Lost foam casting has many kinds of processing methods in China. Different lost foam casting methods have different requirements on coating properties. The casting system and casting body have different requirements on the properties of the material. The gas permeability of the lost foam coating is accurate. It should be permeability, and the permeability of the medium temperature zone has practical value. In the selection of aggregates, the higher the refractoriness, the better. In order to ensure the good permeability of the sand, there are new requirements for the stripping property of the coating. The method of making and using the paint has an effect on the workability and process performance of the paint.
1, the role of lost foam coating
The function of the lost foam coating is to support and protect the foam model, prevent the liquid metal from infiltrating into the sand and sand, absorb the cracked product and allow the cracked gas to pass through the coating, keep the cavity air gap formed by the foam model cracking intact, and hold the liquid Metal heat does not dissipate quickly. Therefore, the use of the lost foam coating can reduce the surface roughness of the casting, ensure the accuracy of the casting, reduce or prevent the casting sand, sand holes, pores, metal penetration, cold insulation, pouring, carbon deposition and other defects. Therefore, the lost foam coating should have sufficient refractoriness, certain mechanical strength, proper thermal and thermal conductivity, proper gas permeability and ability to absorb liquid cracking products, smooth surface, sufficient coating performance, and no foam model. A chemical reaction occurs.
2, the performance of the lost foam coating
The properties of lost foam coatings include many indicators: strength, gas permeability, refractoriness, thermal insulation, rapid cooling resistance, rapid heat, wettability, thixotropy, varnishing, dripping, suspension, etc. These performance indicators can be Classified into two categories: work performance and process performance
Coating strength, gas permeability, refractoriness, thermal insulation, and resistance to rapid cooling and heat are all workability. The most important of these are strength and breathability. Lost foam coatings require high strength and high gas permeability, which is different from other foundry coatings.
The coating properties, dripping properties and suspension properties of the coatings are process properties. In order to reduce the cost of foam casting, water-based coatings are often used. Therefore, water-based coatings and organic foam moldings do not wet, and it is necessary to improve the coating properties of coatings, which is a major process performance of lost foam coatings. Another major process performance is the dripping of the coating. After the dipping coating, the pattern is generally suspended and dried. It is hoped that the coating can be leveled and not dripped as much as possible to ensure a uniform coating of a certain thickness, making full use of the coating without polluting the environment.
3. Composition design of lost foam coating
The basic components of the coating for lost foam casting include refractory materials, carriers, binders, suspending agents, preservatives, surfactants, defoamers, and the like.
Luoyang Liu’s mold reminds you to pay attention to: (1) the selection of coatings should be considered from the aspects of coating performance, preparation operation and procurement cost; (2) the permeability of coatings with alumina as the main aggregate is relatively high; (3) Poor gas permeability makes it possible to add a certain amount of organic binder and organic binder to burn in the foot-filling process to increase the micropores of the coating, which not only increases the gas permeability, but also increases the room temperature strength of the coating.
The above is the knowledge about the lost foam coating summarized by Luoyang Liu’s mold. For more details about the lost foam coating, please contact us.