Torque wrench

Torque wrench is the general term for a hand held screwdriving tool, with which a defined torque can be applied to a fastener such as a screw or nut in order to ensure the required clamping force between the components to be connected during the insertion of the maximum operating power. According to DIN EN ISO 6789, a distinction indicating torque wrench ( torque wrench ) from triggering types ( click or pop key ).

Torque wrenches are available in different sizes and designs, each covering a specific torque range. The maximum achievable torque is partly limited by the power that can be supplied by the user, the other by the length of the lever to which a manual tool remains manageable (about 1.5 meters). Thus, the theoretical limit is about 1500 nm. In practice, keys are rarely encountered with over 1300 Nm. Higher torques can be generated by combining torque wrench with torque multipliers or hydraulic wrenches (see hydraulic wrench ). Colloquially torque wrench are incorrectly referred to as The Nutcracker, power key or key kilos.

Areas of application

The screw is a frequently used in machine connection. To close the fasteners suitable assembly tools must be used. With the standard and customary in practice, fastening tools, for example, with foot- ring and nut drivers most bolting can be performed in the production and maintenance of products. The transmitted with the use of hand-held tools torque is dependent on the physical condition of the user and his individual perception. In addition, for larger key lengths of the lever arm was standardized such that the transfer of the necessary torque without tools is not possible. The demands on a screw and it is required that the bolt can be tensioned with a defined force, a suitable tool is required. This is true not only for fittings that are to be loaded with large prestressing forces, but also for those who may be biased with only small moments. The assembly of delicate semiconductor- loaded electronic boards in the field of mobile communications and microelectronics, are one example. Consistent lightweight construction in the automotive industry also provides for an increase in the prestressed with a precisely defined moment connections because of the increased use of new construction materials such as magnesium, aluminum and plastic means that the number of sensitive screw steadily increasing. The lower tensile strength of lightweight materials in comparison with steel materials resulting in an overload of the screw to damage of the thread, and thus damage.

Car Holder connect the term torque wrench usually with the tightening of the wheel bolts of aluminum wheels with a wheel change. The automotive industry is for each vehicle model, even when using steel wheels, to be followed exactly suit moments before.

Another area of ​​application is the implantation of Medicine, where glands of dental implants or artificial hip joints by using torque wrenches done. But even in the air and space industry is screwed torque accurately. In the modern assembly technology torque wrench have to take a firm position and it is that the use of glands in lightweight components or sensitive mechanical or electronic components will increase in the future.

To prevent stretching or over-tightening of fittings, find different lines of approach. Firstly, there is the rotation angle controlled tightening method, on the other torque-controlled process. The rotation angle -controlled tightening method, the bolt is tightened with a defined angle of rotation, which takes place via a mechanical or electronic sensor. When torque-controlled tightening method to measure torque when tightening and an action is triggered when a predetermined setpoint.

Torque wrench types

Torque wrenches are available in various mechanical or electronic versions with different operating principles. In the group of mechanical torque wrench, there is the so-called kink keys that by kink or break off at the desired torque and thus prevent further introduction of a moment. Also on the mechanical torque wrenches include the triggering torque wrench ( Knack key) and slippers.

Cracking keys require an expert handling by the user, since after the trigger signal the initiation of the moment has to be stopped by the user. In the slippers release accuracy is independent of the skill of the user, as they slip through when reaching the torque limit and prevent further introduction of torque. In electronic torque tools again safe handling by the user is necessary, as a visual or audible indication of the tightening torque signals when applying a torque must be stopped.

Thus the Verschraubungsqualität can be assured of torque tools, they require a high accuracy in reaching the set tripping torque with a corresponding reproducibility of the values ​​( repeatability). This requires a clearly recognizable trigger signal and the least possible influence of handling differences, for example by fast or slow tightening is necessary.

Triggering torque wrench

When clicking torque wrenches a specific target or target torque is adjusted by means of a scale, or by using a tester. Once the torque wrench on the drive part ( force axis ) reaches the preset torque, which is indicated by an audible, tactile and / or visual signal, usually by a small click / crack or a pop-out colored indicator.

The most common models are made of a usually chrome steel pipe, whose length is matched to the area to be covered, with the trigger mechanism housed therein, and a handle connected to the adjustment device together with the scale. The tool carrier is often a reversible or interchangeable push Ratchet ( also called ratchet) integrated. The drive is then via a square pin with dimensions in inches (1/ 4, 3 /8, 1 /2, 3 /4, 1 or 1 1 /2 "), to the various sockets ( sockets ) can be plugged. Other common tool carriers are, for example, the rectangular cavity or the dovetail guide (English: dovetail ) interchangeable tool heads in different profiles such as foot, ring, open ring or hex key, inter alia,

In 1938, the first self -inducing torque wrench in the world was patented and introduced to the market ( Saltus -Werk Max Forst, Solingen ).

Indicating torque wrench

When indicating torque wrenches, the value of the torque is indicated via a mechanical scale, gauge or electronic display, which is applied by the tool on the output part. Many designs use solid lever by a torsion bar as the drive, its rotation can be read with respect to a lever coupled to the scale as a measure of the torque.

The simplest form of this type consists of a long lever arm between the handle and the wrench head, made ​​of a material which bends elastically under torque. A second small rod having an indicator is fixed to the head end and extends parallel to the lever arm. This second arm remains without load and thus straight. At the end of the handle is attached to a calibrated scale and the bend of the main arm causes movement on the indicator scale. When the desired torque is displayed, the operator stops applying the force. The key is simple, durable and cost exactly.

The origins of the flat bar key, as it is known today, go back to the early 1930s when Walter Percy Chrysler a torque wrench developed for the Chrysler Corporation and the Micromatic Hone Corporation, which was then manufactured and sold by the Cedar Rapids Engineering Company. Their regional sales manager, the young engineer and amateur pilot Paul Allen Sturtevant from Elmhurst (IL ), Chrysler developed imperfect idea further, patented his own invention in 1938 and marketed it through its own PA Sturtevant Company, Addison ( IL).

Electronic Torque Wrenches

With electronic (digital -indicating ) torque wrenches, measurement by means of a strain gauge ( DMS) is performed on the torsion bar. The measurement signal obtained is translated and presented on the digital display (display) by the measured value to be displayed in amplifier power unit ( Nm, lbf • ft, etc.). There may be several different screw joints ( joint data or limit values) can be stored. These programmed limit values ​​are visualized during the Verschraubungsanzuges permanent means of LEDs or the display. Parallel can store all the measurements taken by a torque wrench in an internal readings memory this way. This can be printed read out via the interface ( eg RS232 ) or directly connected to a printer. Common application of this type of torque wrench is the production accompanying documentation or QA procedures.

Electronic Torque angle wrench

The torque measurement is performed as in electronic torque wrench, in addition, an angle from a pre-torque / threshold is determined. The measurement of the angle is performed with the aid of an angle sensor or electronic gyroscope. Based on the angle measurement can already be seen bolted connections. By means of the internal data memory can be performed statistical analyzes. Curves can be analyzed using the software via the integrated waveform memory ( force / path graph ). This type of torque wrench can also be the starting torque, more torque and final torque identify a Schraubverlaufes. A special measuring method, the yield strength can be displayed ( yield point controlled tightening ). Primarily this torque wrench of car manufacturers for documentation for torque - angle controlled screw is used, since to the specified torque (Nm) must be applied even to an angle to be screwed connection ( screw). (eg 50 Nm 90 °, taking 50 Nm pre-torque = / threshold and 90 ° = still weiterzuziehende angle from the threshold )

The Saltus -Werk Max Forst GmbH reported in 1995 to the first electronic torque wrench with angle measurement referenzarmloser for international patenting.

Mechatronic torque wrench

The torque measurement is performed as in the triggering torque wrench, in addition, the torque is measured digitally ( click and final torque ) as with electronic torque wrench. It is a combination of electronic and mechanical measurements. As wireless data, all measurements are transferred and documented.

Others

Often, in addition to based on SI units Nm scale is a second appropriate, for example with the unit " ft.lbs " (pounds · ft). The Anglo-American system of weights and measures is still widely used in some international technical areas ( aerospace ). 1 Nm corresponds to 0.73756215 lbf · ft ( pound -force foot), or vice versa 1 lbf · ft corresponds to 1.3558179 Nm. The unit no longer valid kp · m ( Kilopondmeter ) or kgf · m (even m · kg) is only rarely encountered. 1 kgf · m corresponds to 9.80665 Nm, or vice versa 1 Nm corresponds to 0.10197162 kgf · m.

Practicable orders of magnitude for the workshop operation start at about 0 to 6 Nm and range up to about 200 to 800 Nm.

A well-known example of the use is to tighten the wheel nuts or bolts on motor vehicles. It should not be up to the maximum possible by hand, but " gently but firmly " with a torque wrench. With too little torque the wheels can solve, at too high a threat before the visible tearing of the screws or bolts which overstretching, the tension of brake parts, wheel hubs and rims. This is not immediately apparent and therefore dangerous, because the wheel lock at high speeds or can be solved. Typical torque for cars are in the range between 40 and 150 Nm ( between threads M 10 x 1.25 and M 14 x 1.5).

A special form of the torque wrench is the torsion meter, a very precise execution, can be measured with the mechanical frictional resistances, such as steering gears.

For fixed torque values ​​at steady recurring tasks, such as in large-scale production, to assembly lines, automotive, etc. in addition to so-called production keys preferably compressed air or electric power tools ( screwdrivers ) are used, in which a torque limiter is integrated or built as an attachment.

Torque tools are subject to the standard EN ISO 6789:2003. This recommends a Rekalibrierintervall after a service life of 12 months or 5000 load cycles. This is necessary since spring and limiting mechanism subject to wear.