The Belt

The belt is the key element — it carries material and transmits the driving force. A conveyor belt consists of:

  • Carcass: The structural element — woven textile (EP, NN, ST) or steel cord. EP (polyester/polyamide) is the most common for general industrial use. Steel cord belts handle very high tensions and long centre distances.
  • Cover: Top and bottom rubber covers protect the carcass from abrasion, impact, and contamination. Cover thickness and rubber grade (abrasion-resistant, heat-resistant, oil-resistant, food-grade) are specified to match the material and environment.
  • Belt rating: Specified by rated breaking strength (N/mm width) and maximum operating tension. Always use the manufacturer's tension calculation before specifying belt rating.

Idlers (Rollers)

Idlers support the belt and load between pulleys. They rotate freely on sealed bearings. Types:

  • Flat carry idler: Three-roll troughing set at 20°, 30°, or 45° trough angle. Higher trough angle = higher capacity and better edge retention, but more belt flexing.
  • Return idler: Single flat roll or V-return set supporting the empty belt on the return strand
  • Impact idler: Rubber-disc idlers in the loading zone to absorb impact energy and reduce belt damage
  • Self-aligning (training) idler: Pivots in plan view when the belt moves off-centre, steering the belt back — installed every 10–20 m on long conveyors
  • Transition idler: Gradually increases trough angle near head and tail pulleys to reduce edge tension during belt flattening

Idler bearing failure is the most common conveyor maintenance task. Seized idlers (locked up, not rotating) cause rapid belt wear. Inspect weekly; replace any idlers that are seized, noisy, or visibly damaged.

Pulleys

  • Drive (head) pulley: Powered by the drive motor through a gearbox or chain drive. Lagged (rubber-covered) to increase friction with the belt. Most drive pulleys are lagged with diamond or chevron-pattern rubber for wet or oily conditions.
  • Tail pulley: Defines the return path. Has take-up adjustment to control belt tension. Often equipped with a belt cleaner on the inner face.
  • Snub pulley: Increases wrap angle on the drive pulley, increasing traction without enlarging the drive pulley.
  • Bend pulley: Changes belt direction on return path; typically unlagged.

Pulley lagging: worn or missing lagging causes belt slip, mistracking, and accelerated belt wear on the inner surface. Inspect lagging condition annually; replace when rubber shows significant wear, cracking, or delamination.

Belt Scrapers and Cleaners

Material carried back on the return strand of the belt (carryback) causes build-up under the conveyor and accelerates return idler wear. Belt scrapers remove carryback:

  • Primary scraper: Positioned at the head pulley discharge, pressing against the belt face. Polyurethane or tungsten-carbide tipped blades.
  • Secondary scraper: Positioned immediately after the head pulley on the return strand. Removes material not caught by the primary scraper.
  • Return strand cleaner (V-plow): Removes tramp material from the return strand before it reaches the tail pulley, preventing pulley wrap-up.

Scrapers require regular adjustment as blades wear — a scraper blade that has lost contact with the belt provides no cleaning benefit. Replace blades when worn to minimum height (typically 50% original thickness).

Take-Up Systems

Take-up systems maintain correct belt tension as the belt stretches over time:

  • Screw take-up: Manual adjustment at the tail end. Simple and cheap but requires regular manual tightening as belt stretches.
  • Gravity take-up: Counterweight on a moveable tail pulley carriage. Automatically maintains constant tension. Preferred for longer conveyors and higher-duty applications.
  • Winch take-up: Motor-driven, typically with load cell feedback. Used on long or high-power conveyors requiring precise tension control.

Skirt Boards and Chutes

Skirt boards are the side plates at the load point that prevent material from spilling off the belt edges. They must be sealed against the belt with flexible rubber seals (skirt seals). Worn or improperly adjusted skirt seals cause belt edge damage — the belt abrades against the rubber seal or material leaks below.