Bushing for crawler belt and method of manufacture

A crawler belt bushing producing method comprising the steps of heating a crawler belt bushing made of steel to a quenching temperature, then at least one of:

• (a) increasing the cooling rate of the outer circumferential surface of the bushing by first cooling the bushing with a cooling media from its inner circumferential surface in order to reduce heat capacity at the core of the bushing and by second cooling the bushing with a cooling media from its outer circumferential surface starting at a certain time after the first cooling and
• (b) increasing the cooling rate of the outer circumferential surface of the bushing by first cooling the bushing with a cooling media from its inner circumferential surface in order to partially make the core of the bushing unhardenable by utilizing the mass effect of the wall of the bushing and by second cooling the bushing with a cooling media from its outer circumferential surface starting at a certain time after the first cooling,
• whereby a soft layer is formed within the core of the bushing at a cross-sectional position closer to the inner circumferential surface and the hardened depth of the outer circumferential surface is made to be greater than the hardened depth of the inner circumferential surface,
• said processes (a) and (b) being carried out within one cycle of quenching operation, using a hardening system adapted to perform inner circumferential surface cooling and outer circumferential surface cooling.

A crawler belt bushing producing method comprising the steps of induction heating a crawler belt bushing made of steel from its outer circumferential surface such that at least the temperature of an inner circumferential surface of the bushing is raised to a quenching temperature, then carrying out a series of quenching operations comprising:

• (a) firstly cooling the bushing from the inner circumferential surface;
• (b) cooling the bushing from the inner circumferential surface while heating the bushing from the outer circumferential surface;
• and
• (c) cooling the bushing from the outer circumferential surface, so as to form quench hardened layers which extend toward the wall core of the bushing from the outer circumferential surface and from the inner circumferential surface respectively and form a soft layer between said quench hardened layers.

A crawler belt bushing producing method comprising the steps of heating a crawler belt bushing made of steel from its outer circumferential surface by scan induction heating in the axial direction of the bushing, by using at least two vertically aligned, induction coils,

• (a) raising the temperature of the inner circumferential surface of the bushing to a quenching temperature equal to the transformation temperatures of A1, A3 and/or Acm or more;
• (b) partially heating the bushing from the outer circumferential surface by the induction coils while carrying out first cooling from the inner circumferential surface;
• and
• (c) then cooling the bushing from the outer circumferential surface;
• whereby the inner and outer circumferential surfaces are quench hardened so as to be substantially martensitic, said processes (a), (b) and (c) being carried out at a certain position of the bushing.