paint must be filtered and stirred evenly to participate in the paint barrel (tank), and the matter must be washed with a concentrate to clean the spray gun.

3. The level of dryness at the bottom will also affect the electrostatic adsorption results. If the primer layer is not dry, the paint film resistance is large, and the electrostatic adsorption is poor; It is too boring, and the coating surface is lubricated, because of the surface tension, the paint particles are not easy to adhere.

4. The influence of suspension gear on electrostatic spraying is greater. This is due to the fact that after a large amount of production during the Eternal Tribulation, the suspension device is very easy to adsorb the paint as a grounding pole, and if it is not liquidated and replaced, it will constitute a higher resistance and greatly reduce the electrostatic adsorption result. In addition, because of the existence of the Faraday effect in the electrostatic field, special attention should be paid to the hanging method of the workpiece, so as to eliminate the spraying dead angle.

5. Because the temperature has a great influence on the viscosity of the paint liquid, when distributing the paint, even if the temperature of the paint storage occasion, the distribution occasion and the operation site is commensurate.

6. Because the electrostatic spraying is stopped in the DC high-voltage electric field, the voltage up and down is the key to the coating result. The choice of voltage must be considered according to the type of paint and the conductive function. For example, when spraying paint containing metal powders, it is necessary to turn down the voltage appropriately.

Is there a shrinkage porosity for electrostatic powder spraying?

If so, there are several reasons for this:

1.The surface treatment of the workpiece is not clean. Oily.

2.The electrostatic spray gun current is too high. Domestic spray guns can reduce the voltage to reduce the current. If it is a Nordson spray gun, you can directly adjust the current in AFK mode to avoid craters.

3.The distance of the gun to the workpiece is too close.

4.When entering the oven or oven, impurities float up.

5.Poor grounding of the device. It is better to drive an independent grounding pile.

The most effective way to prevent shrinkage porosity is to clean and remove oil before each process, the main reason for shrinkage porosity is the existence of oil and water, and sometimes there will be some oil and water in the compressed air, and it is best to install an oil-water separator.