Hello Michele,

Your query is not clear. You have possibly mentioned that you want the belt to follow curved path by rotation of idlers. Is it so? Are you referring to horizontal curved conveyor? Please clarify.

Regards,

Ishwar G Mulani.

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

Advisor / Consultant for Bulk Material Handling System & Issues.

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 25882916 ■

The forward tilt of wing rolls or tranverse rotation of the complete idler set are used to adjust belt tracking as well as super elevation as I have noted in another response today regarding horizontal curve engineering.

The friction generated can be estimated by calculating the lead angle from twisting the idler out of plane ( plan view) and applying the pressure from each of the center and wing roll sections being rotated out of normal.

Lateral steering force reaches the point of full slip at about two degrees rotation. That is, beyond about two degrees rotation, no furthersignificant transverse force is applied. This assumes the contact friction between belt and steel roll. Hewitt-Robins made a study of this in the 1950's. Conceptually the Steering Force is composed of:

Steering Force = SF = friction (mu) x Sum of Local Belt Force (F) = mu x F

mu = 0 at zero rotation, 100% at 2 degrees rotation (plan view)

mu = sine function of lead angle

Good Luck,

Lawrence Nordell

Conveyor Dynamics, Inc.

www.conveyor-dynamics.com ■

Dear Michele,

Referring to your question, first, I am mentioning the design steps for horizontal curved conveyors, which enables me to answer your question at the end.



1) For usual conveyors, the belt and conveyor is placed on a straight line connecting the tail pulley and head pulley.

2) The conveyor can also have curvature in horizontal plane. Such curvature is incorporated by considering the radius of suitable magnitude. This radius happens to be large in magnitude.

3) Belt tension tries to shift the belt toward the centre of curvature.

4) One needs to find out the inward shifting force at every idler pitch.

5) The aforesaid inward force is to be counteracted by following means to keep the belt stable. This force can only be applied by idlers which are in contact with the belt, and all round prevailing gravity force.

- Banking of idler i.e. idler level which is toward curve center, is somewhat higher compared to outer edge. This is like a banking of road or railway at curvature, but in opposite direction to that provided on roads / rails.

- Positioning the idler slightly skew compared to line perpendicular to belt center line. The idler side, which is towards the curvature center, will be slight ahead of outer side.

- One has to check the belt lateral stability in varied situations i.e. maximum tension and empty belt at that point. This will involve the analysis when the belt conveyor is empty, part load, full load, starting, stopping, steady running, part length loading, etc.

6) The curvature limitation as recommended by belt manufacturers are to be also examined. This curvature limitation arises due to difference in elongation (length) at inner radius and outer radius, and belt modulus of elasticity. The belt should neither buckle nor overstress. ContiTech Germany catalogue on conveyor belt system design provides calculation formulae for this.

Please note that horizontal curved conveyor, is designed and constructed considering the design steps as above and then the belt is laid on the conveyor path and it automatically remains in curved profile due to its frictional grip on the idlers & the action of various forces as mentioned above. It does not take curved path by difference in rotation of idlers etc.

Regards,

Ishwar G Mulani.

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

Advisor / Consultant for Bulk Material Handling System & Issues.

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 25882916 ■