SCOA-P wheel

SCOA-P wheels were developed in the late 1940s by the Steel Company of Australia Ltd (the P in the acronym standing for F. C. Paynter, who patented the design)[1] in response to Victorian Railways experiencing fatigue problems with conventional spoked wheels.

Stronger Boxpok type 'B' wheels had been installed on a number of VR locomotive classes in the late 1940s, but they had the disadvantage of being relatively heavy and also restricted maintenance access to axleboxes, underslung springs, and in some cases boiler washout plugs.

Boxpok wheels were proposed for the forthcoming Victorian Railways R class 4-6-4, which had a relatively heavy 19.5-long-ton (19.8 t) axle load, but it had been discovered that the use of a Boxpok wheel would make coupling rod pin removal difficult.

[2] Using a 100-long-ton (100 t) vertical press, load testing was conducted of the strength and elasticity of the SCOA-P wheel centre against a 2,021 lb (917 kg) conventional spoked driving wheel centre of an A2 class locomotive that had the same diameter, but was engineered for a lower 17.5-long-ton (17.8 t) axle load).

[3] Because the Vulcan Foundry, which built the VR J class, built SCOA-P wheeled locomotives for export until ceasing steam locomotive production in 1956, this wheel type was also seen in many of Vulcan's other export markets.