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Formerly the threads of S&C and fishbolts were manufacured by screw cutting, a process involving the removal of metal from the shank of the bolts by a machining operation.
In future, Cooper and Turner will manufacture the threads of these products by thread rolling, a process involving thread forming rolling dies which apply pressure onto the bolt material causing it to plastically deform to the profile of the die.
Thread rolling offers the following benefits:
- It produces a smoother surface finish without sharp corners in the thread root or tool marks on the thread flanks, which can act as stress raisers.
- Thread rolling is carried out at room temperature. As a result of this cold forming process the surface layer of the thread is put into compressive stress thus providing a thread which is both stronger and posseses higher fatigue strength.
- Accuracy and consistancy during production is greatly improved with rolled threads.
Cooper and Turner limited have introduced this major product improvement in response to customer needs.
From the 1st February 2006* all Cooper and Turner 'V' grade switch and crossing bolts plus 'V' grade and normal grade fishbolts will be manufactured with a rolled thread.
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*Note - there will be a cross-over period where customers may still receive deliveries containing product that has previously been manufactured by screw cutting. Every effort has been made to ensure this overlapping period is as short as possible.
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