--With Clearance Calculation Methods and Selection Tables

Many equipment failures are not due to bearing quality, but because the internal clearance was chosen incorrectly.

Clearance is something invisible and intangible, but if chosen correctly, the bearing will run smoothly for years; if chosen incorrectly, even an imported bearing won't last three months.

This article will thoroughly explain clearance, divided into five parts:

What is clearance? (with diagram)

Types of clearance (with national standard table)

How to select clearance (with calculation examples)

How to check clearance (with wear pattern diagrams)

Common misconceptions (with failure pattern chart)

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1. What is clearance?

Clearance refers to the maximum radial or axial movement of one ring when the other ring (inner or outer) is fixed, in an unmounted bearing.

[Fig.1: Diagram of radial and axial clearance]

Taking deep groove ball bearing 6205 as an example:

Normal group (CN) radial clearance range: 5-20 μm (microns)

1 μm = 0.001 mm, a human hair is about 70-100 μm.

That means the internal gap in a 6205 bearing is only 1/10 to 1/5 of a hair's thickness.

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2. Types of clearance

Depending on the bearing's state, clearance is divided into three types:

[Fig.2: Comparison of three clearance states]

State	Definition	Influencing Factors
Original clearance	Clearance measured by the manufacturer when bearing is new	Manufacturing tolerances
Mounted clearance	Clearance after bearing is fitted onto shaft and housing	Interference fit
Operating clearance	Actual clearance when equipment is running at thermal steady state	Temperature difference + load

Relationship among them:

Original clearance > Mounted clearance > Operating clearance

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3. How are clearance classes divided?

According to national standard GB/T 4604-2006 "Rolling bearings - Radial internal clearance", common clearance classes are as follows:

[Table 1: Common clearance class codes and names]

Class Code	Name	Clearance Size	Typical Application
C2	Small clearance group	Smaller than normal	High precision, low temperature rise
CN (Group 0)	Normal group	Baseline	General applications
C3	Large clearance group	Larger than normal	High temperature, tight fits
C4	Extra large clearance group	Larger than C3	High temperature + heavy load
C5	Maximum clearance group	Larger than C4	Special high temperature conditions

[Fig.3: Bar chart comparing radial clearance ranges for different classes]

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4. Specific values: Deep groove ball bearing clearance table

Taking commonly used 62 and 63 series deep groove ball bearings as examples, radial clearance ranges are as follows:

[Table 2: Radial clearance table for deep groove ball bearings (unit: μm)]

Bore diameter d (mm)	C2	CN (Group 0)	C3	C4	C5
over	incl.	min-max	min-max	min-max	min-max	min-max
10	18	0-9	3-18	11-25	18-33	25-45
18	24	0-10	5-20	13-28	20-36	28-48
24	30	1-11	5-20	13-28	23-41	30-53
30	40	1-11	6-20	15-33	28-46	40-64
40	50	1-14	6-23	18-36	30-51	45-73

Taking bearing 6205 as an example:

Bore diameter 25mm, falls in the 24-30 interval

CN group clearance: 5-20 μm

C3 group clearance: 13-28 μm

C4 group clearance: 23-41 μm

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5. How to select clearance? Three-step method

Step 1: Calculate clearance loss due to fit

When the bearing inner ring is pressed onto the shaft, it expands slightly, reducing the clearance.

[Fig.4: Diagram showing the effect of interference fit on clearance]

Calculation formula:

Δd = Δ × (d / D)

Where:

Δd: clearance reduction

Δ: actual interference of shaft journal

d: bearing bore diameter

D: bearing outer diameter

Example calculation:

Bearing 6205, bore d=25mm, outer diameter D=52mm, shaft interference Δ=15μm.

Clearance reduction = 15 × (25/52) ≈ 7.2 μm

If original clearance is CN group (5-20 μm), take median 12 μm, subtract 7.2 μm leaves only 4.8 μm, close to the lower limit – prone to overheating.

Conclusion: In this case, C3 group should be selected.

Step 2: Calculate clearance change due to temperature difference

During operation, the inner ring temperature is usually 5-10°C higher than the outer ring; thermal expansion further reduces clearance.

Estimation formula:

δt = α × d × ΔT

Where:

α: linear expansion coefficient of steel, approx. 11.5×10⁻⁶ /°C

d: bearing bore diameter

ΔT: temperature difference between inner and outer rings

Example calculation:

6205 bearing, d=25mm, ΔT=10°C

Clearance reduction = 11.5×10⁻⁶ × 25 × 10 ≈ 0.0029mm = 2.9 μm

Adding fit loss 7.2 μm, total loss ≈ 10 μm.

If original clearance is C3 (13-28 μm), take median 20 μm, subtract 10 μm gives operating clearance about 10 μm, still within reasonable range.

Step 3: Look up table for final selection

[Table 3: Quick reference table for clearance selection]

Operating condition	Fit tightness	Temperature rise	Recommended clearance
Ordinary motor	Medium	Low	CN
High-temperature fan	Medium	High	C3
Vibrating screen	Tight	Medium	C3/C4
Rolling mill	Extra tight	High	C4
Precision spindle	Light fit	Low	C2

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6. How to check clearance? Wear pattern method

Used bearings are the best textbook for judging whether the clearance was appropriate.

[Fig.5: Raceway wear patterns corresponding to different clearances]

Wear pattern	Diagram	Conclusion
Wear centered, uniform distribution	[Fig.5-1]	Clearance appropriate
Wear shifted to one side	[Fig.5-2]	Clearance too large, shaft wobbling
Wear at both ends, no wear in middle	[Fig.5-3]	Clearance too small, edge loading

[Fig.5-1: Appropriate clearance – uniform wear in center of raceway]

[Fig.5-2: Clearance too large – skewed wear]

[Fig.5-3: Clearance too small – wear at both ends]

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7. Common misconceptions (with failure pattern chart)

[Fig.6: Clearance-related failure pattern tree]

Misconception 1: Larger clearance is safer

Truth: If clearance is too large, rolling elements are unstable, cage suffers impact, and life is shortened.

Misconception 2: Imported bearings don't need clearance selection

Truth: Imported bearings also have clearance classes; if not specified, CN group is supplied by default.

Misconception 3: Clearance is fixed at factory; user doesn't need to care

Truth: Mounting fit and operating temperature both change the actual clearance; users must consider them.

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8. Practical advice for purchasing and maintenance personnel

1. When purchasing: Write the full designation

Don't just write 6205, write 6205-2RS C3

2. Before installation: Check the suffix

On arrival, check the clearance code on the packaging to ensure it matches the purchase order.

3. During operation: Monitor temperature

If temperature rises suddenly, first suspect insufficient clearance.

4. During maintenance: Keep old bearings

Don't discard removed bearings; their wear patterns can indicate if clearance was appropriate.

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Conclusion

Clearance is not about being as large as possible or as small as possible; it's about being appropriate.

Next time you encounter frequent bearing failures, don't rush to change brands. Calculate the clearance first – the problem may be solved.

If you're unsure how to select, send us your equipment parameters and we'll help you calculate.

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【Industry News】English Version

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Schaeffler Acquires Sweden's Esterer, Intensifying Competition in Wind Turbine Bearing Market

October 28, 2024 Industry News

On October 25, Schaeffler Group officially announced the completion of its acquisition of Swedish bearing manufacturer Esterer AB. The two parties signed the final agreement earlier this month. The transaction amount was not disclosed and is expected to close in the first quarter of 2025.

This is Schaeffler's fifth acquisition in the wind power sector in nearly three years.

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1. The acquisition target: Who is Esterer?

Esterer AB, founded in 1982 and headquartered in Gothenburg, Sweden, is a medium-sized manufacturer specializing in wind turbine bearings.

[Fig.1: Esterer's main products and customer distribution]

Product Category	Application	Key Customers	Market Share (Europe)
Main shaft bearings	Wind turbine main shaft	Vestas, Siemens Gamesa	approx. 12%
Yaw bearings	Connection between nacelle and tower	Nordex, Enercon	approx. 15%
Pitch bearings	Blade root	GE Renewable	approx. 8%

According to public data, Esterer's 2023 revenue was approximately €32 million, net profit about €3.8 million, with 124 employees, of which about 30% are in R&D and testing.

The company has a test center in Gothenburg equipped with two dedicated test rigs for wind turbine bearings, capable of testing main shaft bearings with a maximum outer diameter of 1.2 meters.

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2. Acquisition details: What did Schaeffler buy?

Schaeffler disclosed the core assets of this acquisition in its announcement:

1. Physical assets

Gothenburg production facility (approx. 23,000 m²)

Wind turbine bearing test center (including test equipment)

Dedicated production lines and inspection equipment

2. Intangible assets

Rights to use the Esterer brand

Related technology patents for wind turbine bearings (approx. 23)

Test data and failure case database

[Fig.2: Floor plan of Esterer's Gothenburg factory]

Stefan Spindler, CEO of Schaeffler's Industrial Division, said in the announcement: "Esterer's testing capabilities and technical team will help us better serve our European wind power customers."

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3. Acquisition background: Three changes in the wind turbine bearing market

3.1 Higher requirements for bearings due to larger turbine ratings

Mainstream offshore wind turbines have increased from 5-6 MW to 10-12 MW, with some projects now tendering for 15 MW+ units.

[Fig.3: Relationship between turbine power and bearing dimensions]

Turbine Power	Main Shaft Bearing OD	Pitch Bearing OD	Technical Requirements
3 MW	approx. 1.0-1.2 m	approx. 1.5-1.8 m	Conventional design
6 MW	approx. 1.5-1.8 m	approx. 2.0-2.5 m	Lightweight design
10 MW	approx. 2.0-2.5 m	approx. 2.8-3.5 m	Impact resistance, long life
15 MW	approx. 2.8-3.2 m	approx. 3.5-4.0 m	Special materials + coating

The larger the turbine power, the higher the load on bearings, and the higher the demands on material, heat treatment, and surface treatment.

3.2 Test data becomes a competitive barrier

Wind turbine bearings are designed for a service life of 20+ years; actual validation cycles are long, making test data a core competitive advantage.

According to industry insiders, a complete test for a 10 MW main shaft bearing requires:

Test cycle: 6-8 months

Test cost: approx. €300,000-500,000

Test data volume: approx. 2 TB

Esterer's accumulated test data is a significant asset valued by Schaeffler in this acquisition.

3.3 Rapid growth in aftermarket business

Europe's installed wind power capacity is about 250 GW, with an annual maintenance market of about €8 billion. Bearing replacement accounts for about 15%-20% of maintenance costs.

Esterer has stable channel networks in the European aftermarket, an important piece for Schaeffler to complete its aftermarket布局.

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4. Industry perspectives

A bearing industry analyst who wished to remain anonymous believes this transaction reflects three trends:

First, the technical threshold for wind turbine bearings is rising. Early wind turbine bearings mostly used conventional designs, but today's larger turbines demand higher load capacity and reliability. New entrants without long-term data accumulation find it difficult to secure orders.

Second, industry consolidation is accelerating. The bearing industry landscape is relatively stable, but mergers and acquisitions in niche segments continue. Medium-sized companies with technological distinctiveness and customer base remain targets for leading firms.

Third, testing capability is becoming a key resource. Mere manufacturing capacity no longer forms a barrier; the value of test data and failure case databases is rising.

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5. Domestic market situation

In contrast, the domestic wind turbine bearing sector has also seen multiple mergers, acquisitions, and capacity expansions in recent years.

[Fig.4: Major domestic wind turbine bearing M&A events 2023-2024]

Date	Acquirer	Target	Area
Aug 2024	A leading bearing company	Jiangsu-based wind bearing factory	Yaw & pitch bearings
Mar 2024	A listed company	Zhejiang-based bearing company	Main shaft bearings
Nov 2023	A wind turbine OEM	Shandong-based bearing factory	Full range

Data shows that in 2023, the domestic wind turbine bearing market size was about RMB 18 billion, with top players' market share continuously increasing. However, compared with foreign companies, domestic firms still lag in test data accumulation and high-end product stability.

A purchasing manager at a domestic wind turbine OEM said: "Currently, main shaft bearings for turbines above 10 MW are still mainly imported. It's not that domestic ones can't be made, but the validation cycle is long, and owners are hesitant to switch."

However, he believes that as domestic installations accumulate tens of thousands of validation data points, the gap is narrowing.

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6. Subsequent impact

Schaeffler stated that Esterer will continue to operate as an independent brand, with the existing management team remaining. Schaeffler also plans to invest in expanding Esterer's test center in Gothenburg for R&D testing of larger bearings.

Analysts believe this acquisition will not directly impact the domestic bearing market but may accelerate the reshuffling of the European wind turbine bearing market.

For domestic bearing companies wanting to enter the European market, Esterer's acquisition means:

One less potential cooperation partner

One less European local model to learn from

Possibly higher entry barriers to the European market

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Sources: Schaeffler official announcement, Esterer annual report, industry interviews