Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
2~ 611~6
WO 94123863 PCTIUS94/03936
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A~8R~RLY OF FOIJNDRY 8HAPlSS
TECHNICAL FIELD OF THE lNV~NllON
This invention relates to an assembly of foundry shapes
and a process for making such assemblies by contacting the
foundry shapes with a two-sided substrate having a pressure
sensitive adhesive on both sides of the substrate. The
foundry assemblies are used for casting molten metal. The
temperature of such molten metal for non ferrous metals is
typically from 600C to 1000C while the temperature of
ferrous metals is from 1200C to 1600C. One of the
advantages of this process is that excess adhesive is not
squeezed from between the foundry ~h~p~c when they are
contacted with each other. Excess adhesive results in
casting defects such as porosity and burn-on.
15~ ROUND OF THE lNv~llON
Patterns, molds, cores, and other fou~.d~y shapes are
used in casting metals. Patterns are foundry shapes which
are lightweight, have generally smooth surface areas, and
are the same shape as the casting to be made. Typically,
patterns are made of polystyrene.
The pattern is coated, placed in a container, and
surrounded by unbound sand. Then molten metal is gated into
the pattern. The space occupied by the pattern is filled
with molten metal and the pattern evaporates. The quality
of the casting depends upon how well the coating on the
pattern maintains it shape and allows gases and liquids,
produced by the decomposed pattern, to pass through the
coating to the surrounding unbonded sand when the coated
pattern comes into contact with the molten metal.
Patterns are typically held together in an assembly
with hot-melt glue which is spread around the seams of the
patterns to be joined together. A problem occurs if excess
hot-melt glue is used. The excess glue (as well as the foam
pattern) will generate gases when it comes into contact with
the metal. This results in porosity in the casting.
Additionally, the excess glue will result in an uneven
surface on the pattern which is difficult to coat. Sand can
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enter the uneven surface on the pattern where the excess
glue is present. When this happens and the glue burns, the
molten metal covers the sand resulting in burn-on which is
visible after the metal cools. These defects are frequently
found in foundries and must be removed before the casting is
used. Severe burn-on can cause the casting to be totally
scrapped, particularly in the lost-foam process.
On the other hand, molds and cores are heavier, have
rougher surface areas, and occupy space to keep metal from
entering. They are the inverse shape of the casting to be
made. Typically molds and cores are made from a foundry
aggregate and reactive binder which holds the aggregate
together as a foundry shape. After the molten metal to be
cast is poured into and/or around the mold or core, the mold
or core has to be removed from the casting.
Often it is necessary to use several molds and/or cores
in an assembly and pour the molten metal through and/or
around the assembly. The foundry molds and/or cores must be
held together during the pouring of the molten metal.
Typically the foundry shapes are held together in an
assembly with a foundry adhesive paste. Examples of some
highly effective adhesive pastes are disclosed in U.S.
Patents 4,692,479 and 4,724,892.
Although adhesive pastes are quite effective in holding
foundry shapes together in an assembly, they have drawbacks
similar to the drawbacks associated with the hot-melt glues
used in holding patterns together. It is difficult to meter
out the correct amount of adhesive paste to hold the
assembly of foundry shapes together. Too little paste will
not be effective to hold the molds and cores together in an
assembly and molten metal will penetrate into area which is
not to be part of the casting.
Too much paste will cause seepage from between the
foundry shapes. The excess paste will generate gases when
it comes into contact with the molten metal which results in
porous castings. Additionally, the excess paste will result
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in casting burn-on if sand enters the area where the
adhesive burns.
Finally, these adhesive pastes are used only for making
assemblies of cores and/or molds made from a foundry
aggregate and reactive binder. They are not useful for
making assemblies from patterns, particularly foam patterns.
SUMMARY OF THE lNv~:N~l~loN
This invention relates to an assembly of foundry shapes
and a process for making such assemblies. The process for
making such assemblies comprises:
(a) contacting a first foundry shape and one side of
a two-sided substrate, said substrate having a
pressure sensitive adhesive on both sides;
(b) contacting a second foundry shape and the other
side of said substrate.
The foundry assemblies are used for casting molten
metal. The temperature of such molten metal for non ferrous
metals is typically form 600C to 1000C while the
temperature of ferrous metals is from 1200C to 1600C.
In contrast to adhesives which are sensitive to
temperature and difficult to apply uniformly in proper
amounts, pressure sensitive adhesives are manufactured
according to uniform specifications and can be cut to fit
the shape of the foundry shape. Consequently, the subject
2S process can be used without causing excess adhesive paste to
be squeezed from the point of contact between the foundry
shapes. This is significant because excess adhesive paste
results in casting defects such as porosity and burn-on.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a representative polystyrene pattern 1.
Fig. 2 is coated polystyrene pattern 2 surrounded by
unbonded sand 3 with fill container 4.
Fig. 3 shows a cup of molten metal 5 poured into and
around the coated polystyrene pattern surrounded by the
unbonded sand.
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Fig. 5 shows an assembly of polystyrene patterns 6 with
excess glue 7.
Fig. 6 shows a casting 8 made from the polystyrene
pattern showing burn-on 9 with amplification 10 and
porosity 11 with amplification 12.
BEST MODE AND OTHER MODES OF THE lNV~'N'l'lON
An assembly of foundry shapes is prepared by contacting
a foundry shape and one side of a two-sided substrate having
a pressure sensitive adhesive on both sides, and then
contacting another fo~,.d.y shape and the other side of the
substrate. A pressure sensitive adhesive is an adhesive
which will adhere to a surface and yet can be stripped from
the surface without transferring significant quantities of
adhesive to the surface. "Contacting" means to cause the
surfaces of the foundry shapes to effectively touch the
pressure sensitive adhesive in such a manner so that the
resulting assembly can be effectively used for the making of
metal castings.
For purpose~ of this disclosure, a foundry shape shall
mean a pattern, mold, core or any other shape used in the
casting of foundry parts from molten metal. Patterns are
usually prepared from lightweight materials such as
polystyrene. Molds and cores are typically made by binding
a foundry aggregate together with a chemically reactive
binder.
The patterns used in making mold assembly are usually
coated with a refractory composition to provide
reinforcement and a smoother surface finish for the casting.
Refractory coatings for patterns are used in the foundry
industry well known. Typically such coatings consist of a
refractory material such as silica, aluminum silicate, mica,
talc, zircon, or olivine; and a liquid carrier such as water
or alcohol. The coating usually contains surfactants to
promote wetting of the surface of the foundry shape,
suspending agents to eliminate settlement of refractory
flour particles in the liquid, viscosity modifiers, biocides
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to limit the growth of algae, fungi, bacteria, enzymes,
binders which may be organic or inorganic, metal oxides,
alkali silicates, etc.
Molds and cores are made by shaping a foundry mix made
with a foundry aggregate and chemically reactive inorganic
or organic foundry binder in amount such that the weight
ratio of binder to aggregate is from 100:10 to 100:1. There
are a wide range of aggregates and binders which can be used
and they are well known. Examples are shown in U.S. Patents
3,409,579; 3,676,392; 4,127,157; 4,226,626; 4,526,219; and
4,780,489, all of which are incorporated into this
disclosure by reference.
Generally any substrate having a pressure sensitive
adhesive on both sides of the substrate can be used,
depending upon the specific application. Examples of such
substrates are paper (preferably moisture resistant),
rubber, plastic, film, and other substrates capable of
holding the adhesive and holding up under the particular use
conditions.
The size of the substrate will depend upon the size and
weight of the assemblies to be bonded together, their
surface roughness or smoothness, and their relative degree
of flexibility. The thickness of the substrate will also be
dependent upon the conditions for use. For example, the
thickness of polyester films typically range from 0.1 to 0.8
millimeter, and the thickness of foam substrates may have a
thickness of 0.5 to 1.0 millimeter. Typically, the
thickness of the substrate will range from 0.05 millimeter
to 3.0 millimeters, preferably from 0.1 millimeter to 1.5
millimeters, most preferably from 0.1 millimeter to 1.0
millimeter.
The choice of the pressure sensitive adhesive will
depend upon the surface of the foundry shapes to be held
together, environmental conditions in the foundry,
performance requirements, i.e. the tensile strength needed
and shear forces to which the foundry assembly will be
subjected. Typically used as the pressure sensitive
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adhesive are polymers based on acrylates, polyesters, vinyl
chlorides, acrylonitriles, and polyurethane resins.
Preferably used are rubber adhesives and most preferred are
acrylic adhesives.
Major manufactures of substrates with two-sided
pressure sensitive adhesives are 3M and ADCHEM. Usually
these products are labeled as "adhesive transfer tapes".
Such products include Scotch~ brand Adhesive Transfer Tapes,
ATG Adhesive Systems, Double Coated Tapes, Scotch-Mount
Double Coated ~oam Tapes, and Scotch Very High Bond Tapes
sold by 3M. Foam tapes are preferably used for holding
molds and cores together in an assembly while the very high
bond tapes are preferably used for holding patterns
together.
EXAMPLES 1-2
The examples which follow will illustrate specific
embodiments of the invention. These examples along with the
written description will enable one skilled in the art to
practice the invention. It is contemplated that many other
embodiments of the invention will be operable besides these
specifically disclosed.
Example 1
Example 1 describes how to prepare an assembly of
patterns and how it performs when used to make a metal
casting. Four pieces of two-sided pressure sensitive
adhesive tape are cut and used to connect five polystyrene
patterns together by placing the tape between the block
patterns. Each pattern is 1 1/8" x 1 1/8" x 1 1/2". The
pressure sensitive adhesive tape is cut so that it fit the
shape of the polystyrene patterns to be glued together.
The pressure sensitive adhesive is an acrylic
pressure sensitive adhesive sold by ADCHEM under the
tradename ADCHEM 256. The substrate of the pressure
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sensitive adhesive is a 0.5 millimeter polyester film. No
creases or excess glue are observed.
The assembly, comprised of the five polystyrene
patterns, which are joined together by the pressure
sensitive adhesive, are coated with CERAMCOTE~ refractory
coating and allowed to air dry. The assembly is then placed
in a container and surrounded by compacted sand. Molten
grey iron is then poured into the assembly. The pattern
evaporates and the molten metal is allowed to cool.
Another assembly is prepared as described, except hot-
melt glue is used to hold the five patterns together in an
assembly.
Example 2
This example illustrates the use of two-sided pressure
sensitive adhesive tape to join two 7" sand cores into a
core assembly. The cores are prepared by mixing Manley sand
with 1.25 percent by weight of PEPSET~ 1600/2600 no-bake
foundry binder sold by Ashland Chemical, Inc. at a SS/45
weight ratio, and ramming the mixture into two core boxes
until the foundry mix hardens. The PEP SET 1600 binder
(Part I) contained 1.5 percent by weight of PEP SET 3500
catalyst.
The resulting cores are removed from the core boxes and
then connected with an acrylic pressure sensitive adhesive
tape having a 0.7 millimeter foam substrate sold by Coating
Science, Inc. of Bloomfield, Connecticut. The adhesive
tape is carefully trimmed to match the shape of the cores.
The procedure described was then repeated using a
commercially available urethane forming adhesive paste known
as ISOPASTE~ 2000 PLUS adhesive paste sold by Ashland
Chemical, Inc. Seepage was observed when the cores were
connected with the adhesive film.
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