Refractory bricks - machine press forming method

The machine press forming method is a method of pressing a blank into a green body using a refractory brick press. Generally, press molding refers to a semi-dry molding method with a moisture content of 4% to 9%. Commonly used equipment are friction brick presses, lever brick presses and hydraulic presses.

The molding process is essentially a process of making the particles in the blank dense and air exhausted to form a dense blank. The machine-pressed brick has the advantages of high density, high strength, small drying shrinkage and firing shrinkage, and easy control of product size, so this method plays a major role in the production of refractory bricks. In order to obtain a dense green body, sufficient pressure must be given to the green body. The size of this pressure should be able to overcome the internal friction between the blank particles, the external friction between the blank particles and the mold wall, and the uneven pressure distribution caused by the moisture of the blank, particles and their uneven filling in the mold. The proportional relationship between the three depends on the dispersion of the blank, the particle composition, the moisture of the blank, the size and shape of the blank, and the like. Although the relationship between the pressure and the densification of the green body can be calculated by several theoretical formulas, such as the change of the green body porosity with the logarithmic relationship of the pressure, etc., the pressure per unit area required by the green body is usually determined approximately by the test method, and according to This determines the total pressure that the brick press should have.

In addition to certain requirements for the moisture of the blank, machine press molding also has certain requirements for its particle size. If there should be a reasonable particle size ratio, the bulk density should be as large as possible. Generally, the critical particle size is 3~5mm, and the content of fine powder less than 0.088mm should be in the range of 35%~45%.

The most common defects of machine-formed refractory bricks are spalling and layer density. Spalling is a layered crack formed during the pressing process perpendicular to the pressing direction. Excessive billet moisture, excessive fine powder, too little binder and too high pressure will lead to spalling. Therefore, these parameters must be controlled in production. The layer density phenomenon is that the density of the brick after forming is reversed along the pressing direction. The bricks pressurized in one direction from the top are generally dense at the top and sparse at the bottom, and medium-density and sparse on the same level. This is due to the decreasing pressure caused by the friction between the billet particles and the friction between the billet and the die wall. Using double-sided pressure and applying lubricating oil on the four walls of the mold to reduce the external friction can reduce this phenomenon and reduce the porosity of the green body.