Engineering news
Sir Henry Bessemer is best known for the steelmaking process that is named after him, but he was a prolific inventor who earned a total of 110 patents. Last month a blue plaque commemorating him was unveiled in Northampton Square, London, where he lived from 1833 onwards.
Bessemer was born in Hertfordshire in 1813 to a French engineer father, and showed an interest in engineering as a boy. His first invention was to use brass as a paint additive instead of gold. This greatly reduced costs. He also developed an automated method for mixing paint ingredients. With the help of his siblings, Bessemer managed to successfully produce paint commercially.
This work is an early example of reverse engineering, where a product is analysed and then reconstituted. He kept the process secret and tightly controlled access to the factory, so displaying an early understanding of the importance of protecting inventions from competitors.
The money he made allowed Bessemer to experiment elsewhere. One commercially unsuccessful invention was a method for making a continuous ribbon of plate glass. This gave him experience of working with furnaces.
The Crimean War (1853-56) provided the impetus for Bessemer to become involved with steel. He experimented with projectiles and had success with a method that caused the cannon ball to spin, which helped to stabilise its trajectory. But the method sometimes caused the ball to explode in the cannon.
Bessemer decided that he needed to find a stronger material so that this would not happen. It was known that stable cannon balls could be made from steel but this was not viable, owing to steel’s rarity, as there was no efficient method of producing it. Production relied on taking most of the carbon out of cast iron; this made wrought iron to which carbon was again added to make steel.
Bessemer developed a new production method, converting cast iron to steel. He patented his method, the pneumatic conversion process or Bessemer process, in 1856. 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 that it could be poured.
This allowed for steel to be mass-produced inexpensively. A converter could make 30 tons of high-grade steel every half an hour. Often called Bessemer converters, they are also called Gilchrist-Thomas converters, after their inventor Sidney Gilchrist Thomas.
A clay lining is used in the converter 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). 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 steel had been formed, it was poured into ladles and then transferred into moulds. Afterwards, the liquid metal was recarburised to the desired point and other alloying materials were added, depending on the final product required.
Bessemer 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 sailing ship that was proof against seasickness. He completed it, but it was too hard to steer and crashed in 1875 on its first voyage.
In 1879 he was knighted for his contributions to science. He died in 1898. His impact was lasting, and steel is still made using his process.
The Archive at the IMechE has several letters from Bessemer, which are available to researchers. Email archive@imeche.org to enquire.