Foundry Coating Material
Casting coatings(Foundry coatings) refer to casting auxiliary materials used to coat the surface of the cavity or sand core to change the surface refractoriness, chemical stability, metal erosion resistance, and sand adhesion resistance.
Therefore, the casting process production of casting coatings is very important. Because traditional casting coatings have poor chemical stability and low hardness, they are prone to metal erosion grooves and are not suitable for large-scale industrial production. On the other hand, the separation of casting coatings Poor thermal performance has led to the gradual emergence of cold barriers and pores.
Graphite is a neutral material. It has high ability to chill metals, is not wetted by metals or metal oxides, does not chemically react with molten metal, and has high refractoriness. For example, the melting point of natural flake graphite is as high as 3000 degrees and is generally used in industry. The melting point of graphite is 2100 degrees. Therefore, graphite has excellent fire resistance and is not wetted by liquid metal. These two characteristics are unmatched by any other material. With abundant sources and low prices, graphite powder is the most commonly used refractory filler in the production of sand iron castings, and it is also commonly used in the production of sand and metal casting copper and aluminum castings. Graphite powder is generally not suitable for cast steel, this is mainly because graphite will carburize the cast steel.
In common graphite coatings, flake graphite and amorphous graphite are generally used in combination. If flake graphite is used alone, because flake graphite has a high refractoriness, the coating is difficult to sinter under general casting temperature conditions, and it is easily eroded by high temperature molten iron and loses its effectiveness. If the amorphous graphite is used alone, the coating is prone to cracking after drying or ignition. It is generally recommended that the ratio of earthy graphite to flake graphite is 8:2. If the coating uses other non-graphite refractory materials as aggregates, a small amount of flake graphite can also be added to prevent the coating from cracking and improve the refractoriness.
Due to the color and permeability of graphite, it causes environmental pollution. In recent years, people have developed many graphite alternative materials. The so-called light-colored paint has basically become the main body of the paint.
However, the biggest feature of graphite is its reducibility. It does not wet with molten iron and forms a protective gas film, which is not available in other materials. Therefore, more or less graphite is added to the cast iron coating.
- fire resistance; not wetted by liquid metal