High-torque replacement for hex nut
Original article date: October 1999
In a tensioner designed as a replacement for a hex nut, Alan Quinn uncovers a new solution to an old problem
It’s an old problem: torquing large bolts to capacity with hand tools. The strength of a screw fastener increases with the square of its diameter. To make use of the strength, it is necessary to torque the fastener until it is pre-stressed to a pre-determined level. But while the strength of the fastener increases in the second power of the diameter, the torque required for pre-stressing increases in the third power. Hence, the torque exerted by ordinary torquing devices, such as hand wrenches, torque wrenches and air impact wrenches is limited. For example, bolts greater than 25mm diameter cannot be effectively torqued to capacity with hand tools.
The solution? Superbolt tensioners from Furmanite Silk Engineering are designed as direct replacements for hex nuts. They can be threaded onto a new or existing bolt, stud, threaded rod or shaft.
The main thread serves to position the tensioner on the bolt or stud against the hardened washer and load-bearing surface. Once positioned, the actual tensioning is accomplished with simple hand tools – standard torque wrenches or air tools can generate higher bolt tensions than any other bolting method available – by torquing the jackbolts that encircle the main thread.
Time savings
These simple mechanical devices cost comparatively less than other bolting methods. The number of jackbolts has proven not to be a concern. Some quite significant time savings during installation or removal can be realised, according to the company. Total man hours and downtime can be reduced. Multiple workers can be used for even faster installation or removal.
Properly torqued, Superbolt products will not loosen. Pre-stressed tensioners on bolts or studs should remain tight on vibrating, pulsating or reciprocating equipment, eliminating downtime due to bolting.
Superbolt tensioners eliminate many common injuries which can be associated with other bolting methods.They have been used in awkward locations such as overhead bolts, on top of large equipment and also in hazardous environments such as nuclear power plants.
Most applications can utilise standard Superbolt products. However, specials can be designed to fit a wide variety of limited space applications.
Superbolt tensioners add elasticity to any bolted joint. The joint becomes more resistant to thermal or dynamic cycles. They provide precise tightening control, which is critical for sensitive applications, such as gasketed flanges.
Thread galling and stud seizure are eliminated, due to tightening in pure tension. This prevents the difficulties later to be encountered with removing frozen studs.
- Furmanite Silk Engineering
October 1999