Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-09-24
2002-01-29
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S139000, C523S143000
Reexamination Certificate
active
06342543
ABSTRACT:
FIELD OF THE INVENTION
The subject invention relates to a foundry binder system that cures in the presence of a volatile amine curing catalyst. The binder system comprises (a) a compound containing at least two active methylene hydrogen atoms, (b) an organic polyisocyanate (c) a reactive unsaturated acrylic monomer and/or polymer, (d) an oxidizing agent, and preferably (e) an epoxy component. The foundry binders are used for making foundry mixes. The foundry mixes are used to make foundry shapes that are used to make metal castings.
BACKGROUND OF THE INVENTION
In the foundry industry, one of the procedures used for making metal parts is “sand casting”. In sand casting, disposable foundry shapes, e.g. molds and cores, are fabricated with a mixture of sand and an organic or inorganic binder. The foundry shapes are arranged in molding assembly, which results in a cavity through which molten metal will be poured. After the molten metal is poured into the assembly of foundry shapes, the metal part formed by the process is removed from the molding assembly. The binder is needed so the foundry shapes do not disintegrate when they come into contact with the molten metal. In order to obtain the desired properties for the binder, various solvents and additives are typically used with the reactive components of the binders to enhance the properties needed.
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 compacting it in a pattern, and allowing it to cure until it is self-supporting. In the cold-box process, a volatile curing catalyst is passed through a shaped mixture (usually in a corebox) of the aggregate and binder to form a cured foundry shape.
There are many requirements for a binder system to work effectively. For instance, the binder must have a low viscosity, be gel-free, and remain stable under use There are many requirements for a binder system to work effectively. For instance, the binder must have a low viscosity, be gel-free, and remain stable under use conditions. In order to obtain high productivity in the manufacturing of foundry shapes, binders are needed that cure efficiently, so the foundry shapes become self-supporting and handleable as soon as possible.
With respect to no-bake binders, the binder must produce a foundry mix with adequate worktime and striptime to allow for the fabrication of larger cores and molds. On the other hand, cold-box binders must produce foundry mixes that have adequate benchlife, shakeout, and nearly instantaneous cure rates. The foundry shapes made with the foundry mixes using either no-bake or cold-box binders must have adequate tensile strengths (particularly immediate tensile strengths), scratch hardness, and show resistance to humidity.
One of the greatest challenges facing the formulator is to formulate a binder that will hold the foundry shape together after is made so it can be handled and will not disintegrate during the casting process
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, yet will shakeout from the pattern after the hot, poured metal cools. Without this property, 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. Another related property required for an effective foundry binder is that foundry shapes made with the binder must release readily from the pattern.
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Casting temperatures of poured metal reach 1500° C. for iron and 700° for aluminum parts.
The flowability of a foundry mix made from sand and an organic binder can pose greater problems with respect to cold-box applications. This is because, in some cases, the components of the binder, particularly the components of phenolic urethane binders, may prematurely react after mixing with sand, while they are waiting to be used. If this premature reaction occurs, it will reduce the flowability of the foundry mix and the molds and cores made from the binder will have reduced tensile strengths. This reduced flowability and decrease in strength with time indicates that the “benchlife” of the foundry mix is inadequate. If a binder results in a foundry mix without adequate benchlife, the binder is of limited commercial value.
In view of all these requirements for a commercially successful foundry binder, the pace of development in foundry binder technology is gradual. It is not easy to develop a binder that will satisify all of the requirements of interest in a cost effective way. Also, because of environmental concerns and the cost of raw materials, demands on the binder system may change. Moreover, an improvement in a binder may have some drawback associated with it. In view of these requirements, the foundry industry is continuously searching for new binder systems that will better meet them.
One of the most successful binders used in the cold-box process for making foundry shapes is the phenolic-urethane binder. The phenolic-urethane binder comprises a phenolic resin component and a polyisocyanate component that are mixed with an aggregate to form a foundry mix. The foundry mix is blown into pattern, typically a corebox, where it is cured by passing a volatile tertiary amine catalyst through it to form a cured foundry shape. Phenolic-urethane binders are widely used in the foundry industry to bond the sand cores and molds used in casting iron and aluminum. An example of a commonly used phenolic-urethane binder used in the cold-box process is disclosed in U.S. Pat. No. 3,409,575, which is hereby incorporated by reference. More recently amine curable cold-box binders based on acrylic-epoxy-isocyanate were developed. These binders are disclosed in U.S. Pat. No. 5,880,175, which is hereby incorporated by reference.
SUMMARY OF THE INVENTION
The invention relates to a foundry binder system which will cure in the presence of a volatile amine curing catalyst comprising:
(a) from 1 to 70 weight percent of compound having at least two active methylene hydrogen atoms selected from the group consisting of monofunctional and multifunctional acetoacetates, diketones, malonates, acetoacetamides, cyanoacetates, and mixtures thereof;
(b) from 10 to 70 weight percent of an organic polyisocyanate;
(c) from 5 to 70 weight percent of a reactive unsaturated acrylic monomer, acrylic polymer, and mixtures thereof; and
(d) an effective oxidizing amount of an oxidizing agent,
where (a), (b), (c), and (d) are separate components or can be mixed with another component, provided (b) or (c) is not mixed with (d), and the weight percent is based upon the total weight of the binder system.
Preferably the binder system also contains (e) an epoxy component in an amount of from 1 to 40 weight percent.
The foundry binders are used for making foundry mixes. The foundry mixes are used to make foundry shapes which are used to make metal castings. Foundry shapes made with the binder systems have higher immediate tensile strengths than foundry shapes prepared with comparable acrylic-epoxy-isocyanate binders shown in U.S. Pat. No. 5,880,175 that do not contain an acetoacetate. This improvement is commercially significant in terms of handling the foundry shapes after they are made. Because the tensile strength of the core builds up faster, a foundry can use less binder and catalyst than used in the binder systems shown in U.S. Pat. No. 5,880,175 without sacrificing tensile strengths. Additionally, the binder does not contain any free phenol or free formaldehyde, and has zero or low volatile organic compounds (VOC). Foundry shapes made with binders are resistant to sagging even after storage, which is important in producing castings that are dimensionally accurate.
BEST MODE AND OTHER MODES OF PRACTICING THE INVENTION
It is preferred to package and use the binders system as a two part system. The Part I component c
Carlson Gary M.
Harvey Raymond Scott
Hendershot Don Greg
Moy Thomas M.
Toplikar Edward G.
Ashland Inc.
Cain Edward J.
Hedden David L.
Kataryna Wyrozebski-Lee
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