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

Screw conveyors

Figure 2: Paddle type screws mix material while conveying

Paddle type screws mix material while conveying

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

Hopper with bars across opening to isolate the screw

Figure 4: Hopper guards with restricted movement

Hopper guards with restricted movement

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

Example of sampling device

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.