Some Reasoning:

1. 5 rolls would signify a wider belt, generally speaking, and the need to have more bearings to support the wider belt and its load.

2. 5 rolls will produce more degrees of freedom when trying to control belt tracking and transfer station ore spillage sealing under the skirtboards

3. 5 rolls will decrease the cross sectional capacity due to the first set of banked rolls are at a smaller trough angle

4. 5 rolls allow for a superior U-shape trough and control spillage better than 3 -roll

5. Although I do not recommend using garland for horizontal curve design, 5 roll would provide better horizontal tracking control due to the shape benefit, but, poorer control due the added degrees of freedom.

6. 5 rolls are more likely to cause spillage on steep inclined conveyors due to the flatter region of the center that allows a higher degree of roll back.

7. 5 rolls may create more noise due to higher degrees of freedom.

8. 5 rolls will reduce the impact force of large rock due to the degree of freedom allowed.

9. 5 rolls should not be used on downhill sections due to their nature of promoting belt mal tracking.

10. 5 rolls allow for a reduced belt binding force between idlers on different end rolls of the stringer groups due to their added degree of freedom.

Lawrence Nordell

Conveyor Dynamics, Inc.

www.conveyor-dynamics.com ■

Giridharan,

Good point. Yes, the end roll is notorious in failing bearings due to bad seal design and not having a proper weather shield. Failing in a few months, is more indicitive of a bad idler design and not so much the idler trough angle configuration.

Rolls that have greater than 45 deg orientation, often are equipped with a rain and dust shield that is mounted on the support frame. The shield does not rotate. It prevents direct impingement of refuse and rain. Idler spin keeps the contaminants from accessing the bearing seal.

Lubrication is an issue, if you do not fit the bearing with internal factory grease seal/shields. The high orientation angle does, in time, cause lubricant leakage. It would not fail for many years.

Poor roll TIR, material buildup, mal-tracking, off-center material loading, hydroscopic drying of the lubricant, yada, yada, as well as many other factors may play on the design.

Look to Rhinebraun and other like large 5 roll shiftable systems that are not plagued with faliures. Look to the Precismeca design.

Your success is near.

Lawrence Nordell

Conveyor Dynamics, Inc.

web: www.conveyor-dynamics.com ■

Another Point,

On ocassion, less than reputable bearing manufacturers sell reject bearings for great prices. The race and ball metallurgy is not to industrial standard, and the bore tolerance is not to industrial standard. The end disk concentricity to shell may not be to industrial standard. The end disk to end disk run-out, the roll run-out, and weldment warpage may not be to IS ..........

The proper analysis of the L10 or B-U life is not the simple published formula. The list of pitfalls that may make up your excessive failure rate exceeds my patients to list.

I do wish you sucess.

Lawrence Nordell

Conveyor Dynamics, Inc.

web: www.coneyor-dynamics.com ■

Dear Mr. Giridharan,

In general for the impact zone, all the 5 rollers of garland idlers have same size of bearings. The bearing size is governed by worst impact and other load on central roller. Therefore, although end rollers have unfavorable orientation resulting into axial load on to bearings, but the magnitude of this axial load is comparatively less, because impact and material momentum pressure load are negligible on end rollers. Therefore, bearings should not fail so easily.

The best way is to calculate load on each roller and work out the bearing life, instead of guess-work.

The primary advantage of 5 roller garland idlers at impact zone is that the idler configuration can yield by large magnitude in the direction of load. Now impact energy = Force x Yield distance.

Therefore, impact force will be less compared to three roll garland idlers. You already have my book, please refer serial number 6 of page 89, which mentions this aspect.

Others have already mentioned many points, which I am not referring.

Please analyze the failure reasons of concerned item, and one needs to rectify the size or specification.

Regards,

Ishwar G Mulani.

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

Email : parimul@pn2.vsnl.net.in ■