THE MANUFACTURE OF BUILDING BRICK. 229 



of a particular structure are used. Irregularity of clay supply may 

 also cause laminations. 



Laminations - are sometimes quite noticeable in brick made from 

 many of the New Jersey Clay Marl beds. These are molded at 

 many localities by the stiff-mud process, and while the clays 

 themselves do> not show wide variation, the structure of the bricks 

 often exhibit considerable irregularity, due apparently either to 

 improper mixing or to the machine. The laminated structure is 

 less harmful, however, in common brick than in paving brick, 

 and may at times be considerably diminished by re-pressing or 

 thorough burning. In some instances, however, the shells shrink 

 away from each other during the burning", and the laminated 

 appearance of the product is increased. Judging from the tests 

 made on the New Jersey brick, the presence of these shells did not 

 much affect the strength when the product was hard burned. 1 



The brick made in auger machines are either end cut or side 

 cut, depending on whether the area of the cross sections of the 

 bar of clay corresponds to* the end or side of a brick, and con- 

 sequently the mouth of the die varies in size and shape. The 

 auger machine is probably used more extensively at the present 

 day than either the soft-mud or dry-press machine, especially for 

 making paving brick. It has a large capacity and can produce 

 45,000 or even 60,000 brick in ten hours, the output of the 

 machine being sometimes increased by the use of double or even 

 triple dies, but this is not a desirable practice. When a triple die 

 is employed, the middle stream of clay flows faster than the two 

 side ones. 



As the bar of clay issues from the machine it is received on the 

 cutting table, where it is cut up into bricks. This may be done in 

 several ways, as follows: 



1. Attached to the cutting table is a framework carrying a 

 number of parallel steel wires. When a bar of clay has issued to 

 a sufficient distance, these wires are drawn through it to cut it up. 

 In some machines it is necessary to stop the machines while this 

 is being done; in others the construction is such that the cutting 

 frame moves forward with the stream of clay as it cuts through 



See Tests of New Jersey Brick, Chap. XI, p. 256. 



