There are two types of three-roll troughing idlers (in fixed frame category).

- In-line rollers

- Off-set rollers

In case of “in-line” idlers, all the three rollers are in single vertical plane. In case of “Off-set” idlers, middle roller is in one vertical plane and side rollers are in second vertical plane.

Both these types of idlers can be with forward tilt for side rollers, or without forward tilt for side rollers. The forward tilt means side rollers upper end is leaning by approximately 2 to 3 degrees in direction of belt travel. This leaning angle being small, it will not be visible, and so, idler manufacturer put arrow mark for belt travel direction. Hence, such idlers are directional sensitive. The idlers without forward tilt are not sensitive to direction.

If direction mark is not followed, its aligning action (of marginal magnitude) on belt will be absent. However, it may not make great difference (but one must take the benefit of this when it is incorporated in idler construction)

Regarding offset idlers, usual practice is that belt should travel from middle roller to side roller. This will give small benefit in belt life (by slightly reduced pinching effect).

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 ■