I. High Temperature, The Most Hardest "Exam" for Bearings

In the operation of industrial equipment, for every 10℃ increase in temperature, the oxidation rate of bearing lubricating grease doubles; when the temperature exceeds 150℃, the hardness of ordinary bearing steel begins to decrease and its dimensions start to change; when the temperature exceeds 200℃, conventional lubricating grease has already carbonized and failed - this is not "wear", but "melting".

 

The challenge of high temperature on bearings is systematic. Lubricating grease rapidly oxidizes, cokes, and loses its properties at high temperatures. After the oil film breaks, the rolling elements come into direct contact with the raceways, resulting in increased friction and further temperature rise, creating a vicious cycle. At high temperatures, the steel undergoes a structural transformation, with a decrease in hardness and changes in dimensions, and the clearance becomes uncontrollable. Sealing components age, harden, and deform under high temperatures, and the protective barrier fails. Whether it is the combustion chamber of an aircraft engine, the steel billet of a metallurgical rolling mill, or the sealed cavity of a new energy vehicle electric drive system, high temperature is testing the limits of bearings in the same logic.

 

The global high-temperature bearing market is expanding rapidly. The market size of automotive high-temperature bearings is expected to grow from 3.474 billion US dollars in 2025 to 4.572 billion US dollars in 2032; the broader high-heat bearing market had a valuation of approximately 6.92 billion US dollars in 2024 and is expected to reach 10.71 billion US dollars in 2031. The growth of the market is driven by more and more equipment being pushed to higher temperature boundaries.

 

NMT, a Japanese company with over a hundred years of expertise in bearings, integrates material science, thermal management, and precision manufacturing into the entire industrial chain of high-temperature bearings. With vacuum degassing high-carbon chromium bearing steel, "Ota Bailei" special heat treatment, and high-temperature alloy retaining rings as technical support, it provides high-temperature-resistant, long-life precision bearing solutions for high-temperature scenarios such as aircraft engines, metallurgical rolling mills, new energy electric drive systems, and glass-ceramic kilns.

 

II. Core Failure Modes of High-Temperature Bearings

Understanding the failure mechanism is the prerequisite for solving the problem. In high-temperature environments, the failure of bearings usually evolves along three paths.

 

Path 1: Lubrication Failure. This is the most common starting point for the failure of high-temperature bearings. Conventional lubricating grease begins to accelerate oxidation at 100℃, volatilizes and loses a lot at 150℃, and carbonizes and cokes at 200℃. Without lubrication protection, the metal contact between the rolling elements and the raceways generates a sharp increase in friction, the temperature rise becomes out of control, and the bearings fail within a few hours. Studies show that a considerable proportion of bearing damage is related to poor lubrication.

 

Path 2: Thermal Expansion and Misaligned Clearance. Steel expands at high temperatures, and the thermal expansion coefficients of the inner ring, rolling elements, and retaining rings are different, resulting in varying expansion amounts. The inner ring expands and presses the rolling elements, reducing or even eliminating the clearance; the outer ring is limited in expansion, leading to increased contact stress. When the clearance disappears, the bearing gets stuck, and excessive contact stress causes the inner ring to crack. In a certain thrust self-aligning roller bearing, a circumferential crack occurred in the bearing ring during use, and the fundamental reason was the poor contact between the roller and the edge, resulting in concentrated thermal stress.

 

Path 3: Material Performance Degradation. High temperatures cause the hardness of bearing steel to decrease and the fatigue resistance to drop. Ordinary bearing steel begins to lose hardness and has a significantly shortened fatigue life when used for a long time at 150℃. Although M50 and other heat-resistant bearing steels can work at temperatures below 315℃, the cost is high.

 

III. NMT's Technical Defense Line for High-Temperature Bearings

NMT has constructed a systematic technical defense line from materials to structures, from lubrication to sealing for the three failure paths of high-temperature conditions.

 

High-temperature alloy retaining rings - resisting thermal expansion. The matching degree of the retaining ring's thermal expansion coefficient with the bearing steel directly determines the guiding accuracy of the rolling elements at high temperatures. NMT developed high-temperature alloy retaining rings for angular contact ball bearings, whose thermal expansion coefficient precisely matches the bearing steel, maintaining a reasonable guiding gap in the wide temperature range from room temperature to 300℃. When the bearing temperature rises from normal temperature to 300°C, the cage and the rolling elements expand synchronously, and the guiding clearance remains unchanged - the rolling elements will not be clamped due to the disappearance of the clearance, nor will they shake due to excessive clearance.

 

"External Hardness and Internal Flexibility" heat treatment - against material degradation. NMT uses vacuum degassing high-carbon chromium bearing steel, and through precise forging and secondary quenching processes, reduces non-metallic inclusions to an extremely low level. After "Ottabain" special heat treatment, the surface hardness of the bearing reaches HRC62-64, and the anti-wear performance is improved by 40%. The core part maintains sufficient toughness to resist thermal stress impact. This "external hardness and internal flexibility" characteristic increases the rated life by more than twice compared to industry standards.

 

Wide temperature range lubrication system - against lubrication failure. Lubrication is the lifeline of high-temperature bearings. NMT matches special lubricating grease for high-temperature conditions, maintaining excellent oil retention, water resistance, and corrosion resistance in the high-temperature area. Within the -45°C to 155°C wide temperature range, NMT's long-lasting low-volatile lubricating grease has a volatile content of ≤ 0.003mg/g, and does not lose or carbonize in high temperatures. For extreme conditions exceeding 200°C, NMT can adapt to ceramic mixed bearing solutions, where silicon nitride ceramic rolling elements can withstand higher temperatures and do not require lubrication.

 

Thermal balance simulation design - against cumulative temperature rise. NMT introduces thermal balance simulation during the design stage, optimizing the combination of ball diameter and raceway curvature for different conditions. After the bearing reaches a thermal stable state, the internal clearance is precisely in the optimal range for elastic fluid dynamic lubrication. At the key position of the cage in angular contact ball bearings, a small guiding slope is set to actively direct the lubricant to the entrance of the raceway when the bearing rotates at high speed, while expelling the heated lubricant from the contact area, creating a similar forced convection heat exchange effect. This passive thermal management design reduces the steady-state operating temperature of the bearing by nearly ten degrees Celsius.

 

Four. Core application scenarios

NMT high-temperature bearings mainly serve fields with high temperatures, harsh conditions, and strict reliability requirements.

 

Aerospace engines - the "gatekeeper" of extreme temperatures. Aerospace engine bearings are the technical high ground of high-temperature bearings. The main shaft and turbine bearings of jet engines are exposed to temperatures of approximately 200°C and 300°C respectively. The combination of NMT's high-temperature alloys cage and special heat-stable treated steel maintains dimensional stability and guiding accuracy in the wide temperature range from room temperature to 300°C. In extreme conditions such as lean oil and no oil, NMT bearings can still maintain short-term operation due to material properties.

 

Metallurgical rolling - the high-temperature坚守 of steel water. The rolling machines， continuous casting machines， and straightening machines in the metallurgical industry are subjected to high-temperature radiation and heavy-load impact. Rolling machine bearings operate continuously under the combined conditions of high temperature， heavy load， and eccentric load. NMT high-temperature bearings counter thermal stress impact with "external hardness and internal flexibility" heat treatment， maintain lubrication with wide temperature range lubricating grease， and prevent dust intrusion with multiple sealing structures.

 

New energy electric drive system - high heat challenge in sealed cavities. The drive motor of new energy vehicles operates in a sealed cavity， with limited cooling conditions. The e-Axle uses grease lubrication with ceramic ball bearings， which are lightweight and effectively suppress centrifugal force， reducing heat generation during high-speed rotation. Combined with the synthetic long-life lubricating grease with excellent oil retention in the high-temperature area， the drive motor can operate continuously at high temperatures and achieve long-life.

 

Glass ceramic kilns - extreme test of thousand-degree heat radiation. The conveying roller bearings of glass annealing kilns and ceramic tunnel kilns are subjected to continuous heat radiation. Kiln vehicle bearings are in the high-temperature environment for a long time， and ordinary bearings crack due to insufficient anti-thermal fatigue performance. NMT high-temperature bearings counter thermal stress impact with heat-stable treated steel and high-temperature alloy cages， maintaining dimensional stability and structural integrity under continuous heat radiation. The first step in the selection process is to determine the operating temperature. For temperatures below 200°C, specially heat-treated bearing steel combined with high-temperature lubricating grease can be used; for temperatures ranging from 200 to 300°C, high-temperature alloys for cage and specially heat-treated steel should be selected; for temperatures between 300 and 500°C, heat-resistant steels such as M50 tool steel should be used; and for temperatures above 500°C, silicon nitride ceramic bearings or Inconel alloys should be chosen.

 

Clearance selection. For high-temperature conditions, C3 or C4 large clearances should be selected to provide sufficient space for thermal expansion. The normal CN clearance will disappear due to thermal expansion at high temperatures, causing jamming and locking.

 

Lubrication method. For temperatures below 200°C, polyurethane-based or composite sulfonate calcium-based high-temperature lubricating grease can be used; for temperatures ranging from 200 to 300°C, synthetic oil-based high-temperature grease should be selected; for temperatures above 300°C, solid lubrication or ceramic dry-running solutions are recommended.

 

Installation and maintenance. When installing high-temperature bearings, the impact of thermal expansion on the fit should be considered. Real-time monitoring of the bearing temperature is required during operation. Regular checks for changes in clearance are necessary in high-temperature environments. If the clearance expansion exceeds 15% of the original value, replacement is required. Regular inspection of the sealing condition is necessary to prevent sealing failure due to high-temperature aging.

 

VI. Value Summary

High temperature is the most challenging test for bearings - lubricating grease carbonizes at high temperatures, steel softens at high temperatures, clearance disappears at high temperatures, and seals age at high temperatures. Each failure path challenges the material limits and design boundaries of bearings.

 

NMT high-temperature bearings are supported by high-temperature alloy cages, vacuum degassing high-carbon chromium bearing steel, and "Ottobre" special heat treatment technology. From material source to thermal management, the performance degradation under high-temperature conditions is fully controlled throughout the entire chain. The high-temperature alloy cages maintain a reasonable guiding clearance in the wide temperature range from room temperature to 300°C; the wide-temperature range lubricating grease does not lose or carbonize at high temperatures; the "outer hard and inner tough" heat treatment ensures the structural integrity of the bearing in the combined load of high temperature and impact.

 

When an aircraft engine operates at the extreme temperature, when a metallurgical rolling mill continuously works beside molten steel, when a new energy electric drive system rotates at high speed in a sealed cavity - NMT high-temperature bearings provide stable accuracy and long-lasting lifespan, making high temperature no longer a "roadblock" to the reliability of equipment. Mainstream specifications have ready-to-stock inventory, support for non-standard customization, and professional technical teams provide selection and technical support.