the hob, in correct relationship in a hydraulic press, and the hob forced into the die-block the required depth by hydraulic pressure. By forcing the hob into the die-block, the metal displaced was thrown up around the side of the hob. This surplus metal was removed, and the die hardened. By making the dies in this manner, it was possible to renew the dies at a fraction of the cost of the dies made in the ordinary way. For irregular shaped forgings it would sometimes be necessary to make two hobs-one for the top and one for the bottom die.

CHAPTER III

DROP-FORGING DIES, THEIR DESIGN, CONSTRUCTION, AND USE IN DROP-HAMMER, DROP-PRESS, AND FORGING-MACHINE

Combination Drop-Dies

WHEN a drop-die is fastened into place where it is to be used, it becomes a part of the piece into which it is fastened. The more firmly it is bedded, the more solid it will become, and hence the better it will fulfil its duties. The union of several pieces is intended to make substantially one sole, solid piece. If it is a lower die fixed in the drop-bed, it becomes portion of the anvil, and if it is a top die fixed in the hammerhead, it becomes a portion of the hammer.

It is exceedingly difficult to unite two pieces of iron together, without welding, so that they will be, as to the effect of impact, as solid as one piece.

If you take the blacksmith's hammer in your right hand, and let it fall on the anvil, it will rebound; if, to prevent this, you stiffen your muscles, and exert your will, and bring it down with all your force, straining against a rebound, you will only induce a stronger reaction. If now you take the flatter in your left hand and let it rest on the peen of the hammer while you let the hammer fall, the hammer will strike flat and dead, without rising at all from the anvil. The flatter and hammer, together, are not as heavy as the sledge, but if you let the sledge fall, face down, upon the anvil it will rebound. You take the hammer again in your right hand, and place your left hand on the peen, where you held the flatter, and now let it fall. Do you stop all the rebound? No, it rises slightly from the anvil, and the tingling of your palm tells what occurred at the union of the hammer and the hand. You

are familiar with the facts; every one who has worked in the shop has made the experiments. I mention them only to direct attention to the absolute necessity of making union between two pieces of metal as compact and unyielding as possible, in order to secure the full effect at the impact of the force due to the blow. Much of it may be dissipated in open joints.

Union Between Metal Parts

These phenomena convey the suggestion that a falling compound weight, made up of two components, one above the other, in contact, but not connected, strikes first with the momentum of the lower part, and, second, with the momentum of the upper part, subject to a deduction for interference of the reaction of the first from the place of impact, which the momentum of the upper part must meet and overcome before it can be delivered at the same place. When the two parts are connected this interference will be proportionately less as the connections are more firm and compact. No union, short of welding, can be much more intimate than that of a flatter resting on the ball peen of a hammer, and yet we know that the break in the continuity of the substance, which occurs so slightly between these two pieces, makes a break in the continuity of the momentum of the flatter and the rebound of the hammer-otherwise this combination would rebound at one time like the sledge.

When a die is set in a hammer it transmits as much of the momentum of the hammer to the object which is struck, as overcomes the interfering reaction of the die, and if the die is small, in proportion to the weight of the hammer, there will be less of this interference to overcome than if large.

If it be desired to strike a blow with a drop-hammer that shall not rebound, it is only necessary to arrange a loose weight on and above the hammer, or to have the hammer in two disunited parts, of which two parts in the lower one alone has connection with the uptake and upholds. The greatest effect of impact, in proportion to the power required for lift

ing the combined weight, will be given when the weight of the upper part exceeds that of the lower.

may some

Considerable disappointment is sometimes experienced when it is found that adding to the weight of the dies does not proportionately add to the effect of the blow. The remedy is in adding to the weight of the hammer, but relief times be obtained by getting the dovetailing of the tenon to perfectly match that of the die-seat and fit the keys, so that they will draw the die up, as tight as possible, against the hammer.

But whatever the facts of the case may be in regard to the best method of fastening dies, for the purpose of getting the fullest and best possible results of the blow, it is well to remember that all things in drop-work have to give way before expediency. If it is expedient to fasten dies in a drop-hammer in a certain way, for any special reason, whether by that means the full effect of the blow is secured or not, that is the way to fasten them; and if, when thus fastened, the effect of the blow of a certain sized hammer is not sufficient to accomplish the desired object, then a larger hammer may be used. The principle of drop-forging is not persuasion, it is compulsion; it requires the furnishing of power, potent enough to overcome every interference and drive the reluctant stock into the dies, where it forces it to assume the form of the impression.

Die-Blocks and Impression-Blocks

It is not always necessary to use a piece of steel for a die which is large enough to make a die-block with a tenon of the size which the bed of the drop requires. The die proper, or the steel-block into which the impression is cut, may often be economically made of a much smaller pattern and held in a die-block, as well as have it all solid in one piece. The impression-block can be let into a wrought-iron or steel die-block by drilling and chiseling out a recess in the block, or by planing out enough to receive it, or it may have a block of cast iron around it.

When the steel is used as an impression-block, it is thus employed because its wearing qualities are demanded, and the requisite strength is partially supplied by the material of the block on which it is set.

There has always been a claim in regard to railroad-rails that they have two general functions: one to support strain, and one to endure wear; and as it seemed useless to be obliged to renew the whole rail-whose cost augmented with its weight-simply because it failed, in its less massive function, by wearing out, efforts have continually been made to separate these functions, and as the growing tendency of rails is to increase in weight, this consideration has the same tendency to increase in weight.

In some of these efforts, the scheme has been to make separate parts, to be permanently laid, for upbearing strength, while other parts, intended for wear, were made as light as was consistent with the purpose, and could be easily removed and replaced with similar parts. Other plans crossed the problem, and had the rail made double-headed, so that either side could be used for wear, while the opposite side always contributed its quota of strength.

Making Die to Resist Wear

Ingenuity in different branches suggests similar expedients; the replacing of the worn part of a rail is parallel to the making of the impression part of a drop-forging die of steel, to resist wear only, and hence making it no longer than will suffice for this purpose, leaving it to derive support to resist stress from the bed in which it sets. The double-headed rail finds its counterpart in a mode of making flat-faced dies which have a square cross-section, so as to use each of the four flat faces to sink impressions in. After the impression which has been cut in one side is worn out, another impression can be cut on either of the other sides, each side serving in turn for a face. If the drop has a dovetailed die-seat in the hammer or bed, packing is made of the necessary form, or the keys are modified to suit. Dies with straight sides cannot be drawn