Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-05-23
2002-08-06
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...
C523S145000
Reexamination Certificate
active
06429236
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 Part I component comprising (1) a phenolic resin component, and (2) a free radical initiator, and a Part II component comprising (1) a polyisocyanate, and (2) a multifunctional acrylate. 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 to form a 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 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
1
, 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.
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 satisfy 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.
Another commercially successful cold-box binder uses a two-part system, which involves a hydroperoxide as one part and an acrylate blend as the second. The two parts are mixed on the sand, blown into the tooling, and cured using sulfur dioxide. This technology is described in U.S. Pat. No. 4,526,219.
Each binder system offers a set of advantages and disadvantages. The phenolic urethane offer good hot strength, good erosion resistance, rapid cure, but the foundry mix made with the binder has a short benchlife and castings made from the foundry mixes show poor resistance to veining. The acrylate-based system offers excellent veining resistance and almost unlimited benchlife, but suffers from poor erosion resistance.
Recently a system has been developed which is disclosed in U.S. Pat. No. 5,880,175, which is hereby incorporated by reference, and incorporates aspects of these two prior systems. This binder also uses two parts. The first part is an epoxy/hydroperoxide solution and the second part is a blend of multifunctional acrylates and a polyisocyanate. The two parts of the binder are mixed on the sand and blown into the tooling and cured using an amine gas. This system offers excellent veining resistance and good benchlife, but suffers from poor erosion resistance.
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. a Part I component comprising
(1) a phenolic resin component; and
(2) a free radical initiator,
B. a Part II component comprising:
(1) from 5 to 70 weight percent of a reactive unsaturated acrylic monomer, acrylic polymer, and mixtures thereof; and
(2) from 10 to 70 weight percent of an organic polyisocyanate.
The binder may also contain an epoxy component, which is usually part of the Part I 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 binders shown in U.S. Pat. No. 5,880,175. 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 with
Carlson Gary M.
Fechter Robert B.
Hendershot D. Greg
Toplikar Edward G.
Ashland Inc.
Cain Edward J.
Hedden David L.
Lee Katarzyna W.
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