Screw conveyors

While belt conveyors are open and often used to move discrete items, a screw conveyor is often enclosed in a trough and used to transport loose materials from one place to another, including concrete, dry sand, plaster, chalk, or grain. A feed screw is also used for feeding lumpy materials like gravel, limestone, or ice.

While this guidance has not been updated to reflect current work health and safety legislation (the Health and Safety at Work Act 2015 and regulations), it may still contain relevant information and practices to keep workers and others healthy and safe.

Please read this guidance in conjunction with all relevant industry standards that apply to you as a PCBU. This guidance will be progressively reviewed and either updated, replaced with other guidance, or revoked.

The screw is mainly enclosed for most of its length, however feed (inlet) and delivery (outlet) ends may be exposed where materials enter and exit the conveyor.

Screw conveyor principles apply in appliances, including mincers. In a mincer, material for mincing is carried by the screw with necessary force, towards a grating where it is forced through holes to cut it into smaller pieces.

Figure 1: screw conveyors

[image] Cross section of screw conveyor showing enclosed screw with labels and red arrows pointing to other key components

Figure 2: paddle type screws mix material while conveying

[image] Paddle type screws mix material while conveying

Hazards

  • Entanglement with turning screw
  • Contact, impact or entanglement from moving parts
  • Troughs – reaching or falling
  • Electrical current
  • Slips, trips & falls
  • Entrapment from unexpected movement (during maintenance, cleaning & repairs)

Personal protective equipment (PPE)

  • Eye protection
  • Foot protection
  • Dust protection

Tasks

Task – feed the materials

Hazard

Entanglement with turning screw

Harm

  • Trapped hands, feet or other limbs in a nip
  • Crush injuries

Controls

  • DESIGN should ensure the hazard of the screw is isolated.
  • FIX guarding.
  • RESTRICT guard openings to prevent hands reaching the rotating part of the conveyor (auger).
  • FIT inlet ends with hoppers.
  • NEVER WEAR jewellery or loose clothing, and TIE BACK long hair.

The turning screw can trap limbs. It can also trap loose clothing, long hair, and dangling jewellery. Traps at screws are most commonly at the feed or delivery end. However if the screw turns while the guards are off, traps are exposed along its whole length.

Hazard

Contact or impact from moving parts

Harm

  • Bruising
  • Fractures

Controls

  • GUARD prime mover and moving mechanical transmission to isolate moving parts.

Figure 3: hopper with bars across opening to isolate the screw

[image] Side view of hopper with bars across opening, and isometric view showing how guard openings are smaller at end "A"

Figure 4: hopper guards with restricted movement

[image] Hopper guards showing loops to restrict movement, with labels and red arrows pointing to other key components

Wheel spacing must ensure stability if product is in the top half only of the raised auger, including when the ground is uneven.

Task – sample collection

Hazard

Troughs – reaching or falling

Harm

  • Impact injury from fall
  • Amputation or crushing from being caught in a nip

Controls

  • FIT a bend to the delivery end of the trough, with dimensions to prevent reach.
  • FIT high walls to prevent reaching or falling into the trough.
  • FIT secondary safeguarding for open troughs, e.g. railing or fencing.
  • DESIGN collection points to ensure that hazards remain isolated.
  • LOCK-OUT power before starting work within the trough.

Delivery ends can be safe by position, ie. too high for reach into the hazards, or the delivery end can be designed to isolate the screw.

Figure 5: example of sampling device

[image] Example of sampling device showing sliding plate and conveyor trough

Other (non-mechanical) hazards

Hazard

Electrical current

Harm

  • Electric shock from faulty wiring

Controls

  • If the prime mover is electric, regularly TEST the portable auger to maintain electrical safety.

Hazard

Slips trips and falls

Harm

  • Trapping
  • Cuts
  • Bruising

Controls

  • KEEP up-to-date housekeeping procedures.
  • KEEP the area around conveyors clear of slip and trip hazards.

Task – maintenance, cleaning & repairs

Hazard

Entrapment from unexpected movement

Harm

  • Crush injuries
  • Bruising
  • Fractures

Controls

  • LOCK-OUT all power supplies before maintenance, cleaning or repairs.
  • An auger or screw conveyor that does not have a screen or cover, or is not secured by bolts or clamps, MUST have an INTERLOCKED COVER that cuts the power when raised and does not re-start until the cover is replaced and the starter activated.

Cleaning and maintenance will almost always require removal of covers or guards. The screw MUST not start until people are clear and guards replaced.

Download fact sheet

Screw Conveyors (PDF 465 KB)