BOGIES AND SUSPENSION - South Central Railway

CHAPTER 6 – BOGIES AND SUSPENSION
WAGON MAINTENANCE MANUAL
Page 84 of 121
The particular step size of bearing should always be fitted on the
corresponding step size journal. ‘B’ size bearing should not be fitted on ‘A’ size
journal. The dia of ‘B’ size bearings less than it will rest against the journal on its side
instead of at centre and will result in hot box. In extreme cases, step size ‘A’ bearing
can be used on ‘B’ size journal and the ‘B’ size bearing on ‘C’ size journals. Care
should, however, be exercised that length suits the journal for which lateral play
should be checked. In no case, ‘C’ size bearing should be used on ‘B’ and ‘A’ size
journals and ‘B’ size bearing on ‘A’ size journals.
It is important to identify the step sizes of the bearing and journals.
Identification color strips should be painted at one of the recesses on the top of the
bearing brass to know its step size with following color scheme :-
Step size ‘A’ - Green
Step size ‘B’ - Yellow
Step size ‘C’ - Red.
Suitable span gauges should be used for measuring the diameter of the
journals by which step size of journal can be decided. The length of the journal
mostly falls within step size of the journal based on dia. The lateral play of the brass
may be checked on a dummy journal or on a journal on which the brass will be used.
The gauge to be used for checking the lateral play. Step size brasses, however ensure
adequate initial lateral clearances. The prescribed minimum and maximum lateral
play of the brasses is tabulated below:-
Lateral play of
Trolley
Four Wheeler
brass on journal BG MG
BG MG
Minimum 5 3 5 3
Maximum 10 6 10 10
One of the main reasons for the introduction of step size bearing brass is to
ensure an initial arc of contact of 30 o on the crown. In the course of service, the arc of
contact will increase. At the time of re-packing, if the brass is not found to be sound,
it should be side relieved with hand scraper so as to provide once again a 30 o arc of
contact at the crown. The advantages of providing 30 o arc of contact are as under :-
i. It will ensure an adequate feed of oil to the fluid oil film.
ii. It will permit the bearing to easily adjust itself to the geometry of the
particular axle box
iii. In the event of excessive plastic flow of the white metal, there will be
lesser possibility of the oil feed being blocked by the spread white metal.
Adequate number of bearing brasses of different size should be stocked to
workshop and in sick lines.