Precision casting, also known as lost wax casting, its products are precise, complex, close to the final shape of the parts, can not be processed or rarely processed directly used, so investment casting is a near net form of advanced technology.
Ancient China: wang ziwu ding, copper ban, copper lion and so on, are the masterpiece of investment casting. Since investment casting was used in industrial production in the 1940s, it has been developing at a rapid speed for half a century. In particular, European and American countries are developing rapidly. Investment casting is used in almost all industrial sectors, especially electronics, petroleum, chemical industry, energy, transportation, light industry, textile, pharmaceutical, medical equipment, pump and valve. In recent years, China has also developed rapidly.
The development of investment casting technology enables investment casting not only to produce small castings, but also to produce large castings. The outline size of the largest investment casting is nearly 2m, while the minimum wall thickness is less than 2mm. At the same time, the investment casting is more precise, in addition to linear tolerance, parts can also achieve a higher geometric tolerance. The surface roughness of investment castings is getting smaller and smaller, up to Ra0.4 m.
Ceramic mold casting
Casting method of producing castings by casting with ceramic slurry.Ceramic slurry is composed of ethyl silicate hydrolysate and fine refractory sand with relatively pure texture and high thermal stability, such as electrofused quartz, zirconium and corundum.Calcium hydroxide or magnesium oxide is often added as catalyst to make ceramic slurry bond in a short time.Because the composition and appearance of the refractory materials used are similar to ceramics, it is called ceramic mold.Ceramic mold casting is a new technology developed on the basis of ordinary sand mold casting.Ceramic type has two types: (1) ceramic type by ceramic paste pouring.The production process is to first fix the appearance on the mold plate, coat the sand box, and then pour the ceramic paste into the sand box. After the glue is hardened, the mold is taken off, and then it is roasted at high temperature to become the casting mold.(2) the use of liner, in the liner and the gap between the shape of ceramic paste casting.The bushing can be either sand or metal.A large amount of ceramic slurry can be saved by casting ceramic shell with bushing.The surface roughness of ceramic casting can be up to Ra10 ~ 1.25 micron, the dimensional accuracy is up to 3 ~ 5 grade, can achieve the purpose of less cutting.The production cycle of ceramic mold casting is short and the metal utilization rate is high.The largest casting can reach more than ten tons, mainly used for casting large thick wall precision casting and casting single small batch of punching die, forging die, plastic die, metal die, die casting die, glass die, etc.The service life of the ceramic mold is comparable to that of the mold made by machining, and the manufacturing cost is lower than that of the mold made by machining.
Of the total casting output, 60-70% of the castings are produced with sand molds, and about 70% of them are produced with clay sand molds.The main reason is that compared with other casting methods, the cost of sand casting is low, the production process is simple and the production cycle is short.Therefore, the engine cylinder block, cylinder head, crankshaft and other castings of the automobile are produced by the clay wet sand process.When the wet mold can not meet the requirements, then consider the use of clay sand table dry sand mold, dry sand mold or other sand mold.The weight of a dry clay sand casting can range from a few kilograms to several tens of kilograms, while the dry clay casting can weigh dozens of tons.
Generally speaking, for medium and large castings, castings can be produced by resin self-hardening sand mold, steel castings can be produced by water-glass sand mold, and castings with precise size and smooth surface can be obtained, but the cost is high.
Of course, the casting precision, surface finish, material density and microstructure, mechanical properties and other aspects of sand casting production are often poor, so when these properties of casting requirements are higher, other casting methods should be used, such as investment (wax loss) casting, die-casting, low-pressure casting and so on.