Technology
The shaftless screw conveyor
A component defined by what it lacks: the centre shaft. This page explains what follows from that — technically, not as advertising.
Construction
A shaftless or coreless conveying spiral is a steel strip rolled into a helix. It runs in a conveying tube or a U-shaped trough, rests on a wear-resistant lining and is borne only at the drive end. It is driven by a gear motor, usually at the head.
That is the whole construction. What is missing is what matters: the continuous centre shaft, and the intermediate bearings such a shaft would need to be supported over longer distances.
What follows from it
The cross-section stays clear. Material that could wrap around an axle — films, fibres, wires, cables, grape stalks — finds no axle to wrap around. That is why we supply applications in which shafted screws block regularly.
There are fewer points of wear. Without intermediate bearings in the trough, the maintenance points that long screws otherwise require are gone. The wearing part is essentially the lining — and that can be replaced to plan.
The material is pulled or pushed, not cut. For pellets and other materials that must not be damaged, that is the difference between product and breakage. And because the intermediate bearings that material would otherwise be squeezed past are absent, we achieve up to two thirds more throughput than such systems.
The spiral is flexible. It follows tube bends and works on an incline and vertically. Horizontal and vertical sections can therefore be built as one continuous line — with no transfer station, and so without the most failure-prone point of a multi-part system.
The principle
The difference is what is missing
A conventional screw conveys material around a centre shaft. Anything that can wrap around that shaft eventually does: films, fibres, wires, cables, grape stems. Our spiral has no such shaft — shaftless, also called coreless. The cross-section stays clear.
- 01
Nothing wraps up
Bulky items up to roughly 400 mm, fibrous and stringy material pass straight through instead of bringing the system to a halt.
- 02
Fewer points of wear
Without a centre shaft there are no intermediate bearings in the trough — the usual maintenance points of a long screw simply do not exist.
- 03
Gentle on the material
The spiral pulls and pushes the material rather than cutting it. For pellets and anything else that must not be damaged, that is the difference between product and breakage.
- 04
Enclosed and quiet
Guided in a tube or a covered trough: virtually dust-free, low-noise and energy-efficient.
- 05
Built around the site
The system follows the building, not the catalogue. Length, incline and changes of direction are set by what is already there.
Routing
Your route sets the shape — not the catalogue
Because the spiral is flexible, the conveying line follows the building instead of the other way round. Horizontal, through bends, rising — usually as one continuous system without transfer points. The route shown applies to the flexible design, Type SL(N).
- 01
Intake
From a bunker, silo, moving floor, container or straight out of the process. The inlet geometry follows your bulk material.
- 02
Horizontal run
Trough or tube conveyor. The run is effectively endless: if it grows too long for the chosen spiral type, a transfer carries it on to the next section.
- 03
Bends instead of transfers
On Type SL(N), changes of direction run through tube bends within the same line — every transfer point saved is one fault source fewer. The rigid Type RL(N), by contrast, stays straight; there a change of direction needs a transfer.
- 04
Incline and vertical
Rising sections continue in the same line. Vertical conveyors up to 28 metres are built as the rigid Type RL(N).
- 05
Discharge
Into a boiler, press, silo, container or downstream system — metered, continuous or in intervals.
Where the limits are
No principle fits everywhere, and it helps nobody to keep quiet about that. The shaftless spiral has three limits you should know.
The lining is a wearing part. With highly abrasive media such as waste glass, ash or metal fractions it determines service life. We work there with carbide linings through to surface coatings, but a wearing part it remains.
Particle size is tied to the size built. Bulky material up to roughly 400 mm item length is possible — but only in the large ranges. With flexible systems the limit is considerably lower, between 5 and 45 mm depending on type.
Which materials those are in practice is set out in ourlist of conveyed materials from A to Z— around 250 materials our systems have already moved.
Length and throughput pull against each other. Large diameters move a lot, but over shorter distances; flexible systems bridge any length — with a transfer where needed — but at lower throughput. Which combination carries your task follows from the design — which is why the questionnaire asks in such detail.
Häufige Fragen
What is a shaftless screw conveyor?
A shaftless — also called coreless — screw conveyor moves bulk material with a conveying spiral that has no centre shaft. The cross-section in the middle stays clear. This allows fibrous, bulky and stringy materials to be conveyed that would block a conventional shafted screw.
How does it differ from a shafted screw?
A shafted screw conveys the material around a centre shaft that runs on intermediate bearings in the trough. That shaft is precisely the axle films, fibres, wires and grape stalks wrap around. The shaftless spiral has neither shaft nor intermediate bearings — removing both the most common cause of blockages and the most common maintenance point.
How is the spiral guided without a shaft?
The spiral runs directly on a wear-resistant lining in the conveying tube or trough and is borne only at the drive end. The lining is a wearing part and is matched to the material being conveyed.
Which materials can be conveyed?
Wood chips and pellets, sewage sludge, reject and refuse-derived fuels, electronic scrap, waste glass and plastics, grapes, mash and pomace, powders, granulates and dusts. In short: anything fibrous, sticky, bulky or inconsistent — and free-flowing material just as well.
What throughput and what height are possible?
Up to 600 m³/h at spiral diameters from 30 to 700 mm. Vertically we have built lifts of up to 28 metres, horizontally up to 36 metres with a single spiral and one gear motor.
Does a shaftless spiral need less maintenance?
As a rule, yes. Because the centre shaft is absent, the intermediate bearings in the trough are too — the usual maintenance points on long screws. The wearing part is essentially the lining, and that can be replaced to plan.
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