Difference between revisions of "Pre-stretched Polyester Ropes"
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page is based on a thread on Change-Ringers, May 2005, and summarises contributions from John Harrison, Matthew Higby and Philip Pratt
[[Category:Bells and Fittings]]
[[Category:Bells and Fittings]]
Latest revision as of 20:44, 18 August 2012
Pre-stretched polyester is similar to 'Terylene' which is a commercial brand-name. It is a good material for the top end of bell ropes because:
- it does not shrink in damp weather
- it does not go stiff in damp weather
- it is not springy when new
- it lasts almost indefinitely
Two manufacturers supply products which have been used in towers, Marlow and English Braids. The Marlow rope has orange and black tracers in the rope, while the one from English Braids has blue. Marlow rope has been found to be less springy and is preferred by most users.
Marlow Rope Specifications
Users of Marlow rope have suffered some confusion as the specification has changed at times. A military (MOD) specification rope, has been available in the past with similar colour markings to the sailing grade. This has been 'spun as a yarn' down the pub by many ringers, to suggest that it is a far better rope for bell ropes. There have been a few other manufacturers who have copied Marlows pre-stretched polyester and laid in the same colour identifying markers that Marlow use but have not made them to the same exacting [high] standards.
Batches of pre-stretched polyester top ends have been supplied by Pritchards ropemakers of Loughborough during their last 5 or so years, utilising a yellow or grey fleck. In many towers these yellow flecked top ends have proved un-satisfactory.
The pre-stretched polyester rope supplied to the bell rope makers is tailor made in very large batches to their own specification and does exhibit properties making it more suited to the application of bell ringing than the standard sailing grade, and in particular the stretch tolerance allowed.
The sailing grade rope in 10mm diameter should be suitable for most ropes (up to about 8m), but displays more spring on long draughts. Upgrading to 12mm diameter would be recommended.
It would appear from the Technical Director of Marlow that the MOD specification is almost identical to the sailing grade except there is a change in the coloured marker arrangement; rather than two markers it is a single orange/black fleck. The technical specification for the sailing type of rope is available from Marlow's website in the form of a PDF file and applies to both types.
The 10mm sailing type of rope has a breaking load of over 2300kg (it could singly carry the dead weight of up to a 46cwt bell) which, in terms of its use in bell ringing, is not remotely approached. Since ringing never reaches more than 5% of the break load of the rope, and there may still be stretch (typically 1% extension which makes a huge difference) we should look at increasing the diameter of the rope to 12mm diameter to reduce the loading to say 2% or 3% of its total break load and thus the stretch to 0.5% or less.
Pre-stretched polyester rope can be short-spliced by hand and can also be machine spliced. Theoretically (because of the differing coefficients of friction) it should not be long-spliced with natural fibre rope, but there are several reports of this being achieved successfully in practice.
David Beacham writes: I have had no trouble at all with joining polyester to flax with a conventional long splice, which you need to do if some part of the rope passes over an intermediate pulley. (If you use a short splice in this situation, you will feel the "bump" as the splice runs over the pulley.)
Mark Davies writes: I agree with David, I've long-spliced flax to poly without problems, and the splices have lasted many years. When tucking the ends in, you can't "comb out" polyester so well as natural yarn, since the fibres don't come loose. However, you should still use the comb, and tuck in as usual as best you can. If you like, you can trim half the ends of each poly strand in order to get a neater result. On NO ACCOUNT should you heat-seal the ends of the poly strands, as this will not only look unsightly, but also cause the spliced-in natural rope to wear quickly due to friction with the sharp ends of the heated-sealed polyester. Don't even think about it!
Fitting Polyester Ropes
Remember that you do not need to have yards of "spare" rope wound around the spokes. To do so is a waste of money. About three times round would do. If you wish to have more, extend the rope by tying some old rope onto it.
Natural fibre rope should always be used below the sally.
The above page is based on a thread on Change-Ringers, May 2005, and summarises contributions from John Harrison, Matthew Higby and Philip Pratt.
Avon Ropes (ref Philip Pratt) have developed patent pending Dyneema technology "for the ultimate zero-stretch rope". It is claimed to be thin, light, strong with minimal stretch.