Every VOLUTE™ is a multi-disc screw press. Not every multi-disc screw press is a VOLUTE™
Every multi-disc screw press operating today — fixed rings, moving rings and a slow-turning screw — traces back to one Japanese patent application filed by AMCON in February 1992. This page documents how the mechanism was developed, why it was needed, and where the original invention is recorded.
Inventor
Masaaki Sasaki, founder of AMCON
Priority document
JP H5-228695 (1992)
European grant
EP 0 581 965 B1 (1996)
Fig. 4, EP 0 581 965 B1 — cross-section of the separating element. Fixed rings (6), moving rings (30), screw (31), micro-gap g, liquid guide groove (34).
1970s
The problem
Filter cloths, wash water and clogging: the state of the art before VOLUTE™
AMCON did not begin as a machine builder. Founded in 1974 as a maintenance company, it serviced septic tanks and small wastewater treatment plants at Japanese apartment complexes. Liquid sludge from these on-site tanks had to be hauled to central treatment plants, and thickening it before transport was the obvious way to cut volume and cost — but the thickeners and dewatering presses of the day were prohibitively expensive and difficult to install at that scale.
The dominant separation principle was the filter cloth: sludge is loaded onto a permeable belt, water drains through, solids remain. The weakness is structural. Fine solids progressively blind the cloth, so the belt must be continuously cleaned with high-pressure spray water. The consequences are well known to any operator of that generation of equipment: large wash-water consumption, spray nozzle systems, oversized belts to reach capacity, frequent cloth replacement — and near-total failure on oily sludge, which blinds a cloth irreversibly.
Because AMCON’s staff maintained this equipment daily, the company knew these failure modes first-hand. In 1982 it built its first own machine — a compact filter-cloth thickener. It solved the size and price problem, but inherited every limitation of the cloth itself. The lesson drawn from it set the direction for everything that followed: eliminate the filter cloth entirely.
Archive, AMCON Inc. — sludge handling at apartment-complex septic tanks, 1970s. Liquid sludge was hauled off-site; volume reduction was the economic bottleneck.
Archive, AMCON Inc. — the first in-house machine (1982): a filter-cloth thickener. Compact and affordable, but subject to cloth clogging and wash-water demand.
1991 →
First VOLUTE™
The comb-blade screw press: a working machine with a wear problem
Archive, AMCON Inc. — the comb-blade VOLUTE™ (patent 1990, market launch April 1991): layered ring filter with intermeshing cleaning blades.
Archive, AMCON Inc. — the failure mode: load concentrated on the thin cleaning blades caused breakage after a few hundred operating hours.
R&D restarted around the screw press principle: no cloth, low rotational speed, minimal energy demand. The open question was how to keep the filter element from clogging without spray water. The first answer was mechanical scraping. A cylindrical filter was assembled from stacked rings with narrow gaps, and each flight of the screw carried thin comb-like cleaning blades that reached into the gaps and pushed intruding solids back into the screw channel.
The machine worked, was patented in 1990, and entered the market in April 1991 under the name VOLUTE™ — from the Latin voluta, a spiral. Orders grew. So did a recurring field report: blades were breaking after only a few hundred hours of full-load operation.
The company’s own patent filings are candid about the cause. The blades had to be manufactured thin and to high precision to enter each ring gap correctly; the same geometry concentrated the scraping load on the weakest part. Each blade also had to be mounted on the shaft with high accuracy, driving up cost. Wear, breakage and frequent vane replacement were inherent to the concept, not a manufacturing defect. A different self-cleaning principle was needed — one with no dedicated cleaning part to wear out.
1992
The invention
Moving rings: the self-cleaning mechanism that defined the multi-disc screw press
The decisive idea did not come at a drawing board. Riding a commuter train, founder Masaaki Sasaki watched the row of hand straps swaying with the motion of the car and asked whether rings that move could keep a filter clean by themselves — no blades, no spray. If the cylindrical filter were built from alternating fixed rings and loosely captive moving rings, with the screw itself driving the moving rings, the filter gaps would be scoured continuously by the machine’s own operation.A prototype confirmed the principle, and on 21 February 1992 AMCON filed the patent application for the “solid-liquid separating apparatus” — the multi-disc screw press. The mechanism is worth describing precisely, because it is unchanged in principle in every VOLUTE™ machine produced since:
Fixed rings (6)
Stacked in the axial direction, separated by spacers and clamped by tie bolts into one rigid cylinder. Gap width between rings: G.
Moving rings (30)
One in each gap, of thickness T < G. The difference defines a micro-gap g on each face — e.g. G = 6 mm, T = 5 mm gives g = 0.5 mm. The ring is captive but free to shift radially and to rotate.
Screw (31)
Runs inside the ring pack and conveys the sludge axially. The moving ring’s inner diameter D₅ is smaller than the screw’s outer diameter D₄, so each ring rides on the flight at a single contact point P.
Self-cleaning
Friction at P drags each moving ring into an eccentric rotation around the screw axis, sliding radially with a stroke of D₄ − D₅ per revolution. The relative motion of ring faces continuously expels solids from the micro-gaps.
Filtrate path
Water drains by gravity through the micro-gaps; a circumferential guide groove (34) on each moving ring leads filtrate emerging at the top of the pack downward, preventing re-entry into the screw channel.
Design consequences noted already in the 1992 filing: rings and spacers can be made thick (mechanical strength) while g stays small; ring diameters of 500–1000 mm are feasible; components can be resin, metal or ceramic; assembly and disassembly are simple because no part must intermesh with blade precision.
Fig. 6, EP 0 581 965 B1 — one screw revolution, states (a)–(d).
The moving ring (30) rotates about its own axis X₂ while sliding radially relative to the screw axis X₁; contact point P travels around the circumference.
Fig. 1–12
From the filing
What the 1992 application already contained
The original filing is remarkably complete. It describes not a single machine but the whole design space that AMCON and, later, its imitators would occupy for the next three decades:
Fig. 1, EP 0 581 965 B1 — longitudinal section of the complete separator: inflow (2), separating element (5), filtrate port (4), solids discharge (3), geared motor (17).
特開平5-228695, p. 8 — ring-motion sequence, inclined arrangements (Fig. 7–8), vane-piece screw (Fig. 9–10) and the twin-shaft machine (Fig. 12) in the original Japanese publication.
Thickening mode
Horizontal arrangement: flocculated sludge at 99–98.5 % moisture in, thickened solids at 97–95 % out — gravity drainage through the micro-gaps, gentle enough to preserve flocs (inlet by overflow, not free fall).
Dewatering mode
The same element inclined 45–90°: the sludge column fills the screw channel, internal pressure rises toward the discharge end, and water is pressed out through the gaps — cake below 85 % moisture from a single machine, replacing the previous two-stage thickener + press arrangement.
Screening mode
Declined arrangement for simple removal of coarse impurities from unflocculated wastewater (food processing, meat processing, hotel kitchens).
Vane-piece screw
A screw assembled from individual vane pieces on a spiral ridge, offset 1–5° each, forming stepped micro-protrusions that raise friction against the solids; decreasing the offset angle toward discharge increases internal pressure and cake dryness.
Multi-shaft (cylinder) machines
Several separating elements in one casing, geared to a single drive — the capacity-scaling concept still used in large VOLUTE™ units; however, today, each of the dewatering cylinders has its own drive.
Applications
Beyond municipal sewage sludge, the mechanism was — and remains — applicable to nearly every type of industrial sludge.
Record
Primary sources
The documents: where the invention is recorded
Priority for the multi-disc screw press rests on the Japanese application of 21 February 1992, extended internationally through the PCT and granted in Europe in 1996. Both documents name AMCON (Amukon Kabushiki Kaisha, Tokyo) as applicant and the company’s founder as inventor.
Publication
特開平5-228695 (JP H5-228695 A)
Application
特願平4-69996 · filed 21.02.1992
Published
07.09.1993
Applicant
アムコン株式会社 (AMCON INC.), Meguro-ku, Tokyo
Inventor
佐々木 正昌 (Masaaki Sasaki)
Int. Cl.
B30B 9/14 · B01D 29/17, 29/25, 29/37 · C02F 11/12
Filed
18.02.1993 · PCT/JP93/00199 (WO 93/16867)
Priority
21.02.1992 · JP 69996/92
Granted
28.08.1996 · Bulletin 1996/35
States
DE · FR · GB
Proprietor
Amukon Kabushiki Kaisha, Tokyo
Claim 1
Stationary rings + rotatable screw, characterized by floating rings in the gaps with inner diameter smaller than the screw outer diameter
The characterizing clause of claim 1 — floating rings with D₅ < D₄ — is the legal definition of the multi-disc principle. Every later multi-disc press, whatever the brand on the casing, implements the mechanism first disclosed here.
1991→
Continuity
Three decades of the same principle, continuously developed by its inventor
The multi-disc mechanism removed the last consumable from the screw press: no cloth to blind, no blade to break, no spray bar to feed. It made unattended operation practical and opened sludge types — oily, greasy, food-industry — that cloth-based machines could not touch. AMCON has manufactured the mechanism without interruption since, as the original equipment manufacturer, and has kept extending it.
A huge evolutionary leap occurred in 2021 when AMCON launched the VOLUTE DUO, a completely new type of press, which—thanks to its contactless design—took the utility value of dewatering presses to a whole new level, particularly in terms of maintenance costs.
Practice
One principle, many sludges
Three decades of the same principle, continuously developed by its inventor
A multi-disc press is not a fixed object but a configurable one. The mechanism — fixed rings, moving rings, a slow-turning screw — is invariant, but sludge is not a single material: dry-solids content, fibre content, oil and grease, particle size and floc strength all vary widely by source. The classic VOLUTE™ screw press (as distinct from the later VOLUTE DUO™) is therefore built to be matched to the feed rather than sold as one universal unit. Several parameters are set per application, without altering the underlying principle:
Screw geometry
Flight pitch, vane-piece offset angle and taper set the conveying rate and the internal pressure build-up along the cylinder. The 1992 filing already describes decreasing the offset angle toward discharge to raise cake dryness — the same lever used today to tune a press to a given sludge.
Ring-gap dimensioning
The micro-gap g is chosen from the ring and spacer thicknesses, and is frequently set differently between the thickening zone (inlet) and the dewatering zone (discharge) of the same cylinder, trading filtrate rate against cake dryness across the machine’s length.
Drive selection
Motor and gearbox rating and rotational speed set throughput and residence time; lower speed increases concentration, higher speed increases capacity. Drive is specified to the duty rather than fixed.
Because these are set per application, a single physical press can be tuned across a broad range of sludge types without redesigning the mechanism. What makes that tuning reliable is not the geometry alone but the empirical mapping from feed characteristics to configuration — which screw, which gaps, which drive for which sludge. As the original manufacturer, AMCON has accumulated that mapping over several decades and across many industries, and applies it when specifying each unit.
This is the practical distinction between the originator and later copies of the mechanism. Copy manufacturers typically offer a single fixed configuration and deploy it broadly, regardless of feed. Where the sludge departs from what that one configuration suits, the result is under-dewatering or outright failure to perform — often at the lower price point that made the copy attractive in the first place.
Every VOLUTE™ is a multi-disc screw press. Not every multi-disc screw press is a VOLUTE™ — only AMCON builds the original.