Progress in Turbine Gear Manufacture in Recent Years

Abstract

The problem of producing accurately cut gears for high-speed work has received a great deal of attention, which commenced with the work done by Sir Charles Parsons introducing geared turbines for marine purposes. During the 1914–18 war, a considerable impetus was given to the production of geared turbines, which resulted in an abnormal rate of development. Soon after the war there was an outbreak of gear failures—particularly in double-reduction gears for merchant ships—and investigation showed that the most important requirement was improved accuracy in gear cutting. Between 1920 and 1940 the search for accuracy continued, but there was a backward tendency in demand. An important incentive to improvement during the recent war came from Admiralty requirements for lighter and quieter running gears, and the subject was referred to the British Standards Institution. After the outbreak of war with Japan, marked progress was made in America, both in quantity and quality of production, and there was a regular interchange of information between British and American naval authorities. The hobbing machine still remains the accepted means of cutting high-speed gears, but there has been considerable difference of opinion as to whether creep or non-creep machines were to be preferred. A particular feature of improvement in non-creep machines has been the use of master index wheels having a much finer pitch than was at one time thought suitable, and this, combined with greater accuracy in construction, has led to a decided improvement in gear cutting. Problems associated with the cutting of accurate turbine gears are the production of accurate lead screws and profile-ground hobs for finishing teeth. The process of crossed axis shaving is a relatively new development which has resulted in a higher grade of finish and has been responsible for reducing certain types of error. Reference is made to experiments with carbide-tipped hobs and an indication is given of the use of materials having higher tensile strength and greater hardness as possible future developments.