In the production of bricks, roofing tiles, porcelain and technical ceramics, an important mark of quality is a product free of air pockets. When fired, ceramics containing such pockets can be destroyed in the kiln and, in extreme cases, can even cause the destruction of the entire batch.
In bricks, this quality defect usually takes years to appear; during the winter, water penetrates the surface pores and causes them to burst.
Air removal from clay
After brick clay is loaded into the extruder, a vacuum serves to remove the air, thus preventing the formation of air pockets and the subsequent breakage of bricks. Similar to brick clay, ceramic clay is first placed in a mixer and pressurized with water or water vapour to form a homogeneous mixture. It is then transferred to an extruder where it is pressed into moulds under high pressure. The material is then extruded to the proper length, dried and fired.