In view of the complexity of the many factors affecting the selection of steam generating equipment and their interrelation it is only possible to list them in their major relations and group these relations as logically as possible. The considerations listed below are the most usual. There may be others peculiar to certain specific problems.
accurately, an advantage in many cases of forging, including that done in dies. The arch form has two standards between which the tup is also run in guides, and it is much used for forgework of heavy description, being a very rigid construction. The frame is often built of rolled steel plates and angles instead of cast-iron or cast-steel. The operating mechanism of the B. and S. Massey hammer shown comprises the stop-valve lever which regulates the quantity of steam admitted to the hammer, and the hand-lever that is moved to strike light or heavy blows, or to hold work be tween the pallets as in a vice, for bending purposes, etc. The steam is used expansively, with resulting economy, by the action of the tripper, which begins to close the piston-valve after the tup has moved a certain distance. A self-acting valve-gear can be applied to any type of hammer, so as to cause the hammer to work automatically. Many special shapes of hammer framings and anvils are built for specific purposes. Control is in some cases effected by a treadle, so that one man can use the hammer. Com pressed air may be utilized instead of steam, should it not be convenient to furnish a supply of the latter. The lubricator at
tached to the side of the frame consists of a hand pump with which *The size, type and operating rate of boilers may be limited by quality of water. (J. VAN BR.) Steam-hammers are made in sizes ranging from z cwt. to about 12 tons. The size is merely a nomi nal rating, being the weight of the falling parts—piston, rod, tup, pallet—and takes no account of the pressure of steam which drives the piston down for the blow. As an approximate guide, however, it may be stated that the steam pressure in a 5-cwt. hammer gives a crushing effect on hot iron equal to a load of about 3o tons. Types of hammers are classified in three princi pal forms, the overhanging with slide, the arch and the Rigby (see drawing). In the last-named there is plenty of clearance space for the smith to manipulate work above and around the anvil-block, and the piston has a longer stroke and gives more power than corresponding hammers of other types. The over hanging type hammer has slides reaching down to guide the tup the cylinder and valves can be oiled at any moment without stopping the hammer. To secure efficient results the anvil-block must be of great weight, and supported on a mass of timbering resting on deep concrete or rock. The base also rests on timbers and concrete. (See PRESSES AND PRESSWORK and DROP FORGING.) (F. H.)