Understanding the Essential Components and Classification of Conveyor Belt Idlers for Efficient Material Transport
The primary support mechanism for a conveyor belt is the idler. An idler consists of one or more rollers, each containing bearings to ensure free rolling. The rollers are supported by or suspended from a framework installed across the conveyor stringers. Idlers are the most numerous conveyor components in terms of both the number used on a particular conveyor and the variety of styles and choices available. Despite the many types, all idlers share the same responsibilities: shaping and supporting the belt and cargo while minimizing the power needed to transport the materials.
The Idler Family
Idlers are classified by roll diameter, type of service, operating condition, belt load, and belt speed. They are rated based on their load-carrying capacity and calculated bearing life. CEMA uses a two-character code to express the idler classification and implied load rating, with a letter-based code followed by the idler diameter in inches, resulting in classes from B4 to F8. Other regions may have different classification systems.
Regardless of the codes and classifications, it is essential to ensure consistency throughout each conveyor. All idlers on a given conveyor should conform to the same standards and, ideally, be supplied by the same manufacturer.
There are various general categories of idlers, depending on their intended application.
Carrying Idlers
Carrying idlers support the belt while it carries material. They are available in flat or troughed designs. The flat design typically consists of a single horizontal roll for use on flat belts, such as belt feeders.
The troughed idler usually consists of three rolls: one horizontal roll in the center with inclined (or wing) rolls on either side. The angle of the inclined rollers from horizontal is called the trough angle. Typically, all three rolls are the same length, although some sets incorporate a longer center roll and shorter inclined rollers, known as “picking” idlers. This design provides a larger flat area to carry material while allowing inspection or “picking” of the cargo.
Troughed idler sets are available as incline idlers, where the centerlines of the three rolls are aligned, and offset idlers, where the center roll has a different centerline from the wing rollers. In the offset design, the belt passes over the center roller before the wing rollers. Offsetting the idlers can reduce the overall height of the idler set and is popular in underground mining applications, where headroom is limited. Offset idlers eliminate the gap between the rollers, reducing the chance of a type of belt damage called junction-joint failure.
Return Idlers
Return idlers support the belt on its way back to the loading zone after unloading the cargo. These idlers typically consist of a single horizontal roll hung from the underside of the conveyor stringers. V-return idlers, incorporating two smaller rolls, are sometimes installed to improve belt tracking.