The RotaBolt principle
When a RotaBolt® is installed and tightened, the bolt extends fractionally under the applied load.
The mechanical strain gauge pin within the body of the bolt however does not extend as it is only anchored at one end. As a result, as load is applied to the bolt, the datum face of the indicator disc, positioned under the head of the strain gauge pin, is drawn closer to the machined datum face on the head of the bolt, closing the air gap.
Initially the RotaCap, attached to the indicator disc, can be rotated easily between finger and thumb. However, when the strain gauge pin is drawn down into the body of the bolt to a point where the datum faces on both the indicator disc and the bolt head are forced into contact, the RotaCap is prevented from being rotated. When the RotaCap ‘locks’ in this way it indicates the calibrated pre-set tension of the RotaBolt has been reached and the joint is now clamped to within ±5% of the required design load.
Should tension be lost across the bolted joint - for example, due to deterioration of a gasket or relaxation after thermal cycling - then the two datum faces will move apart re-creating the air gap and making it possible again to rotate the RotaCap by finger-and-thumb. This indicates that remedial action is required and the bolt in question needs re-tightening until the RotaCap locks off and the required tension is once again achieved.
The RotaBolt range...
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