The development of a process for the radius hardening of diesel engine crankshaft journals

Abstract

Radius hardening on journals of forged steel Diesel engine crankshafts is performed in order to increase fatigue life characteristics. This requirement may be necessary if the demands for engine power are to be increased, but where the existing crankshaft design is close to its fatigue limit, such that an increase in loading will cause it to'fail. Induction hardening of journal radii changes the make-up of the material from a coarse to a fine crystalline structure which alters the features of crack propagation. As a consequence of this higher loads can be applied onto the crankshaft without ultimately resulting in catastrophic material failure. Extending the induction hardened zone from the bearing surfaces into the radii of journals, culminates in process difficulties which are not experienced in non-radius hardened Hardening of journal radii induces crankshafts. as well as releases stresses in the crankshaft webs. This results in a deformation of the crankshaft which can be measured in the form of journal runout. Such a problem cannot be overcome by straightening the crankshafts in order to reduce runout, since this will cause Straightening hand induces the radii to crack once hardened. in the unhardened state on the other stresses which will be released again after hardening. This results in an increase in runout. High runout indicates that stresses have been induced into the crankshaft material. This is undesirable since this will make critical manufacturing processes such as grinding, governing of journal lengths, uncontrollable. It can furthermore result in creep of the crankshaft long after the manufacturing date. This results in crankshaft deformation, noticeable through an increase in runout. Since the crankshaft cannot be straightened after hardening, the consequence is that it will be unusable. The process must therefore be developed in such a manner, that all variables which can contribute towards stress induction resulting in journal 'runout, must be investigated and resolved.