Self Aligning Ball Bearings
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Self aligning ball bearings are suitable for applications where misalignment can arise from errors in mounting or shaft deflection. The steel balls, cage, and inner ring can rotate freely at a certain angle, as it is stated that the bearings have self-aligning features. Accordingly, misalignment of the bearing shaft due to the machining and installation of the shaft and housing will be automatically adjusted.
Physical Characteristics of Self Aligning Ball Bearings
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The self-aligning ball bearing has two rows of balls.
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A common concave sphered raceway in the outer ring.
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The center of whose curvature meets that of the bearing itself, so that the inner ring, balls and cage continue to rotate.
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The self-aligning ball bearing with a tapered bore can easily be fit to the shaft with an adapter assembly.
Advantages of Self Aligning Ball Bearings
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Have the lowest friction of all rolling bearings.
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Run cooler even at high speeds.
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Easy mounting and dismounting.
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The permissible operating speed is not dependent on the common criteria like heat generation or cage stability and strength.
Applications of Self Aligning Ball Bearings
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Self-aligning ball bearings are used for commercial ground shafting applications.
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Since axial load capacity is limited, self-aligning ball bearings are not suitable for applications with heavy axial loads.
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Furthermore, if an adapter is used on the tapered bore of the inner diameter, installation and disassembly are much simpler and for this reason adapters are often used on equipment with drive shafts.
Types of Self Aligning Ball Bearings
The two basic designs of double row self-aligning ball bearings are standard and "E" shaped. The "E" shaped have a larger load carrying capacity and can be used in a wider range of applications. They are available in three designs:
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Basic open design - These self aligning bearings may have a cylindrical or a taper bore. The one with a taper bore requires adapter sleeves with locking washers with which the bearings can be secured on to the shafts.
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Sealed Bearings - The sealed bearings have seals on both sides. They are made of oil and synthetic rubber with a sheet steel reinforcement. Operating temperature is -40° C to 120° C. The outside diameter of the seal is retained in a recess in the outer diameter forming a tight seal are filled with a lithium based grease that inhibits rust and can operate on temperature ranging from -30°C to 110°C. These self aligning bearings may have a cylindrical or a taper bore. The one with a taper bore requires adapter sleeves with locking washers with which the bearings can be secured on to the shafts.
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Bearings with Extended Inner Ring - This type of self-aligning ball bearings are used for commercial ground shafting applications. The bore tolerance allows easy mounting and dismounting. They are located axially by pins or screws that fix in a slot on one side of the inner ring. This also prevents the inner ring from turning on the shaft. When used in pairs the slots should either be adjacent or at the outboard position.
Self Aligning Ball Bearings Specifications & Standards
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Standard cage types - All bearing series are equipped with a pressed cage, except 2322S, which is equipped with a machined cage.
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Dimensions -The dimensions are as per the ISO recommendations.
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Misalignment - They are designed to adjust to the angular misalignment from one bearing to the other within the permissible limits.
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Tolerance - They are usually meant for normal tolerance but can be enhanced.
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Ball protrusion - Bearings with part numbers listed in the diagram below have balls which protrude slightly from the bearing face.
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Allowable misalignment angle - Allowable misalignment under normal loads (loads equivalent to 0.09 Cr): 0.07 rad (4°).This degree of allowable misalignment may be limited by the design of structures around the bearing.
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Internal Clearance -The normal radial internal clearance is taken as standard in cylindrical as well as tapered bore but there may be certain variations. The extended inner ring radial internal clearance is C3 + Normal.
Cages - There are standard cages but some may have pressed steel cage, glass fiber reinforced, or machined brass cages.
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Buying Tips
Consider the followings before you go and shop for self aligning bearings:
Allowable misalignment angle
Operational costs
Hardness at operating temperature
Temperature at high speed
Cage materials
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