Engineers at metal specialist Corus have developed a new type of steel that offers big advantages for designers of vehicle gearboxes.
One of the problems frequently encountered by gear manufacturers is the unpredictable level of distortion in the steel used. Usually caused by heat treatment after machining, this a major contributor to increased NVH (noise, vibration and harshness) and also frequently calls for additional finishing operations.
However, Corus claims that its new lean alloy steels have predictablehardening properties that will enable manufacturers to accurately anticipate the level of material distortion and therefore significantly limit its negative impact during manufacture.
David Milbourn, manager of product technology at Corus Engineering Steels, explained that this has been achieved with a bit of clever chemical tinkering, in which the elements that determine the hardenability of the steel are controlled within very tight limits.
Hardenability is a material property that describes the depth to which steel may be hardened during cooling.
‘We can provide a steel with very tight hardenability control that enables gear manufacturers to reproduce the level of distortion more accurately,’ said Milbourn.
He added that once it has been established that a certain hardenability level provides the properties a manufacturer requires, it is possible to consistently repeat these properties.
Milbourn explained that distortion will always occur, but that if it is not controlled then rectification is typically required on every single gear. ‘From batch to batch you won’t know how much distortion will occur, so a hard finishing operation such as grinding is required to correct the gears,’ he claimed, adding that sometimes distortion can be so severe that it can’t be corrected.
He claimed that the new steel dispenses with the need for additional machining, reducing both manufacturing time and cost, and allowing for more environmentally-friendly manufacturing processes.
Milbourn said that the new steels will be of particular benefit to manufacturers of high-volume passenger car and commercial vehicle gearboxes, but while the material is now appearing on a number of Volvo trucks, he was unable to comment on applications in other production vehicles.