BACKGROUND OF THE INVENTION A casting mold assembly consists of a pouring cup, a gating system (including downsprues, choke, runners, and gates), risers, sleeves, molds, cores, and other components. To produce a metal casting, metal is poured into the pouring cup of the casting mold assembly and passes through the gating system to the mold cavity and/or core assembly where it cools and solidifies. The metal part is then removed by separating it from the core and/or mold assembly.

During casting, most metals and alloys undergo a volume reduction or shrinkage during cooling and particularly during solidification. When producing castings, this volume reduction can lead to"shrinkage"holes, cavities, or dimensional inaccuracies in the casting. Because of this, risers (also known as feeders) are often incorporated into the casting mold to provide a reservoir of liquid metal to"feed"the casting as it solidifies and to offset the shrinkage.

Sleeves are sometimes used to surround portions of the riser in order to keep the molten metal in the riser hot and maintain it in the liquid state while the casting cools and solidifies. Sleeves are made of exothermic and/or insulating materials which retain the heat in the riser and thus retard its solidification. Thus the metal from the riser is allowed to remain in a liquid state for a longer period of time, thereby providing metal to the casting as it cools and solidifies. The temperature of the molten metal and the amount of time that the metal in the riser remains molten is a function of the sleeve composition and the thickness of the sleeve wall, among other factors.

Sleeves are made of a single layer with uniform properties. Sleeves are generally made from a mixture of materials such as aluminum metal, oxidizing agents, fibers, fillers, refractory materials such as sand, alumina and aluminosilicate, and aluminosilicate in the form of hollow aluminosilicate spheres.

In order to serve their function, sleeves typically have exothermic and/or insulating properties. The exothermic and insulating thermal properties of the sleeve are different in kind and/or degree than the thermal properties of the casting mold assembly into which they are incorporated. Predominately exothermic sleeves operate by liberating heat which satisfies some or all of the specific heat requirements of the riser and limits the temperature loss of the molten metal in the riser, thereby keeping the metal hotter and in liquid phase longer. Insulating sleeves, on the other hand, do not add heat to the riser, but help to insulate it from the surrounding mold assembly and reduce heat losses. A riser sleeve may have excellent insulating characteristics, but not contain any exothermic material. Alternately it may be highly exothermic, but have poorer insulating properties.

Traditionally, there were three basic processes used to produce sleeves: "ramming","vacuuming", and"blowing or shooting"as described in PCT publication WO 94/23865, which is hereby incorporated by reference into this disclosure. More recently it was shown that sleeves with improved dimensional accuracy can be produced by chemically curing the sleeves by the no-bake (liquid curing catalyst) or cold-box process (vaporous curing catalyst). See PCT publication WO 97/35677 which is hereby incorporated by reference into this disclosure.

DESCRIPTION OF THE FIGURES Figure 1 shows a cross-sectional diagram of a multiple layered sleeve 1 with an outer exothermic layer 2 and an inner insulating layer 3.

Figure 2 shows a cross-sectional diagram of a multiple sleeve 4 with an inner exothermic layer 5 and an outer insulating layer 6.

Figure 3 a shows a cross-sectional diagram of a multiple layered sleeve 7 with three layers 8 of material with different compositions, physical properties, and/or thermal properties.

Figure 4 is a cross-sectional diagram of a multiple layered sleeve 9 having top 10 of exothermic and a bottom portion of insulating layer 11.

Figure 5 is a cross-sectional diagram of a multiple sleeve 12 having an outer insulating layer 13 and an exothermic insert 14.

Figure 6 shows a cross-sectional view of a test casting 15, riser 16, and the safety margin 17.

SUMMARY OF THE INVENTION This invention relates to multiple layered sleeves, preferably riser sleeves, having at least two distinct layers which are in contact with each other. It also relates to preparation and use of such multilayered sleeves in casting ferrous and non ferrous metals, e. g. iron, ductile iron, steel, aluminum, grey iron, and brass. The cold-box process is particularly useful for preparing multiple layered sleeves because dimensionally accurate sleeves can be molded in successive sleeves layers with custom sized tooling.

The object of using multiple layered sleeves is to optimize the performance of the riser. Multiple layered sleeves have improved thermal properties. Thus the heat of the riser is more effectively retained than when sleeves with one uniform layer are used. As a result, the riser is more effective in feeding molten metal to the casting, and it is possible to use smaller risers which provide proportionally higher casting yields.

Another advantage with using multiple layered sleeves is that less exothermic material can be used without sacrificing the effectiveness of the sleeve. In general an exothermic sleeve mix is more expensive than an insulating sleeve mix, but it provides better and more efficient riser feeding than an insulating sleeve. By using a multiple layered sleeve and replacing some of the more expensive exothermic mix with an insulating mix, the total cost of the sleeve can be reduced.

In situations where small risers cannot be used, for example where the metal casting section being fed is thick, multiple layered sleeves also offer advantages. It is known that as

casting sections increase in size (i. e. as the thickness increases), it takes the metal more time to solidify. Consequently, the intensity of the exothermic reaction is completed long before solidification occurs, and the insulating characteristics of the sleeve must take over.

Therefore, it is important to maximize the amount of insulating material available to keep the heat of the riser from escaping after the exothermic reaction is depleted. Multiple layered sleeves enable the sleeve designer greater flexibiltiy in designing sleeves having the most appropriate ratio of exothermic and insulating properties in a sleeve for the most efficient heat profile in connection with risers having larger diameters.

DEFINITIONS The following definitions will be used for terms in the disclosure and claims: Casting mold assembly-assembly of casting mold components such as pouring cup, downsprue, gating system, molds, cores, risers, sleeves, etc. which are used to make a metal casting by pouring molten metal into the casting mold assembly where it flows to the casting cavity and cools to form a metal part.

Downsprue-main feed channel of the casting assembly through which the molten metal is poured.

Exothermic sleeve layer-a sleeve layer which has exothermic (i. e. produces net heat) properties compared to the mold/core assembly into which it is inserted. The exothermic properties of the sleeve are typically generated by an oxidizable material (typically aluminum metal) and an oxygen source which can react to generate heat.

Gating system-system through which metal is transported from the pouring cup to the mold and/or core assembly. Components of the gating system include the downsprue, runners, choke, gates, etc.

Insulating sleeve layer-a sleeve layer having better insulating properties (i. e. lower thermal conductivity and/or heat capacity) than the mold/core assembly into which it is inserted. An insulating sleeve typically contains low density refractory materials such as mineral fibers and/or hollow microspheres.

Insulating/exothermic sleeve-a sleeve layer which has both exothermic and insulating properties.

Multiple sleeve-a sleeve having more than one discrete layer.

Riser-cavity connected to a mold or casting cavity of the casting assembly which, when filled with liquid metal, acts as a reservoir of excess molten metal to prevent cavities in the casting as it contracts on solidification. Risers may be open or blind. Risers are also known as feeders or heads.

Safety margin-distance from the top of the casting surface to the shrinkage cavity within the riser. A positive value indicates that all shrinkage was confine to the riser and the casting was sound. A negative value indicates that shrinkage extended into the casting. The safety margin can be measured in inches or as a percentage of the total height of the original riser. Generally, more positive values indicate better performance.

Sleeve-any formed shape having exothermic and/or insulating properties made from a sleeve composition which covers, in whole or part, the riser, or is used as part of the casting mold assembly. The sleeve may be either inserted into a sleeve cavity after the mold is made or rammed-up in place when the mold is being made. Sleeves can have a variety of shapes, e. g. cylinders, domes, cups, boards, neckdown, spherical, neckdown dome, or insertable sleeves.

BEST MODE AND OTHER MODES FOR PRACTICING THE INVENTION The sleeves must have at least two distinct layers which are in contact with each other. The geometry or type of the multiple layered sleeve is not critical. The sleeve may be a cylinder, dome, cup, board, core, neckdown, spherical, neckdown dome, or insertable.

The materials used to prepare the sleeve layers are any of the materials known in the art.

The layers can be distinct because of their composition, thermal or other properties, density, etc.

Since sleeves are not typically totally exothermic or insulating in their properties, the individual layers of the sleeve having multiple layers may not be totally exothermic or insulating, but in fact may be hybrid or mixed in their exothermic and insulating properties.

They can have better insulating properties than single-layer exothermic sleeves and exothermic properties superior to single-layer insulating sleeves.

For purposes of this invention, an exothermic layer of a multiple sleeve is defined as a layer that produces heat when exposed to the heat of molten metal during pouring. The exothermic layer (s) of the sleeve are formed from (a) an oxidizable material, (b) an oxygen source capable of generating an exothermic reaction at the temperature where the metal is poured, and (c) a refractory or filler material such as fibers, sand, alumina, aluminosilicate refractories, and/or hollow aluminosilicate microspheres. The oxidizable material typically is aluminum, although magnesium and similar metals and certain metal salts can also be used. When aluminum metal is used as the oxidizable metal for the exothermic sleeve, it is

typically used in the form of aluminum powder and/or aluminum granules. The amount of aluminum metal in the sleeve composition typically ranges from 5 weight percent to 50 weight percent based upon the weight of the sleeve composition. The oxidizing agent used for the exothermic sleeve includes iron oxide, manganese oxide, nitrates, potassium permanganate, etc. In addition, the sleeve composition may contain fillers and additives, such as cryolite (Na3AlF6), potassium aluminum tetrafluoride, potassium aluminum hexafluoride, sand, or wood flour.

For purposes of this invention, an insulating sleeve layer of a multiple sleeve is defined as a layer having better insulating properties, i. e. lower thermal conductivity and/or heat capacity, than the mold material. The insulating sleeve layer is constructed from any insulating material such as fibers, particulate refractory materials, and preferably hollow aluminosilicate microspheres.

The size of the exothermic sleeve layer and the insulating sleeve layer depends upon the application. Generally, it can be said that the ratio of the thickness of the exothermic sleeve layer to the insulating sleeve layer decreases as the size of the riser increases, and usually ranges from 4: 1 to 0.05: 1.0.

The layers of the sleeves are prepared according to well know techniques. When using fibers, the sleeves are typically prepared by"ramming","vacuuming", and"blowing" or"shooting"as described in PCT publication WO 94/23865. When using refractory materials and hollow aluminosilicate microspheres, it is useful to chemically cure the shaped sleeve mix as described in PCT publication WO 97/35677 which is hereby incorporated into this disclosure by reference.

Any no-bake or cold-box process can be used to chemically cure the sleeves.

Curing the sleeve by the no-bake process takes place by mixing a liquid curing catalyst with the sleeve mix and binder, shaping the sleeve mix containing the catalyst, and allowing the sleeve shape to cure, typically at ambient temperature without the addition of heat. The cold-box process is particularly useful for creating multiple layered sleeves because dimensionally accurate sleeve layers can be molded in succession with custom sized tooling.

With respect to the cold-box process, a sleeve mix and binder is shaped by blowing or ramming it into a sleeve pattern box, and curing it by contacting it with vaporous or gaseous curing catalyst. Such catalysts include tertiary amines, sulfur dioxide and an oxidizing agent, carbon dioxide (see U. S. Patent 4,985,489 which is hereby incorporated into this disclosure by reference), or methyl esters (used with alkaline phenolic resole resins as describe in U. S. Patent 4,750,716 which is hereby incorporated into this disclosure by reference). Carbon dioxide is also used with binders based on silicates (see U. S. Patent 4,391,642 which is hereby incorporated into this disclosure by reference). Those skilled in the art will know which gaseous curing agent is appropriate for the binder used.

Preferably used as the cold-box process is an ISOSET binder (based upon epoxy- acrylic binders cured with sulfur dioxide in the presence of an oxidizing agent as described in U. S. Patent 4,526,219, which is hereby incorporated by reference), or an ISOCUREX binder (based on phenolic urethane binder cured by passing a tertiary amine gas, such a triethylamine, in the manner as described in U. S. Patent 3,409,579, which is hereby incorporated by reference).

Some of the methods for layering the sleeves to produce sleeves with multiple layers include: 1. Multiple layer riser sleeves can be prepared with cold-box or no-bake equipment in such a way that successive sleeve layers are formed over previously made sleeve layers. Preferably the cold-box process is used. A sleeve layer is made by the cold-box process using patterns which have the inverse shape of the desired sleeve. An initial sleeve layer can be made by blowing a mixture of the sleeve mix and binder into a sleeve pattern shape and curing the resin. Then this cured sleeve layer is placed into a second, larger or smaller pattern, where another sleeve mix having a different composition is blown around the first layer of sleeve and cured to create a distinct second layer.

This can be continued to create as many layers and materials as desired.

2. Similar to method (1), multiple layered sleeves can be formed from a liquid slurry (usually containing fibers) by using a porous pattern which has the desired inner dimension of the sleeve. The pattern is placed in the slurry and a vacuum is applied to remove liquid and deposit material on the outer dimension of the pattern. The wet preforms are then moved to a different slurry where another layer of material is deposited onto the inner layer.

Once the desired number of layers and thickness is built up, the wet preforms are removed from the pattern and heated to remove any residual liquid and to cure the sleeve.

3. Alternatively, individual layers of the sleeves are separately produced with different dimensions so that the different layers fit snugly together ("nested"), one inside the other. If needed a small amount of glue can be used to secure the layers.

To achieve the best overall performance it, it is preferable to have a more exothermic layer as the inner layer and a more insulating layer as the outer layer. This arrangement enhances the performance of the sleeve because the insulating layer retards heat loss of the exothermic and thereby enhances the needed temperature profile.

EXAMPLE 1 The sleeve mix for exothermic sleeve layer comprises 55% aluminum silicate microspheres, 33% aluminum powder, 7% iron oxide, and 5% cryolite. The sleeve mix for insulating sleeve layer consisted of aluminum silicate microspheres. The exothermic sleeve mix and insulating sleeve mix were separately prepared by mixing the sleeve composition and the binder in a Hobart N-50 mixer for about 2-4 minutes.

The exothermic and insulating sleeve layers were produced by the cold-box process in much the same way a core is produced using 8.8% parts of binder, based upon the weight of the sleeve mix. The cold-box binder used was an ISOCURE@ binder sold by Ashland Chemical Company, a division of Ashland Inc. This binder is a two part phenolic urethane cold-box

binder where the Part I is a phenolic resin similar to that described in U. S. Patent 3,485,797.

The resin is dissolved in a blend of aromatic, ester, and aliphatic solvents, and a silane. Part II of the binder is the polyisocyanate component and comprises a polymethylene polyphenyl isocyanate, a solvent blend consisting primarily of aromatic solvents and a minor amount of aliphatic solvents, and a benchlife extender. The weight ratio of Part I to Part II is about 55: 45.

The dimensional accuracy of the sleeve produced in this manner allows the sleeve to be inserted into a pre-molded cavity in the mold without special fixturing or equipment. The sleeve will fit into the cavity tightly with no gap at the bottom of the sleeve that would allow liquid metal to flow up around the sleeve. By using the correct dimensions on the sleeve and the tooling to produce the cavity, it is possible to insert the sleeve into the casting mold assembly so that it is tight at the bottom (top of the casting).

Multiple layered riser sleeves were produced forming standard 2.5"x 3.75" exothermic sleeve and insulating sleeves with a 3/8"wall thickness. The walls of the sleeves were machined down to a 3/16"wall thickness. In order to produce sleeves with multiple layers, either an exothermic or insulating sleeve was placed in the tooling, leaving a 3/16"gap between the sleeve layer and the tooling. Then the sleeve mix which produced an opposite layer was blown into the tooling around the first layer and cured to form a second sleeve layer. When removed from the tooling, the sleeve had two different layers, exothermic and insulating, bonded together. According to this procedure, multiple layered sleeves were produced having (a) an exothermic layer on the inside and an insulating layer on the outside (Ex/In)', or (b) an insulating layer on the inside and an exothermic layer on the outside (In/Ex).

Casting trials were conducted using standard insulating and exothermic sleeves and sleeves with multiple layers. The casting was a low carbon steel 3 1/2"cube with a 2 1/2" diameter and 3 3/4"height riser. Performance was measured by comparing the distance of the shrinkage pipe in the risers from the top surfaces of the cubes. A standard exothermic riser with a 3/8"wall thickness produced a safety margin of 0.32". A standard insulating 'Where Ex = exothermic, In = insulating, and the first abbreviation to appear indicates that it is the inner layer.

sleeve with a 3/8"wall thickness produced a safety margin of 0.15". The layered sleeve with a 3/8"wall thickness having the exothermic material on the inside and an insulating material on the outside (Ex/In) out performed the others with a safety margin of 0.86". The layered sleeve with a 3/8"wall thickness having an insulating layer on the inside and an exothermic layer on the outside (In/Ex) had a safety margin of 0.65", out performing the standard insulating and exothermic sleeves. The results are summarized in the Table 1 whichfollows: PLEASE CONFIRM THAT ALL SLEEVES TESTED WERE OF THE SAME THICKNESS.

TABLE I SAFETY MARGIN OF MULTIPLE SLEEVES COMPARE TO CONVENTIONAL SLEEVES FOR STEEL 3/8"thickness, 3.5" cube test casting EXAMPLE SLEEVE SAFETY MARGIN2 A Ex 0.32" In 0. 15" 1 Multiple Ex/In 0.86" 2 Multiple In/Ex 0.65"

The data in Table I indicates that the multiple sleeves had a larger safety margin than the standard sleeves having only one layer.

EXAMPLE 2 The procedure of EXAMPLE 1 was repeated, but ductile iron was poured instead of low carbon steel. The pouring temperature was 2550°F. The results in Table II show that a significant increase in safety margin was obtained with the double layer sleeve compared to the conventional single layer sleeves. Also significant is that secondary 2 Safety margins set forth in Tables I-III are an average based upon several test castings.

shrinkage was in the riser and not within the casting, as with single layer insulating or exothermic sleeves.

TABLE II SAFETY MARGIN OF MULTIPLE SLEEVES COMPARE TO CONVENTIONAL SLEEVES FOR DUCTILE IRON 3/8"thickness, 3.5" cube test casting SAFETY MARGIN SAFETY MARGIN EXAMPLE SLEEVE PRIMARY SHRINKAGE SECONDARY SHRINKAGE C Ex 0. 85"-0.56" In 1. 50"-0. 10" 1 Ex/In 1. 74" 0.58" EXAMPLE 3 The procedure of EXAMPLE 1 was repeated, except a different exothermic sleeve formulation was used and multiple layer sleeves were prepared in a different way. The exothermic formulation consisted of 48% aluminum silicate microspheres, 34% aluminum powder, 7% iron oxide, 6% manganese dioxide, and 5% cryolite. The sleeve (1) was prepared by blowing an insulating sleeve and an exothermic insert separately. The exothermic insert was placed inside the insulating sleeve at the top and fastened with the adhesive material. The sleeve (2) was prepared in a similar way but in this case the entire top portion of the sleeve was made of exothermic mixture. The sleeves were tested with ductile iron which was poured at 2550°F. The results presented in Table III show the highest safety margin is obtained with insulating sleeve containing exothermic insert inside.

This design also allows to reduce riser size by about 30%, resulting in increased casting yield and reduced cleaning room cost.

TABLE m SAFETY MARGIN OF MULTIPLE SLEEVES COMPARE TO CONVENTIONAL SLEEVES FOR DUCTILE IRON 2x3"sleeves, 3/8"thickness, 3"cube test casting EXAMPLE SLEEVE DESIGN SAFETY MARGIN SAFETY MARGIN PRIMARY SHRINKAGE SECONDARY SHRINKAGE E Ex 1. 15"0. 15" F In 1.05" -0.10" 1 In/Ex Insert 1. 30" 0.34" ISExTop 1. 13"0. 19" In all three examples the layered sleeves outperformed the single, uniform layered sleeves having the same comparable material. Many other designs of multiple sleeves can be developed, resulting in better usage of exothermic and insulating materials.