**6. Composition**

270 Ceramic Coatings – Applications in Engineering

100 150 200 250 300 350

**<sup>35</sup> Lenght**

**0 50 100 150**

Ceramic coatings present an insulation effect influencing liquid metal temperature drop reduction when flowing into a mould; they also influence liquid metal fluidity and the way a mould is filled, certainly affecting the casting quality. Metal fluidity reduction has been noticed while using some types of coatings (based on silica, zircon, graphite); it most frequently resulted in an increment of the coating layer thickness on either a mould or a

With EPC process, when a mould is filled and when polymer pattern degradation and evaporation is carried out, insulation effect of the coating influences liquid metal temperature drop reduction. When the mould is filled up with liquid metal, i.e. when polymer pattern is expended, the coating, due to insulation effect, influences a casting cooling and solidification speed reduction. At the same time, subcooling, created in liquid metal as a consequence of endothermic degradation of polymer pattern in contact with liquid metal, has a significant influence on the casting solidification. If subcooling is huge, fine and tiny-grained casting structure is preferably formed, because such structure provides for the better casting properties. All of that points to the complexity of casting solidification conditions as far as "full mould" is concerned, and to a significant role of ceramic coating in the casting process to form the casting structure and properties. Figure 6

Fig. 6. Coating insulation effect on the metal flow length and mould filling time

**Heat transfer coefficient, W/m2**

**C**

**0**

**2**

**4**

**Time, s**

**6**

**8**

**Coating tickness, mm**

**Time**

polymer pattern (Monroe 1994).

**Lenght, cm**

Fig. 5. Gas permeability dependence on the coating dry film thickness

**Gas permeability, %**

Research showed that, depending on use, most of contemporary foundry coatings represent very complex blends consisting of over 15 components. However, four basic components are the following:

