When the belt has little or no support in the transition zone, the belt/idler wing planes push down on the idler center roll plane, where the only support is at the first/only transition idler. All force of the transition is concentrated at that wing-to-center-roll junction. This junction design is critical to the success of the belt's long life.

If the belt stress in the junction point exceeds practical limits, the belt will fail internally at the junction. You must have a competent engineer evaluate the junction stress and fatigue behavior for/under your operating conditions.

The details cannot be provided in the forum. We do so with finite element modeling techniques. Methods are used to characterize the belt's orthotropic ( composite modulus variations in the 3 planes: x,y,z), and knowledge of fatigue limits in rubber, fabric and steel cords are applied.

This is the same condition that limits using wider idler spacing.

The points of Mr. Brown also apply. ■

Hi there..

If the unsupported transition is at the head end then I would expect the load to spill a bit off the sides of the belt assuming it to be fully loaded.

In this case you often get material on the return belt. This can get entrained in take-up or ground drive pulleys and stuff up the belt.

This is why for example, we never load a tripper conveyor more than 75%

Regards

LSL Tekpro ■

Dear Graham,

Its all in the retention time to discharge between the last troughing idler and the head pulley. If the time is short enough and load is not excessive and/or is highly cohesive, then no spillage will occur.

Raising of the head pulley can exacerbate the disturbance depending on the belt tension. ■

Hi Larry..

True of course, but yer man was asking about long unsupported transitions. If long with slow belt speed, he is looking for trouble as I described.

Tot Siens..

LSL Tekpro ■

Dear Mr. Emerson,

You are referring to long transition distance. Long in what context? Is it within twice the required transition distance or a general investigation?

If you are referring to the transition issue at tail end, because the feed point is somewhat away, then it is advisable to follow the rules for the transition zone that is providing transition idlers at appropriate spacing. Having converted the belt to the required troughing, then you will have an empty belt from this point to the first loading point. In this empty zone you can have a larger pitch of carrying idlers and consequent economy.

The other method is to provide flat idlers from tail pulley to appropriate point near first feeding point and from that point convert the belt to required troughing profile by use of appropriate transition idlers.

Sometimes, the material is getting completely discharged by tripper pulley or tripper of stacker well before the discharge pulley. In this case, people do provide flat carrying idlers at larger spacing for the empty belt near head end.

The zone for loaded belt near head end should be close to the required transition distance, and in this zone, transition idlers need to be provided. The issue of material spillage in transition zone at the head end is generally not of concern, because material will not spread out instantly etc. However, abnormally slow speed conveyor and abnormally long transition distance, to be thought of. Any abnormal / hypothetical problem to be tackled by the designer in an appropriate manner.

The effect of not providing transition idlers, is already stated by Mr. Nordell and others.

Regards,

Ishwar G Mulani.

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

Author of Book : Belt Feeder Design and Hopper Bin Silo

Advisor / Consultant for Bulk Material Handling System & Issues.

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 25871916 ■