The following problems have occurred since the use of alkali phenolic resin sand process:
1. The surface of the casting is seriously bonded with sand, which is difficult to clean. The pouring temperature of steel castings is as high as 1600 ℃, while the refractoriness of silica sand is about 1400-100 ℃, which is very easy to cause the sintering of molding sand and the formation of hot bonded sand. For this reason, it costs quite much amount of money each year to hire outsourcing workers to polish and clean the casting surface.
2. The casting has low dimensional accuracy and poor dimensional stability. Due to the high expansion coefficient of silica sand, the crack of mold at high temperature leads to the formation of veins on the surface of parts, and the deformation of mold leads to the distortion of castings and the reduction of dimensional accuracy.
3. The sand regeneration effect is poor and the film removal rate is low. A few days ago, centrifugal regeneration was used as the main auxiliary for medium temperature roasting, but the regeneration effect was not very good. In addition, the silica sand had many edges and corners, low hardness, and was easy to be broken. A large amount of dust was generated in the process of regeneration and sending, resulting in the addition of resin as high as 1.9% ~ 20%. The high temperature gas evolution of the sand mold increased, and the subcutaneous porosity of the casting increased. At the same time, the production cost increased, the production environment was bad, and the environmental protection pressure was high.
4. The separation effect of chromium ore sand is poor, the recovery ratio is low, and the recovery equipment is imported, so the spare parts are expensive, the maintenance cost is high, and the cycle is long. In order to improve casting quality, save cost and improve environment.
Fused ceramic sand has the following characteristics
(1) Fused ceramic sand has small thermal expansion coefficient, good mold stability, no cracking, and reduces casting defects such as veins caused by sand expansion.
(2) The particle size of fused ceramic sand is close to spherical, the surface is smooth, and the structure is compact, so that the binder can be evenly covered, with good fluidity and easy compaction.
(3) Fused ceramic sand has high hardness, is not easy to break, and almost does not produce ash. The amount of resin added can be reduced by more than 30%, which can reduce the gas generation of core sand and reduce the risk of pore formation.
(4) The mullite phase of fused ceramic sand is much higher than that of sintered products. It has high fire resistance and exceeds the pouring temperature of molten steel. It is suitable for the molding of large steel castings and alloy steel. It can completely replace chrome ore sand and make the molding not stick to sand.
(5) The recycling and regeneration performance is good, and the durability and regeneration recovery rate are high. The regeneration rate is as high as 98%. Compared with chromite sand and zircon sand, its price is only 25-50% of zircon sand. At the same time, because the sand particles are spherical and the total surface area is small, the amount of resin can be reduced by 30%-50%, and the amount of water glass is ≤ 4%; The casting defects caused by binder are reduced and the yield of castings is improved.
Using Fused Ceramic Sand to Improve the Alkali Phenolic Resin Process Conclusion
(1) Because of its production process, fused ceramic sand has the basic properties of high strength, high fire resistance and good air permeability superior to ordinary silica sand. At the same time, we also further verified through laboratory comparative tests that it can still obtain higher compressive strength than ordinary silica sand when the resin dosage is reduced by 50%, and its abrasion resistance is superior to ordinary silica sand, Therefore, we believe that Fused ceramic sand can replace silica sand in terms of technical conditions.
(2) Although the one-time investment of replacing silica sand with fused ceramic sand is large, it is expected to recover the investment cost in 4-5 years.
(3) With the increasing pressure of environmental protection, the quality standard of marine diesel engine steel castings continues to improve, and the labor cost is increasing, the advantages of fused ceramic sand will be more obvious. It is the general trend to realize the sustainable development of casting that fused ceramic sand replaces silica sand.