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Release agent is also called release agent. As the name implies, it is a kind of solvent used to lubricate the mold and separate the workpiece from the mold when alloy casting and plastic product forming. However, its performance is affected by the mold temperature, so it is often a blind spot in the die casting operators to choose the proper mold temperature range of release agent.
However, in the process of die-casting production, mold release agent is an important means of die cooling (in the process of die-casting production, we often hear the workers say: "more spray point water when the temperature is high" die drawing, more spray point water "and so on). Many companies use water-based release agent. When spraying, compressed air with release agent is sprayed on the surface of mold cavity. At the same time, the high temperature of mold indirectly heats the release agent, resulting in the evaporation of water in the release agent. However, due to the uneven temperature of the mold cavity surface, the degree of mold release agent being heated by the mold is also different (different water residual component, different gasification effect). The cooling degree of mold is also different, so the thickness of liquid mold release and lubricating film formed on mold cavity surface of mold release agent is also different.
In the hot area of the mold, the release lubricant and the moisture in it are more affected by the mold temperature and produce gradient volatilization. If the temperature difference between the hot area and the surrounding cold area of the mold cavity is large, the tension gradient formed on the surface of the mold cavity is larger, and the release agent is interfered by the outside (temperature, concentration, etc.), and when the liquid film of the release agent becomes thinner, it will be under the action of the surface tension of the mold cavity (this process is like the process of metal liquid cooling and solidification in the mold cavity), so that The thin part (mould high temperature area) of liquid film flows to the relatively thick part (mould low temperature area). At this time, if the spraying amount is increased, the hot area of the mold cavity will be completely covered by the mold release agent. As a result, too much mold release agent and water will accumulate in the low temperature area of the mold cavity, leading to the formation of air holes, cold shuts or color spots in the die casting. (therefore, many experienced die-casting operators will choose different ways to carry out "spot spraying" to overcome this phenomenon). On the contrary, the hot area of the mold cavity is not covered by the liquid film of the release agent, which affects the lubrication and stripping effect, such as die drawing, die bucking, etc. It can be seen that the mold temperature has a great influence on the effect of mold release agent. How important it is for the performance of mold release agent to keep the mold temperature balanced and generally consistent.
If the mold surface temperature is too high or too low, it will affect the absorption effect of mold release agent.
A. Too low: when the temperature is lower than 150 ℃, the spraying process makes the mold temperature drop below the vaporization point of water. The coating just rushes through the surface of the mold cavity and cannot deposit on the surface of the mold cavity. Too much water and coating accumulated in the mold cavity will make the casting produce diffuse air holes.
B. Too high: when the temperature is higher than 398 ℃, when spraying, the coating will be dispersed and washed away by the steam on the surface of the cavity. Because the temperature does not drop to the wetting temperature, only when the temperature is reached, the spray coating will contact with the cavity surface to form the demoulding liquid film.
For a relatively constant mold temperature, the factors that affect the formation of the film include the impact of droplets, wetting the mold surface, spreading to form a continuous film, and preventing the erosion of subsequent spraying. In addition, there are many uncertain effects on the formation of skin membrane. Including spraying speed, spraying strength, spraying angle, etc. The primary purpose of mold release agent is to form effective skin film in mold cavity, and then to achieve effective mold cooling and less residue.
There are new mold release agents on the market of die-casting consumables. New mold release agents solve some old problems. With the continuous innovation of the surrounding technology of die-casting, we pay more attention to mold temperature control and monitoring, and the tools and equipment used are more advanced, which makes our selection of mold release agents more convenient, scientific and reasonable.