CARBÂ® toroidal roller bearings â a revolutionary ... - Acorn Bearings

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1 Product information 2 Recommendations 3 Product data Self-aligning bearing system Page ............. 12 Page ............. 37 The CARB toroidal roller bearing – the cornerstone of the new self-aligning bearing system The conventional solution Until recently a self-aligning bearing system consisted of two self-aligning ball bearings if there were high speeds and light loads, or two spherical roller bearings when there were heavy loads and moderate speeds. These bearing systems are simple, have good load carrying capacity and can compensate for misalignment resulting from manufacturing or mounting errors as well as shaft deflections (➔ fig 1 ). So far, so good – but what happens if the shaft were to expand axially? In a traditional bearing arrangement, axial expansion of the shaft is accommodated by the non-locating bearing. The fits for this bearing are selected so that one of the bearing rings will be able to move axially on its seating as the shaft expands. Generally this movement is between the outer ring and the housing seating. This movement is always accompanied by friction, which gives rise to induced axial forces in both the bearings (➔ fig 2 ). In addition, the movement of the loose bearing on its seating can create damaging vibrations because the movement is ”stick-slip” and not smooth (➔fig 3 ). The loose fit has a negative effect on the stiffness of the bearing arrangement. The bearing ring with the loose fit can also begin to “wander”, which can wear the seating and lead to fretting corrosion and possibly “weld” the ring to its seating (➔ fig 4 ). The new solution Today, the CARB toroidal roller bearing is available for the non-locating position in a self-aligning bearing system. It is no longer necessary to compromise. 8 Conventional solution Two spherical roller bearings (or selfaligning ball bearings) compensate easily for angular misalignment of the inner ring with respect to the outer ring Axial expansion of the shaft can influence the load distribution in the bearings Load conditions in a conventional solution Changes in axial force in a non-locating bearing during the machine start-up phase; internal axial forces of corresponding magnitude are produced in the locating bearing In a non-locating bearing which has been clamped in its housing bore seating, heavy axial forces prevail in the bearing arrangement after the startup phase and dramatically shorten bearing service life F a /F r 0,2 0,1 0 F a /F r 1,5 1 0,5 0 Fig Fig 2 F r t t Fig Fig 1 3 4
1 Product information 2 Recommendations 3 Product data Self-aligning bearing system Page ............. 12 Page ............. 37 1 °C Fig Fig Fig 5 6 7 The new solution A spherical roller bearing or a self-aligning ball bearing as the locating bearing and a CARB toroidal roller bearing as the nonlocating bearing compensate for angular misalignment of the rings resulting from errors of alignment or deflection under load as well as thermal changes in shaft length, virtually without friction There are no internally induced axial forces. The rings of the non-locating bearing should be axially and radially located CARB toroidal roller bearings are able to compensate for misalignment and accommodate axial displacements within the bearing (➔ fig 5 ). This means that both rings of the nonlocating bearing can be axially located in the housing and on the shaft (➔ fig 6 ). If it is necessary to secure the rings so that they cannot “creep”, they can be mounted with an interference fit, thus enhancing the radial stiffness of the bearing arrangement. This is an optimal solution for applications with undetermined load direction, e.g. vibrating applications, because internal preload and wear to the bearing seating in the housing are eliminated. No longer is there a compromise between a tight fit and axial freedom. A CARB toroidal roller bearing is designed to accommodate axial displacement without inducing additional axial internal forces or friction (➔ fig 6 ). This means that the loads acting on the bearing are determined exclusively by external radial and axial forces. Because of this, a bearing system incorporating a CARB bearing will have lower loads and better load distribution than a conventional bearing system. This translates into lower operating temperatures, higher operating viscosities, extended relubrication intervals, and a significantly longer service life for both the bearings and the lubricant (➔ fig 7 ). With a CARB toroidal roller bearing F r 9 Lower operating temperatures extend relubrication intervals and bearing service life in the non-locating position, the many excellent design characteristics and properties of SKF spherical roller bearings and self-aligning ball bearings can be fully exploited. This provides new opportunities to further optimize machine design.
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CARBÂ® toroidal roller bearings â a revolutionary ... - Acorn Bearings