Main process performance parameters affecting alloy aluminum plate
The alloy aluminum plate is a constant voltage method, and the device is relatively simple and easy to control. The voltage has a great influence on the aluminum alloy plate; the higher the voltage, the thicker the electrophoretic alloy aluminum plate, and the coating capacity can be improved for the difficult-to-paint parts, and the construction time is shortened. However, if the voltage is too high, the surface of the alloy aluminum plate may be rough, and the phenomenon of "orange peel" may occur after drying. The voltage is too low, the electrolysis reaction is slow, the alloy aluminum plate is thin and uniform, and the swimming force is poor. The choice of voltage is determined by the type of coating and construction requirements. Under normal circumstances, the voltage is inversely proportional to the solids content of the paint and the temperature of the paint, and is proportional to the distance between the two poles. The surface of the steel is 40-70V, the surface of the aluminum and aluminum alloy can be 60-100V, and the galvanized part is 70-85V.
The thickness of the alloy aluminum plate increases with the extension of the electrophoresis time. However, when the alloy aluminum plate reaches a certain thickness, the extension of the time is continued, and the thickness cannot be increased, but the side reaction is aggravated; on the contrary, the electrophoresis time is too short and the coating is too thin. The electrophoresis time should be as short as possible, depending on the voltage used, under the conditions of ensuring the quality of the coating. Typical workpiece electrophoresis time is 1 to 3 minutes, and large workpieces are 3 to 4 minutes. If the surface geometry of the object to be coated is complicated, the voltage and the extension time can be appropriately increased. The coating temperature is high and the film formation rate is fast, but the appearance of the alloy aluminum plate is rough, which may cause the paint to deteriorate. The temperature is low, the electrodeposition amount is small, the film formation is slow, and the coating film is thin and dense. During the construction process, due to the partial conversion of electrical energy into thermal energy during electrodeposition, the mechanical friction in the circulation system generates heat, which will cause the temperature of the coating to rise.
Generally, the temperature of the paint liquid is controlled in some aspects from 15 to 30 °C. Commercially available electrophoretic coatings generally have a solids content of about 50%. During construction, the coating solids are controlled to be 10% to 15% with distilled water. The solid content is too low, the hiding power of the alloy aluminum plate is not good, the pigment is easy to precipitate, and the stability of the coating is poor. When the solid content is too high and the viscosity is increased, the alloy aluminum plate is rough and loose, and the adhesion is poor. Generally, the ratio of pigment to base is about 1 to 2. The ratio of the pigment base of high gloss electrophoretic coating can be controlled at 1 to 4. Due to the actual operation, the amount of pigment in the paint will gradually decrease, and it is necessary to adjust the paint with a high pigment content at any time. The pH of the electrophoretic coating directly affects the stability of the bath. If the pH value is too high, the newly deposited coating film will be redissolved, the alloy aluminum plate will be thinned, and the film will be removed after washing. If the PH value is too low, the surface gloss of the workpiece is inconsistent, the stability of the paint liquid is not good, the dissolved resin will precipitate, the surface of the alloy aluminum plate is rough, and the adhesion is lowered. Generally, during the construction process, the pH value is controlled between 7.5 and 8.5.
In the construction process, the cationic ammonium compound accumulates in the paint due to continuous electrophoresis, resulting in an increase in the pH. The raw material solution with a low pH value may be added, the cathode cover distilled water may be replaced, the ammonium ion may be removed by an ion exchange resin, and the pH value may be lowered by an anode cover or the like. If the pH is too low, ethanol ammonium can be added to adjust. The impurity ions of the coated article brought into the alloy aluminum plate from the previous process cause a decrease in the resistance value of the coating, resulting in rough unevenness of the alloy aluminum plate and pinholes and the like. In the coating construction, the paint needs to be purified. In order to obtain a high-quality coating film, a cathode cover device can be used to remove ammonium and positive ions such as calcium and magnesium.