Metal founding – Process – Shaping a forming surface
Reexamination Certificate
2000-07-10
2003-04-29
Elve, M. Alexandra (Department: 1725)
Metal founding
Process
Shaping a forming surface
C164S526000, C523S139000, C523S145000
Reexamination Certificate
active
06554051
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a phenolic resole resin obtained by condensation of a phenol, an aldehyde, and bisphenol-A-tar. The invention also relates to phenolic urethane foundry binders made with the phenolic resins, the use of the binders in making foundry molds and cores, and the use of the cores and molds in the casting of metals.
BACKGROUND OF THE INVENTION
Today's foundries have many different processes to choose from for the manufacture of cores and molds. With core based manufacturing, synthetic resins are primarily used as binders. Among the known processes, the gas hardening processes, in particular the Ashland Cold Box Process described in U.S. Pat. No. 3,409,579, which is of outstanding commercial success.
The Ashland Cold Box Process consists of a two-component system, in which one component consists of polyols with at least two hydroxyl groups in the molecule, and the other component consists of polyisocyanates, with at least two isocyanate groups in the molecule. These two components, in a dissolved form, are mixed together with an aggregate (typically sand) and are cured through the addition of a catalyst.
U.S. Pat. No. 3,409,579 describes binders, which contain, as one component of a two-component system, a resin solution, and as the other component, a hardener. The resin component of the binder according to this patent consists of a phenolic resin of the benzylic ether type and a combination of organic solvents. The phenolic resin is obtained preferably through a reaction of phenols and formaldehydes, which is catalyzed by divalent metal ions dissolved in the reaction medium, as is described in U.S. Pat. No. 3,409,579 and in EP-A-0 183 782. Phenolic resins of the benzylic ether type (also described as resoles) differ from the novolaks which are condensed under acidic conditions, in that they have better solubility and lower viscosity, two properties which are of considerable importance with respect to their suitability for binder systems for the phenolic urethane process. Furthermore, phenolic resins of the benzylic ether type distinguish themselves in this process by higher reactivity.
The hardening component contains a liquid polyisocyanate with at least two isocyanate groups per molecule. These two components are thoroughly mixed with a refractory material (preferably quartz sand), and the mixture thus obtained is shaped in the desired form.
In U.S. Pat. No. 3,409,579, the shaped sand mix is cured by a gaseous amine, which is passed through it. In U.S. Pat. No. 3,676,392, the curing is achieved by a base with a pkB-value in the range of 7-11 (described by D. D. Perrin in Dissociation Constants of Organic Bases in Aqueous Solution, Butterworth, London, 1965). In both of these patents, the favored phenolic resin condensation products are from phenols with the general formula:
in which A, B and C are hydrogen, alkyl groups, alkoxy groups or halogen atoms, with aldehydes of the general formula R′CHO, in which R′ is a hydrogen or an alkyl group with 1-8 carbon atoms. The condensation reaction of phenol(s) and aldehyde(s) occurs in the liquid phase, usually at temperatures under 130° C. in the presence of catalytic concentrations of metal ions dissolved in the reaction medium. The manufacture and characterization of the phenolic resins obtained in this way are described in detail in U.S. Pat. No. 3,485,797. The use of substituted phenols is described in EP-A-183 782. Especially preferred phenols in this regard are ortho-cresol and para-nonyl phenol.
The phenolic resin component of the binder in the phenolic urethane process is usually used, as already mentioned, in the form of a solution in one or more organic solvents. The second component of the well known binder involves an aliphatic, cycloaliphatic or aromatic polyisocyanate, preferably with 2-5 isocyanate groups per molecule. In addition, mixtures of polyisocyanates can be used. The polyisocyanates or their solutions in organic solvents are used in sufficient concentrations to achieve the hardening of the phenolic resins.
An existing problem of a benzylic ether polyol-polyurethane based binder is its oftentimes inadequate hot strength. A certain degree of thermal breakdown is desirable, in order that the molding material mixture can be removed more easily from the cast piece. However, premature thermal decomposition of the binder leads to the emergence of cracks in the molding material in which fluid metal can penetrate, forming so-called veins or leaf ribs. In addition, hot metal can wash away the molding material as so-called erosion. Finally, a refractory coating of the molding material can flake off from the rest of the molding material. One speaks in a case like this of scabbing. All these defects can be reduced or even avoided through binders with higher thermal stability.
In U.S. Pat. No. 4,546,124, it is proposed that the thermal stability of the phenolic resin be raised through alkoxylation. However, although this brings about a certain improvement, the problem is not yet completely solved. In U.S. Pat. No. 3,904,559, foundry binders are shown, in which the polyol component contains a mixture of bisphenol and a polyether polyol. EP-A-2 898 describes a polyol component for a binder system which is hardened at room temperature, which consists of a mixture of bisphenol and a phenolic terpene component. In EP-A-40 497 phenol-ketone resins are mentioned, which are obtained by reaction of phenols or thiophenols with ketones and aldehydes.
The use of bisphenol-A-tar as a raw material for binders with the hot box process is described in U.S. Pat. Nos. 3,318,840 and 5,607,986. These binders include a furan resin, furfuryl alcohol and polyvinyl acetate. The bisphenol-A-tar is used to achieve a higher tensile strength in the casting mixture. To be sure, the heat hardening hot box binders compared to the cold hardening binders of the phenolic urethane process exhibit a number of serious disadvantages. In particular, the production cycles are longer and along with this, the productivity is lower.
U.S. Pat. No. 4,337,344 describes the manufacture of phenolic resins with bisphenol-A distillation residues and formaldehyde under acidic catalysis. A resin obtained in this way is called a novolak resin. Sand is coated with this material at elevated temperatures. This coated sand is put into a molding tool together with hexamethylene tetramine and cured at temperatures of around 250° C. This process is known as Croning, or shell-mold process. In order to reduce the brittleness, in many cases thermoplastic additives are used. The addition of bisphenol-A-tar to such resins results in higher flexibility (lower brittleness and with it, lower vulnerability to tears). Unlike phenolic resole resins, novolac resins (Croning resins), after the curing with hexamethylene tetramine, thermosets, do not exhibit thermal deformation, but are brittle. Novalac and phenolic resole resins are different structurally, are cured with different curing catalysts involving different mechanisms, and their applications are also different.
SUMMARY OF THE INVENTION
The subject invention relates to phenolic resins prepared by the reaction of a phenol, an aldehyde, and bisphenol-A-tar. The invention also relates to the use of these phenolic resins in phenolic urethane binders, the manufacture of foundry molds and cores using the binder, and the use of the cores and molds to prepare metal castings.
It is known that cold box binders based on resole phenolic urethanes pass through a thermoplastic phase by heating, in which the urethane bonds dissociate (A. Knop, W. Scheib, Chemistry and Application of Phenolic Resins, Springer-Verlag Berlin, 1979, S. 57). Surprisingly, it was found that binders containing a phenolic resin made using the bisphenol-A-tar achieved a higher stability during and after the thermoplastic phase than conventional binders based only on phenols, i.e. there was no premature thermal breakdown encountered. This discovery was not expected, particularly since the exchange of pure bisphenol-A-ta
Koch Diether
Werner Andreas
Elve M. Alexandra
Hedden David L.
Kerns Kevin P.
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