The method of making a common hexagonal nut in such a forging machine consists in (1) placing the dies in the forging machine; (2) heating a bar of iron between 1.400° and 1,600° F. — the temperature varying with the character of the iron; (3) thrusting the red-hot end of the bar into the lower die in the forging machine, and throwing the lever to cause the machine to squeeze, which upsets the end of ' the bar and shapes it for a nut; (4) withdraw ing the bar quickly and placing in the upper die; (5) repeating the squeeze, which forces the hole through the nut, leaving the removed metal on the bar, and separating the nut. The nut is delivered with a slight fin, which has to be removed, when it is ready to go to the thread cutter.
The front axle of an automobile may be forged in one of these pressure forging machines in about seven operations. The last squeezing operation delivers the formed axle. Any quantity of more or less in tricately formed parts arc now made of wrought iron and steel in this manner, the heavier operations being done on the steam-hammer, as a rule.
The forging machine is also used for weld ing or joining separate pieces by pressure. It
is just as easy to apply a flux to assist the joining in the forging machine as on the anvil. The Ajax universal forging machine not only compresses the dies, but has an independent vertical press that can be used for any operation within its capacity; also a punching device and a trimmer.
A variety of special forging machines are made for forming common articles, or parts re quired in large quantity. Many of them are named after the work they accomplish. The hot-pressed centre-feed nut machine is simply a small forging machine designed for making nuts. Bolt-heading machines and bolt and rivet headers are other examples of special forging machines.
Pressed steel is made by great hydraulic presses at the steel works. Pieces requiring but slight shaping are pressed in the cold; more or less complicated forms are heated to a cherry red and then light-pressed. Modern railway steel cars are made in this manner. Armor plates are formed in hydraulic presses under immense pressures which are maintained for a considerable time.