One of the most popular and useful air tools, particularly for automotive use in garages and vehicle repair shops, is the air impact wrench. When tightening or loosening wheel nuts and lug nuts, small but powerful air impact wrenches are usually capable of applying more torque than can be achieved by manual wrenches. Torque, however, is a tricky little concept – applying too much or too little torque when tightening a nut can make life difficult and even be dangerous so let’s find out a little more about torque and the use of air impact wrenches.

What is torque? Torque is a rotational force: when you unscrew the cap off a bottle you’re applying torque – a rotational force – to twist the cap off. Think about using a hammer and nail – when you hammer a nail into a piece of wood you’re repeatedly using a ‘pushing’ force to push the nail into the wood. Now think about using a manual screwdriver and screw – to twist the screw into the wood you rotate it with the screwdriver rather than pushing it: here, you’re applying torque rather than pushing.

An air impact wrench offers an easy and efficient means of applying lots of torque to something. This is particularly useful for releasing nuts which have been over-tightened or have rusted solid in place.

The problem of applying too little or too much torque. The purpose of a nut and bolt is to securely clamp two separate items together e.g. to clamp a car wheel onto the car’s axle. The correct application of torque to a wheel nut causes the nut to stretch fractionally, creating a tension with the bolt that results in the clamping force which keeps the two locked together even under conditions such as a wheel bouncing along a road and rotating at high speeds. However, applying too little torque can cause a nut to work loose if exposed to vibration, whilst applying too much torque can cause a nut to deform or become damaged, again giving rise to possible loosening when vibrated.

The good news is that modern air impact wrenches are designed to apply the correct torque when used in accordance with the manufacturer’s instructions. It’s worth noting, though, that certain conditions can affect an air impact wrench’s effectiveness. Fluctuations in the pressure of the compressed air delivered to the tool will affect the degree of torque produced. Air of poor quality that is unfiltered, contains too much condensate or is improperly lubricated can also affect torque and cause unnecessary wear and tear to the air impact wrench. Finally, the use of worn, damaged or rusted nuts and bolts can prevent the correct application of torque. Avoid these pitfalls, and an air impact wrench is one of the most useful, safe and cost-effective air tools you’ll ever own.

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