In the process of die-casting production, whether using automatic or manual spray release agents, adopting the correct process operation method can not only improve the quality of die-casting castings, but also protect the mold and improve its service life, effectively reducing production costs.
1. The function of die-casting release agent
The main function of die-casting release agent is to remove the casting from the mold cavity. After spraying on the high-temperature surface of the mold, it can form a thin film to protect the surface of the mold cavity, prevent the casting from sticking to the mold, reduce the impact of the metal liquid on the mold cavity during casting injection molding, reduce the wear between the casting and the mold cavity, and provide lubrication; In addition, the temperature of each part of the mold can be adjusted to maintain the temperature balance of the mold, improve the formability of the castings, thereby increasing the mold life and ensuring the quality of the die-casting parts to a certain extent.
2. Usage method, spraying process and precautions of die-casting release agent
(1) The container for holding die-casting release agent: The container for holding release agent must be clean, free of oil stains and other impurities.
(2) Water quality: The release agent must be mixed with clean water. When the container or water containing the release agent is contaminated, it is easy to cause the release agent to deteriorate, thereby affecting the release effect of the release agent and causing an increase in the scrap rate of some sensitive die-casting parts. For example, the cylinder block die-casting parts for gasoline engines produced by our company have requirements for air tightness. When the pressure tank containing the release agent is not cleaned for a long time and there is dirt, and other production conditions remain unchanged, the gas leakage rate of the cylinder block castings produced will increase.
(3) The usage time of die-casting release agent: When using release agent, pay attention to its factory time and shelf life. After opening the lid, the release agent should be promptly diluted with water and used up in a short period of time, especially during summer production to prevent deterioration.
(4) Mixing rate: Choose the appropriate mixing rate according to the user manual of the mold release agent manufacturer, usually around 1:100. It is forbidden to mix the water rate too low, mainly determined by the complexity of the shape of the casting and the length of the spraying time. The casting shape is simple and the spraying time is long, so it should be thinner. When the casting shape is complex and the wall thickness is thin, it can be slightly thicker.
(5) Spray distance: The general spray distance is around 100-200mm, not too large or too small. For individual points such as diversion cones, runners, and cores, the distance can be appropriately shortened.
(6) Spray time: On the premise of ensuring smooth demolding and quality of castings, try to shorten the spray time as much as possible.
(7) Spray amount of die-casting release agent: Minimize the spray amount while ensuring smooth demolding and quality of the casting.
(8) Principle of mold temperature control during spraying: The temperature control of the mold cavity during spraying should adhere to the principle of balance to ensure uniform temperature at all points of the mold. It is generally believed that controlling the mold temperature between 140 and 200'12 (empirical value) after spraying is more appropriate. When the temperature is below 280'12 (empirical value), a film is formed within 1 second of spraying the mold. When the mold temperature is below 120'12 (empirical value), the film formation is not good, and it is difficult to form a film when the mold temperature is too high. I believe that the maintenance of temperature uniformity at various points of the spray mold should be understood from the following two aspects: ① The maintenance of temperature uniformity at various points of the mold after spraying is relative. ② After spraying, the temperature of each point of the mold should be kept uniform. The balance of temperature at each point of the mold should be mainly considered when the casting solidifies from liquid to solid. This is conducive to uniform shrinkage of the casting during solidification and avoids casting defects such as cold cracking and hot cracking.
3. Specific operation of mold cavity spraying
(1) Spray coating of mold diversion cone and runner: The temperature here is relatively high, and it should be sprayed with emphasis. The spraying time should be long, and the temperature should be reduced to avoid the mold working at excessively high temperatures, in order to extend the working life of the mold.
(2) Spraying at the inner pouring channel: The temperature here is too high, and it should be sprayed with special attention to reduce the temperature and prevent the occurrence of casting defects. Some castings are prone to crack defects near the sprue.
(3) Spray coating at the direct impact area of the aluminum liquid in the mold cavity: When the aluminum liquid is filled from the inner runner, the direct impact area should be sprayed with special attention. The temperature of the mold at this location can be lowered to prevent aluminum casting from sticking to the mold, avoid the mold working at too high a temperature, and prevent fatigue and slagging of the mold, as well as the appearance of pitting on the casting.
(4) Spray coating of mold core: The core should be sprayed with special attention to ensure smooth demolding of the casting and prevent casting problems, such as the breakage of small cores and difficulties in demolding large cores of gasoline engine cylinder blocks.
(5) Spraying of complex shape casting mold cavity: The grooves, grooves, deep grooves, and other areas of the complex shape casting mold cavity should be sprayed with special attention to prevent sticking to the mold.
(6) Spraying of molds far and near the inner runner: less spraying is required for the mold cavity far from the inner runner, and more spraying is required for the mold cavity near the inner runner. The lower part of the general mold is the pouring system, with more spraying on the lower part and less spraying on the upper part to prevent casting defects such as surface patterns, looseness, and cold insulation on the upper part of the casting.
(7) Blowing and chip removal in mold cavity: Attention should be paid to the blowing and chip removal process, removing residual release agents and aluminum chips to prevent defects such as inclusions and vortices in castings.
