Compositions and methods for improving casting quality and mold sand additives

Abstract

A method of forming a dry molding sand additive may include recovering a non-sand fraction from a foundry waste material and adding the non-sand fraction to a dry molding sand additive formulation to form a dry molding sand additive. Adding the non-sand fraction to the dry molding sand additive formulation may reduce the amount of fresh clay and carbon to produce the dry molding sand additive. A method of forming a molding sand additive may include recovering a waste molding sand additive composition having a clay or carbon content differing from a desired clay and carbon content, recycling the waste molding sand additive as a raw material in production of a fresh molding sand additive, and adjusting the amount of fresh clay or carbon added during production of the fresh molding sand additive to achieve the desired clay and carbon content.

Claims

1. A method of forming a dry molding sand additive having a maximum moisture content of 30% by weight, comprising the steps of: recovering a non-sand fraction from a foundry waste material, wherein said non-sand fraction comprises a recovered clay component and a recovered carbon component further comprising at least partially dewatering the non-sand fraction and wherein said dewatering includes spray drying; and adding the non-sand fraction to a dry molding sand additive formulation to form a dry molding sand additive to reduce an amount of fresh clay and carbon to produce the dry molding sand additive.

2. The method of forming a dry molding sand additive of claim 1, wherein said foundry waste material comprises bag house dust.

3. The method of forming a dry molding sand additive of claim 1, wherein said foundry waste material comprises overflow green sand.

4. The method of forming a dry molding sand additive of claim 1, wherein said foundry waste material comprises a mixture of bag house dust and overflow green sand.

5. The method of forming a dry molding sand additive of claim 1, wherein said foundry waste material comprises molding waste.

6. The method of forming a dry molding sand additive of claim 1, wherein a moisture content of the dry molding sand additive is in a range from about 0% to about 15% by weight.

7. The method of forming a dry molding sand additive of claim 1, further comprising adjusting a composition of the dry molding sand additive such that a methylene blue adsorption value of the dry molding sand additive is in a range from about 70% to about 95%.

8. The method of forming a dry molding sand additive of claim 1, wherein a clay content of the dry molding sand additive is in a range of from about 60 wt % to about 90 wt %.

9. The method of forming a dry molding sand additive of claim 1, wherein a carbon content of the dry molding sand additive is in a range of from about 10 wt % to about 25 wt %.

10. The method of forming a dry molding sand additive of claim 1, further comprising disrupting hydrogen bonding of the non-sand fraction by heating the non-sand fraction to a temperature in a range from about 100 C. and about 350 C.

11. The method of forming a dry molding sand additive of claim 1, wherein a green sand prepared using the dry molding sand additive has a compactability greater than about 45%.

12. The method of forming a dry molding sand additive of claim 1, wherein a green sand prepared using the dry molding sand additive has a green compression strength greater than about 15.5 N/cm.sup.2.

13. The method of forming a dry molding sand additive of claim 1, wherein a green sand prepared using the dry molding sand additive has a green shear strength greater than about 3.5 N/cm.sup.2.

14. The method of forming a dry molding sand additive of claim 1, wherein a green sand prepared using the dry molding sand additive has permeability greater than about 65.

15. The method of forming a dry molding sand additive of claim 1, wherein a green sand prepared using the dry molding sand additive has a dry compression strength greater than about 36 N/cm.sup.2.

16. A method of forming a molding sand additive having a maximum moisture content of 30% by weight, comprising the steps of: recovering a non-sand fraction from an overflow green sand foundry waste, wherein said non-sand fraction comprises a recovered clay component and a recovered carbon component further comprising at least partially dewatering the non-sand fraction and wherein said dewatering includes spray drying; recovering a sand fraction from a green sand bag house dust recovery installation; and adjusting relative levels of clay and carbon in said non-sand fraction.

17. A method of forming a molding sand additive having a maximum moisture content of 30% by weight, comprising the steps of: recovering a waste molding sand additive composition having a clay or carbon content differing from a desired clay and carbon content; wherein recovering a recovered clay component or a recovered carbon component further comprises at least partially dewatering, wherein said dewatering includes spray drying recycling the waste molding sand additive as a raw material in production of a fresh molding sand additive; and adjusting an amount of at least one of fresh clay or carbon added during production of the fresh molding sand additive to achieve the desired clay and carbon content based on the clay or carbon content of the recycled molding waste sand additive.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a graph of deformation of exemplary dry molding sand additives.

(2) FIG. 2 shows a graph of hot strength compression of exemplary dry molding sand additives.

(3) FIGS. 3A-3C show images of exemplary dry molding sand additives.

DETAILED DESCRIPTION

(4) It is to be understood that the figures and descriptions of the present disclosure have been simplified to illustrate elements that are relevant for a clear understanding of the disclosure, while eliminating for purposes of clarity, other elements that may be well known or understood by those of skill in the art.

(5) The present disclosure describes systems and methods that reduce overall waste at casting facilities while at the same time providing valuable pre-mix, such as molding sand additives, used in cast molding. The process of breaking used sand molds after casting results in a significant volume of waste products. Some of that waste (molding waste) is unable to be reused in generating new sand molds and is handled manually for discarding.

(6) A large volume of foundry waste, however, can be captured by the foundry's air evacuation system, for example, when air from the foundry facility is captured and passed through a large filtration system called a bag house. The solid particles collected there are generally referred to as bag house dust and are made up of substantial amounts of clay and organic material, in addition to sand. In some instances, bag house dust may typically include from about 15 wt % to about 70 wt % by weight sand, from about 20 wt % to about 85 wt % by weight bentonite clay, and from about 10 wt % to about 40 wt % by weight organic additives. The high levels of bentonite clay and organic additives present in bag house dust make it a potentially valuable source of raw materials for additives used in green cast molding.

(7) Foundry waste can also be captured in the form of green overflow sand or molding waste. Molding waste may be captured when green sand molds and cores are broken down after casting. In some green sand foundries, the molding waste may contain from about 80% by weight to about 90% by weight sand, from about 6% to about 10% by weight bentonite clay, and from about 1% to about 4% by weight organic additives. Molding waste includes sand that is coated with bond as well as individual particles of sand, bentonite, and organic additives. Green overflow sand refers to excess foundry green molding sand (wet) that is generated in the metal casting process.

(8) The methods and systems of this disclosure may utilize one or more of captured bag house dust, molding waste, or green overflow sand to generate a dry molding sand additive. Dry refers to the feel (touch) of the molding sand additive, not that it is necessarily moisture free. Commercial molding sand additive typically has a maximum of 15% moisture content by weight. In this disclosure, the dry molding sand additive would be similar, however with a maximum of 30% moisture content by weight, for example, a maximum of 20% moisture content by weight.

(9) In some embodiments, the methods and systems of this disclosure may utilize one or more of captured bag house dust, molding waste, or green overflow sand to generate a molding sand additive for cast molding. For example, the sand and non-sand fractions of the bag house dust, molding waste, or green overflow sand are separated from one another using methods known in the art. This separation may allow for adjusting of component levels in the non-sand fraction in the molding sand additive. The high levels of clay and organic additives found in the raw or separated non-sand fraction allow recovered molding waste products to provide important components for casting compositions that can be reused or recycled with non-recycled or fresh materials, such as non-recycled non-sand fractions or non-recycled sand fractions. In some embodiments, the resulting molding sand additive or molding sand composition may include components of previously recycled non-sand or sand fractions.

(10) In some embodiments, the non-sand fraction of the molding waste may have low levels of other impurities (e.g., sulfur) when compared to commercially available pre-mix and thus represents an improvement over the prior art. In some embodiments, the sulfur may be less than 0.03% by weight of the mixture.

(11) In some embodiments, the collected molding waste may be separated using a hydraulic separation process, either alone or in combination with other separation processes.

(12) In some embodiments, the water content of the recovered molding waste may be reduced through dewatering processes, such as, for example, spray drying, flocculation, hydraulic separation, and/or cross-flow filtration. Water reduction may reduce the moisture content of the dry molding sand additive to between 0% and 20% by weight. According to some embodiments, the moisture content of the non-sand fraction may be kept at above 20% by weight, or above about 25% by weight, to maintain beneficial properties of hydrated bentonite in the non-sand fraction.

(13) A slurry of recovered material for use in a molding sand additive or molding sand composition may contain a sand component, a non-sand component, or a combination of both components. If desired, the slurry may be dewatered partially or completely according to a specific requirement for a casting process.

(14) The relative levels of various components found in the non-sand fraction of the recovered portion of the molding waste may be adjusted by addition of clay or organic compounds to achieve the appropriate concentrations to form a molding sand additive having desired properties. The addition of clay or organic components may include non-recycled or fresh clay or organic compounds that are not recovered from a sand molding process. According to some embodiments, the addition of clay or organic components may include previously recycled clay or organic components from a sand molding process. The specific amount of additives will depend on the specific composition of the recovered portion of the molding waste, and will depend on the requirements of the new molding sand composition dictated by customers or the needs of the next casting. The pH of the molding sand additive is generally basic and may be in the range of a pH of about 7 to about 11. Once established, the molding sand additive may be combined with molding sand that has been previously used in a casting process to generate new molding sand able to be used effectively in casting processes.

(15) According to some embodiments, the use of recycled non-sand fractions from molding waste may improve the properties of the dry molding sand additive, such as, for example, by increasing one or more of the green compression strength, the green shear strength, the permeability, the dry compression strength, and/or the cone jolt toughness. The use of recycled non-sand fractions from molding waste may improve the properties of the dry molding sand additive, such as, for example, by decreasing the friability of the dry molding sand additive.

(16) Several specific examples are provided. Each example includes a batch of sand molding medium for forming moldings to be used in the casting of iron articles, although other metals could be cast. The batches of sand molding media in the several examples have commonalities, which facilitate an appreciation of the improvements of the present disclosure.

Examples

(17) A base composition of molding sand additive was obtained containing 65% by weight bentonite (sodium bentonite) clay and 35% by weight of a carbon component (sea coal). Non-sand fractions of clay components and carbon components of bag house dust were recovered using hydraulic separation. The recovered non-sand fractions were separated into two batches and spray dried to dewater the recovered fraction. The first spray-dried batch was dewatered to a 4.4% moisture content (low moisture or LM). and the second spray-dried batch was dewatered to about 18.4% (high moisture or HM). The recovered HM and LM non-sand fractions were then mixed with the base material as shown in Table 1 below.

(18) TABLE-US-00001 TABLE 1 Recovered Spray Recovered Spray Sample Base (wt %) Dried LM (wt %) Dried HM (%) Base 100 0 0 LM 0 100 0 HM 0 0 100 LM25 75 25 0 LM50 50 50 0 LM75 25 75 0 HM25 75 0 25 HM50 50 0 50 HM75 25 0 75

(19) Each sample was then mixed with 7 wt % clay (sodium bentonite) and mulled for seven minutes using a Simpson Laboratory Muller. Water was then added to each sample until a compactability of about 46% was achieved.

(20) Each example was formed into a standard molding sand according to the specified test methods and tested to determine its physical characteristics, including green strength, dry strength, and permeability, using foundry testing methods as outlined by the American Foundry Society in their published Mold and Core Test Handbook, which is hereby incorporated by reference. The procedures used can be found in the edition published by the American Foundry Society (www.afsinc.org), 3rd Edition, 2001. The testing references include AFS 2110-00-s (Clay, AFS Method), AFS 2201-00-s, (Sand Mixture Preparation, Clay Method), AFS 2206-00-s (Tensile, Wet, Mold Sand), AFS 2204-00-s (Shear Strength, Green or Dried), AFS 2211-00-s (Methylene Blue Clay test), AFS 2218-00-s (Moisture Determination, Forced Hot Air Method), AFS 2220-00-s (Compactability of Molding Sand Mixtures, Rammer Method), AFS 2248-00-s (Friability), AFS 2249-00-s (Cone Jolt Toughness), AFS 5234-00-s (Compression Strength, Hot), all of which are incorporated by reference.

(21) The results of the testing are shown in Table 2 below.

(22) TABLE-US-00002 TABLE 2 Test Base LM HM HM25 LM25 HM50 LM50 HM75 LM75 Moisture (%) 2.1 2.7 3.0 2.8 2.5 2.4 2.7 2.7 2.8 Compactability 45 47 47 45 46 45 46 46 44 (%) Green 16.6 15.6 16.1 17.2 17.5 17.1 16.7 15.9 17.1 Compression Strength (N/cm.sup.2) Green Shear 3.9 3.3 3.8 4.5 4.0 3.9 3.8 3.6 4.3 Strength (N/cm.sup.2) Permeability 74 64 63 75 78 73 77 75 76 Wet Tensile 0.38 0.14 0.14 0.42 0.41 0.34 0.34 0.20 0.23 Strength (N/cm.sup.2) Dry 36 80 94 40 42 58 62 77 56 Compression Strength (N/cm.sup.2) Cone Jolt 23 36 42 34 35 33 40 46 36 Toughness Friability (%) 7.4 1.7 2.3 4.7 5.2 3.9 3.8 2.0 4.0

(23) As shown in Table 2 above, the green compression strength, green shear strength, and permeability for each sample LM25, LM50, LM75, HM25, HM50, and HM75 either increased or remained comparable to the base material. The wet tensile strength increased for both HM25 and LM25, but decreased slightly for HM50 and LM50. Dry compression strength and cone jolt toughness both increased significantly for each of LM25, HM25, LM50, HM50, LM75, and HM75. Friability decreased significantly for each of LM25, HM25, LM50, HM50, LM75, and HM75. These results show that recovered spray dried fractions of molding waste can be recycled into a sand mold additive without adversely affecting the properties of the additive. For several properties, as shown in Table 2, the properties of the additive, such as cone jolt toughness, friability, permeability, and various strength measurements may be increased by adding the recovered material.

(24) Deformation of the base sample and samples LM, HM, LM25, and HM25 was measured at various pressures from 0 psi to 200 psi using a Dietert Dialotometer with a deformation gauge and graphed in a computer program. FIG. 1 shows the results of the deformation test. As shown in FIG. 1, each of samples LM, HM, LM25, and HM25 exhibited slightly less deformation than the base material, with LM25 and HM25 exhibiting the lowest amount of deformation.

(25) Hot compression strength of the base sample and samples LM, HM, LM50, and HM50 was measured using a Dietert Dialotometer with a deformation gauge and graphed in a computer program at four temperatures: 538 C. (1000 F.), 816 C. (1500 F.), 982 C. (1800 F.), and 1093 C. (2000 F.). The specimens were prepared using a pneumatic squeezer method (AFS Mold and Core Test Handbook method AFS 2221-00-s) in a plurality of cylinders with 53 to 55 gram specimens based upon the density of the prepared molding sand, the results of which are shown in FIG. 2. As shown in FIG. 2, the hot compression strength for LM, HM, LM50, and HM50 increased significantly as compared to the base material from 700 C. to about 1000 C., and samples HM50 and LM50 showed slightly higher hot compression strength relative to the base material between about 1000 C. and about 1100 C.

(26) FIGS. 3A-3C shows magnified images of the base sample (FIG. 3A) with additives having 5% (FIG. 3B) and 10% (FIG. 3C) recovered non-sand fractions, which were spray dried to form dry molding sand additives. As shown in FIGS. 3A-3C, the visual composition of the dry molding sand additives is unchanged with the addition of the recovered non-sand components.

(27) As shown in these examples, recovered non-sand fractions can be recovered from molding waste, spray dried, and recycled or reintroduced into molding sand additives to beneficially affect the properties of the molding sand additives. The components and physical properties of the raw materials generated from molding waste may be adjusted through addition of components or purification (e.g., through water reduction) to obtain appropriate final levels for a foundry-ready molding sand additive. The present disclosure represents an improvement over prior art both in reduction of foundry waste and production of high quality molding sand additives for casting processes.

(28) Nothing in the above description is meant to limit the scope of the claims to any specific composition or structure of components. Many substitutions, additions, or modifications are contemplated within the scope of the present invention and will be apparent to those skilled in the art. The embodiments described herein were presented by way of example only and should not be used to limit the scope of the claims.