tailieunhanh - An Encyclopedia of the History of Technology part 21

An Encyclopedia of the History of Technology part 21. This one of a kind encyclopedia presents the entire field of technology from rudimentary agricultural tools to communication satellites in this first of its kind reference source. Following an introduction that discusses basic tools, devices, and mechanisms, the chapters are grouped into five parts that provide detailed information on materials, power and engineering, transportation, communication and calculation, and technology and society, revealing how different technologies have together evolved to produce enormous changes in the course of history | PART ONE MATERIALS Apart from the obvious office use of computers for anything from preparing wage statements to scheduling orders so that they go to the works in the most economic way computers are now being used on-line to control actual production processes. A simple example comes from the cutting of billets to suit customers orders. Billets of special and very expensive alloy steel have to be cut into many different lengths to suit individual customers. The billets do not come from the mill in exact lengths and the practice was always for the operator who controlled the billet saw to be given the measured length of each billet as it came to him. He then had to decide the best way to cut it up according to all the orders he had to satisfy and set the saw accordingly so that as little as possible of the expensive material was wasted. However skilled the operator human error was unavoidable. With computer control the billets are measured automatically as they are rolled and this figure is fed into the computer with details of the customers orders. It equates these two sets of information and produces figures for each billet which will use it most economically. There are numerous other examples of computer control in steelmaking and processing and the trend is increasing. In special and alloy steelmaking there is also a great deal of mechanization and process control is highly instrumented but the scale of operations is smaller and the range of products wider. Today all alloy and special steels are made in electric furnaces. The old crucible process is extinct though there is a crucible melting shop preserved in working order at Abbeydale Museum Sheffield. Electric furnaces can be of two types arc or induction. In the arc furnace heat is generated by means of an electric arc and metal is melted by this heat in a refractory-lined vessel of drum shape which can be tilted mechanically to tap the finished steel see Figure . Arc furnaces are now of many sizes .