Product category:
Bearings
News Release from: NSK UK | Subject: L-PPS caged bearings
Edited by the Engineeringtalk Editorial
Team on 09 June 2003
High-capacity bearings keep compressors
running
Novel high-capacity plastic-cage cylindrical roller and angular contact bearings aim to further the rapid growth of screw compressor technology.
NSK is furthering the rapid growth of screw compressor technology with the development of new, high capacity, plastic cage cylindrical roller and angular contact bearings The new bearings benefit from greater load carrying capacity and improved lubrication, enabling them to meet the demands of compressor and refrigerator users for extended trouble-free life and longer intervals between overhauls
This article was originally published on Engineeringtalk on 4 Jul 2008 at 8.00am (UK)
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The greater efficiency and quieter operation of helical screw technology are two of the major reasons why it is increasingly the mechanism of choice for use in air-compressors, refrigerators and gas compressors.
Key to the technology is a design employing helical male and female rotors that mate precisely together to ensure highly efficient gas compression.
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Recently, the already extensive demands placed upon these bearings have increased further, as a result of the market requirement for compressors that operate trouble free for longer periods and have longer intervals between overhauls.
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One bearing manufacturer, NSK, has anticipated this requirement and developed a new range of bearings, with L-PPS plastic cages (linear polyphenylene sulphide).
The bearings provide greater load-carrying capacity and have much improved lubrication capability.
They also offer excellent thermal and chemical stability.
The advantages of bearings employing L-PPS plastic cages are applicable not only in screw compressors, but also in other applications where high temperature and/or special conditions exist.
The L-PPS material is a glass fibre reinforced plastic developed by NSK and subject of a patent application.
Designed for high temperature use, L-PPS can function as a bearing cage material at temperatures up to 190C.
Additional advantages of the material are that its strength and chemical stability change little, even when used with compressor oil, refrigerator oil or ammonia gas.
Cages manufactured from L-PPS are available on both the new types of cylindrical roller and angular contact bearings that NSK has developed for use in screw compressors.
In both types of bearings, substantial improvements in load capacity have been achieved by redesigning the bearing interior to take full advantage of the L-PPS plastic cages.
As a result, basic dynamic load rating has been improved on cylindrical roller bearings by as much as 50%, and on angular contact bearings by a maximum of 20% - when compared to conventional bearing types.
The result is substantial improvements in fatigue life for the two types of bearings.
In respect of cylindrical roller bearings the improvement can be as much as 280% (in the range from 70 to 280%), and that for angular contact bearings up to 70% (in the range from 30 to 70%).
In addition to their improved load capacity and fatigue life, angular contact bearings in the new range are also benefiting from an increase in their axial load limit of between 10 and 25%.
This means that, even if an excessive load is applied, the balls will not override the groove shoulder of the inner and outer rings of the bearing.
Furthermore, in the event of slight shock loads, indentation damage is reduced compared with conventional types.
The final major improvement resulting from the L-PPS design is to lubrication performance.
This is due to a design in which frictional contact - and heat generation - within the bearings is reduced by guiding the highly wear resistant L-PPS cage via the rolling elements, instead of by the inner or outer ring, as is the case with conventional bearings.
In addition, the simplified L-PPS design realises more space within the bearings, with the result that lubricant flow into and out of the bearings is improved, leading to lower running temperatures.
In operational terms these design benefits mean that it is possible to overcome the occurrence of seizure and abnormal wear due to poor lubrication at the guide surfaces of conventional-type bearings.
The new L-PPS caged bearings are available with bore diameters ranging from 25 to 65mm, for both cylindrical roller (NU type) and angular contact ball bearing types, and are suitable for operating temperatures up to 190C.
For special applications where this maximum temperature rating is likely to be exceeded, NSK offers its unique Spacea high-temperature series.
These redefine the operating parameters for high temperature bearings in all areas of manufacturing and processing technology, with a new, patent pending, bearing design that provides outstanding levels of performance in normal atmospheric and vacuum environments at temperatures up to 400C. Request a free brochure from NSK UK ...
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