The hydraulic wrench, which is better known as torque wrench, is the general term for a hand-held screw driving tool, with which a defined tightening torque can be exerted on a connecting element such as a screw or nut to ensure the necessary clamping force between the components to be connected, even during the application of the maximum operating forces. According to DIN EN ISO 6789, a distinction is made between indicating torque wrenches (measuring keys) and triggering types (click or click wrenches).
Hydraulic wrenches are available in different sizes and designs, each covering a specific torque range. The maximum achievable tightening torque is limited on the one hand by the force that the user can apply and on the other side by the lever length up to which a manual tool can be handled (approx. 1.5 meters). As a result, the theoretical limit is around 1500 N m. In practice, keys with more than 1300 Nm are rarely found. Higher torques can be prepared by a combination of a torque wrench with torque multipliers or hydraulic wrenches (see the hydraulic wrench) are generated. Colloquial Torque wrenches are also known as nutcrackers, power wrenches or kilo keys.
The screw connection is a connection that is frequently used in mechanical engineering. Suitable assembly tools must be used to close the connecting elements. With the standardized and common screw driving tools in practice, for example with combination wrenches, ring spanners and socket wrenches, most screwdriver cases can be carried out during the manufacture and maintenance of products. The moment transmitted when using hand-held tools depends on the physical condition of the user and his personal feeling. Also, with larger widths across flats, the standardized lever arm was dimensioned in such a way that it is not possible to transmit the necessary torque without tools. If the demands on a screw connection increase and a pre-tensioning of the screw with a defined force are required, a suitable tool is needed.
Car owners usually associate the term torque wrench with tightening the wheel bolts of aluminum rims when changing a wheel. Another important apparatus required in the process is a tube pilot. The automotive industry specifies tightening torques that must be strictly observed for every vehicle model – even when using steel rims.
Another area of application is implantation medicine, where screwing of dental implants or artificial hip joints is carried out using torque wrenches. But also in the aerospace industry, screwing is carried out to the exact torque. Torque wrenches have a permanent place in modern assembly technology, and it can be assumed that the use of screw connections in lightweight components or sensitive mechanical or electronic components will continue to increase in the future.
Various concepts are used to prevent over-stretching or over-tightening of screw connections. On the one hand, there are tightening methods controlled by the angle of rotation, and on the other hand, torque-controlled methods. In the tightening procedure controlled by the edge of rotation, the screw is tightened with a defined angle of rotation, which is done via a mechanical or electronic sensor. In the torque-controlled tightening process, the torque is measured when stretching, and an action is triggered when a specified set point is reached.