BRICK EOADS. 3 



physical and chemical composition. By carefully mixing the mate- 

 rials from different strata or from different parts of the bank, there- 

 fore, a resulting material of the desired character may usually be 

 obtained. But it not infrequently happens that in order to secure 

 the best results sand qr surface clay must be added in an amount 

 depending on the relative " leanness " or " fatness " ^ of the material 

 used. In this connection it maj be noted, also, that a chemical 

 analysis of a given fire clay or shale does not necessarily indicate its 

 fitness or unfitness for paving brick. The reason for this is that the 

 quality of the brick after " firing" is no less dependent on the physi- 

 cal arrangement of the minerals than on the chemical composition of 

 the material. 



THE MANUFACTURE. 



The general processes of manufacture are the same for both fire 

 clays and shale. The raw material in either case is crushed to com- 

 paratively small fragments and conveyed b}'' some convenient means 

 to a grinding machine, known in the industry as a dry pan. Briefly, 

 this machine consists of a solid iron plate, approximately 5 feet in 

 diameter, surrounded bj^ a perforated iron surface about 2 feet wide. 

 Outside the perforated surface is a rim some 15 inches in height 

 which serves to prevent the material from escaping otherwise than 

 through the perforations. Upon the solid plate rest two massive 

 crushers or mullers, each weighing from 2^ to 3 tons. The pan is 

 revolved rapidly, causing the mullers to rotate by friction. The ma- 

 terial is ground between the mullers and the plate and thrown out 

 by centrifugal force toward the rim, where it escapes through the 

 perforated surface into an elevator, bj^ means of which it is conveyed 

 to the screens. 



The particles too large to pass the screens, which should not exceed 

 three-sixteenths inch in mesh, are returned to the dry pan, while the 

 screened material is passed to the mixing machine or pug mill by 

 means of conveyers. In the pug mill, water is admixed with the clay 

 to form a stiff mud, which is fed continuously into the brick ma- 

 chine proper. 



The brick machine is an extremely heavy mechanism. It con- 

 sists essentially of an auger or propeller conveyer, a tapering barrel, 

 and the die or former. The material is forced by means of the auger 

 conveyer into the. tapering barrel, which terminates in the die, and 

 issues from the die in a solid column under heavy pressure. For 

 " side-cut " brick this column is approximately 4^ inches by 10 inches 

 in cross section, and the brick are formed by cutting through the 

 column, by means of an automatic device, at intervals of about 3^, 



1 '"' Leanness " and " fatness " refer respectively to the lesser or greater amount of 

 silicate present in the material. 



