1 Introduction
"Lost foam casting" is also known as "gasification mold casting", "foamed polystyrene plastic mold casting", "solid mold casting" or "cavityless casting", etc. The essence of this casting method is to use foamed polystyrene plastic to replace the ordinary pattern. After the shape is formed, pour the molten metal without taking out the pattern. Under the heat of the hot liquid metal, the foamed plastic mold gasifies, burns and disappears. The liquid replaces the space occupied by the original foam mold, and the required casting can be obtained after cooling and solidification.
2. Lost foam modeling
The fundamental difference between the lost foam casting process and ordinary casting is that there is no cavity and parting surface.
The most commonly used lost foam casting process is the dry quartz sand or pearl sand molding method without binder.
3. Advantages of solid casting compared with sand casting
a. Simplify the casting production process and shorten the production cycle;
b. Reduced casting rejection rate and improved casting quality;
c. Solid casting can avoid casting size errors and defects caused by common sand casting, core grouping and box closing, etc., and improve casting size accuracy;
d. The degree of freedom of casting design is increased. Since the pattern has no parting surface, many problems that are difficult to achieve in ordinary sand casting are easy to solve in solid casting;
e. The utilization rate of materials has been improved, and the recovery rate of used sand is over 95%.
Lost Foam Casting Products
Black alloy castings of some lost foam casting companies in Europe and America
4. Application of lost foam casting process
The lost foam casting process, like other casting processes, has its shortcomings and limitations. Not all castings are suitable for production by the lost foam process, and specific analysis is required. The larger the batch of castings, the more considerable the economic benefits. The more complex the casting structure is, the more it can reflect the advantages and economic benefits of the lost foam casting process. For the case where there are narrow inner cavity channels and interlayers in the structure, the lost foam casting process needs to be tested in advance before it can be put into production. The size of the casting should consider the scope of use of the corresponding equipment (such as shaking table, sand box).
5. Comparison of filled sand silica sand and pearl sand
Advantages of silica sand:
(1) Abundant reserves, cheap and easy to obtain;
(2) It has a certain degree of refractoriness and can withstand the pouring temperature of most casting alloys;
(3) The particles are hard and can withstand the impact and friction of punching during molding and regeneration of old sand;
(4) It still has the strength to maintain its shape when it is close to its melting point, and can adapt to the basic working conditions of casting.
Disadvantages of silica sand:
(1) The thermal stability is poor, and the phase transition occurs at about 570 °C;
(2) Accompanied by large volume expansion, it is the root cause of expansion defects in castings;
(3) The chemical stability is poor under high temperature conditions, and it is easy to react with Fe2O3 to form fusible fayalite, resulting in sand sticking on the surface of the casting;
(4) The dust generated during crushing will cause the staff to suffer from silicosis;
(5) There is a lot of waste, and with the increasing environmental protection requirements, the cost of waste treatment is increasing;
(6) The particles are irregular, which has a certain influence on the fluidity and filling ability.
Features of Pearl Sand:
(1) Dense spherical particle shape: the particle shape is spherical, the surface is smooth and the surface area is small, and the fluidity and filling are excellent. Therefore, compared with other molding sands, the amount of binder used can be greatly reduced while obtaining good sand mold strength and high air permeability. It also has excellent collapsibility.
(2) Low thermal expansion rate: The thermal expansion rate is lower than other foundry sands. Therefore, the dimensional accuracy of the production castings is high, the cracks and defects are few, and the yield of the castings is high.
(3) Good crushing resistance: The volume of molten ceramic sand is compact and high in strength, and it is rarely broken after repeated regeneration.
(4) High refractoriness: The main component is Al2O3, which is an aluminum-silicon refractory material with good refractory performance and can meet the casting requirements of various metals and alloys.
(5) Small bulk density: The bulk density is lower than that of chromite sand and zircon sand, thereby reducing the cost of using high-quality molding sand.
6. Conclusion
(1) Ceramic Foundry sand is used as filling sand, and its good grain shape has many advantages, such as good fluidity, high air permeability, and energy efficiency to prevent and reduce casting defects such as slag inclusion and pores.
(2) Ceramic Foundry sand is used as filling sand with a refractoriness of ≥1800°C. It can not only produce cast iron and cast steel products, but also can be used to produce high manganese steel and heat-resistant steel products, reducing the raw material and procurement costs of manufacturers.
(3) When silica sand is used as lost foam casting sand, because silica sand is easily broken and pulverized, the workshop environment is poor, and there is a lot of dust, which will cause bodily harm to foundry workers. Ceramic Foundry sand has high refractoriness, low crushing rate and high recovery rate, which not only increases the yield of castings, but also significantly improves the production environment and ensures the health of workers. It is the first choice for lost foam casting.
