High-Temperature Bearings Overview – Why Specification Matters

When equipment operates above 300 °C, standard steel races and polymer cages fail within hours. A correctly specified high-temperature bearing keeps kilns, ovens, and turbomachinery running for years. This guide translates the latest DIN 623-1 and ASTM standards into practical selection criteria, so you can match every specification detail to your real-world thermal load, speed, and contamination profile.

What Are High-Temperature Bearings? Definition & Core Specifications

High-temperature bearings are rolling-element bearings engineered to sustain reliable operation at continuous temperatures beyond 200 °C and peak excursions above 450 °C without measurable loss of hardness, dimensional stability, or lubricating film. Key specification benchmarks include:

• Material heat-treat stability: ≥ 58 HRC at 350 °C
• Radial clearance groups: C4H, C5H (DIN 620-4)
• Cage temperature index: PI ≥ 250 °C for PEEK, ≥ 300 °C for AISI 304 or bronze
• Lubricant evaporation loss: < 5 % after 100 h at 280 °C per ASTM D972

High-Temperature Bearing Temperature Ranges & Material Specifications

Continuous °C	Peak °C	Ring Steel	Ball/Cage	Lubricant
250	300	100Cr6 HTF	Si₃N₄ hybrid	PFPE grease
350	400	X65Cr13 (SS)	SS 316L	Graphite paste
450	500	NiCr20TiAl (Inconel-based)	Full Si₃N₄	Solid MoS₂ coating

Specify stabilisation suffixes S1–S4 per ISO 492 to control residual austenite < 3 %, preventing growth at 400 °C.

Load & Speed Ratings – How to Specify High-Temperature Bearings Correctly

Dynamic load rating (C) drops 5 % for every 50 °C above 150 °C. Adjust catalog C by factor fT = 0.95^((T−150)/50).
Speed limit nθ is governed by cage material and lubricant flash point:
nθ = n25 · (kθ / k25) where kθ = (460 − T)/(460 − 25) (Arrhenius factor).
For graphite-lubricated full-complement cylindrical rollers at 350 °C, reduce DN value to 50 000 mm·rpm vs. 300 000 at room temperature.

High-Temperature Bearing Lubrication Specifications – Grease, Paste, Solid Film

• PFPE grease: Base oil viscosity 420 cSt at 40 °C, evaporation < 1 % @ 299 °C (ASTM D2595). Specify NLGI 2, additive package with 5 % Al-Naphthenate for anti-corrosion.
• Graphite paste: Ash content < 0.1 %, particle size D90 5 µm; apply 2 g per 6210-size bearing.
• MoS₂ solid film: Thickness 3–5 µm, burnished, friction coefficient ≤ 0.08 at 450 °C in vacuum.

Dimensional & Tolerance Standards for High-Temperature Bearings

Order bearings with C4H or C5H clearance to absorb radial expansion. Tolerances follow ISO 492 P6 or P5, but specify “HT” suffix for heat-stabilised rings. Shaft seat recommendation: k5/j5 for 300 °C, transitioning to f6 above 400 °C to allow differential expansion.

Sealing & Shielding Options in High-Temperature Bearing Specifications

• Labyrinth shields (ZZH): 0.3 mm air gap, 302 SS, withstand 500 °C without creep.
• Graphite-impregnated glass-fiber seals (TSH): Reduce contamination ingress by 85 % compared with open types, max 350 °C.
• Integral ceramic spray coating on OD: Creates 25 µm secondary seal surface, specified as suffix “CS”.

Industry-Specific Specification Examples – Furnace, Glass, and Food-Grade High-Temperature Bearings

• Furnace fan: 6312-2ZHTC4S3, 120 °C→400 °C cycle, PFPE grease, 17 000 h L10.
• Glass tempering rolls: NU220ECMS1, full Si₃N₄ rollers, MoS₂-coated, 460 °C, 0.15 m/s.
• Food dryer: Stainless 6203-2RSTH, FDA-compliant graphite paste, wash-down safe, metal-detectable cage.

Common Specification Mistakes When Selecting High-Temperature Bearings

1. Ignoring stabilisation suffix—rings grow 0.15 % at 350 °C without S3.
2. Using ordinary C3 clearance; switch to C4H minimum.
3. Overlooking cage quality—PEEK above 250 °C softens, causing seizure.
4. Applying standard lithium grease—drops to liquid at 180 °C, leading to sudden failure.

FAQ – Quick Answers on High-Temperature Bearing Specifications

Q: Can I relubricate a 450 °C bearing?
A: Only if you specify a relubrication groove (suffix “G”) and use solid MoS₂ powder; PFPE greases oxidise above 320 °C.

Q: What is the maximum rpm at 400 °C?
A: For a 6210 hybrid ceramic, DN = 40 000 → 2 000 rpm. Specify silicon-nitride balls to raise limit 25 %.

Q: Do high-temperature bearings cost more?
A: Expect 3–4× standard price due to heat-stabilised steel, Si₃N₄ elements, and special lubricants; ROI arrives through 5× longer service life.

Conclusion – Specify High-Temperature Bearings with Confidence

Match temperature class, clearance, cage, and lubricant to your operating envelope, and you will cut unplanned downtime by > 60 %. Use this specification guide as a checklist, quote the exact suffixes when ordering, and your next high-temperature bearing will deliver the reliability your process demands.

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