Process for preparing foundry shapes

Abstract

This invention relates to a process for preparing foundry shapes, e.g. cores and molds. The process comprises forming a foundry mix comprising (1) a major amount of foundry aggregate, (2) an acid-curable foundry resin, and (3) an acid catalyst, shaping the foundry mix into a foundry shape, and partially or totally removing water from the foundry shape.

Description

CLAIM TO PRIORITY

Applicant claims priority to provisional application Ser. No. 60/469,936 filed on May 13, 2003, which is hereby incorporated by reference.

FIELD OF THE INVENTION

This invention relates to a process for preparing foundry shapes, e.g. cores and molds. The process comprises forming a foundry mix comprising (1) a major amount of foundry aggregate, (2) an acid-curable foundry resin, and (3) an acid catalyst, shaping the foundry mix into a foundry shape, and partially or totally removing water from the foundry shape.

BACKGROUND OF THE INVENTION

One of the processes used in sand casting for making molds and cores is the no-bake process. In this process, a foundry aggregate, binder, and liquid curing catalyst or co-reactant are mixed to form a foundry mix, which is compacted to produce a cured mold and/or core. One of the problems with the no-bake process is that it is difficult to formulate a binder that has adequate worktime, striptime, and will cure rapidly. Worktime is defined as the time interval that elapses after mixing the binder components and sand and placing the mixture a pattern until the foundry shape reaches a level of 60 on the Green Hardness “B” Scale Gauge sold by Harry W. Dietert Co., Detroit, Mich. Adequate worktime is particularly important in the no-bake process, because some of the foundry shapes prepared by the process may weigh several hundred pounds or more.

On the other hand, the striptime for removing the foundry shape from the pattern must be diminished so that high productivity can be obtained. Striptime is the time interval that elapses after mixing the binder components and sand and placing the mixture a pattern until the foundry shape reaches a level of 90 on the Green Hardness “B” Scale Gauge. For commercial process that require high productivity, a desired worktime ranges from 3 to 10 minutes and a desired striptime of 4 to 12 minutes. The foundry shapes produced must have sufficiently high tensile strength, so they can be handled after the striptime has elapsed.

Additionally, the foundry shapes must cure rapidly in order to maintain a highly productive operation. Foundry shapes are considered cured when they can be handled and used for casting metals. When foundry shapes are made by the no-bake process it may take 20-30 minutes to cure a shape that weighs as little as one pound, and may take several hours to cure a shape that weighs over a hundred pounds.

It is known that oven drying the foundry shapes at temperatures of typically from 250° C. to 350° C. will increase the curing rate of foundry shapes made by the no-bake process. However, the use of heat adds additional expense to the operation, adds time, is not totally adequate in some cases, may require a core wash, and/or requires time for the shape to cool before it can be used to cast a metal part.

In addition to adequate worktime, appropriate striptime, and rapid cure rates, the foundry shapes must have adequate tensile strengths for use. Furthermore, the foundry shapes must also produce effective castings, i.e. castings that do not have defects such as veining, perforations, lustrous carbon, penetration, gas defects, and erosion defects.

A binder commonly used in the no-bake process is a phenolic urethane derived by curing an organic polyisocyanate and phenolic resin in the presence of a liquid tertiary amine catalyst. Phenolic urethane binders used in the no-bake process are satisfactory for casting such metals as iron or steel, which are normally cast at temperatures exceeding about 1370° C. They are also useful in the casting of lightweight metals, such as aluminum, which have melting points of less than 815° C.

This binder provides molds and cores with excellent strengths that are produced in a highly productive manner. Although this binder produces good cores and molds at a high speed, there is an interest in binders that have less volatile organic compounds (VOC), a lower free phenol level, a lower free formaldehyde level, which has less odor and smoke during core making and castings, and that provide better shakeout properties.

Furan no-bake binders, and other acid-curable binders, are a good alternative, but their cure speed and associated work time/strip time ratio are usually much slower and lower than the cure speed of phenolic urethane no-bake binders. Often, cores and molds made with furan binders must set for at least twenty-four hours before being used.

Furan binders have been modified to increase their reactivity, for instance by incorporating urea-formaldehyde resins, phenol-formaldehyde resins, novolac resins, phenolic resole resins, and resorcinol into the binder. Nevertheless, these modified furan binders system do not provide the cure speed needed in foundries that require high productivity.

U.S. Pat. No. 5,856,375 discloses the use of BPA tar in furan no-bake binders to increase the cure speed of the furan binder. Although the cure speed of the binder is increased by the addition of the BPA tar, the early tensile strength of this system does not match those of the phenolic urethane system. Furthermore, these additives have adverse effects on worktime and striptime.

Nevertheless, in spite of these approaches to increasing the cure speed of furan binders, there is an interest in finding alternative methods of improving cure speed, which are economically feasible, do not adversely affect the environment, endanger the health of workers, produces satisfactory cores, and produce defect-free metal castings.

SUMMARY OF THE INVENTION

This invention relates to a process for preparing foundry shapes, e.g. cores and molds. The process, typically a no-bake process, comprises forming a foundry mix comprising a major amount of foundry aggregate and an acid-curable foundry resin, shaping the foundry mix into a foundry shape, and partially or totally removing water from the foundry shape. Athough not necessarily preferred because of economic considerations, it may be useful in some circumstances to apply heat to the foundry shape while water is being removed during the process.

The process is advantageous because the length of time required to cure cores and molds made by the no-bake process is reduced when water is partially or totally removed from the foundry shape during the curing process. Increased productivity results and is accomplished without adversely affecting the worktime and striptime of the sand mix. Furthermore, the foundry shape may be cured in the pattern or cured after the shape has been removed from the pattern. The foundry shapes prepared by the process have adequate tensile strengths for handling.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a photocopy of a photograph of a rectangular pattern box.

FIG. 2 is a photocopy of a photograph of a mold, which was conventionally cured, i.e. without sucking air through the mold, removed from the pattern after 35 minutes.

FIG. 3 is a photocopy of a photograph of the pattern of FIG. 1 showing a vacuum hose connected to the side of the pattern.

FIG. 4 is a photocopy of a photograph of a mold, which had ambient air pulled through it, removed from the pattern after 15 minutes.

FIG. 5 is a photocopy of a photograph of a mold, which has had ambient air pulled through it and hot air forced through it, removed from the pattern after 9½ minutes.

DETAILED DESCRIPTION OF THE INVENTION

Acid curable resins are resins that polymerize by the condensation of monomers and produce water as a reaction by-product. These resins typically are a mixture of polymers and unreacted monomers. The presence of the unreacted polymers in the resin is required in order to have a resin with a sufficiently low viscosity, so that the resin can be effectively mixed with sand. Typically, the viscosity of these resins will range from about 10 cP to 300 cP, preferably from about 20 cP to about 200 cP. Typically used as the acid-curable resin are furan resins or phenolic resins.

The furan resins may be conventional furan resins prepared by the homopolymerization of furfuryl alcohol (hereafter a conventional furan resin), or furans prepared by the homopolymerization of bis-hydroxymethylfuran (hereafter a bis-hydroxymethyluran resin), and mixtures of these resins. These resins are typically prepared by the homopolymerization of the monomer in the presence of heat, according to methods well-known in the art. The reaction temperature used in making the furan resins typically ranges from 95° C. to 105° C. Although not necessarily preferred, modified furan resins can also be used in the binder. Modified furan resins are typically made from furfuryl alcohol, urea formaldehyde, and formaldehyde at elevated temperatures under slightly alkaline conditions at a pH of from 7.0 to 8.0, preferably 7.0 to 7.2.

What all of these furan resins have in common is that they contain unreacted furfuryl alcohol, which forms water as a by-product when the resin is cured by a condensation reaction. The amount of unreacted furfuryl alcohol in the furan resin typically ranges from 50 weight percent to 95 weight percent, based upon the weight of the furan resin, preferably from 60 weight percent to 90 weight percent.

The foundry mix may also contain an activator is, which promotes the polymerization of furfuryl alcohol and is selected from the group consisting of resorcinol, resorcinol pitch, and bisphenol A tar. Preferably used as the activator is resorcinol. The foundry mix may also contain a bisphenol compound, e.g. bisphenol A, B, F, G, and H, preferably bisphenol A. The foundry mix may also contain a polyol. The polyol is selected from the group consisting of polyester polyols, polyether polyols, and mixtures thereof.

The acid-curable phenolic resins are phenolic resole resins. What all of these phenolic resole resins have in common is that they contain unreacted phenol as well as phenol formaldehyde polymers which form water as a by-product when the resin is cured by a condensation reaction. The amount of unreacted phenol in the phenolic resole resin typically ranges from 10 weight percent to 20 weight percent, based upon the weight of the phenolic resole resin, preferably from 12 weight percent to 16 weight percent.

Preferably, the phenolic resole resins are prepared by heating a mixture comprising an aldehyde and a phenol in the presence of a metal hydroxide catalyst.

Phenols suitable for preparing the phenolic resole resins include phenol and substituted phenols. The nature of the substituent can vary widely. Examples of substituted phenols include alkyl-substituted phenols, aryl-substituted phenols, cycloalkyl-substituted phenols, alkenyl-substituted phenols, alkoxy-substituted phenols, aryloxy-substituted phenols, and halogen-substituted phenols. Specific examples of phenols include phenol, o-cresol, m-cresol, p-cresol, 3,5-xylenol, 3,4-xylenol, 3,4,5-trimethyl phenol, 3-ethyl phenol, 3,5-diethyl phenol, p-butyl phenol, 3,5-dibutyl phenol, p-amyl phenol, p-cyclohexyl phenol, p-octyl phenol, 3,5-dicyclohexyl phenol, p-phenyl phenol, p-crotyl phenol, 3,5-dimethoxy phenol, 3,4,5-trimethoxy phenol, p-ethoxy phenol, p-butoxy phenol, 3-methyl-4-methoxy phenol, and p-phenoxy phenol. Preferably used is phenol.

Suitable aldehydes include any of the aldehydes typically used to prepare phenolic resole resins. Typically, the aldehydes contain from 1 to 8 carbon atoms. Examples include formaldehyde, acetaldehyde, propionaldehyde, and benzaldehyde. The most preferred aldehyde is formaldehyde which may be used as its aqueous solution or in its non-aqueous, polymeric form, e.g. paraformaldehyde.

Examples of catalysts used to prepare the phenolic no-bake resole resin include NaOH, KOH, Ca(OH)₂, other metal hydroxides, and mixtures thereof. Preferably used are NaOH and Ca(OH)₂.

Typically, at least one mole of aldehyde is used per mole of phenol make the phenolic resole resins of this invention. Preferably, the mole ratio of aldehyde to phenol is from about 1.2:1 to about 1.3:1.

Preferably a silane is included in the foundry mix. Silanes that can be used are represented by the following structural formula:
wherein R′ is a hydrocarbon radical and preferably an alkyl radical of 1 to 6 carbon atoms and R is an alkyl radical, an alkoxy-substituted alkyl radical, or an alkyl-amine-substituted alkyl radical in which the alkyl groups have from 1 to 6 carbon atoms. Examples of some commercially available silanes are Dow Corning Z6040; Union Carbide A-1100 (gamma aminopropyltriethoxy silane); Union Carbide A-1120 (N-beta(aminoethyl)-gamma-amino-propyltrimethoxy silane); Union Carbide A-1160 (ureido-silane); and DYNASLAN 1506.

Any liquid acid catalyst typically used in the no-bake process to cure the acid-curable resin can be used as the catalyst. Typically the catalyst is an inorganic, organic, or Lewis acid. Preferably, the curing catalyst is a strong acid such as toluene sulfonic acid, xylene sulfonic acid, benzene sulfonic acid, lactic acid, a mineral acid, hydrochloric acid, or sulfuric acid. Weak acids such as phosphoric acid can also be used to cure furan resins. Preferably, toluene sulfonic acid is used. Mixtures of catalysts can also be used.

The amount of curing catalyst used is an amount effective to result in foundry shapes that can be handled without breaking. Generally, this amount is from 1 to 45 weight percent active catalyst based upon the weight of the acid-curable resin, typically from 10 to 50, preferably 15 to 35 weight percent.

It will be apparent to those skilled in the art that other additives such as release agents, solvents, benchlife extenders, silicone compounds, etc. can be used and may be added to the binder composition, aggregate, or foundry mix.

The aggregate used to prepare the foundry mixes is that typically used in the foundry industry for such purposes or any aggregate that will work for such purposes. Generally, the aggregate is sand, which contains at least 70 percent by weight silica. Other suitable aggregate materials include zircon, alumina-silicate sand, chromite sand, and the like. Generally, the particle size of the aggregate is such that at least 80 percent by weight of the aggregate has an average particle size between 40 and 150 mesh (Tyler Screen Mesh).

The amount of resin used is an amount that is effective in producing a foundry shape that can be handled or is self-supporting after curing. In ordinary sand type foundry applications, the amount of resin is generally no greater than about 10% by weight and frequently within the range of about 0.5% to about 7% by weight based upon the weight of the aggregate. Most often, the resin content for ordinary sand foundry shapes ranges from about 0.6% to about 5% by weight based upon the weight of the aggregate in ordinary sand-type foundry shapes.

Although it is possible to mix the components of the binder with the aggregate in various sequences, it is preferred to add the curing acid catalyst to the aggregate and mix it with the aggregate before adding the binder.

Curing is accomplished by filling the foundry mix into a pattern (e.g. a mold or a core box) to produce a workable foundry shape. A workable foundry shape is one that can be handled without breaking.

The novel aspect of this process is that water is partially or totally removed from the foundry shape after it is shaped in the pattern. The water removed from the foundry shape includes water from the resin, water from the catalyst, and/or the water of reaction. Removing the water from the foundry shapes enhances the condensation reaction required to cure the furan binder, resulting in a more uniform through cure.

The method of removing the water of reaction from the foundry shape is not critical. For example, the water of reaction may be removed by forcing air (e.g. via a pump), preferably air with little or no humidity (dry air), and/or an inert gas through the foundry shape; pulling air and/or or an inert gas through the foundry shape; or by applying a vacuum to the foundry shape and sucking the water of reaction from it. Although the air and/or inert gas can be heated, the temperature of the air and/or or inert gas forced and/or sucked through the core or mold typically is not heated and ranges from about 20° C. to about 30° C. Based upon cost considerations, ambient air and/or an unheated inert gas are preferably used. The more rapidly the air is forced through the core or mold, the sooner the core or mold will cure.

To increase the curing rate, heat can also be applied to the foundry shape. Preferably, the heat is applied by blowing warm or hot air and/or and inert gas over and/or around the foundry shape. Because of cost, if heat is applied, it is preferable to apply the heat for a limited time, e.g. less than one hour, preferably less than one-half hour, and at lower temperatures, e.g. less than 300° C., preferably less than 250° C., and most preferably less than 100° C.

The core may be further treated if desirable or necessary. For example, the core may be coated with a refractory material to improve its performance, as is known to those skilled in the art.

Metal castings can be prepared from the workable foundry shapes by methods well known in the art. Molten ferrous or non-ferrous metals are poured into or around the workable shape. The metal is allowed to cool and solidify, and then the casting is removed from the foundry shape.

Abbreviations

The following abbreviations are used in the Examples:

• CHEM-REZ® 243 binder a furan resin having an average degree of polymerization of about 2 to 3, prepared by the homopolymerization of furfuryl alcohol under slightly basic conditions at a reflux temperature of about 100° C., which contains from about 60 to 70 weight percent of unreacted furfuryl alcohol, sold by Ashland Specialty Chemical Company, a division of Ashland Inc.
• CHEM-REZ® 55-816 LI catalyst a liquid no-bake furan catalyst, which is an aqueous solution of toluene sulfonic acid and aminor amount of methanol, sold by Ashland Specialty Chemical Company, a division of Ashland Inc.

EXAMPLES

The examples will illustrate specific embodiments of the invention. These examples, along with the written description, will enable one skilled in the art to practice the invention. It is contemplated that many other embodiments of the invention will be operable besides these specifically disclosed.

The foundry binders are used to make foundry cores by the no-bake process using a liquid curing catalyst to cure the furan binder. All parts are by weight and all temperatures are in ° C., unless otherwise specified.

Example A

Comparison Example where No Air was Sucked Through the Mold

Foundry mixes were prepared by mixing WEDRON 540 silica sand and about 1.0 weight percent (based on the weight of the sand) of CHEM-REZ 243 binder and about 30 weight percent of CHEM-REZ 55-816 LI (based on the weight on the resin) in a continuous mixer. The room temperature was about 23° C. and the relative humidity was about 41 percent.

The foundry mix containing the sand, binder, and catalyst were then forced into a rectangular wooden pattern box, which was 18″×18″×8″, having air vents on the bottom of the pattern (FIG. 1). FIG. 2 shows the mold, which was removed from the pattern after 35 minutes, where no air was forced through the mold. “Soft spots” were observed throughout the mold, which made handling more difficult.

This example illustrates that molds made with furan resins are slow curing.

Example 1

Example where a Suction was Applied to the Mold

Example A was repeated, except a hose was connected to the side of the pattern, as shown in FIG. 3. The hose was connected to a “DRY WALL VAC™” vacuum pump having a container capacity of about 16 gallons, manufactured by Love-Less-Ash. Ambient air (temperature of about 23° C.) was pulled through the mold in the pattern for about 15 minutes to vacuum water from the mold. The water vacuumed from the mold and was deposited in the container of the DRY WALL VAC vacuum pump and/or evaporated into the air.

FIG. 4 is a photocopy of a photograph of the mold, which was removed from the pattern 15 minutes after the foundry mix was added to the pattern. The mold was easy to handle and substantially cured.

FIGS. 1 and 4 clearly show the advantage of using the process as described in this invention. When no air was sucked through the mold, the mold was “soft” and could not be easily handled. When air was sucked through the mold, the mold cured more rapidly and was substantially cured after 15 minutes.

Example 2

Example where Hot Air was Forced Through the Mold While Suction was Applied

Example 1 was repeated, except the pattern containing the mold was covered. The cover contained an opening through which hot air was forced with a small blower, while ambient air was also being sucked through the mold.

FIG. 5 is a photograph of the mold, which was removed from the pattern 9½ minutes. The mold was fully cured. This example illustrates the advantage of blowing heat through the mold while sucking ambient air through the mold.

Claims

1. A process for preparing a foundry shape comprising:

A. preparing a foundry mix comprising a major amount of foundry aggregate, an effective binding amount of an acid-curable resin, and a catalytically effective amount of an acid catalyst;

B. shaping the foundry mix into a foundry shape; and

C. partially or totally removing water from the foundry shape.

2. The process of claim 1 wherein the acid-curable resin is selected from the group consisting of furan resins and phenolic resins.

3. The process of claim 2 wherein the acid catalyst is selected from the group consisting of sulfonic acid, toluene sulfonic acid, benzene sulfonic acid, and mixtures thereof.

4. The process of claim 3 wherein the foundry mix further comprises a silane.

5. The process of claim 4 wherein the resin is a furan resin containing unreacted furfuryl alcohol in the amount of about 50 to about 95 weight percent, wherein said weight percent is based upon the weight of the furan resin.

6. The process of claim 4 wherein the resin is a phenolic resole resin containing unreacted phenol in the amount of about 12 to about 16 weight percent, wherein said weight percent is based upon the weight of the phenolic resole resin.

7. The process of claim 5 wherein the foundry mix comprises: (a) at least 93 weight percent aggregate, and (b) from about 1 weight percent to about 5 weight percent furan resin, where said weight percents are based upon the weight of the foundry mix.

8. The process of claim 7 wherein the amount of acid catalyst is from about 10 to to about 50 weight percent, based upon the weight of the furan resin.

9. The process of claim 5 wherein the foundry mix comprises: (a) at least 0.93 weight percent aggregate, and (b) from about 1 weight percent to about 5 weight percent phenolic resin where said weight percents are based upon the weight of the foundry mix.

10. The process of claim 9 wherein the amount of acid catalyst is from about 10 to about 50 weight percent, based upon the weight of the phenolic resin.

11. The process of claims 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 wherein foundry shape is subjected to heat while water is being removed from the foundry shape.

12. The process of claim 11 wherein the heat is applied by blowing air and/or an inert gas having a temperature of less than 100° C. over and/or around the foundry shape.

12. The process of claims 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 wherein the water is removed by pulling air and/or an inert gas around and/or through the foundry shape.

13. The process of claims 12 wherein foundry shape is subjected to heat while water is being removed from the foundry shape.

14. The process of claim 13 wherein the heat is applied by blowing air and/or an inert gas having a temperature of less than 100° C. over and/or around the foundry shape.

15. A process for preparing a foundry shape comprising:

A. preparing a foundry mix comprising a major amount of foundry aggregate, an effective binding amount of an acid-curable resin, and a catalytically effective amount of an acid catalyst;

B. shaping the foundry mix into a foundry shape; and

C. partially or totally removing water from the foundry shape by pushing air and/or an inert gas around and/or through the foundry shape.

16. The process of claim 15 wherein the acid-curable resin is selected from the group consisting of furan resins and phenolic resins.

17. The process of claim 16 wherein the acid catalyst is selected from the group consisting of sulfonic acid, toluene sulfonic acid, benzene sulfonic acid, and mixtures thereof.

18. The process of claim 17 wherein the foundry mix further comprises a silane.

19. The process of claim 18 wherein the resin is a furan resin containing unreacted furfuryl alcohol in the amount of about 50 to about 95 weight percent.

20. The process of claim 19 wherein the resin is a phenolic resole resin containing unreacted phenol in the amount of about 12 to about 16 weight percent.

21. The process of claim 20 wherein the foundry mix comprises: (a) at least 93 weight percent aggregate, and (b) from about 1 weight percent to about 5 weight percent furan resin, where said weight percents are based upon the weight of the foundry mix.

22. The process of claim 21 wherein the amount of acid catalyst is from about 10 to to about 50 weight percent, based upon the weight of the furan resin.

23. The process of claim 22 wherein the foundry mix comprises: (a) at least 93 weight percent aggregate, and (b) from about 1 weight percent to about 5 weight percent phenolic resin where said weight percents are based upon the weight of the foundry mix.

24. The process of claim 23 wherein the amount of acid catalyst is from about 10 to about 50 weight percent, based upon the weight of the phenolic resin.

25. The process of claims 15, 16, 17, 18, 19, 20, 21, 22, 23, or 24 wherein foundry shape is subjected to heat while water is being removed from the foundry shape.

26. The process of claim 25 wherein the heat is applied by blowing air and/or an inert gas having a temperature of less than 100° C. over and/or around the foundry shape.

27. A process for preparing a foundry shape comprising:

A. preparing a foundry mix comprising a major amount of foundry aggregate, an effective binding amount of an acid-curable resin, and a catalytically effective amount of an acid catalyst;

B. shaping the foundry mix into a foundry shape; and

C. partially or totally removing water from the foundry shape by subjecting the foundry shape to a vacuum.

28. The process of claim 27 wherein the acid-curable resin is selected from the group consisting of furan resins and phenolic resins.

29. The process of claim 28 wherein the acid catalyst is selected from the group consisting of sulfonic acid, toluene sulfonic acid, benzene sulfonic acid, and mixtures thereof.

30. The process of claim 29 wherein the foundry mix further comprises a silane.

31. The process of claim 30 wherein the resin is a furan resin containing unreacted furfuryl alcohol in the amount of about 50 to about 95 weight percent.

32. The process of claim 31 wherein the resin is a phenolic resole resin containing unreacted phenol in the amount of about 12 to about 16 weight percent.

33. The process of claim 32 wherein the foundry mix comprises: (a) at least 93 weight percent aggregate, and (b) from about 1 weight percent to about 5 weight percent furan resin, where said weight percents are based upon the weight of the foundry mix.

34. The process of claim 33 wherein the amount of acid catalyst is from about 10 to about 50 weight percent, based upon the weight of the furan resin.

35. The process of claim 34 wherein the foundry mix comprises: (a) at least 93 weight percent aggregate, and (b) from about 1 weight percent to about 5 weight percent phenolic resin where said weight percents are based upon the weight of the foundry mix.

36. The process of claim 35 wherein the amount of acid catalyst is from about 10 to about 50 weight percent, based upon the weight of the phenolic resin.

37. The process of claims 27, 28, 29, 30, 31, 32, 33, 34, 35, or 36 wherein foundry shape is subjected to heat while water is being removed from the foundry shape.

38. The process of claim 37 wherein the heat is applied by blowing air and/or an inert gas having a temperature of less than 100° C. over and/or around the foundry shape.