Then he improved lead pencils and printers’ type, devised a better means of embossing velvet, and found a new way of making bronze powder, which brought him a useful sum of money. Machinery for crushing sugar cane came next and then a method of making plate glass. When the Crimean War started, in 1854, Bessemer invented a new type of gun, which he offered to the War Office, but got no response. His gun, however, showed the need for a better type of iron to withstand the stresses set up. Although he only began to consider the matter just before Christmas 1854, by 10 January 1855 he had taken out his first patent for ‘Improvements in the Manufacture of Iron and Steel’. Bessemer says in his autobiography that his knowledge of iron and steel at that time was very limited, but that this was in some ways an advantage for he had ‘nothing to unlearn’. His earlier inventions had brought him enough money to be able to experiment on the new idea, working at his bronze-powder factory in London—near to where St Pancras railway station now is—and in a fairly short time he had made what we now know was a new metal, by a process so novel that many people thought it impossible.
More patents followed and then, when Bessemer felt that his ideas were properly protected, he read a paper called ‘The Manufacture of Malleable Iron and Steel without Fuel’ to the British Association meeting at Cheltenham in August 1856. This historic occasion marked the beginnings of what is now called the Steel Age. In fact, after a flying start, the process ran into serious technical trouble and it was a long time before it became widely adopted. Nevertheless the process caused a great stir in ironmaking circles from the start. There were ironmakers in the audience when Bessemer read his paper and straight away they became divided into two camps. Some tried to dismiss the whole idea; others saw it as having great potential and were anxious to try it out in their own works. Bessemer, who had watertight patents, prepared to grant licences to use it, on payment of a royalty.
It is easy to understand why many people scoffed at Bessemer’s idea. He took molten cast iron and blew a blast of cold air through it. Surely, people reasoned, all this would do would be to cool the molten iron down. In fact the iron actually got hotter. Even Bessemer, who was not easily surprised, was alarmed at what happened when he set his experimental apparatus—or converter—to work: he said later that it was like a veritable volcano’, with flames, slag and bits of molten metal shooting up into the air: see Figure 2.3. (This was no exaggeration. The Bessemer process remained to the end—it is virtually extinct now—the most spectacular sight in the iron and steel industry.) He let the process go on, indeed nobody could approach the converter to turn it off, and after some minutes the fireworks stopped and there was nothing but a clear flame from the mouth of the converter. Bessemer tapped the metal he had made and found it behaved like good wrought iron.
It will be remembered that to convert cast iron into wrought iron the carbon has to be removed. In the puddling furnace this was done by heating the iron in contact with fluxes containing oxygen. Bessemer used the cheapest form of oxygen there is, ordinary air, which contains about 21 per cent of oxygen. Because there was so much oxygen, the carbon in the cast iron reacted very strongly with it. The reaction was exothermic, that is, it actually generated heat; so the iron became hotter instead of colder, and produced the pyrotechnics.
Bessemer had achieved his object of making what he called ‘malleable iron’ from molten cast iron without fuel, but what kind of metal, in fact, had he made? His term ‘malleable iron’ is confusing, for strictly it describes a kind of cast iron so treated that it became to some extent capable of being bent or formed with out breaking. In Bessemer’s time the words were often incorrectly applied to wrought iron. Bessemer was really trying to make a better form of wrought iron. In many ways he succeeded, for his new metal—which we now call mild steel —would do almost everything that wrought iron would. And since he could make it much quicker than in the puddling furnace, and in bigger quantities at a time, it could be cheaper once the plant was set up.
His experimental converter was only big enough to deal with about 350kg (770lb) of iron at a time, but it did so in about thirty minutes, compared with a production of about 250kg (550lb) in two hours in a puddling furnace. It was easy to make a bigger converter and, as the time taken by the process was no longer whatever size the converter was, larger outputs were soon possible. It was realized that Bessemer metal was not the same as wrought iron—technically it is different in several ways but it could be used for most purposes where the older metal had been supreme for so long, it was cheaper to make, and the demand for all kinds of iron and steel was still growing. Licences were granted, the necessary apparatus was set up and it seemed that Bessemer would confound his critics. But when the licensees started production there was trouble: all the steel they made was useless. These licensees included the Dowlais and Ebbw Vale works in South Wales and, with a number of others, they had paid thousands of pounds for the privilege of using a process that would not make good steel. Yet Bessemer had done so, and had demonstrated the fact at his St Pancras works. It took more than twenty years for the cause of the trouble to be found and a remedy devised: the Bessemer process was first announced in 1856 but it was not until 1879 that it was modified so that it could be used on a really large scale. Then it spread all over the industrial world.
The Industrial Iron Age: 1800-1850
