Investment Precision Casting | Dewaxing

Investment Precision Casting | Dewaxing

The purpose of dewaxing in precision casting is twofold: one is to remove all remaining wax from the mold shell; One is to prevent cracking of the mold shell. However, in reality, achieving these two points is still not easy. Because dewaxing is actually affected by many factors, such as the physical properties of the wax material, the design of the pouring system, the drying condition of the mold shell, the permeability and dewaxing operation of the mold shell, and the function of the dewaxing kettle. Today, precision casting manufacturer Tianyao Metal will discuss in detail the precautions for dewaxing.

1、 It is the physical property of wax. Wax materials are commonly divided into medium temperature wax and low-temperature wax. Of course, there is also high-temperature wax. The so-called medium temperature and low temperature refer to the melting temperature of wax. Compared to others, low-temperature wax has a lower melting point during dewaxing, so the probability of cracking in the mold shell is relatively lower. In addition, the expansion rate of wax is also an important factor. The higher the expansion rate, the higher the probability of cracking in the mold shell.

2、 The design of the pouring system is also an important factor affecting the occurrence of cracks in the mold shell. When designing the pouring system, process personnel must consider dewaxing cleanliness or near cleanliness as an important consideration in the design. How wax flows smoothly out of the mold shell is an important task in the design of the pouring system. Because the official account cannot be illustrated, it cannot be explained clearly. However, there is a simple method, which is to assemble the mold full of water, weigh it and simulate the dewaxing situation in reverse, and then weigh it again to determine whether the dewaxing is smooth. Of course, it is easy to determine whether the dewaxing process is smooth in general designs. An example I mentioned earlier is poor dewaxing.

3、 Related to the drying condition of the mold shell. The wet strength of the mold shell depends on its drying condition. Good drying and high wet strength can resist the stress of dewaxing and avoid the formation of mold shell cracks.

4、 Related to the breathability of the mold shell. Good breathability, hot steam can quickly pass through the mold shell to the wax mold, causing the surface of the wax mold to melt and instantly release a lot of expansion stress, which also helps the mold shell withstand tensile stress, leading to cracks.

5、 Related to the dewaxing operation. The module should remain in the drying room until dewaxing. Because the drying room is at a constant temperature. Temperature is an important factor affecting the expansion of wax molds. It is often seen that dewaxing personnel assemble the mold into the dewaxing car early and leave the drying room, which is very unprofessional behavior. Especially in summer, this operation can easily lead to cracks in the mold shell. In addition, when the temperature of the dewaxing kettle is not high, try to reduce the dewaxing of thick, circular or rotating products as much as possible, because the mold shells of these products are very prone to cracking.

6、 The function of the dewaxing kettle. Special emphasis is placed on the pressure boosting speed of the dewaxing kettle here. This idea refers to the time it takes for the pressure of the mold shell to rise to 3-5 atmospheres after entering the dewaxing kettle. It is generally required to be within 14 seconds. Otherwise, cracks may occur in the mold shell.

In addition, there are two things to note:

6.1 is the dewaxing index. It is equal to the volume of the wax piece divided by the cross-sectional area of the inner gate. A high index indicates poor dewaxing; A small index indicates smooth dewaxing. Here we need to mention cylindrical and rotary castings, which generally have a high coating index and are prone to cracking. Last time a friend said that his product is prone to cracking, which is this type of rotary casting.

6.2 Try to minimize solid wax parts and solid risers, which are typical examples of poor dewaxing and should be avoided as much as possible.

Precision machining