PNEUMATIC TOOLS are a class of portable mechanical appliances operated by com pressed air. The air pressure is conveyed through a flexible tube from a pressure tank to a miniature self-contained motor, and the tool is adjusted and applied by the hand. They are of two types — percussion and rotary. In the former the work is accomplished by rapidly repeated blows and in the latter by a boring action. They are used for a great variety of mechanical operations, such as drilling, ram ming, hammering, riveting, caulking, boring, screwing, expanding boiler tubes and carving. A good representative of the percussion tools is the pneumatic hammer. It consists of a cylinder in which a piston works with a reciprocating (back and forth) action, actuated by com pressed air admitted to and exhausted from the cylinder by suitably arranged openings.
A loose-fitting tool (such as a rivet-set, in case the appliance is employed as a riveter) is inserted in the front end of the cylinder, to which the compressed air is conveyed by flexible hose connections, and through the handle at the rear. To operate, the device is held by the handle and the tool is pressed firmly against the work. The operator then admits the air-pres sure into the cylinder by pressing on the throttle lever, and starts the reciprocating hammer, which strikes the tool or rivet-set at each for ward stroke. The action is similar to that of driving a chisel with a mallet or hammer, with the exception that the successive strokes are delivered with great rapidity, at a rate of speed as high as 20,000 blows per minute, and sound like a continuous buzz, the efficiency of the appliance being due to the frequency of the strokes rather than to the power of each indi vidual stroke. Pneumatic percussion tools, in general, are made small enough to be operated by the hand, and they are adapted for various uses by simply replacing the tool piece at the front by other tools specially shaped to fit the particular kind of work. The arrangements for actuating and controlling the piston vary greatly in the different makes, but all of them belong to either the valve or the valveless form.
In the valve-hammers, a reciprocating valve acts in combination with the piston and regu lates the admission and exhaust of the com pressed air. They deliver a long stroke at a speed ranging from 1,500 to 3,500 blows a minute with great power, and are suitable for heavy riveting, chipping and caulking purposes. In the valveless hammers, the striking piston acts as a valve and controls the admission of the air-pressure to the alternate ends of the cylinder. They deliver a short stroke at a very high rate of speed, generally over 15,000 blows a minute, and are suitable for stone carving, beading flues, light caulking and other purposes requiring a light chipping action. Owing to their simpler construction, they last longer than the valve hammers and are more economical in air consumption relative to the number of blows delivered. For clipping purposes, the speed is greatly reduced, and the piston is constructed to act on a hinged link so as to impart a pincer like action to the clipping jaws. As riveters,
they range from the portable sizes to heavy stationary machines. Any ordinary pneumatic hammer may be employed in riveting, but such work is better accomplished, generally, by the regular U-shaped riveter designed for that pur pose. (See METAL-WORKING MACHINERY). In riveters the compressed air is used at a pressure of 125 pounds to the square inch, while in the other forms the intensity is somewhat less, gen erally about 90 pounds to the square inch. Ro tary pneumatic tools are commonly known as portable pneumatic drills. In wood-working, they are used for boring and drilling; in metal working, they are employed in, the operations of tapping, reaming, screwing nuts on bolts, boring cylinders, expanding tubes, turning crank-pins, cleaning castings, grinding steam-pipe joints, etc. They are made in a large number of sizes, rang ing from the light forms used for boring small holes up to the large machines requiring a two or three-horse-power motive energy. Originally they consisted of a small rotary engine with an attached feeding mechanism. Subsequently, to avoid the consequent waste of power, small reciprocating engines were designed, bringing them to the present form, in which they are used with marked economy for all purposes where heretofore the hand brace was employed. They are made in two forms — with single-acting or with double-acting oscillating cylinders, and work with an air-pressure ranging from 70 to 85 pounds to the square inch. In the former, the motor consists of two pairs of single-acting cylinders coupled to the opposite ends of a crank-shaft, the pinions of which gear with the spur-wheels on the tool-shaft. The whole me chanism is enclosed in a cylindrical metallic case. In the latter, tyvo double-acting oscillating cylinders are geared to a crank-shaft carrying a single pinion which gears with a spur-wheel on the tool shaft. Another form — the Boyer pis ton drill -L consists of a motor in the form of an oscillating engine composed of three single-act ing cylinders carried in a rotary frame. The pistons being attached to a fixed shaft, the frame is caused to rotate by suitable gears and imparts its motion to the tool-shaft. The com pressed air connections are flexible hose similar to those used in the percussion tools. Other forms of pneumatic tools of special application are the hoist, jack, stay-bolt cutter, mud-ring riveter, ubull-dozers press, paint sprayers, sheep shearers and sand blasts. Their names define the purposes for which they are used. The hoist has largely replaced the ordinary hoisting chain; the jack is a modification of the hoist and is used by being placed under the piece to be lifted. Pneumatic tools are of modern origin and have been principally developed in the machine-shops of the United States, espe cially in connection with the repair depart ments of the railroads, but they are being rapidly introduced in European and other countries.