Our Bessemer letters are now online, free for all to read!
One discusses the affinity of phosphorus and iron and the separation of the two.
Bessemer is most widely known for the process named for him. Born in Hertfordshire in 1813 to a French engineer father, he showed an interest in engineering and invention as a boy. His first invention, was to use brass as a paint additive instead of gold. This greatly reduced production costs. He also developed a method for mixing paint ingredients, it was automated and so staff were not required. With his siblings, paint was successfully produced commercially. It is an an early example of reverse engineering, where a product is analysed and then reconstituted. He kept the process secret and access to the factory was tightly controlled, this displays an early understanding of the importance of protecting inventions from competitors in order to maximise one’s own business. The money he made allowed Bessemer to experiment elsewhere. One unsuccessful invention (commercially speaking) was a patented method for making a continuous ribbon of plate glass. This gave him experience of working with furnaces.
The Crimean War (1853-1856) provided the opportunity for Bessemer to become involved with steel. He began experimenting with new types of cannon projectiles and had success with a spinning projectile. The method caused the cannon ball to spin, which in turn helped to stabilze the trajectory of the ball. It was not without issues however, the method sometimes caused the ball to explode in the cannon before being fired. Bessemer decided that he needed to find a stronger material so that this would not happen. It was already known that stable cannon balls could be made from steel but it was not viable, due to steels rarity, as there was not an efficient method for producing it. Production relied on taking most of the carbon out of cast iron, this made wrought iron to which carbon was re-added to make steel.
Bessemer developed a new production method. He converted cast iron to steel and patented his method in 1856, being the pneumatic conversion process or Bessemer Process. The process removed impurities such as silicon from the molten pig iron by oxidation. The progress of the oxidation was judged by the appearance of the flame issuing from the mouth of the converter; impurities either escaped as gas or formed a solid slag. Oxidation also raised the temperature of the iron mass and kept it molten so it could be poured. This allowed for steel to be mass produced inexpensively, using a Bessemer convertor which could make 30 tons of high grade steel every half an hour.
The process is aided by the convertor, clay linings are used when there is little phosphorus in the raw material (acid Bessemer process) but when phosphorus content is high, dolomite, or magnesite, linings are used (alkaline Bessemer limestone process). Often called Bessemer convertors, they are also called Gilchrist-Thomas converters, after their inventor Sidney Gilchrist Thomas. In order to produce steel with the desired properties, additives such as spiegeleisen can be added to the molten steel once the impurities have been removed. The conversion process was nicknamed the blow.
When the required steel had been formed, it was poured into ladles and then transferred into moulds. Afterwards, the liquid metal was recarburized to the desired point and other alloying materials were added, depending on the desired final product. Bessemer convertors usually operated in pairs, one being blown while another was being filled or tapped.
Bessemer commercialized the process and was able to profit from his invention, although he did not stop there. Among his many other inventions were, a way of embossing velvet, a hydraulic machine for extracting juice from sugar cane and a furnace designed for making sheet glass. In 1869 he attempted to design a seasickness proof sailing ship. He completed it, but it was too hard to steer and crashed in 1875 on its first voyage.
In his lifetime Bessemer earned a total of 110 patents. In 1879 he was knighted for his contributions to science. He died on 14 Mar 1898, in London. His impact was lasting, steel is still made using his process.
He became a member of IMechE in 1861.