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An impact wrench (also known as an impactor, air wrench, air gun, rattle gun, torque gun, windy gun) is a socket wrench power tool designed to deliver high torque output with minimal exertion by the user, by storing energy in a rotating mass, then delivering it suddenly to the output shaft. Compressed air is the most common power source, although electric or hydraulic power is also used, with cordless electric devices becoming increasingly popular in recent times.〔(Side by side: Cordless impact wrenches at agriculture.com )〕 Impact wrenches are widely used in many industries, such as automotive repair, heavy equipment maintenance, product assembly, major construction projects, and any other instance where a high torque output is needed. For product assembly, a pulse tool is commonly used, as it features a reactionless tightening while reducing the noise levels the regular impacts suffer from. Pulse tools use oil as a medium to transfer the kinetic energy from the hammer into the anvil. This gives a smoother impulse, a slightly lower torque to weight ratio and a possibility to design a shut off mechanism that shuts the tool down when achieving the correct torque. Impact wrenches with shut off mechanism often suffer from a very high mean shift, which is why this technology is losing ground. Pulse tools are not referred to as "impact wrenches" as the performance and technology are not the same. Impact wrenches are available in every standard socket wrench drive size, from small 1/4" drive tools for small assembly and disassembly, up to 3.5" and larger square drives for major construction. Impact wrenches are one of the most commonly used air tools, and are found in virtually every mechanic's shop. In operation, a rotating mass is accelerated by the motor, storing energy, then suddenly connected to the output shaft (the anvil), creating a high-torque impact. The hammer mechanism is designed such that after delivering the impact, the hammer is again allowed to spin freely, and does not stay locked. With this design, the only reaction force applied to the body of the tool is the motor accelerating the hammer, and thus the operator feels very little torque, even though a very high peak torque is delivered to the socket. This is similar to a conventional hammer, where the user applies a small, constant force to swing the hammer, which generates a very large impulse when the hammer strikes an object. Because the hammer spins and has velocity before impacting the anvil, the hammer has momentum. Because it has momentum, it must have kinetic energy. Energy is not stored over time, but rather, energy is stored with velocity. This energy is absorbed by the bolt, nut, or screw in question, and since the collision is (theoretically) an elastic collision, most of the kinetic energy of the hammer is transferred to the bolt that is to be turned. This is contrasted with a regular drill that only applies a torque to the bolt. There is no hammer that reaches a set velocity before hitting an anvil; there is no extra energy to apply to a bolt. The hammer design requires a certain minimum torque before the hammer is allowed to spin separately from the anvil, causing the tool to stop hammering and instead smoothly drive the fastener if only low torque is needed, rapidly installing/removing the fastener. == Power source == Compressed air is the most common power source for impact wrenches, providing a low-cost design with the best power-to-weight ratio. A simple vane motor is almost always used, usually with four to seven vanes, and various lubrication systems, the most common of which uses ''oiled air'', while others may include special oil passages routed to the parts that need it and a separate, sealed oil system for the hammer assembly. Most impact wrenches drive the hammer directly from the motor, giving it fast action when the fastener requires only low torque. Other designs use a gear reduction system before the hammer mechanism, most often a single-stage planetary gearset usually with a heavier hammer, delivering a more constant speed and higher "spin" torque. Electric impact wrenches are available, either mains powered, or for automotive use, 12-volt, 18-volt or 24-volt DC-powered. Recently, cordless electric impact wrenches have become common, although typically their power outputs are significantly lower than corded electric or air-powered equivalents. Some industrial tools are hydraulically powered, using high-speed hydraulic motors, and are used in some heavy equipment repair shops, large construction sites, and other areas where a suitable hydraulic supply is available. Hydraulic impact wrenches have the advantage of high power-to-weight ratio. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Impact wrench」の詳細全文を読む スポンサード リンク
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