SCREW CONVEYOR is especially designed for transportation of raw materials, intermediate material like cooked material and press cake, and meals from one process step to the next.
Consist of the screw, trough U-shaped or circular, and gear motor drive and a cover for u-shaped troughs.  The length of screw conveyors can go from 1 meter up to 32 meters and the diameter is standard ø250, ø300, ø350, ø400, ø500, ø600 mm, but practical length is what can fit into a 40 foot (12 meters) container.  Very long screw conveyors can be flanged and joined together and still be transported in 40 foot container.

Construction materials can be made from mild steel or stainless steel or combinations. Some require stainless steel.
ASTW troughs mostly have a 120 degree liner made from hardened steel at the bottom of the trough to reduce wear.
The screw flight pitch is mostly 1:1 pitch/diameter when the conveyor is horizontal or little inclined, or 2/3 = pitch/diam when the conveyor is inclined up to maximum 30 degrees, only sometimes up to 45 degrees.
If more than 30 degrees a “hold back” angle-bar should be mounted at the up-turn side of the screw.
Screws in feeding, surge, metering bins or hoppers with VSD = variable speed drives can have increasing pitch for even emptying of the bin or hopper.

ASTW use screw conveyor for the following industries:

  • Rendering, all waste from slaughter house
  • Un-hogged pieces of animals like cattle bones and heads, using large diameter screw with key-hole shaped trough
  • Fish meal made from whole fish or fish waste

Beyond the actual transportation, the screw conveyor can also be used the following tasks:

  • Pre-heating with a jacket on the trough
  • Cooling by means of air flow inside the screw or cold water jacket
  • Straining, draining of fats or water

ASTW has worked for over 11 years to make efficient and reliable vertical screw conveyors to lift dried meals to be stored in bins and silos, and also for continuous re-circulation and cooling of the meal in the bin.

  • The main advantage is spec saving compared to using 3 units normal scre coneyors
  • We use an octagon = eight-sided trough made from thick stainless steel.
  • Heavy duty vertical screw with high speed
  • The feeding must be by a separate force feed screw into the bottom inlet of the vertical screw
  • Capacity up to 50 tons/hr.
  • Can be combined with air cooling by a blower mounted at the bottom

To drain off loose liquids after twin screw press or HTR – continuous high temp rendering cooker.

  • Example: Raw material 10 tons/hr. Screw conveyor diam. 400 x 10 m. Trough circular.
  • Strainer plate 180 degrees x 2,400 mm with 3 or 5mm holes or both, exchangeable.
  • Trough made of stainless steel 4.5 mm with wear plate.
  • Screws flights made of carbon steel 12 mm with option 9mm stainless steel.
  • SEW – Eurodrive gear motor 15 kW.

It is important to air-cool fishmeal just after drying. The reason is to avoid oxidation and self-heating of the fishmeal and to make the fishmeal par-ticles more free-flowing and brittle before grinding. Rendering materials are less sensitive.
The option to cooling conveyor is to use a dedicated meal cooler, which in any case will be used for larger capacities.

For plant size under 60 tons input per 24 hours one can, to save cost, use one or two units of combined screw conveyor and meal cooler in one unit. One cooling screw conveyor is mounted after the drier and one unit after the hammer mill, and both units cool down the fishmeal by airflow, connected to a cyclone and blower. The warm air outlet can be ducted outside the factory into a water scrubber or bio filter to reduce any smell from the meal.

Key-hole type screw conveyors is the best solution to transport large pieces of un-hogged raw material from abattoir to the rendering plant bin, such as large bones, rib cages and cattle heads. Lamella pumps require pre-hogging and do not pump dry material very well and have high wear and maintenance costs, and occasionally clog up.

A good example is a meat processor in Melbourne: in 2015 they installed 150 meters of key hole, 500mm diameter screw conveyors from abattoir to the raw material bin, installation partly indoor and partly outdoor.
The raw material is un-hogged to reduce deterioration, and the material is only hogged or pre-broken just before entering the processing machinery.

To be used as a metering (feeding)(surge) unit for continuous processes such as cooker, pre-heater, dryer, twin screw press and hammer mill.

  • Hopper or bin can vary in size and should be always kept full or semi full for correct feeding.
  • Mainly used with VSD – variable speed drive.
  • Mostly with variable pitch in the open (bin) area, starting the smaller pitch from the bottom for balanced emptying of the bin.
  • Some rendering materials will have bearing, seal and gear drive at the bottom and open end outlet.