The clay after leaving the horizontal conveyor is next carried to the tempering cylinder of the brick machine and there re ceives its second and usual pugging.
This process does very well for the early spring months; but as the season advances and the ground becomes drier, many little hard lumps pass through the pug-mills without being crushed, and all bricks containing them crack in drying.
The experiment has been tried of first passing the clay be tween crushing-rolls, but the clay either came through in sheets which were hard and smooth and would not temper in the pug mills, or else would adhere to the rolls and give continued trouble to clean them ; and the only satisfactory solution was to use a disintegrator and pass the clay through it before convey ing it to the brick machine.
Hot water tempering is not always an improvement over cold water, as it often makes some clays more sticky and difficult to dump from the moulds. Hot water does not hasten the drying of brick. After a number of experiments, in which brick made by each process were placed side by side, the difference, if any, was too small to compensate for the disadvantage of sticky moulds.
It is often difficult during the winter months to reduce hard frozen clay to that condition necessary to make brick, as it clogs in the rolls or pulverizer and causes loss of both time and patience. A simple method for thawing clay consists, for small works, in laying down a plank floor about 8 feet wide by 20 feet long, with one end of the floor a few inches lower than the other. Then put about four rows of one-inch pipe the full length of this floor, and far enough apart to shovel between them easily. In these pipes, about one foot apart, drill holes about one-sixteenth of an inch in diameter, on alternate sides, so as to allow an emission of a jet of steam every twelve inches, first on one side and then on the other. Connect the pipes at the highest end of the floor by a header, and place a plug in each pipe at the lower end, with a small hole in each plug to carry off the drip or condensed steam. Lastly, drive some staples down over the pipes to keep them in place, and then cover the pipes over with about 3o tons of clay, piled six feet high, fill the boiler well up with water, run the steam down to about 30 pounds pressure, turn the valve connecting the boiler with the clay pile about two turns, and leave it in that condi tion during the night. The next morning, under an outside
crust of about one inch thick, will be found the clay in good condition for use and the frost out of it.
The simplicity, cheapness, and complete success of this plan make it within the reach of all clay-workers who have steam at command.
A great deal of trouble occurs often in elevating the clay to the disintegrator, or from the disintegrator to the brick machine, especially when the clay is a little wet, as it sticks fast and clogs on the belts ; and oftentimes this trouble can be greatly lessened by using a canvas belt, with two chains on sprocket wheels, at the crusher and at the mill, using four-inch rollers about a foot apart to support the intervening space. One of the greatest causes of failure in using belt-elevators is having them too steep and not properly supported.
Fig. 20 illustrates the No. i Granulating Pug-Mill built by the Frey-Sheckler Co. This machine is built very heavy, and is 10 feet long in the pugging chamber, which is made of boiler steel inch in thickness. The shaft is hammered steel 4X inches square. The knives are made of charcoal chilled iron. This machine is used for granulating tough, strong clays before passing to a crusher ; this is a very essential feature in clays of this character. Inasmuch as the stones are liable to catch on the knives and break them, a safety pin is inserted in the driving pinion so as to prevent breakages. It also acts as a distributor or feeder for the crusher.
The clay is dumped in at the rear end by carts or dump cars, and the knives tear the clay to pieces and gradually carry it along while disintegrating it, so that a constant and even stream flows into the crusher, and the rolls take it through readily. This machine is provided with a friction clutch pulley 36 inches in diameter, 10 inch face. Speed, 15o revolutions per minute ; weight, 7,00o pounds.