PUG-MILLS.
The pug-mill is an iron shaft with knives of the same material about eighteen inches long, two and a half inches wide, and three-eighths of an inch thick, extending from the shaft in four directions, but so placed that one does not follow directly under the other. To trace the knives around the shaft would be like following the thread of a screw. At the bottom of this shaft, and all on the same level following consecutively are four broad, curved pieces of iron, called sweeps, pressers, or pushers, which terms are synonymous, and their use is to force the tem pered clay through an opening near the bottom, in the side of the cylinder or box inclosing the pug-mill.
Sometimes the casing which incloses the pug-mill is made square and of wood, two inches thick usually, leaving the clay to pack into the square corners ; at other times the cylinder is formed of iron, cast in sections and bolted together. In the Southern States the entire arrangement of upright shaft, knives, and pressers is more often called a "hopper" than a pug-mill.
The well-known manufacturers of brick and tile yard sup plies—The Frey-Sheckler Co., of Bucyrus, Ohio—through whom all the tools and appliances named in this chapter can be ordered, make four regular sizes of improved pug-mills, also special sizes of pug-mills designed to suit any yard devoted to the manufacture of building-brick, fire-brick, terra-cotta, or tiles.
Mr. Alfred Hall, of Perth Amboy, N. J., has invented an improvement in the construction of pug-mills used in the man ufacture of brick, terra-cotta, fire-clay wares, and pottery, the novelty of which consists in the construction and arrangement of parts in regard to the vertical revolving shaft and the blades or knives.
This invention consists in a peculiar blade or arm (shown in perspective in Fig. 8) and a shaft having a special and peculiar mortise, into which the arm or knife is secured.
Fig. 7 is a vertical central section ; Fig. 8, a perspective de tail of one of the arms or knives ; Fig. 9, details of the parts separated, showing their relative formation.
A is the vertical shaft, to be placed in any suitable cylinder for holding the material to be operated upon. It is supported in position by the framing, so that it can be readily revolved.
It has formed in it a series of cross or horizontal mortises, B, each adapted to hold the tenon D of the blade C. Each mortise B has its upper side made on a horizontal line, while its lower surface, b, is inclined downward from the outer end inward to or nearly to the centre of the shaft, thus giving to the mortise the shape or form in its vertical width of a half-dovetail. The tenon D of the blade C is made in form corresponding to the shape of the mortise is, its under face, d, is cut away so as to give it an upward incline from the outer end to the inner end of the blade proper, and its outer end is made of such size that it will just fit and enter snugly into the mouth or outer end of the mortise. As the tenon is pushed further into the mortise it drops downward on the inclined surface b and away from the upper side of the mortise, and leaves a space above it, into which the key E is driven. When the tenon and key are both inserted the blade will not work loose, because the inclined surface b and the increasing thickness of the tenon operate to give increasing force to hold the blade against any movements tending to draw the blade outward. The material which is being acted upon will exert a pressure on the ends of the keys E and prevent them from working loose. The blade C has its under face flat or made to a horizontal plane. Its upper side is gradually thickened from the edges to a line drawn diagonally from the middle of the outer end to a point on the inner end next the tenon, midway between the middle of the blade and the rear edge.
In Fig. 8 the dotted line x x represents the middle line of the blade. The diagonal line c' is the line of greatest thick ness of the blade. The blade thus formed provides an up wardly-inclined •front face, c, which is wider at its inner end next the shaft and narrower at its outer end. The rear face, c', is wider at its outer end than at its inner end. The peculiar construction of the blade gives much better results in mixing the material in the cylinder or pits. The material is sooner brought into a homogeneous mass and into the required con dition for the moulds.