The actual production precautions of the hub electrophoresis coating line

At present, in the body, parts manufacturing process, in order to improve the quality of coating, reduce costs, most of the use of cathode electrophoresis paint as coating and anti-corrosion treatment of the bottom coating. Electrophoresis coating can be applied to the inner cavity, seams and other parts of the work piece, greatly improving the anti-corrosion performance of these areas.
automotive wheels belong to the typical work parts with seams, in the production line often have hub clamps, welds and other places in front of the treatment of conversion film rust, conversion film incomplete phenomenon . After electrophoresis, the lacquer film foams or there is a similar paint slag-like material flow hanging in the seams. In addition, after the electrophoresis wheels are placed outdoors for a long time, yellow rust water sometimes flows from the hub seams. In production, the smaller the hub seam, the more prone it is to such problems.
of the reasons:
(1) oil removal is not complete. From the process point of view, pre-skimming, skimming two processes, there is spray and impregnation, the general work parts are completely able to remove oil pollution on the work parts, but from the actual effect, but there are gaps and other oil removal phenomenon.
(2) residual acid ions. Hubs in acid washing, because the inorganic acid ion radius is very small, very easy to seep into the hub seam inside, in the back channel washing is also more difficult to clean, these acid ions become a hidden danger of corrosion.
(3) conversion film in the hub seam if pH is high, the workware, solution interface acid-base-medium reaction, hinder or even stop the initial reaction of conversion, not easy or unable to form a conversion film. If the pH in the seam is low, it causes the acceleration and aggravation of metal corrosion, which leads to the poor quality of the conversion film.
improvement measures:
(1) to improve the effect of degreasing, can be considered from the following aspects:
A. process, you can add a hot water spray cleaning process at the front, can effectively remove more than 90% of the surface of the work piece mechanical impurities, reduce the load of the skimming process. In addition, this will also have a certain degree of improvement in the problem of residual acid in the hub sandwich.
B. Choose to optimize the type of skimming agent. According to the different effects of the various parts of the skimming agent, the ratio should be adjusted appropriately, and the sodium silicate content should be reduced appropriately (its cleaning is poor, and the silicone which is difficult to wash off by acid formation is extremely harmful). Give full play to the combined effect of surfactants, adding osmotics, emulsions, to maximize the removal of oil in the seams.
C. Strengthen the management of skimming tank fluid. The effective concentration of degreasing fluid is controlled by free alkalinity, but the effect of degreasing fluid can not be judged by free alkali alone, because although the alkalinity is not reduced, the effective concentration of surfactants will also be lost or failed, so in addition to the need to supplement daily degreasing agent, but also need to change grooves regularly. When changing the groove, the secondary skimming fluid will continue to be used as a pre-lipid fluid, re-allocation of the secondary skimming fluid, which not only improves the utilization rate of the skimming fluid, but also enables the skimming fluid to always maintain the best condition. At the same time in production, strictly in accordance with the requirements of the process of skimming temperature, time and other parameters to control.
(2) strengthen the washing after the work parts degreasing to strengthen the water washing after degreasing, often update the washing water, to prevent dirt in the washing tank on the work piece caused secondary pollution, but also to prevent the work parts in the process of rusting phenomenon.
(3) acid lotion selection commonly used acid lotions are hydrochloric acid, phosphoric acid, sulfuric acid and so on. After on-site experimental verification, when using sulfuric acid to remove rust, the foaming rate of the paint film is high, hydrochloric acid rust removal foaming slightly, phosphoric acid rust removal is the most advantageous. Of course, we should also consider what kind of acid lotion to choose from the cost and adapt to the rhythm of the automated production line, but consider the problem of sandwiching, it is recommended not to choose sulfuric acid.
(4) Control the concentration of the mesothering agent in the process, under the premise of ensuring complete ionization of residual acid at the surface of the hub, seams, etc., to reduce the concentration of the lime agent as much as possible, to prevent the lye from remaining in the hub seam.
(5) transformation film selection and control to improve the quality of the film, improve its rust-proof performance, control the parameters, prevent film flowering, roughness and other issues. In particular, when the workware appears rust return, more attention should be paid to the pre-treatment of the conversion membrane liquid fluid travel parameters control.
(6) Strengthen manual cleaning and cleaning at sandwiches, welds, etc. to reduce the residue of chemical fluid at workwear, welds, etc., work parts before entering the electrophoresis tank, you can arrange manual use of high-pressure clean pure water to clean the clamps, welds and other places. At the same time, it is suggested that artificial use of compressed air for the work parts sandwich, welds, pocket fluid parts to blow water, on the one hand, can reduce the work parts with liquid on the electrophoresis tank liquid pollution, on the other hand, can also reduce the work parts clamps, welds and other places of coating ills.