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PRECAUTIONS

The given loads are those that carry the part to the failure. During designing phase it is very important to consider these data together with the safety factors chosen for each application. Concentrated acids and basic elements could affect the chemical resistance. Bearings are not suitable for a highly corrosive environment. Operating maximum temperature means the one that bearings can withstand for a long period of time without any significant modification. In any case higher operating temperatures are allowed for short periods. Please always contact EuroSnodi in the case bearings should be used with temperature over 100C° and under -30C°. Anyway, at higher temperature, over 100C°, it is recommended an adequate lubrification with special grease, used for high temperature. With reference to the given friction values, the given lower limits indicate what is feasible under optimal conditions; it is advised to base calculations on specific situations during the designed stage. A minimal hardness values of HRC40 are recommended in coupling steel/metal. It could be required a harder counter face material in case of abrasive conditions and high sliding speeds in combination with high loads or vibrations. Please always contact EuroSnodi. A roughness value of 1.6Ra or even less is recommended in coupling steel and metals, but not lower than 0.8Ra. In case bearings are installed in polluted or dusted environments or in heavy operating conditions it is recommended a frequent maintenance and eventually, in addition, a protection system. The main load should be applied in the radial sense of the bearing hole and coaxial with the body. Data written in the catalogue are not binding and could be modified by EuroSnodi in order to increase products features. EuroSnodi is not responsible for non-proper use of their products. EuroSnodi is not responsible for all the damages caused by the buyer due to an inadeguate installation or use of the products, whatsoever not for any sum in excess of the amount received for the goods for which liability is claimed. All the pictures and drawings in our catalogue are EuroSnodi's property, therefore it is not allowed to use them without EuroSnodi authorization.

 

SPHERICAL PLAIN BEARINGS AND ROD ENDS
Spherical plain bearings and rod ends are mechanical items with unified dimensions. They are used as sliding bushes in all applications where it is important a constant direction of the load. They are also designed to allow oscillations, misalignments and light alignment movements.

 

SELECTION OF THE SUITABLE BEARING
A number of factors have to be taken in consideration when selecting the type of the bearing to be used in a specified application. Their combination affects bearing size, material and service life. Due to a not exact rule in the selection of bearing, it is very important to consider the factors of safety. The instructions given as follow will help the designers in the selection of the suitable bearing they need for their application. The following information mentioned together with the experience and the common sense of the designer give a good idea about the better choice.

 

LOADS
Bearings could be subjected by the following loads:
- Fr = Radial load
- Fa = Axial load (not too high)
- Fr + Fa = Combined load

Spherical plain bearings are mainly designed for radial loads, however they could also work under condition of combined loads. Bearing should be adequate to the application in order to satisfy service life and operational reliability requirements.

 

BEARING SIZE
The bearing size has to be adequate to the loads to be carried in respect of the service life required by the application. Therefore the bearing size is strictly related to the duration and not only to the loads. The designer has to analyse the loads to be carried in order to evaluate the impact on the bearing that will affect the service life.
It is possible to summarize loads as static loads and dynamic loads, besides the above mentioned directions:

- Static Loads: this is a constant acting load during a long period of time or load acting when the bearing is not working or doing just light alignment movements.

- Dynamic loads: this is a non constant acting load, an alternated load or load acting when the bearing is working.

During their work, radial spherical bearings can accommodate radial load and simultaneously little axial loads. In order to calculate the duration of the bearing, it is important to summarize the loads in one equivalent load, that represents and finally has the same effects (duration/wear) of the original load on the bearing.

The equivalent load is calculated as follow:

where:

The equivalent load obtained has to be compared with the:
- Dynamic load coefficient C, through the Duration formula
- Static load coefficient C0, through the Strength formula

C and C0 are the extreme loads (maximum) over that the bearing will fail immediately.
Moreover C and C0 are calculated in a hypothetic conditions and they should be referred to the real application thanks to some factors (as follows) that can help the designer in selecting EuroSnodi products.

 

DURATION FORMULA FOR DYNAMIC LOADS

Where:
D = Theoretic rating service life, calculated as number of oscillations or number of cycles.
DH = Theoretic rating service life calculated as operating hours.
C = Dynamic load coefficient in N (see catalogue)
P = Equivalent dynamic load in N
d1 = Bearing sphere diameter in mm (see catalogue)

were:
= Half angle of oscillation () Half angle of oscillation
= Half angle of tilt
ƒ = Frequency of oscillations or load reversal speed in min
k1 = Inversion factor
k2 = Maintenance factor
k3 = Temperature factor
k4 = Sliding friction factor
k5 = Fatigue factor
k6 = Material coupling factor

 

INVOLVED FACTORS

 

STRENGTH FORMULA FOR STATIC LOADS
P ≤ Co · k7 · k3 = Pamm
Co = Static load coefficent in N (see catalogue)
k7 = Load direction factor

were

 

MEDIUM SLITHERING VELOCITY
The medium sliding velocity is calculated by: v = 5.8 · 10-7 · d1 · β1 · ƒ
were
v = Medium slithering velocity in m/s
d1 = Bearing sphere diameter in mm (see catalogue)
where:
= Half angle of oscillation () in case of rotation
= Half angle of tilt
ƒ = Frequency of oscillation or load reversal in min-1

 

SPECIFIC PRESSURE
The specific pressure is calculated by:

Where
p = Specific pressure in N/mm2
P = Equivalent dynamic bearing load in N
C = Dynamic load coefficient in N (see catalogue)
k = Pressure factor in N/mm2

 

ADMISSIBLE SLITHERING VELOCITY
LSlithering velocity is submitted to the dimensions of the bearings, loads to be carried, coupling materials and temperatures. For this reason it is important to compare the bearing working parameters with the admissible one calculated as follows:

 

LUBRIFICATION AND MAINTENANCE
Rod ends that require maintenance have to be periodically lubricated or greased in order to increase their life. It is possible to use the common grease made of mineral or synthetic oils used in mechanical field. In case of temperature over 100C°, it is recommended an adequate lubrication with special grease, used for high temperature (please contact EuroSnodi in these cases).

 

TEMPERATURES OF OPERATIONS
The suitable bearing material at a related temperature are as follows:

The suggested temperature range allow the longer duration of the bearing. The limit temperature should never be overpassed, unless special loads situations or bearing working. In any case, over the limit temperature it is no longer valid the given formula of bearing duration, because over the limit temperature the working life of the bearing decreases in an unforeseeable way.

 

SUGGESTED CLEARANCE FOR BEARING HOUSING

 

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