Problems

Phenomena and Causes

Remedies

Non-stick coating flows

Coating “sweats” before dry.
Possible causes: Viscosity of the coating is too low; wrong thinner is used; coating film is too thick.

1. Dilute it with a solvent of higher volatility;
2. Reduce coating film thickness;
3. Preheat the work piece before applying coating.

Die cast work piece has holes

The die cast work piece has holes or heaves, some air existing inside the metal is expanded and escape during heating, and leaves holes on the metal surface.

1. Let the work piece’s preheating temperature higher than heating temperature, if there is no blister, cool down the work piece before applying coating;
2. Use a coating that needs lower heating temperature.

SEEDY
Particle pollution
SEEDY

Hard particles exist on coating surface.
Possible causes: Dry coating particles have entered the coating in the barrel;
Dusts from surrounding area or furnace fall on the coating surface.

1. Filter the coating before application;
2. Keep the application area clean and remove dusts.
3. Use a suction machine to absorb the dusts from the furnace.

Flaking off

。
Part of the coating film flakes off from the surface of the work piece.
Possible causes: Surface of the work piece is polluted or is improperly processed;
Improper mixing or tempering; improper heating temperature.

1. Improve work piece cleaning procedure to remove all greases or other pollutants;
2. Mix the coating material uniformly;
3. Improve coating material heating procedure;

Air holes or pinholes

There are tiny holes on the coating surface.
Possible causes: Coating materials are stirred excessively and air enters inside the coating;
The equipment leaks air during coating material pumping;
The volatility of the solvent in the coating is too high.

1. Reduce stirring time, pay attention to coating pumping.
2. Use solvent of lower volatility; heat the work piece gradually, firstly dry the surface under low temperature, and then heat it under high temperature.

Cracking

Coating surface has many cracks, just like cracks of dry earth.
Possible causes: The viscosity of the coating is too high (generally, cracks occur in water-born coating), heating speed is too fast, or heating temperature is too high.

1. Reduce viscosity of the coating;
2. Reduce coating film thickness;
3. Pay attention to coating film dry procedure.