Carpets turn to clevis pins for quality

Clevis pins fitted with strain gauges provide a simple solution to checking weft tension on carpet looms

It is vital for quality carpet production to maintain an even tension across the full width of the carpet. Since looms are some 25ft in width, when carpet maker Brinton wanted to check the weft (cross-thread) tension on its looms this turned out to be a bigger job than at first thought.

Brinton’s instrumentation engineers investigated the problem and decided that to measure tension at each end of the camshaft – which spanned the whole width of the machine – was the best way to proceed. However, they were reluctant to modify the loom’s well proven mechanical systems in any way, in case that should give rise to additional problems.

For a solution to the problem, Brinton called in Variohm Components, who advised that the best course of action was to simply replace the two existing clevis pins with two similar units which were fitted with strain gauges. This would overcome the need to modify the system and provide a simple method of adjusting the tension.

The clevis pins supplied were made by Strainsert, with the company having the ability to fit extremely accurate strain gauges down the centre (or neutral) axis of the pins. Positioning the gauges in this manner has several advantages: shear force is at a maximum on the neutral axis; temperature effects are minimised; accuracy is not affected by bending and torsion; the gauges are sealed and protected against moisture ingress; and the pins can be fitted and removed at any time without damaging the gauges.

Each of the clevis pins had a maximum rating of 3000lb, although for this application they would normally only measure forces in the region of 600lb to 1500lb.

The level of mechanical protection provided enabled Briton to move the pins from loom to loom, so only one calibration kit was required for the whole mill. The kit comprises two clevis pins and two indicators housed in an IP65 sealed box, together with a custom made carrying/storage case.

Variohm Components Tel: 01327 351004