THE SCIENCE OF CLAY -WORKING. 465 



The machines for making brick or tile, although almost infinite in number, 

 "Can still be reduced to a few general classes. 



CLASSIFICATION OF MODERN BRICK MACHINES. 



Knight classifies the brick machines as follows: 



Class I. — Those in which a slab of clay exudes from the brick mill and is 

 cut into lengths which form brick. The cutter is a wire or knife and either 

 travels with the slab while cutting or moves in an oblique path — or in case of 

 intermittent action of clay remains at rest. This class will include nearly all 

 our tile machines and a large portion of our brick machines. 



We will make two subdivisions of this class in accordance with mechanism 

 used : 



Suhdlvision 1st. — Plunger machines. 



In these machines clay is forced out from the bottom of the pug mill by a 

 cam of some sort or by a piston. 



The Penfield Machine, Chandler & Taylor, and many others are illustra- 

 tions of this class of machine. 



SuI)dicLsio}i2iid — The Auger Machines — In which the clay is ground and 

 pressed through the dies by steel or iron knives arranged spirally. This 

 machine should be of especial interest to us, as it no doubt was invented by 

 an honored resident of this State and a member of this society. More than 

 that, its principal improvements have been made by residents of Michigan 

 and its construction is more extensively carried on in this State than in any 

 other. For the manufacture of drain tile this machine is unrivalled. It 

 gives a steady stream of tile, thus insuring a steady strain on all the working 

 parts. The liability to break out cogs, due to the intermittent action, is very 

 great in the plunger machines. This machine is better in that respect. So 

 far as tile making is concerned, this machine has a motion peculiarly fitted 

 to fill the die and make a sound and strong tile. 



The auger machine is said to be inferior to the plunger machine for mak- 

 ing brick from the fact that the rotary motion of the feed mechanism is not 

 so well adapted to filling the square corners of the brick die. 



In the practical and actual use of these two machines this objection is no 

 doubt a valid one, but from some observations I have made of the workings 

 of various brick yards I have come to the conclusion that although this differ- 

 ence does exist, it exists simply because the auger machine is not handled 

 with the same care as the plunger machine. 



It is the custom, and it is a pernicious one too, of digging the clay from 

 the bank and of running it through the brick machine as dry as it possibly 

 can be worked. The result is, that you have bricks in shape at least, but if 

 you examine the structure of such a brick you will find it composed of twisted 

 wads of clay, stratified in concentric layers and anything but homogeneous in 

 structure. Such a brick when exposed to the weather soaks water irregularly, 

 and there is often actual spalling or shelling from the action of moisture 

 alone. 



From the fact of continuous working the auger machine will work clay 

 much drier than the plunger machine. It will work clay when very stiff, 

 just how stiff I do not know, but it will work clay very much stifEer than the 

 plunger machine — probably with one-half as much water. I have seen an 

 auger machine work clay easily while the same clay put in a plunger machine 

 caused the breaking off of fifteen |-inch bolts which held the die in place. 

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