In rotating equipment, shaft and housing alignment is not always perfect. Installation errors, shaft deflection, vibration and changes in operating conditions can create a small angular deviation between the shaft and housing. If a conventional bearing cannot accommodate this movement, additional stress may be transferred to the raceways and rolling elements.
A Self-aligning Ball Bearing with Cylindrical Bore is designed for this type of working condition. Its spherical outer ring raceway allows the inner ring, balls and cage to adjust their position around the bearing center, helping compensate for a certain degree of misalignment between the shaft and housing.
How Does a Self-Aligning Ball Bearing Work?
The main difference between a self-aligning ball bearing and a conventional radial ball bearing is the shape of the outer raceway.
A self-aligning ball bearing normally has two rows of balls and a common spherical raceway on the outer ring. When the shaft is slightly out of alignment with the housing, the inner ring and rolling elements can adjust their position relative to the spherical outer raceway.
This design is useful when accurate shaft and housing alignment is difficult to maintain. It can also accommodate misalignment caused by shaft bending during operation.
The cylindrical bore refers to the straight inner bore of the bearing. Unlike a tapered-bore bearing, it is mounted directly onto a shaft with a matching cylindrical diameter. This makes the design practical for equipment where direct shaft mounting and straightforward maintenance are preferred.
Why Use a Cylindrical Bore?
Bearing selection is not only about load capacity and speed. The way the bearing is mounted also affects which bore design is appropriate.
A cylindrical bore bearing provides a direct connection between the bearing inner ring and shaft. During replacement, maintenance personnel can work with the shaft diameter and bearing dimensions without needing a tapered-bore arrangement or adapter sleeve.
This is particularly useful for machinery where the shaft has already been designed for a standard cylindrical bearing seat.
The BearingZWZ product range includes cylindrical-bore self-aligning ball bearings in 12, 13, 22 and 23 series. The 12 series is more compact, while the 22 and 23 series provide progressively higher load ratings for applications requiring greater radial load capacity.
What Are the Main Applications?
Self-aligning ball bearings are commonly considered when shaft deflection or mounting misalignment is part of the operating environment. Typical applications include transmission systems, fans, blowers, pumps, conveyors and general industrial machinery.
The BearingZWZ product page also lists mining and cement equipment, electric motors, generators, ventilation systems, speed reducers and material-handling equipment among typical applications.
For example, a conveyor shaft may experience slight alignment changes because of installation tolerances or structural movement. A self-aligning bearing can accommodate the resulting angular displacement within its permissible operating range, reducing the need for extremely precise alignment.
Series Selection: 12, 13, 22 and 23
The series number provides an initial indication of the bearing's size and load characteristics.
12 Series
These bearings have a relatively compact design and are suitable where installation space is limited. The BearingZWZ page lists models such as 1204, 1205, 1206, 1207 and 1208.
13 Series
The 13 series provides a balance between size, load capacity and operating speed, making it suitable for a range of general industrial machinery.
22 Series
Compared with the 12 series, 22-series bearings generally provide higher load capacity while retaining the self-aligning structure. Models listed on the page include 2205 through 2210.
23 Series
The 23 series has larger dimensions and higher load ratings within the listed range, making it suitable for equipment subject to greater radial loads or more demanding operating conditions.
The correct series should ultimately be selected according to shaft diameter, housing dimensions, load, speed, lubrication and operating environment rather than series number alone.
Cylindrical Bore vs. Tapered Bore
Both cylindrical-bore and tapered-bore self-aligning ball bearings provide self-aligning capability, but their mounting arrangements are different.
A cylindrical bore has a straight inner diameter and is normally mounted directly onto a matching shaft. A tapered bore has a conical inner surface and can be installed using an appropriate adapter arrangement.
Therefore, the choice is usually determined by the existing shaft and housing design. If the machine already uses a cylindrical shaft seat, replacing it with a tapered-bore bearing is not simply a matter of choosing the same bearing size.
Checking the original bearing designation, shaft diameter, mounting dimensions and installation method before replacement can prevent compatibility problems.
Internal Clearance and Cage Options
Internal clearance is another factor that should not be overlooked.
The BearingZWZ page states that its self-aligning ball bearings are available with C2, CN, C3, C4 and C5 internal clearance options. Different clearance levels can affect bearing behavior under operating temperature, load and speed conditions.
Cage construction also varies. The listed options include pressed steel cages, machined brass cages and nylon cages. According to the product information, pressed steel cages are standard for bearings with an outer diameter up to 200 mm, while larger bearings use machined brass cages; nylon cages are stated to withstand operating temperatures up to 120°C.
The cage and clearance should therefore be selected according to the actual working environment rather than treated as interchangeable specifications.
How Much Misalignment Can It Accommodate?
Self-aligning does not mean that the bearing can operate with unlimited shaft misalignment.
NSK specifies a permissible dynamic misalignment of approximately 0.07 to 0.12 radians, or about 4° to 7°, under normal loads for its self-aligning ball bearing designs, while noting that the actual allowable angle can depend on the surrounding structure.
This distinction is important during bearing selection. If a machine has severe shaft deflection, heavy radial loads or substantial shock loads, a self-aligning ball bearing may not be the appropriate solution. Spherical roller bearings, for example, are designed for different load and speed conditions.
What Should Be Checked Before Replacing the Bearing?
When replacing a self-aligning ball bearing, checking only the bearing's outside diameter is not enough. The following information should be confirmed:
Shaft diameter
Housing bore
Bearing width
Original bearing designation
Required radial load capacity
Operating speed
Internal clearance
Lubrication method
Cage material
Expected shaft misalignment
Operating temperature
For example, the BearingZWZ specifications show that different models have different basic dynamic load ratings, static load ratings and permissible speeds. The 1205TN1, 2207TN1 and 2309M are therefore not interchangeable simply because they belong to the same general self-aligning bearing family.
Conclusion
A self-aligning ball bearing with cylindrical bore is particularly useful when a rotating shaft may experience small alignment errors, shaft deflection or installation deviations. Its double-row ball arrangement and spherical outer raceway allow the bearing to accommodate angular misalignment while maintaining smooth rotation.
For equipment such as conveyors, fans, pumps, motors, reducers and general industrial machinery, choosing the right bearing requires more than matching the bore diameter. Series, load rating, speed, internal clearance, cage design and mounting conditions should all be considered together.
Understanding these factors makes it easier to select a suitable Self-aligning Ball Bearing with Cylindrical Bore and avoid premature bearing wear caused by an incorrect specification.