Torque wrench, calibration, calibration beam, torque, UKAS, torque wrench - products

By: Norbar  11-11-2011
Keywords: Calibration, beam, Geological Survey

This easy to use software allows data from a Norbar torque measuring instrument to be down loaded onto a PC and formatted as a torque calibration certificate.

Norbar's Test Beams are designed for the static calibration of Torque Transducers. They are ideally suited to Norbar's transducers, but can be employed on other manufacturer's equipment.

Torque is generated by the application of a known force at a known radius from the centre of rotation of the torque transducer.

Designed to remove potential sources of measurement error, these beams can be used to calibrate Norbar torque transducers, and torque transducers from other manufacturers (where design permits), as well as mechanical test devices. UKAS length certification is provided with each beam.

The Beams are designed with square drives machined to the top limit of ISO 2725:1987. This minimises any play between the beam and the transducer. However, a combination of square drive tolerances, misalignment of fittings and elastic rotation of the transducer shaft inevitably cause the beam to rotate from the horizontal under load.

Norbar's Radius Ended Beams are designed with a +/-8% degree usable arc within which the calibration accuracy is unaffected.

Additionally the beams are designed to apply load on a vertical plane which cuts through the square drive inside the transducer. This minimises bending moments on the transducer and, for safe operation, ensures that the beam will not fall out of the transducer.

Gravitational Effects

It is very important that the gravitational value for the Laboratory is established. The effect of not doing this could be a variation in the force produced by the weight of perhaps 0.5% of reading.

It is therefore stronly recommended that you establish the local value of gravity (g)  for your Laboratory and use weights that have been calibrated at that gravitational constant.

The ideal solution is to have the gravity measured on site by the national geological survey agency.

The second best solution is to ask the national agency for a figure calculated from gravitational contour maps.

The third approach is to calculate the value from knowledge of the latitude, and height above sea level in metres. This will give an uncertainty of approximately +/-0.005% but will not reflect local differences due to rock structure etc. Norbar will perform this on request if the above information is provided.

Norbar will supply weights calibrated to gravitational constants specified by the customer. However, if the customer does not specify a value for 'g' they will have been calibrated at an estimated gravitational constant for the customers' location.

Buoyancy Effects

The Norbar system uses calibrated weights to generate a downwards force.

This means that Archimedes principle applies, ie. air pressure under the weights causes an upwards force. This reduces the effective force generated by the weights and therefore the mass must be increased to allow for this.

Under standard conditions (ie. Air density 1.2kg/m3 abd 20 degrees centigrade and working in conventional mass terms) the increase required is by a factor of 0.015%.

Weights purchased from Norbar will already have this factor taken into account.

Weights that are calibrated to standard procedures do not have this factor taken into account because the air buoyancy affects both sides of the mass balance and can be ignored. It is important that weights used for torque transducer calibration are adjusted for air buoyancy.

It should also be noted that the double ended beam design employed by Norbar means that each half of the beam is balanced with regard to buoyancy of the beam. This is a significant advantage over single-arm counterbalanced systems.

Norbar gearboxes are built to an extremely high standard of precision. All gears rotate on needle roller bearings about hardened and ground journal pins. As a result, Norbar Handtorques can be relied upon to have a torque multiplication accuracy of +4%, throughout the operating range, taking the uncertainty out of high torque tightening.

No gearbox is 100% efficient and so the velocity ratio (the number of turns that the input has to make to achieve one revolution of the output) is not the same as the torque multiplication ratio. Norbar multipliers are engineered such that each gear stage has a velocity ratio of typically 5.45:1 which results in a true torque multiplication factor of 5:1.

Torque output calculations are therefore a matter of simple arithmetic with little risk of incorrect bolt loading due to conversion errors. Other manufacturer's multipliers often require graphs or formulae to calculate the input torque to achieve a particular output.

The Norbar Handtorque is the most comprehensive multiplier range available. Standard products are available up to 47,500 N·m (35,000 lbf·ft) and 'specials' to 100,000 N·m (73,000 lbf·ft). A range of 'nose extensions' for reaching difficult to access bolts and full range of torque transducers for highly accurate torque monitoring are available. 

Hand operated torque multipliers are ideal for low volume or intermittent use or when there is no power source available. However, for production lines or whenever a large number of bolts is involved, a powered multiplier will save a considerable amount of time.

Pneutorque operation is quiet - less than 85dB(A) with absolutely no impacting. These two factors make Pneutorques comfortable for the operator to use, reducing fatigue and consequently increasing safety.

Pneutorques provide accurate torque control - on a given joint they will stall repeatably to within +5%. Using electronic shut off, this repeatability can be improved to +1%.

The Pneutorque consists of a robust air motor driving a Norbar multiplier with three or more stages of epicyclic gearing.

Torque control is achieved by adjustment of the air pressure. An air pressure versus torque graph and a calibration certificate is supplied with each tool and allows specific torque values to be set. For more critical applications, Pneutorques can be fitted with a torque transducer and the precise torque output displayed. The tool can then be shut off at the desired torque either manually or automatically using suitable control circuitry. 

Models are available up to 100,000 N·m (73,000 lbf·ft).

Norbar's torque transducers have established an excellent reputation based on exceptional quality and accuracy.  A very wide torque range is covered, 0.04 N·m to 100,000 N·m and three basic transducer configurations are offered; Static, Impulse Rotary and Annular.

All transducers up to 100,000 N·m are supplied as standard with a UKAS accredited calibration certificate from Norbar's in-house laboratory.

For customers who wish to take advantage of Norbar's transducers but have an existing, non Norbar display instrument, transducers can be provided with a mV/V calibration.

Norbar's instruments and transducers are complimented by a wide range of ancillary products.  Within this group are the products that would be required to set up a torque calibration laboratory, for example, torque wrench loaders meeting ISO requirements and precision beam and weight systems for calibration of torque transducers.

Norbar manufacture an extensive range of high quality torque wrenches to cover torque values from 1 N·m to 2000 N·m. They are designed and manufactured to exceed international standards for accuracy.

In addition to the normal 'adjustable' torque wrenches, Norbar offer Production 'P' Type versions which can be pre-set and dedicated to a particular application. This setting system is designed to discourage unauthorised alteration.

All Norbar torque wrenches are offered as standard with a quality ratchet. For applications where interchangeable end fittings are required, 'Torque Handles' are also available in various models up to 550 N·m.

In certain critical bolting applications, factors such as friction or bolt/joint geometry are such that the measurement of applied torque alone will not provide the degree of accuracy necessary to control the preload to be monitored over the service life of the fastener. In these applications, ultrasonic measurement of fastener elongation and/or load has frequently proven to be the most accurate, reliable and cost effective solution.

Ultrasonic measurement of bolt preload is made possible by introducing a sonic pulse at one end of the fastener and accurately measuring the time of flight (TOF) required for the echo to return from the opposite end. Using material constants, the USM-3 converts this TOF into an "ultrasonic length" of the fastener, providing a baseline from which future measurements will be made. When the fastener is tightened, the TOF increases and the USM-3 will again utilise material constants to eliminate the effects of stress and temperature variations on sound velocity, providing an accurate elongation or load measurement.

The USM-3 uses state of the art hardware and software to achieve these measurements with maximum automation, and minimizes the need for operator interpretation. Offering digital recording and transmission of data, in addition to analog signal output the USM-3 provides a complete system for measurement, recording, and control of fastener tension in the most demanding applications.

For further information or help with our Ultrasonic equipment, please use the following contact details:

USA & South America
Ultrasonic Bolting Hotline (USA): 1 407 923 3724
Norbar USA Toll Free: 1 877 566 7227
Norbar USA Telephone: 1 386 774 1184
Norbar USA Fax: 1 386 774 5648

Tel:  +61 (0)8 8292 9777
Fax: +61 (0)8 8292 9799

Tel: +86 21 5146 0368
Fax: +86 21 6145 0369

Tel: +65 6841 1371
Fax: +65 6841 1372

UK and Rest of World
Tel: +44 (0)1295 270333
Fax: +44 (0)1295 753643

Keywords: beam, Calibration, Geological Survey, Torque Measuring, Torque Transducers,

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Torque wrench, calibration, calibration beam, torque, UKAS, torque wrench - Default

Weights that are calibrated to standard procedures do not have this factor taken into account because the air buoyancy affects both sides of the mass balance and can be ignored. It is therefore stronly recommended that you establish the local value of gravity for your Laboratory and use weights that have been calibrated at that gravitational constant.