Modern gas carburizing technology for the automotive industry

Increased demands in cost effectiveness, reduction of gas consumption, internal oxidation and distortion caused the development of a new generation of gas carburizing furnaces. This paper deals with three different examples of modern furnace design. A three track pusher furnace, showing a throughput capacity of 1430 kg/h gross weight for 1.2 mm case hardening depth, was equipped with a bottom inlet and outlet sluice. The reached quality parameters, the gas consumption and the energy consumption are reported and compared with values of conventional carburizing plants. The second example shows an automatic gas carburizing and fixture rotation hardening plant for TDI-camshafts, which allows a cost-effective hardening of 67 camshafts/h with a reproduceable distortion of 0.02 - 0.1 mm. Finally an improved ring hearth furnace design with seperated heating, carburizing and diffusion zones is shown. The new design combines high heat treatment quality with low gas and energy consumption. Depending on the demands, an oil bath, press hardening or a gas quenching module can be used. The advantages and disadvantages of this concept will be discussed in comparison with a modern pusher-type furnace design. over-all execution of the plants differed according to the specific requirements of the customer. The high temperature furnaces, for example, had to be designed according to the required throughput capacity, the treated material grade and the desired case hardening depth (CHD). For high throughput capacity and high case depth two- and three track pusher furnaces are usually used. Furthermore different CHD values can be processed simultaneously. The main features of the new plant design will be shown by the following example.