NTN : Development of “Machine Tool Spindle Bearing with Air Cooling Spacer for Grease Lubrication”〈Product〉

Industry's first, proprietary bearing air-cooling technology contributing to higher speed and higher rigidity machine tool spindles

NTN Corporation (hereafter, NTN) has developed the industry's first 'Machine Tool Spindle Bearing with Air Cooling Spacer for Grease Lubrication' by applying its proprietary air-cooling technology to increase high-speed rotational performance and rigidity of grease lubricated bearings by approximately 10%. This allows the usage limit of high-speed rotation for grease lubricated bearings to be increased from the previous dmn value*¹ of 1.4 million to 1.6 million. This means that grease lubricated bearings, which are beneficial from cost and environmental perspectives, can be used in machining centers, multi-function machines and other high-speed equipment where air-oil lubrication is conventionally required.

Machine tools are increasingly being used in recent years to machine parts with complex shapes or hard-to-cut materials like titanium. There is also higher demand for increased productivity, with greater need for multi-function machines and 5-axis machining centers with numerous machining functions in a single unit. With such demands, bearings for spindles also need a greater level of high-speed rotational performance and rigidity than conventional products. There is high demand in particular for environmentally friendly grease lubrication without the need for lubricant tanks or supply units. However the amount of heat generated within bearing increases when grease lubricated bearings operate at high-speed rotation. This makes the grease deteriorate quicker so that reducing heat generation during bearing rotation was a major issue.

To address this issue, NTN has applied the technology used in the air-oil lubricated 'Machine Tool Spindle Bearing with Air Cooling Spacer'*² released in 2016 for the development of a new grease lubricated bearing.

The developed product consists of the bearing and inner/outer ring spacers. The outer ring spacer features a 'cooling air nozzle' which injects compressed air for cooling (hereafter, cooling air) toward the inner ring spacer. This enables cooling of the inner ring spacer and adjacent inner ring. The result is an approximately 10% increase in bearing high-speed rotational performance and rigidity compared to conventional products without cooling air supplied.

As machining processes become more centralized, demand for increased productivity and lower environmental impact are expected to increase significantly into the future. NTN will offer a grease lubricated bearing with both high-speed rotational performance and high rigidity that achieves a much lower level of heat generation.

NTN will exhibit the developed product at 'The 29th Japan International Machine Tool Fair (JIMTOF2018)' to be held at Tokyo Big Sight from November 1 to 6, and will propose it to various machine tool manufacturers and spindle manufacturers.

1. The dmn value represents bearing rotational performance. dmn value = dm (bearing pitch circle diameter, mm) × n (rotational speed, min^-1)
2. NTN TECHNICAL REVIEW No.84, (2016) No.52

Applications

Machine tool spindles (machining centers, lathes, multi-function machines), etc.