Impact wrench
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An impact wrench (also known as an impactor, impact gun, 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. It was invented by Robert H. Pott of Evansville, Indiana.[1]
Impact wrenches are widely used in many industries, such as
Impact wrenches are available in every standard socket wrench drive size, from small 1⁄4 in (6.4 mm) drive tools for small assembly and disassembly, up to 3+1⁄2 in (89 mm) and larger square drives for major construction.
In operation, a rotating mass is accelerated by the motor, storing energy, then suddenly connected to the output shaft (the
Power source
Compressed air is the most common power source for impact wrenches,[
Sizes and styles
Impact wrenches are available in all sizes and in several styles, depending on the application. ¼" drive wrenches are commonly available in both inline (the user holds the tool like a
Various methods are used to attach the socket or accessory to the anvil, such as a spring-loaded pin that snaps into a matching hole in the socket, preventing the socket being removed until an object is used to depress the pin, a hog ring which holds the socket by friction or by snapping into indents machined into the socket, and a through-hole, where a pin is inserted completely through the socket and anvil, locking the socket on. Hog rings are used on most smaller tools, with through-hole used only on larger impact wrenches, typically ¾" 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. ¼" 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. Adapter attachments can be purchased that allow hex drive tools to couple to square drive sockets, and vice-versa.
Many users choose to equip their air-powered impact wrenches with a short length of air hose rather than attaching an air fitting directly to the tool. Such a hose greatly aids in fitting the wrench into tight areas, by not having the complete coupler assembly sticking out the back of the tool, as well as making it easier for the user to position the tool. An additional benefit is greatly reduced wear on the coupler, by isolating it from the vibration of the tool. A short length of hose also prevents the air fitting from being broken off in the base of the tool if the user loses their grip and the tool is allowed to spin.[citation needed]
Effects of impact drive
As the output of an impact wrench, when hammering, is a very short
Hammer mechanisms
The hammer mechanism in an impact wrench needs to allow the hammer to spin freely, impact the anvil, then release and spin freely again. Many designs are used to accomplish this task, all with some drawbacks. Depending on the design, the hammer may drive the anvil either once or twice per revolution (where a revolution is the difference between the hammer and the anvil), with some designs delivering faster, weaker blows twice per revolution, or slower, more powerful ones only once per revolution.
A common hammer design called a ball and cam mechanism has the hammer able to slide and rotate on a shaft, with a spring holding it in the downwards position. Between the hammer and the driving shaft is a steel ball on a ramp, such that if the input shaft rotates ahead of the hammer with enough torque, the spring is compressed and the hammer is slid backwards. On the bottom of the hammer, and the top of the anvil, are dog teeth, designed for high impacts. When the tool is used, the hammer rotates until its dog teeth contact the teeth on the anvil, stopping the hammer from rotating. The input shaft continues to turn, causing the ramp to lift the steel ball, lifting the hammer assembly until the dog teeth no longer engage the anvil, and the hammer is free to spin again. 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. The process then repeats, delivering blows every time the teeth meet, almost always twice per revolution, although impact tools with three impact dogs have been produced. If the output has little load on it, such as when spinning a loose nut on a bolt, the torque will never be high enough to cause the ball to compress the spring, and the input will smoothly drive the output in the same manner as a drill or powered screwdriver. The ball and cam impact mechanism is most commonly seen in electric impact tools, as it allows the power source to be continuously rotating even while impacting, which prevents the motor from stalling. 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. This design is often seen after a gear reduction, which reduces the speed and increases the torque of the motor driving the impact mechanism, and compensates for the lack of acceleration time by delivering more torque at a lower speed.
Another common design uses a hammer fixed directly onto the input shaft, with a pair of pins acting as clutches. When the hammer rotates past the anvil, a ball ramp pushes the pins outwards against a spring, extending them to where they will hit the anvil and deliver the impact, then release and spring back into the hammer, usually by having the balls "fall off" the other side of the ramp at the instant the hammer hits. Since the ramp need only have one peak around the shaft, and the engagement of the hammer with the anvil is not based on a number of teeth between them, this design allows the hammer to accelerate for a full revolution before contacting the anvil, giving it more time to accelerate and delivering a stronger impact. The disadvantages are that the sliding pins must handle very high impacts, and often cause the early failure of tool.
Yet another design uses a rocking weight inside the hammer, and a single, long protrusion on the side of the anvil's shaft. When the hammer spins, the rocking weight first contacts the anvil on the opposite side than used to drive the anvil, nudging the weight into position for the impact. As the hammer spins further, the weight hits the side of the anvil, transferring the hammer's and its own energy to the output, then rocks back to the other side. This design also has the advantage of hammering only once per revolution, as well as its simplicity, but has the disadvantage of making the tool vibrate as the rocking weight acts as an eccentric, and can be less tolerant of running the tool with low input power. To help combat the vibration and uneven drive, sometimes two of these hammers are placed in line with each other, at 180° offsets, both striking at the same time.
A new (as of 2016) design encases the pounding mechanism in hydraulic fluid to reduce the amount of metal to metal contact, greatly reducing noise and vibration.[3]
Sockets and accessories
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. Even so, the use of multiple extensions,
Commonly used brands
Pneumatic impact wrench brands that are commonly used in shop and construction application include
Compared to an impact driver
An impact wrench typically delivers more torque and accepts larger tool bits than an impact driver. 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.
See also
- Socket wrench
- Torque multiplier
- Pneumatic torque wrench
- Impact driver
- Hydraulic torque wrench
- Air tool
References
- ^ US patent 2012916A, Robert H Pott, "Impact tool", issued 1935-08-27
- ^ "Side by side: Cordless impact wrenches". 25 December 2007. Archived from the original on 25 December 2007.
- ^ "A New Breed of Impact Drivers Cuts the Noise in Half". Popular Mechanics. 11 October 2016.
- ^ "Behold the Thunder Gun, Nascar's Secret Weapon". Popular Mechanics. 2012-09-05. Retrieved 2023-07-14.
- ^ "Paoli Wheel Guns". United Race Parts. Retrieved 2023-07-14.