Process introduction of dewaxing casting

Dewaxing castingIt is one of the forming methods of glass processing. The main process is to heat the glass to a higher temperature to make it fluid and flow into the prefabricated mold shell for forming. Because the mold shell is made by heating to remove the wax mold, it is called dewaxing casting.

1. Because lead oxide glass (commonly known as artificial crystal) has diamond-like high refractive index and high high temperature fluidity, artificial crystal is often used as a material for casting glass. Now in the Chinese market, the above-mentioned dewaxed cast lead crystal glass products are usually called colored glaze. Casting by dewaxing method can be made into crafts with complex shapes and exquisite craftsmanship. 2. The precision casting method dewaxing casting process is a new process developed from the ancient casting process. As early as the late Neolithic period more than 5,000 years ago, the ancient craftsmen of our country have widely used the dewaxing casting process in the production of bronzes. According to the characteristics of plasticity and thermal volatility of beeswax, the craftsmen first carve the beeswax into the required shape, and then put the clay on the beeswax model, leaving a small hole, and roasting after drying to make it vaporize and volatilize. At the same time, the clay becomes a ceramic shell, leaving a female mold on the inner wall of the shell. At this time, the molten metal is injected into the shell along the small hole, and it is cooled and broken to obtain the required metal casting billet. The basic principle of contemporary lost wax casting process is no different, just more precise. It is mainly reflected in the higher requirements for the accuracy of the wax mold. In modern technology, the production of wax mold is not only the direct engraving of wax, but also the female mold can be obtained by silicone molding the metal original mold (plate surface), and then the wax mold can be obtained after the silicone female mold is waxed. The casting material is no longer clay, but instead is replaced by gypsum. This product is much more sophisticated than the ancient casting. Process editing

The process flow of dewaxing casting is: mold design-mold opening-wax injection (mold)-repair wax mold (mold)-wax tree (mold)-shell mold-shell mold roasting-pouring-vibration shell-sand removal processing Each process is described separately below.

Molds for making products;

Ordinary molds use aluminum molds and steel molds, but it is very inconvenient to use. After the factory got the drawings, the engineering department designed the corresponding molds and gates according to the drawings. Then a series of machining is performed on the aluminum material by a CNC machine tool to make a mold.

2. Wax injection

After the mold is opened, the waxing work can be carried out. Pay attention to factors such as wax temperature, pressure and compression of the rubber mold during wax injection operation.

The wax used in the wax mold is generally blue wax, its melting point is about 60℃, and the wax injection temperature is about 65℃. Other colors of wax are also slightly different. The wax injection temperature and wax injection pressure are controlled by the wax injection machine. Waxing machines are generally divided into two types: air pressure type and vacuum type. The molten wax is injected into the rubber mold with air pressure. The wax injection principles of the two wax injection machines are basically similar. The difference is that the vacuum wax injection machine can draw a vacuum and inject wax into the rubber mold; while the pneumatic wax injection machine can only inject wax directly into the rubber mold. Therefore, the general operation of vacuum wax injection machine is easier to master, while the wind pressure wax injection machine requires certain experience.

The heater and temperature sensor in the wax sprayer can make the wax liquid reach and maintain a certain temperature. Under normal circumstances, the waxing temperature of the waxing machine should be controlled at 70~75℃, so as to ensure the fluidity of the wax liquid. If the temperature is too low, the wax liquid is not easy to be injected into the wax mold, causing the wax mold to be incomplete; on the contrary, if the temperature of the wax liquid is too high, the wax liquid will overflow or overflow from the gap of the rubber mold, and it is easy to form flashing or burn fingers.

The internal pressure of the wax cylinder of the wax injection machine should be provided by an external air pump, and should generally be maintained at 0.5~0.7at (or kgf/cm2), that is, between 0.051 and 0.071 bar, and it can also be adjusted appropriately according to the volume and complexity of the wax mold.

Before wax injection, the plastic mold should be opened first, and its integrity and cleanliness should be checked. If you have used the rubber mold, you should spray the dewaxing agent into the rubber mold, especially in the thin and complex parts, you can also sprinkle a small amount of talcum powder to facilitate its removal; secondly, the wax injection machine should be preheated , Turn on the air pump of the wax injector to adjust the pressure and temperature.

When injecting wax, use both hands to fix the rubber mold in the splint (which can be a plexiglass board, wood, aluminum, etc.) together. Pay attention to the distribution of fingers to make the rubber mold evenly pressed; place the nozzle of the rubber mold parallel to the wax injection nozzle Push in, hold the wax injection nozzle firmly and hold the wax injection switch with both hands, gently step on the wax injection switch with your foot, and then release it. After holding both hands for 1 to 2 seconds, lay the rubber mold flat and open the rubber mold (if there is a bottom, first Pull out the rubber mold) and take out the wax mold. Check carefully after taking the wax. If there are serious problems such as missing edges or broken feet, this wax model is a waste product. If there are minor defects, the wax mold should be refurbished.

Trim the wax mold.

Under normal circumstances, the wax mold taken out after wax injection will have some problems more or less, such as: flash, multilateral, broken claws, visible trachoma, partial or overall structural deformation, small holes are not smooth, and the flower head is not clear. , Huatou and so on. Surgical blades can be used to repair defects such as flashing, multilateral, unclear flower heads, and flower heads. For defects such as blisters and broken claws, they can be repaired by wax welding; for small holes that are not ventilated, they can be pierced with soldering needles; for wax Mold deformation can be corrected in hot water at 40~50℃.

In addition, for rings with different hand sizes, it is undoubtedly time-consuming and laborious to wait for the ring to be changed after holding the model. Therefore, the general manufacturer always changes the finger ring directly when repairing the wax mold. The finger ring of the wax welder is very convenient to replace, and the weld can be trimmed with a blade after welding.