Second cylinder is cast for Churchward 47XX ‘Night Owl’
THE second cylinder block for GWR ‘Night Owl' 2-8-0 No. 4709 was cast in early May, opening up the possibility of the locomotive reaching the rolling chassis stage later this year.
Boro Foundry in Smethwick filled the mould with 2,646kg of molten metal at an average temperature of 12,800C. The pour took less than five minutes; the culmination of many weeks of work, planning, testing and preparation.
Paul Carpenter, the Great Western Society project's chief engineer, said: “We were holding our breath. This foundry work using polystyrene patterns is at the very edge of technology, and a huge learning and discovery process for us all.”
Throughout the pour, flames leaked spectacularly from every joint in the sandbox as the hot metal ignited the gases generated by the burning of the polystyrene pattern.
The massive cylinder block then sat for the best part of a week, taking several days to cool sufficiently for it to be examined to check that the pour was successful.
The casting has now joined the first one produced several weeks earlier. Both will be heat treated to relieve internal stresses, after which they will be machined and eventually joined as a pair.
The cylinders will be a critical part of No. 4709's front end.
“In addition to their role in converting steam to motion, the cylinders will also provide a physical datum for measurements and alignment for the horn guides, wheels, axles and motion,” explained Paul.
“Once we've got this casting in place, we can start planning for No. 4709 to become a rolling chassis. Hopefully, that will be late this year.”
What is the tenth member of the Churchward class is being built using a mixture of new parts and others recycled from former Barry scrapyard locomotives. New mainframe plates were cut in 2012 and assembled at Llangollen, and in August 2020 were transported to the premises of Leaky Finders at Hele, near Exeter, where the rolling chassis will be assembled.
However, it was recently confirmed that parts of what is intended to become No. 4709's pony truck have, as predicted, become corroded and need to be replaced.
Assessment
The pony truck resembles the letter A, and was originally fabricated from many components that were common steel sections at that time, or heavy items which had been forged, bent and curved in three dimensions.
Understandably, many of these sections are no longer available, so renovation for main line use involves a detailed and thorough assessment of each component.
No modern-day fabricators are able to bend the T sections that the pony truck radius bars were fabricated with, so the originals have been sent away for specialist weld repairs to meet the approval of the Vehicle Acceptance Body. A new frame stay casting is needed, and a 3D model was produced for the patterns, which have been completed by Caddick and Moss of Bristol and are due to be cast shortly.
Patterns have also been commissioned for the compensating beams to be cast in steel.
Work is also progressing with the machining of 14 new spring hanger brackets and the ongoing refurbishment of the reusable components from the pony truck assembly.
➜ To donate to the 47XX project, visit www.4709.org.uk