Refractory bricks are made by pressing.  The moulds, called dies, are made of thick, hardened steel.  The outer casing is prismatic, with a top plate and bottom plate fitting snugly inside it.   The moulds are filled with a specific mass of material and pressed under high pressure to a specific thickness.  Usually the material is filled by a feeder which slides over the mould to fill it and then retracts, scraping off the excess material.  The top plate is then pushed down to the predetermined level, held for a short while so that the trapped air can escape through the narrow gaps around the outer casing.  The top plate is lifted, and the bottom plate is raised to the top of the casing, and the pressed brick is pushed out forwards, where it is manually removed and packed onto a tunnel kiln car or this is done robotically.  The packing is done so that there are air gaps between the bricks for combustion gases to circulate.

There are several different designs of presses.  Mechanical presses use leverage to attain high pressure.  Hydraulic presses use large hydraulic cylinders to create high pressure.  Some presses incorporate vibration and some use sudden impact.

If the brick mixture is too fine, the trapped air has difficulty escaping and the pressure causes the brick to laminate, leaving planes of gaps in the bricks.  If there is an excess of coarse aggregate, the coarse particles can shatter.  Imbalance of the particle size distribution leads to 3 different types of undesirable porosity.  Cracking if there is an excess of coarse particles, parting if there is an excess of fines, which shrink away from the aggregate during sintering, and …………

If the particle packing is perfect, the pore size distributing in even and the pores are very fine.  This leads to high density but reduced thermal shock resistance.

Brick dies are slightly oversized to allow shrinkage by sintering.  The shrinkage is slightly higher in the vertical direction, because of the mass of bricks pushing down on those below them.  The orientation of bricks on the kiln car has to be constant because of this die design.  The bricks on the top layer are very slightly larger than those on the bottom layer due to the pressure of the weight above them.  

Brick mixes usually contain some clay for good cohesion and sintering.  They also usually contain an organic binder which burns out during firing.

Isostatic pressing is done in a hydraulic pressurised chamber, using fine material in a rubber bag, usually around a highly polished steel mandrel.  This is a slow and tedious process, but produces very high quality products.

Extrusion is a low pressure forming system, mainly used for building bricks.  The material is highly plastic, with a high clay content.  The clay is mixed by rotating blades on a horizontal shaft in a pug mill.  The blades move the clay forwards into an auger which forces them through a die.  The die on the tip of the extruder is usually 230mm x 114mm or slightly oversize.  As the solid column of clay comes out of the tip, it is sliced into bricks 76mm thick, usually by a series if thin wires.  Building bricks are usually air dried before packing onto kiln cars or clamp kilns or various other types of kilns, such as Bulls Trench, Vertical shaft, tunnel kilns or variant hybrid kilns.  In some arrangements the bricks move through different drying, heating and cooling zones, in other arrangements the bricks remain in one place and the fire moves progressively over them.