Idler dimensions are fixed by CEMA, DIN, SABS, AS & MHEA to name just a few authoritative bodies.

Some companies feign adherence to a Standard and when the Owner finds out that the adherence is missing he finds himself well shafted and the Contractor is in the money for replacements. Ask some emerging salesmen what idlers they are fitting and they "...will have to come back to you on that one." Such firms should be binned as soon as the phone has clicked off. ■

Hi there..

If you have the face length of a roll (preferably to a standard like SABS 1313), then add 10mm to get the gauge length, which is from support bracket to support bracket. Then, for shaft deflection calcs etc, subtract 50mm from each end to get the bearing centres.

Cheers

Taggart LSL ■

Hello,

Your query is about bearings centre to centre distance for roller of particular face width. This means you have to find out the distance from centre line of bearing width to the roller edge and thereafter the distance from there to the bracket support centre line at spindle. The distance between centre of bearing width and spindle end support point is known as bending arm (BA). This BA is very important because bending moment and stresses are proportional to its dimension. Therefore the designer tries to keep BA value minimum i.e. bearing assembly at roller end should be compact to the extent possible.

You have two options to know the BA value. If idler rollers are boughtout items for you / your company, then refer to the prospective suppliers and get this value. Roller end assembly construction is standardized feature for each company and they will very rarely make it tailor-made to your need provided your order is in huge quantity.

The other option is that you are developing the arrangement of the end assembly and then you want to calculate this dimension. In this case some information is as below:

1) Bearing inner race has to firmly remain in place on spindle.

2) Bearing outer race has to firmly remain in place in housing.

3) There will be one inner seal (at bearing back side) to prevent grease leakage in roller shell.

4) There will be one set of outer seal (at bearing front side) to prevent grease leakage on outer side (atmosphere).

5) There will be some circlip/s to keep the components in place.

6) The components shape, size, etc. should be such that while fitting from open end, one by one, should keep definite clearance / space, automatically, in foolproof manner.

7) Grease quantity in / around bearing chamber should be adequate to provide lubrication for design life (say 3 - 4 years, etc.).

8) Finally the end assembly i.e. roller so designed has to be sold in market, and therefore same should be at least comparable to available rollers for performance and economy. Otherwise it will be of no use. Hence designer has to first study various products in market, technically and commercially, and then commence his activity.

9) Decision about component material, manufacturer, outsourcing and assembling methods, requires extensive knowledge about workshop means, processes and facility required in shop, and also about the material sources.

10) After concluding end assembly design, find out load acting on roller and thereby bearing life, size, spindle stress, deflection , etc. and then you will have required information (BA value).

As will be seen deciding about roller assembly is a very comprehensive issue, and it happens to be team decision, along with management sanction for investments to create facility and to put in practice.

Ishwar G. Mulani

Author of Book : Engineering Science And Application Design For Belt Conveyors (new print November, 2012)

Author of Book : Belt Feeder Design And Hopper Bin Silo

Advisor / Consultant for Bulk Material Handling System & Issues.

Pune, India.

Tel.: 0091 (0)20 25871916

Email: www.conveyor.ishwarmulani.comwww.conveyor.ishwarmulani.com ■