Nine IHBC NW members enjoyed a fascinating visit to Longbottoms Cast Iron Works in Holmfirth, West Yorkshire, on Wednesday 12th April, organised by Mark Watson.
The author of this post (an enthusiast for lesser known railway lines) began the day with the additional bonus of a misty journey on the train to Brockholes, the nearest station on the sleepy Huddersfield to Sheffield line, and an impromptu cyclocross session carrying my bike much of the way up and down the (many) hills on the way to Holmfirth.
Longbottoms is a family firm in continuous operation on the same site and in the same building since 1919, whilst the fabrication process is virtually unchanged since the mid-19th century and involves almost no mechanisation. The company is one of the very few remaining providers in the UK of pattern cast as opposed to imported die cast iron.
The company produces all types of non-structural architectural cast iron, primarily rainwater goods including gutters, downpipes, and hopper heads, but also traditional cast iron air bricks, decorative castings and a huge range of specials are available on request.
We were given a detailed tour of the works by Simon, the current manager, and an opportunity to see each stage of the casting and finishing process in action.
Almost all of the raw material is recycled, primarily from unwanted cast iron drain covers, the market for which collapsed around 15 years ago – Longbottoms still hold vast stocks. Beyond this a small amount of new iron is added, along with additives, to each batch.
The iron is melted in small quantities (approx. 10lb of metal each time) in a graphite crucible heated within an electrically powered furnace. The site retains a much larger traditional coke furnace which is still occasionally used, but for most purposes the electric furnace is more efficient.
Whilst the iron is being melted sand moulds are prepared using green sand. This is made on site and is, confusingly, black in colour. The primary ingredient is natural red sand, which is mixed with coal dust, additives and a very small amount of water to give the correct consistency and to enable the mould to retain its cohesion.
The moulds are given their form using a huge range of retained patterns or originals. These are kept in racks next to the moulding area and are painted in a bright red pattern paint so as to distinguish them from the grey colour of the completed products.
The sand moulds are enclosed using boxes, also of cast iron, which are also made on site and for which the patterns are retained to enable them to be reproduced.
When, after around an hour, the molten iron reaches approximately 1200 – 1300 degrees centigrade and is ready to be poured, it is carried by hand in ladles from the furnace to the moulds and poured in through holes left in the moulds for that purpose.
This is a team effort requiring simultaneous pouring from three ladles into the corresponding pour holes; the speed required combined with the serious consequences of a trip or fall demand a high level of coordination and trust between the operatives.
Within 10-20 minutes the cast is complete and the completed castings can be broken out of the moulds, although they are still far too hot to touch and are left to cool. The heat from the cooling sections can be felt from several metres away.
After the casting process is complete the finished product moves to the fettling workshop for removal of the rudders, cast iron nodules which form at each of the pouring holes. Any remaining green sand is brushed or shot blasted away before the final stage which is a dip tank application of a grey spirit based primer.
In an alternative version of the process, usually for smaller more intricate castings, the mould is made using a yellow sand laced with a glue which allows for the production of more complex designs.
There is also a separate workshop for the fabrication and repair of smaller details including non-standard rainwater details and decorative plates.
The end product has a lifespan of at least 100 years, a thought provoking figure to present to clients wishing to use UPVC or aluminium instead.
If required, the whole casting process can be completed within a day and the product shipped that evening, however most orders are completed from stock to allow the foundry to concentrate on more specialist work.
Longbottoms’ catalogue is available to download from the following location: http://www.longbottomfoundry.co.uk/.
To see this process of hand production of cast iron architectural details in action, unchanged since the 19th century, was a very informative and in fact a rather moving experience and we are most grateful to Longbottoms for welcoming us and providing an exceptionally interesting tour.
Contributed by Matthew Williams, Heritage Architecture