Casting coating is an auxiliary material coated on the surface of the mold or core, which plays an important role in improving the surface quality of castings. China’s early casting craftsmen, more than 3000 years ago, have prepared and successfully used casting coating, making a significant contribution to the development of casting technology.
With the development of production and technology, the requirements for casting quality are increasing day by day. In order to enhance the competitiveness of their products, many foundries devote themselves to the research of coatings in view of the problems in production.
The following, briefly about the casting coating of several problems.
First, the solid content and strength of the coating
Now, the coating used for resin bonded sand requires its high solid content and high strength, which is mainly due to two considerations.
1. Adapt to the characteristics of sand mold
In the past, clay sand wet sand type not paint, paint only used for clay sand dry type. Due to the strength of the clay sand dry type is very low, and to make the casting castings are important or large castings, the requirement of coating not only to form isolation layer, and it requires infiltration casting coating the surface of the following, best involving 3 ~ 4 sand, make the mold surface is enhanced, therefore, the viscosity of the paint can’t is too high, the solid content is not too high.
2. Consider energy saving, environmental protection and reducing production costs
Liquid carriers used in coatings, mainly water and alcohols. 20 centuries 70 ~ 80 time, had used does not need to dry or ignite, can volatilize chlorine generation hydrocarbons, such as dichloromethane, as the carrier of paint. Because of its toxicity, its negative impact on the environment as it evaporates into the atmosphere, and its high cost, it is now largely unused.
Second, the raw materials used for coating
There are many kinds of raw materials used in casting coating, and they will be supplemented constantly on the basis of the development of material industry.
1. refractory aggregate
Refractory aggregate is the main component in the coating, and its quality and selection have great influence on the use effect of the coating. At the same time, when choosing aggregate, we should also make a more comprehensive analysis in industrial hygiene and economy.
2. the carrier,
The main carriers used in casting coatings are water, alcohols and chlorinated hydrocarbons. At present, due to the consideration of price and environmental aspects, very used to chlorine hydrocarbon as the carrier of the coating, the general is water based coating and alcohol based coating.