Metal founding – Process – Shaping liquid metal against a forming surface
Reexamination Certificate
2002-02-14
2003-08-12
Dawson, Robert (Department: 1712)
Metal founding
Process
Shaping liquid metal against a forming surface
C164S016000, C164S138000, C164S526000, C164S529000, C523S139000, C523S145000, C523S147000, C523S436000, C523S466000
Reexamination Certificate
active
06604567
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not Applicable.
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 foundry binder systems, which will cure in the presence of sulfur dioxide and a free radical initiator, comprising (a) an epoxy resin; (b) an acrylate; (c) an alkyl silicate; 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, particularly ferrous 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 core/mold assembly, which results in a cavity into 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.
A cold-box process widely used in the foundry industry for making cores and molds is the “SO
2
cured epoxy/acrylate system”. In this process, a mixture of a hydroperoxide (usually cumene hydroperoxide), an epoxy resin, a multifunctional acrylate, typically a coupling agent, and optional diluents, are mixed into an aggregate (sand) and compacted into a specific shape, typically a core or mold. Sulfur dioxide (SO
2
), optionally diluted with nitrogen or another inert gas, is blown into the binder/aggregate shape. The shape is instantaneously hardened and can be used immediately in a foundry core/mold system.
This system is currently sold by Ashland Specialty Chemical Division, a Division of Ashland Inc., under the trademark of ISOSET® and has been in use approximately 18 years. About ninety percent of these binders typically use bisphenol-A epoxy resin or bisphenol-F epoxy resin as the epoxy resin component. The multifunctional acrylate most commonly used is trimethylolpropane triacrylate. The hydroperoxide most commonly used is cumene hydroperoxide.
Though the process has been used successfully in many foundries, one of the major weaknesses of the system has been the erosion resistance of foundry shapes made with the binder. Erosion occurs when molten metal contacts the mold or core surfaces during the pouring process and the sand is dislodged 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 results is that sand, which has eroded from the foundry shape, is carried into the metal casting, creating weak areas in the casting. A dimensional defect is also created on the surface of the casting.
To correct this problem, foundries have historically resorted to coating the foundry shape with a refractory coating to prevent erosion. Thus, core and mold assemblies are dipped into or sprayed with a slurry composed of a high melting refractory oxide, a carrier such as water or alcohol, and thixotropic additives. When dried on a mold/core surface, the coating very effectively prevents erosion, in most cases. The problem with this approach is that the coating operation is messy, requires expensive gas fired, microwave, or radiant energy ovens to dry the wash onto the core surface. When the core/molds are heated during the drying process the strength of the organic binder to aggregate bond weakens significantly. This results in problems with handling the hot cores and reduction in productivity due to core distortion or cracking. This is especially true with microwave drying.
BRIEF SUMMARY OF THE INVENTION
The subject invention relates to foundry binder systems, which cure in the presence of gaseous sulfur dioxide and a free radical initiator, comprising:
(a) 20 to 70 parts by weight of an epoxy resin;
(b) 5 to 50 parts by weight of an acrylate;
(c) 1 to 20 parts by weight of an alkyl silicate; and
(d) an effective amount of a hydroperoxide,
where (a), (b), (c), and (d) are separate components or mixed with another of said components, provided (b) is not mixed with (d), and where said parts by weight are based upon 100 parts of binder.
It has been found that addition of the alkyl silicate the binder system results in or molds with enhanced hot tensile strengths, enhanced hot impact resistance, and/or enhanced hot strength properties, which is reflected in improved erosion resistance. These improvements result in better castings and fewer casting defects when the foundry shapes are used to make metal castings. These improvements are even more noticeable if a phenolic resin is added to the binder system.
In particular, foundry shapes made from binders based on epoxy novolac resins, bisphenol-F epoxy resins, or mixtures of bisphenol-F/epoxy novolac resins show enhanced erosion resistance. On the other hand, foundry shapes made with binders based on bisphenol-A epoxy resins exhibit improved hot tensile strength and hot impact resistance, which is particularly significant when the foundry shapes are coated with an aqueous refractory coating and oven-dried.
The foundry binders 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.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
Not Applicable.
DETAILED DESCRIPTION OF THE INVENTION
The detailed description and examples will illustrate specific embodiments of the invention will enable one skilled in the art to practice the invention, including the best mode. It is contemplated that many equivalent embodiments of the invention will be operable besides these specifically disclosed. All percentages are percentages by weight unless otherwise specified.
An epoxy resin is a resin having an epoxide group, i.e.,
such that the epoxide functionality of the epoxy resin (epoxide groups per molecule) is equal to or greater than 1.9, typically from 2.0 to 4.0.
Examples of epoxy resins include (1) diglycidyl ethers of bisphenol A, B, F, G and H, (2) halogen-substituted aliphatic epoxides and diglycidyl ethers of other bisphenol compounds such as bisphenol A, B, F, G, and H, and (3) epoxy novolacs, which are glycidyl ethers of phenolic-aldehyde novolacs, (4) mixtures thereof.
Epoxy resins (1) are made by reacting epichlorohydrin with the bisphenol compound in the presence of an alkaline catalyst. By controlling the operating conditions and varying the ratio of epichlorohydrin to bisphenol compound, products of different molecular weight can be made. Epoxy resins of the type described above based on various bisphenols are available from a wide variety of commercial sources.
Examples of epoxy resins (2) include halogen-substituted aliphatic epoxides, diglycidyl ethers of other bisphenol compounds such as bisphenol A, B, F, G, and H, and epoxy novolac resins. Examples of halogen-substituted aliphatic epoxides include epichlorohydrin, 4-chloro-1,2-epoxybutane, 5-bromo-1,2-epoxypentane, 6-chloro-1,3-epoxyhexane and the like.
Examples of epoxy novolacs (3) include epoxy cresol and epoxy phenol novolacs, which are produced by reacting a novolac resin (usually formed by the reaction of orthocresol or pheno
Shriver H. Randall
Woodson Wayne D.
Ashland Inc.
Aylward D.
Dawson Robert
Hedden David L.
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