Induction Shrink Fitting Bearings

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Brand: HLQ

Description

Induction Shrink Fitting of Bearings: Induction Bearing Heater for Mounting and Dismounting

Quick Answer

Induction shrink fitting of bearings means heating a rolling bearing with an induction heater until its inner ring expands, so that it slides onto the shaft without force. As the bearing cools, it grips the shaft with an interference fit.

Temperature: Heat to about 110 °C, roughly 90 K above the shaft. Do not exceed the maker’s limit, which is typically 120 °C. Sealed or pre-greased bearings should stay at or below about 80 °C.
Equipment: Yoke-type bearing heaters for maintenance, HLQ UHF/HF heaters with a helical coil for production, and flexible-cable heaters for large bearings.
Speed: Small bearings (Ø25–89 mm) heat in 30–60 s with a 6 kW, 180 kHz coil. Larger bearings take minutes.
Always: Put the temperature probe on the inner ring, demagnetise after heating, and mount the bearing immediately.

Large rolling bearing heated with an induction cable coil for shrink fitting onto a shaft — Large bearing heated with an induction cable coil for mounting.

What is Induction Shrink Fitting of Bearings?

Bearing inner rings are usually mounted on the shaft with an interference fit. Pressing them on cold needs high force, can damage the raceways and rolling elements, and can score the shaft. Heating the bearing about 90 K above the shaft temperature expands the bore enough for the bearing to slide on freely. When it cools, it locks onto the shaft.

An induction bearing heater generates heat directly in the bearing rings. It heats evenly to a set temperature, measured by a probe on the inner ring, and demagnetises the bearing at the end of the cycle. The same principle is used for gears and couplings; see induction shrink fitting of gears onto shafts.

Method	Speed	Temperature control	Risk
Induction heater	Seconds to minutes	Probe on the inner ring, automatic stop	Needs demagnetising (automatic)
Oil bath	Slow	Limited	Contamination, fire risk, oil disposal
Oven or hot plate	Slow	Moderate	Uneven heating, long cycle
Open flame	Fast	Poor	Local overheating and damage; never use
Cold press	Fast	—	Brinelling of raceways, shaft scoring

Key Applications

Industry	Typical bearings	Typical heater
Electric motors and pumps	Deep-groove ball and cylindrical roller bearings	Yoke heater or HF helical coil
Gearboxes and reducers	Tapered and spherical roller bearings	Yoke heater
Steel, paper, mining, cement	Large spherical roller bearings on rolls and shafts	Large yoke heater or flexible cable
Rail, wind, marine	Axle-box, main-shaft and stern-tube bearings	Flexible-cable heater
Production assembly lines	Small bearings in high volume	HLQ UHF/HF heater with a fixed coil

Application cases

Induction cable coil and insulation on a large bearing ring for dismounting — Large bearing ring heated with a cable coil and insulation for dismounting.

Induction coil heating a large bearing ring for assembly or removal — Large ring heated with an induction coil for assembly or removal.

Induction coil fixture for thermal assembly and disassembly of bearings and couplings — Coil fixture for heating bearings and couplings.

For very large bearings, couplings and propeller hubs, see induction heating for large bearings, couplings and propeller hubs.

Suitable Materials

Bearing type or material	Max heating temperature	Notes
Open bearings, through-hardened bearing steel (e.g. 100Cr6 / 52100)	≤ 120 °C (typical maker limit)	Mount at ≈ 110 °C
Bearings with a polyamide (PA66) cage	≤ 120 °C	Cage limit
Sealed or shielded, pre-greased bearings	≤ 80 °C	Grease and seal limit
Precision and super-precision bearings	Per maker (often ≤ 70 °C)	Dimensional stability
Case-carburised bearing steel	≤ 120 °C	Same rule as open bearings
Separate rings, sleeves and labyrinth rings	Per material	Same heater, temperature mode

Always follow the specific bearing maker’s mounting instructions.

Working Principle

Principle diagram of induction bearing heating: yoke heater, HF helical coil and flexible cable coil, with bearing temperature rules — Principle diagram: three ways to induce current in a bearing, and the temperature rules.

Yoke heater (50/60 Hz): Works like a transformer. The bearing hangs on the removable top yoke and acts as a one-turn short-circuited secondary winding.
HF helical coil: A multi-turn coil carries high-frequency current. The bearing sits inside it with its axis across the coil axis, so one coil heats a range of bearing sizes evenly.
Flexible cable coil: Medium-frequency cable is wound on large bearings and rings, in the workshop or on site.
Expansion and mounting: The inner ring grows by ΔD = α · d · ΔT and slides onto the shaft. The heater then demagnetises the bearing.

Background: how induction heating works.

Bore growth and required temperature rise (bearing steel, α ≈ 12 × 10⁻⁶ /K)

Bearing bore d	Bore growth at ΔT 90 K	Max interference, m6 shaft*	ΔT needed for that interference
50 mm	0.054 mm	0.037 mm	≈ 62 K
100 mm	0.108 mm	0.055 mm	≈ 46 K
200 mm	0.216 mm	0.076 mm	≈ 32 K
300 mm	0.324 mm	0.087 mm	≈ 24 K

* ISO 286 m6 shaft with a normal-tolerance bearing bore. Heating 90 K above the shaft leaves a margin for an easy slide-on. Small bearings with tight fits need a relatively higher ΔT, so check it against the maker’s limit.

Technical Specifications

Heater type	Frequency	Bearing size	Supply	Key features
Yoke-type induction bearing heater	50/60 Hz	≈ Ø20–600 mm bore, by model	Single- or three-phase, by model	Temperature mode, automatic demagnetising, swing-out yoke
HLQ UHF heater + helical coil (e.g. DW-UHF-6 kW)	≈ 100–400 kHz (180 kHz in the case below)	Ø25–89 mm in one coil	Single-phase	Cart-mounted, 30–60 s per bearing
HLQ HF heater + custom coil (DW-HF)	30–80 kHz	Bearings and rings in production lines	Three-phase	Fixed coil, automation I/O
MF flexible-cable heater	2–36 kHz	Large bearings and rings, Ø300 mm to 3 m	Three-phase	Cable wound on the ring; site work

Heating time by bearing mass and heater power (20 → 110 °C, η 0.6)

Bearing mass	2 kW	5 kW	10 kW	25 kW
1 kg	34 s	14 s	7 s	3 s
5 kg	173 s	69 s	35 s	14 s
20 kg	690 s	276 s	138 s	55 s
50 kg	1725 s	690 s	345 s	138 s

t = m · c · ΔT / (P · η), with bearing steel c ≈ 0.46 kJ/kg·K. Large bearings should be heated more slowly so that the inner and outer rings stay at a similar temperature.

Recommended Model Selection

Requirement	Recommended	Reason
Small bearings in production (Ø25–90 mm)	UHF 6 kW + helical coil	One coil for all sizes, 30–60 s
Maintenance workshop, bearings up to ≈ 300 kg	Yoke-type bearing heater	Temperature mode and automatic demagnetising
Large bearings and rings, on site	MF flexible-cable heater	No size limit; portable
Dismounting inner rings	Cable or custom coil, high power	Heat the ring quickly, before the shaft warms
Mixed bearings, gears and couplings	Portable shrink fitting machine	One system for several part types

For mixed workshop jobs, see the portable induction shrink fitting machine.

Process Workflow

Induction bearing mounting process flow chart from fit check to heating, demagnetising, mounting and inspection — Process flow chart for induction bearing mounting.

Step	Action	Check
1	Check the shaft size, interference and the bearing’s maximum temperature	Open or sealed bearing?
2	Clean the shaft and seat; apply a light oil film; set the axial stop	No burrs or dirt
3	Load the bearing on the yoke or in the coil; put the probe on the inner ring	Probe has good contact
4	Set the target to ≈ 110 °C (≤ 120 °C), or ≤ 80 °C for sealed bearings	Temperature mode, not time only
5	Heat until the set point is reached	Automatic stop
6	Demagnetise (automatic at the end of the cycle)	Cycle complete
7	Slide the bearing on at once and push it to the shoulder	Within about 30 s
8	Hold it against the shoulder until it grips, then let it cool	No gap at the shoulder
9	Inspect	Free rotation, correct axial position

Typical mounting station layout

Layout diagram of an induction bearing mounting station with bearing heater, mounting stand, shaft and hoist — Layout diagram: bearing store, induction heater, mounting stand and lifting tool within a few steps.

Common Problems and Solutions

Problem	Likely cause	Solution
Bearing stops before reaching the shoulder	The ring cooled during transfer, or ΔT was too low	Mount at once; hold it against the shoulder; keep the heater close to the shaft
Gap at the shoulder after cooling	The bearing shrank axially and pulled away from the shoulder	Hold axial pressure until the bearing grips
Bearing overheated	Time mode used, or the probe was on the outer ring	Use temperature mode with the probe on the inner ring
Bearing attracts metal particles	Residual magnetism	Use the automatic demagnetising cycle
Grease leaking from a sealed bearing	Heated above ≈ 80 °C	Limit sealed bearings to ≤ 80 °C
Inner ring hot, outer ring cold (large bearings)	Heating too fast	Reduce the power; allow time to equalise
Cannot remove the bearing	The shaft heats along with the ring	Heat the inner ring fast with a puller in place; see induction thermal disassembly

Engineering Selection Guide

Factor	Question to answer	Guideline
Bearing size and mass	Bore, OD, width, weight?	Choose a yoke size or coil that fits the bore and mass
Bearing type	Open, sealed or precision?	Set the temperature limit: 120 / 80 / per maker
Volume	Bearings per day?	High volume: UHF/HF fixed coil; maintenance: yoke heater
Location	Workshop or on site?	On site and very large: flexible-cable heater
Job	Mounting, dismounting or both?	Dismounting needs fast, high-power heating of the inner ring
Other parts	Gears, couplings, sleeves as well?	See the induction shrink fitting machine range

Advantages and Limitations

Advantages	Limitations
Fast, even heating to a set temperature	The temperature must stay within the bearing maker’s limit
No oil, flame or press force	Bearings must be demagnetised (automatic on bearing heaters)
No damage to raceways or the shaft	Very small, tight-fit bearings may still need a press
Automatic demagnetising and temperature hold	Keep watches, tools and implants away from the yoke field
The same heater can be used for dismounting	Large bearings need lifting equipment

Why Choose HLQ?

Strength	What it means for you
Every bearing size	Yoke heaters, UHF/HF coils and MF cable heaters
Temperature control	Probe on the inner ring, automatic stop and hold
Automatic demagnetising	Clean bearings, ready to mount
Custom coils	Helical, split and cable coils for your parts
Mounting and removal	One heater for both jobs

Yoke-type induction bearing heater with digital temperature control.

Application example: roller bearings Ø25–89 mm

Item	Value
Bearings	Steel roller bearings, 25–89 mm (1–3.5 in)
Power supply	DW-UHF-6 kW, single-phase, remote heat station with 2 × 0.1 μF capacitors (0.2 μF)
Frequency	180 kHz
Coil	Multi-turn helical coil; bearing axis across the coil axis (transverse heating)
Temperature check	Temperature-indicating paints
Result in test	150–175 °C in 30–60 s; bearings slid onto the shafts without force
Recommended production setting	≈ 110 °C (≤ 120 °C maker limit), which also shortens the cycle
Benefit	One coil for the whole size range; the single-phase supply allows a mobile cart

10 Core FAQs

1. What temperature should a bearing be heated to for mounting?

About 110 °C, which is roughly 90 K above the shaft. Do not exceed the maker’s limit, typically 120 °C.

2. Can sealed bearings be heated by induction?

Yes, but only to about 80 °C, because of the grease and the seals.

3. Why must bearings be demagnetised?

Induction leaves some residual magnetism, which attracts wear particles. Bearing heaters demagnetise automatically at the end of the cycle.

4. Where should the temperature probe go?

On the inner ring, because the inner ring is what has to expand to fit the shaft.

5. How long does heating take?

Small bearings take 30–60 s with a 6 kW HF coil. A 20 kg bearing takes about 2–5 minutes on a 5–10 kW heater.

6. How much does the bore expand?

ΔD = α · d · ΔT. At ΔT 90 K, a 100 mm bore grows by about 0.11 mm, which is more than the maximum interference of an m6 fit.

7. Can induction be used to remove bearings?

Yes. Heat the inner ring quickly with a puller in place, so that it expands before the shaft warms, then pull it off.

8. Is an oil bath or a torch acceptable?

An oil bath is slow and dirty. An open flame causes local overheating and should never be used. Induction is faster, cleaner and temperature-controlled.

9. What frequency do bearing heaters use?

Yoke heaters run at 50/60 Hz. HF coil systems use about 100–400 kHz for small bearings (180 kHz in the case above). Flexible-cable heaters use 2–36 kHz for large rings.

10. What is the largest bearing that can be heated?

Yoke heaters cover bores up to about 600 mm, depending on the model. Flexible-cable heaters have no practical size limit and are used on rings up to several metres.

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