The lost foam casting process classification and characteristics

The lost foam casting can be divided into self-hardening sand  (damp type with binder) lost foam casting and dry sand (dry type without binder ) lost foam casting according to its cast mould material. According to casting condition, it can be divided into ordinary(under atmospheric pressure) lost foam casting and vacuum negative pressure lost foam casting. Compared to the traditional sand type casting, the lost foam casting by large quantity of production has following characteristics:

① The model shape is completely consistent with cast mould. The size is only different in metal shrinkage amount. The foam plastic model retains in the casting model to form “full mold”cast mould, instead of traditional sand mould “ empty cavity” cast mould(that is, empty mold).

② The sand mould is the dry silica sand without binder, moisture and any addition. Or it chooses Magnesium olivine sand, chromite sand, magnesite sand and Ceramic Sand and so on according to alloy kinds.

③In the casting process, the foam plastic model constantly decomposes, splits, gasifies and the alloy liquid replaces the model under the alloy effect of the high temperature liquid, instead of the traditional “empty cavity” (empty mold) casting. It is the process of alloy liquid filling the mold cavity. To make a casting requires one foam plastic model to disappear.

④ The foam plastic model can be divided into blocks for molding. And then it bonds and combines. The model shape(and casting shape) basically hasn’t any limit(manual cutting, molding by machine or combination binding).

  Figure 1-1 is the comparison of mass produced traditional clay sand casting and lost foam casting process characteristics

(1) The problems that we should pay attention to by adopting lost foam casting process. Although the lost foam casting process has incomparable advantages, any casting process is only applied for some range. Therefore, for adopting lost foam casting process, we must think these problems carefully.

① We should consider the complex economical benefit: for specific casting, material, size, shape, structure, batch and price and so on, we should make detailed economy assessment, cost accounting and technical ability assessment.

② The process technology needs to prepare fully: “copy, imitate or buy lost foam production line hurriedly” are inadvisable. For example, some factory buys the lost foam production line of ductile iron pipes quickly, but they haven’t technical engineers and they haven’t the salesman for pipe products. By a period of time, the pipe production is unsalable due to market change. Therefore, they stop the line hastily. The production line is set aside.

③ We should consider material casting application: copy, imitate or buys the lost foam casting production line without considering the factory’s real situation. There are many problems after buying the lost foam production line. For example, some factory introduces 1000t/Y small lost foam cast steel factory. The equipment price is 20,0000- 30,0000. Because one set of process is matched according to high manganese steel casting process. Forsterite sand is used as dry sand and powder material is used as coating aggregate. The casting’s qualified rate is very high. The finished product quality is very good. It is profitable. However, the casting is ZT25. The output party doesn’t understand ZG25 production process. The input party is looking forward to output party to solve it. Therefore, they introduce technicians to produce after they explore for a long time. The loss isn’t small.

④ We should consider the production and development factors: some factories buy the lost foam production line, but they haven’t considered the production and development leeway. For example, some factories buy the lost foam production line, introduce pipes and wearing resistance castings. They plan to work by one shift or two shifts. Later, this area has larger casting requirement. It needs two shifts or three shifts to work. The great improvement of production quantity exposes that the equipment hasn’t delayed effect. It affects model deformation. The cooling treatment capacity isn’t enough. They want to improve the production quantity, but the equipment can’t meet this production quantity. It is a pity to take these equipment down. They haven’t economical power to buy larger production capacity of lost foam production line. Advance or retreat is in a dilemma. After struggling for a long time, it waits for production tasks due to no long-term casting business. Some factory buys one 3000t/Y cast steel lost foam production line. After it completes 1／3 production task, they haven’t casting production task due to many reasons. So they stop the equipment and wait for production tasks.

⑤ The casting which isn’t suitable for lost foam casting process: for example, low chromium cast iron grinding balls. When we make the low chromium cast iron grinding ball by lost foam casting process, it should adopt quenching or normalizing treatment to improve hardness and abrasive resistance performance due to slow dry sand cooling speed. However, the performance can’t reach metal mold casting grinding balls. On one hand, it can get uniform shape distribution casting hard cover same with carbide size on the grinding ball surface--corresponding grinding ball; on the other hand, it can adopt cast state normalizing or fog quenching to reduce cost. The foam model 0.03～0．04 RMB／g. The cost can be removed.

⑥ We should correctly understand and scientifically treats lost foam casting process: some people work on sand mold foundry. They visit some lost foam casting factories or near workshops by lost foam production. Especially the factory adopting simple lost foam casting process thinks it is simple and convenient. The foam model can buy EPS package material waste or board for cutting, machining or joining together. The coating is made by themselves. The three-dimension vibration table is made by themselves. They buy the vacuum pump to out into the lost foam production. After struggling for more than half a year, they buy lost foam casting mechanics equipment and foaming & molding equipment of white area again to produce the abrasion resistance castings lining board or pipes and so on.

Some high manganese steel foundries completely copy same industry’s lost foam casting lining board and hammer head and so on. The sandbox is imitated.The box wall is drilled holes by electric drill. The model adopts waste package foam material to cut and bind. After production, it is never stable. Because the model quality isn’t uniform.

In conclusion, by careful,systematic, comprehensive analysis and integrated plan, all large and medium lost foam casting factories get excellent effect. Some medium and small factories buy lost foam production process willfully. The above situation always occurs. They think“Getting half the result with twice the effort”. It can’t reflects the advantages and characteristics of lost foam casting process.