The history of Vertical Extruders to make ceramics

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Anyone who has taken part in one of our 11:30 factory tours will know that a distinctive aspect of our method of making pots is the initial use of a vertical extruder to make a cylindrical blank.  However, vertical extruders were not designed to make pots – they were designed to make sewer pipes.  These humble machines have made a huge contribution to the provision of safe drinking water supplies all over the world.  With the recent events in Havelock North putting into sharp focus the danger of taking clean water for granted, this is a good time to review the machines’ history.

In 1854, there occurred one of the frequent outbreaks of cholera in London.  A doctor named John Snow plotted the geographical locations of cholera cases on a map of the area and was able to conclude that the source was a public well in Broad Street, Soho.  He persuaded the authorities to remove the handle of the pump and so brought the outbreak to an end.  Now, my great, great grandparents and their family lived just around the corner from this well, so without Dr Snow’s timely action I may not have been here to write this account.

A few years earlier in 1846, across the Thames in Lambeth, Henry Doulton was also thinking about water pollution.  In that year, he founded a company which later became part of the famous Doulton & Co – who 125 years later, provided me with my first employment. Doulton believed that a major factor in the safe disposal of sewage was transporting it in pipes which did not leak (unlike most of the pipes available at that time).  The most suitable material would be stoneware – a type of high fired pottery which was impervious to water.  Fortunately this was the material manufactured at his father’s factory.  Doulton’s first pipes were hand thrown, like pots, but this method was far too slow to meet demand.  The ideal manufacturing process was extrusion – forcing clay under high pressure through a die.  Engineers all over the country were devising ways of producing clay ware by steam-powered machines, and Doulton was keen to use this expertise.  A common device for producing the high pressures needed was a rack and pinion. The disadvantage was that the process was not continuous - after a short run the machine had to be stopped and refilled with clay.  Much better was Henry Franklin’s idea of using an Archimedean screw. Pipes of small diameter could be extruded horizontally, but large diameter pipes would collapse under their own weight, so these had to be made vertically. Equally important was the socket and spigot method of joining the pipes together, and Doulton was one of the first to use Thomas Spencer’s patent machine to form these. The next important development in clay extrusion came with the invention of the de airing extruder in 1902.  By enclosing the machinery in an airtight case and removing the air with a powerful vacuum pump the clay could be made to undergo a greater degree of distortion without breaking.  This new technology was not generally adopted by industry until the 1930’s.

The manufacture of stoneware sewage pipes was a major industry until the 1980’s when PVC and concrete pipes became the standard, except for a few specializes applications.  The use of vertical extruders to form the walls of pots would seem to be a logical development, but in fact it has rarely been attempted.  The technique is used successfully by Errington Reay Ltd in Northumberland, U.K. but few others.  Storage jars were made using a horizontal extruder in New Zealand as early as the 1840’s, and the Crum pipe works in Auckland is known to have tried some experiments.  Morris & James’ vertical extruder was made by H.V. Hampton Ltd in Melbourne, Australia.  Anthony purchased it second hand in 1982 from a dealer in Perth.  Such machines were still expensive at that time, and Anthony had some difficulty raising the money to buy it.  Ironically, about five years later the Mc Skimmings pipe works in Benhar on New Zealand’s South Island closed down and three British – manufactured machines became available.  Anthony bought them anyway, with a view to the eventual expansion of Morris & James, but they were never used.  They lay under a crude shelter in the company’s yard for more than a decade and were then sold for scrap.


By Mike Rose