Crawler bushing and method and device for producing the same

A method of producing a track bushing wherein,

• in a series of quenching processes in which by use of a quenching system capable of carrying out induction heating from the outer circumferential surface of a track bushing and capable of independently carrying out inner circumferential surface cooling and outer circumferential surface cooling while pressing a partition jig against each end face of the track bushing such that a cooling medium for the inner circumferential surface of the track bushing and a cooling medium for the outer circumferential surface do not interfere with each other, after setting a track bushing material, which has been entirely heated to a quenching temperature by induction heating from the outer circumferential surface or by another process, in the quenching system capable of additional induction heating from the outer circumferential surface, preceding cooling of the track bushing material from the inner circumferential surface is carried out, or cooling from the inner circumferential surface is effected while carrying out induction heating from the outer circumferential surface and after an elapse of a specified time, cooling from the outer circumferential surface is carried out, or alternatively, the induction heating from the outer circumferential surface is stopped to effect cooling,
• by adding a step in which during the induction heating from the outer circumferential surface or during the time from when the induction heating is stopped until when the cooling from the outer circumferential surface is finished, the cooling from the inner circumferential surface is stopped and the inner circumferential surface is tempered within a short time by heat diffusion from the outer circumferential surface to the inner circumferential surface,
• quench-hardened cases extending from the outer and inner circumferential surfaces, respectively, to the wall center of the track bushing are formed, with an unhardened quenched layer left between the quench-hardened cases on an inner circumferential surface side and an outer circumferential surface side, such that the quench-hardened case on the outer circumferential surface side is deeper than the quench-hardened case on the inner circumferential surface side, such that the unhardened quenched layer has a structure containing one or more selected from ferrite, pearlite and bainite which precipitate in the course of cooling from the quenching temperature, and such that the inner circumferential surface quench-hardened case has a tempered martensitic structure.

A method of producing a track bushing wherein

• in a series of quenching processes in which by use of a quenching system capable of cooling the inner circumferential surface and outer circumferential surface of a track bushing material and/or carrying out induction heating from the outer circumferential surface, after the track bushing material has been heated to a quenching temperature, preceding cooling of the inner circumferential surface of the track bushing material is effected, or alternatively, preceding cooling of the inner circumferential surface is effected while carrying out additional induction heating from the outer circumferential surface, and after an elapse of a specified time, cooling from the outer circumferential surface is carried out, or alternatively, the induction heating from the outer circumferential surface is stopped to cool the outer circumferential surface,
• at least the inner circumferential surface of the track bushing is cooled by a cooling medium flowing in parallel with the inner circumferential surface and axial direction of the track bushing, so that a quench-hardened case can be formed without irregularities in the inner circumferential surface of a long track bushing having a small inside diameter or in the inner circumferential surfaces of a plurality of track bushings while forming a quench-hardened case in the outer circumferential surface by the cooling from the outer circumferential surface, such that an unhardened quenched layer is left between the quench-hardened cases on inner and outer circumferential surface sides, such that the quench-hardened case on the outer circumferential surface side is deeper than the quench-hardened case on the inner circumferential surface side;
• and such that the unhardened quenched layer has a structure containing one or more selected from ferrite, pearlite and bainite which precipitate in the course of cooling from the quenching temperature.

A track bushing which is formed such that

• by a series of quenching processes in which after the material of a track bushing has been entirely heated to a quenching temperature, preceding cooling from the inner circumferential surface of the track bushing material is carried out, or preceding cooling from the inner circumferential surface is effected while carrying out induction heating from the outer circumferential surface of the track bushing material and after an elapse of a specified time, cooling from the outer circumferential surface is carried out,
• quench-hardened cases extending from the outer and inner circumferential surfaces, respectively, to the wall center of the bushing are formed, with an unhardened quenched layer left between the quench-hardened cases on an inner circumferential surface side and an outer circumferential surface side, such that the quench-hardened case on the outer circumferential surface side is deeper than the quench-hardened case on the inner circumferential surface side and such that the unhardened quenched layer has a structure containing one or more selected from ferrite, pearlite and bainite which precipitate in the course of cooling from the quenching temperature and such that the surface layers of flat sealing portions at both end faces of the track bushing are respectively quench-hardened to a depth no less than one-half the wall thickness of the track bushing from the outer circumferential surface.

A track bushing which is formed such that

• by a series of quenching processes in which after the material of a track bushing has been entirely heated to a quenching temperature, preceding cooling from the inner circumferential surface of the track bushing material is effected while carrying out induction heating from the outer circumferential surface of the track bushing material and after an elapse of a specified time, cooling from the outer circumferential surface is carried out, the series of quenching processes further including a step in which during the induction heating from the outer circumferential surface or during the time from when the induction heating is stopped until when the cooling from the outer circumferential surface is finished, the cooling from the inner circumferential surface is stopped to temper the inner circumferential surface within a short time by heat diffusion from the outer circumferential surface to the inner circumferential surface,
• quench-hardened cases extending from the outer and inner circumferential surfaces, respectively, to the wall center of the track bushing are formed, with an unhardened quenched layer left between the quench-hardened cases on an inner circumferential surface side and an outer circumferential surface side, such that the quench-hardened case on the outer circumferential surface side is deeper than the quench-hardened case on the inner circumferential surface side, such that the unhardened quenched layer has a structure containing one or more selected from ferrite, pearlite and bainite which precipitate in the course of cooling from the quenching temperature, and such that the quench-hardened case on the inner circumferential surface side has a tempered martensitic structure.

A track bushing producing apparatus comprising:

• a supporting device for supporting a track bushing such that a specified quenching process can be effected after the material of the track bushing has been induction heated to a quenching temperature from its outer circumferential surface, or such that a specified quenching process can be effected after setting the track bushing material which has been entirely heated to a quenching temperature in a different process;
• a induction heater for carrying out induction heating of the track bushing supported by the supporting device, from its outer circumferential surface;
• a pressure device for pressurizing and fixing the track bushing by pressing partition jigs against both end faces of the track bushing such that a cooling medium for the inner circumferential surface of the track bushing and a cooling medium for the outer circumferential surface of the track bushing do not interfere with each other;
• and
• a cooling system for independently carrying out inner circumferential surface cooling and outer circumferential surface cooling.

A track bushing producing apparatus comprising:

• a heater for substantially uniformly and entirely heating the material of a track bushing to a quenching temperature;
• a quenching system capable of induction heating the track bushing material from its outer circumferential surface;
• and
• a conveyor for carrying the track bushing material into the quenching system after the track bushing material has been heated by the heater and carrying the track bushing out of the quenching system after a treatment has been applied to the track bushing by the quenching system,
• wherein the quenching system is designed such that while preceding cooling from the inner circumferential surface of the track bushing material is carried out, heating from the outer circumferential surface is stopped after an elapse of a specified time to cool the outer circumferential surface.