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Information about torque wrenches: High accuracy screw tools
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How does a torque wrench work?
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How is a torque wrench structured?
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To select the appropriate torque wrench
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What are the advantages of a calibrated torque wrench?
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These features are important for torque wrenches
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The right accessory for your torque wrench
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Tips for using torque wrenches
In industry and trade, the screw connection is one of the most frequently used connection types. Sufficiently dimensioned, it holds very firmly and can be dissolved again without destruction in contrast to many other connections. Torque wrenches are calibrated precision tools that allow you to accurately adhere to the specified tightening torques for screw connections. They use nuts and bits to install bolts and nuts securely with an exact tightening for a smooth and gentle grip. The torque-controlled screw connections ensure the greatest possible clamping force between the components even at maximum mechanical load.
A torque wrench gives you safety and prevents damage to material and screws. Screw connections are often too tight with conventional tools. Classics are too firmly mounted aluminum rims on tires in cars, steering bearings on bicycles or milling or cutting heads on machine tools. Typical consequences are an over-threaded or torn thread that needs to be repaired or even replaced, causing unproductive downtime. Tightening beyond the specified starting point can also lead to increased material stress and premature wear. In addition, connections that are too tight or over-tightened can be easily loosened.
Screw connections that are tightened too weakly are not tight enough and do not secure the connected components sufficiently. Loose screws are a considerable safety risk, they can become loose under load, through vibrations or under stress and thus endanger people and property.
By using a calibrated torque wrench as a turning tool and measuring tool in one, you can no longer leave it to your gut feeling or to your employees' day's constitution whether nuts and screws are seated correctly. Among the most famous manufacturers of torque wrenches are BGS, Facom, GEDORE, HAZET, Herder, KS Tools, Projahn, STAHLWILLE, TOOLCRAFT, Wera and Wiha.
How does a torque wrench work?
Torque wrenches prevent the torque applied by the user from acting freely on the connecting piece. Here's how it works:
Set the torque on the wrench handle using a scale or digital display in Newton meters (Nm or N-M). First, unlock the locking mechanism, which prevents unintentional adjustment during work. The force is pre-selected within the working range specified in the product description in which the tool is adjustable.
Many models have a two-stage setting: Use the coarse setting scale to select the next low scale value at the specified Nm value. Use the fine scale to add the camshaft value that is still missing from the target torque.
For a reversible model with clockwise and anti-clockwise rotation, set the direction of rotation on the changeover lever or by means of a through-square drive. Now attach the necessary socket, socket or screwdriver attachment to the drive square on the head of the torque wrench – you're ready to go.
Operate the key only by the handle and press evenly. The preload determines when the tool is triggered. This achievement of the preselected force is signaled to you in a "triggering" model by a well audible crackling noise or also tangible through triggering of a sliding mechanism. Then the device is immediately ready for use again for further screw connections.
How is a torque wrench structured?
Even though the torque wrench is apparently a simple tool consisting of a ratchet and a metal tube as a lever, there is a lot of know-how in it.
Depending on the model, the inner workings of the handle tube are made up of several components. These include the pre-tensioned spring, a folding lever, a transmission and the drive, which together form a lever chain. This design reduces the effort and the load on the mechanics to a minimum.
To select the appropriate torque wrench
Screw and measuring keys are available for a wide range of applications and requirements of the controlled suit. Among other things, the models are designed for installation and repair work on motor vehicles, machines, metal constructions and production plants, for use on construction sites, in craftsmen and DIY workshops.
Triggering torque wrenches
In the case of a torque wrench that triggers, a spring-coupling mechanism inside the handle actively monitors the torque. The target or target torque is set using a scale. The selected torque is achieved acoustically, haptically or visibly.
Electronic torque wrenches
With a digital torque wrench, the tightening torque is measured by a strain gauge. The user specifies the desired target and target values via control elements on the handle. The torque is displayed via LEDs or on a digital display. An electronic signal indicates that the desired torque has been reached.
Indicating torque wrench
Indicating torque wrenches work purely manually without release mechanism. These variants are easy to use and inexpensive to purchase. They indicate the tightening force and thus the torque on a mechanical scale or dial gauge. The user stops the screwing process when the desired torque is displayed. He is therefore responsible for the compliance with the request.
Practical advice
In addition to torque wrenches working with socket wrenches or attachment tools, there are torque screwdrivers with adjustable or specified torque. They can be fitted with bits and are suitable for fine work and for use in confined spaces. An alternative is torque indicators, which are preset at the factory to a specific screw size, profile type and torque.
What are the advantages of a calibrated torque wrench?
Individually calibrated torque wrenches are recommended for applications where the highest precision is required. The spring tension and mechanics of these high-quality models are adjusted in the factory in such a way that the tightening torques that are to be observed are exactly maintained. The test certificate, which is usually supplied, is used as proof of calibration.
As a natural consequence of frequent use, the pre-tension of the spring and thus the accuracy of the tool decreases over time after a certain number of inserts. Occasional calibration allows the mechanics to be re-adjusted and the torque wrench is returned to its original accuracy. The recommended number of uses or years of calibration depends on industry specifications, tolerances, materials and individual use of the equipment.
With an electronic tester you can test whether the set target torque is reached within the desired tolerances. Professional calibration (recalibration) is carried out by the manufacturer of the device, who offers a calibration service for this purpose, or by an independant testing workshop. After the adjustment by the customer service department, the key works as precisely as at the beginning.
Tip: With regard to safety, liability and insurance issues, it is advisable to check the calibration of the devices used. A regular check ensures the desired accuracy in the long term.
These features are important for torque wrenches
The tools are available in versions with different sizes, shapes, forces and specific equipment such as ergonomic handles and downforce suitable for socket wrench inserts of different sizes.
Torque:
The manufacturers shall indicate for each torque wrench the approved working area in which the tool is adjustable and may be used. Typical values are 40 to 200 Nm, 20 to 120 Nm and 5 to 25 Nm.
The accuracy of the keys is greatest in the middle field of the specified Nm working range. If precision is important, it is worthwhile to buy several torque wrenches with smaller application areas and not a model with a large Nm measuring range.
For safety-sensitive applications, working on the conveyor belt and series production, there are keys without adjustment scale with factory-fixed torque. An alternative are models that you can individually adjust to the required torque using a test device or a calibration system.
Size
Buy a controlled torque wrench of the correct size. The size specified in the product description refers to the drive in the ratchet head and is expressed in inches. Common sizes are 1/2 in (12.5 mm), 1/4 in (6.3 mm), and 3/8 in (10 mm). Depending on the size of the drive, it depends on which sockets and attachments you can attach.
The larger the drive, the larger the socket that the torque wrench can accept. Keys with 1/4 inch are relatively small and are mainly used for repair work on bicycles, electric scooters and in fine areas. However, the 1/2 inch torque wrench is the most widely used when working on a car, motorcycle or other vehicle. Larger models are also used in industry, mechanical engineering and manufacturing.
Material
The materials used have an impact on the haptics, robustness, durability, rust protection and also on the price. Keys made of high-quality industrial steel are particularly insensitive, resistant to mechanical wear and are also suitable for the toughest continuous loads.
Safety and comfort features
The large manufacturers equip their torque wrenches with safety and comfort features, such as non-slip, ergonomically shaped handles, clearly readable display and easily accessible unlocking mechanisms for quick change of the insertion tools. These ensure a pleasant and safe handling of the tool, even over a longer period of time.
Extension;
The torque is transmitted depending on the lever arm. Operation outside the handle or the use of extension tubes usually affects the torque. There is an undesired value shift and influence on the accuracy. The product description indicates whether the respective model can be operated outside the handle or with an extension tube without changing the values.
Right and Left Running
Some models allow you to quickly change from right to left, so you can rotate in both directions, depending on the situation. For this, the square simply has to be changed over to the other side or the change-over lever on the ratchet has to be actuated.
Marking
Torque wrenches are usually marked with the manufacturer's name and model designation and the permissible application area. High-quality models carry a clearly attached serial number for identification and instructions for calibration.
Loosen the screw connections
Torque wrenches are built exclusively for the controlled screw suit with force measurement. The product description indicates whether you can use the model for loosening screw connections within the maximum tightening torque.
The right accessories for your torque wrenches
Controlled keys are available individually and as a set in practical sets. With a torque wrench set, you can use the actual tool grip as well as various bit tools for square attachment. Additional attachments are available as accessories. When selecting plug tools, pay attention to the size of the drive to which they are matched.
Tips for using torque wrenches
The following tips will help you use torque controlled wrenches.
- Preset: Take the time to set the target value on the grip scale or the electronic display. The more precise you select the torque, the more precise the tightening force is maintained.
- Note limit: Do not turn the tool beyond the measuring range after triggering.
- Release: After working, set the torque wrench to the lowest torque (lowest scale value). This relaxes the mechanics and the accuracy is retained for a long time.
- No extension: Do not use handle extensions, levers or pipes.
- Be careful not to immerse the key in water, oil, grease, solvent or paint. For cleaning, it is sufficient to wipe it occasionally with a dry cloth.
- Storage and transport: Many torque wrenches are supplied in a storage box. The case protects the device during take-away and storage.
- Lubrication: If not used for a long time, loosen the torque wrench several times with a low scale setting to obtain correct lubrication.