Note: Descriptions are shown in the official language in which they were submitted.
SPLIT WEDGE AND METHOD FOR MAKING SAME
BACKGROUND
[0001] This application claims priority to U.S. provisional application
Serial No.
61/715,010 filed October 17, 2012.
[0002] Railway cars typically consist of a rail car that rests upon a
pair of truck
assemblies. The truck assemblies include a pair of side frames and wheelsets
connected together via a bolster and damping system. The damping system
includes a set of friction wedge dampers. The car rests upon the center bowl
of the
bolster, which acts as a point of rotation for the truck system. The car body
movements are reacted through the springs and friction wedge dampers, which
connect the bolster and side frames. The side frames include pedestals that
each
define a jaw into which a wheel assembly of a wheel set is positioned using a
roller
bearing adapter.
[0003] The components may be formed via various casting techniques. The
most
common technique for producing these components is through sand casting. Sand
casting offers a low cost, high production method for forming complex hollow
shapes
such as side frames and bolsters. In a typical sand casting operation, (1) a
mold is
formed by packing sand around a pattern, which generally includes the gating
system; (2) The pattern is removed from the mold; (3) cores are placed into
the mold
and the mold is closed; (4) the mold is filled with hot liquid metal through
the gating;
(5) the metal is allowed to cool in the mold; (6) the solidified metal
referred to as raw
casting is removed by breaking away the mold; (7) and the casting is finished
and
cleaned through the use of grinders, welders, heat treatment, and machining.
[0004] In a sand casting operation, the mold is created using sand as a
base
material, mixed with a binder to retain the shape. The mold is created in two
halves -
cope and drag which are separated along the parting line. The sand is packed
around the pattern and retains the shape of the pattern after it is extracted
from the
mold. Draft angles of 3 degrees or more are machined into the pattern to
ensure the
pattern releases from the mold during extraction. In some sand casting
operations, a
flask is used to support the sand during the molding process through the
pouring
process. Cores are inserted into the mold and the cope is placed on the drag
to
close the mold.
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[0005] When casting a complex or hollow part, cores are used to define the
hollow interior, or complex sections that cannot otherwise be created with the
pattern. These cores are typically created by molding sand and binder in a box
shaped as the feature being created with the core. These core boxes are either
manually packed, or the core is manufactured using a core blower or shell
machines. The cores are removed from the box, and placed into the mold. The
cores are located in the mold using core prints to guide their placement. The
core
prints also prevent the core from shifting while the metal is poured.
Additionally,
chaplets may be used to support or restrain the movement of cores, and fuse
into
the base metal during solidification.
[0006] The mold typically contains the gating system, which provides a
path for
the molten metal, and controls the flow of metal into the cavity. This gating
consists
of a sprue, which controls metal flow velocity, and connects to the runners.
The
runners are channels for metal to flow through the gates into the cavity. The
gates
control flow rates into the cavity, and prevent turbulence of the liquid.
[0007] After the metal has been poured into the mold, the casting cools and
shrinks as it approaches a solid state. As the metal shrinks, additional
liquid metal
must continue to feed the areas that contract, or voids will be present in the
final
part. In areas of high contraction, risers are placed in the mold to provide a
secondary reservoir to be filled during pouring. These risers are the last
areas to
solidify, and thereby allow the contents to remain in the liquid state longer
than the
cavity of the part being cast. As the contents of the cavity cool, the liquid
metal in
the risers feeds the areas of contraction, ensuring a solid final casting is
produced.
Risers that are open on the top of the cope mold can also act as vents for
gases to
escape during pouring and cooling.
[0008] In the various casting techniques, different sand binders are used
to allow
the sand to retain the pattern shape. These binders have a large affect on the
final
product, as they control the dimensional stability, surface finish, and
casting detail
achievable in each specific process. The two most typical sand casting methods
include (1) green sand, consisting of silica sand, organic binders and water;
and (2)
chemical or resin binder material consisting of silica sand and fast curing
chemical
binding adhesives such as phenolic urethane. Traditionally, side frames and
bolsters have been created using the green sand process, due to the lower cost
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associated with the molding materials. While this method has been effective at
producing these components for many years, there are disadvantages to this
process.
[0009] Friction wedge dampers produced via the green sand operation
described
above have several problems. First, the relatively large draft angles required
in the
patterns result in corresponding draft angles in the friction wedges which may
be
ground down to meet customer specifications. This is especially problematic on
the
column face of friction wedges. Second, obtaining flat and smooth surfaces on
critical portions of the friction wedges typically requires extra finishing
steps, such as
grinding of surfaces. This can result in inconsistent final product
dimensions,
increased finishing time, or scrapping of the component if outside specified
dimensions. Other problems with these casting operations will become apparent
upon reading the description below.
BRIEF SUMMARY
[0010] A first aspect of the application is to provide a method of
manufacturing a
friction wedge for a rail car. The method includes forming, in drag and cope
portions
of a mold, at least one cavity that defines at least some exterior features of
at least
one friction wedge. At least one core is inserted into the mold adjacent to
the cavity.
The core includes at least one surface configured to define a column face of
the
friction wedge. Rigging is formed in the drag and cope portion of the mold.
The
,rigging includes a down sprue, at least one ingate, and at least one runner
for
directing molten material to the cavity. Molten material is poured into the
mold to
form the friction wedge casting. The friction wedge casting is removed from
the mold
and the rigging is removed.
[0011] A second aspect of the application is to provide a friction wedge
for a rail
car with a column face that, prior to finishing operations, is substantially
flat with a
surface finish less than 500 micro-inches RMS and chamfered edges with a
radius of
about .30 inches.
[0012] A third aspect of the application is to provide a friction wedge
for a rail car
that includes a column face with substantially flat top and bottom regions and
a
concave middle region. The maximum distance between a plane within which the
top and bottom flat regions are disposed and an apex of the concave middle
region is
between .020 and .060 inches.
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[0013] A fourth aspect of the application is to provide a friction wedge
for a rail car
that includes a column face with a recessed portion.
[0014] A fifth aspect of the application is to provide a friction wedge
for a rail car
having an acicular gray iron microstructure that comprises Bainite,
Martensite,
Austenite, Carbide, and no more than about 5% Pearlite.
[0015] A sixth aspect of the application is to provide a friction wedge
for a rail car
having a hardness of between 420-520 BHN.
[0015a] A seventh aspect of the application is to provide a railcar truck
comprising
a: a bolster having an outboard end section, the outboard end section having
first
and second shoe pockets; a side frame including a bolster opening defined by a
pair
of side frame columns, a compression member, and a spring seat, the bolster
opening sized to receive the outboard end section of the bolster; a group of
springs,
the group of springs positioned between the outboard end section of the
bolster and
the spring seat, the group of springs resiliently coupling the bolster to the
side frame;
a first friction wedge and a second friction wedge, each friction wedge
comprising: a
column face, the column face having chamfered edges providing a smooth
transition
between the column face and adjacent sides of the friction wedge; a sloping
face; a
bottom side; and a wear indicator on a side of the friction wedge; a first
wear plate
and a second wear plate, each wear plate positioned between the respective
column
faces of the friction wedges and the respective side frame columns; and a
first wedge
insert and a second wedge insert, each wedge insert positioned between the
respective sloping faces of the friction wedges and the respective shoe
pockets;
wherein the column face as-cast, without further finishing, of each of the
friction
wedges is substantially flat and has a surface finish less than 500 micro-
inches RMS;
wherein each of the friction wedges has an acicular gray iron microstructure
that
comprises Bainite, Martensite, Austenite, Carbide, and no more than about 5%
Pearlite; and wherein each of the friction wedges has a hardness of between
420-
520 BHN.
[0015b] An eighth aspect of the application is to provide a friction wedge of
a rail
car comprising: a column face, the column face having chamfered edges
providing a
smooth transition between the column face and adjacent sides of the friction
wedge;
a sloping face; a bottom side; and a wear indicator on a side of the friction
wedge;
wherein the column face as-cast, without further finishing, has a surface
finish less
than 500 micro-inches RMS.
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[0015c] A ninth aspect of the application is to provide a friction wedge of a
rail car
comprising: a column face, the column face having chamfered edges providing a
smooth transition between the column face and adjacent sides of the friction
wedge;
a sloping face; a bottom side; and a wear indicator on a side of the friction
wedge;
wherein the column face as-cast, without further finishing, has a surface
finish less
than 500 micro-inches RMS; and wherein the friction wedge has an acicular gray
iron
microstructure that comprises Bainite, Martensite, Austenite, Carbide, and no
more
than about 5% Pearlite.
[0016] Other features and advantages will be, or will become, apparent
to one
with skill in the art upon examination of the following figures and detailed
description.
It is intended that all such additional features and advantages included
within this
description be within the scope of the claims, and be protected by the
following
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The accompanying drawings are included to provide a further
understanding of the claims, are incorporated in, and constitute a part of
this
specification. The detailed description and illustrated embodiments described
serve
to explain the principles defined by the claims.
[0018] Fig. 1 illustrates a side view of a side frame of a railway car
truck along
with a cut-away close up view of the bolster opening;
[0019] Fig. 2 illustrates a detailed view of a bolster opening of the
side frame of
Fig. 1 with a cut-away view of the outboard end section of a bolster inserted
therein;
[0020] Fig. 3 illustrates a first exemplary friction wedge embodiment;
[0021] Figs. 4A and 4B illustrate different views of exemplary rigging
that may be
provided in a mold to manufacture the friction wedge;
[0022] Fig. 5A illustrates details of a core that may be utilized in
cooperation with
the rigging and mold to form the first friction wedge embodiment;
[0023] Fig. 5B illustrates the interaction of the core with a completed
friction
wedge;
[0024] Figs. 6A and 6B illustrate a second exemplary friction wedge
embodiment
and a core for manufacturing the same; and
[0025] Figs. 7A and 7B illustrate a third exemplary friction wedge
embodiment that
defines a concave column face and a core for manufacturing the same.
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DETAILED DESCRIPTION OF THE DRAWINGS
[0026] Fig. 1 illustrates a side view of a side frame 100 of a railway
car truck. The
railway car may correspond to a freight car, such as those utilized in the
United
States for carrying cargo in excess of 220,000 lbs. Gross Rail Load. The side
frame
100 defines a bolster opening 110.
[0027] The bolster opening 110 is defined by a pair of side frame columns
112, a
compression member 114, and a spring seat 116. The bolster opening 110 is
sized
to receive an outboard end section 115 of a bolster, a cut-away of which is
illustrated. A group of springs 117 is positioned between the outboard end
section
115 of the bolster and the spring seat 116 and resiliently couple the bolster
to the
side frame 100.
[0028] Referring to Fig. 2, wear plates 202 are positioned between
respective
column faces (Fig. 3, 300) of friction wedges 206 and the side frame columns
112.
Wedge inserts 208 are positioned between respective sloping faces (Fig. 3,
302) of
the friction wedges 206 and shoe pockets 204 of the bolster. During operation,
the
column face 300 and the sloping face 302 of each friction wedge 206 bear
against a
corresponding wear plate 202 and wedge insert 208, respectively. The friction
wedges 206 slide against the wear plates 202 and wedge inserts 208, creating
friction and dissipating energy to function as dampers that prevent sustained
oscillation between the side frame 100 and the bolster.
[0029] Fig. 3 illustrates an exemplary friction wedge 206. The friction
wedge 206
includes a column face 300, a sloping face 302, and a bottom side 304. A wear
indicator 306 is defined on one side of the friction wedge 206. The wear
indicator
306 facilitates the determination of the amount of service life left in the
friction wedge
206.
[0030] Column face edges 308a-d are chamfered with a radius that provides
for a
smooth transition between the column face 300 and adjacent sides of the
friction
wedge 206. In one implementation, the column face 300 of the friction wage 206
is
substantially flat. The radius of the chamfered edges 308a-d may be about .30
inches. As described in more detail below, the respective edges 308a-d are
formed
with a core rather than after casting by subsequent finishing operations.
[0031] Figs. 4A and 4B illustrate different views of exemplary rigging
400 that
may be provided in a mold (not shown) to manufacture the friction wedges 206,
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described above. The rigging is typically formed with the patterns (not shown)
that
are used to form the cavities for the friction wedges 206. It is understood
that Figs.
4A and 4B illustrate exemplary rigging, cores 402, and finished wedges 206 as
they
would look after a shake-out process. The cope and drag are not shown for
clarity.
While the exemplary rigging 400 illustrates the manufacture of four friction
wedges
206, it is understood that the rigging 400 could be adapted to manufacture a
different
number of friction wedges 206. Furthermore, the rigging may be adjusted to
modify
the positions of the down sprue, runners and ingates as necessary. The shape
of
the down sprue, runners and ingates could also be modified.
[0032] Referring to Figs. 4A and 4B, the rigging 400 includes a down
sprue 404
that is connected to ingates 407. The ingates 407 are in turn connected to
runners
408. The runners 408 lead to cavities in the mold for forming the exterior
shape of
the friction wedges 206. In one implementation, the runners 408 are arranged
so
molten material fills the cavity from a side of the cavity that forms the
bottom side
304 of a friction wedge 206, which is a less critical dimension of the
friction wedge
206.
[0033] Cores 402 are inserted into the mold. The cores 402 form the
column face
300 of the respective friction wedges 206. Each core 402 may be utilized to
form the
face of two friction wedges 206. In alternative implementations the cores 402
could
be configured to form faces 300 for a different number of friction wedges 206.
For
example, a square core (i.e., a core with four sides) could be utilized to
form the
column faces of four friction wedges 206. It is understood that the number of
friction
wedges 206 that could be formed by a single core is limited only by the number
of
sides that the core has.
[0034] Figs. 5A and 5B illustrate details of the core 402. For clarity,
Fig. 5B shows
a completed wedge 206 positioned against a core 402 to show the interaction
between the core 402 and the finished wedge 206. The core 402 may be an
isocure
core, no bake core, or shell core. An interior section 404 of the core 402
defines the
column face 300 of a friction wedge 206. In one implementation, the interior
section
is a generally flat surface. Interior edges 406a-d define the chamfered column
face
edges 308a-d of the friction wedge 206. The edges 406a-d may have a radius of
about .30 inches. The core 402 also includes a region 406 that forms the wear
indicator 306 of the friction wedge 206.
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[0035] Flatness of the friction wedge 206 is important because the column
face
300 of the friction wedge 206 interacts with the wear plate 202, which is a
hot rolled
steel plate and, therefore, very flat. Forming the column face 300 in the mold
(i.e.,
with green sand) would introduce artifacts as a result of draft angles and
parting
lines. Without additional finishing, these artifacts would prevent the
friction wedge
206 from sitting correctly against the wear plate 202. In an non-illustrated
embodiment of the core 402, the interior section 404 and chamfered interior
edges
406a-d are eliminated in favor of a completely flat face which formed the
corresponding column face 300 of the wedge 206. In an additional non-
illustrated
embodiment of the core 402, the interior section 404 is included without the
chamfered interior edges 406a-d.
[0036] By contrast a core can be made much harder and more accurately than a
production green sand mold, creating a higher quality casting surface. The
improved
surface finish reduces the size of the as-cast asperities in the friction
wedge 206.
These asperities are removed as the friction wedge 206 slides against the wear
plate
202 at initial break-in. The reduction in the size of the asperities reduces
the time
required to break-in the friction wedge 206, and reduces the size and amount
of grit
in the assembly. Faster break-in leads to decreased wear and, therefore,
longer part
life. Less and smaller sizes of grit can eliminate the effects of 3 body wear
mechanism's and therefore reduce the wear rate of the system. In some
implementations, use of a core facilitates the manufacture of a friction wedge
206
that has a column face 300 with a surface finish less than about 500 micro-
inches
RMS.
[0037] Moreover, defining interior chamfered edges eliminates the need
for
grinding of on the column face 300 subsequent to casting, which would
otherwise
create large gouges and scratches, which affect the break-in of the friction
wedge
206. Grinding produces other inconsistencies in the casting as well.
[0038] Figs. 6A and 6B illustrate a second exemplary friction wedge
embodiment
602 and a core 600 for manufacturing the same. The core 600 defines a groove
602
around the perimeter of a flat middle section 604. The friction wedge 602
includes a
column face that defines a recessed portion 608 and a raised portion 606. The
recessed portion 608 is formed by the flat middle section 604 of the core 600.
The
raised portion 606 is formed by the groove 602. The recess 608 formed in the
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column face facilities the insertion of a friction control material (not
shown), such as a
brake shoe material, a clutch material, or other dry friction material. This
recess 608
provides a way of capturing and containing an inserted material without the
necessity
of adhesives, or other bonding techniques.
[0039] As with the core described above, the groove 602 forms a radius on the
raised portion 606. The radius forms a corresponding radius around the edge of
the
column face, thus eliminating or substantially reducing the need for finishing
(e.g.,
grinding) of the column face.
[0040] Figs. 7A and 7B illustrate a third exemplary friction wedge
embodiment
702 that defines a concave column face and a core 700 for manufacturing the
same.
An interior of the core 700 defines top and bottom regions 704a and b that are
generally flat and lie in substantially the same plane. A middle region 706 is
defined
between the top and bottom regions 704ab and is proud/forward of the top and
bottom regions 704a and b. The middle region 706 may be curved. The top,
bottom, and middle regions 704a and b and 706 cooperate to form a friction
wedge
column face with a generally concave middle region 710, and flat top and
bottom
regions 708a and b, as illustrated in Fig. 78.
[0041] Applicant has observed that during servicing, center regions of
column
faces of known wedges tend to wear less than the top and bottom regions.
Similarly,
the wear plates 202 exhibit a large amount of wear in the center, and very
little wear
at the top and bottom. The concave column face of the third friction wedge
embodiment 702 results in more even wear between the friction wedge 702 and
the
wear plate 202. This, in turn, increases the useful service life of the
friction wedge
702. Applicant has observed that a recess amount, D, of between .020 and .060
inches produces an optimal wear evenness over the service life of the friction
wedge
702.
[0042] It is understood that the recess amount, D, may be different and
may be
adjusted based on the amount of wear that occurs for a given combination of
friction
wedge and wear plate 202. In some implementations, a friction control material
may
be arranged within the recess to control friction levels, and further control
wear
evenness between the friction wedge and the wear plate 202.
[0043] In some implementations, to improve the longevity of the friction
wedges, a
heat treatment may be applied subsequent to casting. Applicant has observed
that
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the useful service life of the friction wedges may be maximized if the
friction wedges
are hardened to a hardness between 420-520 BHN, which is generally not
achievable with known friction wedge manufacturing methods, such as the method
disclosed in U.S. 4,166,756. To achieve this hardness, the friction wedges are
heated to a temperature above 1200 F after casting. The friction wedges are
held
at this temperature for a period of time and then rapidly cooled by submerging
in a
quench media, such as oil, water, or molten salt, which may be at a
temperature of
between 1000 and 500 . The final hardness and microstructure of a friction
wedge is
determined based on a number of factors that include the temperature of the
friction
wedge at the time of quenching, the time held at that temperature, the
temperature
of the quench media, and the alloy of the friction wedge.
[0044] Generally, after quenching, the friction wedges become brittle,
contain
residual stresses, and are unfit for service. Tempering is used to further
refine the
microstructure, restore ductility, increase toughness, and relieve the
residual
stresses. Tempering is typically carried out by heating the friction wedges to
a
prescribed temperature, then slowly cooling them at a prescribed rate.
[0045] In one implementation, the friction wedges comprise an iron alloy
that
includes Copper and/or Nickel. In this case, after quenching and tempering,
the
resulting alloy exhibits an acicular gray iron microstructure that comprises
predominantly Bainite and Martensite, with some retained Austenite, traces of
Carbide, and no more than 5% Pearlite.
[0046] While various embodiments of the embodiments have been described, it
will be apparent to those of ordinary skill in the art that many more
embodiments and
implementations are possible that are within the scope of the claims. The
various
dimensions described above are merely exemplary and may be changed as
necessary. Accordingly, it will be apparent to those of ordinary skill in the
art that
many more embodiments and implementations are possible that are within the
scope
of the claims. Therefore, the embodiments described are only provided to aid
in
understanding the claims and do not limit the scope of the claims.
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