Expandable bolts save time and money

Superbolt Expansion Bolts offer a simple and quick bolting solution for large machinery couplings that will save time and costs.

Simply put, Superbolt Expansion Bolts are adjustable fitted bolts with an outer diameter that can be expanded to fit the actual bore size. They can replace fitted bolts where the parts to be connected must be precisely aligned and high shear forces act on the connection. Typical applications include coupling bolts on high power drive shafts, such as ship drives, as well as thermal, hydro and wind turbines.

In the majority of cases, when fitted bolts are used, either the fitted bolts are machined to fit the bores or the bores are reworked to match the fitted bolts. Both methods are costly and time consuming because the dimensions must be measured accurately on site and then adapted. In the meantime, work is at a standstill.

Furthermore fitted bolts never fit perfectly. There is always some minute sliding in the joint, which causes the fitted bolts to tilt inside the bores. Contact between the fitted bolt and the bore is limited to four points at which the flange is plastically deformed by the extreme contact pressure. These deformations may not only cause the flange to eventually fail, but make removal of the fitted bolts during maintenance impossible.

An Expansion Bolt consists of five parts. The tapered sleeve is placed in the bore and centered by the spacer. The tapered stud is pulled into the sleeve by tightening the Superbolt tensioner on one side. The sleeve is split along the entire length so it can expand radially and adjust to the bore (yellow arrows, to the left), while a second Superbolt tensioner on the other side is then tightened to clamp the joint together axially (red arrows, to the left).

Superbolt Expansion Bolts not only produce an optimal fit despite manufacturing tolerances, they can additionally preload the bore in a radial direction. The radial preload helps maintain the contact with the bore and prevents detrimental tilting. Understandably, expansion bolts can carry much higher loads than fitted bolts.

As a result, Superbolt Expansion Bolts save both time and money. The savings are highest for new designs where the joint can be made smaller while requiring less bores with wider tolerances. Our engineers will gladly support you in optimising the joint. But retrofits also benefit from no on site machining, fast installation and full reusability. For positive connections, Superbolt Expansion Bolts are simply the best choice.

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