Metal founding – Process – Shaping a forming surface
Reexamination Certificate
2000-03-21
2001-09-11
Foelak, Morton (Department: 1711)
Metal founding
Process
Shaping a forming surface
C164S529000, C164S359000, C521S054000, C523S218000, C523S219000
Reexamination Certificate
active
06286585
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to exothermic and insulating sleeve mixes comprising (1) a sleeve composition comprising stabilized hollow aluminosilicate microspheres, and (2) a chemically reactive binder. Sleeves are formed from the sleeve mix and are cured in the presence of a catalyst by the cold-box or no-bake curing process. The invention also relates to a process for casting metal parts using a casting assembly where the sleeves are a component of the casting assembly. Additionally, the invention relates to the metal parts produced by the casting process.
BACKGROUND OF THE INVENTION
A casting assembly consists of a pouring cup, a gating system (including downsprues, choke, and runner), risers, sleeves, molds, cores, and other components. To produce a metal casting, metal is poured into the pouring cup of the casting assembly and passes through the gating system to the mold 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.
Risers or feeders are reservoirs which contain excess molten metal which is needed to compensate for contractions or voids of metal which occur during the casting process. Metal from the riser fills such voids in the casting when metal from the casting contracts. Thus, the metal from the riser is allowed to remain in a liquid state for a longer period, thereby providing metal to the casting as it cools and solidifies. Sleeves are used to surround or encapsulate the riser and other parts of the casting assembly in order to keep the molten metal in the riser hot and maintain it in the liquid state. The temperature of the molten metal and the amount of time that the metal in the riser remains molten are a function of the sleeve composition and the thickness of the sleeve wall, among other factors.
Typical materials used to make sleeves are aluminum, oxidizing agents, fibers, fillers and refractory materials, particularly alumina, aluminosilicate, and aluminosilicate in the form of hollow aluminosilicate spheres. The type and amount of materials in the sleeve mix depends upon the properties of the sleeves that are to be made, particularly the insulating and exothermic properties of the sleeve.
Three basic processes are used for the production of sleeves, “ramming”, “vacuuming”, and “blowing or shooting”. Ramming and blowing are methods of compacting a sleeve composition and binder into a sleeve shape. Ramming consists of packing a sleeve mix (sleeve composition and binder) into a sleeve pattern made of wood, plastic, and/or metal. Vacuuming consists of applying a vacuum to an aqueous slurry of a refractory and/or fibers and suctioning off excess water to form a sleeve. Typically, when vacuuming is used to form the sleeve, the sleeves formed are oven-dried to remove contained water and cure the sleeve. If the contained water is not removed, it may vaporize when it is exposed to the hot metal and result in a safety hazard.
These compositions are modified, in some cases, by the partial or complete replacement of the fibers with hollow aluminosilicate microspheres. See PCT publication WO 94/23865. This procedure makes it possible to vary the insulating and exothermic properties of the sleeves and reduces or eliminates the use of fibers which can create health and safety problems to workers making the sleeves and using the sleeves in the casting process. WO 98/03284 discloses a cold-box and no-bake process for making sleeves with certain hollow aluminosilicate microspheres. The hollow aluminosilicate microspheres disclosed in these patent applications are of two basic types. One type is high in alumina (at least 38 weight percent based upon the weight of the microspheres) and contains small amounts of alkaline impurities. The other type is low in alumina (less than 38 weight percent alumina based upon the weight of the microspheres), high in silica, and contains a higher amount of alkaline impurities, such as Na, K, Ca, Mg. The low alumina hollow microspheres release alkaline materials when they are heated to high temperatures of about 700° C. and higher. These resulting alkaline materials are not desirable by-products. These decomposition products contaminate the sand and the sand is less effectively bonded when used again to make molds and cores for use in the casting assembly.
SUMMARY OF THE INVENTION
This invention relates to exothermic and insulating sleeve mixes comprising:
(1) a sleeve composition comprising pH or thermally stabilized hollow aluminosilicate microspheres having an aluminosilicate content of less than 38 weight percent based upon the weight of the microspheres, and
(2) a chemically reactive binder.
The sleeve mixes are used to prepare exothermic and insulating sleeves. The sleeves are cured in the presence of a catalyst by the cold-box or no-bake curing process. The invention also relates to a process for casting metal parts using a casting assembly where the sleeves are a component of the casting assembly.
The major advantage of using these sleeve mixes is that sleeves made from the sleeve mixes do not produce alkaline impurities, such as Na, K, Ca, and Mg cations, during the casting of metal. This is not the case when sleeve mixes prepared with aluminosilicate microspheres that are not pH stabilized are used. These sleeve mixes produce such alkaline impurities. The alkaline impurities may come into contact and mix with the sand used in the molds and cores of the casting assembly. As a result, the sand cannot be easily reclaimed or reused. Since sand reclamation is an important economic and environmental concern, there is an interest in using sleeves that will not generate alkaline impurities.
Additionally, changes in pH affect the ability of a binder to hold sand together, resulting in a loss of strength and increased casting defects.
DEFINITIONS
The following definitions will be used for terms in the disclosure and claims:
Casting assembly—assembly of casting components such as pouring cup, downsprue, gating system (downsprue, runner, choke), molds, cores, risers, sleeves, etc. which are used to make a metal casting by pouring molten metal into the casting assembly where it flows to the mold assembly and cools to form a metal part.
Chemical binding—binding created by the chemical reaction of a catalyst and a binder which is mixed with a sleeve composition.
Cold-box—mold or core making process, which uses a vaporous catalyst to cure resins, used to make the mold or core.
ISOCURE® cold-box binder—a two part polyurethane-forming cold-box binder where the Part I is a phenolic resin similar to that described in U.S. Pat. No. 3,485,797. The resin is dissolved in a blend of aromatic, ester, and aliphatic solvents, and a silane. Part II 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.
Insulating sleeve—a sleeve having greater insulating properties than the mold/core assembly into which it is inserted. An insulating sleeve typically contains low-density materials such as fibers and/or hollow microspheres.
Mold assembly—an assembly of molds and/or cores made from a foundry aggregate (typically sand) and a foundry binder, which is placed in a casting assembly to provide a shape for the casting.
No-bake—mold or core making process which uses a liquid catalyst to cure the mold or core, also known as cold-curing.
Riser—cavity connected to a mold or casting cavity of the casting assembly, which 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
Aufderheide Ronald C.
Twardowska Helena
Ashland Inc.
Foelak Morton
Hedden David L.
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