Impact wrench
[2] 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.
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.
Compressed air is the most common power source for impact wrenches,[citation needed] providing a low-cost design with the best power-to-weight ratio.
Most impact wrenches drive the hammer directly from the motor, giving it fast action when the fastener requires only low torque.
3⁄8 in (9.5 mm) impacts are most commonly available in pistol grip form and a special inline form known as a "butterfly" wrench, which has a large, flat throttle paddle on the side of the tool which may be tilted to one side or the other to control the direction of rotation, rather than using a separate reversing control, and shaped to allow access into tight areas.
Very large impact wrenches (up to several hundred thousand foot-pounds of torque) usually incorporate eyelets in their design, allowing them to be suspended from a crane, lift, or other device, since their weight is often more than a person can move.
Hog rings are used on most smaller tools, with through-hole used only on larger impact wrenches, typically 3⁄4 in (19 mm) drive or greater.
Pin retainers used to be more common, but seem to be being replaced by hog rings on most tools,[citation needed] despite the lack of a positive lock.
1⁄4 in (6.4 mm) female hex drive is becoming increasingly popular for small impact wrenches,[citation needed] especially cordless electric versions, allowing them to fit standard screwdriver tips rather than sockets.
If the output is springy or capable of absorbing energy, the impulse will simply be absorbed, and virtually no torque will ever be applied, and somewhat counter-intuitively, if the object is very springy, the wrench may actually turn backwards as the energy is delivered back to the anvil, while it is not connected to the hammer and able to spin freely.
[citation needed] A wrench that is capable of freeing a rusted nut on a very large bolt may be incapable of turning a small screw mounted on a spring.
[citation needed] Many air impact wrenches incorporate a flow regulator into their design, either as a separate control or part of the reversing valve, allowing torque to be roughly limited in one or both directions, while electric tools may use a variable speed trigger for the same effect.
The hammer then springs forward to the bottom of the ball ramp, and is accelerated by the input shaft, until the dog teeth contact the anvil again, delivering the impact.
This design has the advantage of small size and simplicity, but energy is wasted moving the entire hammer back and forth, and delivering multiple blows per revolution gives less time for the hammer to accelerate, making this design less efficient than the pin clutch or counterweight mechanisms seen in pneumatic impact tools.
Another common design uses a hammer fixed directly onto the input shaft, with a pair of pins acting as clutches.
Yet another design uses a rocking weight inside the hammer, and a single, long protrusion on the side of the anvil's shaft.
[3] Sockets and extensions for impact wrenches are made of high tensile metal, as any spring effect will greatly reduce the torque available at the fastener.
This makes the impact wrench more suitable for large bolts and nuts in heavy mechanical settings (like for instance lug nuts), while the impact driver with its lesser torque and smaller tool bit is more suited towards driving smaller screws, like for instance in construction work.
