1. Cooling rate
The cooling methods of centrifugal casting composite roll are generally divided into air cooling and water cooling, which have a great impact on the microstructure and properties of composite materials. With the increase of cooling rate, the matrix grain size becomes smaller, the mesh structure increases, and the local phenomenon of isolation and broken mesh occurs. When air cooling is used, with the decrease of cooling rate, chrysanthemum lamellar cellular structure appears in the microstructure, and the number of cellular structure increases with the decrease of cooling rate. Controlling the cooling rate can significantly improve the hardness, toughness and other mechanical properties of the material.
2. Pouring temperature
The pouring temperature has a great influence on the composite effect of bimetal composite roll and ceramic particle reinforced metal matrix composite roll. In the ceramic particle reinforced metal matrix composite roll, the pouring temperature affects the volume fraction of ceramic particles in the matrix. Under the same conditions of other parameters, within a certain range, the higher the pouring temperature, the larger the volume fraction of ceramic particles in the matrix, and the maximum can reach about 80%. In the bimetal composite roll, the pouring temperature of the inner and outer layers of metal is different. For the outer layer metal, when the pouring temperature is too high, the strength of the embryo shell is low at the initial stage of solidification, and cracks are easy to occur, and segregation is also easy to occur when high-speed steel is used as the outer layer metal; When the pouring temperature is too low, it is easy to cause defects such as poor filling and slag inclusion. When the pouring temperature of the inner metal is too high, it is easy to cause “reverse corrosion” between the two metals, resulting in cracking due to high stress in subsequent heat treatment; If the pouring temperature is too low, the two metals can not be effectively combined.
3. Centrifugal speed
Rotating speed is an important technological parameter of centrifugal casting. If the rotating speed is too low, the “rain” phenomenon of molten metal will occur during centrifugal casting, and the shrinkage porosity, slag inclusion and uneven defects on the inner surface will also occur in the tube blank; If the rotating speed is too high, the tube blank is prone to crack, segregation and other defects.
In ceramic particle reinforced metal matrix composites, the rotational speed of the centrifuge also has an effect on the volume fraction of ceramic particles. With the same other parameters, the higher the rotational speed, the higher the particle volume fraction. The relationship between rotational speed and volume fraction of ceramic particles is shown in Formula (1) Stocks equation:
Vcent= d2( ρ p- ρ m ) ω 2/ (18 η)
Where, Vcent is the velocity of the added particles in the direction of centrifugal force in the matrix melt; ρ p- ρ M is the density difference between the added particles and the matrix melt; ω Is the angular velocity of mold rotation; D is the added particle diameter; η Is the dynamic viscosity coefficient of the matrix melt. According to the formula, in the same η The higher the speed, ω The larger the size, the faster the external particles migrate to the outer layer, and the higher the volume fraction.
4. Pouring time
The pouring time is mainly for bimetal composite rolls. The interval between pouring the inner and outer layers of metal should not be too long or too short, otherwise the two metals will not be effectively compounded. Control the pouring time between layers. When the metal layers are poured at 30~100 ℃ below the melting point, the effect is best, and the interlayer has good bonding strength. The interval time is approximately 5~13 s depending on the metal.