A matching pair...

There was a great exhalation from the 4709 team this week, when the brand new casting for the loco’s second cylinder emerged from its giant sand mould.

“We were holding our breath,” said 4709’s Chief Engineer, Paul Carpenter. “This foundry work using polystyrene patterns is at the very edge of technology and a huge learning and discovery process for us all.”

Poured on Thursday morning last week, Boro Foundry in Smethwick filled the mould with 2646Kg of molten metal, at an average temperature of 1280 deg C. The pour took less than five minutes; the culmination of many weeks of work, planning, testing and preparation.

Throughout the pour, flames leaked spectacularly from every joint in the sand box, as the hot metal ignited the gases generated by the burning of the polystyrene pattern.

The massive cylinder then sat for the best part of a week; “We’ll strike the mould next Tuesday or Wednesday, but expect the metal to still be red hot,” said Boro’s Sam Edwards at the pour. “It’ll take several more days to cool sufficiently for us to examine and check that the pour was successful.”

It was and the cylinder shot blasted and had its running (pour) system removed. It will now join its sibling, cast several weeks ago. Both will will be heat treated to relieve internal stresses, after which they will be machined and eventually, joined as a pair.

Completed and installed in 4709’s chassis, the cylinders will be a critical part of 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 hornguides, wheels, axles and motion.”

“Once we’ve got this casting in place, we can start planning for 4709 to become a rolling chassis,” adds Paul. “Hopefully, that will be late this year.”