Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-01-25
2003-01-21
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, C523S147000
Reexamination Certificate
active
06509392
ABSTRACT:
FIELD OF INVENTION
This invention relates to no-bake foundry binders that produce foundry shapes with improved hot strength. The binder comprises a polyol component that contains at least one polyether polyol, a polyisocyanate component and a catalyst component that contains a catalyst that promotes the trimerization of polyisocyanates to form polyisocyanurates. The catalyst component may also include supplemental catalysts that promote the reaction of the isocyanate with the polyols. Foundry mixes are prepared by mixing the binder with a foundry aggregate at ambient temperature. Foundry shapes, including cores and molds, having improved hot strength are prepared by shaping the mix and setting the binder using the no-bake process.
BACKGROUND OF THE INVENTION
One of the major methods used by the foundry industry to produce metal castings is sand casting. In this process, sand or other aggregates are bonded together to give shaped cores or molds using organic or inorganic binders. Molten metal is then poured into the bonded sand mold and allowed to cool producing metal castings having the shape of the sand mold.
Many kinds of binders have been used to make foundry cores and molds. They include hot box binders, cold box binders, shell process binders, no-bake binders, clay binders, and baking binders such as core oil. The binders strengthen the molds and cores.
A major process used in the foundry industry is the no-bake process. In this process, a binder system that will cure at ambient temperature is mixed with a foundry sand or other aggregate and allowed to cure at room temperature to produce resin bonded molds and cores. Generally a catalyst is added to control the cure speed of the binder system. Sufficient work time is needed to allow the binder system to be mixed with the sand and the foundry core or mold patterns to be filled and compacted before the binder hardens. Varying the catalyst type and quantity is a convenient way to adjust the cure speed of the different no-bake binder systems used in foundries.
One type of no-bake binder that has been used for casting non-ferrous metals such as aluminum, magnesium and lightweight metals is amine-based polyol urethane binders. They are used in these applications because of the quick breakdown and excellent shakeout at relatively low metal casting temperatures. U.S. Pat. Nos. 4,448,907 and 4,273,700 are examples of the prior art.
Another example is polyether polyol urethane systems cured with liquid tertiaryamine catalysts. U.S. Pat. Nos. 5,455,287 and 5,859,091 are examples of this prior art.
One of the limitations of the amine polyol based binder systems or the amine catalyzed polyol systems is their low hot strength and easy shakeout. In some non-ferrous and ferrous casting applications, they breakdown too rapidly causing erosion of the sand molds and cores and other metal casting defects. Sometimes, these problems can be reduced or eliminated by applying a refractory coating to the surface of amine polyol urethane bonded cores and molds. Even where this works, it adds cost and process time to the metal casting process.
Foundry binders based on urethanes produced from polyester-based polyol have been described in the prior art, e.g. U.S. Pat. No. 5,698,613. The polyester-based polyol systems do not have increased hot strength and those systems that are based on aromatic polyester-based polyols tend to produce an untoward level of smoke in use.
Therefore, there is a need for a binder system that maintains the good characteristics of amine polyol such as very low odor, low volatile organic chemical emissions, no free formaldehyde, and no free phenol while providing increased hot strength and resistance to mold erosion during the casting process.
SUMMARY OF THE INVENTION
It is an objective of this invention to provide a foundry binder composition that can be used to produce foundry shapes with improved hot strength. The binder comprises a polyol component that contains at least one polyether polyol, a polyisocyanate component and a catalyst component that contains a catalyst that promotes the trimerization of polyisocyanates to form polyisocyanurates. The catalyst component may also include supplemental catalysts that promote the reaction of the isocyanate with the polyols. The foundry molds and cores made with binders that develop polyisocyanurate structures have improved hot strength. The foundry molds and cores made with binders that develop polyisocyanurate/polyurethane structures cure quickly and have improved hot strength. The increased hot strength reduces casting defects such as mold and core erosion.
It is a further objective of this invention to provide a foundry binder that allows the hot strength to be varied to meet different casting requirements by using trimerization catalysts in combination with tertiary amine catalysts. The ratios can be varied to adjust cure speed and hot strength of the binder system.
Another objective of the invention is to provide binders that do not contain any free formaldehyde or phenols and preferably do not contain any unreactive solvents. The systems are essentially odorless. When reactive solvents or no solvents are used, there are no volatile organic compounds (VOC's) present in the binder system. Thus, the compositions of this invention are environmentally attractive.
A further objective of this invention is to provide foundry cores and molds with improved hot strength when used to make metal castings. The higher hot strength cores and molds show greater resistance to casting defects such as erosion and burn in during the casting process. The use of refractory coatings to protect the cores and molds from erosion during the casting process with non-ferrous metals may be reduced or eliminated. The cost of any needed coatings and the process time to apply the coatings may be reduced or eliminated.
BEST MODE AND OTHER MODES OF PRACTICING THE INVENTION
The binder of the present invention comprises a polyol component that contains at least one polyether polyol, a polyisocyanate component and a catalyst component that contains a catalyst that promotes the trimerization of polyisocyanates to form polyisocyanurates. The catalyst component may also include supplemental catalysts that promote the reaction of the isocyanate with the polyols.
The foundry binders of the present invention may be used as either two or three part systems. In a three-part system, the three parts are a polyol component (sometimes referred to as “Part I”), a polyisocyanate component (sometimes referred to as “Part II”) and a catalyst component (sometimes referred to as “Part III”). In a two-part system, the catalyst component is incorporated into the polyol component to create Part I, while the polyisocyanate component functions as Part II. Alternatively, some of the catalyst can be incorporated into the polyol component to form Part I and the remainder of the catalyst component is used as a Part III. A three component system is preferred because it allows the cure speed to be adjusted as required to meet foundry productivity needs.
The Polyol Component
The polyol component of he present invention must include at least one polyether polyol. Suitable polyether polyols are produced by reacting an alkylene oxide with polyols such as ethylene glycol, diethylene glycol, propylene glycol, trimethylol propane, pentaerythritol, sorbitol, hydroxyquinone di(&bgr;hydroxyethyl) ether, and sucrose. The alkylene oxides used to prepare the polyether polyols include ethylene oxide, propylene oxide, butylene oxide, styrene oxide and mixtures thereof. The polyols useful in this invention have a functionality of two (2) or greater. The polyether polyols may have primary and/or secondary hydroxyl groups. The preferred polyether polyols of this invention have a hydroxyl functionality from about 2 to about 8. Diols may be used and still achieve sufficient crosslinking to produce strong cores and molds because isocyanurates formed by the trimerization of the isocyanates causes significant crosslinking to occur. However, it is generally
Aranha Anita F.
Jhaveri Satish S.
Johnson Calvin K.
Mancina Frank
Cain Edward J.
Egan Donald E.
H.A. International LLC
Lee Katarzyna Wyrozebski
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