Rod ends are ready-to-install spherical bearing units. In some places they are also called ball joints. They consist of the rod end housing with threaded shaft and the mounted or pressed-in spherical plain bearing. Rod ends are available with a female thread, that means the threaded shaft has a hole into which the thread is cut, or with a male thread, in which case the thread is on the outside of the threaded shaft. Depending on the direction of rotation of the thread, it is a right-hand thread or a left-hand thread.
Our rod ends are available in a wide range of variants and designs, in dimension series K and E. Whether maintenance-free (with PTFE sliding layer film) or requiring maintenance (relubrication), whether made of stainless steel, free-cutting steel, rolling bearing steel or highly quenched and tempered materials, with bronze and brass, with male or female thread, with right-hand thread or left-hand thread, optionally with sealing, classically with sliding bearing ASKUBAL or especially with rolling bearing ASKUROL - you can rely on our rod end.
A special case are the rod ends with roller bearings, whose function is comparable with self-aligning ball bearings or barrel bearings. The dimensions correspond to the rod end standard, the load capacities are derived from the rolling bearing standards. 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.
Steel/bronze, steel/steel or steel/PTFE are used as friction pairings. The friction pairings steel/bronze and steel/steel require a lubricant film and are therefore maintenance-required, i.e. they must be relubricated regularly. Rod ends requiring maintenance are suitable for alternating loads, for medium to large swivel movements and for medium sliding speeds. The sliding combination steel/PTFE sliding layer film is maintenance-free and does not require any maintenance. It is preferred for one-sided loads and for small to medium impact loads.
The function of the rod end is determined by the spherical plain bearing. Like spherical plain bearings, rod ends ensure spatial adjustment movements between the shaft and housing; allow swivel movements, tilting movements up to a certain tilt angle and orbital movements at relatively low sliding speeds and compensate for misalignments.
Rod ends are mainly used in lever and linkage connections. Another area of application in the pneumatic and hydraulic industry is the connection between cylinders and connecting parts. For this purpose, there are special hydraulic rod ends that have been developed to fit the hydraulic cylinders and piston rods.
Askubal rod ends are made of machining steel, bearing steel, bronze, brass, stainless steel and PTFE sliding film. Depending on the load, we use tempered or highly tempered materials.
Rod ends are subject to the DIN ISO 12240-4 standard, which specifies dimensional series, dimensions, tolerances and radial internal clearance. The standard is very broadly defined so that a large number of friction pairings, surface treatments, materials, etc. are possible. The designations, the load ratings and 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.
We manufacture our ASKUBAL rod ends at our company site in Korntal near Stuttgart.
The areas of application are diverse and range from plant construction to filling plants, conveyor technology, agricultural machinery, textile machinery, pneumatics, hydraulics, robotics, road construction, vehicle construction, rail vehicles, food technology, medical technology and much more to feeding technology. The rod end is also present outside of mechanical engineering, e.g. in organ pipes, shock absorbers, door opening systems and much more.
We will work with you to develop your rod end, your coupling joint or whatever you need, and whatever you call it, for customer-specific areas of application and a wide range of loads. Contact us - we are your partner even for difficult applications. Benefit from the quality and reliability of our ASKUBAL rod ends made in Germany.
Technical basics rod ends
Rod ends are ready-to-install spherical plain bearing units. They consist of a housing with a connection thread (male or female thread) and the installed spherical plain bearing. The function is determined by the spherical plain bearing. The spherical sliding surfaces enable swivelling, tilting and orbital movements without edge pressures. Design-related necessary misalignments are made possible and manufacturing-related misalignments can thus be compensated.
Determination of rod end size
The selection and determination of the size of the rod end is based on the load capacity, the occurring loads and the requirements for service life and operational safety. The load capacity of the rod ends is given in the dimension tables, which serve as decisive characteristic and calculation values. The load capacities of the various manufacturers are not readily comparable with each other, as there is no uniform standardised definition of the load capacities.
Operating temperature
Our rod ends can be used without restriction in the operating temperature range from -10°C to +80°C. For rod ends with RS sealing and our roller bearing version, the temperature ranges can be found in the technical type description.
Load ratings
Rod ends 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.
Rod ends 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.
Rod end selection
The selection of rod end sizes must be based on the specified load , the direction of load and the type of load.
Load directions are differentiated as follows:
Type of load
Depending on the load type, the following load factors must be taken into account for the permitted max. radial housing load capacity Fr perm.
The coefficients SB and SK serve to estimate the load limit.
The max. permissible enclosure load capacity Fr zul. is thus reduced as follows:
Fr perm. (KN) = stat. Load rating C0 (KN) x SB x (SK)
The load coefficient SK takes into account the weakening of rod ends with external thread and lubrication hole or grease nipple as well as for housings with roller bearings. This can only serve as a rough guide value. Coefficients for shock loads such as those caused by increasing bearing clearance or for additional loads caused by simultaneous rotary motion of the bearing are not included.
Note: If the component is to be loaded to the load limit, especially if the failure of the component poses a danger to life and limb or causes damage, the use must in any case be proven by practical tests.
Furthermore, it should be noted that special requirements are made for use in aircraft. Our standard products do not meet these special requirements.
Dynamic load
In the case of dynamic loading, two tests are required for the above reasons:
- Check of the housing load capacity.
- Checking the dynamic load capacity of the installed spherical plain bearing using the service life calculation.
Equivalent rod end load
In the case of rod ends with plain bearings, the axial load capacity is limited by:
- The type of mounting of the spherical plain bearing in the rod end housing or the design of the rod end
- The maximum bending load capacity of the housing shaft at the clamping point.
However, the design of the Askubal rod ends ensures the transmission of the resulting axial force component, which results when the radial load capacity is fully utilised under a tilted position up to the permissible tilting angle α.
Selection of bearing type
We will support you in the best possible way with your selection.
The following bearing types are available:
Tolerances
(Tolerance symbols DIN ISO 1132, ISO 6125)
Rod end housings
h, h1: Height size from shank end to bearing bore centre
d3: Shank thread
Spherical plain bearing outer ring
Spherical plain bearing inner ring
Radial clearance
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 rod ends with plain bearings
Radial bearing clearance for rod ends with roller bearings
Mounting instructions
Tilt angle limitation
For all Askubal 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 (Fig. a). At the same time, however, no ajor 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 (Fig. b).
Installation
All Askubal 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 rod ends must be kept in their original packaging until shortly before their mounting, 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.
- In order for the rod ends 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 interferance 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 interferance between the housing and the bearing outer ring causes contraction of the outer ring. Too high interferance 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 interferance is not sufficient, in which case greater interferance may be required. When installing spherical bearings and rod ends, ensure that the following limit values are not exceeded, in order to guarantee perfect bearing installation:
Maintenance and lubrication
The useful life of all rod ends 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 unfavourable effect on the formation of a film of lubricant. A load which acts in one direction only is also unfavourable 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
In order to avoid incompatibility of various lubricants that may be used by ASK and the customer, rod ends 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 characterised 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.
Lubrication nipple shapes
Please note, that the use of a non-standard lubricating nipple (DIN 3405 shape D) causes a cross sectional variation for housings with male thread which means a reduction of the static load capacity C0 .
Useful life
The useful life of a rod end or a spherical plain bearing is given in the number of swivel movements (from one end position to the other and back) or in operating hours. It is limited by operationally disturbing wear increase (bearing clearance) as well as by impermissible friction increase.
In principle, an exact calculation of the service life is not possible due to the operating conditions and influencing factors that are often difficult to determine. However, our empirically determined calculation method, which is based on a large number of endurance tests on our ASK test rigs under various load conditions as well as our many years of experience, provides practical guide values.
Equivalente spherial plain bearing load
If rod ends or spherical plain bearings are not loaded purely radially but additionally axially, an equivalent bearing load F [kN] is used in the calculation, which is determined as follows:
Fr = Radial component of load
Fa= axial component of load
Y = axial factor (from table)
lf the spherical bearing is loaded purely radially, the equivalent bearing load is equal to the radial load.
Surface pressure
Surface pressure is the compressive stress at the contact point between two components. The contact surface is assumed to be a level surface at right angles to the direction of force.
lt is calculated as follows:
p = surface pressure (N/mm²)
F = equivalent bearing load [kN]
dk = inner ring ball diameter [mm]
c = outer ring width [mm]
Sliding speed
The mean sliding speed can be calculated for continuous movement from the following formula:
v = mean sliding speed [m/min]
dk = inner ring ball diameter [mm]
β = half swivel angle [°] (insert β = 90° for complete revolutions)
f = swivel frequenzy of speed [min-1]
Calculation of useful life 1
Rod ends and spherical plain bearings with plain bearings (dimension series K)
Nominal service life
When using the maintenance-free spherical plain bearings and rod ends with friction pairing on PTFE , a radial clearance increase of approx. 0.1 to 0.2 must be expected, especially with higher alternating loads (p > 5N/mm²).
Example calculation 1:
A rod end is tobe mounted at the oscillating reciprocal effective end of a crank mechnism. The operating conditions are as follows:
- half swivel angle β 0 20°
- load in the end positons F = max. 1000 N
- swivel frequency f = 100/min
- ambient temperature approx. 50°C
- max. spherical size: 16
- max. enlarged radial clearance: 30 µ
- periodic lubriction is possible
- required useful life: 1000h
Solution: Due to the low permissible enlarged radial clearance of max. 30 μm, a rod end with mating materials steel on high-duty bronze is chosen. Since the load is relatively low, a rod end KI 10 is to be checked for its suitability in this situation.
Rod end data:
Inner ring ball diameter dk = 19,05 mm
Outer ring width D = 10,5 mm
Static load capacity C0 = 15 kN
Checking the rod end housing load capacity:
Since the max. load 1000 N = 1 kN, there is a 2.49 times safety factor for the permissible load.
Calculation of useful life:
Example calculation 2:
A swivelling mechanism is tobe operated with a maintenance-free rod end by means of an air cylinder.
- half swivel angle β = 30°
- max. load F = 1500 N one-sided effective
- load direction : uniform
- swivel frequency 30/min
- ambient temperature120°C
- required alternating load number
Solution: A rod end for air cylinders in accordance with Cetop RP103P/ DIN 24335 is selected: KI 16-DM16x1.5
Rod end data:
Inner ring ball diameter dk = 28.575 mm
Outer ring width C = 15 mm
Static load capacity C0 = 34 kN
Checking the rod end housing load capacity:
Since the max. load 1500 N = 1.5 kN, there is a 7.5 t imes safety factor for the permissible load.
Calculation of useful life
Calculation of useful life 2
Rod ends with ball or roller bearings (ASKUROL)
The basic design of these rod ends with antifriction bearings is the same as the construction principle for self-aligning ball bearings (sizes 6 to 16) and barrel roller bearings (sizes 16 to 30). For this reason, the method of calculation is identical to the calculations used for antifriction bearings.
Dynamc load capacity C
The dynamic load capacity Cis the load at which 90% of a large quantity of identical rod ends reach 1 million revolutions before they fail owing to fatigue of the rolling surfaces.
Static load capacity C0
The static load capacity C0 for these rod ends is expressed by the static radial load which causes a total permanent deformation of 0.0001 x rolling element diameter at the most highly stressed contact point between the rolling element and the raceway.
Determining rod end size
In determining the rod end size it is necessary to establish whether the inner ring rotates in the loaded condition or is loaded during slow swivel movements. The former is a dynamic load and the latter is a static load.
Calculation of the dynamic load is based on the start of material fatigue being the cause of failure. This is an inevitable process in which the raceway becomes pitted, and depends on the load and rotational speed.
Calculation of the static load takes into account that indentations can occur in the raceway or the rolling elements when the inner ring is stationary, or during short swivel movements (<5°). lt is assumed in the calculation that a permanent deformation does not impair the function of the rod end.
Equivalent load for rod end
Nominal service life
Example calculation:
A rod end is to be mounted at the oscillating reciprocal effective end of a crank mechanism.
The operating conditions are as follows:
- half swivel angle β = 50°
- load in the end positions P = max. 2, 8 kN
- swivel frequency = 300 min-1
- ambient temperature approx 60°C
- required rod end size: 20 (Innengewinde)
- required useful life: 70000 h
Solution: Due to the relatively low load and relatively high swivel frequency and large swivel angle, a rod end KI 20204 is tobe checked for its suitability in this situation.
Rod end data:
Static load capacity C0 = 13,2 kN
Dynamic load capacitiy C = 19,9 kN
Roller bearing
Verification of housing load capacity
Static load capacitiy housing C0 = 42 kN
Since the max. load 2.8 kN, there is a 2.46 times safety factor for the permissible load.
Calculation of useful life
The required useful life of 70.000 h = operating hours is therefore fulfilled .