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The process requirements for manufacturing casting shells using paraffin stearic acid low-temperature crystallizer, investment casting, and precision casting silica sol as crust agents were introduced. This article mainly studies the melting method, silica sol shell method, and calcination method. The production practice in the past five years has fully proved that the precision casting technology for manufacturing silica sol shells is mature, providing technology for producing qualified shells and precision castings.

Keywords: investment casting; Investment casting; Investment casting; Investment coating; Adhesive; Silica sol; Type shell; roasting

Using a paraffin stearic acid low-temperature crystallizer, investment molds (commonly known as wax molds) of precision castings such as turbine impellers and nozzle rings were made. Precision casting silica sol was used as the shell adhesive to produce the turbine impeller shell and nozzle ring castings. This article mainly studies the investment casting manufacturing process, silica sol shell process, and calcination process, providing technical support for the production of qualified shells and precision castings.

All kinds of wax melting tools and wax melting tools should be cleaned thoroughly. The wax melting machine should be cleaned at least once a month. Water and dirt must not enter the wax solution. Overheating of wax is strictly prohibited. When preparing paste wax, slowly add the shaved wax to the continuously stirred wax solution, and the amount of wax added depends on the specific situation. The temperature of the paste wax is between 45~48 ℃. The paste wax is stirred evenly to prevent air from being sucked in during the stirring process, which may cause bubble defects in the wax mold and prevent cracking and deformation due to insufficient pressure. Wrinkles or prolonged cooling time due to thin wax paste.

Mold ratio: 50% paraffin wax, 50% stearic acid (weight ratio); Mold melting temperature: 70~75 ℃; The wax temperature should not exceed 90 ℃.

Before waxing, check if the mold model meets the requirements. Before waxing, clean up any remaining wax, water droplets, and other attachments. When cleaning, try not to use it to avoid damaging the mold. Molds and moving blocks should be kept clean. After waxing, clean, lubricate, and store the mold according to regulations. During the wax pressing process, release agent should be applied to the surface of the mold and moving block in a timely manner to facilitate quick and easy demolding. Transformer oil is used as a mold release agent. After dipping the dry yarn head or gauze in the release agent, wipe it on the mold seat to make it thinner and even. Oil stains must not be visible to the naked eye. After removing the wax mold, it should not be placed in cooling water for more than 20 minutes.

Remove excess burrs and flying edges on the wax mold, flatten the wax injection mold, and do not trim other parts. During trimming, the working surface of the casting must not be damaged, and welding or trimming of the machining reference surface is not allowed.

Welding can only be carried out after the wax mold passes self inspection and special inspection. According to the requirements of the module, the distance between the wax molds should be greater than 5mm. The welding temperature between the wax mold and the gate should be around 80 ℃, and the welding should be smooth to ensure a smooth transition between the wax mold and the gate. Wax pimples and crevices are not allowed. The sprue should be ironed flat with a hot knife, without scratches or concave convex defects. Virtual welding is not allowed for welding strength.

Self inspection is the main focus, with specialized inspection as a supplement. Unqualified wax molds shall not be welded into the mold. The inspectors conduct appearance quality inspection on the wax mold (inspect the appearance of the wax mold, and ensure that there are no shrinkage, cracks, wrinkles, or bulges on the surface), size inspection (randomly check the size and shape of the wax mold), and control the wax making process.

There is no standard for silica sol used in investment casting, only the technical requirements of the aviation industry standard HB5346-1986 "Silica Sol Used in Investment Casting" (see Table 1). Silica sol is a water-based binder used for high-quality silica sol investment casting, applied to all layers (surface and back layers). Silica sol is easy to prepare high-quality coatings with high powder to liquid ratios, and the coatings are stable. The shell made of silica sol does not require chemical hardening, and there is no air pollution during the manufacturing process of the shell.

When the environmental temperature and relative humidity are difficult to adjust, they can be controlled at a certain relatively stable value: temperature is 22-25 ℃, humidity is 45% -65%. Adopting water bath dewaxing, with a water temperature of 90-95 ℃ and a dewaxing time of more than 20 minutes, to prevent sand or paint from entering the shell due to boiling water.

The self inspection of the mold shell is completed by the operator themselves. When there are layers, bubbles, cracks, and rotten heads that are not qualified, excess paint and uneven attachments on the gate must be removed, otherwise it is unqualified. After each demolding, drain the wax water and pour it into the wax ingot. When injecting wax, use a 160-200 mesh sieve to remove the residue from the wax solution. Drain the water from the tank and clean the dewaxing tank thoroughly. Add clean water again during the next dewaxing process. Place the mold with its head facing downwards into the furnace, calcine at a temperature of 900 to 1050 ℃, and hold for 1 to 2 hours before starting to remove and pour; When a box is needed, it should be less than 450 square meters before being discharged from the furnace.