Drive Belt Tension vs Temperature
Drive Belt Tension vs Temperature
(OP)
I would like to talk to someone with indepth belt drive design experience.
I am working on a 50hp drive design using Gates GT2 Polychain cog belt. One of the problems of the design that Gates Engineering has not been able to address adequately is the effect of thermal expansion on belt tension. The design does not allow for a tensioner. The belt uses a Kevlar cord as its back bone. Kevlar has a backward coeficcient of thermal expansion. Gates confirms that the molded belt assembly changes length in sink with plain Kevlar. Therefore, when my machine sees 40 below zero the steel frame will shrink (center to center dist of drive)and the belt will grown in length. From first calculations this will remove all tension from the belt. Gates says a cog belt without tension will probably fail immediately. They also say they do not have a problem in real applications with temperature driven tension changes. I don't see how that can be. Have any of you had experience to shed light on this? If not experience then a theory of why cog belts with Kevlar would work over wide ambient temp conditions.
I am working on a 50hp drive design using Gates GT2 Polychain cog belt. One of the problems of the design that Gates Engineering has not been able to address adequately is the effect of thermal expansion on belt tension. The design does not allow for a tensioner. The belt uses a Kevlar cord as its back bone. Kevlar has a backward coeficcient of thermal expansion. Gates confirms that the molded belt assembly changes length in sink with plain Kevlar. Therefore, when my machine sees 40 below zero the steel frame will shrink (center to center dist of drive)and the belt will grown in length. From first calculations this will remove all tension from the belt. Gates says a cog belt without tension will probably fail immediately. They also say they do not have a problem in real applications with temperature driven tension changes. I don't see how that can be. Have any of you had experience to shed light on this? If not experience then a theory of why cog belts with Kevlar would work over wide ambient temp conditions.





RE: Drive Belt Tension vs Temperature
Rod
RE: Drive Belt Tension vs Temperature
What is a Gilmor drive?
How bad were your alignment problems and what did you do about them? Our design will be 37mm wide (about 1.5") so I hope that will make belt life less sensitive to alignment. What total anglular tolerance did you work to during installation? How difficult was it to attain your alignment tolerance? What tools did you use to do so?
Did your alignment vary after installation in a transient or permanent manor? These changes could be due to vibration, external frame loads, belt tension variations, or different torque loads on the drive. How were you able to see this and how did you adapt your design to these problems?
RE: Drive Belt Tension vs Temperature
The allignment was allways critical but once in a good setup, it seemed to stay that way. As to special tools---the factory sent all sorts of diagrams, papers, angles etc. but none were any better than 'eyeballing' with a straight edge and then running at low speed to adjust for any minor variations. Much like lining up the conveyors that these particular drives were operating.
The one tool that we did use regularly was the 'tension guage' as these belts require very high tension preloads.
Sorry to say that your small belt will still require good allignment and a bit of "tuning" after you get it running.
We also found that pulleys that had 'retainer' fences on the edges only served to destroy the belt if it got out a bit. The motor base can be set up with tensioner bolts in most cases and often the driven end also. Not rocket science but, considering the high cost of these belts it sure pays to be cautious. Work safely.
Rod
RE: Drive Belt Tension vs Temperature
I don't understand your comment that the design does not allow for a tensioner. Are you referring to the Polychain belt or your machine? You can use a tensioner with these belts, but will have better luck if you do not "backbend" the belt.
As far as your machine use at -40° F or C, I would suspect that this machine will not see these temperatures in a rapidly fluctuating environment. It will get cold and stay cold for several months. You have to be used to maintaining gearboxes and bearings at these temperatures, so it won't be that much of an extra effort to check your belt tension every month.
Also be careful if you have a high starting inertia or the possibility of your machine suddenly stopping or jamming. These belts won't slip and something will have to give, unlike v-belts which will slip.
RE: Drive Belt Tension vs Temperature
RE: Drive Belt Tension vs Temperature