时间：2011-03-11 23:18来源：蓝天飞行翻译 作者：航空 点击：次
|
shaded-pole motor (AC electric motor). A type of alternating current induction motor used for light-duty, constant-speed loads, such as fans, blowers, and tape players. A coil excited by single-phase alternating current is wound around a laminated steel frame, and a squirrel-cage rotor is mounted in bearings attached to the frame. Shading coils made of one or two bands of heavy copper are installed around diagonally opposite pole shoes, the part of the frame around the rotor. Current induced into the shading coils by the AC in the exciter coil demagnetizes the part of the pole shoe around which it is wound. The AC alternately magnetizes and demagnetizes the corners of the pole shoes, producing a rotating magnetic field which the squirrel-cage rotor follows. Shaded-pole motors have a relatively constant speed, but their torque is quite low. shaft horsepower. The horsepower actually available at a rotating shaft. shaft runout (engine overhaul measurement). The amount the end of the crankshaft of an aircraft reciprocating engine is bent. Shaft runout is measured by mounting the shaft in a set of V-blocks and holding the arm of a dial indicator against the edge of the shaft at its end. When the shaft is rotated, the pointer of the dial indicator shows the amount the shaft is bent or out of round. shake (wood defect). Longitudinal cracks in a piece of wood, usually between two annual rings. shank of a drill. The smooth part of the body of a twist drill that fits into the drill chuck. The three basic parts of a twist drill are the shank, the body (the flutes), and the point. shaving (metal-cutting operation). An operation in which thin layers of metal are removed from the outer surface of the device being shaved. shear. To cut by causing the parts to slide over each other. shear failure (structural failure). The failure of a riveted or bolted joint in which the fastener, rather than the material being joined, fails. The fasteners (rivets or bolts) shear off, rather than the material tearing at the fastener hole. A joint should be designed so it will fail in shear rather than in bearing. When a joint fails in shear, only the fasteners must be replaced; but if it fails in bearing, the torn material must be repaired. shear nut. A thin nut used on a clevis bolt to hold the bolt in place. Shear nuts are used when the fastener on which they are screwed is loaded in shear only. They do not have enough threads to allow their use for a tensile load. shear pin. A pin used to protect a piece of equipment by intentionally shearing if the equipment should seize. A shear pin is used in the drive shaft of some engine-driven pumps. If the pump should seize, the shear pin will break and allow the shaft to turn, but the pump is protected from further damage. shears (cutting tools). A type of cutting tool used to cut sheet metal, paper, or cloth. Shears are similar to scissors, except that they are usually larger and more powerful. Power shears, used to cut thick sheets of metal, are driven by an electric motor. |
