| The
Crucible Steel Process Lifting the crucible out of the furnace Teeming the molten steel into an ingot mould How Walker got Huntsman's secret |
Benjamin Huntsman 1704 - 1776Inventor of Crucible SteelBenjamin
Huntsman was born in Lincolnshire, England in 1704. His parents
had moved here from Germany shortly before his birth. The boy being
of an ingenious turn, was bred to a mechanical calling and becoming
celebrated for his expertness in repairing clocks. As a young man, he
eventually set up in business as a clock maker and mender in the town
of Doncaster. He also undertook various other kinds of metal work, such
as the making and repairing of locks, smoke-jacks, roasting-jacks, and
other articles requiring mechanical skill. He was remarkably shrewd,
observant, thoughtful, and practical; so much so that he came to be
regarded as the "wise man" of his neighbourhood, and was not only consulted
as to the repairs of machinery, but also of the human frame. He practised
surgery with dexterity, though after an empirical fashion, and was held
in especial esteem as an oculist. His success was such that his advice
was sought in many surgical diseases, and he was always ready to give
it, but declined receiving any payment in return. Like most
of the people who manufactured steel products, he obtained his steel
from Germany. Unfortunately, he found that this material was not suitable
for the springs and pendulums of the clocks which he was making. After
many years of experimenting, he finally perfected his crucible steel
process and realised that this process could be used to make superior
tools and cutlery. When he tried to interest the local cutlers in using
his steel for their products, he had little success. The Sheffield cutlers
refused to work with his steel which was harder than that which they
were used to. Huntsman then turned his attention to the French who were
quick to take advantage of the new steel and bought all his produce.
The Crucible Steel ProcessThe crucible steel process starts with the manufacture of special clay pots or crucibles. These are about 50 cm. tall and about 20 cm. wide. Each one can hold about 20 kg. of steel.The crucibles are heated in a coke fired furnace set in the floor of the furnace shop. When they are at white heat, they are filled with broken bars of steel and a flux to collect impurities. A lid is then placed over the pot and the furnace is charged with more coke. The steel is then melted for about three hours. The furnace operator keeps adding more coke and checks the melting steel at the same time. To start with, the steel bubbles as it melts. Eventually the bubbling stops and the surface of the melt becomes clear. The steel is now ready for teeming. Lifting the crucible out of the furnaceThe pot is lifted out of the furnace using long handled tongs which grip round the outside of the crucible. The pot is then stood on the furnace room floor and picked up using another set of tongs which fit round the middle of the crucible.Teeming the molten steel into an ingot mouldThe molten steel is then poured from the crucible into a cast iron ingot mould. When the steel has solidified and cooled, the mould is opened so that the steel bar can be removed.After the steel has been poured, the crucible is replaced in the furnace and another charge of raw steel is added for melting. Most of the crucibles can be re-used for three melts before becoming too weak, when they are thrown away. How Walker got Huntsman's secretThe crucible steel process was developed by Benjamin Huntsman in great secrecy. Many attempts were made by rival businesses to discover Huntsman’s secret process. One story about these attempts involves an iron founder called Walker who had a foundry at Grenoside, on the northern outskirts of Sheffield and it was certainly there that the making of cast-steel was next begun.It has been written that Walker adopted the "ruse" of disguising himself as a tramp, and, feigning great distress and abject poverty, he appeared shivering at the door of Huntsman’s foundry late one night when the workmen were about to begin their labours at steel-casting, and asked for admission to warm himself by the furnace fire. The workmen’s hearts were moved, and they permitted him to enter. The above facts were handed down from the descendants of the Huntsman family; but we add the traditional story preserved in the neighbourhood, as given in a well-known book on metallurgy: "One cold
winter’s night, while the snow was falling in heavy flakes, and the
manufactory threw its red glared light over the neighbourhood, a person
of the most abject appearance presented himself at the entrance, praying
for permission to share the warmth and shelter which it afforded. The
humane workmen found the appeal irresistible, and the apparent beggar
was permitted to take up his quarters in a warm corner of the building.
A careful scrutiny would have discovered little real sleep in the drowsiness
which seemed to overtake the stranger; for he eagerly watched every
movement of the workmen while they went through the operations of the
newly discovered process. He observed, first of all, that bars of blistered
steel were broken into small pieces, two or three inches in length,
and placed in crucibles of fire clay. When nearly full, a little green
glass broken into small fragments was spread over the top, and the whole
covered over with a closely-fitting cover. The crucibles were then placed
in a furnace previously prepared for them, and after a lapse of from
three to four hours, during which the crucibles were examined from time
to time to see that the metal was thoroughly melted and incorporated,
the workmen proceeded to lift the crucible from its place on the furnace
by means of tongs, and its molten contents, blazing, sparkling, and
spurting, were poured into a mould of cast-iron previously prepared:
here it was suffered to cool, while the crucibles were again filled,
and the process repeated. When cool, the mould was unscrewed,
and a bar of cast-steel presented itself, which only required the aid
of the hammerman to form a finished bar of cast-steel. How the unauthorized
spectator of these operations effected his escape without detection
tradition does not say; but it tells us that, before many months had
passed, the Huntsman manufactory was not the only one where cast-steel
was produced." |