Machine Pressing Molding Method of Refractory Materials

Currently, the most commonly used molding method is the machine pressing molding, which presses the raw materials into green body with the brick pressing machine and steel mold. Since the semi-dry raw materials contain about 5% moisture, it is also called semi-dry molding method. 

Refractory bricks made by this method have dense structure, high strength, small drying and firing shrinkage and easy-to-control size. It can also be divided into single-sided pressurization and double-sided pressurization. The latter can reduce the layer density phenomenon. 

 

The refractory bricks made by this method have layer spalling and layer density phenomena. Layer spalling refers to the layered cracks perpendicular to the pressing direction during pressurization. If the raw materials contain too many moisture and fine powder and too few binders and the pressure is too high, all these may cause layer spalling. Therefore, during production, those parameters should be strictly controlled. The layer density phenomenon is the contravariance of the density along the pressurization direction. Single-sided pressurization bricks have dense upper part and loose lower part and, on the same horizontal plane, dense inner part and loose outer part. This is caused by the decreasing pressure caused by the friction between particles and friction between raw materials and the mold. Double-sided pressurization and coating the mold with lubricant oil can reduce this phenomenon and reduce the porosity of refractory bricks. 

 

It is impossible to eliminate the layer density phenomenon, but measures can be taken to reduce it to the minimum. 

 

The characteristics of machine pressing molding are closely related to the properties of the semi-dry materials. The materials contain a low content of moisture. The mud particles are rearranged with high molding pressure. Raw materials have elastically deformation and brittle deformation when pressurized. Under the combined effects of mechanical bonding, electrostatic attraction and friction, the particles combine each other into a green body. For different mud, because of particle shape, moisture content, fine powder and binders, the above-described various forces are also different. Therefore, when developing molding system, it is important to fully consider the properties of each material.

 

Commonly used pressing molding machines include friction brick pressing machine, hydraulic pressing machine, lever-type pressing machine, turntable pressing machine and isostatic pressing machine. The most commonly used machine is the friction brick pressing machine. For most plants, the nominal pressure of the friction brick pressing machine is between 1000-6000kN. 
 

When selecting molding equipment, take into account the quality requirements, shape, size and quantity of refractory bricks. For bricks with simple shapes, small size, massive quantity and normal quality requirements, lever-type pressing machine with high production efficiency can be selected. For products with high quality requirements, friction brick pressing machines with a pressure of no less than 3000kN can be selected. High-stroke friction pressing machines are suitable for the production of products with a large size, complex shape and massive quantity. Hydraulic pressing machines are suitable to produce products with high quality requirements.