U.S. patent application number 11/695341 was filed with the patent office on 2007-10-18 for high performance thread forming screw.
This patent application is currently assigned to ACUMENT INTELLECTUAL PROPERTIES, LLC. Invention is credited to David R. Price, Gary Shattuck.
Application Number | 20070243043 11/695341 |
Document ID | / |
Family ID | 38604987 |
Filed Date | 2007-10-18 |
United States Patent
Application |
20070243043 |
Kind Code |
A1 |
Price; David R. ; et
al. |
October 18, 2007 |
HIGH PERFORMANCE THREAD FORMING SCREW
Abstract
A thread forming screw having a minimum surface hardness of HRC
56. The screw can form threads in a workpiece having a surface
hardness which exceeds HRC 23. A method of surface hardening a
screw includes carbon enriching the screw to at least a 0.48 carbon
level, and then quenching the screw. Then, the screw is tempered
such that the surface hardness does not exceed the core hardness by
more than 3 Rockwell C points, and both the surface and core are at
a Rockwell C33-C39 hardness. Subsequently, the point is induction
hardened, and the screw is quenched again. The screw is again
tempered such that the lead threads and the first 3-4 full threads
are at a Rockwell C56 minimum hardness, preferably to a depth of at
least 0.008 inches, and the core of the fastener is at Rockwell
C33-C39 hardness. Finally, a finish is applied.
Inventors: |
Price; David R.; (Rockford,
IL) ; Shattuck; Gary; (Poplar Grove, IL) |
Correspondence
Address: |
TREXLER, BUSHNELL, GIANGIORGI,;BLACKSTONE & MARR, LTD.
105 WEST ADAMS STREET, SUITE 3600
CHICAGO
IL
60603
US
|
Assignee: |
ACUMENT INTELLECTUAL PROPERTIES,
LLC
Troy
MI
|
Family ID: |
38604987 |
Appl. No.: |
11/695341 |
Filed: |
April 2, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60744974 |
Apr 17, 2006 |
|
|
|
Current U.S.
Class: |
411/386 |
Current CPC
Class: |
F16B 33/06 20130101;
C21D 9/0093 20130101; F16B 25/00 20130101; F16B 25/0021 20130101;
B21K 1/46 20130101 |
Class at
Publication: |
411/386 |
International
Class: |
F16B 25/00 20060101
F16B025/00 |
Claims
1. A thread forming screw configured to cold form threads in a
workpiece having a surface hardness which exceeds HRC 23, said
thread forming screw comprising a head and a threaded shank
extending from the head, wherein at least some of the threads of
the shank have a surface hardness of at least HRC 56, thereby
enabling the thread forming screw to be used to cold form threads
in the workpiece having a surface hardness which exceeds HRC
23.
2. A thread forming screw as recited in claim 1, wherein the
threaded shank comprises lead threads proximate an end of the
screw, opposite the head.
3. A thread forming screw as recited in claim 2, wherein the lead
threads taper to the end of the screw.
4. A thread forming screw as recited in claim 2, further comprising
a plurality of full threads on the threaded shank, disposed between
the lead threads and the head of the screw.
5. A thread forming screw as recited in claim 4, wherein the lead
threads and at least three of the full threads of the screw have a
surface hardness of at least HRC 56, to a depth of at least 0.008
inches.
6. A thread forming screw as recited in claim 5, wherein a core of
the screw has a hardness in the range of Rockwell C33 to 39.
7. A thread forming screw as recited in claim 6, wherein a first
portion of the screw, proximate the end of the screw, has a minimum
induction hardened area at HRC 56 min., and a second portion of the
screw has a maximum induction hardened area at HRC 56 min.
8. A thread forming screw as recited in claim 7, wherein a third
portion of the screw has a surface hardness within 3 points HRC of
the core.
9. A method for forming a thread forming screw which is configured
to cold form threads in a workpiece having a surface hardness which
exceeds HRC 23, said method comprising providing a wire made of
steel; drawing the wire at a cold heading machine; forming threads
on the wire to form a screw; performing a heat treating process on
the screw, by carbon enriching the screw, and induction hardening
lead threads and at least three full threads of the screw, such
that the thread forming screw has a head and a threaded shank
extending from the head, and at least some of the threads of the
shank have a surface hardness of at least HRC 56.
10. A method of forming a thread forming screw as recited in claim
9, further comprising quenching and tempering the screw after
carbon enriching the screw and before induction hardening the lead
threads and at least three full threads of the screw.
11. A method of forming a thread forming screw as recited in claim
9, further comprising quenching and tempering the screw after
induction hardening the lead threads and at least three full
threads of the screw.
12. A method of forming a thread forming screw as recited in claim
9, wherein the step of carbon enriching the screw comprises leaving
the screw in a furnace for 90 minutes while the furnace is at
1600-1700 degrees Fahrenheit while controlling the furnace
atmosphere to 0.6 to 0.7% carbon potential, wherein a depth of a
carbon restored zone of the screw is at least 0.008 inches.
13. A method of forming a thread forming screw as recited in claim
9, further comprising quenching and tempering the screw after
carbon enriching the screw and before induction hardening the lead
threads and at least three full threads of the screw, wherein the
step of quenching the screw comprises quenching the screw in oil at
140-160 degrees Fahrenheit.
14. A method of forming a thread forming screw as recited in claim
9, further comprising quenching and tempering the screw after
carbon enriching the screw and before induction hardening lead
threads and at least three full threads of the screw, wherein the
step of tempering the screw comprises tempering the screw for 90
minutes at a temperature of 850-950 degrees Fahrenheit, wherein the
surface hardness of the screw does not exceed the core hardness by
more than 3 Rockwell C points, wherein both the surface and the
core of the screw are at a Rockwell C33 to 39 hardness.
15. A method of forming a thread forming screw as recited in claim
9, wherein the step of induction hardening the lead threads and at
least four full threads of the screw comprises momentarily feeding
the screw into the influence of an electric field in such a way as
to induction heat the threads to a hardening temperature of
1650-1750 degrees Fahrenheit.
16. A method of forming a thread forming screw as recited in claim
9, further comprising quenching and tempering the screw after
induction hardening the lead threads and at least three full
threads of the screw, wherein the step of tempering comprises
tempering the screw at 300 degrees Fahrenheit for a minimum of one
hour, thereby lowering a brittleness of the screw, wherein the
tempering step and the carbon enrichment step provide that the lead
threads and at least the first three full threads are at a Rockwell
C56 minimum hardness, to a depth of at least 0.008 inches, and the
core of the fastener is at Rockwell C33 to 39 hardness.
17. A method of forming a thread forming screw as recited in claim
9, further comprising quenching and tempering the screw after
induction hardening the lead threads and at least three full
threads of the screw, wherein the tempering step and the carbon
enrichment step provide that the lead threads and at least the
first three full threads are at a Rockwell C56 minimum hardness, to
a depth of at least 0.008 inches, and the core of the fastener is
at Rockwell C33 to 39 hardness.
18. A method of forming a thread forming screw as recited in claim
9, further comprising providing that the wire comprises an alloy
steel, AISI C4037 grade analysis with a composition of: carbon
0.35-0.40 percent; manganese 0.70-0.90 percent, sulphur 0.040
percent max., phosphorous 0.035 percent max., silicon 0.20-0.35
percent and molybdenum 0.20-0.30 percent.
19. A method of forming a thread forming screw as recited in claim
9, wherein the step of carbon enriching the screw comprises carbon
enriching the screw such that the screw obtains at least a 0.48
carbon level.
Description
RELATED APPLICATION (PRIORITY CLAIM)
[0001] This application claims the benefit of U.S. Provisional
Application Ser. No. 60/744,974, filed Apr. 17, 2006, which is
hereby incorporated herein by reference in its entirety.
BACKGROUND
[0002] The present invention generally relates to thread forming
screws and methods of forming same, and more specifically relates
to a fastener, such as a thread forming screw, at least a portion
of which has a minimum surface hardness of HRC 56 (Rockwell
Hardness C-scale), and to a method of forming such a thread forming
screw.
[0003] Currently, the industry recommends that thread forming
screws be able to cold form threads in a workpiece having a
hardness of Rockwell C23 and below. As such, current thread forming
screws are sufficiently hard to cold form threads in such
workpieces. However, there are some applications where it would be
desired to have a thread forming screw be able to form threads in a
workpiece which has a hardness which exceeds HRC 23. For example,
after High Strength Low Alloy (HSLA) material is formed, such as by
punching holes in the material, the hardness in and around the hole
area could reach and exceed a Rockwell C40 hardness.
[0004] Conventional thread forming screws are not hard enough to
successfully cold form threads into workpieces which exceed a
Rockwell C23 hardness. For example, some commercially available
thread forming screws are processed so that the point and the first
three to four full threads are at a Rockwell C45 minimum hardness,
and the core of the fastener is at Rockwell C33 to 39 hardness. A
thread forming screw such as this is not hard enough to
consistently cold form threads into a material which exceeds HRC
23. When driving such a thread forming screw into HSLA material (or
any other material) having a hardness of HRC 40 or more, thread
collapse occurs. This collapse, or deformation of the threads,
causes joint failure. When forming threads in materials such as
steel, it is required to have the fastener have a hardness much
greater than the material into which the fastener is being
threaded, in order to form the threads properly without
collapsing.
[0005] Because current thread forming screws are not sufficiently
hard to cold form threads into workpieces having a hardness which
exceeds HRC 23, in such cases it has been necessary to provide
mating threads, such as by providing a threaded joint in the
workpiece (which requires a drill and tap operation), or by
providing weld nuts, loose nuts, a weld boss, threaded inserts, or
by providing a similar feature or using a similar method for
providing mating threads. These structures/methods require
additional operations, hardware and time, resulting in a more
costly, time-consuming process.
[0006] As such, a market exists for fasteners capable of forming
threads in workpieces, such as HSLA material or any other material,
which has a hardness which exceeds Rockwell C23.
OBJECTS AND SUMMARY
[0007] An object of an embodiment of the present invention is to
provide a thread forming screw at least a portion of which has a
surface hardness that is sufficiently high such that the thread
forming screw can be used to cold form threads in a workpiece which
has a hardness that exceeds HRC 23.
[0008] Another object of an embodiment of the present invention is
to provide a thread forming screw at least a portion of which has a
minimum surface hardness of HRC 56.
[0009] Still another object of an embodiment of the present
invention is to provide a thread forming screw which has a minimum
surface hardness of HRC 56, at least to a depth of 0.008 inches,
for at least some of the threads of the screw.
[0010] Briefly, and in accordance with at least one of the
foregoing objects, an embodiment of the present invention provides
a thread forming screw which has a head and a threaded shank
extending from the head. At least some of the threads of the shank
are surface hardened, preferably to a minimum surface hardness of
HRC 56, thereby enabling the thread forming screw to thereafter be
used to cold form threads in a workpiece having a surface hardness
which exceeds HRC 23.
[0011] Another aspect of the present invention provides a method of
forming such a thread forming screw. The method includes performing
a heat treating process whereby the screw is carbon enriched to at
least a 0.48 carbon level, and is quenched, such as in oil. Then,
the screw is tempered in order to lower the brittleness and to
allow for a more ductile core. Preferably, the tempering is
controlled such that the surface hardness does not exceed the core
hardness by more than 3 Rockwell C points. Preferably, after the
tempering, both the surface and core of the fastener are at a
Rockwell C33 to 39 hardness. Subsequently, the point, such as the
lead threads and three to four full threads of the screw, is
induction hardened and the screw is quenched, such as in water or
in a synthetic quench. Then, the screw is tempered again to a lower
brittleness. Preferably, this tempering step is controlled such
that, for example, the lead threads and the first three to four
full threads are at a Rockwell C56 minimum hardness, preferably to
a depth of at least 0.008 inches, and the core of the fastener is
at Rockwell C33 to 39 hardness. Finally, preferably a finish is
applied to the fastener.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The organization and manner of the structure and operation
of the invention, together with further objects and advantages
thereof, may best be understood by reference to the following
description, taken in connection with the accompanying drawings,
wherein like reference numerals identify like elements in
which:
[0013] FIG. 1 is a side view of one type of screw which can be
surface hardened in accordance with an embodiment of the present
invention;
[0014] FIG. 2 is a partial cross-sectional diagram of the screw
shown in FIG. 1; and
[0015] FIG. 3 is a flow chart illustrating a method of making a
surface hardened thread forming screw, where the method is in
accordance with an embodiment of the present invention.
DESCRIPTION
[0016] While the present invention may be susceptible to embodiment
in different forms, there is shown in the drawings, and herein will
be described in detail, an embodiment thereof with the
understanding that the present description is to be considered an
exemplification of the principles of the invention and is not
intended to limit the invention to that as illustrated and
described herein.
[0017] One aspect of the present invention relates to a fastener,
such as a thread forming screw, at least a portion of which has a
surface hardness of HRC 56. Another aspect relates to a method of
surface hardening a fastener, such as a thread forming screw, such
that at least a portion of which has a surface hardness of HRC 56.
While the method can be used in connection with a wide range of
screws, U.S. Pat. No. 3,935,785 discloses a screw with which a
method in accordance with an embodiment of the present invention
can be used, and the '785 patent is hereby incorporated herein by
reference in its entirety.
[0018] As shown in the '785 patent and in FIG. 1 of the present
application, the screw 10 includes a head 12 and a threaded shank
14 which extends from the head 12. Proximate the end 16 of the
screw 10, opposite the head 12, are a plurality of lead threads 18
which taper somewhat to the point 16 of the screw 10. Between the
lead threads 18 and the head 12 are a plurality of full threads 20,
wherein reference numeral 22 identifies the first full thread and
reference numeral 24 identifies the fourth full thread. More detail
regarding the shape and function of this particular screw can be
found in the '785 patent. However, an example of a preferred,
specific embodiment of the present invention provides as shown in
FIG. 2, wherein the lead threads 18 as well as the first three or
four full threads of the screw, are surface hardened to a Rockwell
hardness of at least HRC 56, to a depth (i.e., dimension 26
identified in FIG. 2) of at least 0.008 inches. Preferably, the
core of the screw 10 is at Rockwell C33 to 39 hardness, such that
the screw 10 has a relatively ductile core. As shown in FIG. 2, the
portion identified with reference numeral 28 has a minimum
induction hardened area at HRC 56 min., while the portion
identified with reference numeral 30 has a maximum induction
hardened area at HRC 56 min. The portion identified with reference
numeral 32 is a hardened, quenched, and tempered area, having a
surface hardness within 3 points HRC of the core.
[0019] FIG. 3 illustrates a method which is accordance with an
embodiment of the present invention, and the method can be used to
form a thread forming screw 10 such as shown in FIGS. 1 and 2. The
method provides that, for example, a wire made of steel 4037 steel
or a similar alloy is provided, and the wire is drawn at a cold
heading machine. The material may be an alloy steel, AISI C4037
grade analysis with a composition of: carbon 0.35-0.40 percent;
manganese 0.70-0.90 percent, sulphur 0.040 percent max.,
phosphorous 0.035 percent max., silicon 0.20-0.35 percent and
molybdenum 0.20-0.30 percent, normally specified as killed, fine
grain, spherodized annealed steel. Of course, other material may be
used while staying entirely within the scope of the present
invention. Once the cold heading is completed, threads are formed
on the screw. These steps are conventional and well known.
[0020] Once the screw is formed, a heat treating process in
accordance with an embodiment of the present invention is
performed. In the heat treating process, the screw is carbon
enriched using a controlled process, in a quality furnace, such
that the screw obtains at least a 0.48 carbon level. The carbon
enrichment allows the surface of the fastener to be hardened harder
than the base material. Specifically, the screw can be left in the
furnace for 90 minutes while the furnace is at 1600-1700 degrees
Fahrenheit. The furnace atmosphere is preferably controlled to 0.6
to 0.7% carbon potential (with no nitriding). Preferably, the depth
(i.e., dimension 26 in FIG. 2) of the carbon restored zone is at
least 0.008 inches. Preferably, the surface hardness after
tempering (at the temperature selected for the core requirement)
does not exceed the core hardness by more than 3 Rockwell C (30
Vickers) points equivalent. A 1 to 2 Rockwell C (10-20 Vickers)
equivalent surface hardness increase would be an objective in
selecting furnace parameters. A microhardness tester can be
employed to measure the hardness and depth of the carbon restored
zone, in order to help set the furnace parameters.
[0021] Once the screw is carbon enriched, the screw is quenched,
such as in oil at 140-160 degrees Fahrenheit. After quenching, the
screw is tempered, such as for 90 minutes at a temperature of
850-950 degrees Fahrenheit, in order to lower the brittleness and
allow for a more ductile core in the fastener. Preferably, this
step is controlled such that the surface hardness does not exceed
the core hardness by more than 3 Rockwell C points). At this point,
preferably both the surface and the core of the fastener are at a
Rockwell C33 to 39 hardness.
[0022] Subsequently, the point of the screw, such as the lead
threads 18 and the first three to four full threads, is induction
hardened, wherein the lead threads of the fastener are momentarily
fed into the influence of an electric field in such a way as to
induction heat the threads to the hardening temperature
(approximately 1650-1750 degrees Fahrenheit). The screw is
thereafter immediately quenched, such as in water spray or
viz-a-viz a synthetic quench.
[0023] Subsequently, the screw is tempered, such as at 300 degrees
Fahrenheit for a minimum of one hour, in order to lower the
brittleness. This tempering step along with the previous carbon
enrichment step preferably effectively combine to provide that the
lead threads and the first three to four full threads are at a
Rockwell C56 minimum hardness, preferably to a depth of at least
0.008 inches, and the core of the fastener is at Rockwell C33 to 39
hardness. While different tempering temperatures and durations may
be used, preferably the temperature is sufficiently low to keep the
point at a Rockwell C56 minimum hardness. Finally, preferably a
finish is applied to the fastener.
[0024] One aspect of the present invention provides a fastener at
least a portion of which has a minimum surface hardness of 56 HRC.
For example, the fastener could be a thread forming screw such as
is shown in U.S. Pat. No. 3,935,785, where the lead threads and the
first three or four full threads have a minimum surface hardness of
56 HRC. As such, the screw can be used to cold form threads into a
workpiece which has a hardness which exceeds 23 HRC, such as HSLA
material or any other material having a hardness of 40 HRC or
more.
[0025] Another aspect of the present invention provides a method of
surface hardening at least a portion of a fastener, such as the
thread forming screw shown in U.S. Pat. No. 3,935,785, such that at
least a portion of the screw has a minimum surface hardness of 56
HRC. For example, the lead threads and the first three or four full
threads have a minimum surface hardness of 56 HRC, whereby the
screw can be used to cold form threads into a workpiece which has a
hardness which exceeds 23 HRC, such as HSLA material or any other
material having a hardness of 40 HRC or more.
[0026] Still another aspect of the present invention provides a
product by process, specifically a fastener made by using the
process described hereinabove.
[0027] While embodiments of the present invention are shown and
described, it is envisioned that those skilled in the art may
devise various modifications of the present invention without
departing from the spirit and scope of the disclosure. For example,
while it is described above that the surface hardness can be
effected with regard to lead threads and the first three or four
lead threads, the surface hardness can be implemented with regard
to either more or less threads while staying fully within the scope
of the present invention. Additionally, while the foregoing
description specifically discusses HSLA material, the present
invention can be used to form threads into other material besides
HSLA material.
* * * * *