Patent Application
20200017944
The present invention relates to metal extrusion quenching methods and systems, and more particularly to such methods and systems in which quenching occurs differently at different and locations in the quenching process.
Methods and systems for quenching metal extrusion profiles are well known. Examples of such methods and systems are illustrated in U.S. Pat. No. 5,425,386 to Gentry et al; U.S. Pat. No. 5,337,768 to Gentry; U.S. Pat. No. 5,325,694 to Jenista; U.S. Pat. No. 5,027,634 to Visser et al; and other references identified in the Information Disclosure Statement filed with the present application. The disclosures of the noted patents are incorporated by reference.
The properties of high-performance extruded profiles are affected by the quench rates used in cooling the profiles. The classic, published quench rates of the past were typically specified to meet the minimum specification for ultimate strength of standard aluminum alloys such as 6061. The more complex requirements of automotive and other applications have pushed the limits of what were previously accepted industry standards.
To illustrate this change in specified quench rates, the recommendations from a major ingot supplier have changed over the years. In 2002, the ingot supplier recommended a cooling rate for 6082 alloy of 5.5-11° C. (10-20° F.) per second—a cooling rate that can easily be reached using simple quenching methods. However, in 2014, the same aluminum ingot supplier recommended a cooling rate of 42° C. (75° F.) per second for a specific, specialized 6082 alloy variant.
High-impact spray quenching provides the highest performance water quench systems available. Spray quench performance is typically limited by the formation of the steam barrier around the profile at elevated temperatures. The period of maximum temperature differential between the profile and the water is where the steam barrier interferes with the heat transfer. The nominal breakdown of the steam barrier (called the Leidenfrost temperature) is about 250° C. (480° F.). At breakdown, the heat transfer coefficient increases dramatically, but the temperature differential drops so low that the average heat transfer rate remains low. Increasing the impact velocity of the water droplets can increase the Leidenfrost temperature to as high as 600° C. (1100° F.).
Desired quench rates have increased for high-performance sectors of the extrusion market. However, increased quench rates create higher temperature differentials within the profile, which induce mechanical stresses that can exceed the yield strength of the metal extrusion at the extrusion temperature. This can result in distortion of the profile that is undesirable or even unacceptable. Consequently, known quenching technologies do not provide desired quench rates without affecting the quality of the extrusion.
The present invention provides a method and system for improving the overall quench rate of a metal extrusion quench system.
The method includes first and second quenching steps. The first quenching step includes quenching the metal extrusion relatively gently until the temperature of the metal extrusion approaches the critical temperature range of the alloy. The second quenching step includes quenching the metal extrusion relatively aggressively and relatively quickly as the temperature of the metal extrusion passes through the critical temperature range.
The corresponding system includes first and second zones in which the first and second quenching steps are performed.
In the disclosed embodiment, the effective length of the first step or zone may be changed. This entry zone may be physically divided into subzones, each of which may be selectively controlled (e.g. to be turned on or off). The number of activated subzones controls the effective length of the entry zone.
The present method and system provide 1) relatively gentle, relatively slow quenching where needed to avoid distortion and to increase the yield strength of the extrusion and 2) relatively aggressive, relatively fast quenching after the yield strength of the extrusion has increased sufficiently to withstand such quenching. The overall result is an increase in the quenching rate provided by the method and the system.
These and other advantages and features of the invention will be more fully understood and appreciated by reference to the description of the current embodiment and the drawings.
Before the embodiments of the invention are explained, it is to be understood that the invention is not limited to the details of operation or to the details of construction; and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention may be implemented in various other embodiments and may be practiced or carried out in alternative ways not expressly disclosed herein.
In addition, it is to be understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use of “including” and “comprising” and variations thereof encompasses the items listed thereafter and equivalents thereof as well as additional items and equivalents thereof. Further, enumeration may be used in the description of various embodiments. Unless otherwise expressly stated, the use of enumeration should not be construed as limiting the invention to any specific order or number of components. Nor should the use of enumeration be construed as excluding from the scope of the invention any additional steps or components that might be combined with or into the enumerated steps or components. Any reference to claim elements as “at least one of X, Y and Z” is meant to include any one of X, Y or Z individually, and any combination of X, Y and Z, for example, X, Y, Z; X, Y; X, Z; and Y, Z.
Directional terms, such as “vertical,” “horizontal,” “top,” “bottom,” “upper,” “lower,” “inner,” “inwardly,” “outer” and “outwardly,” are used to assist in describing the invention based on the orientation of the embodiments shown in the illustrations. The use of directional terms should not be interpreted to limit the invention to any specific orientation(s).
A C-curve for aluminum alloy 6061 is illustrated in
The pre-critical temperature range is illustrated by the single-headed arrow 12 in
When in the pre-critical temperature range 12, the metal extrusion may be relatively easily distorted, for example, by high-impact quenching water. Distortion may be reduced in one of two ways. First, distortion may be reduced by reducing the quench rate. Second, distortion may be reduced by increasing the yield strength of the profile by reducing the temperature of the extrusion.
The critical temperature range is illustrated by the double-headed arrow 14 in
The present invention discovers, and takes advantage of, the reality that the rate at which the temperature of the extrusion is reduced (i.e. quenched) should depend on the temperature of the extrusion as it moves through the quenching process. The cooling rate of the extrusion will vary according to the extrusion speed and the extrusion geometry, and there can be no single location in the quench at which the critical temperature is reached for all shapes and speeds. The present invention therefore provide a balance of 1) preventing shock cooling in the pre-critical temperature range and 2) cooling as rapidly as possible across the critical temperature range. For example, one aluminum ingot supplier suggests quench rates of 80° F. per second through the critical temperature range.
The C-curve illustrated in
As configured in
As configured in
By extension (although not specifically illustrated), the system 20 may be configured to provide quenching in subzone 36 but not in subzones 30, 32, and 34. In such a configuration, the effective quenching length of the entry zone 22 is the length of the subzone 36.
By further extension, the system 20 may be configured to provide quenching in all four subzones 30-36. In such a configuration, the effective quenching length of the entry zone 22 is the combined lengths of all four subzones 30-36.
By yet further extension, the system 20 may be configured not to provide quenching in any of the four subzones 30-36. In such a configuration, the effective quenching length of the entry zone 22 is zero.
The configuration of the system 20, and particularly the activation of quenching within the subzones 30-36, is selected to relatively slowly reduce the temperature of the metal extrusion through, or approximately through, the pre-critical temperature range of the alloy of which the metal extrusion is fabricated. Because the quenching within the entry zone 22 is relatively gentle, distortion of the metal extrusion is insignificant or even nonexistent. This enables the metal extrusion to be cooled to a condition where its yield strength is sufficient to withstand more aggressive quenching in subsequent zones 24, 26, and 28.
Relatively aggressive and/or relatively rapid cooling is provided in quenching zones 24, 26, and 28. Such cooling may be provided using techniques well known to those skilled in the art. These techniques may include the use of high-pressure and/or high-volume water as the quenching medium. Such quenching provides relatively high rates of cooling as the temperature of the metal extrusion moves through the critical temperature range, which is desired for the reasons noted above.
The supply of quenching water to the subzones may be controlled in other ways not currently illustrated in the drawings. For example, quenching water could be supplied to each zone independently of whether or not quenching water is supplied to the other zones.
The two-step quenching provided by the present invention includes 1) a first step in which the quenching is relatively gentle and/or relatively slow in order to provide relatively slow cooling of the metal extrusion in the pre-critical temperature range and 2) a second step in which the quenching is relatively aggressive and/or relatively fast cooling through the critical temperature range. Consequently, the invention provides slow quenching where appropriate and fast quenching where appropriate depending on the temperature of the metal extrusion at any location through the quench system 20.
The above description is that of current embodiments of the invention. Various alterations and changes can be made without departing from the spirit and broader aspects of the invention as defined in the appended claims, which are to be interpreted in accordance with the principles of patent law including the doctrine of equivalents.
This disclosure is illustrative and should not be interpreted as an exhaustive description of all embodiments of the invention or to limit the scope of the claims to the specific elements illustrated or described in connection with these embodiments. For example, and without limitation, any individual element(s) of the described invention may be replaced by alternative elements that provide substantially similar functionality or otherwise provide adequate operation. This includes, for example, presently known alternative elements, such as those that might be currently known to one skilled in the art, and alternative elements that may be developed in the future, such as those that one skilled in the art might, upon development, recognize as alternatives.
Further, the disclosed embodiments include a plurality of features that are described in concert and that might cooperatively provide a collection of benefits. The present invention is not limited to only those embodiments that include all of these features or that provide all of the stated benefits, except to the extent otherwise expressly set forth in the issued claims. Any reference to claim elements in the singular, for example, using the articles “a,” “an,” “the” or “said,” is not to be construed as limiting the element to the singular.
