Design and safety guidelines

The chapter Technical principles brings together the essential guidelines on the subjects of friction, rating life and the adjacent construction.

Principles of lubrication

The lubrication of spherical plain bearings requiring maintenance is covered in detail in the corresponding chapter for spherical plain bearings.

Relubrication

Rod ends requiring maintenance must be lubricated.

They have relubrication facilities, except for smaller rod ends of some series that do not have lubrication grooves and lubrication holes. These rod ends are indicated in the dimension tables.

Rod ends to DIN ISO 12240-4, dimension series E with bore diameter d = 15 mm to 20 mm are relubricated via a hole in the rod end eye housing, ➤ Figure. For reasons of housing strength, these rod ends do not have lubrication nipples.

Relubrication via hole

 Grease gun with tapered nozzle

Dimensioning

In the case of rod ends, the permissible static load of the housing and shank must always be checked. In calculation of the rating life of the rod end, the decisive factor is the rating life of the spherical plain bearing fitted in the housing.

The direction of load and the type of load determine the design of the rod end and the sliding contact surface of the spherical plain bearing.

Permissible loading of rod ends

The permissible load depends on the type of load.

Pulsating or alternating loads subject the material of the rod ends to greater stress than constant loads. For calculation, these operating conditions must be taken into consideration by means of the load factor f_b , see table.

Loading of rod end

The following applies:

The permissible load on the rod end P is calculated as follows:

Load factors

Basic static load rating

In this case, the basic static load rating C_0r indicates the load carrying capacity of the housing and shank under static tensile load. At room temperature, it includes a safety factor of at least 1,2 in relation to the yield strength of the material used for the housing and shank. The basic load rating describes the maximum permissible static tensile load when utilising 83% of the material yield strength at the most highly stressed cross-section.

Basic dynamic load rating

The basic dynamic load rating C_r refers to the spherical plain bearing fitted and is a parameter for calculating the bearing rating life. It is dependent on the sliding contact surface and has a significant influence on the rating life of the rod ends.

Calculation example for radial rod end GIKR25-PB

The rating life of the radial spherical plain bearing is calculated on the basis of the steel/bronze sliding contact surface.

Given data

The given data for calculation of the rating life are as follows:

• machine on a packaging line
• pulsating load.

Operating parameters

Bearing load	Fr min	=	10 000 N
	Fr max	=	20 000 N
Swivel angle	ß	=	45°
Swivel frequency	f	=	20 min–1
Time required for indexing operation (cycle)		=	3 s
Number of indexing operations		=	300 cycles/h
Relubrication interval	Iw	=	40 h
Operating temperature	ϑ	=	21 °C

Bearing data

Radial rod end			=	GIKR25-PB
	Basic dynamic load rating	C r	=	47 100 N
	Basic static load rating	C0r	=	72 900 N
	Sphere diameter	dK	=	42,85 mm

Required

• Bearing with the required rating life L_hN(ED) ≧ 5 000 h.

Calculation of rod end size

The permissible static load on the rod end is calculated using the load factor f_b = 3, see table.

The rod end GIKR25-PB with the basic load rating C_0r = 72 900 N is suitable.

Checking of permissible loads

Specific bearing load

The specific bearing load must be calculated with the aid of the specific load parameter K and checked for validity. In the case of a concentrically acting, variable force F, P = F_max = 20 000 N:

Sliding velocity in swivel motion

The sliding velocity must be calculated with the aid of the sphere diameter d_K and the swivel angle β and checked for validity:

Specific frictional energy pv

The specific frictional energy pv must be checked for validity:

Determining the rating life equation

For calculation of the rating life, the valid rating life equation must be selected and then subjected to correction.

Selection of the valid rating life equation

For plain bearings requiring maintenance, the following applies:

Correction factors, as a function of bearing type

The correction factors necessary for the steel/bronze sliding contact surface must be selected from the matrix and used to correct the rating life equation appropriately.

Rating life equation following correction

Calculation of rating life

The values for the correction factors in the corrected rating life equation must be taken from the diagrams. The specific plain bearing factor K_L = 2,3.

Correction factors

Rating life L_h

The rating life is calculated as follows:

Rating life L_hN with periodic relubrication

The rating life can be increased by means of periodic relubrication as a function of the relubrication interval.

The necessary relubrication interval and preferred relubrication interval must be calculated and checked for validity:

Based on a relubrication frequency L_h/l_W = 280 h/40 h = 7, a correction factor f_NH = 2,1 is determined. Based on a swivel angle β = 45°, the correction factor f_Nβ = 3,2.

Taking account of the operating duration

3 s/cycle gives 20 cycles/min at a utilisation of 100%. The number of indexing operations of 300 cycles/h gives 5 cycles/min

The operating duration ED is calculated as follows:

Rating life L_hN taking account of the operating duration ED:

Result

The selected radial rod end GIKR25-PB fulfils the requirement for a rating life L_hN(ED) ≧ 5 000 h.

Welding of hydraulic rod ends

The thermal distortion occurring during welding must be kept as small as possible.

Recommendation

The following procedure has proved effective in the welding of rod ends:

• The thickness of the weld seam should be as small as possible. This should be based on the load.
• If thicker weld seams are necessary, these should be welded in several layers.
• Electrodes with low heat generation should be used, such as Kb electrodes.
• The current strength selected for welding should be towards the lower limit.

Tightening torques for fixing screws in hydraulic rod ends

The fixing screws in hydraulic rod ends must be tightened according to a defined scheme, ➤ Figure and table.

Hydraulic rod ends

Slotted on both sides ·

Slotted on one side · A, B, C, D = hexagonal socket screw

Tightening torques