The casting process of silica sol castings

1. Manufacturing mold

The mold is the type used to press the shape of the casting. In order to ensure the quality of the wax model, the mold must have high dimensional accuracy and a small surfaceroughness value. When the precision of silica sol castings is not high or the production batch is not large, it can be cast directly on the master mold by fusible alloy, epoxy resin and gypsum; Alloys and aluminum alloys are made by cutting, and general enterprises use more aluminum alloy molds.

2. Pressed wax mold

Press the processed wax paste into the mold cavity, take it out after being condensed by the ice water machine, put it in the pool for a period of time, and after trimming and inspection, a single wax model is obtained. A wax pattern can be understood as a pressure casting part.

3. Repair mold

The quality, surface quality, and degree of deformation of the wax pattern determine some important parameters of the product. Therefore, the wax pattern workshop needs constant temperature control to minimize the deformation of the wax pattern. At the same time, each wax pattern must also be inspected on the surface. The traces should be washed away, and the burrs, flashes and parting lines of the wax parts should be removed when the mold is repaired, and the trace defects should be repaired.

4 combination wax models (group tree)

After mold repair, for qualified individual wax molds, in order to increase productivity, single wax molds are welded on the prefabricated wax public gating system to form a wax mold group. Usually, 2 to 80 wax patterns can be welded on one wax pattern set. The tree grouping plan determines the yield of the product and the utilization rate of molten steel. The tree grouping plan should be carefully considered during the design, and whether the tree grouping plan is convenient for wax recovery and reuse should also be considered.

5. Clean the wax mold

The wax molds after tree formation can be cleaned after standing for more than 45 minutes. Before the shell making and slurrying, the wax molds after the number of sets must be cleaned to remove the wax chips and grease on the surface and improve the adhesion of the shell making. Immerse the module in the cleaning solution and reciprocate three times for a total of about 4 seconds. After taking it out, use compressed air to dry the module and then sizing the shell.

6. Manufacture the shell

After dipping and hanging the paint on the wax mold, put it into the shell-making room to dry. The surface layer adopts the method of natural drying, and the transition layer and the back layer adopt the method of rotary air drying to speed up the drying. Repeat the coating and hanging for 5 to 7 times (small castings) 5-6 layers, 6-9 layers for large castings. Use finer sand for the surface layer, slightly coarser sand for the transition layer, and coarser sand for the last few layers), until the coating forms a hard shell of 7-15mm. A hard shell mold of sufficient strength is called a shell.

7. Dewaxing and wax treatment

Pour the shell into the steam dewaxing ax to melt the wax mold and flow out from the bottom, separate it through the water separator, collect the wax liquid, put it into the water removal bucket to further separate the wax water and remove impurities in the wax, 12 After one hour, put the wax liquid through the filter screen into a still bucket for 6 to 8 hours, and finally put the wax liquid into an incubator to keep warm for reuse. The shell after the wax pattern flows out is the casting mold.

8. Shell roasting, pouring, shakeout and cleaning

The shell after dewaxing should be baked during pouring. Put the shell into an oil furnace or electric furnace at 1100°C for 50 minutes. The main purpose is to remove the residual wax liquid after dewaxing and improve the The strength and air permeability of the shell prevent the shell from being deformed or broken during pouring. Another extremely important factor is to reduce the temperature difference between the pourable molten steel and the shell to reduce the shrinkage cavity of the workpiece. When the moltensteel is melted, heat-preserved, stable, and pourable, take out the shell that has reached the roasting heat-preservation time in the roasting furnace and then pour it. After the casting is condensed, the mold is destroyed, the gating system is removed, the burrs are cleaned and shot blasting is performed to obtain the target casting. The surface of silica sol castings usually needs to be pickled and passivated.