Metal treatment – Process of modifying or maintaining internal physical... – Heating or cooling of solid metal
Reexamination Certificate
1999-08-17
2001-01-16
Yee, Deborah (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Heating or cooling of solid metal
C148S641000, C148S640000, C266S134000
Reexamination Certificate
active
06174389
ABSTRACT:
TECHNICAL FIELD
This invention is generally directed to a fixture and method for maintaining a preselected area of a workpiece at a temperature above that of a quenched area during quenching, and more particularly to a fixture for quenching a first predetermined area of a workpiece and maintaining a second predetermined area of the workpiece at a temperature above the first predetermined area during quenching, and to a method for maintaining the second predetermined area of the workpiece at a temperature above that of the first predetermined area during quenching.
BACKGROUND ART
Heat treated articles, for example articles that are formed of metal alloys such as steel, are typically quenched from elevated temperatures by coolants, such as water, water-based liquids, oil, or other liquid media, to effect metallurgical hardening. Often certain areas of the workpiece need to be protected from the coolant to preserve low hardness and high ductility in those areas. A quench fixture is often employed to direct the coolant to some areas and partially exclude it from other areas.
Examples of cooling selected areas of a workpiece are described in U.S. Pat. No. 5,000,798 issued Mar. 19, 1991 to Murray A. Nott, et al and titled
Method for Shape Control of Rail During Accelerated Cooling
. In the Nott apparatus, coolant is sprayed onto selected areas of the workpiece to control the shape or straightness of the article. Much earlier, U.S. Pat. No. 1,828,325 was issued to Heinrich Kurz on Oct. 20, 1931, for
Process for the Manufacture of Rails with Hardened Heads
. The Kurz patent describes a quench fixture, and method of using the fixture, in which different coolants are directed to separate preselected areas of the workpiece to develop different metallurgical properties in different portions of the workpiece. For example, air or steam is directly against the upper side of the web of a rail while a liquid coolant is directed to the head of the rail.
In an attempt to prevent the quench media from effecting areas of the workpiece that are not to be hardened, shrouds intended to contain the quench media have been used, but with only limited success. For example, U.S. Pat. No. 4,486,248 issued to Robert J. Ackert, et al on Dec. 4, 1984 for
Method for the Production of Improved Railway Rails by Accelerated Cooling In Line with the Production Rolling Mill
describes quench media spray heads disposed within a shroud structure. As mentioned above, such shrouds have been only partially successful in preventing the quench media from effecting areas of the workpiece in which hardening is not desired. Leaks of the coolant past the shroud results in quenching and transformation hardening in areas intended to remain soft, and can cause breakage of the workpiece during future service. Attempts to pressurize the unquenched areas with air can result in localized cooling and unintended hardening. Vacuum devices to siphon coolant flows are not always effective.
The present invention is directed to overcoming the problems set forth above. It is desirable to have a heat treat fixture and a method of heat treating in which areas of the workpiece that are not to be cooled by the quench media are protected by pressurized steam which disburses any quench coolant that may inadvertently pass through a barrier between the quenched and unquenched areas of the workpiece. It is also desirable to have such a fixture and method where the steam pressure is maintained at a value sufficient to exclude quench coolant from contacting preselected nonquenched areas of the workpiece. Furthermore, it is desirable to have a pressurized steam chamber wherein the steam temperature can be held at a temperature sufficient to maintain the preselected nonquenched areas at or above the transition temperature, i.e., the Martensite start temperature (M
s
in the case of steel), to allow slow cooling of the nonquenched areas after quenching the workpiece.
DISCLOSURE OF THE INVENTION
In accordance with one aspect of the present invention, a heat treating fixture for quenching a first predetermined area of a workpiece and maintaining a second predetermined area of the workpiece at a temperature above the first predetermined area during quenching, includes a shroud extending over the second predetermined area and having an inlet port, a vent port, and a seal member positionable between the shroud and the workpiece at a boundary between the first and second predetermined areas. The fixture also includes a supply conduit in fluid communication with the inlet port of the shroud and with a source of steam, and an exhaust conduit in fluid communication with the vent port of the shroud.
Other features of the heat treating fixture embodying the present invention include a throttle valve disposed in the supply conduit at a position between the inlet port and the source of steam. Yet another feature includes the exhaust conduit having a pressure regulator valve disposed therein. Still another feature includes the seal member disposed between the shroud and the workpiece being formed of a heat-resistant material such as steel.
In another aspect of the present invention, a method for maintaining a second predetermined area of a workpiece at a temperature above that of a first predetermined area during quenching includes positioning a shroud, having at least one sealing edge, over the second predetermined area of the workpiece, thereby forming a sealed chamber that is defined by the second predetermined area of the workpiece and the shroud. A pressurized flow of steam is directed into the sealed chamber, and the first predetermined area of the workpiece is quenched while simultaneously maintaining positive steam pressure within the sealed chamber. After quenching is completed, the quenching is stopped and the flow of steam into the sealed chamber is interrupted prior to removing the shroud from the workpiece.
Other features of the method embodying the present invention includes controllably regulating the flow of steam introduced into the chamber. Yet another feature includes controllably regulating the flow of the steam vented from the sealed chamber. Still another feature includes maintaining the steam pressure in the sealed chamber at a pressure of about 70 kN/m
2
(10 psi).
Another feature of the present invention includes the workpiece having a steel composition, and the steam directed into the sealed chamber having a temperature sufficient to maintain the second predetermined area of the workpiece at a temperature above the transformation temperature of the steel composition of the workpiece, for a period of time sufficient to provide cooling of the second predetermined area at a rate less than that of the first predetermined area of the workpiece.
REFERENCES:
patent: 125650 (1872-04-01), Woodbury
patent: 1828325 (1931-10-01), Kurz
patent: 2263621 (1941-11-01), Frickey
patent: 3765660 (1973-10-01), Taylor et al.
patent: 4486248 (1984-12-01), Ackert et al.
patent: 4810311 (1989-03-01), Economopoulos
patent: 5000798 (1991-03-01), Nott et al.
patent: 5390900 (1995-02-01), Ginzburg
patent: 5553106 (1996-09-01), Enomoto et al.
Caterpillar Inc.
McFall Robert A.
Yee Deborah
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