Note: Descriptions are shown in the official language in which they were submitted.
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RISER SLEEVE WITH AIR GAP
Technical Field
[0001] The disclosed embodiments of the present invention relate to a riser
sleeve for
use in the casting of molten metal, and, in particular, to a riser sleeve that
is shaped
around an exterior surface thereof to provide closed cavities when the riser
sleeve is
inserted into a riser cavity of a foundry mold. In an even more particular
embodiment,
the cavities are positioned in the sleeve to run as generally vertical
depressions along
the sleeve exterior when the riser sleeve is operationally positioned in the
foundry mold.
Background of the Art
[0002] As described in US Patent 6,640,874, among other prior art references,
riser
sleeves and their use are well known in the prior art. A riser sleeve operates
in a
foundry mold as a conduit and as a reservoir. When molten metal is poured into
a
preformed cavity shaped in the nature of the product being formed, a portion
of the
poured metal flows into and accumulates in the riser. As the metal in the
cavity
solidifies, shrinkage of the solidified metal in the mold would result in
dimensional
changes and possibly internal cavities, in the absence of a riser.
[0003] The loss of heat from the metal in the riser cavity primarily occurs at
the
interface of the metal with the mold. By strategically placing one or more
riser sleeves
in the foundry mold, with each riser sleeve in gravity-feed liquid
communication with the
cavity, and by maintaining the molten metal in the sleeve in its molten state,
at least
preferentially to the metal in the casting, molten metal is available after
the pour to flow
from the sleeve into the mold, offsetting the shrinkage. If this objective is
not achieved,
the metal in the riser sleeve simply solidifies and becomes another
appurtenance to the
casting that needs to be removed in finishing the product.
[0004] The riser sleeves themselves are not a part of the finished casting.
Once the
casting has properly cooled, the risers are removed as a part of the foundry
mold.
[0005] It has been an ongoing effort in the casting industry to provide riser
sleeves
that achieve their objective in an effective manner. The continuing nature of
this effort
speaks loudly about the need for additional improvement.
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[0006] Thus, there exists a need in the prior art for an improved riser
sleeve.
Summary of the Invention
[0007] This and other unmet advantages are provided by a riser sleeve for use
in a
foundry molding operation. The sleeve has a body with an outside wall that
extends
from a bottom to a top of the body. The riser sleeve is characterized by a
plurality of
cavities that are formed on the side wall, extending from the top in an axial
direction of
the body.
[0008] In some instances, the body is cylindrical. In other instances, the
body is
frustoconical, preferably with a diameter that decreases uniformly from the
bottom to the
top.
[0009] In some instances, each of the plurality of cavities is preferably
substantially
semi-cylindrical, each cavity having an axis that is preferably aligned along
a virtual
circumferential area of the outside side wall that does not comprise the
cavities. In
some of these instances, each cavity is characterized by a radius, such that
the axes of
adjacent cavities are spaced apart by a distance of at least four radii around
the
circumference of the riser sleeve. In some of these, each cavity preferably
subtends an
angle in the range of from about 120 to about 180 , as measured from the axis
of the
cavity.
[0010] In some instances, each cavity extends along the outside wall over a
majority
of a distance from the top towards the bottom, but each cavity terminates
above the
bottom.
[0011] In some instances, the plurality of cavities are substantially
uniformly spaced
around a circumference of the body.
[0012] In some instances, the body is substantially hollow, with an interior
wall or
surface that is cylindrical or that tapers from bottom to top in a manner that
corresponds
to the side wall.
Brief Description of the Drawings
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[0013] A better understanding of the disclosed embodiments will be obtained
from a
reading of the following detailed description and the accompanying drawings
wherein
identical reference characters refer to identical parts and in which:
FIG. 1 is a perspective view of a formed riser sleeve as known in the prior
art
before imparting the air gaps of the claimed invention;
FIG. 2 is a perspective view of the formed riser sleeve of Fig. 1, after the
air gaps
have been formed thereon; and
FIG. 3 is a perspective view of a riser sleeve of the claimed invention, shown
in
partial sectional view on a mold pattern.
Detailed Description
[0014] In general, riser sleeves are one of two types. Blind riser sleeves
comprise a
hollow dome-shaped riser sleeve, which is open at the bottom. Open-top riser
sleeves
are generally annular shaped, that is, open at both top and bottom. Blind
riser sleeves
are more expensive to manufacture. Their use is typically reserved to special
applications. Open-top riser sleeves, on the other hand, allow the casting
operator to
see the progress of the cast by visualizing the level of the molten metal in
the riser
sleeve. For purposes of this patent specification, the term "riser sleeve" is
used
generically to apply to both types, unless there is specific reference to one
of the types.
[0015] The riser sleeves may be inserted into the mold cavity after the mold
is formed.
This is generally referred to as an insertable sleeve. The riser sleeve may
also be
placed on the pattern and the mold formed around the sleeve to create the
riser cavity.
This is generally referred to as a "ram-up" sleeve). Generally in the prior
art, the wall of
the sleeve will have a uniform thickness and fit tightly into the mold with
negligible gap
between the sleeve and the mold.
[0016] Again, speaking still in a general manner, riser sleeves are
manufactured from
heat insulating materials, with the intent of slowing the solidification of
the molten metal
contained within the riser sleeve before it passes to the cavity in the
foundry mold.
Alternatively or additionally, the riser sleeves may be made from exothermic
materials
intended to generate heat to maintain fluidity of the molten metal. Typical
riser sleeves
are manufactured from refractory materials, including man-made fibers. They
may
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include fuels such as aluminum or silicon which are used to produce their
respective
heat insulating oxides during an exothermic reaction within the riser sleeve.
Properties
sought to be optimized in riser design include low density and high porosity,
as these
facilitate the heat insulating properties.
[0017] Feeding aids are used to slow and control the solidification of the
riser. These
may be insulating or exothermic sleeves or "hot topping". A sleeve consists of
material
that lines at least part of the riser cavity, to slow the heat loss from the
riser by providing
insulation or additional heat input from an exothermic material or both. Hot
toppings are
insulating or exothermic material used to cover the top of the riser after
pouring where
the riser is open through the top of the mold.
[0018] Sleeves can be manufactured from a variety of different materials
including
refractory fibers, sand, hollow refractory spheres, as well as other
refractory materials.
Refractory fiber sleeves are typically formed by depositing the fiber and
other
ingredients onto a wire mesh form that creates the internal dimensions of the
sleeve.
The fiber and other ingredients are in a water-based slurry and are deposited
on the
form by drawing a vacuum on the interior of the form. This creates a sleeve
with a
somewhat rough external surface. Sleeves made from sand or from hollow spheres
plus other ingredients can be formed by blowing a mixture of the dry
ingredients and a
liquid foundry binder into a mold/corebox and curing the binder in the mold to
create a
solid sleeve with both internal and external shapes formed by the mold. The
walls of a
riser sleeve made from sand or hollow spheres will tend to be more uniform
than those
made from fibrous materials and this may make the sand/hollow sphere riser
sleeves
more amenable to the implementation of the inventive concept.
[0019] The insulating or exothermic properties of a riser sleeve is
predominantly
determined by the material used to create the sleeve. For instance, a fiber
refractory
sleeve will typically have a lower density than the mold material and provide
insulation
because of lower heat capacity and thermal conductivity. A sand exothermic
sleeve
may contain a relatively high percentage of exothermic material, typically
thermite of a
mixture of metallic aluminum powder and iron oxide. When the riser is filled
with molten
metal the thermite ignites and provides a secondary heat source for the riser.
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[0020] Turning attention now to FIG. 1, a perspective view of a riser sleeve
blank 10 is
shown. This sleeve blank 10 is shown as being slightly frusto-conate, with a
diameter
that decreases uniformly and monotonically from a bottom or base to a top 12.
Both the
top 12 and the base are depicted as being normal to a central axis of the
blank 10.
Depending upon the application, it may be desirable in some applications to
round off
the top surface into more of a bullet point shape, especially when the riser
sleeve will be
of the blind type that will be inserted in a "ram up" manner. Although riser
sleeve blank
is of the blind-type, it has the flattened top 12.
[0021] It should be clear from the depicted embodiment that the sleeve blank
10 could
easily be cylindrical, with a consistent diameter from top to base. The sleeve
blank 10
shows a smooth and consistent texture to the outside walls 14 and can be
produced
from a variety of different materials.
[0022] A perspective view of an embodiment 100 of a riser sleeve having the
inventive
concept is provided in FIG. 2. In the specific embodiment 100, which is also
depicted
as being of the blind-type, there are ten depressions or cavities 102 formed
on the
outside wall 14. This plurality of cavities 102 is depicted as arranged in a
substantially
uniform spacing around the circumference of the outside wall 14, although the
uniform
spacing is not considered critical to the efficacy of the riser sleeve being
formed. While
the body of the embodiment 100 is depicted as cylindrical, it will be known to
those of
skill that some casting situations will require other shapes, such as an oval
or flat-faced
shape, but that these shapes can also be formed with a plurality of cavities
in the same
manner as is depicted with the cylindrical embodiment.
[0023] The depressions or cavities 102 on the embodiment 100 are depicted as
being
substantially semi-cylindrical. An axis of each semi-cylindrical cavity 102 is
generally
aligned along the outside wall 14, with the effect being that the respective
axes reflect
the slightly conate or generally cylindrical nature of the overall riser
sleeve 100. A top
end of each cavity 102 is open and provides a "scalloped" circumference to the
top 12.
The cavities 102 are depicted as extending a substantial portion of the height
of the
riser sleeve 100 from the top of the sleeve in an axial direction of the
sleeve, but each
cavity clearly terminates above the base. This results in a cylindrical ring
around the
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base of the riser sleeve, with the intent of forming a tight seal with the
mold, preventing
liquid metal from flowing into the cavities during the pour.
[0024] With regard to the size and number of the cavities 102, it may be
expected
that, in the case of semi-cylindrical cavities having a radius R, the axes of
adjacent
cavities will be spaced apart by a distance of at least 4R around the
circumference of
the riser sleeve 100. Worded somewhat differently, at least one-half of the
original
surface of the outside walls 14 will be preserved for contact with the mold,
although it
may prove to be desirable to have about 40% of the side wall removed in the
creation of
the cavities.
[0025] As depicted, the cavities 102 are semi-cylindrical, that is, the axis
of the cavity
is effectively located along the surface or outside wall 14, and an angle of
approximately
180 is subtended between adjacent edges of a given cavity. In general, it may
be more
preferred to include less than 180 , that is, to position the axis outside of
surface 14,
than to have more than 180 of the cylinder subtended, which would result when
the
axis would be positioned inside of surface 14. This would prevent forming a
thin re-
entrant surface along the edges of the cavity that would be subject to
breakage. In any
case, the subtended portion of the cylinder would be at least 120 and in
almost all
cases will be less than180 .
[0026] By imposing these cavities 102, a corresponding number of closed air
gaps are
formed between the sleeve and the mold when the sleeve is inserted into the
mold.
These cavities 102 will trap air in them. The air-filled cavities 102 would
have very low
heat capacity and thermal conductivity compared to both the mold material and
the
sleeve. They will further reduce the contact area between the mold and the
sleeve,
reducing conductive heat loss. The cavities 102 also provide additional
insulation. This
could result in better performance by the sleeve and would also result in
lower sleeve
weight and material cost, as the primary thickness of the riser sleeve blank
would not be
increased in order to impose the cavities.
[0027] While not fully tested, it is expected that the sleeve 100 can improve
feeding
efficiency and allow the use of smaller risers and sleeves for improved
casting yield.
[0028] The use of the riser sleeve 100 is shown in a perspective schematic
manner in
FIG 3, in which the riser sleeve is shown mounted on a mold pattern 40, and,
more
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particularly, on a mounting plug 42 of the mold pattern. For "ram-up"
applications where
the riser sleeve is placed directly on the pattern and molding sand is
compacted around
the sleeve to form the sleeved riser, a paper, cardboard, plastic film, or
similar material
covering can be placed over the sleeve, with the paper or similar material
forming the
outside surface of the air filled cavity and preventing infiltration by the
molding sand as
the mold is rammed into position.
[0029] As clearly shown in Fig 3, the riser sleeve 100 will be significantly
hollow, either
due to the process by which it is initially formed or from the removal of
material. The
interior surface 104 will have preferably have a taper from bottom to top 12
that will
correspond to that of outer surface 14, except for the cavities, which are
found only on
the outer surface.
[0030] The depicted riser sleeve having the inventive features is a so-called
"blind"
riser sleeve as described above. However, it is well within the skill of one
of ordinary
skill in the art to apply the teachings of the present specification to
provide the same
inventive features on an open-top riser sleeve.
[0031] Having shown and described a preferred embodiment of the invention,
those
skilled in the art will realize that many variations and modifications may be
made to
affect the described invention and still be within the scope of the claimed
invention.
Thus, many of the elements indicated above may be altered or replaced by
different
elements which will provide the same result and fall within the spirit of the
claimed
invention.
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