BMG’s Superbolt® multi-jackbolt tensioners – part of the Nord-Lock range – are designed to reduce downtime and eliminate unsafe and laborious bolting methods, particularly in harsh operating conditions and in areas with limited working space.

“These multi-jackbolt tensioners, which replace or retrofit nuts and bolts, only require hand or air tools for the installation and removal of any size tensioner,” says Maryna Werner, business unit manager, Fasteners division, BMG. “Bolts need to be easily removable during maintenance procedures, but must resist the loosening effects of vibrations and dynamic loads.

“This quick and efficient bolting method is based on a design which splits one big torque into a number of smaller ones. Superbolt, which has numerous advantages over conventional bolting products, ensures joints can be tightened with high accuracy, without the need for specialist skills or heavy tooling. Tightening in pure tension allows higher preloads on the same size bolt than conventional tightening methods.

“Generating a preload high enough above the separating forces means bolting will not vibrate loose on properly designed joints and the added elasticity increases fatigue life of the bolted joint, which eliminates costly downtime. Only small hand tools are required for installation – this means there are no safety hazards from immense hydraulic pressures, no pinching hazards, no lifting of large tools and no risk of sockets breaking under high pressure.

“Multi-jackbolt tensioners are easy to install, even in confined spaces and although there are multiple jackpoints to tighten – by using hand or air tools – installation times are faster than other bolting methods.”

A conventional bolting system, like the sledgehammer, gives little control, is inconsistent and can cause injuries. Thermal tightening, crane and hydraulic wrenching and hydraulic tensioning are often costly, inaccurate, time consuming and unsafe.

Superbolt devices are 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 the load bearing surface. Once positioned, actual tensioning of the bolt or stud is accomplished with simple hand tools by torquing the jackbolts which encircle the main thread. The jackbolts transfer the preload evenly into the main thread and consequently onto the joint. Jackbolts have a small friction diameter and can therefore create a high thrust force, with relatively little torque input. The main thread is tightened in pure tension.

Superbolt tensioners are used in diverse industries, including mining, hydropower, wind turbines, gas and steam turbines, nuclear, steel, shipbuilding, offshore, chemical and transportation. OEMs specify Superbolt multi-jackbolt tensioners in their design, to improve performance of equipment.

The high preload capacity and accuracy of this system has resulted in the design of smaller bolt sizes. Compact dimensions and decreased tooling sizes allow for a reduction in the size of machinery, reducing material and machining costs.

BMG offers a technical advisory service to determine the dimensions and load conditions of existing or required bolted joints. Current tightening methods are evaluated and bolt preloads, for absolute reliability and durability, are calculated by the highly-skilled team.