BOGIES AND SUSPENSION - South Central Railway

CHAPTER 6 – BOGIES AND SUSPENSION
WAGON MAINTENANCE MANUAL
Page 97 of 121
Demetalled shells, which pass the dimensional check, should then be given the
ringing test individually. Shells, which do not give satisfactory sound, should be
rejected.
The demetalled shell should also be visually inspected for cracks. Shells
having cracks, will not normally give satisfactory sound in the ‘ringing test’. But in
any case, cracked shells should be rejected.
Shells which are warped and do not permit even a true slipper plate to sit
square on the back of the shell, should, if possible, be rectified by machining or
otherwise rejected. It is important that the surface to be lined with white metal is
prepared very satisfactorily. This must be carried out either by machining or by
grinding with a coarse portable grinder until the surface is bright all over. It must be
ensured that any serrations found on the surface of the shell are properly ground and
where necessary machined.
The under-cuts of anchorage grooves, recesses, awkward corners and pockets
should be scrapped so as to remove all dirty spots and sharp edges, thereby
eliminating cracking of the white metal lining when the bearings are put into service.
The most effective method is by immersion in a hot alkaline cleaning solution
(solution of caustic soda 10-15%) followed immediately by washing in cool running
water.
A freshly machined new shell or a demetalled shell where surface preparation
has been satisfactorily carried out may not require the degreasing operation if it is
immediately taken in hand for tinning. There is often some lapse of time between the
machining and tinning operations of a shell and it is, therefore, desirable that the
degreasing bath is also introduced in the bolt to ensure complete elimination of any
oily substance on the shell.
The pre-heating should be carried out in thermostatically controlled electric
furnace fitted with pyrometer and preferably with a conveyer. The pre-heating
temperature range should be between 200 o C and 250 o C.
The degreased shell should be given an application of liquid flux on the
surface to be tinned and then placed in the pre-heating furnace. Remove the shell
from the pre-heating furnace and apply liquid flux by brush uniformly on the surface
to be tinned. The flux should be prepared by adding zinc chipping to cold
concentrated commercial hydrochloric acid (gravity not less than 1.15) till no more
dissolves (about 245 grams of zinc per litre of acid). The solution should be allowed
to stand over-night with excess of zinc then decanted. To this solution should be
added 60 grams of Ammonium chloride (salt) per litre of the decanted zinc chloride
solution.