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.

Typically, 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 having 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 sleeve 1 with polystyrene foam 2 between the sleeve 1 and the mold 3 wall to create a gas filled cavity when the mold is poured.

Figure 2 shows a cross sectional diagram of a test casting 4, riser 5, and the safety margin 6.

SUMMARY OF THE INVENTION This invention relates to casting mold assembly comprising at least one sleeve, preferably a riser sleeve, wherein in said sleeve is contact with a consumable material prior to pouring. It also relates to preparation and use of such 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 sleeve used in the casting assembly may be an exothermic, insulating, or both. It also relates to the design of such casting assemblies.

These sleeves have several advantages. The thermal properties of the sleeve are improved because the consumable material burns during pouring and is consumed. The result is that a gap of gases or air partially or totally surrounds the sleeve. Consequently, the heat of the riser is more effectively retained (i. e. the bulk thermal conductivity is reduced) because of the insulating properties of the air gap. Thus the metal of the riser can be maintained at a higher temperature longer. As a result, it is possible to use smaller risers resulting in proportionally higher casting yields. Alternately, the creation the air gap by the burning of the consumable material can reduce the volume and/or cost of material needed in the sleeve to produce the same results.

DEFINITIONS The following definitions will be used for terms in the disclosure and claims: Air Gap-a cavity separating the sleeve from the mold material or within the body of the sleeve that is filled with air or gas.

Casting mold assembly-assembly of casting 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-a sleeve which has exothermic properties (i. e. produces net heat) 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-a sleeve 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 fibers and/or hollow microspheres.

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

Riser-cavity connected to a mold or casting cavity of the casting assembly which, when filled with liquid metal, acts as a reservoir for 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 confined to the riser and the casting was sound. A negative value indicates that shrinkage extended into the casting. 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 open, closed, insertable, or mold-in-place. Sleeves can have a variety of shapes, e. g. cylinders, domes, cups, boards, cylindrical, neckdown, spherical, neckdown dome, or insertable sleeves.

BEST MODE AND OTHER MODES FOR PRACTICING THE INVENTION The type and shape of sleeve used not critical. The sleeve may be a cylinder, dome, cup, board, core, neckdown, spherical, neckdown dome, or insertable. The materials used to prepare the sleeves are any of the exothermic and insulating materials known in the art. The sleeves can be prepared with any methods known in the art. Usually, sleeves are not totally exothermic or insulating in their properties, but have both exothermic and insulating properties.

For purposes of this invention, an exothermic sleeve is defined as a sleeve that produces heat when exposed to the heat of molten metal during pouring. The exothermic sleeve is 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, nitrate, potassium permanganate, etc. In addition, the sleeve composition may contain fillers and additives, such as cryolite (Na3AlF6), potassium aluminum tetrafluoride, potassium aluminum hexafluoride, sand and wood flour.

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

The novel feature of this invention is that the sleeve is in contact with a consumable material prior to pouring. Any material that will burn during the pouring of the metal can be used as the consumable material. Examples of consumable materials include polystyrene foam, urethane cellular foam, polymethyl methacrylate, corrugated cardboard, low density paper, and consumable plastic.

The sleeve is manufactured with a different taper, draft, geometry, or height than the mold cavity into which it is inserted so that a consumable material can be inserted between the sleeve and mold cavity. An air gap is formed by the burning of the consumable material and acts as an insulating layer for the insertable sleeve. This is particularly useful where the consumable material is placed around the outer layer of the sleeve and inserted into the mold, or for "molded-in-place"sleeves, where the sleeve and consumable material is placed on the pattern during molding and remain in the mold after the mold is formed and removed from the pattern.

In these situations, the foam is consumed (e. g. vaporized or disintegrated) by heat when the metal is poured. This leaves a cavity filled with gas surrounding portions of the sleeve, i. e. where

the foam was present, as the casting solidifies. Although the foam initially provides additional insulation to the sleeve, the air space created upon pouring further insulates the sleeve and retards solidification of the riser metal.

In many cases, the sleeve is preferably shaped at the bottom to prevent metal from flowing into the gap. A breaker core can also act as a seal at the bottom of the sleeve.

Additional insulation may be provided to the sleeve by adding insulating material, preferably hollow aluminosilicate microspheres, to the sleeve mix used for making the exothermic sleeve.

The exothermic 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.

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 making sleeves because dimensionally accurate sleeves 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 used with an ISOSETS 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). Any no-bake or cold-box binder 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.

EXAMPLE 1 The sleeve mixes used to prepare the exothermic sleeves comprised 55% aluminum silicate hollow microspheres, 33% aluminum powder, 7% magnetite, and 5% cryolite. The sleeve mixes used to prepare the insulating sleeves were comprised of aluminum silicate microspheres.

The sleeve mix and 8.8% parts of binder, based upon the weight of the sleeve mix are mixed in a Hobart N-50 mixer for about 2-4 minutes. The exothermic sleeves were produced by the cold-box process in much the same way a core is produced. The cold-box binder used in the examples is an ISOCUREX binder sold by Ashland Chemical Company, a division of Ashland Inc. This binder is a two part polyurethane-forming 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 sleeves used in the experiments were prepared by mixing an exothermic sleeve mix and curing by the cold-box process.

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 mold 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 mold cavity, it is possible to insert the sleeve into the mold cavity so that it is tight at the bottom (top of the casting), but so a cavity or air gap is created around the upper sides and top of the sleeve when the consumable material burns. In some instances it may be recommended to mold certain surfaces in the core print to serve as locators for the sleeve to provide extra support and dimensional accuracy in sleeve placement.

Trials were conducted using a"shrink cube"casting with the sleeves prepared. (See Figure 3.) The"shrink cube"was a 3 1/2"cube that is cast in steel and used to evaluate the relative performance of sleeve materials. Molds were produced using mold-in-place 2 1/2"x 3 3/4"riser sleeves.

Six castings were poured with steel. Control A used the standard exothermic sleeve placed in the sand mold. The castings of Examples 1 and 2 used the same sleeve, but with 3/16" and 3/8"of foam around the outside of the sleeve. Control B used an insulating sleeve made from microspheres. The castings of Examples 3 and 4 used the same insulating sleeve with 3/16"and 3/8"of additional foam around the outside of the sleeve. All castings were poured with low carbon steel at 2950° F.

Following casting, the molds were broken open and examine. Where the sleeves were molded directly against the sand mold (Control A and Control B), the sleeve materials remained in contact with the metal riser on the inside and with the sand mold on the outside. Where foam was used around the sleeves, the casting of Example 1,2,3, and 4, there was a visible cavity in the shape of the foam surrounding the sleeve and separating it from the sand mold.

The sleeve performance was evaluated by measuring the distance from the top of the cube casting to the bottom of the shrinkage pipe in the riser. This is referred to as the"safety margin". Control A had a shrinkage pipe that extended to within 0.32 inches of the top of the casting. The casting of Example 1 had a safety margin of. 49" and the casting of Example 2 had a safety margin of 0.75". Control B had a safety margin of 0.15". The castings of Examples 3 and 4 had higher safety margins at 0.90" and 1.04". For both exothermic and insulating sleeves, the performance of the sleeve was enhanced by the foam and the cavity that was subsequently produced around the riser sleeve. The results of the experiments are shown in Table 1.

TABLE 1 SAFETY MARGIN OF SLEEVES WITH A FOAM COMPARED TO CONVENTIONAL SLEEVES WITHOUT A FOAM FOR STEEL 3/8"thickness, with 3.5"cube test casting CASTING SLEEVE SAFETY MARGIN (inch) Control A Standard Ex 0. 32 1 Ex +3/16"Foam 0. 49 2 Ex +3/8"Foam 0.75 ControlB Standard In 0. 15 In +3/16"Foam 0. 90 In +3/8"Foam 1. 04

EXAMPLE 2 The procedure of EXAMPLE 1 was repeated with a different exothermic formulation and smaller sleeve sizes. The objective was to determine if riser size can be reduced using exothermic sleeves with foam. The composition of exothermic mix was as follows: 66% microspheres, 25.7% aluminum powder, 5.3% magnetite and 3% cryolite.

The results are presented in Table 2.

TABLE 2 SAFETY MARGIN OF SLEEVES WITH A FOAM COMPARE TO CONVENTIONAL SLEEVES WITHOUT A FOAM FOR STEEL 2x3"sleeve 3/8"thickness, with 3.5"cube test casting CASTING SLEEVE SAFETY MARGIN (inch) ControlC Ex 0.39 4 Ex + 1/8"Foam 0. 87 Ex + 1/4"Foam 1.

Table 2 shows that adequate safety margin is obtained with 2x3"riser when foam is used with exothermic sleeve. This results in a higher casting yield and a lower cost of casting.

EXAMPLE 3.

The procedure of EXAMPLE 1 was repeated but ductile iron was poured instead of low carbon steel. The composition of exothermic mix was as follows: 66% microspheres, 25.7% aluminum powder, 5.3% magnetite and 3% cryolite. The pouring temperature was 2550°F. The results summarized in Table 3 show significant increase in safety margin with the use of foam for ductile iron.

TABLE 3 SAFETY MARGIN OF SLEEVES WITH A FOAM COMPARE TO CONVENTIONAL SLEEVES WITHOUT A FOAM FOR DUCTILE IRON thickness 3/8", with 3.5"cube test casting CASTING SLEEVE SAFETY MARGIN SAFETY MARGIN PRIMARYSHRINKAGESECONDARY SHRINKAGE Control D Ex (no foam) 1.61"-0.20" 6 Ex +1/4T 2. 32" 0.56" The results in the Tables clearly show the advantages of using foam with exothermic and insulating sleeves. The greater safety margin indicates that sleeves, in contact with foam that creates an air gap, have improved thermal properties when the foam burns. The heat of the riser is evidently more effectively contained than when no air gap is present. Thus the metal of the riser can be maintained at a higher temperature longer.