At present, most engines, whether gasoline engines or diesel engines, use turbocharging technology, that is, the pressure of exhaust gas from the engine is used to drive the turbine to rotate at high speed, and the turbine drives the coaxial impeller to compress the air sent by the air filter pipe, so that the air increases pressure and enters the cylinder to increase the output power of the engine. The working temperature of the turbine end of the turbocharger shell is generally more than 600 ℃, and some even as high as 950-1050 ℃. The shell material needs high temperature resistance and good casting performance. The shell structure is more compact, the wall thickness is thin and uniform, and the inner cavity is clean, etc., so the requirements are extremely stringent. At present, the turbocharger shell is generally cast with heat-resistant steel, and heat-resistant ductile iron.
Turbo housing of a 1.8 T engine, material: 1.4837, namely gx40crnisi25-12, main chemical composition (%), pouring temperature 1560 ℃. The alloy has high melting point, large shrinkage, strong hot cracking tendency, high casting difficulty, strict requirements for residual carbides and non-metallic inclusions in the metallographic structure of the casting, and specific provisions for casting defects. In order to ensure the casting quality and production efficiency, the molding process adopts the core assembly pouring with the film coated sand shell core as the main part (there are also some cold box and hot box cores) (see the core assembly schematic photo in Figure 5). At first, 50/100 mesh scrub sand was used, and then over baked silica sand was used, but problems such as sand sticking in the inner cavity, burr, hot crack and porosity occurred to varying degrees. On the basis of investigation and test, the factory decided to use the special sand - Fused Ceramic sand. It initially purchased the finished coated sand (100% Fused Ceramic sand), and then purchased the regeneration and coating equipment. In the production process, it continuously optimized the process and used Fused Ceramic sand and scrubbing sand to mix the raw sand.
In recent years, the production process of the plant has operated stably, the casting quality is good, and the economic and environmental benefits are remarkable. The summary is as follows:
a. The use of Fused Ceramic sand or the mixing of Fused Ceramic sand and silica sand for core making eliminates the defects of sand sticking, sintering, veining and hot cracking of castings, and realizes stable and reliable production;
b. Core assembly casting, high production efficiency, low sand iron ratio (generally no more than 2:1), less raw sand consumption and lower cost;
c. The core casting is conducive to the overall recovery and regeneration of waste sand, and the thermal regeneration is adopted uniformly. The performance of reclaimed sand has reached the level of scrubbing sand and new sand, and the effect of reducing the purchase cost of raw sand and the discharge of solid waste has been achieved;
d. It is necessary to frequently detect the content of Fused Ceramic sand in reclaimed sand to determine the addition amount of new Fused Ceramic sand;
e. Fused Ceramic sand has round shape, good fluidity and large proportion, which is easy to cause segregation when mixed with silica sand. If necessary, the sand shooting process needs to be adjusted;
f. High quality phenolic resin shall be used as much as possible during film covering, and various additives shall be used with caution.
Fused Ceramic Sand Utilization Conclusion
The application of Fused Ceramic sand in the engine casting industry has improved the production efficiency, improved the labor environment, solved the casting defects, and achieved remarkable economic benefits and good environmental protection benefits.
The engine foundry industry should continue to strengthen the regeneration of large-scale core sand, further improve the use efficiency of Fused Ceramic sand and reduce solid waste emissions.
According to the application effect and scope, Fused Ceramic sand is the casting special sand with the best comprehensive performance and the largest amount in the engine casting industry.