Proper Bearing Mounting: Cold Press, Induction Heating, Hydraulic — Avoiding Brinelling

Bearing installation is the process of fitting a bearing onto a shaft and into a housing using mechanical, thermal, or hydraulic methods — ensuring that clearance, concentricity, and preload conform to design specifications.

According to the SKF Mounting Handbook, 27% of premature industrial bearing failures originate from improper mounting — including direct hammer blows, open-flame heating, failure to verify clearance after installation, and mismatched methods for shaft size. A correct mounting procedure eliminates this entire 27% failure category and allows bearings to reach or exceed their calculated L₁₀ service life. This article details three mounting methods by shaft diameter, adapter sleeve and withdrawal sleeve techniques, tapered roller bearing clearance adjustment with a dial indicator, floating seal installation for track rollers, brinelling causes and prevention, six common mounting errors observed in Vietnamese factories, and induction heater temperature guidelines — based on documentation from SKF, FAG/Schaeffler Mounting Guide, NSK Technical Report, and the geometrical tolerancing standard ISO 1101.

Three mounting methods by shaft diameter

Selecting the correct mounting method depends primarily on the bearing bore diameter (d). Using the wrong method is the most common cause of damage at the point of installation. Three standard methods are recommended by the SKF Mounting Handbook and the Schaeffler Mounting Manual:

Cold press fitting — bore diameter d < 80 mm

Cold press fitting applies to ball bearings and small bearings with bore diameters under 80 mm. Procedure:

1. Apply a thin film of oil to the shaft and bearing bore — reduces friction during mounting. Do not use heavy grease as it creates uneven resistance.
2. Use a mounting sleeve that bears evenly on the inner ring — NEVER strike the bearing directly with a hammer.
3. Use a hydraulic press or hammer with mounting sleeve: the pressing force must be applied evenly and perpendicular to the shaft axis. Force through the inner ring when mounting on a shaft; through the outer ring when mounting into a housing.
4. Press until the bearing seats against the shaft shoulder — verify with a 0.03 mm feeler gauge: the gauge must not enter the gap between the inner ring and shoulder.

Reference pressing forces: bearing 6205 (d = 25 mm) requires 5–8 kN; bearing 6310 (d = 50 mm) requires 15–25 kN. Exceeding these forces deforms the raceways and causes immediate failure.

Induction heating — bore diameter 80–200 mm

For self-aligning bearings and medium-sized bearings with bore diameters of 80–200 mm, cold pressing is impractical due to the excessive force required. Induction heating is the standard method:

1. Place the bearing on the induction heater — ensure the bearing sits level, not tilted.
2. Heat to 80–100°C above ambient temperature, NEVER exceeding 120°C — see the detailed temperature table below.
3. Demagnetize after heating — SKF TIH and FAG HEATER units demagnetize automatically. If using a heater without this feature, demagnetize separately.
4. Mount quickly — after removing the bearing from the heater, there is a 30–60 second window to slide it onto the shaft before contraction begins.
5. Push firmly against the shaft shoulder and hold in place with a shaft nut until the bearing cools completely.

An induction heater heats the entire bearing uniformly in 3–8 minutes (depending on size), compared to 20–40 minutes in an oil bath, and is far safer than open-flame heating.

Hydraulic mounting — bore diameter d > 200 mm

Large bearings (d > 200 mm) such as the 22344 (d = 220 mm) or 23060 (d = 300 mm) require hydraulic mounting:

1. Inject high-pressure oil through holes in the shaft into the contact surface between the inner ring and the tapered seat — creating an oil film that reduces friction.
2. Use a hydraulic nut to drive the bearing up the tapered shaft by a calculated axial advance.
3. Control the axial advance using a dial indicator and cross-reference the manufacturer's clearance reduction table.

Oil injection pressure typically ranges from 50–150 MPa depending on bearing size. The SKF TMMA and TMHP systems provide integrated oil pumps with pressure gauges.

Mounting method summary by size

Adapter sleeve and withdrawal sleeve

Adapter sleeve — mounting bearings on plain shafts

An adapter sleeve (designations H, OH, HA) allows self-aligning bearings to be mounted on plain (non-tapered) shafts — particularly useful when the shaft is long and the bearing cannot be slid from the shaft end.

Procedure for H-series adapter sleeves:

1. Slide the adapter sleeve onto the shaft to the desired position.
2. Place the bearing onto the tapered surface of the adapter sleeve.
3. Tighten the lock nut — this draws the bearing up the taper, creating an interference fit.
4. Check clearance with a feeler gauge or dial indicator — confirm that the clearance reduction falls within the permissible tolerance.
5. Bend the lock washer tab into the nut slot.

Advantages: no tapered shaft machining required, bearing can be positioned anywhere along the shaft, easy removal. Disadvantage: lower axial load capacity compared to direct tapered-seat mounting.

Withdrawal sleeve — safe bearing removal

A withdrawal sleeve (designations AH, AHX) is used to remove bearings from tapered seats without damage:

1. Remove the lock nut and lock washer.
2. Thread the hydraulic nut onto the withdrawal sleeve.
3. Apply pressure — the nut pushes the sleeve outward, simultaneously releasing the bearing from the taper.

At a steel mill in Ba Ria - Vung Tau province, technicians previously used chisels and sledgehammers to remove 22328 bearings from rolling-mill shafts — averaging 4 hours per bearing and routinely damaging both the bearing and the shaft surface. After equipping the maintenance team with AHX 3128 withdrawal sleeves and a hydraulic pump, removal time dropped to 25 minutes, shafts remained undamaged, and removed bearings could be reused if they still met inspection criteria.

Tapered roller bearing clearance adjustment with a dial indicator

Tapered roller bearings have separable inner and outer rings, and axial clearance is adjusted by shifting the outer or inner ring along the shaft axis. Incorrect clearance produces two failure modes:

• Excessive clearance: uneven load distribution — only a few rollers carry load, causing premature fatigue.
• Insufficient clearance (excessive preload): increased friction, elevated temperature, rapid grease degradation, failure within hours to days.

Adjustment procedure using a dial indicator

1. Mount the dial indicator on the housing with the probe tip contacting the shaft end face.
2. Push the shaft fully to one side — zero the indicator.
3. Push the shaft fully to the opposite side — read the value: this is the current axial clearance.
4. Compare against the manufacturer's clearance table:

5. Tighten the adjusting nut or add/remove shims until the clearance falls within the permissible range.
6. Rotate the shaft 10–15 revolutions to allow the rollers to seat, then re-measure — repeat if necessary.
7. Lock the nut with a tab washer or locking pin.

A common mistake: tightening the adjusting nut "by feel" instead of measuring with a dial indicator — this results in excessive preload in roughly 40% of cases, based on internal surveys at cement plants in northern Vietnam.

Floating seal for track rollers

Track rollers on excavators and bulldozers operate in mud, soil, and water — a floating seal (also called a duo-cone seal) is the standard solution for protecting the internal bearing.

Floating seal construction

A floating seal consists of two precision-ground metal rings (seal rings) pressed together by elastic rubber O-rings. One ring rotates with the shaft; the other is stationary. The metal-to-metal contact face creates a complete seal that prevents mud and debris from entering.

Floating seal installation procedure

1. Clean the housing flange and hub surfaces thoroughly — no oil, grease, or dust.
2. Fit the O-ring into the groove on the seal ring — ensure the O-ring is not twisted.
3. Apply clean engine oil to the ground sealing face of the seal ring.
4. Install the seal rings into the housing and hub — one ring per side.
5. Assemble the housing and hub — the two seal rings press together to form the seal.
6. Check the seal height — per manufacturer specifications, typically 1.0–2.5 mm.

If a floating seal is worn (sealing face grooves deeper than 0.3 mm or O-ring elasticity lost), replace the entire pair — never replace a single ring.

Brinelling — causes and prevention

What is brinelling

Brinelling is the formation of indentations on the raceway caused by impact loading or excessive static load, imprinted in the pattern of the rolling elements. True brinelling differs from false brinelling (fretting corrosion caused by micro-vibration while the bearing is stationary).

Primary causes

1. Improper transportation: machines transported by truck over rough roads — continuous vibration creates impact loads on bearings already mounted in the equipment.
2. Direct hammer blows during installation: localized impact forces exceed the elastic limit of bearing steel.
3. Excessive static load: heavy loads placed on equipment while the shaft is not rotating — load concentrates through a few rolling elements.
4. False brinelling: standby equipment absorbs vibration from adjacent running machinery — micro-vibration wears the raceway at the contact points.

Preventing brinelling

• Transportation: lock the rotor/shaft when moving equipment; use transportation locks on large motors.
• Installation: use mounting sleeves, presses, or induction heating — never strike the bearing directly.
• Storage: rotate the shaft of standby equipment every 2 weeks (per SKF recommendations); lubricate before long-term storage.
• Standby equipment: install vibration-dampening pads under the machine base, or run standby equipment briefly each week.

At a cement plant in Ha Nam province, all standby ID fans suffered false brinelling after 8 months of storage — four sets of 22328 C3 bearings required replacement. After implementing a shaft rotation protocol (15 minutes every 2 weeks) and installing vibration-dampening pads, no recurrence was observed over the following 2 years.

Six common bearing mounting errors in Vietnamese factories

Error 1: Striking the bearing directly with a hammer

This is the most widespread error in small machine shops and untrained maintenance teams. Hammer blows generate localized impact forces of 10–50 kN on a very small contact area — causing brinelling, inner ring cracking, or cage fracture. Solution: equip teams with a mounting tool kit — a one-time investment that serves hundreds of installations.

Error 2: Heating with a torch or in a contaminated oil bath

A torch heats unevenly, creating temperature gradients exceeding 50°C across the bearing — inducing thermal stress, distortion, and metallurgical changes (if temperatures exceed 250°C). Contaminated oil baths introduce particles into the raceways. Solution: use an induction heater — uniform heating, precise temperature control, and overheat alarms.

Error 3: Failing to check clearance after installation

Many technicians start the machine immediately after mounting, skipping axial clearance measurement (for tapered roller bearings) or radial clearance measurement (for self-aligning bearings on tapered adapter sleeves). Consequence: excessive preload or excessive clearance — both drastically shorten bearing life. Solution: make post-mounting clearance measurement mandatory using a feeler gauge or dial indicator, and record the value on the installation report.

Error 4: Installing tapered roller bearings in the wrong orientation

Tapered roller bearings mounted in pairs use either an O arrangement or an X arrangement (back-to-back or face-to-face). Reversing the orientation changes an O arrangement into an X arrangement (or vice versa), fundamentally altering load capacity and stiffness characteristics. Solution: mark the mounting direction on the housing and shaft before disassembly; train technicians to recognize DB (back-to-back) and DF (face-to-face) designations.

Error 5: Out-of-tolerance shafts and housings

Worn shafts, oval housings, or surfaces with ridges or scratches — a new bearing installed on a defective seat becomes misaligned, has uneven fit, and exhibits high vibration from the start. Per ISO 1101, shaft cylindricity tolerance for bearing seats must achieve IT5–IT6. Solution: measure the shaft and housing with a micrometer before installation; remachine if specifications are not met.

Error 6: No initial lubrication or wrong grease type

Installing a bearing "dry" (without applying grease to the raceways before first startup) causes metal-to-metal contact in the first few seconds. Using the wrong grease type (for example, simple lithium grease in a high-temperature application) reduces bearing life by 50–70%. Solution: apply the correct grease type in the correct quantity (30–50% of free space) per the guidelines in the bearing lubrication article.

Induction heater temperature guide

Heating temperature must be sufficient to expand the inner ring for a slip fit onto the shaft — but must not exceed thresholds that alter steel microstructure or damage the grease inside sealed/shielded bearings.

Heating temperature table by bearing size

Temperature safety rules

• 80–100°C: optimal safe range for most open bearings.
• 100–120°C: permissible for large bearings (d > 150 mm), requires continuous monitoring.
• > 120°C: NEVER — grease inside sealed bearings begins to decompose at 120°C; 100Cr6 bearing steel starts austenite transformation at 150°C; NBR rubber seals deform at 130°C.
• Sealed bearings (2RS, LLU): maximum 80°C — internal grease cannot be replaced, and heat damage is permanent.

Modern induction heaters (SKF TIH 030, TIH 100, FAG HEATER 300/600) feature automatic temperature controllers and alarms when the set temperature is reached. Always set the target temperature before activating the heater; never heat by guessing based on time alone.

Three real-world case studies

Case 1: Cement plant — bearing failure on ID fan due to flame heating

A 5,000-ton/day cement plant in central Vietnam experienced repeated failure of self-aligning bearings 22328 C3 on the ID fan — actual service life was only 8–12 months versus the calculated 3–5 years. Root cause analysis:

• Technicians used a gas torch to heat bearings before mounting — localized temperature on one side reached 200–250°C (measured with an infrared thermometer), while the opposite side was only 60°C.
• The thermal gradient distorted the inner ring, reducing radial clearance from C3 specification (0.07–0.09 mm) to near zero after cooling.
• Clearance was not measured after mounting — the bearing operated with slight preload, temperature rose progressively, grease degraded, and failure occurred within 8–12 months.

Solution implemented: procurement of an SKF TIH 100 induction heater, technician training on post-mounting clearance measurement with feeler gauges, and documentation in maintenance records. Result: bearing life increased to 4+ years and unplanned ID fan shutdowns were reduced by 3 incidents in the first year.

Case 2: Steel mill — false brinelling on standby cold-rolling motor

A steel rolling mill in Hai Phong had two 450 kW cold-rolling motors fitted with NU 326 and 6326 C3 bearings. After 10 months in standby storage, the reserve motor exhibited vibration 5 times above normal when placed into service (velocity 12.5 mm/s RMS versus a 2.5 mm/s baseline). Inspection revealed evenly spaced indentations on both bearing raceways matching the roller pitch — classic false brinelling.

Root cause: the motor was stored on a concrete floor 3 meters from a running motor — vibration transmitted through the foundation for 10 consecutive months. Solution: standby motors are now placed on rubber vibration-dampening pads, shafts are rotated 10 turns every 2 weeks, and re-lubrication occurs every 3 months regardless of operating status. Cost avoided: two sets of NU 326 + 6326 C3 bearings and 16 hours of rolling-line downtime.

Case 3: Excavator fleet — track roller failure due to improper floating seal installation

A fleet of PC200 excavators at a quarry in Quang Ninh province experienced consecutive track roller failures after only 800–1,200 hours — versus an expected service life of 4,000–6,000 hours. Inspection showed mud and rock debris inside the roller, complete bearing wear, and lubricating oil turned to "thick sludge."

Root cause: when replacing track rollers, mechanics installed floating seals without checking seal height — O-rings were twisted, seal ring faces were not parallel, creating a 0.5–1.0 mm gap. Mud penetrated from the first week. Solution: mechanic training on the 6-step floating seal procedure (as described in the section above), seal height verification with calipers, and new O-ring replacement at every disassembly. Result: track roller life increased to 5,000+ hours, significantly reducing undercarriage costs across the fleet — see also the construction equipment bearings article.

Standard bearing installation tools

Investing in dedicated mounting tools is a small expense compared to the damage caused by improper installation. Essential tool list:

• Mounting tool kit: SKF TMFT 36, FAG FITTING TOOL ALN — includes plastic/metal rings from 10–110 mm diameter, impact rings, and handles.
• Induction heater: SKF TIH 030 (bearings up to 40 kg), TIH 100 (up to 100 kg), TIH 230 (up to 230 kg); FAG HEATER 300, HEATER 600.
• Dial indicator: 0.01 mm resolution, 10 mm travel — for measuring axial and radial clearance.
• Feeler gauge set: 0.02–1.00 mm — for checking shaft shoulder clearance and radial clearance on self-aligning bearings.
• Hydraulic oil pump: SKF TMHP series — injects oil through shaft holes for large bearings.
• Hydraulic nut: SKF HMV series — replaces hand-tightened nuts for bearings with d > 200 mm.
• Temperature measurement: infrared thermometer or thermocouple — verifies bearing temperature during heating and after commissioning.

Post-installation verification procedure

Installation is not complete when the bearing is seated. Post-installation checks:

1. Hand rotation check: rotate the shaft by hand — it must turn smoothly with no binding or abnormal "heavy spots."
2. Clearance measurement: use a feeler gauge (radial clearance) or dial indicator (axial clearance) — record the value and cross-reference the tolerance table.
3. Shaft shoulder check: a 0.03 mm feeler gauge must not enter the gap between the inner ring and shaft shoulder.
4. Running-in period: operate without load for 15–30 minutes while monitoring temperature — a gradual rise to 40–60°C followed by stabilization is normal. If temperature climbs continuously above 70°C, stop the machine and investigate.
5. Baseline vibration measurement: record initial vibration values (velocity mm/s RMS) as the baseline for the vibration monitoring program.
6. Installation record: date, bearing designation, measured clearance, heating temperature (if applicable), and technician name — this data supports root cause analysis if premature failure occurs.

Key takeaways

1. Match the method to the bore size: cold press for d < 80 mm, induction heating for 80–200 mm, hydraulic for > 200 mm — no single method fits all bearings.
2. Never exceed 120°C during heating: 80–100°C is the optimal range; sealed bearings must not exceed 80°C.
3. Always measure clearance after mounting: use a dial indicator for tapered roller bearings, a feeler gauge for self-aligning bearings — measure with instruments, not by feel.
4. Adapter sleeves and withdrawal sleeves save 5–10 times more labor than crude methods while protecting both the bearing and the shaft.
5. Brinelling is preventable: secure equipment during transport, install vibration-dampening pads for standby units, and rotate shafts on a regular schedule.
6. Invest in proper tooling: a mounting tool kit and induction heater pay for themselves within 3–5 installations through avoided bearing damage.
7. Correct floating seal installation determines track roller service life — inspect the O-ring and verify seal height at every disassembly.
8. Document every installation parameter in the maintenance record — this data is the foundation of a predictive bearing maintenance program.

References

1. SKF Group. SKF Bearing Mounting and Dismounting Handbook. skf.com/group/products/maintenance-products/mounting.
2. Schaeffler Group. FAG Mounting and Maintenance of Rolling Bearings. schaeffler.com/en/products-and-solutions/industrial/services/mounting-and-maintenance.
3. NSK Ltd. NSK Technical Report — Mounting and Handling. nsk.com/products/techreport.
4. ISO 1101:2017. Geometrical product specifications (GPS) — Geometrical tolerancing. iso.org/standard/66777.html.
5. ISO 15243:2017. Rolling bearings — Damage and failures — Terms, characteristics and causes. iso.org/standard/63147.html.