Hammer , a tool for communicating force by impact. There are three varieties, those which are moved by the arm, those which are moved by their own gravity, and those which are moved by compressed steam or other power. The two latter kinds are called power hammers. The first kind comprises small or hand hammers, and sledges. The hand hammer consists of a head, to give momentum, and a small helve or handle fitted into an eye, which is usually in the middle of the head. Their weight varies from an ounce to one or two pounds. Sledges are large hammers, to be wielded by both arms, and vary in weight from 2 to 20 lbs. Large wooden hammers, bound with iron, used by woodsmen in driving wedges, are called beetles; smaller wooden hammers are called mallets. - Power hammers are of various forms, moved by water, steam, and sometimes by horse power. The common forge hammer is made of a heavy head of iron, 5 to 10 tons in weight, faced with steel, and having a helve of cast or wrought iron, or wood, the centre of motion being at the end of the helve. The hammer is raised by cams upon a wheel, the lifting force being applied near the head. The force of the blow is the momentum attained by the mass in falling through a height of from 16 to 24 in. The speed is usually from 50 to 100 strokes per minute.
Tilt hammers have much the same construction as the common forge hammer, except that the head is raised by depressing the opposite end of the helve by a cam wheel, as represented in fig. 1, the centre of motion being between the head and the point of application of power. They are lighter and move with greater rapidity, and are used for lighter kinds of work. Both kinds must be substantially supported by solid foundations. The steam forge hammer, in which steam is used as a propelling force to the hammer, patented by Mr. Nasmyth of England in 1842, and also by M. Creusot of France in the same year, is a much more efficient machine. Nasmyth's hammer is the one generally known. The hammer head is fixed to the end of a massive piston rod working vertically in a high-pressure steam cylinder, placed above, the whole being held in a strong iron frame having two standards. The hammer block weighs many tons, and must rest upon very strong and solid foundations, common to the whole. The lift or stroke of the hammer is from 5 to 9 ft., depending upon the size of the machine. The momentum will of course vary with the steam pressure and length of stroke, which, from the construction of the cylinder, may be varied to suit circumstances.
A monster steam hammer of a construction similar to Nasmyth's is employed in Krupp's cast-steel works at Essen, Germany. The hammer head is 12 ft. long, 5 1/4; ft. wide, 4 ft. thick, and weighs a little over 50 tons, and has a stroke of 9 ft. The depth of the foundation is 100 ft., consisting of three parts, masonry, timber, and iron, bolted together. Four cranes, each capable of bearing 200 tons, serve the hammer with material. Smaller steam hammers of much higher speed are used in forging smaller articles, such as swords, scythes, axes, carpenters' tools, steel bars, etc. One of these, exhibited at the Vicuna exposition in 1873 by Gustav Brinkmann and co. of Westphalia, is represented in fig. 2. While the frames of the large hammers have two standards, this has only one, an advantage allowed by its smaller size. The admission of the steam is effected by a simple slide valve worked by a hand lever, as shown in the engraving. In this machine, in consequence of the manner in which the steam is admitted, the length of stroke is constant; in this individual case, 7 1/2 in. The weight of the hammer is 4 cwt., and the average number of blows when worked with steam at a pressure of 45 lbs. per square inch is 360 per minute.
The piston rod, 6 1/2 in. in diameter, is cast steel, forming with the piston one piece. The hammer head is fastened to it by means of keys. The greatest height of pieces which can be forged under the hammer is 4 1/2 in. The bottom of the frame is 3 ft. square, and its total height to the flanges of the cylinder is 5 1/2 ft. The total weight of the machine is 4 1/2, tons.
Fig. 1. - Tilt Hammer.
Fig. 2. - High-Speed Steam Hammer.