U.S. patent application number 13/733273 was filed with the patent office on 2014-03-06 for system for preventing the formation of martensite in metals joining applications.
This patent application is currently assigned to EDISON WELDING INSTITUTE, INC.. The applicant listed for this patent is David P. Workman. Invention is credited to David P. Workman.
Application Number | 20140061282 13/733273 |
Document ID | / |
Family ID | 49170557 |
Filed Date | 2014-03-06 |
United States Patent
Application |
20140061282 |
Kind Code |
A1 |
Workman; David P. |
March 6, 2014 |
SYSTEM FOR PREVENTING THE FORMATION OF MARTENSITE IN METALS JOINING
APPLICATIONS
Abstract
A system for joining materials such as metal alloys that
includes a first component, wherein the first component includes a
first alloy having a known austenization temperature below which
martensite forms when the component is heated and then cooled at a
predetermined rate of cooling; a second component, wherein the
second component includes a second alloy; and a welding apparatus
operative to create a weld between the first and second components
without crossing the austenization temperature of the first
alloy.
Inventors: |
Workman; David P.; (Dublin,
OH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Workman; David P. |
Dublin |
OH |
US |
|
|
Assignee: |
EDISON WELDING INSTITUTE,
INC.
Columbus
OH
|
Family ID: |
49170557 |
Appl. No.: |
13/733273 |
Filed: |
January 3, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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61697675 |
Sep 6, 2012 |
|
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|
Current U.S.
Class: |
228/2.1 |
Current CPC
Class: |
B23K 20/129 20130101;
B23K 20/227 20130101; B23K 20/1205 20130101; B23K 2101/26
20180801 |
Class at
Publication: |
228/2.1 |
International
Class: |
B23K 20/12 20060101
B23K020/12 |
Goverment Interests
STATEMENT REGARDING FEDERALLY FUNDED RESEARCH
[0002] This invention was supported in part by contract number
DTFR53-12-C-00002 from the Federal Railroad Administration, Track
Research Division. The U.S. Government has certain rights in the
invention.
Claims
1) A system for joining materials, comprising: (a) a first
component, wherein the first component includes a first alloy
having a known austenization temperature below which martensite
forms when the component is heated and then cooled at a
predetermined rate of cooling; (b) a second component, wherein the
second component includes a second alloy; and (c) a welding
apparatus operative to create a weld between the first and second
components without crossing the austenization temperature of the
first alloy.
2) The system of claim 1, wherein the first component further
includes heat-treated steel.
3) The system of claim 1, wherein the first component is a length
of train rail.
4) The system of claim 1, wherein the second component further
includes an appurtenance, wherein the appurtenance is operative to
provide a surface to which a signal wire or other device may be
attached.
5) The system of claim 4, wherein the appurtenance is a stud, bolt,
or block.
6) The system claim 1, wherein the second component further
includes at least one low-sulfur, low-lead alloy.
7) The system claim 1, wherein the second component further
includes C464 Naval Brass, C172 Class 4 copper, C260 Brass, Muntz
Metal. Ni-12P braze alloy, or combinations thereof.
8) The system of claim 1, wherein the welding apparatus is
operative to perform solid-state welding.
9) The system of claim 1, wherein the welding apparatus is an
inertia friction welding machine.
10) The system of claim 9, wherein the second component is a hex
stud that further includes C464 brass, and wherein the inertia
friction welding machine operates at a speed of 4000-4500 rpms, an
inertial mass of 1.21 WK.sup.2, and a thrust load of about 5200-lbs
force to 6000-lbs force.
11) A system for joining materials, comprising: (a) a first
component, wherein the first component includes a first alloy
having a known austenization temperature below which martensite
forms when the component is heated and then cooled at a
predetermined rate of cooling; (b) a second component, wherein the
second component includes at least one low-sulfur, low-lead alloy;
and (c) a welding apparatus operative to create a weld between the
first and second components without crossing the austenization
temperature of the first alloy.
12) The system of claim 11, wherein the first component further
includes heat-treated steel.
13) The system of claim 11, wherein the first component is a length
of train rail.
14) The system of claim 11, wherein the second component further
includes an appurtenance, wherein the appurtenance is operative to
provide a surface to which a signal wire or other device may be
attached, and wherein the appurtenance is a stud, bolt, or
block.
15) The system claim 11, wherein the second component further
includes C464 Naval Brass, C172 Class 4 copper, C260 Brass, Muntz
Metal. Ni-12P braze alloy, or combinations thereof.
16) The system of claim 11, wherein the welding apparatus is
operative to perform solid-state welding, and wherein the welding
apparatus is an inertia friction welding machine.
17) The system of claim 16, wherein the second component is a hex
stud that further includes C464 brass, and wherein the inertia
friction welding machine operates at a speed of 4000-4500 rpms, an
inertial mass of 1.21 WK.sup.2, and a thrust load of about 5200-lbs
force to 6000-lbs force.
18) A system for joining materials, comprising: (a) a first
component, wherein the first component includes a first alloy
having a known austenization temperature below which martensite
forms when the component is heated and then cooled at a
predetermined rate of cooling, wherein the first component further
includes heat-treated steel, and wherein the first component is a
length of train rail; (b) a second component, wherein the second
component includes at least one low-sulfur, low-lead alloy, wherein
the second component further includes an appurtenance that is
operative to provide a surface to which a signal wire or other
device may be attached, and wherein the appurtenance is a stud,
bolt, or block; and (c) a welding apparatus operative to create a
weld between the first and second components without crossing the
austenization temperature of the first alloy, wherein the welding
apparatus is operative to perform solid-state welding, and wherein
the welding apparatus is an inertia friction welding machine.
19) The system claim 18, wherein the second component further
includes C464 Naval Brass, C172 Class 4 copper, C260 Brass, Muntz
Metal. Ni-12P braze alloy, or combinations thereof.
20) The system of claim 18, wherein the second component is a hex
stud that further includes C464 brass, and wherein the inertia
friction welding machine operates at a speed of 4000-4500 rpms, an
inertial mass of 1.21 WK.sup.2, and a thrust load of about 5200-lbs
force to 6000-lbs force.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This patent application claims the benefit of U.S.
Provisional Patent Application Ser. No. 61/697,675 filed on Sep. 6,
2012, and entitled "System and Method for Joining Materials," the
disclosure of which is incorporated by reference for all purposes,
as if fully rewritten herein.
BACKGROUND OF THE INVENTION
[0003] The present invention relates generally to a system and
method for joining two components to one another, particularly
where one of the two components is a hardened metal, and more
specifically to a system and method for attaching a stud or other
appurtenance to a specific location on a length of steel rail for
the purpose of attaching a signal wire to the stud.
[0004] Railroad signaling systems are essential for enabling safe
and efficient movement of rail traffic. Many modern railroad signal
systems employ a track circuit to detect the presence of a train
within a section of track known as a signal block. The basic
principle behind the track circuit involves the connection of the
two rails by the wheels and axle of locomotives to short out an
electrical circuit. This circuit is monitored by electrical
equipment to detect the absence of the trains. An integral part of
the track circuit is the two parallel running rails on which a
train runs. Various types of signal devices are typically connected
to these rails to complete the track circuit. Known techniques for
connecting a wire to a rail include exothermic welding processes
where the wire is welded to the rail. Other techniques include
compressing a metal sleeve including the wire in a hole drilled in
the rail or clamping a wire directly to the rail. Many signaling
system incidents are known to be caused by failures at the
rail-wire interface, where track wires, bond wires, or
propulsion-current bond wires are attached to the rails to provide
an electrical path for controlling train control signals. These
failures contribute to train delays and additional maintenance
costs for emergency and unplanned repairs and are highly
undesirable for these and other reasons.
[0005] As indicated above, signal wires are attached to rails to
allow for positive train control and to sense breaks in the rails
for avoiding accidents. A reliable signal wire-to-rail connection
is essential for signal system functionality and failures cause
service disruptions and can affect the integrity of the rail,
leading to rail failure. Currently used methods for attaching a
signal wire to a length of track involve the use of an appurtenance
or stud that is attached directly to the rail. The signal wire is
then attached or connected to the stud. Common attachment
methodologies include brazing, soldering, drilling, and/or clamping
the stud/wire to the rail. Many brazing methods require preheating
the rail section to which the stud will be attached and then
precisely controlling the rate of cooling to avoid the undesirable
formation of untempered martensite in the rail. With brazing
methodologies there is also the risk of liquid metal embrittlement
as the rail is under tensile stress to maintain neutral temperature
and a liquid metal is present during the process. Accordingly, it
is a common precautionary practice to locate the studs at the
neutral axis of the rail due to the possible formation of a brittle
layer around the joint caused by overheating of the stud/wire to
rail connection point. The placement of welds/braze joints on the
head of the rail is known to have resulted in the formation of
martensite in the head of the rail, which initiated cracks that led
to several train derailments; thus the neutral axis is generally
safer from a catastrophic failure perspective. However, placement
at this location makes the wire harnesses susceptible to snagging
by maintenance equipment and the formation of martensite in this
area may still lead to cracking and rail failure. Furthermore, most
known attachment methodologies require a degree of operator skill,
the absence of which may result in inconsistent or incorrect
installations and ultimately in failure of the stud/wire
connection, particularly in mass production. Thus, there is an
ongoing need for an improved system and method for attaching a stud
or appurtenance to a specific location on a length of steel
rail.
SUMMARY OF THE INVENTION
[0006] The following provides a summary of certain exemplary
embodiments of the present invention. This summary is not an
extensive overview and is not intended to identify key or critical
aspects or elements of the present invention or to delineate its
scope.
[0007] In accordance with one aspect of the present invention, a
first system for joining materials is provided. This system
includes a first component, wherein the first component includes a
first alloy having a known austenization temperature below which
martensite forms when the component is heated and then cooled at a
predetermined rate of cooling; a second component, wherein the
second component includes a second alloy; and a welding apparatus
operative to create a weld between the first and second components
without crossing the austenization temperature of the first
alloy.
[0008] In accordance with another aspect of the present invention,
a second system for joining materials is provided. This system
includes a first component, wherein the first component includes a
first alloy having a known austenization temperature below which
martensite forms when the component is heated and then cooled at a
predetermined rate of cooling; a second component, wherein the
second component includes at least one low-sulfur, low-lead alloy;
and a welding apparatus operative to create a weld between the
first and second components without crossing the austenization
temperature of the first alloy.
[0009] In yet another aspect of this invention, a third system for
joining materials is provided. This system includes a first
component, wherein the first component includes a first alloy
having a known austenization temperature below which martensite
forms when the component is heated and then cooled at a
predetermined rate of cooling, wherein the first component further
includes heat-treated steel, and wherein the first component is a
length of train rail; a second component, wherein the second
component includes at least one low-sulfur, low-lead alloy, wherein
the second component further includes an appurtenance that is
operative to provide a surface to which a signal wire or other
device may be attached, and wherein the appurtenance is a stud,
bolt, or block; and a welding apparatus operative to create a weld
between the first and second components without crossing the
austenization temperature of the first alloy, wherein the welding
apparatus is operative to perform solid-state welding, and wherein
the welding apparatus is an inertia friction welding machine.
[0010] Additional features and aspects of the present invention
will become apparent to those of ordinary skill in the art upon
reading and understanding the following detailed description of the
exemplary embodiments. As will be appreciated by the skilled
artisan, further embodiments of the invention are possible without
departing from the scope and spirit of the invention. Accordingly,
the drawings and associated descriptions are to be regarded as
illustrative and not restrictive in nature.
BRIEF DESCRIPTION OF THE FIGURES
[0011] The accompanying images, which are incorporated into and
form a part of the specification, illustrate one or more exemplary
embodiments of the invention and serve to explain the principles of
the invention, and wherein:
[0012] FIG. 1 is a side view of a portable inertia friction welder
mounted on a length of rail in accordance with an exemplary
embodiment of this invention;
[0013] FIGS. 2a-b are front and side views respectively, of an
exemplary stud or appurtenance suitable for mounting on the length
of rail shown in FIG. 1;
[0014] FIG. 3 provides a high-magnification metallurgical section
of a weld joint created by the method of the present invention
showing no apparent change to the underlying rail steel material;
and
[0015] FIG. 4 provides a macro view of a weld stud mounted on rail
material in accordance with the method of the present
invention.
DESCRIPTION OF THE INVENTION
[0016] Certain exemplary embodiments of the present invention are
now described with reference to the Figures. Although the following
detailed description contains many specifics for purposes of
illustration, a person of ordinary skill in the art will appreciate
that many variations and alterations to the following details are
within the scope of the invention. Accordingly, the following
embodiments of the invention are set forth without any loss of
generality to, and without imposing limitations upon, the claimed
invention.
[0017] As previously stated, the present invention relates
generally to a system and method for joining two components to one
another, particularly where one of the two components is a hardened
metal, and more specifically to a system and method for attaching a
stud or appurtenance to a specific location on a length of steel
rail for the purpose of attaching a signal wire to the stud. The
system and method of this invention have applicability beyond use
with rails and signal wires because the process can also be used to
attach appurtenances to hardenable materials without negatively
affecting the underlying material properties. For example,
attaching a bolt on location to a hardened cutting surface that is
heat treated would be possible without deleterious effects to the
pre-hardened material. Essentially, the system and method of this
invention may be used for any number of applications that require
the attachment of one metal component to another metal component
wherein the use of more traditional joining or welding techniques
would potentially damage the substrate metal. Using the system and
method of this invention, the risk of liquid metal embrittlement
and martensite formation are substantially eliminated because there
is no melting of a stud or braze material to infiltrated the grain
boundaries in the steel and the welding temperature is kept below
the critical transformation temperature of hardened steel. Various
exemplary embodiments of this invention are described in greater
detail below.
[0018] The present invention typically includes two or more metal
components that are joined together using a welding technique that
avoids damaging either component during the joining process. In one
exemplary embodiment, the first component is a length of hardened
steel rail used for train track. Modern track typically uses hot
rolled steel with a profile of an asymmetrical rounded I-beam.
Unlike some other uses of iron and steel, railway rails are subject
to very high stresses and are typically made of very high-quality
steel alloy. Attachment of an appurtenance to heat-treated steel is
typically very difficult due the nature of this alloy. The second
component is a lower-strength appurtenance such as a stud to which
signal wire is or will be attached. This stud is joined to the
steel rail at a desired location using a welding process, such as
friction welding, which prevents the occurrence of liquid metal
embrittlement in the rail alloy. Friction welding is a solid-state
welding process that generates heat through mechanical friction
between a moving workpiece and a stationary component, with the
addition of a lateral force called "upset" to plastically displace
and fuse the materials. The combination of fast joining times (on
the order of a few seconds), and direct heat input at the weld
interface, yields relatively small heat-affected zones. Friction
welding techniques are generally melt-free, which avoids grain
growth in engineered materials, such as high-strength, heat-treated
steels. Another advantage of friction welding is that it allows
dissimilar materials to be joined to one another. Normally, the
wide difference in melting points of two dissimilar materials would
make it nearly impossible to weld using traditional techniques, and
would require some sort of mechanical connection. Friction welding
provides a "full strength" bond with no additional weight.
[0019] With regard to a steel rail component, the system and method
of the present invention produces a weld on rail steel without
crossing the known austenitization temperature for such steel,
thereby avoiding the need for tempering post weld or controlled
cooling to avoid martensite formation. Austenitization involves
heating iron, an iron-based metal, or steel to a temperature at
which it changes crystal structure from ferrite to austenite.
Martensite refers to a very hard form of steel crystalline
structure and is formed by rapid cooling (quenching) of austenite
which traps carbon atoms that do not have time to diffuse out of
the crystal structure. This martensitic reaction begins during
cooling when the austenite reaches a known martensite start
temperature and the parent austenite becomes mechanically unstable.
Since quenching can be difficult to control, many steels are
quenched to produce an overabundance of martensite and then
tempered to gradually reduce its concentration until the right
structure for the intended application is achieved. Too much
martensite leaves steel brittle, too little leaves it soft. With
regard to an appurtenance or stud component, certain materials
(e.g., low-sulfur, low-lead alloys) exhibit highly desirable
characteristics, which permit friction welding of the stud to the
rail without a temperature in excess of the austenitization
temperature of the rail or steel without demanding thrust loads
that are too high for a portable inertia welding system. The use of
a hexagonal shaped stud with a circular face minimizes machining
cost for the stud and provides wrench flats during in-service
work.
[0020] One embodiment of this invention utilizes a portable
battery-powered inertia friction welder that is mounted on a length
of rail for low-energy input welding. The use of a low mass
flywheel coupled with high surface velocity allows for a
lightweight portable unit. The controls for speed and thrust load
control are specific to the machine tool mounted to the rail. The
use of a preloaded spring assembly or a precharged air or hydraulic
cylinder provides weld force/thrust load in the portable system and
a pin/ball release holds the thrust load on the spring. A
lightweight clamp attaches the system to the head of the rail and a
locator placed under the ball of the rail ensures repeatable
placement on the rail regardless of wear condition. Location for
the stud is dictated by reference to the under head radius region
that transitions into the web of the rail. This configuration
allows for reliable installation of studs with little operator
influence on the process as all critical parameters are
predetermined and mechanically controlled. As shown in FIG. 1, an
exemplary embodiment of welding system 10 includes a length of rail
12 upon which restraining clamp 10 is mounted. Chuck 16 houses the
stud (see FIGS. 2a-b) or other appurtenance, and flywheel 18 is
connected to chuck 16. Front mount guide plate 20 supports bearing
end plate 22, which is connected to bearing assemblies 24 which
provide motor decouple and force engagement control. Rear mount
guide plate supports bearing assemblies 24 and spring pack 28,
which includes an air cylinder for providing thrust load. Motor
coupler 32 is connected to drive shaft 34, which passes through
back up plate 30 and connects with spring pack 28.
[0021] In accordance with this invention, welds may be produced
using an portable inertia friction welding machine such as that
disclosed in U.S. Pat. No. 6,779,709 (Stotler et al.), which is
incorporated by reference herein, in its entirety, for all
purposes. The device disclosed in U.S. Pat. No. 6,779,709 is
referred to as the m120 inertia friction welder and is a stationary
programmable inertia friction welding machine that is capable of
varying thrust load from 2000 lbs. to 24,000 lbs.; varying rotating
mass from 1.21 wk.sup.2 to 19 wK.sup.2, and varying initial spindle
speed from 300 to 13,000 RPM. This device typically uses collet
type clamps to hold parts and or tooling in the headstock and
tailstock. Additionally, surface velocity, thrust load, and inertia
may be varied to control heat input. Suitable alloys for the
appurtenance (i.e., stud) include low-sulfur, low-lead alloys
generally and C464 Naval Brass, C172 Class 4 copper, C260 Brass,
Muntz Metal (National Bronze and Metals, Houston, Tex.; Southern
Copper, Pelham, Ala.) and Ni-12P braze alloy, specifically. Studs
such as that shown in FIGS. 2a-b, can be made from 1/2-in hex stock
to allow for easy torsion energy delivery and to simplify
production. Weld strengths approached 6000 pounds for the hex parts
welded which is roughly 35ksi tensile strength or 50% of the cold
worked C464 brass. With a hex stud design, a speed of 4000-4500
rpms, an inertial mass of 1.21 WK.sup.2, and a thrust load of
5200-lbs force to 6000-lbs force may be employed with work hardened
Naval Brass. FIGS. 1-2 show metallographic and SEM analysis
conducted on weld joints to verify that no martensite was formed
due to the fact that the critical temperature in the steel was not
exceeded during welding. Pretinned studs or appurtenances with an
alloy to create a solid state braze joint such as 50/50 Pb--Sn
solder, are also compatible with this invention. As will be
appreciated by one of ordinary skill in the art, the process of
friction welding is scalable based on variables such as the surface
area and mean diameter of the appurtenance (i.e., second
component).
[0022] Advantageously, the present invention permits the
installation of signal wires and studs on the head of the rail as
no deleterious effects occur to the underlying rail material, i.e.,
brittleness and other weaknesses do no occur (see FIGS. 3-4).
Currently, signal wires are located on the neutral axis of the rail
making these connections susceptible to damage by maintenance
equipment that snags and breaks studs and wiring located on the web
neutral axis of the rail. Thus, the point of attachment may be
moved from a low stress area to a critically loaded area (i.e.,
high stress area) without creating noticeable changes in the
microstructure of the underlying alloy or problems with the
integrity and strength of underlying substrate metal.
[0023] While the present invention has been illustrated by the
description of exemplary embodiments thereof, and while the
embodiments have been described in certain detail, it is not the
intention of the Applicant to restrict or in any way limit the
scope of the appended claims to such detail. Additional advantages
and modifications will readily appear to those skilled in the art.
Therefore, the invention in its broader aspects is not limited to
any of the specific details, representative devices and methods,
and/or illustrative examples shown and described. Accordingly,
departures may be made from such details without departing from the
spirit or scope of the applicant's general inventive concept.
* * * * *