Cog Belt Drives
Cog Belt Drives
(OP)
We have been having a rash of failures in cog belt drives on fin-fans. I found an issues that I think may be the basic problem. Our supplier has been providing a mixuture of two different patterns of cog belt. The original design used cogs that were round; basically half-circles. Some new designs use cogs that are shaped like gear teeth; rounded sides but flat on the tip. We are ordering belts and sprockets of the old round-tooth type. But the supplier is sometimes substituting the gear-tooth shaped pattern. They claim that the belt of one pattern can be run on the sprocket of the other pattern. Does anyone have experience with this. I would like to have some ammunition to go back on our supplier and force them to sell us what we want. By the way, we have a corporate alliance with this supplier, so I can't go to a different supplier to get what I want. Any help will be greatly appreciated.





RE: Cog Belt Drives
I would say the short-term answer is immediately return and not pay for any and all incorrect belts. Make it a headache for your vendor to do this to you.
RE: Cog Belt Drives
P30-14M-85-2517
P32-14M-85-2517
The first one has the rounded grooves. The second one has the gear-tooth shaped grooves. These parts should be identical except for the fact that one has 30 teeth and the other has 32 teeth.
I am hoping there is a belt expert out there who can say with absolute certaintly that these different patterns cannot be run against one another. Any vendor contact that I have would have a conflict of interest. Of course the belt manufacturer wants me to buy their sprockets.
RE: Cog Belt Drives
RE: Cog Belt Drives
What Manufacturer of belts and pulleys are you using?
RE: Cog Belt Drives
RE: Cog Belt Drives
I would hope that your "corporate alliance" would allow you to go to another supplier if your "corporate ally" can not supply you with equipmnet that works.
RE: Cog Belt Drives
(1) verify pitch of pulley (BOTH pulleys), use same pitch on belt
(2) verify tooth form of pulley, use compatible form on belt. Some manufacturers claim certain different forms are compatible.
ALSO:
(3) verify correct application:
(3a) correct belt tension (too little will destroy your belts, too much will destroy your bearings)
(3b) suitable pulley spacings, idlers, wraparounds, etc.
(3c) horsepower loads and belt sizings
(3d) verify correct alignment & parallelism of pulleys to avoid uneven loading on tooth forms
TygerDawg
RE: Cog Belt Drives
RE: Cog Belt Drives
As to your issue I'm a little confused, has the belt profile changed or has the pulley changed? or is it both?
I've dealt with Martin Sprocket and Gear for years and have had pretty good luck with them. The two part numbers you list are standard off-the-shelf numbers in their catalog. you can contact them from their web site:
http://www.martinsprocket.com/
RE: Cog Belt Drives
There are several different profile shapes out there, and there are also a few pitches that are close, but not exact matches.
Anytime you need extra tension on a toothed belt to keep it from jumping teeth, something is _very_ wrong. Your techs should be instructed to replace both pulleys and the belt when that happens.
If you are getting mismatched parts under the same number, you need to replace your distributor immediately.
Mike Halloran
Pembroke Pines, FL, USA
RE: Cog Belt Drives
I used to do FEA on synchronus (ie toothed) belt profiles for one of the companies mentioned in this thread. The simple fact is that a belt of one profile running on a sprocket of another will wear out quicker than if both profiles are the same. Tension is very important as the belt pitch is only "correct" for a given tension and other environmental variables (eg temperature).
Different profiles are designed for different loading conditions so changing to something that looks "similar" need not work sucessfully.
Go with what works rather than changing. The belt manufactures mentioned will be able to check the profiles you've been using and give advice accordingly.
RE: Cog Belt Drives
RE: Cog Belt Drives
The other aspect I should have mentioned is that the same belt geometry in different materials can have a big effect. Some elastomers are much stiffer than others leading to a different amount of stretch on tensioning. If you replace a belt with one from a different material you could also get the problems you have experienced. The suppliers know all this and will advise accordingly.
Incidentally I have simulated the belt climbing you have witnessed using FEA by simply changing the belt tension.