﻿VITRIFIED BRICK AS MATERIAL FOR COUNTRY ROADS. 3 



indicate its fitness or unfitness for paving brick. The reason for this 

 is that the quality of the brick after "firms:" is no less dependent on 

 the physical 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 by 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 by 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 1\ to 3 tons. The pan is revolved 

 rapidly, causing the mullers to rotate by friction. The material is 

 ground between the mullers and the plate and thrown out by cen- 

 trifugal force toward the rim, where it escapes through the perforated 

 surface into an elevator, by 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 conveyors. In the pug mill, water is admixed with the 

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

 machine proper. 



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

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

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

 conveyor 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£ inches. For "end-cut" brick the column has a cross section 

 , approximately 4 inches by 4 \ inches and is cut into sections about 

 10 inches long. 



Paving brick, whether end or side cut, have usually in the past 

 been re-pressed. This process smooths and rounds the corners, and 

 forms on one side of each brick small lugs or projecting trademarks 

 which serve to produce uniform spacing between the courses of the 

 pavement. Suitable lugs may also be formed at the time the brick 

 are cut, however, and the process of re-pressing is then omitted. 

 Much discussion has taken place as to which of these methods pro- 



