Ration Of Top:Bottom Belt Cover Thickness ≪4:1
Originally Posted by sganesh
What is the relation between top & bottom cover thicknesses? I have been told that the ratio between these two should not exceed 3:1 for the fabric belts. Though the cover thicknesses can put little effect on the trough-ability, I do not understand how this number was derived.
Regards,
You should not exceed the ration of top to bottom cover thickness by more than 4:1. During curing the covers and fabric amount can shrink with sufficient differential to cause the belt to cup in a concave fashion the causes tracking and other related problems with large shape change. Fabric can take a greater and lesser differential than steel cord depending on the carcass construction.
Troughing can also become a problem. The top wear cover resists bending more so than the bottom or pulley cover. Thus, the thickness of the top cover should be in some balance with the bottom. There is more to this than some simple ratios. ■
Re: Relation: Top & Bottom Cover Thicknesses
Just to mess with everybody's preconceptions about cover thickness, consider that in some cases for long belts, the bottom cover should equal or greater thickness than the top cover as the material is loaded at infrequent intervals and the carrying idlers are represent the greatest contribution to cover wear. ■
Preconception - That's One For The Coroner, Y'r Honour
Estimated Pre-Speaker,
it is my belief and my gratitude towards so many collegues here that this forum is a very valuable place not to develop (or show; or perhaps to loose, at that) preconceptions. It is rather a great gift to be able to receive the knowledgeable input of so many professionals, so many points of view from different angles. Perhaps the value shines through only if no "diss - qualification" of other peoples opinions diminishes that value, as their dedication to support someone they very often do not know and have no personal obligation to help whatsoever (and nothing of a pecuniar recompensation).
So I would like to forward the point of view, that no post here should be qualified as preconception, but rather as a point in an ongoing discussion.
And an enterprise successfully selling their equipment and not being sued around the planet, how to qualify their (their, at that) experience & common rules as preconceptions? Talk to them if you need, that's it. If one is qualified enough.
R. ■
Re: Relation: Top & Bottom Cover Thicknesses
Hi there Sganesh..
For the last generation (or two) I have heeded the words of Goodyear.
They say on fabric belts use 1.6m bottom cover for belts up to 750mm wide and 1.6mm to 2.5mm for above 750mm
For top cover, work out the cylce time, and look up the top cover thickness with respect to lump size and abrasiveness.
This has worked fine and I have never had a problem. If the ratio works out to 3:1 then this would be by coincidence only.
I have no idea who came up with this rule, but as far as I can see, its not valid at all in practice.
I am just dissapointed that so many have taken it to be Gospel, and has wasted so much money because of it.
I fairly recently had my designs for a conveyor project audited, and the audit enginneer said he was surprised at my choice of covers as the were not 3:1 and implied I should know better!
Fact of the matter was, I had only used the client's standard covers on the existing plant (nowhere near 3:1), as he had great success with them.
(I rest my case for the defence, your honour..)
Cheers
Taggart LSL Tekpro ■
1:3 Derivation - One For The Defence, Y'r Honour
Dear Mr. Sganesh,
i have here in front of me a manual of a reputable belt supplier which states in the lines of ...
if fabric belt top & bottom cover should have different thicknesses, then don't exceed a ratio of 3:1... for if the difference is greater then natural shrinkage of rubber after vulcanization can (can!) lead to harmful tensions in the belt...
This is evidently part of their professional experience & as a base rule followed, wherever a belt is supplied by this specific manufacturer, at least what concerns common cases. So, in reverse thinking, if one
- has a reason to neglect this unspecifical rule and is wilful to undergo in-depth investigation and/or
- knows better from the beginning and/or
- the choosen knowledgable belt supplier states along another line:
As always in engineering, the commonplaces will be overruled by the actual requirements & facts.
Final Plea to the Prosecutor:
And this: Fortunately, as it gives engineering it's renewable task field & sustainable character and chances of employment to people who are called engineer.
Regards
R. ■
Re: Relation: Top & Bottom Cover Thicknesses
Hi there Roland..
Its surprising how many "reputable people" have fallen into the same trap with this 3:1 ratio
One would have to be a bit gullible to believe in theory and over-rule track record, but so many do, it would appear
I go by what I have found true in practice
Others may have had different experiences in practice.. lets hear from them.. thats what this forum is for.. (blind faith forbidden!!)
Cheers
Taggart LSL Tekpro ■
Re: Relation: Top & Bottom Cover Thicknesses
Interesting dicsussion.
Perhaps Graham, Larry, you could dicuss the reasons for 'reverse cupping of belts' as clearly noticed on return side where flat return idlers are used.
The belting suppliers typically refer to this being caused by differential tesnioning of top and bottom covers resulting from too large a ratio between cover thickness.
I have noted this on quite a few installations (Graham you will remember the Grootegeluk phase 4 extensions?) and these generally had large top/bottom cover ratios (like 10mm top; 1.6mm bottom).
Regards,
Adi ■
Re: Relation: Top & Bottom Cover Thicknesses
Hi Addi..
Funny you should mention cupping on the return belt..
I recently had to do a 3rd party audit a troublesome conveyor with cupping on the return belt which made it pretty much imposibble to train as there was not enough contact with the return rolls.. and yes! you have guessed right.. it had a 3:1 belt on it!
What causes this problem is the return idler spacing is simply too close.
There has to be enough belt mass to hold the return belt down onto the rolls
Taking out every second idler doubles the hold down mass and does the trick. If there is not enough belt mass on the return idler to make the belt sit down nicely, then you can bet that there is not enough to overload the shafts and bearings.
Concave curves on returns are often notorious for this effect
Cheers
Taggart LSL Tekpro ■
Relation: Top & Bottom Cover Thicknesses
Dear Experts,
What is the relation between top & bottom cover thicknesses? I have been told that the ratio between these two should not exceed 3:1 for the fabric belts. Though the cover thicknesses can put little effect on the trough-ability, I do not understand how this number was derived.
Regards, ■