ELORA TOOL CATALOGUE

240 05 Why is controlled fastener tightening important? Anyone involved in modern engineering will already know how important controlled tightening is. To ensure safe, dependable threaded joints, clearly defined tightening forces are essential, irrespective of whether the forces to be applied are large or small (such as is the case with light-weight materials with a low yield point). The decision on the correct tightening force is subject to a number of factors. These include the fastener's thread pitch, the friction in the thread and the material under the nut or screw head. Once all the relevant factors have been taken into account, this results in the required tightening force that will ensure the bolted joint will not become loose even under dynamic loading. By the same token, this tightening force must not be too high as this can also cause the bolted joint to fail. What exactly is torque? Torque is a physical quantity in mechanics. The international unit of measure for moment of force, or torque, is the newton metre, Nm. Torque is defined as a force acting perpendicular to a moment arm. M = F x r A torque wrench is constructed in such a way that it is operated by applying force to the handle. If the lever ratio is changed in any way, this will result in incorrect torque values – a key issue that is referred to in the documentation for all ELORA torque wrenches. Screw tightening using torque and tightening angle In many cases, it is sufficient to tighten a bolt or screw to a certain defined torque. To ensure the application of accurate, defined tightening forces, special expanding screws are used. Screws of this type may only be used once. In the first stage, they are tightened to a defined torque and then a specified tightening angle is applied to tighten the screw beyond the elastic limit of the bolt. This enables a much more accurate tightening force to be achieved. In addition to an ELORA torque wrench, angle controlled tightening requires a mechanical angle measuring instrument (ELORA no. 2184...). Conformity Test and Calibration The DIN EN ISO 6789:2017 has been divided into 2 parts. Part 1 determines requirements for construction and manufacturing, including contents of the declaration of conformity. Part 2, above all, determines the requirements for traceable calibration certificates and includes a procedure to calculate measurement uncertainties. The ELORA Torque Wrench Calibration Laboratory is covering both parts. Each torque wrench will be delivered with a declaration of conformance, because for most users, this is absolutely sufficient. In case of not being differently mentioned within inspection equipment monitoring, the DIN EN 6789:2017 specifies a working life of 12 months or 5000 load changes being the interval for conformity test or calibration. The interval starts with the first use of the torque tool. CLICKING TORQUE WRENCHES Torque Tensile strength of the screw Force Preload Joint Thread with friction Nut engaging surface Preload