We've been using these HTD drive belts for about 5 years now on our largest HOT fans, with 6 blades about 55-60 inches in diameter. Driven by 250hp Toshiba motors. We have 6 of these...Ever since going to these we would be lucky to get 1 year service from these before they either fly off, or lose the alignment and get shredded up on the fan guard. The drive sheaves use a pressed on ring which guards against the belt running off the sheave. I don't like those and never did.

It happened today again. The ring on the sheave came off and the belt followed...Belt was only two months old. Aside from alignment issues, is there any other thing which would cause these to fail this early? And what should we expect to see as far as life expectancy of these belts? I'm quite frankly getting tired of seeing these belt last for only a few months, and in some rare occasions up to 12 months...

I have some ideas of my own, but I'd like to hear of your experiences with these belts. We do use laser and string on these for alignment, and also the Goodyear belt tensioner which operates off vibration measurement when belt is struck with a wrench, and the sensor picks up the vibration freq, and the measurement is in Newton or Htz...

Thanks,

Take a close look at the "ring" that came off. Is it worn through or real shiny where the edge of the belt could have been riding against it? If so, sounds like an alignment issue. These drive set ups are real finicky when it comes to alignment. The belt needs to track between the 2 lips "rings" on the sheave. If this is a continual problem, I would get the sheave / belt rep in and show him some of your problems. I never really paid attention how those rings are attached to the sprocket. If it's pressed on, the belt could be riding against one side, heating things up and then the ring comes off, then the belt. But again, if the alignment was really good the belt should still stay on. Have any pictures to post?

Can you view the belt on the drive sheave while in operation to see if it's tracking in the center of the sprocket?

Use only the laser or a straight edge. Take into account the thickness of the ring on the sheave, usually the larger sprocket does't have one.

Try to get all the crabbing string banned for using on sheave alignments!

Rod,
Are you able to look at these belts/sheaves using a strobe? If you can get the right view, you can tell a lot about the installation.

If you can spot some early stage damage, then checking every couple of days to see how it progresses and develops might point you in the right direction for a fix.

Yes, I went back up there yesterday before I went home and did look at it with a strobe. Looked like it was favoring the side of the sheave with the ring. But the alignment was right on after we installed the new sheave...Will keep an eye on it...

Thanks,

quote:

Originally posted by Buzz LightYear:
Rod,
Are you able to look at these belts/sheaves using a strobe? If you can get the right view, you can tell a lot about the installation.

If you can spot some early stage damage, then checking every couple of days to see how it progresses and develops might point you in the right direction for a fix.

I am not particularly familiar with sync belts (as opposed to normal vee belts that slip).

From what I know, sync belts give a little higher efficiency, but are much more sensitive to small deviations in alignment. And I think perhaps have unique wear mechanisms not present on vee belts.

I may be speaking from ignorance, but I have a suspicion the problems would disappear with vee belts. Ceratinly we have many vee belt applications and none with so many problems as you described.

What drives an application towards using sync belts? Is there any reason the application couldn't be converted to vee belts?

We resolved a number of related type issues by understanding that these types of belts need dramatically more tension. If tensioned to the level that v belts are set up the life will be dramatically shortened. The manufactures information will give the appropriate level. There is even a tool available.
On a side note when moving to this type of belt the side loading on the motor bearing increases, which may require a bearing upgrade.