Hello Shane,

You are right. The catenary idler will result in more drag on belt, when applicable conveyor (portion) is not horizontal.

This is due to the reason that the catenary idler plane is always vertical (nearly). Hence, when conveyor is inclined / declined, its side rollers axis will not be at right angle to the belt motion, and thereby the slow sliding of belt corresponding to velocity component will create drag.

This issue has been discussed in detail alongwith numerical examples in my book on belt conveyors.

Regards,

Ishwar G Mulani.

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

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 5882916 ■

Hello Shane:

Mr. Mulani discusses one point that highlights the differences between fixed and catenary idler behavior wrt the belt, idlers and their wear, tracking, et al.

BELT WEAR:

Regarding your first point of cover wear, it is not normally considered to be a major concern. One could invent a case where it might be an issue. The German, Indian, and Southern hemisphere lignite coal operators have a great deal of experience in this area and have published on it.

BELT POWER:

We have measured the difference on horizontal belts, where the downward gravity force and the multi-body degrees of freedom push the idler set forward. Belt power increases about 5-6% in the empty case and 1-2% in the loaded case. One could claim the added power must resolve itself in wear.

BELT TRACKING:

We have knowledge of conveyors where the horizontal and sloped belt path (0-12 degrees) causes extreme errors in tracking when the wing carry or return roll center hinge point is canted forward of the outer hinge point by the belt reaction forces. In some cases, the central hinge point had to be wired down and pulled back against the belt path to control belt tracking. Uphill conveyors have return catenary tracking problems. Downhill carry catenary idlers have tracking problems.

The force fluctuations cause cable fatigue/breakage. This then becomes a maintenance issue.

Lawrence Nordell

Conveyor Dynamics, Inc. ■

One obvious advantage with catenary idlers is the ability to trip them out of service 'on-the-fly' rather than disrupt operations. Catenary sets are often more practical for higher utilization (>80%). Optionally, a trippable fixed set could be employed at a premium. ■

To: Michael A. Carniato, P.Eng

There is a hardware attachment that allows conventional rigid frame idlers to be dropped out of service on the fly. If anyone has an interest please contact me on same.

I am curious on your claim of >80% availablility gain. Its easy to say. Please back up such handsome gain with some facts to appreciate this claim.

I claim the contrary. Catenary idlers will by their nature cause greater maintenance due to the moving pieces and added wear to these pieces together with idler barrel and belt wear.

Lawrence Nordell

Conveyor Dynamics, Inc.

email: nordell@conveyor-dynamics.com ■

I make no such claim sir. What I meant by utilization (an easily confused term) was in reference to the conveyor operating hours. For example, if a system is expected to operate >7,000 hrs per annum, the ability to trip idlers out of service on-the-fly may become an important feature.

Anyhow, I generally prefer fixed sets. But, to my knowledge, the catenary set is the most practical 'trippable' solution dispite the higher maintenance related costs (for reasons you state). And one more: during switch out, catenarys are often changed out with 2 good rolls finding the trash bin. ■

Dear Michael,

You are right and wrong.

First, I agree with the idea that changeable idlers, on-the-fly, can increase ultilization.

Second, it is not obvious that the higher maintenance of the catenary roll set will achieve the same available hours recorded for the fixed frame roll sets. Syncrude had a much higher failure rate of catenary rolls than Suncor's fixed frame assys. Syncrude conducted further tests, using fixed frames, and found a sharp reduction in repair rate Circa 1992-1993.

Third, I further claim that fixed frame idlers can be "tripped" on the fly.

Lawrence Nordell

Conveyor Dynamics, Inc.

www.conveyor-dynamics.com ■

Shane,

I am overseas at the moment and don't have access to my files.

Since I don't know you affiliation, I feel some discomfort in making a request to Syncrude on your behalf. Please try Mr. Jim McTurk. Jim was the Syncrude manager of our studies during the 3 year research period. I do not have his present coordinates. Syncrude's switchboard will.

Lawrence Nordell

Conveyor Dynamics, Inc. ■

Hi Shane..

To get back to the basic plusses and minuses of garlands vs fixed, I have found that under load, the carry garlands move to almost normal to the belt even on inclines, so you can have either.

I prefer fixed myself, as it makes the conveyor module much simpler.

However, ...when you have ROM or large primary crushed material such as overburden with big lumps, its nice to have the flexible "give" that the garland affords you. Such conveyors are often shiftable which tend towards the garland anyway.

For fine stuff on long overlands its fixed for me.

I have done all my overlands with horizontal curves, Dual Carry Conveyor (with swop over "Pretzel") and so on with fixed idlers.

These are perfect to guarantee the theoretically calculated geometry.

Hope this helps

Graham Spriggs

LSL Tekpro South Africa

gspriggs@global.co.za ■

Hi Shane,

A couple of comments:

1. The additional power requirement is minimal, occurs mainly during start-up where the idlers are 'pulled' to their normal running position. Additional Wear is also minimal.

2. Your comment regarding the "throw away" good rolls is typical and would generally result in higher roller consumption statistics.

4. The catenary type idler softens the blow on both belt and roller in large ROM conditions.

5. The 'degrees of freedom' in a catenary idler allow some load centralising effects which are useful in shiftable conveyors and rapid advance/retreat systems.

6. Note that there are some 'pseudo' catenary idlers offered where the wing roller is rigidly fixed to the suspension point. This reduces the degrees of freedom resulting in a 'fixed idler without a frame'. The true catenary/garland idler has all connections being 'swivel links'. Another option is to have a spring loaded end fixing into the wing roller.

7. Take care when using on inclines - as per L Nordell. ■