In the 1940s it was recognised that having honed the cylinder bores of aircraft engines, this precision could be undone through the uneven tightening of the cylinder head. Norbar’s first torque wrenches were designed to correct this problem, and are still used for this today, along with a host of other applications.
Precision is key to aerospace and Norbar torque wrenches are designed to hold their calibration over many thousands of tightening cycles. The mechanism itself operates in one direction and anticlockwise operation is achieved by means of a ‘push through’ square drive. Furthermore, when they need adjustment, this can normally be achieved without complete disassembly, unlike ‘rocking cube’ torque wrench mechanisms. The bi-directional ‘rocking square’ mechanisms are also notoriously difficult to maintain in calibration in the clockwise and anticlockwise directions. Only a single direction of calibration is required with the Norbar system.
Unlike the all-metal torque wrenches that are very common in the aircraft industry, Norbar torque wrenches are easy to read, easy to set and comfortable to use. All of the plastics used in Norbar wrench handles are tested for their resistance to aviation hydraulic fluids.
Many aircraft fasteners are impossible to reach with standard tools and there has been an example of aircraft loss due to the simple reason that a fastener could not be reached and was therefore never tightened correctly. Norbar offer an Engineer to Order (ETO) service to manufacture special fittings to reach these fasteners.
Hand Operated & Powered Torque Multipliers
Torque multipliers are geared devices that allow very high torques to be accurately produced from a compact tool package. Take for example Norbar’s HT-52 multiplier which can produce 1,000 N•m from a package weight with a suitable torque wrench of around 3 kg – around half the weight of a typical 1,000 N•m torque wrench. Given the tight confines of most airframes, the fact that this tool package utilises a wrench length of around 300mm is also a major advantage.
The most common use for Norbar HandTorque® multipliers in the aircraft industry is helicopter rotor blade bolting. Norbar’s ‘Chinook Kit’ was the first purpose built example, but Norbar multipliers have since been adapted for several helicopter models.
Powered multipliers exchange the torque wrench input of the HandTorque® multiplier for a pneumatic or electric motor input. This gives a tool with low noise, exceptionally low levels of vibration (less than 2.5m/s²) and high torque accuracy. In their more sophisticated form, these tools are fitted with a transducer measuring the torque at the output coupled with a control system that will shut-off the tool at a pre-determined torque. These tools achieve accuracies of better than 2% of reading.
Aircraft wheel rim bolting is an excellent application for Norbar’s PneuTorque® pneumatic torque multipliers. The use of a tool fitted with a transducer allows torque data to be retained for quality control purposes.
Aircraft turbine maintenance requires a host of special offset torque multipliers for applications such as the main bearing retaining nut. A growing application for the PneuTorque® pneumatic multiplier is to provide the drive unit for these torque multipliers, as it is critical that the bearing retaining nuts are not over or under torqued. The use of the PneuTorque® as the driver offers a more precise solution than the gearbox vendor’s pneumatic motor.
PneuTorque® is also ideal for the disassembly of turbine stages. This is because, although installed to a modest torque, the break out torque after the engine has seen service can be extremely high, often causing the bolt to shear. With Norbar’s special reaction tooling, a PneuTorque® makes light and easy work of this otherwise difficult task.
Norbar’s torque calibration instruments are trusted to be the equipment of choice for military, airlines and equipment manufacturers around the world.
The torque measurement range starts with simple to use but accurate testers called TruCheck™ that can be sited line side in production facilities or in aircraft hangers. The main purpose of these testers is to provide a confidence check at the point of wrench use. The measurement range progresses in sophistication and accuracy through to the flagship T-Box XLTM instrument. T-Box XLTM, together with its PC based Torque Data Management Software (TDMS), provides a complete torque audit and torque tool data management solution.
Aerospace customers often require control over the entire calibration hierarchy for their torque measurement equipment. Norbar have supplied several airlines with beam and weight calibration master systems for the calibration of torque measurement devices.
All Norbar torque transducers from 0.005 N•m to 108,500 N•m are supplied with a UKAS accredited calibration certificate. Since 2004 the National Institute of Standards and Technology (NIST) have confirmed to the FAA that certificates issued by UKAS accredited laboratories can be regarded as equivalent to NIST traceable. If clarification is required on this, please check our calibration page or consult Norbar.
Torque Calibration Services
Norbar have established a worldwide network of torque calibration laboratories with third party accreditation by a government approved body. These laboratories are located in UK (accredited by UKAS), Australia (NATA), USA (NVLAP), Singapore (SAC-SINGLAS) and China (TAF and CNAS). All of the laboratories are equipped to the same standard as the UK factory based laboratory ensuring consistency and repeatability between the laboratories. All of the laboratories operate to BS EN ISO/IEC 17025:2005 which sets the standard for the technical competence of laboratories.
In addition to offering calibration of torque transducers, Norbar can provide calibration for many of the special tools provided for aircraft maintenance by companies such as Hydratight Sweeney and Power-Dyne.
USM - Ultrasonic Bolt Measurement
USM-3 uses ultrasound to measure the change in length of bolts during and after the tightening process. Unlike indirect methods of tension control such as torque or torque and angle, ultrasonic measurement of bolt load or elongation in situ on the actual joint stack-up means significantly more accurate bolt tension without costly strain gauging or the introduction of devices which will change the joint stiffness or the joint stack-up height. The net effect of the numerous causes of friction variations which determine the torque versus tension relationship can be empirically analysed; likewise, long term issues such as measuring joint relaxation, gasket creep, sealant migration and performing post flight analysis are easily achievable.
The ultimate accolade for the USM was that after over one year of testing against competitive instruments at NASA’s Stennis Space Center, it was selected to replace the aging fleet of instruments which had been used on over 40 safety critical applications on the Space Shuttle Main Engines (SSME). Norbar’s USM family of instruments has been selected for use on ultra-critical applications found on the Space Shuttle, expendable launch vehicles and satellites. These include: Delta 4 Launch Vehicles; SSME High Pressure LOX & Fuel Turbo pumps, Main Combustion Chamber to Powerhead and HP Ducting; likewise, USM-3 was used for the Hardpoint bolts, Keel bolts and Trunnion bolts on the Spacelab Logistics Pallet (SLP) used for payload mounting on such missions as STS-123 (Dextre Robotics for ISS) and STS-125 (Hubble Space Telescope Servicing Mission 4).
ETO Project Information Sheets