Manufacture of Brick

MANUFACTURE OF BRICK Methods. Most of the brick in common use are made of soft paste, of clay and water. When water is used very freely, the manufacture is said to be by the wet or soft-mud process.

When the clay is not so wet, the stiff-mud process is used; and when only 4 per cent to 6 per cent of water is in the clay, the method is known as the dry-press process. In this last process, the clays are sometimes actually dried rather than dampened before being made into brick.

Many of the small brick-making plants use the wet or soft-mud process, on account of the resulting plasticity and ease with which the clay is moulded. The best results, however, cannot be secured by this method; but some very ser viceable brick are thus made.

The larger and better-equipped plants use a stiffer mixture, requiring considerable force to fashion the clay into the desired forms. As compared with the "wet" process, this method requires less water to be taken from the mud brick, and is more economical of time and fuel.

Moulding and Drying. In

the dry-press process, the clay is forced into chambers, and compressed by a plunger under heavy pressure, 75 tons or so being applied to the side of a brick.

In the stiff-mud process, the clay is forced from the moulds by a screw or auger mechan ism, in a continuous strip. This strip of clay is carried along on a belt or other type of con veyor, and is cut at proper intervals by fine wires passing through it while it is still in motion.

In using the soft-mud process, the wet clay is forced by a plunger into a set of moulds. As the plunger is raised, the clay on the top of the moulds is struck off, the full moulds are withdrawn, and the empty ones put in their place before the succeeding descent of the plunger. To prevent the sticking of the mud to the moulds, the latter are passed through sand at frequent intervals.

The latter two methods merge into each other, and the above description of the mould ing is the usual but not unvarying custom.

Re-pressed bricks

are made of soft mud that has been partially dried and then re-formed under great pressure. These bricks are very

uniform in shape, but are not particularly strong or hard.

Drying.

As the brick comes from the mould, it may contain as much as 30 per cent of moisture. To subject it immediately to intense heat would cause steam to form, and explosions, warping, and cracking would ensue. In order to avoid these results, the bricks are dried for several days on stacks or shelves which allow free circulation of air. The drying may be hastened by surrounding the stacks with steam pipes, which may be arranged according to many different designs. After most of the moisture has evaporated, the bricks are removed to the kilns and arranged for burning.

Burning.

The clay is burned to dry it out, and so deprive it of its plasticity; and also to cause partial fusion of the silica and to produce and the latest tests that are at hand show that these bricks are strong enough for facing and other uses where extreme strength is not required. Table X gives data regarding the strength, absorption, etc., of sand-lime brick.

Each of the numbers in the table is the mean of several tests. The sequence of the numbers is of no significance; that is, the numbers in the first line are there by chance.

The modulus of rupture was obtained by breaking the brick, placed on edge between sup ports six inches apart, the load being in the middle.

The compression pieces were half-bricks, im bedded on both sides in plaster of Paris.

The absorption test was made by heating the bricks to dry them out, and then keeping them in water for forty-eight hours. Upon being taken from the water, they were wiped dry and then weighed; and the increase in weight was divided by the weight of the dry brick, and the result multiplied by 100.

portion were satisfactory. This condition led to the adoption of the names : Arch-brick, or those forming the top of the oven; Soft or salmon brick, or those named from the lack of color or hardness; Body brick, or those taken from the middle of the kiln.