Belt guidance system 3

[quadamage76]

Hi,
I'm looking for a book/an article on how to guide a flat belt, I saw many drawings on how to keep centered but nothing on how to calculate rolls' shape.

Thanks Matteo

 

[Compositepro]

Google can be very handy.

http://www.fennerdunlopamericas.com/pdf/TrackingFDA0105.pdf

This is a subject I've studied over the years and therefore have an interest but it is way to broad to discuss here. There are plenty of other references on the internet. The key is using the right search words. The link above will give you a start.

 

[dvd]

Like Compositpro says, there are plenty of references out there. You need to be a little more specific about what you want to do. I assume this is a conveyor application. The following are off the top of my head.

http://www.forbo-siegling.com/Siegling/Siegling.nsf/pages/brochurestechnicalinformation

http://www.gilbertandnash.com/

http://www.cemanet.org/publications/index.html

 

[SteveWag]

Your best bet is to find a copy of The American Machinist's Handbook by Stanley and Colvin from the teens or Twenties. Mine recommends a crown height of 1/20 of the width of the pulley for leather and 1/150 for cotton. It also talks about 1/16 to 1/8 inch per foot taper from center for high speeds and 1/4 inch for low speeds. (I have never seen or used a pulley with anything more than 1/16 inch) I also have a chart showing dimensions of some pulleys, 12 dia. x 6 face having 5/32 thickness at the rim and 1/4 at center, 20 x 8 having 3/16 and 5/16. If you have a diameter and face in mine I can see if I have dimensions. Most of the time I use a mixture of leather and synthetic and both seem to run on the same pulleys.
Steve

 

[EdDanzer]

Depending on the width to length ratio, reinforcement type, pulley diameter, level of contamination, and type of contamination you may find crowning the pulleys may not help. Short wide conveyors with small pulleys may require a guide V added to the back of the belt to make it run centered for long time periods.

Ed Danzer

http://www.danzcoinc.com

http://www.dehyds.com

 

[quadamage76]

Thank you so much for your answers. My question was posed because I have a problem similar to the one described for belts, so I'm not looking for examples on how to solve it, but I'm looking for something that will explain in details the physics of the problem. The exact problem I have now is on a plant, realized by me, that accumulates a metal sheet during the operation of welding a steel coil's head with a steel coil's tail, this accumulator reels off the sheet accumulated on rubber rolls during welding phase, while a pinch&roll system feeds the machine posed at the end of the accumulator. In such operation the metal sheet swerves, so I have to find the way of keeping it on centre, but I cannot use a solution typical of belt problem withou having calculated it, because her we're talking about a sheet 690mm large, 1.2-6mm thick, 50m long.

Thanks Matteo

 

[dvd]

You might find some useful information at the Sandvik website. They sell steel belts.

http://www.processsystems.sandvik.c...InternetWeb)/013C134BD28363BDC1256E62004C4EF5

 

[MikeHalloran]

Ah. Pulley crowning relies to some extent on belt tension.

Accumulator loops don't work the same way.

Such loops were heavily studied when they were part of high performance random access magnetic tape drives... but I think they were mostly edge guided passively, i.e. the tape loop was captured in an air column, and not actively steered.

There do exist, commercially, 'web guides' that actively or passively steer/align webs of paper or plastic in production of sheet/coil goods. Good luck distinguishing them from guides to the WWW, but advanced search should eventually get you some hits.

The web guides I have seen comprise a dancer roll with a passive linkage that steers the roll, and hence the web.

You would probably need one with active elements, and strong ones at that, but the technology does exist.





Mike Halloran
Pembroke Pines, FL, USA

 

[Compositepro]

There are many different ways to solve your problem and crowned rollers is probably not one of them. Crowned rollers use belt tension over the crown to distort the belt approaching the roller toward the centerline of the roller. An active guidance system that senses the edges of your strip would be the most robust solution and work with the largest range of materials. Keep in mind that the strip itself needs to be straight to begin with (good quality splices).

 

[quadamage76]

I suppose that crowned means something like "rounded", is it right? At the moment we have:

-the strip is not well cut, one side can be ticker than the other or can be longer than the other, unfortunately I cannot make anything on this...

-I'm going to unmount most of the rolls to round them with a grinding machine, then I will boost tension level (at the moment it's very low, apprx 2 N/mm^2) hoping that it can help to keep the strip on center (it flow 7 m/min max, it's very slow!)

-if the previous solution is not enough, I will move some part of the following plant to introduce an active guide.

I'm going to search on "web guides theory" hoping to find something.

 

[dvd]

The key to guiding a web, or belt, is that the web will try to align itself at a right angle to the next downstream roll. The crown on a roller, with the center at a larger diameter than the outer portions will cause the outside edges of the belt move outward until the forces balance from one edge of belt to the other. This works because the belt is elastic. If you crown your rollers and try to convey a sheet that is not flat the crown will grab the low spots on the sheet and try to align at a right angle locally. I believe that crowning the rollers will cause more problems than it would solve, because it is permanently adjusting the roller geometry. I think that a belt tracking device which senses the edge location and corrects in a feedback loop would be preferrable. I have used the Gilbert and Nash products in the past. You can search for "belt tracking" to find similar systems.

 

[HEC]

To continue dvd's response "The key to guiding a web, or belt, is that the web will try to align itself at a right angle to the next downstream roll" Paper machine "felts" are guided with a steering roller. This is a roller wiith minimal wrap that is pivoted at one end and "steered" at the other end. From memory the steering movevment is in the directin of the web or felt. The control for steering the web is driven off edge guides.

Mark Hutton

 

[cb92]

I may be off base, but a belt sander has an adjustable (and crowned) roller. If you could devise a steering rod feeling which way the belt was wandering and compensate, you might get the belt in control. It's what I have to do with an old sander, keep one hand on the adjustment. Also I'm brought to mind the front wheels on an old steam locomotive; they guided the unit down the track. It didn't mind if the track was not so good, it just kept the big wheels aligned.

 

[WoodyPE]

Maybe I'm just missing it here, but why wouldn't you just use pulley flanges the same as you use on timing belt pulleys?