What are the functions of lost foam coatings? What is p […]
What are the functions of lost foam coatings? What is performance?
There are many methods of lost foam casting in our country. Different lost foam casting methods have different requirements for coating performance, and the requirements of the casting system and casting body are also different. The air permeability of the lost foam coating is more accurate. It should be permeability. The permeability in the middle temperature zone has practical value. In the choice of aggregates, the higher the refractoriness, the better. In order to ensure good air permeability of the sand, there are new requirements for the peelability of the coating. The production and use methods of the coating have an impact on the working performance and process performance of the coating.
1. The role of lost foam coating
The role of the lost foam coating is to support and protect the foam model, prevent the liquid metal from penetrating into the sand and sticky sand, absorb the cracked product and let the cracked gas pass through the coating, maintain the integrity of the cavity air gap formed after the foam model is cracked, and maintain the liquid state Metal heat will not dissipate quickly. Therefore, the use of lost foam coatings can reduce the surface roughness of the castings, ensure the accuracy of the castings, and reduce or prevent defects such as sand sticking, sand holes, pores, metal penetration, cold isolation, inability to pour, and carbon deposits. Therefore, the lost foam coating should have sufficient refractoriness, a certain mechanical strength, appropriate thermal insulation and thermal conductivity, appropriate air permeability and the ability to absorb liquid pyrolysis products, a smooth surface, sufficient painting performance, and no foam model A chemical reaction occurs.
2. The performance of lost foam coating
The performance of lost foam coatings includes many indicators: strength, air permeability, refractoriness, thermal insulation, resistance to rapid cold, rapid heat, wettability, thixotropy, coating, dripping, suspension, etc. These performance indicators can Summarized into two categories: work performance and process performance
Coating strength, air permeability, refractoriness, thermal insulation, and rapid cooling and heating resistance are all working performance. The most important ones are strength and air permeability. Lost foam coatings require high strength and high air permeability, which is different from other casting coatings.
The coating properties, dripping and suspension properties, etc. belong to the process performance. In order to reduce the cost of lost foam casting, water-based coatings are often used. Therefore, water-based coatings and organic foam molds do not wet, and the coating properties need to be improved. This is a major process performance of lost foam coatings. Another major process performance is the dripping property of the paint. After the pattern is dipped in the paint, it is generally hung to dry. It is hoped that the paint can be leveled and not dripping as much as possible to ensure a uniform coating of a certain thickness and make full use of the paint without polluting the environment.
3. Composition design of lost foam coating
The basic components of coatings for lost foam casting include refractory materials, carriers, binders, suspending agents, preservatives, surfactants, defoamers, etc.