FORGING PRESS. Forging by machine can be done under steam and pneumatic hammers, drop-hammers, horizontal die f orging machines, and hydraulic presses. The last-named give a squeeze to the metal, instead of a blow, with consequent absence of shock and vibration; the pressure penetrates into the interior of the forging, consolidating the metal and making it of uniform texture. The press will also continue its squeeze and reduce a forging by several inches in thickness at one stroke, which a ham mer cannot do. The number of strokes in high-speed presses may be made to equal those of a hammer, up to 120 per minute. This not only enables the smith to complete the forgings at the quickest rate he can manipulate them under the press, but produces better results than usual with the older slow-speed presses, because the metal does not have a chance to cool down to any serious degree.
Although the hydraulic press has long been used for big work in preference to the steam hammer, it is now in competition with it for making forgings of quite moderate size, the power for such being from 'co to 800 tons. All sorts of links, rods, levers, collars, bolts and nuts, spindles, shackles, hooks and such-like are pro duced thus. Under the larger presses big shafts, bolts, rods, levers, wheels, anchors, tubes, cylinders, guns, shells and armour-plate are forged. Presses for the last-named product have been made to exert a pressure of 14,000 tons. Operations effected under the press apart from actual finish forging are togging, which signifies the reduction of a steel ingot to suitable dimensions for rolling, or for tilting, the latter being the further reduction in the press of cogged ingots to the required section and surface finish. Shingling, the making of iron from puddled ball, is likewise performed in the press, and straightening, bending and welding before or after the actual forging of pieces. Some presses have three rams—above, below and at the side—to do bending and welding, and move dies in some cases to stamp railway wagon and other repetition articles. Other presses have an extra long stroke for piercing or forging hollow pieces, such as shells. In most forging presses the ram descends from above while the work is supported on a fixed anvil.
The smaller presses have C-shaped frames and the smith is able to move around freely at the open gap to manipulate the forgings with hand tongs, or the help of a light crane.
Large presses are built up with four steel bolts or columns, hold ing a base in the ground with the anvil or bottom tool so called, the top head taking the pressing cylinder, and the press head being forced by the ram to slide upon the columns. The hydraulic pressure is delivered to the cylinder from pumps, or accumulator, or from a steam-hydraulic intensifier ; this consists of a large steam cylinder with piston exerting pressure upon a small. hydraulic plunger, so obtaining a pressure of about 21. tons per square inch. The presses of Davy Brothers, Ltd., of Sheffield, who build sizes up,to the largest, have two lifting cylinders (see the diagram) in which steam pressure gives a very rapid lift for the return stroke, rods from the pistons being connected to the press head. A pre filler charges the main cylinder with water at a very low pressure, the full hydraulic force coming on when the top tool touches the work. This saves expense in regard to the supply of pressure water. Control gear is so designed that the movements of the press head exactly imitate those of the lever which the attendant works, slowly or rapidly or for instant arrest. A 2,000 ton press of the type illustrated measures over 3 of t. in height from the foot of the base to the top of the cylinders. Large presses have two pressing cylinders. If cheap electric or water power is available, the intensifier can be operated with compressed air produced from either of these power sources, instead of by steam.
An overhead crane becomes essential to support the outlying ends of the massive forgings done under the big presses. In order to take advantage of the quick action of the high-speed press, a Davy electric turning gear is suspended from the crane hook, and carries the link chain that encircles the forging. An electric motor and gears revolve a drum on which the link chain laps and so it in consequence revolves the forging. A slipping clutch allows the chain to stand still while forging pressure is on, and drives again when the forging is released giving it a partial turn ready for another squeeze.
As the anvils or tools for the large presses are of great weight, facility of changing to the different sorts must be given rapidly by power methods. This is effected by hydraulic manipulating gear in the floor, a powerful cylinder and ram sliding plates along with the tools mounted thereon. For instance, to change from flat tools to V-tools (for forging crankshafts), the top tool is re leased and dropped on to its bottom companion, and the set slid away; the others then come into position and the head picks up its top tool. Hydraulic manipulation is also required to control a heavy bar used to forge tubes and cylinders upon. (F. H.) FORK, an implement formed of two or more prongs at the end of a shaft or handle, the most familiar type of which is the table-fork for use in eating. In agriculture and horticulture the fork is used for pitching hay, and other green crops, manure, etc. ; commonly this has two prongs, "tines" ; for digging, break ing up surface soil, preparing for hand weeding and for planting the three-pronged fork is used. The word is also applied to many objects which are characterized by branching ends, as the tuning f ork, with two branching metal prongs, which on being struck vibrates and gives a musical note, used to give a standard of pitch; to the branching into two streams of a river, or the junction where a tributary runs into the main river; and in the human body, to that part where the legs branch off from the trunk.
The farce, two pieces of wood fastened together in the form of the letter A, was used by the Romans as an instrument of punish ment. It was placed over the shoulders of the criminal, and his hands were fastened to it. Condemned slaves were compelled to carry it about with them, and those sentenced to be flogged would be tied to it ; crucifixions were sometimes carried out on a similar shaped instrument.