METHOD OF MANUFACTURING BRICK 



171 



Scove kilns, clamps or down-draft kilns are used for~ burning 

 the product. The principle of burning is much the same in all 

 three, although many manufacturers claim that the burning can 

 be better regulated in clamps and down-draft kilns, while others 

 claim the opposite. In the latter the bricks in the upper portion 

 of the kiln receive the greatest amount of heat, whereas in a 



Down-draft kiln. 



scove kiln or clamp the arch bricks, which have to bear the 

 weight of the overlying bricks, are heated the most and often 

 become crushed out of shape. Regarding the rectangular and 

 circular down-draft kilns, the latter are bound easier than the 

 rectangular ones, this being of course necessary in order to pre- 

 vent a bulging of the walls during burning. 



Boll crushers. — This type of machine is extensively used in the 

 preparation of tough or stony clays. They consist of two or 

 four steel rolls, which revolve at different velocities. They are 

 usually enclosed and the clay is charged into a hopper above 

 them. The crushed material passing out below is received on a 

 traveling belt and carried to the pug mill. Crushers are objected 

 to by many on the ground that they make the clay flaky, in 

 which condition it does not make a good brick. Subsequent 

 pugging, however, usually does away with this. By many manu- 

 facturers rolls are used as a means of breaking up the stones and 

 thus avoid drying the clay and screening it. There is no 



