Machinery's Handbook, 31st Edition
1468 Mechanical and Hydraulic Presses wear. Erosive wear most commonly occurs in hydraulic systems that contain servo or proportional devices. Two of the most commonly used lubricant systems are: Lost Lubricant Systems: Lost lubricant systems are used on smaller gap presses. Older presses are usually lubricated by grease, and newer ones by oil. A hand pump is often used in lost lubricant systems. The major disadvantages of this system are that used lubricant must be cleaned periodically, and if a hand pump is used, lubrication of the machine depends on the reliability of the operator. Re-circulating Lubricant Systems: In these, oil is pumped from a reservoir, filtered, and then distributed to all lubrication points. The pump is powered by an electric motor or by a press-driven mechanical device. The circulating oil lubricates, cools, and flushes small particles from the bearing and friction surfaces. If the failure of the lubrication system is not detected early, serious damage to the machine will occur. Thermo-chromatic indicators are often used for early detection of lubrication system failure. By the use of thermo-chromatic indicators, mechanical or electrical problems can be detected immediately by the operator or maintenance person. The machine can then be inspected and repaired before serious damage occurs. A few dollars invested in thermo-chromatic indicators can save thousands of dollars on expensive repairs and production losses. Another sign of lubrication system failure is the presence of bronze particles around the bearing. In this case, it is usually too late for inexpensive repairs because serious damage of the bearing or friction surfaces has already occurred. Press Selection.— When selecting a press, compromises must be made if more than just one type of stamping operation is desired; there is not a single universal type of press that provides productive and efficient operation. Such compromises include consideration of the following primary factors: tonnage; energy capacity; press size and frame design; speed; and control system for press. Other factors can be considered as well, such as the number of operations to be per formed, quantities and production rates, size, geometry and accuracy of workpieces, and equipment costs. A press-rated tonnage for mechanical presses is the maximum force that should be exerted by the slide against the workpiece at a given distance above the bottom of the stroke. The higher the rating, the greater the torque capacity of its drive members and its capability of delivering more flywheel energy. Presses with flywheel-type drives are basi cally used for light blanking and piercing operations. The energy requirements of these machines are small and the machines operate at relatively high speeds. Single-geared presses are mostly used for shallow drawn workpieces and require more energy than fly wheel types. Double-geared presses are used for deeper draw operations when a larger amount of energy is needed. As stamping operations become more automated, the use of CNC system and various electro-mechanical systems to feed material to the press must also be factored in. There are mechanical blank handing systems where manual handling is not practical due to speed and size. High volume feeding is done with coil stock, which also requires an investment in additional feeding equipment.
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