Against the background of intensified global competition, NSK will further take quality as a link and work with Panasonic Zhuhai to write a new chapter of supply chain collaboration and innovation.
In the face of large bearings, complex workpiece disassembly efficiency is low, the risk of damage and other industry pain points, SKF innovative technology to respond to market demand, the launch of the new SKF TWFH flexible coil induction heater.…
The Chanllenge丨To help carbon neutrality, expanding the potential of grease lubricated bearings-Previously
During the research and development process, the team analysed in depth the laws of motion of the grease inside the bearings and obtained important results that can be applied to the development of various types of bearings in the future. The following is an interview with members of the development team.
June 24, 2025
Moulded resin cage that achieves the industry’s highest level of high-speed rotational performance
The trend toward shorter machining times has led to the development of high-speed machine tools, and in recent years there has been a growing demand for high-speed rotational performance in spindle bearings for machining centres (machines that can automatically change cutting tools for a variety of machining operations). There are two types of lubrication for machining centre spindle bearings: oil-air lubrication and grease lubrication. Although oil-air lubrication is generally considered to be more suitable for high-speed rotating scenarios, it consumes more electricity, a characteristic that has become a pressing issue against the backdrop of the current urgent need for carbon neutrality.
Against this backdrop, NTN has continued to develop grease-lubricated bearings for high-speed rotation, and in October 2024 released a grease-lubricated bearing product with a new moulded resin cage. This product has a dmn value (bearing performance index, calculated as bearing pitch circle diameter [mm] x rotational speed [min-1]) of 1.35 million. During the research and development process, the team analysed in depth the movement law of the grease inside the bearing, and obtained important results that can be applied to the development of various types of bearings in the future. The following is an interview with members of the development team.
Shoichi Kanazawa, Product Design Department, Bearing Business Division
Masahiro Kasai, Development & Testing Department, Bearing Business Division
Development of cages to reduce heat generation in bearings
1 Oil-air lubrication and grease lubrication
There are two types of lubrication for machining centre spindle bearings: oil-air lubrication and grease lubrication. Conventional high-speed bearings tend to use oil-air lubrication because the viscosity of grease is higher than that of lubricating oil, but there is resistance to agitation when the grease is discharged while the bearing is rotating. However, oil-air lubrication requires equipment such as oil-air supply and oil-mist recovery, resulting in increased power consumption. In contrast, bearings that are simply pre-filled with grease do not require additional equipment or electricity, and are more in line with the trend toward carbon neutrality, so the market for high-speed grease-lubricated bearings continues to grow. Shoichi Kanazawa, who led this development, noted:
“The biggest problem when rotating at high speeds is heat generation. Oil-air lubrication, in which a thin lubricant is mixed with air and injected through a compressor, is effective in controlling heat generation, and is indeed advantageous, especially in scenarios where superior high-speed performance is required. However, there are many high-speed rotating applications that do not require extreme ultra-high speeds, where grease lubrication offers significant advantages in terms of reduced energy consumption. As a result, we have received a great deal of demand for high-speed grease lubricated bearings and continue to push forward with research and development.”
2 Balancing cost and volume production
In order to create a grease-lubricated bearing that can cope with high-speed rotation, the focus of this development was on the cage inside the bearing. The cage is a ring-shaped part that holds the rolling elements (rollers and balls) in place and is mounted between the inner and outer rings, and the goal of the development was to optimise its design in order to curb the heat generated by the bearing.
Conventional machine tool spindle bearing cages are made of heat-resistant phenolic resins, but this development innovatively chose an engineering plastic that can be injection moulded. Although engineering plastics are generally less heat-resistant than phenolic resins, high-performance heat-resistant varieties have emerged in recent years, and the injection moulding process is more conducive to mass production. The research and development work was carried out by Kanazawa in charge of design and Kasai in charge of experiments, with numerical analysis and technical support provided by NTN’s R&D department, the CAE Development Research Institute, and the NTN Next Generation Collaborative Research Institute, which is a joint venture with Osaka University.
Spindles that rotate end mills for machine tool machining
In order to shorten machine tool machining time
Spindles are moving to higher speeds
Therefore, the demand for high-speed performance of spindle bearings is increasing.
3 Iteration of experimental and numerical analysis to explore the ideal shape.
4 Experimentally capturing the movement of grease at the moment of a temperature spike.
R&D began by observing the state of the grease inside the bearing. Kasai, who was in charge of the experiments, made observations by changing the rotational speed and other conditions, and accidentally discovered a key phenomenon:
“From the beginning of the rotation to the completion of the overall coverage of the grease, there was a moment when the temperature rose sharply. Continuous monitoring revealed that at the moment when the grease started to flow to the rolling surface, a “clicking” sound of flow was heard, and at the same time, the temperature increased significantly. This phenomenon has been clearly verified experimentally.”
The grease flow at the moment of temperature rise was a completely new discovery for the two men. After further comparing experiments with different shaped cages, the team made a new discovery. Kanazawa explains:
“Different cage designs lead to differences in grease movement. Not all cages experience a sudden temperature rise in grease flow to the rolling surface during rotation. This suggests that we may be able to control grease flow and thus suppress heat generation through cage design.”
5Numerical analysis based on experimental data, applied to design
The team, led by Kanazawa, carried out numerical analysis, constructed a 3D model of the bearing in combination with experimental phenomena, and analysed the air flow and grease movement during rotation. Kanazawa pointed out:
“Just by slightly changing the clearance between parts and components, the air inside the bearing will change its direction of flow, which in turn will drastically change the movement of the grease. Simply put, when grease flows towards the rolling surfaces, the different dimensions of the various parts of the cage can cause air flowing in an undesired direction to change its direction of flow. On the other hand, when the grease does not flow towards the rolling surface, it is also possible, by means of different cage shapes, to bring the air to a state where it does not affect the grease flow. Understanding this, we know how to design the cage.”
Example of grease motion analysis: When the rotational speed increases, the phenomenon of grease originally located in the inner ring gradually spreading in the direction of the outer ring is reproduced. When the rotational speed exceeds a specific value, an air flow from the left side of the image to the right side is generated near the outer ring (as shown in the figure on the right), causing the grease that had been accumulated on the upper left side to move to the right side and flow towards the rolling surface.
On the other hand, is it feasible that if grease does not flow to the rolling surface, the rapid temperature rise can be suppressed? This is not the case. In order to ensure the durability of bearings for long-term high-speed operation, the grease needs to be kept in the ideal position – i.e. accumulated on the inner ring side of the cage. According to the grease distribution after the endurance test, the grease is consumed faster on the inner ring side of the cage. In other words, even if grease accumulates on the outer ring side, it is difficult to be consumed. Therefore, it is necessary to accumulate more grease on the inner ring side. Kanazawa concludes:
“The grease needs to flow neither to the rolling surface nor to accumulate on the inner ring side of the cage. In our calculations in various cases, we have found that grease in unfavourable positions is more likely to flow towards the rolling surface, whereas grease in the right position is more or less likely to stay in place. This means that designing the inner ring to allow grease to accumulate more easily not only improves durability, but also prevents grease from flowing to the rolling surface, thereby effectively suppressing heat generation. As for the design solution, it was clear.”
This event is the first time that SKF, after organising the Green Supply Chain Forum in 2024, has joined hands with a number of important domestic and international ESG associates to jointly organise a seminar on ESG industrial ecology.
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NSK was also awarded a certificate of inclusion and a trophy for its 25th consecutive year of participation in the S&P Global Corporate Sustainability Assessment (CSA) at the annual Sustainability Yearbook 2025 Forum held on 8 April.
As an important part of cost reduction and green transformation, bearing reconditioning is gradually becoming one of the strategic choices for industrial customers to achieve sustainable development.
Looking ahead, NSK and Wuxi Pilot will closely follow the national ‘dual-carbon’ strategic objectives and ‘new quality productivity’ development direction, focusing on high-end equipment in the field of intelligent manufacturing, and continue to deepen the ‘global industrial chain synergy’ development strategy.
The products and technologies used by SKF in the Faroe Islands space programme demonstrate not only its leadership in bearing manufacturing, but also its commitment to sustainability.
