Re: Slipping Drive Pulley And Manual Tu
Kinda skimpy data. Some things that could point you in the right direction are:
1. Type of drive and its torque vs RPM signature may lead to an ephipany
2. Drive and other rotating component inertias - are they known? An engineer could just take a stab, without engineering a thing.
3. A little better sketch of the belt slope and drag action of the steel trough. The belt slope is important. More slope leads to a slightly different strategy
4. What is a "b/w"? Is it like a Beemer?
5. I had it and then the Chilean wine took it...... Got it back - put GTUP at tail. This can use the downhill belt mass to assist the gravity TUP at the tail. If GTUP is at the head, its on the wrong side to ake advantage of the return belt mass.
I could go on, but, we offer advice more than engineering detail.
The steel trough could be adding a higher semi-static starting friction which puts a higher pause at peak motor load.
The motor must travel the torque signature curve with a high (250%) to very high (350%) point of maximum breakdown torque.
A high motor breakdown torque, must be crossed no matter if belt is empty or full. The difference is the time it takes to cross the Alp. Moisture and heat become more effective with the longer duration. Even though slip may occur to some extent, it is not there long enough to be a nusance.
When the belt takes the momentary high motor pull-out torque hit (>250%), it results in a higher than normal incomming tension (T1), and because of the fixed TUP (does not move) the T2 (slack) side drops from the belt's elastic stretch crossing the drive pulley. The T1/T2 ratio then can be exceeded. Normally, this ratio should be around 3.5 ( an engineering feat). This depends on the lagging and the presence of water. Longer dwell in this unstable region mean greater propensity to slip.
Some off the wall comments:
1. Gravity Take-up would help
2. Soft-start would help - fluid coupling, voltage regulated start,...
3. Ceramic lagging would help
4. More wrap would probably not help (too far gone)
THe above are fairly rough guesses when in the dark dark.
Others will add more. ■
Re: Slipping Drive Pulley And Manual Tu
Whats stopping you from applying more TUP tension? Have you run out of belt rating, structural capacity, pulley ratings. ....? ■
Re: Slipping Drive Pulley And Manual Tu
Your configuration is pretty standard for the wood industry.
The way you latch on to to reducing the sag between the idlers on the return strand suggests that you have way to lower tension in the system. An indication of what the sag measurement is would help.
I would not use ceramic linings on a conveyor with a bare back belt unless you want to shred it to pieces. Fix the basic problem first.
If you have bought cheap belt with oodles of stretch you may have run out of take-up travel. Consider pre-tensioning and re-spicing.
The glues and gums that carry over in the water onto the underside of the belt increase the drag of the belt but do nothing for increasing the grip of the drive pulley. you will need a good quality diamond lagging to help you out here. (Chevron if you have a water problem).
You do not say when your drive slip occurs. It could be that you are over loading the tail section when you stop, or that you stop for extended periods allowing the belt to slick to the slider bed. ■
Thanks For The Replies
To be clearer...
1. Belt is horizontally loaded
2. drive config describes 's-drive' very near head end with take-up on on the t2 side
3.'wet' means heavy-not soaking.
4. b/w means between
and advice is good, but I am not at the location and I am getting data from a client who isn't clear or easy to get hold of.
so...
1. no room for gravity tu or we would have done so, not an option
2. don't know why more tension can't be added, I have had thoughts of come-a-longs pulling the tu as tight as possible if they can't use a wrench with a pipe on it for some reason.
3. I am assuming the slip occurs at startup from a dead stop with a conveyor fully loaded. like I say, the details are sketchy even to me.
4. concerning running out of tu travel 
to show what I am dealing with, our first question was, did they tighten the t/u after belt installation? we got a long slow silence. so, who knows.
5. ceramic lagging would shred the fabric backing. might be possible to put the drive on the carry side, since its rubber, ceramic lagging might help, but since its on the dirty side now, might not.
6. reducing sag: the purpose of that was to fix a possible problem, too much sag creates excess tension. so, turn off belt, physically raise sag between idlers, increase tu with no effort. now have less sag between idlers and maybe that was the difference. it might help, might not, but cheap and easy to do.
6. the client handled belt bids and purchase, no idea what they bought but 300+ piw for inside the sawmill is typical.
7. lagging is slide type, no idea of grooves etc.
8. the motor is 20hp, 1800 rpm. speed was 550 fpm but i believe they slowed it down. if they slowed it down to ~300 fpm, and loading rate is the same, i have 5hp too much. might be the difference and spare motors lying around a sawmill is normal, so also cheap and easy to try.
is a conveyor fully loaded better for drive traction than tail only (not overloaded)?
Big Question: is the manual tu on the wrong side of the drive? Should it be on the t1 side since it doesn't move with changing tension?
Jeff ■
Re: Slipping Drive Pulley And Manual Tu
Ok you've given lots of answers here.
If you client has slowed the belt down; the power will be less but the tension requirement is higher. You will therefore generate slip during start due to lack of tension. Beware increasing the tension may overstress the belt or give you extra stretch (if your client bought a cheap belt)
You need to sit down and recalc the conveyor checking the new tensions required and the effects on pulleys shafting structures and the like.
If the conveyor is feeding a chipper then slowing it down will effect the instantaneous loading and chip quality will fall as a result.
Quick cheap fix is revert back to the original speed and watch the problem disappear. ■
Slipping Drive Pulley and manual TU
Hello All,
I have reviewed some posts that resulted from a search of manual takeups on this forum. It provided some great general knowledge, but don't see a solution for me there.
So, here is my problem:
A 24" wide belt (slider back) ~160 ft. long carrying wet lumber in a steel trough has a manual screw tu (36" lg.) and a drive pulley that when loaded, slips during restart.
The configuration (going with belt direction) is Head Pulley, angled down to Drive Pulley (rubber lagged), TU, return idlers and Tail Pulley. The belt travels straight from the head to the drive and the height of the top of the tu pulley is pretty much equal to the return idlers (10' apart). The wrap angles would give a min. of ~205 degrees, which for our low hp app's is pretty standard.
My thoughts:
1. would leaving the config. as is, but physically raising the sag b/w idlers then retensioning the tu be a good first (cheap) possible fix?
2. next: would adding some sort of soft start, as mentioned in one of these manual takeup threads, help in our situation (smaller motor easiest for us) to lower the belt tension during accel?
3. The tu may be on the wrong side. I believe with some sort of automatic tu, the slack side (T2) is best. however, with this configuration, I think we have the tu on the wrong side? should it be on the T1 side b/w the head and drive pulley?
Thanks for any help!
Jeff ■