Electrophoresis of industrial aluminum yellow reason and solution
Electrophoresis industrial aluminum yellowing phenomenon summarized the cause of the following: electrophoresis paint itself;
Conductive oxide bad;
Before electrophoresis bath not completely;
Cure too much;
By nitric acid oxidation tank liquid pollution.
Oxidation in industrial aluminum conductive yellowing phenomenon caused by the bad industrial aluminum and conductive pole poor contact, contact resistance will be increased, the aluminum end will be fever, oxide film generated too fast accompanied by burning phenomenon, appear even pulverization of oxide film.
When the oxide film of some turbidity, color of yellowing, if again for electrophoresis production will appear very obvious yellowing phenomenon.
This yellowing phenomenon usually only a few in a row, and that there are basically at the end of the profile.
Therefore, must take steps to ensure good industrial aluminum contact with conductive rod.
Electrophoresis before washing the yellowing phenomenon caused by the incomplete oxidation film is honeycomb, the cellular structure determines the residual sulfuric acid oxidation film hole.
As is known to all, used for electrophoresis aluminum if water is not completely, there is likely to yellowing phenomenon.
For this kind of yellowing phenomenon, is generally considered to be of oxide film hole acid radical reaction with electrophoresis paint so that the electrophoretic paint film of yellowing, actually this kind of yellowing doesn't happen the yellowing of paint film, but the yellowing oxide film.
Normal oxidation film was clear and transparent, if the residual more sulfuric acid root oxidation film hole, high temperature conditions, oxidation film can react with sulfuric acid root, making clear and transparent oxide film become turbid, transparency;
At the same time combined with electrophoresis paint film of high transparency, highly reflective of light, so that this kind of defect get amplified, yellowing have said.
Therefore, electrophoresis before a few washing is critical, not only to ensure the water quality, and ensure that water temperature and washing time.
By nitric acid oxidation tank liquid pollution caused by ash yellowing phenomenon in order to achieve good results, adding a certain proportion of nitrate in neutralizing tank this understandable, but if after neutralization water control is not good, will be taken to nitrate oxidation groove, industrial aluminum nitrate in oxidation tank reaches a certain concentration, would have certain effects on the oxidation, even cause yellowing of the aluminium profile.
Oxidation in the process, enter the nitrate of oxide film hole can have etching effect of oxide film and corrosion barrier layer of oxide film, make the oxidation film hole deep, thus changing the structure of the film hole.
The corrosion of oxide film two effects: 1, the thinning of the barrier layer of oxide film, and compactness of the aluminum substrate joint, resulting in lower oxidation film adhesion.
2, under the condition of normal water washing, it is difficult to put in the film hole sulfuric acid to eradication.
Under the condition of the production by electrophoresis aluminum also experience yellowing phenomenon.
How to avoid this kind of yellowing phenomenon?
Before the hot wash tank, neutralizing agent is added to the pure water tank PH 8 ~ 9.
5, 2 ~ 3 minutes, wash with amine and sulfuric acid root of oxide film hole, electrophoresis production again, won't appear yellowing phenomenon.
Curing the yellowing phenomenon caused by the excessive electrophoresis paint used on the market at present basically is at 180 ℃ oven curing X30min conditions.
Under normal conditions, the paint film is basically yellowing is not going to happen.
But some aluminum manufacturers uneven curing furnace temperature, the local temperature difference even above 30 ℃;
Some manufacturer curing furnace temperature control system is poor, the actual temperature and the temperature difference is too big, poor quality of the electrophoretic paint under the condition of the yellowing phenomenon is very obvious, even like the color.
Good quality electrophoresis paint of the extreme conditions of bear ability is strong, even if some electrophoresis paint under the condition of 230 ℃ baking, yellowing phenomenon will not occur.
In order to prevent the formation of yellowing, the uniformity of furnace temperature, temperature control system of sensitivity is required, use good quality electrophoresis lacquer is necessary.
Yellowing phenomenon caused by the electrophoresis paint itself anodic electrophoretic paint is mainly composed of acrylic resin and amino resin.
Electrophoresis aluminum in the baking process, resin crosslinking reaction, generate smooth, transparent film.
But some electrophoresis QiChang home because of the production process is not mature, or is in order to reduce costs using poor quality of chemical raw materials, resulting in its solidification range is narrow.
Baking slightly insufficient, film hardness is not enough;
Bake for a little over the top, paint film yellowing occurs, bring certain difficulty to the production management.
So it is suggested to choose the product quality is stable, have certain popularity coating suppliers.