Custom OEM Magnetic Couplings

FAIZEAL

OEM Magnetic Coupling Outer Rotor

Why the Outer Rotor — and Why It Defines the Coupling's Real Capacity

A magnetic coupling's outer rotor is the part most engineers see, most operators touch, and most often mis-specify. It is the larger, cup-shaped, driven-side component that mounts on the pump shaft, surrounds the containment can, and locks magnetically to the inner rotor's rotating field. Its diameter, its magnet count, its cup body, and its sealing determine the coupling's actual torque capacity, its pressure rating, and how long it survives in chemical, sanitary, or cryogenic service.

For a matched magnetic coupling set, the inner rotor and outer rotor must be designed as one circuit. Yet on most OEM drawing packs they are sourced separately, and the magnetic mismatch shows up only after install — as torque shortfall, as overheating, as demagnetization in service. FAIZEAL has built inner and outer rotors together since 2011. Both halves are on one engineering thread, balanced as a matched set, and shipped with a circuit-spec report you can hand to your customer.

This page is for the outer rotor — the cup, the magnet ring, the drive-side hub interface — and the engineering choices that make it survive in your application.

What Is a Magnetic Coupling Outer Rotor?

A magnetic coupling outer rotor (also called mag-drive outer rotor, driven-side magnet ring, or outer magnet cup) is the larger, can-side component of a magnetic coupling. It mounts on the driven shaft (pump impeller, mixer, agitator, fan), carries a ring of high-energy permanent magnets arranged in a multi-pole or Halbach pattern on its inner circumference, and synchronizes with the inner rotor's magnetic field through the containment can. The outer rotor is always larger than the inner rotor in diameter — the annular gap between them is the magnetic air gap plus the can wall.

A FAIZEAL outer rotor is typically built as:

• A one-piece cup or drum body in 316L stainless steel, duplex stainless, 17-4PH, 4140, titanium, Hastelloy, or Inconel

• Precision-ground sintered NdFeB (or SmCo) arc segments arranged on the inner circumference in a radial multi-pole or Halbach array

• Inner magnet ring encapsulated in epoxy (potted construction) for chemical and moisture resistance

• Welding, brazing, or spin-closed seam on the cup body to make a hermetic sealed unit

• Customer-specified shaft bore: press-fit, keyed, splined, or with a proprietary locking feature

• Optional banded construction (outer sleeve) for high-rpm or hazardous-duty service

• 100% dynamic balance to ISO 1940 G2.5 / G6.3 per order specification

Every dimension, every pole count, every grade is engineered to match your inner rotor and your actual service envelope. We do not ship catalog outer rotors.

Why the Outer Rotor Is Always Larger

This is a simple geometric fact with deep consequences. The outer rotor's magnet ring sits outside the containment can; the inner rotor's magnet ring sits inside. The can wall plus the air gaps on both sides add up to the diameter difference. That diameter difference is the largest single contributor to torque capacity in a magnetic coupling — torque scales with the cube of the air-gap radius.

A larger outer rotor, at the same axial length, transmits dramatically more torque than a smaller one. It also allows more poles, which reduces torque ripple and magnetic cogging. That is why OEM coupling engineers will push the outer rotor as large as the housing envelope allows, and why the outer rotor — not the inner rotor — usually defines the maximum torque a given coupling can deliver.

Where FAIZEAL Outer Rotors Are in Service

• Magnetic drive centrifugal pumps and canned motor pumps (API 685, ASME B73.3) for acid, alkali, solvent, and hydrocarbon transfer

• Hermetic agitators and mixers for pharmaceutical API, biotech, and sterile fluid production

• Sealless centrifugal pumps for semiconductor wet process (HF, SC1, SC2, NMP, IPA, Cu plating chemistries)

• Food and beverage processing — sanitary outer rotors for syrups, dairy, oils, and CIP-cleaned lines

• Cryogenic pump and compressor outer rotors for LNG, LPG, and air-separation plants

• High-temperature hot-oil and molten-salt pump outer rotors in solar and chemical plants

• Hazardous-area ATEX / IECEx equipment where zero spark risk is mandatory

• Diesel and gas turbocharger magnetic couplings, hydraulic pump couplings, and marine propulsion couplings

• Reverse-engineered replacement outer rotors for legacy OEM couplings (Sundyne, Sundstrand, Magnatex, Tuthill, CECO, March, etc.)

If your process fluid must never touch a mechanical seal, the outer rotor is the visible side of that promise — and we have already built a version for your chemistry.

Full-Custom Engineering — Designed to Your Inner Rotor and Your Can

Most magnetic coupling problems show up at the interface between inner rotor, can, and outer rotor. We engineer all three in-house, so the geometry is closed on a single drawing tree, not negotiated across three suppliers. Tell us the inner rotor you have (or the one we are also building) and the can you need; we will back-propose a matched outer rotor.

Size — No Upper Limit

• No upper size limit. Outer rotors from Ø30 mm precision instruments to Ø800 mm+ heavy-duty process pumps

• Outer / inner diameter, axial length, shaft bore, and pole count are all per your drawing

• Need an odd aspect ratio or a non-standard pole pitch for an existing OEM pump? Tell us the OEM model and the magnetic circuit spec — we reverse-engineer the outer rotor and ship a drop-in

Cup / Drum Body Material & Construction

• 316L stainless steel — the workhorse for chemical, pharmaceutical, and food-grade service

• 2205 / 2507 duplex stainless for chloride-rich, offshore, and sour-service duty

• 17-4PH precipitation-hardened stainless for high-torque, high-rpm applications

• 4140 alloy steel for cost-driven high-torque service

• Titanium (Gr2 / Gr5) for low-mass and high-corrosion service

• Hastelloy C-276 / C-22 and Inconel 625 / 825 for hot, oxidizing, or halogenated chemistry

• Construction: one-piece welded (TIG / laser) or brazed cup / drum; spun-closed; clamshell (two-piece) for in-situ magnet service

• Internal surface finish: as-machined, bead-blasted, passivated, or electropolished (sanitary service)

Magnet Grade & Pole Count — Matched to the Inner Rotor

• Magnet grade: N35 to N52 for NdFeB; SH / UH / EH for high-temperature and high-coercivity duty

• Sm2Co17 (SmCo) for sustained operation above 200 C, or for oxidizing chemistry where NdFeB coatings are at risk

• Pole count matched to the inner rotor: 4 / 6 / 8 / 12 / 16 / 24 / 32 poles — or any non-standard count you need

• Halbach array option (single or dual layer) for ~20-30% higher torque density in the same envelope

• Pole-pitch and magnet-arc width tuned to your can-side air gap and your torque-ripple target

Shaft Bore & Mechanical Interface

• Press-fit, keyed (DIN 6885 / ANSI B17.1), splined, threaded, or with a proprietary locking feature

• End-cap option for through-shaft designs and for OEM pumps that mount the impeller inside the outer rotor cup

• Two-piece clamshell bore available for in-situ magnet service without removing the driven shaft

Sealing, Coatings, and Balance

• Epoxy fill (potted construction) for magnet pocket sealing against process fluid ingress

• Optional outer banding sleeve (316L or titanium) for high-rpm containment of magnet fragments in the event of a rotor failure

• Surface finish: passivation, electropolishing, PTFE coating, or multi-layer coating stacks for chemical exposure

• Dynamic balance to ISO 1940 G2.5 / G6.3 / G16 per rotor mass and service speed

• 100% dimensional and magnetic inspection with full traceability per batch

Duty-Specific Variants We Regularly Deliver

• High-temperature outer rotors up to +200 C (EH-grade NdFeB) or up to +350 C (SmCo)

• Low-temperature / cryogenic outer rotors for LNG and air-separation (-196 C)

• Sanitary / CIP-cleanable outer rotors for food, beverage, and pharmaceutical service

• ATEX / IECEx certified construction for Group II Category 2 / 3 hazardous areas

• High-purity clean-room assembly and packaging for semiconductor and biotech service

• Pressure-rated outer rotors for can-side service up to 100 bar (geometry dependent)

Inside the Magnetic Circuit — Why Matched Pairs Transmit More Torque

The outer rotor is half the magnetic circuit. The decisions that matter are made before the first arc segment is ground:

• Pole-count parity: the outer rotor pole count must match the inner rotor pole count exactly. A 24-pole inner rotor needs a 24-pole outer rotor. Off-by-one or off-by-two poles is the most common reason a coupling is short on torque

• Magnet grade parity: the outer rotor's magnet grade should match the inner rotor's. A N42 inner with a N35 outer will underperform, even though the magnets are made of the same family

• Pole-arc tuning: magnet arc width is tuned to the can-side air gap, not a generic 50%. A wider arc pushes more flux at the cost of more leakage; we tune to your actual gap

• Back-iron (cup wall) thickness: the cup wall behind the magnets is the outer rotor's back-iron. It must be thick enough not to saturate, and thin enough to keep the air gap small

• Air-gap budget: the gap between the magnet and the can is the single biggest variable in torque — we design the outer rotor's inner diameter and magnet position to hit your actual gap, not a nominal zero

• Eddy-current loss: high-rpm outer rotor losses are real; we spec the magnet grade, the lamination, and the can-side wall to keep total heating inside your service envelope

• Temperature stability: HcJ, urec, and irreversible loss budget computed for your max operating temperature, with margin for short-term excursions

End-to-End In-House Production — Magnet, Outer Rotor, Optional Can

We do not outsource the steps that define your coupling's performance:

• Sintered NdFeB (and SmCo) production, grain-boundary diffusion, and pulse magnetization through controlled, audited supply chains

• Multi-axis grinding of arc segments to +/-0.03 mm (precision +/-0.01 mm)

• CNC machining of cup / drum bodies in 316L, 2205, 17-4PH, 4140, titanium, Hastelloy, and Inconel — boring, key-cutting, magnet-pocket machining, balancing features

• Welding: TIG, laser, and brazed cup / drum construction, with full-penetration weld verification

• Magnet pocket epoxy fill (potted construction) and banding sleeve installation

• 100% dynamic balance on in-house balancer to ISO 1940 G2.5 / G6.3 / G16

• Pulse magnetizer up to multi-Tesla, with field-mapping for Halbach and high-pole-count builds

• Full traceability: per-rotor batch record, magnet lot, hub material cert, balance report, and optional magnetic flux map

Technical Specifications

All values are typical ranges — every parameter is customized on request.

Why Engineers Choose FAIZEAL for Magnetic Coupling Outer Rotors

1. 10 years of magnet-component engineering — NdFeB, SmCo, Halbach arrays, magnetic couplings, inner and outer rotors, and pot magnets. We do not subcontract magnetic know-how

2. Both halves of the circuit in-house — outer rotor, inner rotor, and the containment can, on one engineering thread, balanced as a matched set

3. Custom is our default — every outer rotor BOM is open to your torque, speed, temperature, pressure, and chemistry constraints

4. Materials matched to the fluid, not the catalog — 316L, duplex, 17-4PH, Hastelloy, titanium, Inconel, all in-house machinable

5. No upper size limit — from Ø30 mm precision outer rotors to Ø800 mm+ heavy process outer rotors

6. Standards-ready documentation — API 685, ASME B73.3, ISO 5199, ATEX / IECEx, REACH / RoHS / CE

7. Reverse-engineering capability — send us an existing OEM outer rotor or coupling drawing, we will back-propose a drop-in

8. Export-ready logistics — DDP / FOB / EXW, NDA-friendly engineering workflow, sample and production lead times to your project schedule

Frequently Asked Questions

What is the difference between a magnetic coupling inner rotor and outer rotor?

The inner rotor is mounted on the drive (motor) shaft, inside the containment can. The outer rotor is mounted on the driven (pump / mixer) shaft, outside the can, and is always larger in diameter. Both rotors carry permanent magnets arranged at the same pole pitch; the inner rotor's rotating field crosses the can and locks the outer rotor into synchronous rotation. We manufacture both halves as a matched set, on one engineering thread, with a circuit-spec report you can hand to your customer.

Why is the outer rotor always larger than the inner rotor?

The outer rotor sits outside the containment can; the inner rotor sits inside. The can wall and the air gaps on both sides add up to the diameter difference. Because torque scales with the cube of the air-gap radius, a larger outer rotor dramatically increases torque capacity. It is the outer rotor's diameter — not the inner rotor's — that usually defines a coupling's maximum torque.

Can you reverse-engineer an existing OEM outer rotor?

Yes. Send us the OEM model number, the existing outer rotor OD / ID / length, and (if you have it) the magnet grade and pole count. We will back-propose a drop-in replacement outer rotor, including a magnetic circuit spec and a balanced matched set if you need both halves.

What is the relationship between the outer rotor and the containment can?

The outer rotor's inner diameter defines the can's outer diameter (plus a small clearance). The can's inner diameter defines the inner rotor's outer diameter. The three components — inner rotor, can, outer rotor — share one air-gap stack. We engineer the full stack in-house; you get a single circuit-spec, not three independent supplier drawings.

NdFeB or SmCo for my application?

NdFeB is the default — higher torque density, lower cost. SmCo is the choice when (a) sustained operating temperature is above ~180 C, (b) the process chemistry is strongly oxidizing and there is risk to NdFeB coatings, or (c) the customer requires the higher Curie temperature for safety margin. We help you choose per your service. The outer rotor's magnet grade should match the inner rotor's grade.

What is the maximum torque your outer rotors can transmit?

Torque scales with outer rotor OD, axial length, magnet grade, and pole count. Because the outer rotor is always larger than the inner rotor, it is the outer rotor diameter that dominates. We have delivered matched sets from sub-1 N.m (instrument pumps) to several thousand N.m (large process pumps). Tell us your torque target and your envelope; we will back-propose the outer rotor geometry.

What about pressure rating on the can-side of the outer rotor?

The cup body is designed to the pressure rating you specify. We have delivered outer rotors rated up to 100 bar at the can-side, geometry dependent. The cup body can be a one-piece welded / brazed / spun-closed structure for higher pressure, or a clamshell (two-piece) for in-situ serviceability at lower pressure. Tell us the service pressure and we will spec the cup construction.

Can you do ATEX / IECEx certified outer rotors?

We supply ATEX / IECEx-ready construction (spark-safe materials, banding sleeve, certified material certificates) and the full documentation pack. We are not a notified certification body, but we provide the engineering record and test data your notified body requires.

What are your typical lead times?

Prototype / sample outer rotor: 10-20 working days after drawing freeze. Production: 20-45 working days depending on volume, material, and cup body construction. SmCo and Halbach orders may run longer — we confirm a date at quotation.

Can you keep spare outer rotors for our fleet?

Yes. We offer scheduled batch-rotation stock for OEM customers, with a 5-year material and process reproducibility guarantee per fleet reference.

Get a Custom Quote — Fast

Send us:

• Outer rotor OD x magnet ID x axial length (or your existing outer rotor drawing / OEM model)

• Driven shaft bore, keyway / spline / lock feature details

• Required torque, max speed, and slip tolerance (synchronous mag-drive assumed)

• Operating temperature range and process fluid / chemistry

• Cup body material preference (316L / duplex / 17-4PH / titanium / 4140 / Hastelloy / Inconel)

• Containment can requirement: supplied by FAIZEAL, supplied by customer, or no can needed

• Pole count, magnet grade preference (or let us specify, matched to your inner rotor)

• Balance grade (G2.5 / G6.3 / G16) and any certification pack (ATEX, food-grade, nuclear)

• Quantity and target delivery date

We typically return a feasibility and indicative pricing note within 2 working days, and a firm quotation within 5-7 working days.

FAIZEAL — magnetic coupling outer rotors and matched inner rotors, engineered for zero-leak, zero-contact, zero-maintenance service.