Abrasive bulk solids shorten screw conveyor life by attacking flight faces, trough walls, and hanger bearings, so flight and trough material must be specified together with the trough loading and screw geometry rather than as an afterthought [S1][S3].
Material factors (F) in published guides span roughly 0.8 for dry cement up to 4.0+ for wet filter cake, and that four-to-five-times swing in resistance is what drives both motor sizing and the wear-rate of the conveyor components [S4]. For a side-by-side comparison of common material options used in screw conveyors, see Screw Conveyor Materials: Carbon Steel vs Stainless vs AR400.
Why Abrasion Drives the Material Decision
Conveying capacity for a screw conveyor is calculated volumetrically in ft³/hr and then converted to tons/hr using bulk density, and the same throughput formula applies whether the unit is moving plastic pellets or sand [S1]. The variables that change are the trough loading limit and the material factor: KWS notes that recommended trough loading is lower for abrasive bulk materials than for non-abrasive ones, and that the Material Factor (MF) used in horsepower calculations captures the resistance of the bulk to being conveyed [S1].
Manxing's engineering data places typical trough loading between 15% and 45% of the trough cross-sectional area, with free-flowing pellets sitting at the top of that band and sluggish wood chips held toward the bottom [S4]. For a baseline volumetric reference, see the screw conveyor encyclopedia entry, which defines the geometry that sets those loading limits. Holding loading low for an abrasive service reduces the mass sliding across each flight face per revolution, which is the single biggest lever on wear rate per ton conveyed.
Material Options: Carbon Steel, Stainless, and AR Plate
Carbon steel A36 is the default construction for normal, non-corrosive, non-abrasive service such as dry mineral powders and seeds, and it can be finished with epoxy, food-grade, or high-temperature paint [S5]. A36 has no meaningful abrasion resistance beyond mild steel, so it is the wrong pick once the bulk has any cutting or gouging character, including sand, clinker, alumina, or mineral concentrate.
Type 304 stainless is the standard pick when corrosion resistance and food-grade compliance dominate, and Bega lists a maximum service temperature of 880°C in continuous service and 840°C in intermittent service, with a sensitization window between 425°C and 900°C where intergranular corrosion is a risk [S5]. Type 316 stainless pushes corrosion resistance further for salts and chemical pulps, sharing the same 880°C continuous / 840°C intermittent ceiling, and is the right move when chlorides or wet chemicals are present alongside the abrasion [S5]. Stainless fights corrosion, not abrasion, so on pure wear duty it is outperformed by quenched-and-tempered abrasion-resistant plate.
Hardox 400, 450, and 500 are the dominant abrasion-resistant (AR) choices, with nominal hardnesses of 400, 450, and 500 HBW respectively; Hardox 450 is the most widely specified for structural screw conveyor parts because it balances wear life with formability and weldability [S5]. For broader wear-component context, the bulk bag encyclopedia page covers the upstream FIBC handling that often determines the contamination profile (and therefore the abrasive content) reaching the conveyor inlet. In practice, AR plate is used for the flight faces, flight tips, and trough liners, while the pipe, couplings, and shafts remain in lower-cost carbon or alloy steel to control total cost.
Sizing the Screw Around the Abrasive Material
Two geometry rules dominate abrasive service: a screw diameter of at least four times the largest particle size to prevent jamming, and trough loading held to the lower end of the 15% to 45% range for sluggish or cutting materials [S4]. Screw diameter in standard industrial units runs from 6 inches up to 24 inches, with larger custom sizes for extreme capacities [S4].
Pitch selection is the second lever: standard pitch (pitch = diameter) suits most free-flowing material, short pitch (about two-thirds of diameter) gives better control on inclined conveyors and for fragile products, and long pitch (greater than diameter) is reserved for high-capacity, low-friction products like grain [S4]. For inclined abrasive service, short pitch combined with reduced RPM is a common combination, because it lowers the sliding velocity at the flight face. Variable pitch screws are used less for abrasion control and more for uniform discharge in metering duties [S4].
Shaftless screws are commonly chosen for wet, sticky, or stringy abrasive materials such as grit, dewatered sludge, or screenings, because there is no center pipe or hanger bearing inside the trough for the material to wrap or pack against. For a comparison reference on related drive and coupling hardware, see Taper Bushing Hubs on Industrial Jaw Couplings: Specs, Sizing, and Selection.
Comparing Material Choices on Decision Criteria
The common material choices line up against four decision criteria as follows. Cost (per kg of fabricated flight or trough liner) is lowest for A36 carbon steel, intermediate for AR400/Hardox 400, and highest for 304/316 stainless and Hardox 500. Abrasion resistance (wear life per ton conveyed) is poor on A36, good on AR400/Hardox 400, better on Hardox 450, and best in this group on Hardox 500, while 304/316 stainless offer no meaningful wear advantage over AR plate. Corrosion resistance is essentially zero on A36, limited on AR plate (it will rust if not coated or lined), good on 304 stainless in atmospheric and mild chemical service, and best on 316 stainless in chloride and chemical-pulp service. Maximum continuous service temperature tops out around 400°C for standard AR plate without special temper considerations, while 304 and 316 stainless are rated up to 880°C continuous / 840°C intermittent by the manufacturer, and A36 carbon steel sits between, limited mainly by the paint or lining system [S5].
The decision tree is short: if the bulk is dry, non-corrosive, and mildly abrasive, use A36 with hard-facing on the flight tips; if the bulk is abrasive and mildly corrosive, specify Hardox 450 flights and trough liners with an A36 or 304 pipe and shaft; if the bulk is corrosive-abrasive (wet chemicals, salt, pulp), use 316 stainless for the product-contact surfaces, accepting a wear-life penalty relative to AR plate, or a hybrid of 316 trough with Hardox flight faces. KWS also reminds designers that lump size is governed by the radial clearance between the outside diameter of the center pipe and the inside radius of the trough, so enlarging a screw from 9 inches to 12 inches in an abrasive service often lets a marginal material handle lumps it could not handle before [S1].
Component-Level Wear Hot Spots
Flights, trough liners, and hanger bearings carry the bulk of the wear budget in an abrasive service, which is why KWS publishes a component series (alphabetical code for general component class, numerical code for hanger bearing recommendation) and ties the recommendation to material class rather than to a single material [S1]. Heavier-duty component series are recommended for sluggish and abrasive bulk materials, with lighter-duty construction reserved for free-flowing, non-abrasive products [S1].
Shaftless screws eliminate the center pipe and most hanger bearings, which removes two of the three dominant wear sites in a shafted abrasive-duty conveyor, and this is one of the reasons shaftless units dominate in municipal wastewater and grit handling. For an adjacent selection question on bucket elevators handling similar abrasive lump feeds, see Round link vs bush vs plate chain bucket elevators: selection reference.
What This Specification Is For, and What It Is Not For
This material selection framework is for continuous-duty industrial screw conveyors moving dry to damp, free-flowing to sluggish abrasive bulk solids at ambient or moderately elevated temperature, where the design target is years of service between flight and liner replacements. It is not a complete basis for high-temperature (above ~400°C with AR plate) or sanitary bio-pharma service, where metallurgy, surface finish, and cleanability constraints dominate over abrasion. It also does not replace site-specific material testing: a shear cell or abrasion index test on the actual bulk is the only way to confirm the assumed Material Factor and the wear rate before procurement [S4].
The two trackable signals to watch over the next design cycle are: (1) whether suppliers continue to publish Hardox 450 as the default flight-and-liner plate (a 450 HBW nominal hardness remains the dominant AR grade cited for screw conveyor parts) [S5], and (2) whether published material factor F for wet filter cake and similar sludges shifts in updated CEMA-aligned guides (current published F values reach 4.0+ for wet filter cake) [S4].
Spec-level background on the components involved: ball screw.