October 20, 2006

Development of "New Grease Lubrication System"
for Angular Contact Ball Bearing in Machine Tool Main Shaft

Realized high-speed rotation with dmn* value of 2.0 million
under grease lubrication without external equipment.

NTN Corporation (Hereafter, NTN) has developed a "New Grease Lubrication System" for angular contact ball bearings in machine tool main shafts. This system enables high speed running at a dmn value of 2.0 million (fixed pressure preload method), completely free of maintenance.

Today, for the main shaft systems of machining centers and compound machine tools, there is a demand for very high-speed rotation. This high speed allows increased efficiency and improved surface finish. There is also a demand for the use of grease lubrication in order to improve work environment and reduce environmental impact.

Therefore, NTN is now putting precision angular contact ball bearings with sealed grease (BNS type) on the market. These bearings, known as the ULTAGE series for machine tools, attain a dmn value of 1.4 million. However, at such a high speed, the amount of base oil must be maintained and heat generation must be reduced in order to increase the life of the grease.

In addition, a system which supplies a required amount of grease to maintain the amount of base oil by force from outside of the bearing needs piping, additional equipment and an energy source for driving the grease. This requires maintenance and increases operating cost.

NTN has developed a mechanism that automatically supplies a small amount of base oil to the raceway. This oil is separated from the thickener of the grease, which is stored in a grease reservoir at the bearing side face. The oil is fed to the raceway on account of the temperature variation due to operation. By using this mechanism, we enabled high-speed operation with a dmn value of 2.0 million with fixed pressure preload method and 1.8 million with fixed position preload method. These values were difficult to attain in angular contact ball bearings with conventional grease lubrication.

This system will be exhibited for reference at the 23rd Japan International Machine Tool Fair (JIMTOF2006), held from November 1 through 8 as "a proposal for the most advanced technology of manufacturing."

Note: dmn = pitch circle diameter [mm] * rotational speed [min-1;]

[Features]

1. High speed rotation exceeding the conventional grease lubrication
   and as high as air oil lubrication
   • Fixed pressure pre-load method dmn value of 2.0 million
             (40% up vs. our conventional product)
   • Fixed position pre-load method dmn value of 1.8 million
             (30% up vs. our conventional product)
2. Completely maintenance free
   • Completely maintenance free mechanism that does not need any additional equipment for lubricant supply or drive energy supply. The bearing adopts a newly developed mechanism to supply small amount of base oil from grease reservoir provided at the bearing side face.
3. Reduced environmental impact (compared to air oil lubrication)
   • Low noise, energy savings and environmental impact reduction due to lack of any external driving equipment and the lack of oil mist generation.

[Application]

Machine tool main shaft supporting bearing (Machining center, compound machine tool, etc.)

[Photo of Product]

<Features>

• High Speed:
  • Fixed pressure preload: dmn value of 2.0 million
            (40% up compared to our conventional product)
  • Fixed position preload: dmn value of 1.8 million
            (30% up compared to our conventional product)
• Completely maintenance free:
  • No external driving equipment to supply lubrication necessary
• Reduction of environment impact (energy saving):
  • No generation of oil mist, no need of driving equipment, low noise

<Application position>

• Machine tool main shaft:

<Design>

<Exhibition>

• This system will be exhibited for reference at The 23rd Japan International Machine Tool Fair held from Nov. 1 through 8, as "a proposal for the most advanced technology of manufacturing".

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