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June 1, 2020
With many different options on the market, it can be challenging to know what features to look out for when selecting an impact wrench. This guide provides a brief overview of the technology and outlines some simple steps to help you get started.
An impact wrench, also known as an impact driver or an impact gun, is designed to tighten or untighten bolts. It is commonly used in mechanical and industrial applications, for example when changing tires and disassembling car wheels, or performing maintenance on oil platforms. There are electrical, battery-powered, or pneumatic options available, each associated with different benefits and challenges.
The operating principle is relatively simple. An impact mechanism composed of an anvil, an impactor (hammer) and a spring, enables the wrench to tighten and untighten as required. The tool accumulates energy by the hammer cage over one or more revolutions and once the hammer hits the output shaft (anvil), it creates the tightening or untightening torque.
The design of the tool can play a key role in improving productivity. For example, a well-positioned center of gravity is a great benefit, as it enables better support over extended periods, while different handle shapes and trigger positionings can improve user comfort.
The material of the tool is another critical consideration. Metallic tools are usually more robust, but also heavy to use over long periods. Composite tools, on the other hand, are much lighter, enabling better maneuverability, but the material has made them less durable. Fortunately, advancements in material development over the last decade have improved the mechanical resistance of composite, improving its strength and making it a good alternative to metal in many applications.
It is good to remember that the clutch housing and the body of the tool can be made of different materials. When you compare tools, make sure you check which part is composite and which is metal. As a rule of thumb, impact wrenches larger than ¾” tend to be made of metal.
Always choose a tool with a maximum torque that is superior to the torque needed for your application. This will reduce the time you spend using the tool and the vibrations you are subjected to. The graph below illustrates the different torque values commonly found in manufacturers’ catalogs.
Beware of overtightening! In some applications, for example when changing tires in small vehicles or trucks, tightening requires precision and torque control. Using tools with torque limited functions, coupled with a torque wrench, will optimize the application without overtightening and damaging the studs.
You can identify the ideal tool square by looking at the size of the thread. If the square is too small compared to the thread, it will not be suitable and is likely to break. However, if the square is too large, it will be too strong and break the screw when tightening it.
It is vital to pay attention to factors that affect user safety and ergonomics, such as the sound level and vibration. The sound level is usually governed by the ISO15744 standard and the lower the value, the safer the user experience. The same goes for vibration levels, usually governed by ISO28927: lower vibration levels equal a safer and more comfortable user experience. Some impact systems are designed to enable low vibration levels and safety and comfort can also be further enhanced with the use of vibration-absorbing gloves.
By considering these seven points you will improve safety associated with using tools in the workplace, therefore protecting operators. An additional benefit to these responsible practices is that you will improve efficiency too!
Noise and vibration levels are factors to consider when choosing the tool to use for your application. Usually, when using keys below ¾”, operators are more sensitive to noise. However, above 3/4”, vibrations are more important to ponder.
Knowing what you need to consider when looking for the right impact wrench for your application is a good start, but sometimes reviewing technical values is not enough to enable a well-informed purchase decision. To ensure the tool can meet your needs, it is always a good idea to discuss your requirements with the manufacturer and request a trial. Trying the tool out in your target application will give you confidence that it is a good fit for the task, the environment and ultimately, the way you work.