U.S. patent application number 09/898678 was filed with the patent office on 2003-01-09 for method for strengthening a steel channel member.
Invention is credited to Powers, Buren K. II.
Application Number | 20030005985 09/898678 |
Document ID | / |
Family ID | 25409871 |
Filed Date | 2003-01-09 |
United States Patent
Application |
20030005985 |
Kind Code |
A1 |
Powers, Buren K. II |
January 9, 2003 |
METHOD FOR STRENGTHENING A STEEL CHANNEL MEMBER
Abstract
A conventional steel C-channel used as a side rail in a truck
frame is strengthened by forming, after heat treating,
strengthening lips on the edges of the C-channel flanges while the
C-channel is still hot from the final tempering step of the heat
treating process. The method obviates the need to use more
expensive quenching dies and is advantageously performed
immediately after tempering.
Inventors: |
Powers, Buren K. II;
(Troutville, VA) |
Correspondence
Address: |
ANDRUS, SCEALES, STARKE & SAWALL, LLP
100 EAST WISCONSIN AVENUE, SUITE 1100
MILWAUKEE
WI
53202
US
|
Family ID: |
25409871 |
Appl. No.: |
09/898678 |
Filed: |
July 3, 2001 |
Current U.S.
Class: |
148/653 |
Current CPC
Class: |
C21D 1/18 20130101; C21D
8/00 20130101; C21D 2221/02 20130101; C21D 9/0068 20130101; C21D
7/00 20130101 |
Class at
Publication: |
148/653 |
International
Class: |
C21D 008/00 |
Claims
I claim:
1. A method of forming strengthening lips on a low carbon steel
channel member including a web and a pair of parallel flanges
joined by the web, which member has been heat treated to produce a
martensitic grain structure including the steps of rapid quenching
of the member after heating to an austenitizing temperature,
followed by reheating to an tempering temperature in the range of
about 800 to 1000.degree. F., said method comprising the additional
step of: forming lips along the edges of the flanges while the
member is at a temperature of at least about 500.degree. F.
2. The method as set forth in claim 1 wherein the step of quenching
includes restraining the member against distortion.
3. The method as set forth in claim 1 wherein said forming step is
performed at a temperature in the range of about 800 to 900.degree.
F.
4. The method as set forth in claim 1 wherein said lips are formed
inwardly of the channel at an angle of about 90.degree. to the
flanges.
5. The method as set forth in claim 1 wherein the forming step
comprises rolling.
6. The method as set forth in claim 1 including the additional step
of air cooling the formed member to ambient temperature.
7. A method of strengthening a low carbon steel channel member of
the type having a pair of generally parallel end flanges joined by
a central web, comprising the steps of: (1) heating the member to
an austenitizing temperature of at least about 1400.degree. F.; (2)
quenching the member with a turbulent flow of water while
restraining the member in a quenching die; (3) reheating the member
to a tempering temperature of at least about 800.degree. F.; and,
(4) forming lips along the edges of the flanges while the member is
at a temperature greater than about 500.degree. F.
8. The method as set forth in claim 7 wherein the austenitizing
temperature is in the range of about 1400 to 1700.degree. F.
9. The method as set forth in claim 7 wherein the tempering
temperature is in the range of about 800 to 1100.degree. F.
10. The method as set forth in claim 7 wherein the forming
temperature is in the range of about 500 to 900.degree. F.
11. The method as set forth in claim 7 wherein the forming
temperature is in the range of about 800 to 900.degree. F.
12. The method as set forth in claim 7 wherein the forming step
comprises rolling.
13. The method as set forth in claim 12 wherein the rolling step is
performed with series of progressive rollers.
14. The method as set forth in claim 7 wherein the lips are formed
to extend from the flanges inwardly at an angle of about
90.degree..
15. The method as set forth in claim 7 wherein the lips are formed
to extend from the flanges inwardly at an angle in the range of
about 80.degree. to 100.degree..
16. The method as set forth in claim 7 wherein the forming step is
performed while the member is at the tempering temperature.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention pertains to a method for strengthening
a structural steel channel member and, more particularly, to a
method of forming strengthening lips on the end flanges of a
channel member after the member has been heat treated.
[0002] High strength, low carbon steel channel members, sometimes
referred to as C-channels, are widely used as the longitudinal side
rails in the fabrication of truck frames. A typical C-channel
includes a central web and a pair of parallel flanges extending
perpendicularly from the opposite edges of the web. C-channels are
typically cold rolled from a low carbon steel and then initially
heated to develop a desired austenite grain structure which is
converted to a martensite structure by rapid quenching in water,
and then tempered to create a desired toughness. The foregoing
process is particularly desirable for C-channel members used as
side rails in heavy truck frames where steel having a tensile
strength well in excess of 50,000 psi is required.
[0003] The rapid, high volume water quench used to convert the
austenite grain structure to martensite is known to cause extreme
distortion of the C-channel member. Such distortions may be removed
after quenching, but the preferable method has been to utilize
quenching dies that restrain the member from distortion while a
high volume flow of water is directed through the die to all
surfaces of the member. However, quenching dies are extremely
costly and are only practical for use in very high volume standard
steel sections.
[0004] It is also known that the stiffness and strength of a
C-channel can be increased by forming a small lip on the free edge
of each of the flanges. Such lips are formed by rolling or
otherwise turning the edges of the flanges toward one another such
that the lips extend generally perpendicular to the flanges.
Although it would be possible to form strengthening lips on a
C-channel in the initial cold rolling process from which the member
is formed, such preformed sections would require even more complex
and costly quenching tooling than a C-channel without preformed
strengthening lips. This is because a typical quenching die
utilizes a collapsible configuration that necessarily becomes even
more complex when it must be constructed to accommodate the
presence of in turned lips. Furthermore, because heavy truck
manufacturers have varying size and gauge requirements for
C-channels used as frame side rails, customized quenching dies
would be required for each different size and gauge, a situation
that would be completely cost-prohibitive.
SUMMARY OF THE INVENTION
[0005] In accordance with the present invention, a method is
provided for forming strengthening lips on flanges of a channel
member after heat treating. The preliminary heat treating comprises
the steps of heating the member to an austenitizing temperature of
at least about 1400.degree. F.; quenching the member in a quenching
die; and reheating the member to a tempering temperature of at
least about 800.degree. F., followed by the step of forming lips
along the edges of the flanges while the member is still hot,
preferably at or close to the tempering temperature.
[0006] The method of the present invention is particularly well
suited for channel sections made from low carbon steels (having a
carbon content in the range of about 0.20 to 0.30 weight percent).
Such steels are amenable to heat treating as described above to
tensile strengths in excess of 100,000 psi.
[0007] The preliminary austenitizing step is preferably performed
at a temperature in the range of about 1400-1700.degree. F. After
quenching, the tempering step is preferably performed at a
temperature in the range of about 800-1000.degree. F. The final lip
forming step is preferably performed at a temperature in the range
of about 500-900.degree. F., more preferably in the range of about
800-900.degree. F.
[0008] The strengthening lips are preferably formed by rolling. The
rolling step is preferably performed with a series of progressive
rollers. The formed strengthening lips may extend from the flanges
inwardly at an angle of about 90.degree., but an angle in the range
of about 80.degree. to 100.degree. is satisfactory.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a cross sectional view through a conventional
C-channel member.
[0010] FIG. 2 is a cross sectional view through a lipped C-channel
formed in accordance with the method of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0011] A C-channel 10 of the prior art is shown in FIG. 1 and
comprises a central web 11 that interconnects a pair of end flanges
12 at radiused corners 13. As is well known in the art, a C-channel
is formed by cold rolling a steel sheet with rollers to
progressively form the finished cross section. The flanges 12
extend generally perpendicularly from the web 11 and the dimensions
and thickness or gauge of the material may vary considerably
depending on its final use. However, when used as a side rail in a
heavy duty truck, the gauge of the material may be in the range of
about 6 to 12 mm, the length of the side rails may be as great as
30-40 feet, and the section may have an overall height in the range
of about 8 to 14 inches.
[0012] Although the C-channel could be used as initially formed, it
is preferable particularly for heavy truck applications, to first
heat treat the steel to increase its strength and to enhance other
properties. Thus, the section is typically first heated to produce
an austenite grain structure which, in low carbon steels, is
preferably performed at a temperature in the range of about
1400-1700.degree. F. The section is then rapidly quenched in a high
volume water quenching die to convert the austenite grain structure
to the preferred fine grained martensite structure. To minimize
distortion during quenching, quenching dies have been developed to
hold the section during quenching while accommodating normal
shrinkage. Such a quenching die has a fairly complex construction,
one such die being shown in U.S. Pat. No. 3,252,695, the disclosure
of which is incorporated by reference herein. After quenching, the
section is reheated to a tempering temperature, preferably in the
range of about 800-1000.degree. F., to reduce the brittleness and
increase the ductility and toughness of the steel.
[0013] It is known that, for the same size and gauge of a section,
a C-channel can be strengthened considerably by forming, as shown
in FIG. 2, a lipped C-channel 14. The lipped C-channel 14 has a
substantially greater stiffness and rigidity as compared to the
simple C-channel 10 of FIG. 1. Thus, the use of a lipped C-channel
14 can provide a desired increase in side rail rigidity and, at the
same time, provide the possibility of reducing the material gauge
and therefore the weight of the member.
[0014] Although the conventional C-channel 10 of FIG. 1 may be
quenched and simultaneously restrained against distortion utilizing
quenching tooling of the type described in the above identified
patent, the use of such tooling is impractical and/or prohibitively
costly for a lipped C-channel 14 because of the increased
complexity of the tooling and the wide range of dimensions utilized
by the various heavy truck manufacturers. It is with this in mind
that the method of the present invention forms the lips 15 on the
C-channel 14 after heat treating has been completed using a
conventional C-channel 10 and conventional quenching dies.
[0015] As indicated above, the final step in the conventional
C-channel heat treating process is to temper the member by
reheating it to a temperature of at least about 800.degree. F. and,
preferably, somewhere in the range of about 800-1100.degree. F. In
accordance with the present invention, the strengthening lips 15
are formed as the heat treated member exits the tempering furnace.
At this point, the steel will be in a significantly softer state,
making the formation of the strengthening lips 15 much easier with
less chance of cracks occurring in the formed radii 16. Although
the temperature of the C-channel 10 as it exits the tempering
furnace will be greater than or close to at least 800.degree. F.,
it is believed that strengthening lips 15 could be successfully
formed at a temperature as low as about 500.degree. F. It is a
significant feature of the method of this invention that no
separate heating step is required for forming the strengthening
lips since they are formed immediately after tempering.
Conventional progressive rolling dies are used in the presently
preferred method of forming the lips 15.
[0016] As shown in FIG. 2, the lips are generally parallel to the
web 11 and perpendicular to the flanges 12 on which they are
formed. However, the lips 15 may be formed within a range of up to
plus or minus 10.degree. from a true perpendicular orientation of
90.degree.. Thus, the strengthening lips 15 may have an angle with
respect to the flange 12 in the range of about 80-100.degree..
After the strengthening lips have been formed, the modified
C-channel 14 is then allowed to air cool to ambient
temperature.
[0017] Not only is the rigidity and strength of the lipped
C-channel 14 substantially increased over the conventional
C-channel 10 from which it is formed, the radiused corners 16
provide protection against potential edge breakout when the flanges
12 are punched for the connection of frame cross members or other
frame attachments. Indeed, it is well known in the heavy truck
industry that there is a reluctance to make connections of any kind
through the flanges 12 of conventional C-channel side rails 10.
Thus, the opportunity is provided to have a side rail of
substantially increased strength without changing the material size
or gauge and to adapt the improved channel to the use of improved
connections and attachments not previously possible. For example,
instead of attaching a frame cross member with two spaced
connections through the web 11, two additional connections could be
provided for the same cross member, one through each of the flanges
12.
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