There are plenty of factors of low zinc coating binding force, but the following five kinds of situations are relatively seen by people.
(1) Add too much additive. The brightness of zincate galvanized layer is less than potassium chloride galvanized layer. Some people think that adding more brightener can enhance brightness. As a result, this action not only can not reach the expected aim, but also has a severe impact on the adhesion strength of the coating.
Solution: Dilute and adjust the solution composition, and add a few but frequently at ordinary times.
(2) Too long time of staying in the galvanized tank before galvanizing workpiece. Some people think that the zincate galvanized solution is alkaline. People hang the pretreated workpiece in the galvanized tank and it will be sent to galvanize plating after gathering a slot. This process can passivate workpiece, thereby affecting the zinc coating binding force.
Solution: Avoid the workpiece staying too long in the slot.
(3) Too thick coating. Too thick coating can make internal stress and the brittleness of coating increase. The edge parts of the workpiece coating appear bubbles, peeling.
Solution:
Coating thickness should be controlled within 20 um.
(4) Oil stain is floated on the surface of the plating solution. The workpeice which are all in the plating tank is surrounded by the pollutant. The pollutant is made up by the oil stain and brightener on the surface of plating solution, causing the plating peeling.
Solution: The oil slick shall be removed with a thick layer of toilet paper at any moment. Shake several times in the plating tank after putting the workpiece in it. This can make the oil stain break away from the surface of the workpiece.
(5) Oil removal of the workpiece is not complete. Some people hold the view that zincate plating must owns oil removal ability because it is alkaline. So, they think the pretreatment can be done a little carelessly. When the smeary workpiece is put into the tank, zinc ion will forestall to separate out through electrical discharge before reacting with alkaline substances. Zinc coating deposits on the thin layer of the oil slick. So, the binding force will be reduced although the plating solution is alkaline.
Solution: Strengthen the pretreatment process.