Cost Analysis Of Investment Casting Water Glass Shell Changed To Silica Sol Shell

Abstract: The current trend of investment casting development is to realize green casting as well as improving andstabilizing the quality of the casting, The problem that the traditional water glass (or composite) shell substitutedto silicon-soluble shell in the investment casting industry is the low price of products and the inerease of the mamufacturing cost, The long production cycle and poor peeling performance can be solved by the improved silica solfast drying technology and the cost reduction.

In recent years, A Company has improved the conventional silica sol shell process and applied it in more than 30 silica sol shell production lines. The castings and manufacturing costs of different manufacturers are analyzed and improved, and better results are obtained.

1 Process analysis of silica sol fast drying shell

Table 1 shows the preparation process of silica sol fast drying shell. To achieve "fast drying" of silica-sol shell and shorten the shell making cycle, fast drying agent and strengthening agent are added in the slurry preparation process of silica-sol, and the coating - sanding - drying processes are completed in the silica-sol 1 and 2-layer shell making line and the silica-sol reinforced layer shell making line [1, 2]. The synchronous production of the two lines can dry the conventional silica-sol shell (5 and a half layers)

The time is shortened from the original 63h to 8 ~ 10h. It can be seen that the production cycle of silica sol process is shorter than that of water glass shell.

2 Cost analysis of two shell making processes

The raw and auxiliary materials used in the water glass shell are only suitable for the production of low-priced carbon steel precision castings, and the surface roughness Ra is 12.5 ~ 50μm, and the dimensional accuracy is CT8-CT9. Using silica sol fast drying process instead of water glass process, although the cost has increased, but the casting quality (Ra 6.3 ~ 12.5μm, CT6-CT7 grade) has been greatly improved.

The mold shell cost of each t qualified cast produced by water glass process is about 824.98 yuan (see Table 2). The Class A raw materials that affect the cost are water glass and aluminum chloride, which are two materials that can be replaced by the silica sol process.

The whole shell making process uses 7 raw materials, and the shell cost of each t qualified investment casting is about 988.27 yuan (see Table 3). As can be seen from Table 3, Class A raw materials that affect the cost, such as silica sol and mullite powder, will be the key process improvement objects. The quick drying process of silica sol shell is feasible instead of water glass shell process. The average weight loss of 5 layers and a half shaped shells produced by the water glass process shell production line and the silica sol fast drying process shell production line was 36.09% (see Table 4). After weight reduction, the roasting time of silica sol shell is 1.5 h, which is 2h shorter than that of water glass shell, and the natural gas consumption is reduced.

The material consumption per t of the silica sol shell is 756.6kg, and the water glass shell material consumption is 1338.1kg, which is reduced by 43.45% compared with that of the silica sol shell, saving the material cost and handling costs. Silica sol shell cost 988.27 yuan/t, compared with water glass shell cost 824.98 yuan/t increased shell manufacturing cost 16.52%. The cost of silica sol quick drying process is basically the same as that of water glass shell. For aluminum-silicon refractory materials used in water glass shell, the use of silica sol quick drying process can reduce the manufacturing cost.

3. Process improvement plan and effect

Silica sol fast drying process cost of Class A two raw materials (silica sol and mullite powder) accounted for 72.1% of the total cost. In view of the high strength of the silica sol shell, under the premise of not affecting the performance of the shell, 20% to 25% pure water can be added to 1 or 2 layers of silica sol to reduce the silica sol consumption: 149.6 × 25% × 2.60 = 97.24 yuan/t. Reducing mullite powder by 50% and adding common quartz powder (270 mesh) by 50% in the reinforced coating can reduce the cost to: 334.80 yuan/t- (223.2 × 50% × 1.50 + 223.2 × 50% × 0.60) = 100.44 yuan/t, with a total cost reduction of 197.68 yuan/t. The actual cost of the quick drying process of silica sol shell is 790.59 yuan/t, which is lower than the process cost of water glass shell.