Fig. 2. Accu-load fasteners are individually machined and calibrated to suit the joint design and they can be used indefinitely.
Crane has improved the processing speed of its wrenches to improve the sampling rate, and operators have a choice of visual, audible and physical alarms to indicate the status of the fastening process. Visual indications are provided by multicoloured LEDs on both the front and back of the wrench. A real-time graph on the display gives a clear indication of the process characteristics such as target torque, lower and upper torque specification, or angle. In situations where the operator cannot look at the
wrench, the tightening status can be signalled by a vibrating handle or audible alerts. Tentec, a manufacturer of bolt tightening equipment,
celebrated a record year in 2010, despite the recession. Newly appointed managing director Mike Gethings explained: “Our order book has been strong throughout the year. As well as pleasing sales for our standard bolt tensioning equipment, we have seen demand for our customised engineering skills also increase. Our in-house engineers continue to design innovative and cost-effective solutions for challenging applications and our manufacturing facility ensures that customers receive their products on time and within budget.”
Hydraulic and pneumatic
In 2010, Tentec launched a series of hydraulic and pneumatic torque wrenches to complement its existing bolt tightening products. The SD, CD and PN ranges have been developed for engineers who require robust, easy-to-use and accurate tools for torque applications throughout industry. Another UK company with global sales is James Walker
Rotabolt, which reports that South East Asia has become one of its strongest growth areas. A recent success story relates petrochemical processing
in Taiwan, where leak-free operations have been achieved and this has opened up a wealth of opportunities for the company’s tension control technology. The first substantial
order in the region resulted in Rotabolt technology being fitted to crane slewing bearings in Malaysia, Thailand, Vietnam and the Gulf oil fields. What made the fasteners an attractive proposition was their ability to achieve the correct design tension across the critical slewing bearing joint and then accurately maintain it over time.
Tension control
Wind turbine manufacturer Vergnet is now fitting tension control fasteners on its GEV HP system. This French company uses thirty M90 Rotabolt fasteners on the main structural joint between the two halves of the turbine nacelle. The design allows the main turbine to be quickly disassembled into two halves so that the upwind nacelle section, complete with rotors, can be lowered to the ground and easily secured. This can be either as a protective measure in extreme weather conditions, or for quicker service and maintenance operations. Traditional tightening practices using standard bolts only
measure the force that is being applied to tighten the bolt; the clamping force, or tension across the joint, is unmeasured and unknown, yet it is critical to the joint’s reliability. In addition to achieving joint integrity during installation,
the fasteners can be finger-tip checked during maintenance inspections to establish whether tension has been lost. This is because the Rotacap on the head of each bolt locks in position at the correct design tension but, as soon as any tension is lost, it spins freely, making it quick and easy to check without the need for tools or instrumentation (Fig. 1). Accu-Load, a manufacturer of specialist fasteners, offers
bolts and studs that are capable of monitoring and indicating the tensile load during tightening and in use. Each fastener features a visual or digital readout option,
which is built into the head of the device and indicates a percentage of the proof load. The bolts are individually machined and calibrated to suit the joint design and they
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