Machinery's Handbook, 31st Edition
1462 Pipe and Tube Bending small iron and steel pipes. Before bending copper or brass pipe or tubing, the latter should be annealed. Alloy of Low Melting Point Used as Filler: Filling tubes with lead may result in satisfac tory bends, but the comparatively high melting point of lead often negatively effects the physical properties of the tube. Commercial alloys such as “Cerrobend” and “Bendalloy” have melting points of about 160 degrees F. They are composed of bismuth, lead, tin, and cadmium. With these materials, tubes having a wall as thin as 0.007 inch have been bent to small radii. The metal filler conforms to the inside of the tube so closely that the tube can be bent just as though it were a solid rod. This method has been applied to the bending of copper, brass, duralumin, plain steel, and stainless steel tubes with uniform success. Tubes plated with chromium or nickel can be bent without danger of the plate flaking off. The practice usually is economical for tubes up to 2 inches in diameter. The method is considered ideal when the number of tubes of a given size or kind is more or less limited or when the bend is especially severe. When a tube-bending operation has been completed, removal of the metal filler is accomplished by heating the tube in steam, in a bath of boiling water, or in air of about the same temperature. The metal can then be drained out and used again and again. Presses for Sheet Metal Working A stamping press is a metal working machine tool that utilizes the force and speed of a moving ram to transmit force, or an amount of tonnage, to a specific die in order to achieve a workpiece’s final shape, often with little or no scrap, and whenever possible, with mini mal operator intervention. There are two major types of press brakes, which are classified by the nature of their drive systems: mechanical and hydraulic. Mechanical and hydraulic sheet metal working presses are available in several basic designs and a wide range of sizes, tonnage capacities, and operating speeds. The moving forces of the presses are generated by either mechanical or hydraulic mechanisms that are mounted in the frame. The two most common types of frames are the gap-frame (C-frame) and the straight side frame. Each has its advantages and disadvantages. Frames may be fabricated by casting or by welding heavy rolled steel plates. Both mechanical and hydraulic sheet metal stamping presses are classified by the following main characteristics: frame, drive, action, tonnage, stroke, and strokes per minute. Mechanical Presses.— Mechanical presses are manufacturing devices designed and built to operate all types of dies. Mechanical presses typically store energy in a rotating flywheel driven by an electric motor. The flywheel revolves around a crankshaft until en - gaged by a clutch device. The energy of the rotating flywheel is transmitted to the vertical movement of the ram by the use of a press drive mechanism. Drive: The press drive refers to the style of mechanism used to obtain the ram movement. The most common press drive mechanisms for mechanical presses are the crankshaft, the eccentric, the screw, and the knuckle. The crankshaft is a mechanical element for translating the rotational motion of the elec trical drive motor to the linear motion of the ram assembly in an up-and-down motion. In the press, each revolution of the crankshaft drives the ram through one complete up- and-down cycle of the machine. In a flywheel press, the flywheel is connected directly to the crankshaft, and each revolution of the flywheel completes one ram movement. The function of the flywheel is to store the necessary energy to carry out a pressing operation. Eccentric —many of the newer presses are made using an eccentric for translating the rotational motion of the electric drive motor to the linear motion of the ram. The main disadvantage of the eccentric press drive is the limitation of press strokes. To obtain more press strokes, the eccentric offset must be increased in diameter. The screw drive press is not as widely used, but the unique characteristics of the screw press have driven an increase in its use. As the name suggests, this type of press drive
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