Re: Thermal Issues On Fixed Length Conveyor
Fabric belts are very tricky. As a rule, you must obtain specific data from the manufacturers or do the experiment yourself.
Steel cord expansion coefficients in English or metric units are:
CE (english) = 0.0000065 in/in/ degree F >> metric x 1.8 C from F
CE (metric) = 0.0000117 mm/mm degree C
Yes, thermal expansion has a major effect on belt tensions, if the conveyor has a fixed or winch style take-up. Some major name designers have been caught with system problems because they ignore this fact.
I did not check your result, but it can be an epiphany.
You could say it is the difference between night and day. ■
Re: Thermal Issues On Fixed Length Conveyor
Thanks Lawrence,
I have tried all over the internet and can find nothing from the major manufacturers. I have even contacted Australia's biggest manufacturer and they can't give me any figures as they say they don't test or publish data on that.
I guess I will have to pursue some more manufacturers.
Thanks again
Ross ■
Re: Thermal Issues On Fixed Length Conveyor
Ross,
If you seek fabric belt expansion coefficients, you will likely not find such. I have seen a number of fabric belt test results and understand why the mfgrs do not wish to guaranty a specific behavior. Add to this the creep effect due to weave relaxation, and polymer relaxation which are also temperature dependent. Then you have long term tensile loading verses short term and their changes in belt elongation.
Go to a book on polymers and you can find expansion coefficients. For 6/6 nylon , the expansion coef. is 55 x 10E-6. However, this is good for only a narrow temperature spectrum.
Polymers have a very non-linear elasticity as a function of temperature, such as during the formation of crystalization which can begin above 0 degree C. You can see this effect in rubber polymers from our website and papers. The polymer elasticity has viscoelastic components E' and E". You need to obtain the dynamic modulus E' which is also strain and strain rate dependent. You cannot measure this directly.
Also the polymer specific gravity or density changes with temperature.
Then factor in the denier construction, fabric weave, primer coatings for rubber adhesion, and then fabrication preshrink and pretensioning. They all effect the thermal result.
There are more conditions, but this gives some idea.
This is probably more than you wish to know and why mfgrs. would need to print a bible on the qualifications. ■
Re: Thermal Issues On Fixed Length Conveyor
Sorry, on a read of my posting I did not specify the units. The 6/6 nylon thermal exp coef. is in centigrade. About 5 times steel. Note, conveyor belts do not have this behavior. ■
Re: Thermal Issues On Fixed Length Conveyor
Ross
As Larry noted, an experiment may be the way to go.
All you have to do is go and find an established fabric conveyor with a gravity take-up and note the take-up travel at different belt temperatures. This can be done by noting the travel in the early morning versus midday.
The belt would have to be stopped and empty. The early morning reading would probably have a constant temperature throughout but a midday reading would have varing temperatures that may require a little arithmatic to account for. A laser thermometer would be ideal.
The longer the conveyor is, the better. ■
Re: Thermal Issues On Fixed Length Conveyor
True MAtt, but, what if the need is for some new belt?
Get a manufacturers sample. Then find a cold meat locker or refrigeration truck. Select three temperatures of equal delta, and measure the growth of a 1,2, or 3 meter strip of the belt in question with a few differing loads.
Better yet, pay the manufacturer, with the order, who does the experiment. ■
Re: Thermal Issues On Fixed Length Conveyor
Thanks guys,
I guess I will have to probably do that in the end. But we are at pre-bid stage at the moment, so we do not know what belt we are using yet. I am running various designs to come up with the final figures. As part of bidding for pulleys etc we have to give tensions. This temperature issue makes a significant difference to the tensions we quote to the pulley tenderers.
I would have thought this would have been a common problem for designers and there would be accepted and published figures for design engineers to use. Can't very well go through the belt bidding process, award the belt, do the belt test and then finally do the pulley bid. That would slow the whole process down. I can't think why the belt manufacturers would not come accross this issue again and again, and therfore publish some figures. Maybe not many people make fixed length conveyors with heavy duty belt? ■
Thermal Expansion
Dear sir
Bonder rubber creates permanent bond between steel chord and rubber. Rubber is penetrated inside chords
As thermal expansion of steel wire chords and rubber compound. are different.. Due to temperature difference is there any development of stresses on rubber compound / steel wire chords
A R SINGH ■
Re: Thermal Issues On Fixed Length Conveyor
Dear Rosss,
If you are using BELTSTAT, the code will automatically calculate the expansion and contraction forces for the given fixed take-up position, any steady-state or rigid-body dynamic condition (start/stop), for any variation in temperatures. This is for steel cord belt. ■
Thermal Issues on Fixed Length Conveyor
I am looking at the implications of thermal growth of the belt on a fixed length conveyor.
Am I right in saying that the change in belt length due to thermal expansion and contraction will have a major effect?
On the conveyor I am designing, if I assume a steel cord belt has the same linerar expansion as steel (12.3um/m/degC), then I get a 25kN change in Tension for a 35degC change. (1600mm ST500 Belt).
Will this be more or less for a fabric belt? I cannot seam to find any data an the thermal expansion coefficients for Fabric or Steel belts.
Thanks in advance for anyones input.
Ross ■