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Thread: Belt Stretch

  1. #1
    George Baker

    George Baker

    Regional Sales Manager

    TELSMITH Inc

    TELSMITH Inc

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    Belt Stretch

    How much stretch is there in a typical rubber belt 3 ply 3/16" over 1/16" in a product called GARLOCK Bullog or even generally.

    We have a mechanical designer today........actually insisting to our belt supplier/splicer .........that they needed to PRETENSION OR STRETCH the conveyor belting.........check this out......for 3 days!!! prior to vulcanizing same.

    This seems........simply wrong to me. In my uneducated opinion on this topic......the PERCENTAGE of SLACK in typical 3 ply belts is at best.......1-3 percent? You are not going to get this slack out by pretensioning for 3 hours or 3 days are we???

    Another source of mine says.........all this is nonsense.....and simply pretensioning for a number of hours will suffice?

    DOES IT MAKE A DIFFERENCE IF LOW GRADE BELTING Vs SAY GOODYEAR HIGH QUALITY BELTING?

    Help please...........George

  2. #2
    Lawrence K. Nordell

    Lawrence K. Nordell

    President and CEO

    Conveyor Dynamics Inc. [eDir]

    Conveyor Dynamics Inc.

    Professional Experience 55 Years / 11 Month Lawrence K. Nordell has 55 Years and 11 Month professional experience

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    Dear George,

    I dont know about Garlock Bulldog. I do know there is a ton of cheap often called scab belt from a Jack and Judy shop where QC control and customer satisfaction is low but the purchasing officer says is the best selection based on price not withstanding delaminations, et al.

    Large stretch is a product of no pretreatment of the fibers. The higher priced spreads Resorcinol treat the fibers to give a preshrink effect. The individual fibers then can carry greater loads, load share between fiber groups, and stretch less. These belts are in the 1-2% range. Polyester, the normal selection for the tension strand, and nylon for the transverse fiber for impact resistance and compliance for troughing and training.

    Cheap belts need to be ironed -- run in for a while to control the excessive stretch. Three days may be a little short. These belts need to be loaded for a while maybe up to 10 days to get to an equivalent level of a pretreated belt tensile fiber.

    Lawrence Nordell
    www.conveyor-dynamics.com

  3. #3
    George Baker

    George Baker

    Regional Sales Manager

    TELSMITH Inc

    TELSMITH Inc

    Professional Experience 37 Years / 0 Month George Baker has 37 Years and 0 Month professional experience

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    Prestretched........

    Nordell: Wow........that was not the answer I was hoping for.......even longer for cheaper cost belting.

    This belt I am inquiring about.........also has a very SHINY look to it..........almost like plastic........is that normal?

    TKS George

  4. Hello George..
    Conveyor belt covers are SBR rubber, and if treated nicely look like black mirrors, especially on the return side.
    Regarding stretch, as L K N indicated, there are two main components in the re-inforcing.
    The Warp (longways)is often made from EP or polyester
    The Weft (crossways) is often made Nylon ans stretches more therefore making it good for troughing.

    Sometimes you get a belt made from only nylon, and this can cause a lot of stretch especially over time.
    We had a project where each day the counterweights were at the top and next day they were at the bottom. We kept cutting lenghts out until it settled down.
    This nasty stretching also caused the belt to form tube shapes in the concave curves.
    So don't go for nylon warp.
    Otherwise you can buy from where you like really as long as the fabric is crimped in the weft direction and virtually straight in the warp, and there is no ply or cover separation.

    Regrds from LSL Tekpro
    Graham Spriggs

  5. #5
    George Baker

    George Baker

    Regional Sales Manager

    TELSMITH Inc

    TELSMITH Inc

    Professional Experience 37 Years / 0 Month George Baker has 37 Years and 0 Month professional experience

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    Graham Spriggs

    Thanks for the info Graham.........appreciated GB

  6. #6
    George

    I believe what your man is talking about is the permanant stretch as I will attempt to describe. Conveyor belt elongation consists of two type of stretch, permanent & elastic. Permanent is the stretch that occurs during the first few weeks of operation of a new belt and elastic is the normal stretch that a belt undergoes during normal operation of the system. Take-up travel is usually calculated based on a total of these two factors, (which can be determined by your belting supplier) in every case you need to determine the amount of take-up that needs to be designed into a system. If the sytem is not designed to take up the total of the two types of stretch you will need to remove the permanent stretch. In my opinion you will not get all of the permanent stretch out of a belt in only 2 or 3 days. Especially with an all nylon belt such as Graham has mentioned.

    It might be better to install a mechanical splice initially until the permanent stretch is out of the belt and then do the vulcanized splice at a later date. Then take-up travel is normally sufficient for the elastic stretch of the belt.

    Hope this helps,

    Gary

  7. #7
    George Baker

    George Baker

    Regional Sales Manager

    TELSMITH Inc

    TELSMITH Inc

    Professional Experience 37 Years / 0 Month George Baker has 37 Years and 0 Month professional experience

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    Gary

    Thanks for sharing your expertise.........it helps very much actually.

    Best regards,

    George Baker

  8. Dear George,

    First of all, the Garlok brand name represents is a good one. The Garlok belt is definately not a cheap one (produced in Paragould, Arizona, USA).

    That being said, high initial belt stretch will depend on factors such as the type of carcass weave, the amount of fabric tensioning during belt manufacture, the type of material used in the warp strands, the tension used during belt rolling, et cetera. Generally, nylon warps will give substantially higher stretch than polyester warps. Loosely rolled belts will have a higher initial stretch than tightly rolled belts. Belts made with highly tensioned carcasses will stretch less than belts of the same carcass material produced under low tension. Etc., etc.

    As far as pretensioning is concerned, it only helps to get rid of the minor stretch factors - such as belt roll tensioning, unless you apply a lot of force. Even then, the only part of the belt that gets Pre-Stretched is that section close to the weights - unless you prestretch for a long time (30+ days), which is too long to tie up equipment. The idlers, pulleys, and carcass weft strands all act as tension modifiers as you move away from the pretensioning wieghts (or force) and the initial stretching of the rest of the belt will start once you start to move it around the system. That is, in my opinion, pretensioning is of very limited value.

    If you know that you have a belt that is likely to stretch past your take-up allowance, you would be better served to start off with mechanical fasteners and take them out once the rate of stretching has stabilized.

    Hope this helps.

    Regards,
    Dave Miller
    ADM Consulting
    10668 Newbury Ave., N.W.,
    Uniontown, Ohio 44685 USA
    Tel: 001 330 265 5881
    FAX: 001 330 494 1704
    E-mail: admconsulting@cs.com

  9. Dear Mr. George Baker,

    There are two types of elongation in belts, during course of operation. These are known as elastic elongation and permanent elongation. The belt normally operates at nearly 10% of breaking strength. The belt subjected to the load of the value of 10% of breaking strength, will have following percent of elongation (this is only an approximation).
    - Elastic elongation for EP belt : About 1%
    - Permanent elongation for EP belt : About 0.8 to 1.5 %

    Now, the entire length of belt is not uniformly under 10% of breaking load, so above elongation values are to be adjusted in accordance with tension diagram, and then converted into stroke of the take-up.

    Permanent elongation occurs more during initial phase. It is due to straightening of fabric and creep elongation of fiber material. The elastic elongation is in response to tension in the belt. If the belt is not pre-stressed then belt elongation will be more during short time interval and one has to re-vulcanize the belt, as take-up will reach its limit. If the belt is pre-stressed, such need for re-vulcanizing will occur after comparatively more time interval.

    In important plants belt is vulcanized on conveyor, operated for certain duration of time as per the contractual condition and then the plant supplier is required to re-vulcanize the belt eliminating all the elongation! So, the belt stretch reality after installation cannot ignored and is to be taken care appropriately.

    Regards,
    Ishwar G Mulani.
    Author of Book : Engineering Science and Application Design for Belt Conveyors.
    Advisor / Consultant for Bulk Material Handling System & Issues.
    Email : parimul@pn2.vsnl.net.in
    Tel.: 0091 (0)20 25882916

  10. #10
    Ingolf Neubecker - Thyssenkrupp Robins, USA Guest

    Belt Stretch

    Dear George,
    We are pretensioning our belts and let them sit and stretch one day. If it stretched a lot we will add another day and then perform the final splice. Depending upon the supplier of belt and which belt you have you may have to make another splice 6 months later. If you do not let it stretch you may have to do two or three splices in the first month.

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