This section is from the "Modern Machine Shop Construction, Equipment, And Management" book, by Oscar E. Perrigo. Also see Amazon: Modern Machine Shop Construction, Equipment, And Management.
The blower is driven from a line shaft running the length of the shop near its center. In front of the first fire is located a large steam hammer of the arched pattern, and capable of handling work up to 10 inches in diameter. At the next fire is a smaller, single-column steam hammer of about half the capacity. The necessity of providing the larger hammer will be a matter to be decided by the size of the largest forgings to be made. For instance, if only a few forgings which come up to its capacity are to be made, it will be more economical to purchase them of some large forge shop than to provide a large hammer that may be idle much of the time. The smaller hammer should be provided for even moderate-sized work, for any plant of modern pretensions.
Next to the small hammer two drop presses are located, with a special heating furnace for use in connection with them. These drops should carry hammers weighing from 150 to 600 pounds, according to the work which they are to do.
The heating furnace need not be over 30 inches square outside, built with a cast iron shell lined with fire bricks, supported on four cast iron legs, and provided with a vertical sliding, balanced door in front. The heating chamber will be about 20 inches square and from 10 to 12 inches high. A blast pipe leads up to it, and a smoke pipe from its rear side leads to the nearest chimney. Such a furnace will heat work for drop forging much more economically and satisfactorily than the usual open forge fire. They may be purchased at a very moderate cost.
The forge fires not occupied with steam hammer work will be used for ordinary hand forging, tool forging, tool dressing, tempering, and similar work. Where much tempering of special work is necessary, that is, when a large number of pieces of the regular product of the plant is to be so treated, special arrangements as to heating furnaces, dipping baths, etc., must be provided, and in many cases special automatic heating and hardening furnaces are employed. Obviously, the great variety of this class of work precludes a detailed description in this chapter.
Near the end wall, at the rear, is located an annealing and case-hardening furnace of ample capacity. As this will be built on the premises, and as information in reference to its requirements and its construction may not be readily available, drawings have been made showing the details of its construction and giving all necessary dimensions.
While this is for a furnace of quite large capacity for a machine shop plant, a smaller one may be readily constructed on proportionate dimensions, with good and practical results. If it is to be of say one half these dimensions, or one fourth the capacity, the lower heating ducts will be single instead of double, and it will be preferable to build it with a cast iron casing inclosing all four sides, forming the door frames, and the separate pieces being bolted together at the corners, instead of having the brickwork held together by binders and rods as shown in the drawings.
The construction is clearly shown in Figs. 124, 125, and 126, being respectively a front, side, and a rear elevation. Fig. 127 is a cross-section through the fire box A, showing the bridge wall B, the form of the covering arch F, and the position of the blast pipe G. Fig. 128 is a longitudinal section showing the fire box A, heating chamber C, heating ducts D, D, and sections of the front and rear doors. Fig. 129 is a cross-section through the heating chamber C, the heating ducts D, D, dividing wall M, and the main door N. The foundation] should be laid deep enough to support the weight of the furnace and its charge, and will be quite similar to that provided for boiler settings. The shaded portions indicate fire bricks, the balance being ordinary, hard, red bricks. The grate bars are of any convenient pattern, but must have ample air spaces so as not to impede the air blast delivered through the blast pipe G. The top arch is of fire brick and is carried all the way through both front and back walls, for convenience in making repairs upon it.
Fig. 124. Front Elevation of Annealing and Case-hardening Furnace.
Fig. 125. Side Elevation of Annealing and Case-hardening Furnace.
The floor of the heating chamber is composed of fire brick tiles 5 inches thick, 9 inches wide, and 24 inches long, their outer ends supported by the inwardly projecting side walls, and their inner ends by the dividing wall M.
They are laid about an inch apart so as to permit the gases and smoke to pass down between them to the heating ducts D, D, and out through the smoke pipe attached to the rear door L. The frame and door of the fire box are from the same pattern as the rear door K, while the frame of the ash pit door 7, and the smoke door L, are from the same pattern. The doors are different, of course, as the door L must be provided with a circular sleeve to which the smoke pipe is attached, its other end connecting with the nearest chimney. The main door N, through which the annealing boxes are introduced and removed, is of special construction and fitted with a fire-brick lining, perforated by a circular opening or "peek hole," and held in place by four bolts (as shown in Fig. 125), which pass through iron straps on the inside of the fire brick lining. The stopper P is of tubular form and has an inwardly-projecting flange at its inner end for the purpose of holding the lining, which is composed of fire clay packed in as solidly as possible while it is slightly wet. This stopper may be removed at any time to obtain a view of the interior of the heating chamber and its contents during a heat, as all the doors are tightly closed and the cracks luted with fire clay as soon as the fire is well under way, one charge of coal being usually sufficient for the heat after the furnace has been heated up. The blast pipe furnishing the blast for the forges will also supply this furnace, the pressure required being the same, and will be connected to the fixture G located in the wall of the ash pit for that purpose.