SKF's time-saving Supergrip Bolt concept can dramatically cut costs in the mounting and dismounting of large rotating flange couplings. In some cases, Supergrip Bolts have cut remounting times from three hours to just three minutes.
Fitted bolts have to be 'mauled' into place with a sledgehammer and, even after time-consuming honing of the holes and individual grinding of the bolts, it is hard to achieve an interference fit. In most cases there will be a small gap, which may increase with service, resulting in high bolt stresses and vibrations. Furthermore, at some point the bolts will have to be removed and the job will be further complicated by trying to drive out conventional bolts that have seized in the hole due to fretting, overstressing or the fit being too tight.
However, the Supergrip Bolt is easily inserted into the hole by hand and then expand to create a radial interference fit. The bolt is then hydraulically tensioned against one nut while the other is hand-tightened. For removal, once the tension and expansion pressure has been released, each bolt is claimed to slide out as easily as it went in.
More secure assembly
As well as the tremendous time savings afforded by this system, the coupling halves are held together much more securely, eliminating slippage, and there is no need to worry about the bolts jamming or seizing in the holes. Maintenance costs are further reduced by the Supergrip Bolts being fully interchangeable and able to be used repeatedly, therefore dispensing with the need for a set of spare bolts.
Supergrip Bolts are designed specifically for high-torque applications such as propeller shafts, rudder assemblies, turbo generators and rolling mills. A study released by the Swedish State Power Board showed a 90 per cent reduction in the time required to disassemble and reassemble the couplings of two turbo sets (eight couplings) when using Supergrip Bolts.
Supergrip Dowel Pins
Similar in concept to the bolts, Supergrip Dowel Pins can also be used to firmly position machinery and plug drainpipes or holes in pressure vessels. The dowel pins are also said to be excellent for plugging holes in nuclear power reactor vessels; Supergrip Dowel Pins have already been proven in a reactor vessel during modification programmes when the piping connected to the reactor vessel had to be removed.