Causes of daily defects in die castings and solutions

  • 1. Mold spots often appear on the appearance of die castings, which severely affect the appearance quality of castings, mainly caused by mold release agents. At present, there are many manufacturers of mold release agents on the market, and many of them have various quality problems. The most important one is the corrosion effect on die castings. Generally speaking, die casting plants are not very important. If the die casting is placed for a long time, the appearance will have white spots (frosty, black after removal). In fact, corruption has already occurred. It is mainly composed of a factor that causes corrosion in the release agent. Therefore, we must not only seek low prices, but also favor cost performance.
  • The release agent generally does not penetrate into the die casting. However, a poor mold release agent will cause the appearance of the die-casting parts to corrode and penetrate into the die-casting parts; in addition, if the release agent contains a large amount of air, pores will be formed in the die-casting parts. If the paint such as release paste is used improperly, defects such as slag inclusion will occur.
  • 2. After shot blasting, the appearance of china die castings often appears peeling off. The reasons are generally as follows: ①The mold or injection chamber (melting cup) is not cleaned. ②Insufficient injection pressure (the mold must be moved carefully during injection to see if it retreats); ③There is a problem with the gating system, and there is turbulence when the alloy liquid enters the cavity. ④Mold temperature; ⑤The molten metal flies and splashes severely during spraying.
  • 3. Blistering of zinc alloy coating. The electroplating process and the appearance quality of the die-casting parts lead to poor electroplating. The appearance of die castings is of good quality, and there are no defects such as pores, cracks, pores, bubbles, shrinkage holes, cold lines, pinholes, etc. Otherwise, the appearance of the castings after electroplating is easy to bubble, and the electroplating layer is separate from the substrate. When polishing before electroplating, be careful not to over polish. In the solidification process of die castings, the appearance of die castings is quenched to form a dense chilled layer, and the internal structure may have defects such as porosity and shrinkage. Don’t wear out this good appearance layer when polishing, otherwise there will be pitting and bubbles during electroplating. In addition, the polishing wheel should not be pressed too tightly and overheated to prevent the abrasive from adhering to the product, resulting in poor product plating.
  • 4. There are small pimples on the appearance of die castings after electrostatic spraying. How to deal with them? The reason is the quality of the die casting parts. ①The purity of zinc alloy raw materials. ②Degassing and slagging during die casting. Mold exhaust and release agent. ③Zinc alloy die-casting is different from aluminum alloy die-casting, and the above-mentioned problems must be dealt with in detail. In addition, the maximum temperature at the instant of melting of the zinc alloy does not exceed 450°C, and the pouring temperature is 400°C. No matter which appearance measures are taken, the temperature must not exceed 150°C.
  • 5. There are pores on the die casting. The reasons are as follows: ① The metal flow is not in the correct direction, and it has a positive impact with the casting cavity, resulting in a vortex, which traps the air and generates bubbles. ②The inner door is too small and the metal flow is too large. Before venting, the vent hole was blocked prematurely, leaving the gas in the casting. ③The cavity is too deep and it is difficult to discharge; ④The design of the exhaust system is different, so the exhaust method is difficult to adjust. Solution: ① Correct the size and shape of the diversion cone to prevent metal flow from having a positive impact on the cavity. ② Increase the inner door appropriately. ③Improved mold design ④Design the exhaust groove reasonably and increase the ventilation holes.
  • 6. During the die-casting process, the molten metal splashed out. The reasons are as follows: ①The moving and fixed molds are not tightly closed and the gap is large. ②Insufficient clamping force. ③The die-casting parts can be moved, and the fixed mold base plates are not parallel. ④The support plate has a large span. The injection force deforms the sleeve plate. Produce spray. Solution: ①Install the mold from the beginning; ②Increase the clamping force. ③Adjust the die-casting machine so that the movable and fixed mold mounting plates are parallel to each other. ④ Increase the support plate on the movable mold to increase the rigidity of the guard plate.
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