Spherical plain bearings are ready-to-install bearing elements. They consist of a spherical inner ring and an outer ring that can move against each other. They ensure spatial adjustment movements between shaft and housing; enable swivel movements, tilting movements up to a certain tilt angle and orbital movements at relatively low sliding speeds and compensate for misalignments. In combination with a housing, a ready-to-install unit is created which is called a rod end.
In contrast to rolling bearings and ball bearings, spherical plain bearings do not have rolling elements but transmit static and dynamic loads (including alternating loads) directly via the sliding surface to the machine elements. Spherical plain bearings are therefore sliding bearings. Steel/bronze, steel/steel or steel/PTFE are used as the friction pairing between the inner ring and outer ring. The friction pairings steel/bronze and steel/steel require a lubricant film/lubrication and are therefore subject to maintenance, i.e. they must be relubricated regularly. Spherical plain bearings requiring maintenance are suitable for alternating loads, for medium to large swivel movements and for medium sliding speeds. The friction combination steel/PTFE film is maintenance-free and does not require any maintenance. It is preferably used for one-sided loads and for small to medium impact loads. The specified maximum tilt angle must not be exceeded.
Our spherical plain bearings are available in a wide range of variants and designs, e.g. type S with a widened outer ring and in the dimensional series K, E, G and W. Whether maintenance-free (with PTFE film) or requiring maintenance (relubrication), whether made of stainless steel (Niro), bearing steel, free-cutting steel or highly quenched and tempered materials, optionally with sealing, classic with plain bearing ASKUBAL or especially with roller bearing ASKUROL - you can rely on our spherical plain bearing.
A special case are the spherical plain bearings with roller bearings, whose function is comparable with self-aligning ball bearings or barrel bearings. The dimensions correspond to the spherical bearing standard, the load ratings are derived from the standards for roller bearings. They are preferably used for alternating loads, large swivel movements at medium to high speeds as well as full rotations at medium to high speeds. These spherical plain bearings also become a rod end together with a housing.
Spherical plain bearings, a special type of plain bearing, are subject to the standard DIN ISO 12240-1. The standard specifies dimensional series, dimensions, tolerances and the radial internal clearance. The standard is very broadly defined, so that a large number of friction pairings, materials, surface treatments etc. are possible. The designations, the load ratings as well as the service life calculations are not subject to the standard and differ from manufacturer to manufacturer. At first glance, this makes interchangeability between individual competitors difficult, but in most cases an alternative product can be found.
The areas of application are diverse and range from plant construction to bakery machines, conveyor technology, agricultural machines, food technology, textile machines, robotics, road construction, vehicle construction, rail vehicles, medical technology and much more to feed technology.
For customised areas of application, we will develop your spherical plain bearing, your coupling joint or whatever you need and whatever you call it, together with you. Contact us - we are your partner even for difficult applications. Benefit from the quality and reliability of our ASKUBAL spherical plain bearings made in Germany.
Technical basics spherical plain bearings
Spherical plain bearings are ready-to-install bearing elements based on plain bearings. They consist of a spherical inner ring and an outer ring. Their spherical sliding surfaces enable swivel, tilting and rotary movements without edge pressure. They allow for structurally necessary misalignments and can compensate for manufacturing-related misalignments.
Determination of spherical plain bearing size
The selection and determination of the size of the spherical plain bearing is based on the load capacity, the occurring loads as well as the requirements for service life and operational safety. The load capacity of the spherical plain bearings is expressed by the load ratings given in the dimension tables; these serve as decisive characteristic and calculation values. Load ratings of different manufacturers are not easily comparable with each other, as there is no uniform standardised definition of load ratings for spherical plain bearings.
Operating temperature
Our spherical plain bearings can be used without restriction in the operating temperature range from -10°C to +80°C. or spherical plain bearings with RS sealing as well as our roller bearing design, the temperature application ranges can be found in the technical type description.
Load ratings
Spherical plain bearings with plain bearings
Static load rating C0, plain bearing:
The static load capacity C0 is the radially acting static load which does not cause any permanent deformation of the components when rod end is stationary, i.e. the load condition without pivoting, swivelling or tilting movements. lt is also a precondition here that the operating temperature must be in the normal room temperature range and the surrounding components must possess sufficient stability.
Dynamic load rating C, plain bearing:
Dynamic load capacities are used as calculation values for estimating the service life of rod ends subjected to dynamic loads. They do not themselves provide any information about the effective dynamic load capacity of the rod end. For this purpose, additional influencing factors such as load type, swivel or tilt angle, speed curve, maximum permissible bearing clearance or bearing friction, lubrication conditions, temperature, etc. must be taken into account.
Spherical plain bearings with roller bearings:
Our rod ends with integrated roller bearings (ball or spherical roller bearings) are a special feature. The function of the bearings is comparable with self-aligning ball bearings or spherical roller bearings. The load capacities of the rod ends with roller bearings were derived from the standards for roller bearings.
Basic static load rating C0, rolling bearing:
For rod ends, the static load rating corresponds to the load at which the total permanent deformation of rolling elements and raceways is 0.0001 of the rolling element diameter.
Basic dynamic load rating C, rolling bearing supported:
For rod ends, the basic dynamic load rating corresponds to the load at which 90% of a larger quantity of identical bearings reach 1 million revolutions before failing due to fatigue of the rolling surfaces.
Spherical plain bearing selection
The selection of spherical plain bearing sizes must be based on the specified load , the direction of load and the type of load.
Load directions are differentiated as follows:
Load capacity spherical plain bearing
Compared to the rod end housing, the mounted spherical plain bearing has a higher static load capacity as can be seen in the comparison with the static load rating between rod ends and the corresponding spherical plain bearings.
Dynamic load
In case of dynamic load, it is necessary to check the dynamic load capacity of the mounted spherical plain bearing by means of the service life calculation.
Selection of bearing type
The following bearing types are available:
We will support you in the best possible way with your selection.
Tolerances
Spherical plain bearing outer ring
Spherical plain bearing inner ring
*) The tolerances for the outer diameter are only valid for not cracked or not divided outer rings. As a result of the cracking, there is a slight out-of-roundness on the outer ring. However, after installation in a dimensionally accurate housing bore, the original roundness is restored.
Bearing clearance
[Translate to English:]
Bearing clearance is defined as the rad ial and axial freedom of motion of the inner ring.
The axial clearance can basically be a multiple of the radial clearance..
Radial bearing clearance for spherical plain bearings with plain bearings
Radial bearing clearance for spherical plain bearings with ball or roller bearings
Mounting instructions
Tilt angle limitation
For all Askubal spherical bearings and Askurol rods ends, the maximum tilt angle specified in the tables must not be exceeded while mounting or during operation, otherwise the bearing or washers and cover washers may be damaged.
The assembly must be constructed so that the rod end or spherical bearing is effectively prevented from moving further than the given angle. At the same time, however, no major forces may be applied to the housing. lt is also important to ensure that there is always sufficient space available for the seal (particularly with 2RS models), in order to prevent contact with the surrounding components.
Installation
All Askubal spherical bearings and rod ends are very high precision, ready-to-fit bearing elements. For this reason, they must be stored carefully and installed correctly. lt is important to comply with the following points:
- The spherical bearings and rod ends must be kept in their original packaging until shortly before their installation, so that they continue to be effectively preserved for as long as possible. Ensure during the installation process that foreign particles are on no account allowed to enter the outer ring of the bearing.
- The forces required for installation and removal should on no account be transmitted from the spherical form to the bearing shells or raceways of the bearing outer ring.
- For the spherical bearings to run smoothly, the sliding movement must take place between the sliding faces of the bearing inner ring and outer ring. Sliding movements on the shaft or in the housing cause damage and premature failure. For this reason, it is essential for there to be an interference fit between the bearing housing and bearing outer ring and between the bearing inner ring and the connection shaft. This can be achieved by using tight fits and with axial tensioning of the bearing rings. However, the consequence of using tight fits is an alteration in the bearing clearance. Too high interference between the housing and the bearing outer ring causes contraction of the outer ring. Too high interference between the connection shaft and the inner ring causes the inner ring to expand. The following fits have proven suitable for balancing out these alterations as far as possible.
The following fits are a recommendation and may differ in individual cases!
lt is, however, still important with these fits to check that connections are still tight, i.e., in many cases the interference is not sufficient, in which case greater interference may be required.
When installing spherical bearings and rod ends, ensure that the following limit values are not exceeded, to guarantee perfect bearing installation:
Maintenance and lubrication
The useful life of all spherical plain bearings with metallic mating materials is greatly dependent on regular lubrication. A one-off initial grease filling is only adequate if operating loads are very low. The effectiveness of lubrication is mainly dependent on the load, type of load (constant, pulsating or alternating), the swivel angle and sliding speed. Numerous tests in our ASK laboratory have shown that small swivel angles and both very low and very high sliding speeds have an unfavorable effect on the formation of a film of lubricant. A load which acts in one direction only is also unfavorable compared to an alternating load. To ensure optimum and even distribution of the lubricant, initial lubrication and subsequent lubrication should be carried out with the spherical bearing or rod end in an unloaded condition.
Note
To avoid incompatibility of various lubricants that may be used by ASK and the customer, spherical plain bearings are supplied only with an anticorrosive coating. For this reason, spherical bearings and rod ends which need maintenance should be given initial lubrication before commissioning or directly after installation.
We recommend carrying out initial lubrication after a running-in time of approx. 1 hour. Whenever this lubrication is carried out, the bearing must be in an unloaded condition, so that the lubricant can spread without obstruction. Lubrication should continue until the lubricant emerges between the bearing outer ring and the inner ring . For rod ends with a female thread, it is also advisable to fill the space in the shank thread with lubricant up to the threaded connection journal before installation. This reduces the amount of work involved in lubricating with the lubricating nipple.
In case of relubrication via a central lubrication system, pay attention to the dosage, especially for the sealed versions. These could be loosened by too high a pressure or too high a dosage.
Friction pairing steel on bronze
For this friction pairing we recommend corrosion-protective lithium-based pressure-resistant greases or lithium complex metal soap greases. The temperature application range should be between -20°C and +110 °C. For load conditions in the upper limit range, a friction reduction and service life extension can be achieved by using solid lubricants.
Friction pairing steel on steel
For this combination, we also recommend corrosion-protective pressure-resistant greases based on lithium soap with higher base oil viscosity and molybdenum disulphide additives.
Friction pairing steel on PTFE
This friction pairing is characterized by low friction. The sliding foil is made of a material that makes lubrication superfluous and therefore enables maintenance-free operation.
Roller bearings
These rod ends are given initial lubrication with a lithium soap grease.
Useful life and calculation of useful life
Information about useful life is available here.
An exemplary service life calculation for spherical plain bearings of dimensional series K is available here.
An exemplary service life calculation for spherical plain bearings with roller bearings is available here.