PM-CY series · modified cycloidal pinwheel drive

The screw mixer is fine. The reducer on top of it is the problem.

A conical screw mixer hangs a loaded screw from a gearbox that the catalogue never intended to carry. We modify the output bearing, the thrust capacity, the sealing and the flange — then machine it to the bolt circle you already have. 500 to 5000 litres.

Modified cycloidal gearmotor mounted through the bottom head of an unpainted conical screw mixer shell, in the assembly bay — A modified cycloidal drive mounted on a mixer shell before painting: rigid output flange, thrust pair, double-lip seal with dust collar, and an IEC motor interface.

Six ways a catalogue reducer dies on a conical mixer

We learned this by being shown broken gearboxes, not by reading a datasheet. Every row below is a failure we have seen twice or more.

Observed failure modes and the fixMost of these show up between month four and month eighteen, which is exactly the window in which a warranty claim becomes an argument.
What fails	Why it happens on a conical mixer	What we do about it
Output bearing cracks the housing boss	The screw is pushed into dense powder and the whole thrust lands on one bearing. Catalogue units are rated for a supported, mostly radial driven load — not a suspended screw.	Two tapered roller bearings in opposition, sized for your calculated axial load with a 1.5× margin, sitting in a thicker boss machined after welding.
Oil weeps from the top cover and shaft entry	Vertical mounting keeps the entire gear set immersed. Standard lip seals assume a horizontal shaft with a splash, not a static head of oil.	Double-lip seals, a labyrinth dust collar, and an oversized breather with a drain-back that actually returns oil.
Powder gets into the bearing race	A blending room is full of fine dust, and it finds the one gap in the shaft entry. Then the race scores and the gearbox howls.	Labyrinth plus lip as standard, and a purge-able entry gap on request for talc, calcium carbonate and silica duties.
Output flange bolts shear	Starting a full cone takes two to three times the running torque. A key alone is not enough, and the bolt circle takes the shock.	Thicker flange, 10.9 bolts, dowel-located hub, and key plus bolt circle sharing the load rather than the key carrying it alone.
It runs hot; the oil breaks down early	Single-stage cycloidal units at high ratio are not efficient machines, and the mixer runs for hours without resting.	Ratio chosen so the input stays near 1450 rpm instead of being over-driven, larger sump, and an oil cooler where ambient exceeds 40 °C.
The screw back-drives when the motor stops	A loaded screw wants to turn the reducer backwards. Most catalogue units have no backstop, so the batch keeps moving after you think it stopped.	Integral backstop fitted, or we specify the holding brake with you and quote the motor flange to take it.

What we change, item by item

01 · LOAD PATH

Output bearing group and thrust pair

Tapered rollers in opposition, set to a measured end-float at assembly. Bearing brand stated on the quote — SKF, NSK or HRB — and we do not substitute silently.

02 · STRUCTURE

Housing, boss and flange

Ribbed, stress-relieved and machined after welding so the output face is square to the shaft within 0.05 mm. That squareness is why the thrust bearings last.

03 · GEARING

Cycloidal discs and pin bushes

Discs ground, not just punched. Pin bushes carburised and hardened to 58–62 HRC. Case-hardened eccentric bushing, matched to the input shaft rather than picked from stock.

04 · SEALING

Vertical-duty seal arrangement

Double lip, labyrinth collar, oversized breather, and a shaft sleeve that replaces instead of the housing being scrapped once a groove is worn into it.

05 · LUBRICATION

Oil, sight glass and service access

Synthetic PAO gear oil as standard for export. Fill and drain positioned so you can service the unit with the mixer standing where it is.

06 · INTERFACE

Your bolt circle, your motor

Machined to the drawing of the mixer you have or the mixer you are building. IEC motor flange, your country's motor brand, or we supply the motor.

Selection table

Start from mixer volume and bulk density, then check the axial number. If your batch density is above what is listed, tell us — that is the variable that changes the answer most.

PM-CY drive selection for single-screw conical mixersOutput speed is 1450 ÷ i on a 4-pole input, so you can check every row yourself. Service factor 1.5 on the axial load; batch density as shown. Run the screw slower on a VFD — the speed your material wants is yours to set, not ours.
Mixer	Screw Ø	Density to	Screw speed	Reducer	Ratio i	Rated torque	Max axial	Motor
500 L	219 mm	0.8 kg/L	≈ 63 rpm	PM-CY-8060	23	1 600 N·m	22 kN	4 kW
1000 L	273 mm	0.8 kg/L	≈ 50 rpm	PM-CY-9070	29	2 800 N·m	30 kN	5.5 kW
1500 L	325 mm	0.9 kg/L	≈ 41 rpm	PM-CY-10080	35	4 200 N·m	38 kN	7.5 kW
2000 L	377 mm	0.9 kg/L	≈ 31 rpm	PM-CY-11080	47	6 000 N·m	48 kN	7.5 kW
3000 L	430 mm	1.0 kg/L	≈ 25 rpm	PM-CY-11090	59	9 500 N·m	65 kN	11 kW
4000 L	530 mm	1.0 kg/L	≈ 20 rpm	PM-CY-12100	71	13 500 N·m	80 kN	15 kW
5000 L	600 mm	1.2 kg/L	≈ 17 rpm	PM-CY-13110	87	19 000 N·m	100 kN	18.5 kW

Single-stage ratios we stock parts for: 9, 11, 14, 18, 23, 25, 29, 35, 47, 59, 71, 87
Two-stage where the screw must run slower than 20 rpm, with a larger thrust pair. Same torque, lower power, and a bigger axial number — at that ratio the thrust pair is what limits you, not the gear teeth. 121, 187, 289, 391, 473, 595, 807
Double-screw cones need a different calculation entirely. Send the drawing and we will do it; do not size a twin-screw from this table.
Everything here is also built for the reverse case: you have a good gearbox and a worn cone. We will quote the cone, screw and lid without a drive.

Ordering from a drawing — or from a photo

This is the part that makes a retrofit work. If your mixer is stopped because a gearbox failed, we can usually build a unit that drops onto the holes that are already there.

Send us these ten things

Clear photo of the old reducer nameplate, ratio and serial.
Bolt circle: number of holes, hole diameter, pitch circle diameter, flange thickness.
Output connection: shaft diameter and length, keyway, or hollow-bore diameter.
Mixer volume, screw diameter and screw pitch.
Material, its bulk density, and maximum fill weight.
Required screw speed in rpm.
Motor you have, or the voltage and frequency you need.
Mounting orientation and whether you need a backstop or brake.
Ambient temperature, dust level, and whether washdown happens.
Destination port and whether you want a landed price.

What comes back

Within one working day: a marked-up outline drawing showing our interface against your dimensions, the ratio and torque we recommend and why, the bearing and seal arrangement named by brand, and a price split into base unit, modifications, motor, spares and packing.

If we think your existing bolt circle cannot carry the load, we say so in the same email and show you the machining needed to fix it. A drive that fits but fails in a year is not a saving.

Send your drawing

Oil, climate and the tropics

Small thing, large consequences. We fill for the climate the machine will live in, not the climate the factory is in.

Standard export fill

Synthetic PAO ISO VG 220. Runs stable in a 45 °C plant room and does not thin out in Gulf summer. Food-grade H1 available for mixer drives above open product.

Cold start

For altiplano, Patagonia or Central-Asian sites below −10 °C: VG 150 synthetic and a heater strip in the sump with a thermostat.

Service kit

Two years of filters, breather elements, seal kits and oil shipped with the drive. Cheaper by sea with the machine than by air later.

Catalogue unit against ours, same frame size

What the modifications buy youSame housing centre distance, same footprint, same price band. The differences are all in the load path and the sealing.
Item	Catalogue cycloidal reducer	PM-CY modified drive
Output bearings	One deep-groove ball bearing	Tapered roller pair in opposition, set to measured end-float
Axial capacity	Not stated for suspended-screw duty	Stated per size, with a 1.5× design margin on your batch weight
Shaft sealing	Single lip, horizontal assumption	Double lip + labyrinth collar + replaceable sleeve
Output flange	Standard pattern, key-driven	Your pattern, dowel-located, key and bolts sharing load
Housing squareness	As-cast datum	Machined post-weld, ≤ 0.05 mm runout on the output face
Backstop	Not offered	Integral, or brake interface specified with you
Oil for hot climate	Mineral VG 220	Synthetic PAO as standard
Documentation	Generic sheet	English GA drawing, bearing list, torque table, spare-part drawing to your tag number

Interfaces we supply with the drive

Rigid flange couplingShaft and key to your boreMotor adapter flange (IEC)Belt guard and coupling guardSupport frame and vibration padsHolding brakeIntegral backstopOil cooler and thermostatVFD for soft start on a full coneDust hood over the lid

We do not build pressure vessels — no reactors, no jacketed vacuum tanks, no code work. A conical mixer body is sheet-metal fabrication rather than code pressure work, so we can quote you the cone, screw and lid off the same drawing if you want one point of responsibility. If you would rather buy the cone locally and the drive from us, that is usually the cheaper call, and we will tell you what to check on the fabricator’s quotation.

Send a photo of the nameplate.

That is usually enough to start. We will tell you within a day whether a modified unit drops onto your existing bolt circle, and what it costs.

Request a quote Send a photo on WhatsApp