Modern conveyor design, fabrication tolerances, and installation control suggest that self aligning idlers are not required.

This comment is certainly true for overland steel cord belt design.

Why are self aligning idlers used?

To correct belt mistracking with various causes:

a) varying load mal-centering,

b) wind,

c) structural settlement/alignment,

d) belt construction and splice installation errors,

e) use of tilted wing rolls and local moisture influence,

f) idler installation errors

g) material build-up on idlers and pulleys

h) fill in blanks of other conditions .........

All of these conditions can be prevented with the proper design criteria controls and/or from observation that pin-points the cause of field related effects which then proper corrective action can follow.

Most but not all self aligning idler design kinematics exacerbate belt misalignment until the belt has moved off-center sufficiently to engage the side guide rolls.

In my opinion they are not required on any conveyor when good practices are applied.

Lawrence Nordell

Conveyor Dynamics, Inc. ■

Belt tracking problems can be many and varied. Here is a partial list of items to check and correct:

1. Belt cupping (curvature of the belt, concave or convex across the belt perpendicular to line of travel) May be caused by incorrect belt for trough angle, heat, chemical, overtension, or ratio of top cover to bottom cover incorrect.

2. Belt camber- a banana like curve to the belt. Can be created at time of manufacture or during shipping or storage. Seen as slow side to side movement of belt.

3. Crooked splice seen as quick side to side movement in splice area. Often confused with belt camber.

4. Stucture and component misalignment

5. Loading conditions (offcenter, segregated, or surge)

6. Incorrect belt cleaner installation

7. Incorrect belt for application (does not rest correctly in trough loaded and unloaded)

8. Tracking devices that are tied in one position

9. Gravity takeup misalignment

10. Skirt board rubber adjustment (not equal both sides)

11. Material buildup on rolling components ■

In over 12 years of dealing with belt tracking I have yet to find a belt that runs in the centre all the time.

As from the list of causes to belt misalignment as provided by the gentlement above, one can see that the preventative measures are many.

In my experience the manpower provided per conveyor is being reduced continually placing more emphasis on automated products and products that require as little maintenance as possible as well as products than prevent or correct problems that would normally require manpower.

Its unfortunate that many designers neglect to incorporate belt tracking devices at regular intervals into the conveyor system, as this would definately increase belt life and decrease structural damage, spillage, maintenance and costly downtime.

If you have problems with belt tracking please feel free to contact us.

Kind Regards

Mark Hupertz



E-mail : mark@waloni.com

web: www.waloni.com

Tel +2711-660-5050

Fax: +2711-660-1213 ■

I’d have to agree with Mark here, as you can see by the extensive lists above.

Trying to achieve “In my opinion they are not required on any conveyor when good practices are applied” is virtually impossible.

The typical nature of our Industries does not allow for perfect conditions 24 hrs a day, 365 days a year.

Call it insurance if you will, for the sake of a few dollars compared to production loss, cleanup costs and damage they are at least a piece of mind. ■

Dear Mr. Ashwani K Bhatnagar:

Everyone appears to agree that self-aligners are not required under perfect conditions where the system has been well designed and is well maintained. Agreement also appears to be made that aligners are an acceptable method compensating for poor maintenance practices, outside influences such as wind, and minor system misalignment.

All of the above is true.

My concern with these tracking aids is that they are frequently used improperly and are not maintained themselves. I've seen too many self-aligners tied-off, frozen, or jambed with material to make me comfortable with a total reliance on them. They help, but it all gets back to the original design and user preventive maintenance practice. If the user does not maintain their conveyors, self aligning idler sets will not help and may make conditions worse. If the users have a reasonable PM practice, the self-aligners are very valuable.

Regards, ■

Dear Mr Miller

I agree with the statement that far too many, self aligning products do not perform as they should and require regular maintenance which is not carried out.

I too have seen thousands of self aligning products tide back in some way as to give some form of belt tracking.

When this is applied it simply means that the product does not work and was poorly designed.

The key concept of any self aligning frame or roller is that it should run maintenace free. Since one of the reasons for having to install a belt tracking device is because there is not enough manpower to employ best practice methods on the conveyor, it is of little use if that product then requires the time you wanted to save.

We made it one of the key considerations when we designed our products The Sureguide® such as the displayed in the picture above have achieved life spans of up to 10years on a coal ash plant .Sasol Fuels in Secunda South Africa (SureGuide).

To tell you this section of the plant has 32km of conveyor and has close on 700 of our units installed. Their reasoning being that the conveyors running on the ash dumps cannot be alligned as the ash surface sags and cannot be controlled. The SureGuide are installed as a preventative measure against belt edge damage and structural damage and the fact that they have only 8 hours per week in which to do maintenance on the belt and that they would rather use this time on other issues.

Its unfortunate that too many mines fall prey to simple, cheap and ineffective products which ultimately give the entire products category a poor name.

Our products are not the cheapest but at least they do not require periodic maintenance and are robust enough to work in the mining enviroment.

kind regards

Mark Hupertz ■

The use / effectiveness of self-aligning idlers is subjective issue. People do have some apprehensions. But as on now, when the finally reckoning comes for the decision makers they have temptation to put them (with the idea that it is safe to put them rather than not to have them). My analysis indicates that :

1) Pivoted type self-aligning idlers, which are generally used, would be somewhat effective when belt tension is not very high i.e. light duty conveyors. “Somewhat” can be worked out in mathematical figures.

2) Such idlers would not be effective (result oriented) when belt tension is very high. That is aligning actual force will not be capable to shift high-tension belt. In fact, belt would dictate the idlers position. Therefore, such idlers are not used for long distance high-tension conveyors.

The effectiveness of the conventional self-aligning idlers can be analysed in each case (conveyor condition), and one can take decision accordingly.

Therefore, this type of idlers can have certain area of application, and caution for one-sided opinion. One neccessity is to improve the design features of such idlers, so that it will perform better in its area of application.

Regards,

Ishwar G Mulani.

Author of Book : Engineering Science and Application Design for Belt Conveyors.

Advisor / Consultant for Bulk Material Handling System & Issues.

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 25882916 ■

I agree with Mr. I G Mulani point that “The effectiveness of the conventional self-aligning idlers” is debatable.

There’s an article at http://www.mining-services.com/cgi-b...;ID=208807&d=1

which may be of interest.

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Quote………….……

The "AB Tracker" system also gives you the competitive edge

with its revolutionary swivel plate assembly which corrects misalignment

by way of tilting & slewing simultaneously.

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The tilting and slewing action of this system enables it to make immediate changes to the belt alignment without the force required by conventional tracking idlers.

I’ve seen the system in action on many occasions and would be happy to comment on its effectiveness.

Attachments

abtracker (JPG)

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Use v-return idlers. They work and do not require special maintenance. ■

Loeffler Engineering Group:

Is Frank still practicing? Tell him hello.

Two roll Vee returns do steer and aid belt tracking better as do 3-roll trough (carry side standard). In fact, 3-roll trough belts can give greater benefit in tracking and increased idler spacing. Less edge flap vibration is produced due to the smaller wing section belt mass.

We have applied 3-roll return idlers, at 10 meter spacing on 5, 9 and 16 km single flight overlands, with great success. THey are usually used in horizontal curves but more often now in straight sections as well.

A major caveat is: beware of the belt center to wing roll junction fatigue stress. The fatigue condition is increased without belt turnovers.

Lawrence Nordell

Conveyor Dynamics, Inc.

www.conveyor-dynamics.com ■