Metal founding – Process – Shaping a forming surface
Reexamination Certificate
2002-04-10
2004-02-03
Dawson, Robert (Department: 1712)
Metal founding
Process
Shaping a forming surface
C164S015000, C164S016000, C164S529000, C523S139000, C523S145000, C523S427000, C523S436000, C523S438000, C523S466000
Reexamination Certificate
active
06684936
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable.
REFERENCE TO A MICROFICHE APPENDIX
Not Applicable.
BACKGROUND OF THE INVENTION
(1) Field of the Invention
This invention relates to erosion resistant foundry binder systems, which will
cure in the presence of sulfur dioxide and a free radical initiator, comprising (a) an epoxy resin; (b) a multifunctonal acrylate; (c) a phenolic resin that is soluble in (a) and (b); and (d) an effective amount of a free radical initiator. The foundry binder systems are used for making foundry mixes. The foundry mixes are used to make foundry shapes (such as cores and molds) which are used to make metal castings.
(2) Description of the Related Art
In the foundry industry, one of the procedures used for making metal parts is “sand casting”. In sand casting, disposable molds and cores are fabricated with a mixture of sand and an organic or inorganic binder. The foundry shapes are arranged in casting assembly, which results in a cavity through which molten metal will be poured. After the molten metal is poured into the assembly of molds and cores and cools, the metal part formed by the process is removed from the assembly. The binder is needed so the molds and cores will not disintegrate when they come into contact with the molten metal.
Two of the prominent fabrication processes used in sand casting are the no-bake and the cold-box processes. In the no-bake process, a liquid curing catalyst is mixed with an aggregate and binder to form a foundry mix before shaping the mixture in a pattern. The foundry mix is shaped by putting it into a pattern and allowing it to cure until it is self-supporting and can be handled. In the cold-box process, a gaseous curing catalyst is passed through a shaped mixture (usually in a corebox) of the aggregate and binder to cure the mixture.
The core or mold produced from the binder must maintain its dimensional accuracy during the pouring of the metal, but disintegrate after the metal cools, so that it can be readily separated from the metal part formed during the casting process. Otherwise, time consuming and labor intensive means must be utilized to break down the binder so the metal part can be removed from the casting assembly. This is particularly a problem with internal cores, which are imbedded in the casting assembly and not easily removed.
U.S. Pat. No. 4,526,219 discloses a cold-box process for making foundry shapes, whereby certain ethylenically unsaturated materials are cured by a free radical mechanism in the presence of a free radical initiator and vaporous sulfur dioxide. Typically, these binders are packaged in two parts. The Part I and Part II of the binder are mixed with a foundry aggregate, typically sand, to form a foundry mix. The total amount of binder used to form the foundry mix is typically from about 0.5 to 2 weight percent based on sand (bos). The foundry mixed is blown or compacted into a pattern where it is gassed with SO
2
to produce a cured core or mold. Foundry mixes made with these binders have extended benchlife and foundry shapes made with the binder have excellent physical properties.
This binder system, currently sold by Ashland Specialty Chemicals Division, a division of Ashland Inc., under the trademark “ISOSET”, has been in use approximately 18 years. The multifunctional acrylate most commonly used is trimethylolpropane triacrylate. The hydroperoxide most commonly used is cumene hydroperoxide. Though the binder has been used successfully in many foundry applications, the cores produced with binder often erode when the hot molten metal is poured over them. Erosion occurs when molten metal contacts the mold or core surface during the pouring process and sand is dislodged from the core at the point of contact. This occurs because the binder does not have sufficient heat resistance to maintain surface integrity until the pouring process is complete. The result is that sand is carried into the metal casting, creating weak areas in the casting. A dimensional defect is also created on the surface of the casting.
In order to reduce core erosion, foundries have historically coated the cores with refractory coatings. Core and mold assemblies are dipped into or sprayed with a slurry composed of a high-melting refractory oxide, a carrier such water or alcohol, and thixotropic additives. When dried on the mold/core surface, the coating prevents erosion in most cases. The problem with using coatings that is that the coating operation is messy, requires expensive gas fired, microwave, or radiant energy ovens to dry the wash onto the core surface, and can itself cause casting defects if the wash is not properly dried.
U.S. Pat. No. 4,518,723 discloses binders, cured with sulfur dioxide and in the presence of a free radical curing agent, which additionally contain an epoxy resin. These binders are also packaged as two-part binders. One part (Part I) is a mixture of a bisphenol-A epoxy resin (bisphenol-F epoxy resin is also used, but not as commonly) and cumene hydroperoxide (free radical initiator). The other part (Part II) is a mixture of a bisphenol-A epoxy resin, a multifunctional acrylate, and optional components. The Part I and Part II of the binder are mixed with a foundry aggregate, typically sand, to form a foundry mix. Examples VI, VII, and VIII of this patent describe a binder containing a base-catalyzed phenolic resole resin. These base-catalyzed phenolic resole resins are not benzylic ether phenolic resole resins, which are prepared with a divalent metal catalyst.
The binder disclosed in Examples VI, VII, and VIII of the '723 patent was a mixture composed of 80% Epon 828 (a bisphenol-A epoxy resin), 10% phenolic resin, and 10% methanol. This blend was then divided into three parts and modified 20% with trimethylolpropane triacrylate, furfuryl methacrylate, and furfuryl glycidyl ether, respectively. Cumene hydroperoxide was added at 30% based on the weight of the resin composition, and standard tensile specimens were cured with sulfur dioxide. The examples demonstrated that the described compositions made usable cores.
The purpose of using the base-catalyzed phenolic resole resin in these examples was to provide a low-cost reactive diluent that would also polymerize in the presence of the acid generated by the sulfur dioxide and cumene hydroperoxide. Although this purpose was accomplished, several problems existed with this binder. Though the binders containing the base-catalyzed phenolic resole resin produced adequate strength, long-term stability of the compositions was a problem. First, the base catalyzed resoles (sodium hydroxide or lithium hydroxide catalyzed), prepared at a basic pH (pH 8.5-9.0), contained a high percentage of reactive methylol groups, which made the resin highly polar and not very soluble in epoxy resins. This necessitated the use of a polar solvent (methanol) which caused odor and flash-point problems in actual foundry practice. Secondly, the reactive methylol groups tended to self-condense during storage of the compositions, generating water which made the phenolic less soluble and shortened the effective storage life of the binder.
Also, these base-catalyzed phenolic resole resins could not be dehydrated without gelling. The lowest water content that could be achieved was about 4%, compounding the solubility problem and requiring that substantial amounts of methanol or ethanol be added to the formulation to co-solubilize the water. These alcohols lowered the flash point of the mixture substantially, and would have required a flammable label for shipping and storage. It was also discovered that this type of resole had an inhibiting effect on the polymerization of trimethylolpropane triacrylate, an essential ingredient in most formulations, and though the binder containing the base-catalyzed phenolic resole resin would still produce useful cores, better tensile strength performance in the cores and molds, as evidenced by standard tests, was obtained without it's inclusion. Because of these problems, phenolic resole-modi
Archibald James J.
Shriver H. Randall
Woodson Wayne D.
Ashland Inc.
Aylward D.
Dawson Robert
Hedden David L.
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