In the first case the brick is lifted off from the plate after pressing, and in the other the plate is removed before the pressed brick is lifted entirely from the mould.
A third method is to have the matrix fastened to the cap, top-plate, or follower, as the case may be, according to the kind of press you are using, and when the cap is lifted off, the matrix is lifted with it, and then the brick is lifted from the press without the danger of distortion, such as the other methods present, in attempting to remove the plate from the brick. Each of these processes has its respective advantages, and the manufacturer must use such a one as to him seems best.
To manufacture to the best advantage, three presses should be used, one for large tile, one for brick, and one for edge work, but one press may be made to answer by changing the press-box and follower plates.
Various substances are employed to prevent the matrix ad hering to the clay. Oil is generally used for this purpose, but in designs having great relief or depressions it is sometimes almost impossible to remove the matrix from the ware without injury ; others use dust of some kind—very fine sand—which will burn a good color ; pulverized coal, charcoal, etc., are also used.
Brick-dust passed through a bolting cloth is the very best thing that can be utilized—burns, of course, the same color as the clay, and produces a rich, velvety surface, and the brick never stick.
When the ornament required is very bold, it is best to re press twice.
After the first pressing, which should not be very hard, the brick is dusted.
When it has shrunk just enough to drop easily into the mould box, the superfluous dust is blown off, either by a bellows or lung power, and then pressed the second time firmly. The subsequent treatment consists in carefully remov ing any superfluous clay from the edges, a little hand-rubbing, and careful drying and burning.
The main thing to insure success in ornamental work, either with mouldings or pressed work, is thorough preparation of the clay.
It should have sand or " grog" enough in it to prevent undue shrinkage, or liability to crack, in drying or burning. For the higher classes of ware, clay that had been once burned and pul verized should be used to the extent of about 25 per cent.
The Northwestern Terra-Cotta Works, of Chicago, Ill., buy all the bats from the Anderson Pressed-Brick Company that they have to spare, and grind them up by a slow-motion large diameter crusher. One crusher crushes the bats to the size of a hickory-nut. They then pass through another crusher, and everything is ground fine. The works named use crushed brick to the extent of 4o or 5o per cent. in some of their wares, and always with good results.
Mr. Batley, in speaking of the use of pulverized bricks, or " grog," for preventing the excessive shrinking of clay dur ing the process of manufacture, said : " In South Wales we were engaged in making enameled glazed brick, fire-brick and sewer-pipes, and when we came to the question of anything over half an inch to three-fourths in thickness, it used to warp and crack all to pieces, and it soon put me to thinking what to do to prevent the clay from cracking; and while there en gaged in making 24-inch sewer-pipe, I have had to use as much as 6o per cent. of grog,' and the clay is not in existence,
as far as my experience goes, that cannot be prevented from cracking." After the " grog," or pulverized brick, has been mixed with the green clay, the mixture should be allowed to remain for one week in the tempering pit after being wet, and as long after pugged the first time as possible, before being run into mould ing or for pressed ware.
Success in ornamental brickmaking, as in all other manufac turing enterprises, is determined largely by attention to details.
Fig. 70 shows a front view of the Panel Re-press, which is manufactured by the Frey-Sheckler Co.
This was the first and is the only machine of its class manu factured in the United States. It is especially designed to meet the wants of brick manufacturers producing a high grade of brick for enameled glazing, where it is very essential to have all of the brick of an exact thickness. It is also adapted for pressed and ornamental brick when a fine finish of product is required. This machine is constructed on new and scientific principles, as will be seen by the illustration. The shafts are made of steel. The gears are extra heavy and of new design. The machine is mounted on an extra heavy cast-iron box bed. It is simple in construc tion, easily accessible, and no parts liable to get out of order. All of the gears and mechanical movements are so arranged as to be entirely free from clay, etc., so as to prevent wear. The feed and discharge of the brick in this machine is strictly auto matic. Machines of this class from abroad do not enjoy this in genious mechanical device, but must be stopped at the pressing of each brick in order that the same may be removed from the mould. This machine is supplied with a friction-clutch pulley, so as to enable the operator to start or stop the machine at will. Capacity from 6,000 to 10,000 highly-finished brick per day ; weight of machine 4,500 pounds.
Fig. 71 shows a front view of the Eagle Double Mould Re press, which is manufactured by the Frey—Sheckler Co. It is intended for re-pressing front brick, roadway paving brick, fire brick, etc., and has a capacity of 15,000 to 28,00o every ten hours.