What are the uses of bearings
intact. Ludwig Meister's blog
For the 2nd part housing bearing units
Rolling bearings are absolute precision parts that place high demands on the installation situation. Just think of the necessary dimensional accuracy and surface properties of the bearing seats on the shaft and in the housing. But also the necessary meticulous accuracy when aligning the bearing, since bearings are already tensioned with the slightest misalignment of the shaft. With normal deep groove ball bearings, for example, misalignments of just 2 to 10 angular minutes are tolerable. An arc minute is the sixtieth part of an angular degree.
A well-designed bearing enables astonishing performance in terms of numbers of revolutions, load ratings or concentricity. The only problem is that in many applications such a high performance is not required that would justify such an effort.
In these cases, the use of housing bearing units is often suitable, the main advantages of which are their ease of attachment and their ability to compensate for misalignments. Due to the particularly good sealing of these bearings, they are also ideally suited for difficult environmental conditions.
Housing bearing units consist of radial insert ball bearings that are installed in suitable standard housings. A large variety of housing variants enables a similarly large variety of applications as normal deep groove ball bearings despite standardized individual parts.
Structure and properties of housing bearing units
Radial insert ball bearings are based on deep groove ball bearings with a spherical outer ring. The housing bearing units can compensate manufacturing or assembly-related misalignments of the shaft very well due to the correspondingly spherical receiving bore of the radial insert ball bearing housing.
The compensation of misalignments and angular errors of up to 5 ° is possible if the housing bearing unit does not have to be relubricated later during operation.
If relubrication is to be possible during operation, misalignments of up to 2 ° can still be compensated.
In concrete terms, this means that the surrounding construction and the alignment of the bearings during assembly do not have to be as precise as with normal deep groove ball bearings.
As with normal deep groove ball bearings, it is also possible to compensate for operational shaft deflections within a few angular minutes. Housing bearing units do not allow any axial displacement and can therefore normally not compensate for changes in the length of the shaft caused by heat.
Fixing the radial insert ball bearing on the shaft
Radial insert ball bearings can be easily pushed onto the shaft during assembly. This is because, unlike standard metric bearings, the inner rings of radial insert ball bearings are manufactured with a plus tolerance. This means that the inside diameter is always larger than the specified nominal size within the permissible dimensional deviation. This results in transition or sliding seats for standard shafts with h tolerances (the shafts are tolerated to minus).
In contrast, normal metric bearings are always tolerated to minus. With a corresponding shaft as a counterpart, a tight fit is created that has a positive effect on the load-bearing capacity of the bearing. It is therefore usually necessary to knock the bearings onto the shaft or to thermally expand them prior to assembly.
There are different types of fastening to fix radial insert ball bearings on the shaft.
Grub screw fastening
The most common is the threaded pin fastening, in which the bearing is fixed to the shaft by means of two threaded pins. The two threaded pins have a fine thread and are self-retaining thanks to the cup point at their tip. The holding ability is improved by flattening the shaft. This type of fastening for radial insert ball bearings is also suitable for changing directions of rotation if the loads are not too high.
Eccentric ring attachment
The second very common variant is the eccentric ring attachment. Here the eccentric ring is pushed over the inner ring collar and rotated in the direction of rotation of the shaft until it clamps. The eccentric ring is then secured with grub screws.
Since the ring clamps on the shaft with a segment of a circle, it is gentle on the shaft. At higher speeds, the eccentric ring is only suitable if the direction of rotation remains the same.
Other types of attachment
Adapter sleeve fastenings or bearings with a cylindrical seat are rarely found.
These types of mounting keep the shaft concentric in the bearing. This results in a smoother running of the bearing, a possible change of direction of rotation and significantly higher possible speeds. The bearing properties (speed, direction of rotation, etc.) are then identical to those of standard bearings. However, the surrounding construction must then also be designed as with standard deep groove ball bearings. The main benefit of these bearings compared to normal bearings is therefore only the compensation of misalignments via the spherical outer ring, no longer the simple attachment option.
Sheet steel housings, cast housings and plastic housings are available as materials.
Sheet steel housing
Sheet steel housings are the cheapest option and are very easy to assemble. However, they are not highly resilient and only allow moderate speeds. In addition, sheet steel housings cannot be relubricated. They are therefore only used for the simplest of applications. In combination with rubber insulating rings, which can be mounted between the housing mounting hole and the radial insert ball bearing outer ring, vibrations can be dampened well. This reduces the running noise of the storage. In addition, the rubber ring allows a certain amount of leeway to compensate for wave expansion.
Cast housings are the "classic". They are very robust and can withstand significantly higher radial and axial loads. They can also be used for higher speeds and have a device for relubrication. Cast housings therefore offer the broadest field of application.
Plastic housings are mainly found in the food industry. They are combined with radial insert ball bearings made of stainless steel or bearings with galvanized bearing rings. This makes them corrosion-proof and chemically resistant to the media that often occur in the food industry. A smooth surface of the housing as well as highly effective multiple seals of the radial insert ball bearing enable regular, proper cleaning of the housing bearing units. To create an additional seal against heavy soiling, radial insert ball bearing units are also available with additional end covers. These can be closed or have a shaft leadthrough.
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