Bearing Up.
First you buy some regular schedule pipe from the stockholder; making sure there is enough machining allowance to provide shaft to outer shell concentricity within the final assembly tolerances you want. Do a sum for the bending fatigue bit, if you must. Ideally it should have minimum rolling inertia but if you expect the manufacturer to skim the inner face of the pipe he'll probably tell you where to stick the roller.
There is a European Standard but most folk find it easier to just buy idlers from those nice people who wrote/influenced the standard in the first place. Have a glance through the Rulmecca book....you haven't already...have you?
Strictly speaking 'roller' is the correct description. ■
Re: Idler Shell Thickness
What is the difference between "idler" and "roller" ?
Regards, ■
Idler / Roller
Dear S. Ganesh,
in the area around here the idler is defined as the complete (rigid) station, with 1, 2, 3 ..+ rollers and with the support. The garland is named in short as such, in length: garland idler, containing suspended rollers, links, hooks.
But then there's also definitions for both types as: set, station, ...
But the roller is always the element with the rotating shell, the bearings etc.
Regards
R. ■
Idler Shell Analysis & Thickness Selection
You should be requesting this information from the idler manufacturers and their standards.
The selection is based on some simple criterion -to name a few pointers:
1. Based on idler diameter - carry the shell stress to the end disk connection for the expected spacing
2. Make allowances for standard scuffing (alignment) wear and corrosion
3. Be compatible with the end disk design for welding, swaging, or other interference factors
4. Type of materials for shell and end disk - polymer shell or shell covers, and similar end disk properties are becoming vogue when noise is a factor
5. Control stress in shell and end disk when material build-up is a factor
6. Life rating is not a factor such as sand & gravel, low volume production, low mine or quarry life, etc.
7. Rock size, belt speed, idler spacing, et al may require shell thickness to sustain high impact forces.
Typically, low density ore, and smalll idler spacing only require a shell thickness of ~ 3.5 mm
Medium duty small operations use 4 mm
Typical coal operation use 5 mm
Typical heavy duty, high tonnage, hard & large rock operations specifiy 6 mm
These values are in part a product of extended use in the various fields.
If you are serious about the question, talk to a number of well know suppliers with good track records and extended user references. If you are fishing for some techniques, then you are asking for IP, which many providers pay to develop and keep under wraps. It would be easy for any interested party to apply a FEA model to validate the numbers for stress fatigue. CDI does this on a routine, when designing overland systems, high tonnage system, and systems where optimization of all components lead to a TOTAL LIFE CYCLE COST OPTIMIZATION. ■
Idler Shell Thickness Selection
A major factor not given above is:
8. Idler shell dimensional tolerance by Total Indicator Reading (TIR).
Sorry for this omission. I am sure others can contribute to the generalities of this thread. ■
Shells Bells
Dear Mr. Shakee,
there's no standard as such that i know of. An existing european standard for coal mine underground operation specifies a minimum thickness of 4 mm, but then defines influence parameters just as Mr. Nordell here above which must be considered. So it is a general design decision to be made. All that is well explained above, from a mechanical point of view i'd like to underline especially the necessary stiffness of the shell / bearing support / bearing sector. For heavy duty rollers of diameters around/above 200 mm i've seen thicknesses greater 7 mm.
So, case 1 if you received a supply of doubtful rollers with thin shells you probably would like to consult an in-depth knowledgeable consultant as offered above.
Case 2 you want to do sthg on your own: This requires thorough engineering and does not boil down to only one simple formula as --> required shell thickness = f (x,y,z), in addition: there's testing to be done etc. Again pls. cf. to Mr. Nordells post.
Regards
R. ■
Idler Roll Shell Thickness
Have a look at South African Standard SANS 1313 - this defines an idler and a roll and also gives recommended minimum shell thickness based on roll diameter.
Others have given good indications as to factors influencing selection such as belt speed and type of material being conveyed.
SANS 1313 comes in 3 parts and is possibly the top idler specification available in that it specifies all critical dimensions to ensure the interchangeability of complete idlers or idler bases (transoms) or rolls from different manufacturers.
The specifications also cover performance aspects and also maximum loading for specific series of rolls (defined by shaft diameter and bearing type)
Cheers
Adi ■
Polymer Roller With Individual Shafts
Polymer rollers are less weight compared to steel rollers. If each bearing is fixed on an independent shaft, the roller life can be much increased.
Are such ideas covered in the standards ?
Regards, ■
Idler Shell Thickness
How is idler shell thickness calculated?
Is there is any standard for calculating the same?
Regards,
Shakee. ■