They’re those gadgets that enable highly trained team personnel to change wheels at incredible speed.
Also sometimes known as impactors, impact guns, or torque guns, these wrenches are one of the most commonly used of all compressed air tools. And as such, they have a wide range of industrial and commercial applications including construction, car and vehicle repairs, product assembly, and the maintenance of heavy equipment.
Thy should not be confused with the also common and similarly powered impact drivers, which are fitted with bits enabling them to rapidly drive screws into the toughest wood or metal.
No matter what environment it’s being used in, the purpose of an impact wrench is essentially the same - to enable the rapid, safe and simple removal of even the tightest or most badly corroded nuts and bolts.
How Impact Wrenches Work
The tools do this by creating and delivering extremely high levels of torque while requiring very little force from the user.
When the wrench is powered, up a rotating mass within its body is accelerated to store a large amount of energy before engaging with the anvil (output shaft) and socket attachment.
A hammer mechanism in the tool then uses powerful and very rapid concussive blows to deliver a huge torque impact to the target. But the design of the tool is such that the hammer will spin freely after impact so that the operator will feel very little of the torque being generated.
In visual terms it’s observed that the socket initially moves slowly as the nut or bolt works loose, before accelerating suddenly as the torque does its work. For this reason, although it’s possible to use an impact wrench for tightening nuts and bolts, great care is needed because it’s all too easy to strip their threads.
Impact wrenches are compatible with all standards sizes of socket wrench - from small ¼” units for domestic use right up to 3 ½” and above for major industrial and construction purposes.
Use only the right sockets
Such is the power of these tools, however, that it’s crucial to use heavy impact sockets specifically designed for use with them. Using regular sockets is to risk them breaking under the enormous torques to which they will be subjected.
Use hearing protection
Another important cautionary note is that even the smaller, domestic wrenches are extremely noisy, so that the wearing of ear protectors is highly recommended. You might also want to warn your neighbors of what you’re going to be doing.
How to Choose an Impact Wrench
The right selection of impact wrench depends largely on what it is to be used for and the power source you want to use.
A wide range of tools are now available for domestic purposes such as putting up decking and other DIY projects. Having a unit in your car can also be invaluable if you need to change a wheel at the roadside.
Domestic wrenches now commonly use hydraulic or electric power, although more traditional compressed air units are still available.
These air-powered units tend to be favored by tradesmen and mechanics because of their superior power and the reliability of the power source.
In recent years, however, electric and cordless, battery powered wrenches have become increasingly popular for home use. These tools can generate more than enough power for most purposes, but there are some considerations to be borne in mind.
Battery Operated Impact Wrenches
Firstly, the batteries used by the wrench will impact the power it can deliver; higher voltages generally delivering more torque. Battery life also varies considerably from unit to unit and careful research is advised before purchase
Secondly, it’s important to be aware of the two types of motor that are now available.
Brushed motors are an older technology and typically deliver less power than the more advanced brushless motors. These latter are also more efficient in that they can adjust the amount of force they produce in accordance with the requirements of a particular task. Naturally, this superior performance is reflected in the price of the unit
Measuring the Performance of Impact Wrenches
The performance of impact wrenches is measured in terms of speed and torque.
Speed is expressed in revolutions per minute (RPM) and is a measure of fast the wrench will turn a nut or bolt. Proprietary brand tools typically offer anywhere between 1,700 and 7,000 RPM, although some advanced models now offer variable speed settings, to be selected according to the nature of the task at hand.
But probably the most important performance consideration is the amount of torque (turning force) that the tool can generate, since it is this force that actually works to loosen or tighten the nut or bolt.
Torque is measured and expressed in newton-meters (Nm), or occasionally the old “foot-pounds”, and generally the higher this figure the better the tool will perform.
Proprietary brands typically offer maximum torques of anywhere between 200 and 400 Nm, although figures as low as 7 and as high as 1898 Nm can also be found. Many models also now offer variable settings.
High-performance impact wrenches are an indispensable part of the tool kits of construction workers, plant and site maintenance experts, and a huge variety of tradesmen such as plumbers and mechanics.
For a number of reasons, these professionals are likely to prefer traditional compressed-air powered units.
But lightweight, battery-powered versions are now extremely popular with home DIY and auto enthusiasts and can be used for a huge range of tasks in the home, garden or garage.
Find Out More
Models aimed at the home user now come with a wide variety of performance standards and price tags, and some careful research is therefore recommended before purchase.