Dear Sanjay,

We have a very detailed theory, with significant field work to demonstrate the reasons for twist or rotation. We also know special belt construction techniques to minimize or eliminate rotation.

If you wish input with substance please provide conveyor arrangement details. These must include the elevation and plan view path, drive, belt specs. idler specs., takeup specs., material properties, tonnage and speed. ■

Dear Sanjay

With Respect this is not so much a theoretical problem, it is a practical setting up problem.

I have set up and commissioned many pipe conveyors in the last 25 years.

The pipe conveyor must be set up / tracked empty and then with material and in different conditions.

Usually pipe conveyor is more stable when full with material but with some materials at low fill it is like there is no load so this setting up is important.

In recent time we commissioned 800 meter pipe conveyor with many curves including 1 X 85 deg and it runs true.

If you require any further help please be free to contact me. ■

Dear Sanjay

I have come across this before where people avoid running empty but this is not a cure for the cause for the problem only the symtom.

It should be tracked empty starting from the tail end one part at a time methodically and observed until the whole length is correct and then material can be put in either full or partial amount.

In Europe and other cold climates we can get other situations in winter but this is other issue.

What about the curves in your case are they large angle or tight radii.

Regards ■

I look at your layout and have strong doubts that Mr. Holt's method will solve your problem.

There will be a dramatic tension difference from empty to full along the curve path and elevation.

Some clue can be telling if you can post or email me a set of photos showing images looking toward the head, from the tail, that illustrates the direction of overlap and camera location wrt to the seam. Hopefully, also one at mid curve and at high tension end of curve. If we are correct and can model it, we can also tell you what "best hope" you have.

There are a number of possilbe conditions. Maybe Mr. Holt's method will work and maybe not. Before you try and possibly are not successful, let me see the present configuration and then I can tell you more about the nature of what is going on within the belt.

The layout give some good clues, the photos or sketches will, I hope, seal the deal. ■

Dear Sanjay,

It would be good if you posted the photos and the configuration on this page. You would then get multiple views on the problem. Belt twist is not usually a complicated problem and as an example I have induced a twist during commissioning to teach the maintenance staff how to remove and control it.

You say the system was uprated from 55kW to 90kW. Was this to increase capacity or to correct a design flaw? How did the belt behave before the upgrade? Unless you also changed the take-up an empty belt is an empty belt and should have behaved the same.

The behavior of the old portions of belt and the new portions could be an influence however this must be observed during empty running. Does the same section of belt twist or is it random? You must have found out by now that you can manually untwist a conveyor of this size. It's a laborious job but you need to determine the cause of the twist and correct it. ■

Dear Sanjay

Of course this can be analysed theoretically in detail but in the end something practical has to be done and so that the problem does not repeat itself.

It must be correctly tracked for the conditions.

Also re theory- when a new belt it installed and it is correctly tracked and working, then in 1,2 or 3 months time it must be returned to as the belt will change in this time be more supple and touch less and or different idlers.

This will vary from belt to belt and from installation to installation so must be done by experience. ■

Dears Sirs

I mention again for this part of the job it does not matter how much theory you investigate it has to be done correctly in pactice on the job.

It is true that under or over tension can make the belt twist clockwise or anti clockwise at a curve depending on if it is RH or LH curve, further the tension in the belt is changing and varying all the way down the length of the belt and more so between empty and full.

When first installed it is not easy to know it some structure or idlers are giving false tracking, also if some site vulcanised joints or factory vulcanised joints are causing false tracking.

All this being so you have to tract the belt at the site with the conditions and equipment you have in real time, not in classroom.

Regards ■

Dear Paul,

You continue to disparage science-physics of pipe conveyors. Why? Sounds like sour grapes.

Quite unlike your comments - I paraphrase: " try it then fix it, if it needs it". We practice: "get it right the first time". No need for a second time.

Know the physics and use it to direct good design practice.

You maybe lucky, if your physics is not comprehensive. You claim: "does not matter how much theory", and I paraphase again "other factors are sure to prevail". I acknowledge that if you study the effects, you get an understanding of the physical principles. That does not equate to knowing the degree of actions and reactions - designing with science on your side.

I do note a request for your pipe conveyor "DIN f" factor when you claimed pipe conveyors are less power hungry than trough conveyors. I see you now have published this same arguement again, but still no "DIN f". Can it be that you do not wish to let the world know the design level? In the final analysis, the arguement is flawed. If you knew the power equation theory, this would be obvious.

Maybe a read of: Spaan, Jonkers, Hager, Hintz, Lodewijks, Qiu, Wheeler, Rudolphi, and the many ancient Doctorates, that have published on the pressure and power influence between rollers and belt.

You cannot:

a) apply exaggerated belt bending and expect to have lower contact pressure.

b) have more belt mass and have less contact pressure.

c) concentrate the belt- idler roll pressure zones and expect lower enegy loss.

d) include many more rotating rolls (bearings and seals) and expect lower drag.

e) introduce additional fabric reinforcements to inhibit pipe collapse and not know the fabric will resist bending and increase the forming forces = more power.

If you designed both pipe conveyor and trough conveyor, your arguement might be considered plausible. However, to compare a poor design of either pipe or trough belt with a better design methodology, is a tainted arguement.

We publish a great deal of our design performance. This is how a client can differentiate our performance vs. others.

At least one belt supplier claims the pipe design should not consider efficient power usage. We know where and why they make that arguement. It hides their ignorance and it is insulting to the end user to make such an arguement. Don't go there. ■

Dear Larry

Please do not interpret incorrectly my comments.

1. Regarding power consumption if you recall recently I acknowledged that generally pipe conveyors consume more power for a given capacity, they have to, there is power to form, pipe, power to maintain pipe and power to traverse curves. But it can be very different with different belts high profile belt, high rigidity belt or normal, this is more so than with conventional belts. Having designed many of these (pipe) and conventional conveyors.I have experienced some cases where the overall power consumption has been less with the pipe than conventional due to layout and elimination of transfers etc. But I agree will not be the case normally when like for like.

2. Regarding the problem of Sanjay and twisting, I have seen many things cause twisting and of course like everthing in life there is a science behind it. We like you will analyse the route and determine the best design acpects and engineering approach however it is only when the conveyor and particularly the belt is installed that you can see what is to be done.

Again depending on the type of belt in relation to diameter sometimes the belt will touch all six idlers sometimes only 3, when going around curves it will pull into the inside on the curve, more interestingly when going through a concave curve the belt can pull up against the top idlers when empty and sit down on the bottom idlers when full. When going through a convex curve it will pull down on the bottom idlers when empty or full.

Although the initial theory and assessment must be done, and rightly so, only when this is seen with the actual belt, in the actual structure in the actual conditions, with the actual tensions can the correct adjustments be made. If this is done correctly (i.e. commissioned correctly there should not be a problem. ■