Part 2 – Whitemetalling
Continuing on from the earlier update for the Keep K163 Going project, the Axlebox assessment (Part 1) , in this part we will try to describe the ‘dark art’ of whitemetalling.
As mentioned in Part 1, K163 has a plain bearing configuration as opposed to more modern rolling element bearings which is typical in modern day rollingstock.
Plain bearings comprise a bronze bearing shell which is lined with whitemetal on the actual bearing surfaces. As the locomotive operates, gradually the whitemetal bearing materials wear due to friction and bearing the weight of the engine. Luckily when K163 was initially restored in 1986, she was not long from a major examination during her Victorian Railway career (1941-1968). In effect we were relying on residual maintenance from the VR days until now.
The first step to prepare for re-metalling of the bearings, is to remove them from the axleboxes. The bearings have been removed from the boxes so that during the process of pouring we can maintain the required temperature for proper bonding without having to maintain this temperature on the axlebox. This involves punching out (where possible) the dowel pins which retain the bearings into the axleboxes. In some cases where the dowels could not be punched out, they are drilled out, a time consuming task! Once complete the bearing can then be pressed out of the axleboxes. In the case of K163 the left and right driven bearings were loose in the axleboxes so this step was not required.
The next phase of metalling involves alot of heat, for this you need a large burner!
The whitemetal melting point is around the 250 – 300 deg.C mark (pouring 350-400) so a propane gas torch is sufficient to melt out the old whitemetal lining from the bronze bearing. Once the whitemetal is removed, the next step involves heating the bronze bearing with sustained heat to expel oil from the porous material. This is required to ensure the surface is free of oil during the re pouring stage to achieve proper bonding of the fresh material.
Any contaminants, dirty and grim are then removed from the bronze bearing with a thorough sand blasting.
With the bearings now prepared and clean the next step is to start relining with the new whitemetal. Firstly it is required to ‘tin’ the bearings with solder so that the new whitemetal will bond with the parent bearing material.
In order to cast the new whitemetal a special mould is fabricated providing sufficient material to allow for machining to achieve the required surface finish (smoothness) at the correct journal size plus running clearance. The mould and bearing shell are then heated together to ensure the metal being poured does not solidify on contact with a cold surface. The pour is a task requiring steady hands that work quickly to ensure all of the material is poured before it starts to cool, without splashing molten metal everywhere!
Once the bearing is removed from the mould the bearing is then ready to be pressed back into the axlebox prior to machining. The machining process will be described in a later update.
We hope that you have enjoyed our description of the ‘dark arts’ associated with steam locomotive maintenance. Please support the Keep K163 Going campaign so we can continue our progress and realise the benefits of this process once we return to some sort of normality post COVID-19.