THE PROCESS OF MANUFACTURING ROOFING-TILES.
When the process of manufacturing roofing-tiles is conducted by hand, the method is nearly the same in this country as in England, and but few improvements have been made in this mode of production ; but by the machine process we are en abled to manufacture very satisfactory roofing-tiles at but a small cost.
The clay of which the tiles are made is dug and spread out in shallow beds to disintegrate, and a hot sun or dry frosty weather is best for this.
In all cases the clay should next be finely pulverized by pass ing through iron rollers or other suitable appliances, and too much care cannot be given to this branch of the preparation of the clay, as has before been observed.
A good pug-mill is one which can have the knives made larger at the top than at the bottom and used for tempering the clay when the tiles are made by hand.
The usual form of pug-mill employed in England is generally six feet high, three feet in diameter at the larger or upper part, and two feet at the bottom.
The clay is kneaded and completely mixed by a revolving cast-iron spindle, which carries a series of flat steel arms, so ar ranged as to form by rotation a worm-like motion upon the clay, which is pressed from the larger to the smaller diameter of the tub in which the clay is confined, and finally comes oozing out of an aperture in the bottom. In this manner of tempering great cohesive power is given to the clay.
The clay is then ready to make roofing-tiles ; the moulding is usually conducted in a shed, and most of the manufacturers prefer to place their tiles in the open air, if the weather allows.
The moulding table or bench is supported on four legs, which are well under the table, leaving the two ends of the top of the table to project liberally. The coal-dust box, 14x8 inches, is at the left hand of the moulder, at the corner of the table, and the moulding-board, 14x10 inches, is usually placed slightly to the right of the coal-dust box.
The mould employed is 12x73% inches and inch thick, made of oak, and usually plated with iron.
The moulder works a lump of clay by hand into an oblong square, the mould is placed on the bench, and fine coal-dust sprinkled over it ; the lump of clay is then taken up and thrown into it with force, which is cut off level with the top of the mould by a brass wire, strained upon a wooden bow ; the lump of surplus clay is removed, and that in the mould is finished by adding a little clay to it, if necessary, and smoothing the face over with a wooden tool.
The moulded tile is then placed upon a thin board, first sprinkled with fine coal-dust, and so the process is repeated, the lump of clay being added to every time six tiles that are moulded. The off-bearer carries two tiles at a time, one on his head and one on his hands, to the floor. where they are. al lowed to remain for four hours out of doors in fair weather, and then collected and placed together, the nib end changed alter nately, so as to hack them closely and squarely.
In this condition they remain for two days, so as to allow them to toughen ; the situation of this hacking should be dry, but not hot.
The set or curved form is then given by placing six of the tiles at one time on the top of the horse, which is a three-legged stool, having the top about three-quarters of an inch longer than the tile, the top being a convex curve to a radius of about 10 feet and 3 inches, and having a height of about 2 feet 7 inches from the level of the ground to the top of the block.
The nib end is reversed each time so as to allow the tiles to lie closely together without injury, and a wooden block lifted on top of the tiles, raised by the projecting ends, and three quick blows given with it on the tiles; this block is concave and curved, so as to correspond with and fit neatly over the upper surface of the horse.
The tiles are then carried away and stacked edge together in the shape of a half diamond, three tiles being used to form each side ; two laths are then placed on the top of the first hack of tiles, one lath at each outer edge ; another hack of tiles is placed on the laths, so arranged as to form a full diamond with the openings left between the first course of tiles ; two laths are then placed in the same way on the top of the second course of tiles, and the third course is then hacked so as to form a full diamond, with the openings left between the second course of tiles.