What is investment casting?
Investment casting is an advanced forming technology and can produce high quality castings employed in the defense industry and aerospace fields, as well as traditional civilian industrial sector. In recent years, whatever in the native and foreign, investment casting has been put forward as a continuous high speed development. Investment casting surface materials have direct influence on the final quality of the castings, so the choice of the shell surface materials is of particular importance.
At present, investment casting surface layer refractory materials commonly used zircon sand, fused corundum and fused silica, zircon sand is widely used investment casting surface material due to with high fireproof performance, small and uniform thermal expansion coefficient, good thermal chemical stability, and many other excellent performance . But zircon sand reserves few around the world, mainly in Australia and South Africa, our country mainly relies on imports, and zircon sand supply market is not stable, price fluctuation is bigger. In addition, the United States, Europe and other countries studies show that zircon sand containing radioactive elements which is harmful to the body.
Fused Ceramic Sand Situation
Fused Ceramic Sand is independently developed an artificial sand in our country, according to statistics, the output of each year in more than forty thousand tons, mainly exported to distant countries. The main properties of Fused Ceramic Sand are high refractoriness, small density, low thermal expansion rate, good liquidity, also has the very good breakup, and the price is low. Fused Ceramic Sand applied in investment casting surface material, can not only make full use of resources in our country, still can save a lot cost for foundry enterprises.
Using Fused Ceramic Sand as Surface Layer Materials in Investment Casting
1. Fused Ceramic Sand conforms to the requirements of the selection of surface materials. The thermal expansion rate of Fused Ceramic Sand was lower than that of zircon sand, it was far easier to get good casting quality, proportion was smaller than zircon sand a lot, the quality of the Fused Ceramic Sand was small under the condition of the same volume, it can save material so as to achieve cost savings. In according to accumulation model, we find that there were both minor contact and the surface contact between zircon sand particles, and there were all surface contacts between Fused Ceramic Sand particles. So the shell has good air permeability and easy for cleaning.
2. The preparation process of investment casting shell, compare the characteristics of three type shell (sodium silicate type, compound, silicon sol), this experiment finally selects high quality silica sol shell, surface sand use Fused Ceramic Sand and zircon sand. Casting stainless steel pump cover, calcination temperature is 1050℃, time is 2h, pouring temperature is 1570 ℃.
3. With surface layer sprinkles two layers Fused Ceramic Sand, mold shell had high intensity good sintered density and can effectively prevent metal liquid immersion. In addition, it was easy to shell mold. There was no obvious interface reaction when pouring stainless steel liquid, castings had a good surface quality. No obvious defects such as adhering sand, burr, etc. were detected. The surface quality was similar or better. However, when surface layer sprinkles only one layer Fused Ceramic Sand, mold shell surface is easy to cause sand covering uneven, adhering occurred in the casting surfaces.