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| Bearing designs for paper machines | |||||||||
Rolling bearings used in the production of paper must withstand continuous production cycles, high- temperature conditions, increasing loads and higher speeds. | |||||||||
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As a major supplier of rolling bearings for papermaking machines, NSK has researched the many operating problems of bearings in the industry. The result of this research is a new generation of bearing products that address the specific requirements and problems associated with all areas of the papermaking process. One of the major problems addressed is the trend to higher operating temperatures in the dryer sections of papermaking machines. These temperatures, which can be as high as 200°C on newer machines, cause high thermal stresses, which can lead to the fracture of the inner rings of the spherical roller bearings used in the dryer sections. The same problem can occur as a result of rapid dryer warm up. The excessive thermal stresses that result can lead to broken bearings and costly downtimes. NSK has analysed the mechanism of inner ring fracture, and established a strength evaluation method that has enabled them to develop the TL (Tough and Long-Life) specification. The TL specification is a special surface treatment of an original steel type. It attains high raceway surface hardness and dimensional stability under temperatures of up to 200°C while. At the same time is has the same level of compressive residual stress at the raceway surface as conventional carburised steel. This feature increases the fracture resistance performance commonly experienced with conventional spherical roller bearings. In fact TL specification bearings have higher inner ring fracture resistance compared to bainite steel and bearing steel. The raceway surface hardness of the TL material also exceeds that of bainite bearing steel and carburised steel. This means that TL specification steel achieves a longer life, when foreign debris is present, than any of the other bearing steels. In addition to their use in dryer sections, TL Series spherical roller bearings offer operating and enhanced life benefits in drying cylinders, pv, canvas, paper and breaker stack bottom rolls, soft calendars, and yankee dryers Innovative materials and design technology helped also in developing the HPS series of spherical roller bearings for use in other small diameter rolls in the papermaking process: these include canvas rolls, paper rolls, felt rolls and rider. The HPS series is a design of spherical roller bearing (SRB) that offers twice the running life of conventional SRB of the same size, together with a 20% increase in running speed. These performance advantages translate into benefits such as cost saving, and reduced maintenance and energy costs. | |||||||||
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