Impact Tools
Impact tools are designed to store energy in a rotating mass and deliver it as high-torque force in short, sudden bursts. This method imposes minimal stress on the tool user and makes for a very powerful torque tool.
Impact wrench tools are another name for impact tools. The reason is that most impact tools use socket wrench bits that fit over a nut or bolt head. Since impact wrench tools are often used to drive nuts, screws, and other fasteners into materials, they are sometimes called impact driver tools too.
In an impact tool, a motor rotates a heavy mass called a hammer at high speed, building up great kinetic energy. Then the hammer is allowed to make sudden contact with an anvil, and the hammer's energy is delivered to the anvil in a sharp, hard strike. The anvil is connected to the socket wrench and the energy is transmitted to the socket wrench as high torque. After striking the anvil, the hammer returns to rotating freely to build up momentum again.
The right gearing, rotation speed, and mass of the hammer give tool makers precise control over the amount of torque delivered to the work piece. Thus, an impact wrench is ideal for driving a bolt or screw exactly tight enough.
The user feels very little reaction force when using an impact tool, so he or she does not become fatigued from driving fasteners over many hours. Also, at low rotation speeds the hammer does not make impact but applies torque smoothly, allowing an impact tool to be used like a regular rotary tool.
Air impact tools are the most common design. Compressed air is an economical and safe fuel for impact tools in auto mechanics' shops and other work areas where flammable gasoline fuels may be present.
Electric impact tools may be driven by alternating current (AC) from a power cord, or by direct current (DC) delivered from a battery at voltages ranging from 12v to 24v. Cordless impact tools are often used around auto repair shops, but they supply lower power for shorter periods of time than corded impact tools.
Impact tools may have a right-angle handle like a conventional hand drill. But some impact tool are more or less straight sticks like a screwdriver. The straight variety typically has a D-shaped handle on its rear end to help the worker hold the tool steady.