Foundries for Iron, Brass and Bronze
A foundry pours liquid metal into moulds to make castings, these can be iron, steel, bronze, brass, aluminum, magnesium alloys, or various alloys, which often include lead, tin, and zinc (notably white metal used for many small modelling accessories). At an iron or steel works the areas where the metal is cast into pigs, billets or blooms is called a foundry although the liquid metal is poured from a very large ladle, holding several hundred tons of material. The discussion below concentrates on smaller foundries which might form a smaller line side industry. These foundries will specialise, iron and steel at one, bronze, brass and aluminium at another with specialist firms working with other materials.
An iron foundry takes in pig iron to make cast iron, you would normally have a foundry associated with an iron works but there were also small establishments catering to local industry (most towns had at least two small foundries) and larger engineering works often had their own foundry on-site. Iron foundries tend to be larger than the other types, they generally produce larger castings.
At a foundry producing cast iron goods the pig iron, and perhaps some scrap iron, are mixed with coke in a furnace called a 'cupola' and re-melted. The re-melting process removes more of the impurities but cast iron still has a lot of carbon in it and is brittle. The cast iron drawn from the cupola is however very fluid can be poured directly into moulds with intricate shapes. Cast iron is easy to machine and is very strong under compression. To harden the metal as it sets in the mould metal plates are added to the mould that produce rapid local cooling, similar to the tempering done at a forge. From the early part of the twentieth century steel was sometimes added to the mix to give 'semi-steel'. Once the cast was broken out of the mould they were passed to a 'fettler' for 'fettling', which means removing flash and other errors from the surface of the cast. The fettlers also look for cracks in the castings, at the moment one common method used in Britain relies on Azo dyes, although in several other countries the use of these dyes was banned in the 1990s.
A typical small iron foundry cupola consists of a heavy base with a tall metal tube extending about twenty five feet upwards, that is through both floors of a two storey building and sticking out of the roof. Not all foundries had a building round the cupola, in smaller establishments this might be in the open as shown below. On the upper floor was a door or hatch in the side of the tall tube to allow the adding of raw materials, called 'charging', at the bottom was an arrangement for tapping off the molten iron. The very base of the cupola was raised perhaps three feet above the ground and was fitted with drop-doors to allow the residue of red-hot slag to be dropped out. This could be modelled, adding a red LED under some PVA glue 'slag' with a small smoke generator feeding through a pipe from under the baseboard. This gives the impression of 'something going on' without the complication of having people moving about.
The cupolas once running could be kept going for several days if sufficient raw material was to hand. The resulting molten iron is tapped off, usually into a container, then poured into moulds to produce ornamental structural pieces, motor car engine blocks, manhole covers and the like.
The molten metal can be run off into a sand mould but where complex shapes such as balls were required a multi-part mould is used. In this latter case it was usual to run the molten iron into a bucket or ladle and pour from this into the mould. At larger works the ladle would be a big steel bucket suspended from an overhead gantry type crane at a small establishment it would be a small crucible carried by two men using a pair of long steel rods. Multi-part moulds can be made in various ways but if a large number of similar items were required they would be made of steel. These were formed in a series of circular units called 'flasks' which could be stacked on top of one another, the moulds being connected by a network of cores called the 'sprue'.
These flasks would be stacked and clamped together and the molten metal could then be poured into the tops of the sprue holes to produce several layers of the desired shapes. After cooling each layer is lifted off by a crane so the castings can be removed. Also associated with a foundry would be a workshop an possibly a stores for the pattern makers. These skilled individuals made the shapes for impressing in the sand to form a mould. The patterns were generally made in wood. The sketch below shows a small foundry.
Fig ___ Small foundry
The very early cupola furnaces were small, typically three feet in diameter by about ten feet high with a wooden platform about eight feet square about five feet up the central pipe, the cupola described above dates from the mid nineteenth century, however similar furnaces were still operating into the 1950's.
The cupola is a very distinctive feature and should preferably be included on the model in plain view. Adding a few bits and pieces, such as a gantry crane and a 'yard crane' on a loading bank gives the thing a more industrial air, the example below is based on the terminus at Ashburton but modified to a three platform small town terminus ('arrivals' and 'departure' platforms with a carriage siding behind the bay line). This layout, if running four coach trains and three coach DMUs, would be about four feet (1.3m) long in N, you can get it into a one foot wide baseboard but that is a bit cramped and requires rather thin platforms, fifteen inches (36cm) is much better. Accessing the works from a platform line is unavoidable and was seen on the prototype at smaller termini where passenger services were infrequent.
Fig ___ Track plan for a small works at a terminus station
I have shown two cupolas, more than you need (one would do) but it makes the foundry seem more important which helps to justify a railway siding. To reinforce the sense of 'heavy industry' adding a crane or two definitely helps. Works handling larger castings found that a mobile crane was often useful, the steam example shown below left is typical. By the later 1930s petrol cranes were commonplace, one popular machine born in the 1930s which served well into the 1970s was the Chaseside crane, a modified tractor fitted with a fixed jib.
Fig ___ Steam mobile crane and Chaseside petrol crane
Incoming cargo would depend on the type of foundry, for those producing cast iron there would be loads of pig iron and scrap metal, the occasional load of sand, regular shipments of coal and (where a gas heated oven was in use) coke for the producer gas plant.
Outgoing cargo could include all manner of cast metal goods, from baths (made from medicine 'bubble packs') to lamp standards (Ratio kits or home-made) and all manner of smaller items (many of which would be shipped in wooden cases and crates although less valuable goods were shipped loose in open wagons, usually in a bed of straw or bracken). Motor engine blocks were shipped in crates, as were any castings requiring a little additional protection from knocks on the journey.
Larger works could produce much larger castings, these often left the factory in a fairly rough unfinished form. Depending on their weight they might require a heavy wagon to shift them, for really heavy stuff they used 'armour plate wagons' as described in 'Goods Rolling Stock Design - Specialised Rolling Stock'. To model such a load any odd bits cut from packaging can be painted 'iron' with a dry brushing of 'rust' and secured with twisted wire 'chains'.
The larger foundry building sketched below was part of an engineering works, the sketch assumes you will be using the Peco engine shed kit for most of the parts, this comes with an extra set of curved-top main doors and two small roof vents.
Fig ___ larger foundry building
I believe in Britain the cupolas were phased out in the later 1970s, replaced by electric induction furnaces (similar in principle to but much larger than the example in the photographs below). The sand used in casting is black (when new it is sand coloured, it is actually a mix of sand with 2-5 percent bentonite clay and about 1-2 percent water, it is re-used and turns black), there is always a ready supply of this, stored under cover somewhere on the site often with a rectangular fine wire mesh sieve about three feet square on a two wheeled trolley used to filter out any scraps of metal when returning it to the pile between jobs. On the main floor of the foundry there will be many of the small pouring crucibles and several sets of handling irons for these.
The works where wrought iron was produced was commonly called a 'finery' but the foundries soon adopted the basic techniques and offered wrought iron goods. Wrought iron was quite a common material up to the 1930's but it has now been superseded by mild steel (discussed under Iron and Steel) for most purposes.
Bronze
Is an alloy of copper and tin, it wears well and is used for machine parts and name plates on buildings. The usual mix for common bronze is eight parts copper, ten parts tin with two parts zinc but there are a number of types of bronze each with different constituents and used for different jobs.
Gun metal is a form of bronze used for steam and water fittings.
Manganese bronze, made from copper, zinc, tin and manganese is used for casting ships propellers because it is not eaten by sea water. Ships propellors could get quite large, the really big ones required a drop-centre wagon and the load was supported on timber baulks (see 'Wagon Loads and Materials Handling - Unusual and Out of Gauge Loads' for a sketch of such a load)
Brass
Basic brass is an alloy of copper and zinc, usually including a small amount of tin, it is not as strong as bronze. The usual mix is seven parts copper to three parts zinc but there are many kinds of brass, yellow brass has lead added and 'Naval' brass has more zinc than tin. Brass does not rust, so its used in pumps and plumbing fittings, but it does tarnish so it is often plated for domestic uses. Electric furnaces are usually used to make the stuff and it is then cast at a foundry to produce salable goods (see also Lineside Industries - Scrap metal Yards, Foundries and Forges).
Small foundry operating in 2007
The photographs below were taken at a local foundry (Derbyshire Castings on Churchill Road in Broadheath near Altrincham). This firm specialises in small castings and so does not employ a cupola, instead they melt the materials in the crucible using oil fired, gas fired or electric induction ovens. The gas (A) and oil fired (B) ovens are set into a rectangular hole in the ground, the electric induction ovens (C) stand above ground.
Fig ___ Ovens in a small foundry
In the photographs below the induction oven is being used to melt aluminium alloy, this is then lifted out and placed on the floor where a man with a metal bar scoops out the slag floating on the top. Additional materials were then added and the crucible was stirred before emptying into the moulds (with a third man using the metal bar to control the residual slag). These scenes could be glimpsed through the large doors of the foundry, adding a red LED with a fibre optic feed to the crucible would add to the scene.
Fig ___ Testing the temperature with a pyrometer
Fig ___ Lifting the crucible of molten metal from the oven
Fig ___ Clearing off the slag from the surface
Fig ___ Pouring the molten metal into a mould
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