Hello
As a Mechanical Fitter well I used to be, I served my apprenticeship in a BSC Foundry where Iron was cast. The term moulder would be a time served person who, made the moulds that the iron was cast into
The moulds were usually made in two halves, a wooden pattern would be placed into the "cope" (bottom section) damp sand would be packed around the mould, a "runner" and a "riser" placed onto the pattern the sand is tightly packed into the mould, then the "Drag" is placed on top of the drag and this is packed with sand.
The mould would be split and the pattern, runner and riser removed leaving an impression, the two halves then reassembled and fastened together, the molten iron then poured into the "Runner" untill it has filled the mould and the iron has filled the "riser" ( the riser serves two purposes, its where the air inside the mould is forced out, and once the riser is full then the mould must be full.
This is a quick overview of the process, there is a bit more to it and a lot of this process was taken over by the "Continuous Casting Process".
So an Iron Moulder would not be specific to one area however it would be to in groups of places around the country such as Workington, Cumbria, I can't think off the top of my head of others but steel wasn't just produced at Sheffield, but in a number of places, including Workington.
Any thats what an Iron Moulder does, and where you get a iron being moulded you get: Foundrymen, Pattern Makers and Dressers
Anyway hoped that helped
Andrew