Metal treatment – Process of modifying or maintaining internal physical... – Heating or cooling of solid metal
Reexamination Certificate
1999-10-04
2001-12-11
King, Roy (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Heating or cooling of solid metal
C148S645000, C148S646000, C266S117000, C266S259000, C266S260000
Reexamination Certificate
active
06328829
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to constrained hardening of bar-shaped workpieces for preventing warping. In particular, this invention is directed to a hardening method and apparatus suitable for odd-shaped workpieces such as steering rack bars for automobiles which have a tendency to warp during hardening.
Hardening of bar shaped machinery parts is very popular. In order to harden axially symmetrical parts such as a body of simple revolution, rotation around the axis during quenching for equalization of cooling is adopted for prevention of warping. Moreover prevention of warping by exerting constraining force is also adopted. For example, a round bar is rotated among three rolls extending therealong during quenching as shown in Japanese laid-open patent No. Sho 54-67504.
However, bar workpieces having a deformed (odd) shape such as a bar workpiece having a rack gear along its side tend to bend by hardening because the cooling rate is not uniform about their axes. Moreover, these workpieces mentioned above cannot be rotated during quenching, so that press quenching is usually used for prevention of warping during hardening. In the press quenching, all or a part of a workpiece heated to an appointed hardening temperature is held in a set of dies having determined cavities. Then the workpiece is cooled down under pressure by a method such as immersing into a cooling liquid tank.
Recently there has been a trend of cutting weight of automobiles by hollowing such aforementioned bar parts with a rack gear along its side to form pipe parts. However, the pipe parts are very liable to create bending during the hardening process compared with solid bars. Moreover, the pipes could be collapsed by a pressing force in the aforementioned press quenching. If the pressing force is limited for preventing collapse, warping might not be suppressed and strain might arise when being pressed in the dies after being cooled down. Moreover, even if the pressing force is considerably increased and the workpiece is made straight in the dies, warping might arise by existence of residual stress as the workpiece is taken out from the dies. Such residual stress is usually controlled by regulating a cooling rate by partly changing a cooling liquid amount blown against a workpiece depending on the workpiece shape. However, occurrence of warping is not so simple as it changes depending on steel constituents in relation to transformation temperature, because strain during the hardening process is a sum of thermal strain and transformation strain.
SUMMARY OF THE INVENTION
As explained above in some cases (especially in hollowed deformed-shape workpieces), warping cannot be suppressed merely by pressing between dies because of limited pressing force. Moreover, even if deformation is thoroughly suppressed within the dies, warping might occur by residual stress when the workpiece is taken out from the dies. Therefore, complete prevention of warping is difficult as matters now stand. The present invention is intended to minimize warping during hardening of odd-shaped bar workpieces which are difficult to prevent from warping completely in prior constrained hardening processes by dies.
Namely, the present invention is a hardening method which include heating a section of a workpiece of an odd-shaped bar and quenching while constraining the workpiece; section in dies. The quenching is executed while the workpiece is being pressed in at direction perpendicular to its longitudinal direction by a pressing means which is installed adjacent to at least one side of the workpiece section constrained in the dies. Moreover, this invention includes a method in which test quenching is executed while the pressing means is retracted from the workpiece. Proper quenching is then executed while setting the pressing means in a pressing direction, and in at least one of a pressing stroke and a pressing force, so as to reform bending that occurs in the test quenching. By this method, bending in the workpiece can be minimized after hardening.
Moreover, the present invention is a constraining quenching apparatus for quenching a section of a workpiece being constrained in dies, comprising a pressing means which is installed adjacent to at least one side of the workpiece section constrained in the dies. The pressing means comprises at least one pressing member which presses around the workpiece in a direction perpendicular to its longitudinal direction. Each of the pressing members comprises a pressure regulating means for regulating at least one of a pressing stroke and a pressing force independently during pressing conditions by the dies.
In another embodiment of the apparatus, this invention is a constraining quenching apparatus for quenching a longitudinal section of a workpiece being constrained in dies, comprising a pressing means which is connected to the dies at a place adjacent to at least one side of the workpiece section constrained in the dies. The pressing means comprises at least one pressing member which presses around the workpiece in a direction perpendicular to its longitudinal direction. Each of the pressing members comprises an advance-and-retreat position regulating means for regulating a pressing stroke. In this apparatus, the advance and-retreat position regulating means may comprise the pressing member being threaded, whereby the pressing member moves in an advancing and retreating direction by rotation. Moreover, in each of the above apparatuses, the dies may have a plurality of projections defining a contour corresponding to a contour of the workpiece. Recesses are defined between the projections, and a cooling liquid spouting hole is provided at at least one of the recesses of each die.
REFERENCES:
patent: 5492308 (1996-02-01), Yao et al.
patent: 5626693 (1997-05-01), Yao et al.
patent: 31 11 705 (1982-10-01), None
patent: 0 628 641 (1994-12-01), None
patent: 0 632 137 (1995-01-01), None
patent: 0 754 771 (1997-01-01), None
patent: 54-67504 (1979-05-01), None
patent: 358050144A (1983-03-01), None
patent: 407098021A (1995-04-01), None
patent: 09071819 (1997-03-01), None
patent: 10-158742 (1998-06-01), None
The Making, Shaping and Treating of Steel, 1985, United States Steel, 10th Edition, p. 795.
Fukuhara Tetsukazu
Kato Jun-ichi
Seto Yoshiki
Yao Yugo
King Roy
Neturen Co. Ltd.
Wenderoth , Lind & Ponack, L.L.P.
Wilkins, III Harry D.
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