Re: Vulcanizing Steel Cord Belt Gap Specifications
Nordell I remember a long time ago watching belt splicers laying the cables down on the bottom panel and then putting noodle rubber on top of the cables.The splices looked ok and seemed to last. Only SR1000 splices. ■
Re: Vulcanizing Steel Cord Belt Gap Specifications
With regard to splicing it seems that “Real Life” is a doubtful teacher to engineers. Most are simply not interested. By the time a splice fails, the splicers and frequently the mine staff have moved on, the former has finished the “job” and the latter were essentially only interested in getting the plant running. The area is “cleaned up” and the “evidence” is removed off site. Very seldom is a failed splice available for “post mortem”. The following example is an exception
Splicing procedures have not changed in half a century, The chemistry and behavior of rubber from latex to completed conveyor belt covers and “splice kit material” has been scientifically researched and well documented, accurate repeatable parameters have been established for the production of “on site” splices, Laboratory tests have confirmed Finite Element Analysis, but still we have “looks good to me”.
In a belt the cords take all the loads – in the splice the filler rubber between the cords transmits the loads in shear. If left working long enough the splice will fail in fatigue anyway. Any lessening of bond between the cords (i.e. in a section with negligible filler) will mean that the remaining “good sections” of lay-up will be higher stressed and the splice will fail. There are numerous reasons for lack of bonding but preparing the lay-up with none or virtually no rubber between the cords will guarantee a failure sooner rather than later. In the instance illustrated of changing a 2 step splice to a 1 step resulted in sections with virtually no filler between cords. There is no way 5 cords shown on the left in the attachment could pass a “Pull out Test” A life <3 months instead of >6 years when belt would have been replaced due to wear. All had to be replaced, plus an insert. 6 re-slices in an operating mine-site. Any splicer can “hide” a bad splice and too many engineers who say “ looks good to me” instead of asking “Why have you done that?” .
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The attachment illustrates a splice (one of five on a ST2000 Steel Cord, sections of bottom cover have been removed to inspect the lay-up.
Anyone interested in receiving a copy of a paper “Splicing – Art or Science” presented at ICOMS 2001 e-mail me : dmellis@delmec.com.au
Attachments
p2450 position 4 st 2200 1 step (JPG)
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Vulcanizing Steel Cord Gap Specs.
Most reputable splicing companies that can perform steel cord splicing here in the US strictly follow each manufacturers splice procedures. I am intimately familiar with 3 of the largest splicing companies here in the US that are the most reputable in steel cord splicing. It would be interesting to find out if the work was here or abroad. Cord gap is key to splice life to lessen the friction/heat within the splice. However, it has become more common that the operations engineers in charge of contracting the splicing companies are not present at time of the splice/installation. But realistically, it that engineer were there, would they know what they were looking at. Probably not. That being said, if the splice is laid up & it is not to spec., it could last as long as the traditional splice warranty in the industry. Typically, splices are warranted for 1 year. The companies Iam familiar with do excellent work & are contracted nationwide for their expertise in splicing & installation of steel cord belting. Not many other companies have the expertise, experience & equipment to handle the larger installations. So yes, technically, lessening the gaps could work, but the life expectancy if the splice would be compromised although they may last through the warranty period.
Buddy Wilson
Application Engineer / TSM-Southeast
Fenner Dunlop Americas ■
Re: Vulcanizing Steel Cord Belt Gap Specifications
Buddy,
I appreciate your reply, however I think we may be approaching from two different directions, but our answers are effectivley the same.
All other factors equal splices which have been layed-up with “filler rubber” of 1 mm or less will have a considerably shorter “life” than splices with around 2.5 mm. The illustration used was when 1 step splice is installed instead of 2 step effectively providing minimum filler rubber between the cords.
Your last statement would appear to agree with me. Quote: “So yes, technically, lessening the gaps could work, but the life expectancy of the splice would be compromised although they may last through the warranty period “.
It could work but the life would be compromised. If splicers are only aiming to meet the warranty period, maybe industry should be specifying "whole of belt life" warranties.
My experience is not in the US although I doubt if it is much different there, across the splicing industry, the manuals are the same. ■
Vulcanizing Steel Cord Belt Gap Specifications
I recently witnessed a steel cord belt installation where the splice contractor constructed a splice that should have been installed with a 2-step splice. However, the contractor installed the splice with a single step. The single step has a rubber gap between cables of less than 0.5 mm. When I witnessed this, I instructed the owner there might be a safety issue in not allowing sufficient gap to control the stress-strain to a reasonable limit. No belt manufacturer would install the belt with less than 2 mm under most circumstances.
Has anyone else seen installations, with near zero rubber gap dimension between steel cords, operate successfully for many years of service? I would appreciate to present this as supporting evidence that the practice might be safe.
We will make tests, given the client cooperates. We will also due a theorectical evaluation. In the past, we have constructed a Finite Element Analysis model to enable the evaluation of abnormal splice configurations.
Still, real-life is the best teacher. ■