Shaftless Screw Conveyor Selection Guide for Sugar Mills and Paper Mills

Why Sugar and Paper Mills Need Shaftless Screw Conveyors

Bagasse and paper pulp waste are typical fibrous bulk materials. Bagasse has long, loose fibers and retains significant moisture after milling. Paper mill rejects contain plant fibers, pulp lumps, and shredded material with uneven particle size. In shafted screw conveyors, these fibers wrap around the center shaft and pack progressively tighter between the shaft and the screw flights, eventually causing jams, motor overload, and shutdowns for cleaning.

A shaftless screw conveyor eliminates the center shaft. Material is pushed by a continuous ribbon flight along a U-shaped trough, leaving no shaft surface for fibers to wrap around and no space between shaft and flights for pulp lumps to accumulate. This is why sugar milling lines and paper mills commonly use shaftless configurations to handle bagasse, coarse pulp, and rejects.

Key Selection Parameters

Screw Diameter and Conveying Capacity

The WLS series offers six standard sizes with screw diameters ranging from 150mm to 500mm, covering a maximum conveying capacity of 0.5–28 m³/h. Bagasse has low density and high bulk volume, so volumetric selection often leads to WLS400 or WLS500. For paper mill rejects containing pulp lumps, a larger diameter is recommended to accommodate irregular bulky material.

Conveying Distance and Inclination

A single unit can convey up to 30 meters (WLS400/WLS500 sizes) at an allowable working inclination of 0°–30° (WLS250: 0°–25°). Common layouts include horizontal conveying of bagasse from the milling shop to the boiler fuel bin, and short-distance transfer of rejects from the waste pit to baling or treatment stages. Capacity decreases when inclination exceeds 20°, so a design margin should be reserved.

Material Selection

Bagasse and pulp rejects are moisture-bearing and slightly acidic, and coastal mills face additional salt spray. Stainless steel (commonly 304) for both trough and screw is recommended to extend maintenance intervals. The U-shaped trough uses flanged sections joined by bolts, allowing the conveyor length to be adjusted to match each process stage.