Offset vs Forward Tilted Idlers

Posted in: , on 2. Dec. 2010 - 13:46


I understand that if the idler rollers are tilted little bit in belt direction (forward tilt), this will help in belt tracking. In this case the full idler roller set are in SAME plane but NOT vertical but inclined.

But we have other type of arrangement where the idler roller planes are still vertical but are OFFSET. That means the belt touches the bottom centre roll first and then the wing rolls.

1. Do these two arrangemnts perform same way functionally.

2. Does offset type really help in belt tracking.

3. Is it OK to have the centre roll in belt exit direction instead of roller being in belt entry direction.




Re: Offset Vs Forward Tilted Idlers

Posted on 3. Dec. 2010 - 02:47

Dear Mr.Ranga,

The offset is given particularly for higher width conveyors.

When you need to change the centre roller, remove the bolts of the carrying roller frame.

Tilt frame forward or back ward according to the rollers arrangement.

In your case, backward - I visualize.

This will make the centre roller become free from the belt.

Now centre roller can be easily changed.

If the above off set is not available, it may be more difficult to replace the centre roller.

I will learn some thing new , if some one adds few points in this thread.

Thanks & regards,

To Tilt Or Not To Tilt Wing Ilders?

Posted on 5. Dec. 2010 - 04:47

Forward tilt of 3-roll carry wing rolls is pitched about two degrees forward. This causes the wing rolls to apply opposing thrust force, by friiction, on to both belt contacts with wing idlers. If the belt is not centered, the larger contacting wing idler will push the belt back to its center. This procedure was used when installation practices were poor.

There is a problem with this notion. Belt tracking by tilting only works when the rollers and belt contact zone are dry. Steering friction does not work when the contact zone betweeen belt and rollers are wet. If you tune the conveyor to steer by friction when dry, you will not be able to steer it when the belt is wet. This creates a big problem for maintenance crews.

Some still argue to use the steering aid when routing a horizontal curve.

Today we do not use this procedure for any overland. We only use belt gravity forces which work independent of friction and its many variables.

You must be able to first center the belt with load. Next, center it with respect to carry and return 3-roll system. If you properly center the belt, you can easily see:

a) all factory belt construction defects,

b) installation defects from splice contractor

c) alignment defects from badly installed idlers and idler supports

d) badly placed material onto the belt at the loading stations

e) why add idler tilt and friction irregularities?

Lawrence Nordell Conveyor Dynamics, Inc. website, email & phone contacts: phone: USA 360-671-2200 fax: USA 360-671-8450

Offset Idler Vs. In-Line Ilder Trough Arrangement

Posted on 5. Dec. 2010 - 05:11

In-Line idlers tend to support the belt with fewer axial tensile members and apply greater local force on the belt in contact with the remaining idler surfaces. Two penalties are then created.

First, the greater localized force will increase wear distress on the belt cover and cause irregular cover wear. This can lead to localized accelerated wear damage, proportional to the pressure, to the belt in the form of divits, and have proud unworn zones, between idler wing and center rolls that cause pulley lagging wear from the added local shear. The divits are formed above the steel cord helical twist. They can be at every twist pattern or every other twist pattern due to modal vibrations. Divit creation is a very complex separate topic. I will post a photo of this anomoly when back in the office.

Second, the greater localized force will increase power demand due to the viscoelastic response of the belt rubber cover under pressure differential that increases power: being proportional to kW = f(p^4/3) as has been established by many researcher. Our rheological based rubber cover viscoelastic energy model shows this effect. Professor Craig Wheelers FEA model also shows this effect.

Thus, we claim offset idlers provide improved wear and lower power than in-line idler pattern.

Lawrence Nordell Conveyor Dynamics, Inc. website, email & phone contacts: phone: USA 360-671-2200 fax: USA 360-671-8450

Offset Idler Aids Tracking

Posted on 5. Dec. 2010 - 05:16

Forgot to add:

Offset idler pattern aids in belt tracking by cupping the belt surface in a manner similar to tilting the wing rolls. If you install the idlers backwards, with offset rolls, you will see the reverse. The belt will not track properly unless you overcome the cupping with addition construction stiffnes. The added construction stiffness will then cause a greater power demand with the higher differential pressure distribution.

Lawrence Nordell Conveyor Dynamics, Inc. website, email & phone contacts: phone: USA 360-671-2200 fax: USA 360-671-8450

Re: Offset Vs Forward Tilted Idlers

Posted on 6. Dec. 2010 - 11:13

Hi Nordell,

Thx on the responses. May I know what you mean by "added construction stiffness"