MXPA94003437A - A method to improve the properties of the recovered sand, used in the production of molds and nucleos of fundic - Google Patents

Abstract

The present invention relates to a composition for use in the manufacture of casting molds and cores, which comprises a mixture of a particulate refractory aggregate with, as an additive thereof, a particulate clay, characterized in that the particulate refractory aggregate contains elutable alkali and It comprises reclaimed sand from cast molds and cores of cast iron and optionally new sand and because the particulate clay is capable of reacting with alkali metal salts and has a particle size of less than 0.5mm and is present in an amount of 0.05% to 5% by weight based on the weight of the sand recovered

Description

A METHOD TO IMPROVE THE PROPERTIES OF RECOVERED SAND. USED IN THE PRODUCTION OF MOLDS AND FOUNDRY NUCLEI mmmmm * PaHipe * María Taaaaaiat, a Naloa nationality, with gift in 1 * Cnaavia daa llf a, 7 * f4ß ßt. Martin úm Boneharrilla, Franciaj Vajriß Mabart. Qaawal, «your nationality FraMtOiAf «ialMHia4N H? Ia ^ lJHV * a ANM * FMHMMMMf of Wffil OTMI 1.1 na" lf daaaaa, can address to * KlaianlaaJc 3LÍ # afta * CV * INMI. F? Í9t B ^ ** 'jf # «MUM ^ MMI Aft &?? &MaVMat * # gives tMtff t flMWi 11 ??? Grané Qußvilly, France. WemWuWnWhKOkt Bordaa Franca • ««, ** 4th nationality franoaaa, coa doaicllio «n 3 ßt 5 Kuß Barba, BP 102 7tasß Dßvilla-laa ~ Ji» nan, France.

EXTRACT The present invention relates to a method for the treatment of reclaimed sand, to improve its utility in the production of new casting molds and cores. DESCRIPTION The use of alkaline phenolic resins, cured with ester, for the production of casting molds and cores, has had a major influence in the industry, due to the improvements in the possible finish of castings and in the environmental benefits achieved. The techniques were first developed commercially by Borden (United Kingdom) Limited. Examples of these techniques are described in EP-A-085512 and EP-A-086615. Despite the advantages achieved by the use of ester-cured phenolic resins, a series disadvantage is that the cohesion forces obtained with the sands recovered from the molds and cores made with phenolic resins cured with ester, are generally much lower than the forces obtained with a new sand or with sand recovered from other processes. This is also true in silicate resin systems cured with ester and CO2-. For environmental and commercial reasons, it is advisable to recycle as much reclaimed sand as possible and thus limit, as far as possible, the discharge of the waste sand. Several treatments have been proposed that seek to improve the cohesion strength of phenolic resins cured with ester in the recovered sand. Most common treatments are mechanical friction and thermal recovery, although other processes, such as wet scrubbing and the use of additives, have been used. One of the most successful additives employed is that described in patent EP-A-130584. The procedures that employ the thermal recovery of the sand (which reduce the loss in ignition due to the accumulation of organic residues) can result in a greater cohesion force than the sand treated by simple mechanical rubbing. There is some evidence (for example Sedla et al., In Cast Metals, Vol. 3, 2, 1990) that suggests that the poorer cohesive forces in the reclaimed sand correlate with the level of the alkali eluble in the sand. The heat treatment alone does not reduce the level of the eluble alkali. In fact, it can be increased by the release of the metal salts from the organic matrix. Also, the presence of the alkali metal can cause the sand particles to melt through the formation of glass, which prevents the use of certain heat treatment processes, such as those using fluidized beds. We have now found that by using certain inorganic additives, the levels of the alkali metal eluble in the particulate refractory aggregates, which contain the eluble alkali, can be drastically reduced. The invention, which is based on this discovery, is particularly applicable in reducing the level of the alkali eluble in the sand recovered or recovered from the molds and spent cores of the foundry, which have been produced with the use of alkaline binder systems to join the sand with each other. Also, the problem of silicate melting, associated with the presence of these materials during thermal recovery, can be eliminated according to the invention.

An object of the present invention is to provide a novel treatment of the particulate refractory aggregate, which contains eluble alkali, such as recovered or recovered from cast molds or cores of the foundry, to improve its usefulness in the production of new molds and cores. A further object is to provide a casting molding composition, which contains the refractory particulate aggregates, recovered or recovered from the molds and spent cores of the foundry. Still another object is to provide a method for obtaining casting molds and cores that use the refractory particulate aggregate recovered or recovered from the molds and spent cores of the foundry. The present invention provides a particulate refractory composition for use in the manufacture of casting molds and cores, which comprises a mixture of refractory aggregates particulate containing alkali eluble with, as an additive thereof, a particulate active clay, which has a particle size less than 0.5 mm. The use of the particulate active clay additive in the composition has the effect of improving the resistances of the casting molds and cores, which are produced using the composition, in comparison with the case where no active clay additive is incorporated in the refractory material. particulate By the term "particulate active clay additive" is meant a particulate clay having a particle size of less than 0.5 mm, which is capable of reacting with the eluble alkali present on the surfaces of the particulate refractory aggregate material and which is added to the particulate refractory aggregate to achieve the benefits of the present invention. Thus, the particulate active clay additive will not be confused with clays that can naturally occur in a refractory aggregate material, such as foundry sand. These naturally occurring clays are, in any case, inactive towards the alkali eluble in such aggregates which, typically, according to the present invention, will be derived from the recovery of spent molds and cores. The invention provides special benefits, where the aggregate material of the foundry, obtained from the spent molds and cores of the foundry, is recycled for use in the production of new casting molds and cores. The reclaimed sand, which has been treated with the particulate clay, according to the invention, has been found to provide improved cohesion forces with a number of binder systems, so that a vast majority of the sand used can be recycled.

The particulate clay, which can be a thermally treated clay, reacts with the alkali metal salts, which are present on the surface of the refractory material, so that the ions of the alkali metals are unable to affect, in any substantial way, the subsequent reaction of the binding systems used in the production of casting molds and cores, to join together the particulate refractory material. The reactions of these materials with alkali are well known (see RM Barrer, in Chemistry of soil minerals, Part XI Hydrothermal trans formations of metakao-linite in potassium hydroxide (Chemistry of soil minerals, Part XI. -caolinite in potassium hydroxide), J. Chem-Soc., Dalton Transactions, No. 12 (1872) pages 1254-9; GL Berg et al. in Nature of the Thermal Effects of the Reaction of Kaolinite with Some Bases (Nature of the thermal effects of the reaction products of kaolinite with some bases), Izv. Vyss, Ucheb, Zaved, Khim, Tekhnol., 13, 1 (1970), pages 93-6, and a revision is provided by Davidovits, Joseph, Geopolymer '88, Vol.l, pages 25-48). The composition of the "polymeric" products and their use for preparing molded articles has been described in WO 92/00816 and EP-A-026687. The specific intervals that cover the level of Na2? and K2O are specified for these compositions for satisfactory use in the production of the molded articles and the inorganic material is the main binder for the molded articles produced therefrom. Other applications described for this type of compositions have included the preparation of ceramic-ceramic composites (WO 88/02741) and the above high strength concrete compositions (EP-A-153097). The clays have been used in the process of • Greensand 'for many years, as part of the binder system for foundry molds. This process again relies on the clay to impart resistance to the molded article, which acts to bond the refractory aggregate material. (Kirk Othmer, Clays (study), pp. 212-4). The particulate clay that can be used in the present invention can be of any type that is capable of reacting with the alkali metal salts. Examples of suitable materials include kaolins, heat-treated kaolins, smectites, montmorillonites, bentonites, see iculites, attapulguitas, serpentinos, glauco-nitas, illitas, allophan and imogolita. Of these materials, kaolin and heat-treated kaolin are preferred. It has been found that, to be effective in the present invention, the particle size of the particulate clay must be less than 0.5 mm. The use of a particle size greater than 0.5 mm has been found to result in no or only very little improvement in the cohesive strength of the sand recovered in the production of molds and cores. In the present invention, the level of Na2? or the K2O, obtained by the treatment of the recovered particulate refractory aggregate material, with the particulate clay, is not important, except that it will be a normal practice to add enough particulate clay to the aggregate material, to treat the available alkali metal ions. The level of addition required will be modest and can be determined by measuring the free or elutable alkali metal content of the particulate aggregate material. This will normally not exceed 1% and, therefore, the additions of the particulate clay will be in such an amount in the range of 0.05 to 5%, preferably 0.05 to 2%, by weight, based on the weight of the aggregate of particulate clay having a particle size of less than 0.5 mm, usually adequate to generate the desired effect. The water is incorporated, preferably, into the mixture of the particulate refractory aggregate and the particulate active clay., in order to improve the performance of the composition. The water can be added separately or it can be previously mixed with the particulate clay to form an aqueous paste of the clay, which can then be added to the refractory aggregate. Typically, water will be added in an amount of 0.05 to 5%, preferably 0.05 to 2% by weight, based on the weight of the particulate refractory material. The particulate refractory aggregate that can be treated with the particulate clay, according to the present invention, can be any type of aggregate that can be used in the production of casting molds and cores and which contains alkali eluble. The aggregate can be one that occurs naturally or can be spent material from an industrial process. The invention, of course, is especially useful for treating aggregates, particularly sand, which is recovered or recovered from spent foundry molds and cores. By the expression of 'spent foundry molds and cores', these molds and cores are understood to remain after the casting of the metal and the removal of the configurations of the molten metal in a foundry, and the pieces of waste and broken thereof. . The aggregate can be subjected to a mechanical recovery treatment before it is mixed with the particulate clay or it can be subjected to a heat treatment. The recovery processes are often accompanied by a separation of the fine particles from the aggregate. Thus, any active clay that may be present is probably lost. Therefore, it is beneficial to make a recent addition of clay after each recovery cycle. According to a preferred embodiment, the spent cast aggregate containing the eluble alkali is mixed with the particulate clay and, optionally, the water before any heat recovery treatment, and the mixture is then subjected to a thermal recovery treatment. This has the advantage that the presence of the particulate clay in the thermal recovery stage prevents or reduces glass formation or "sintering" which would otherwise occur. Likewise, of course, thermal recovery reduces the level of organic contaminants in the aggregate, which could also adversely affect the characteristics of the cohesive force. The problem of poor strength with reclaimed sand is more severe when the binder used to make the mold and the core has been an ester-cured phenolic resin or an ester-cured silicate or CO2. Therefore, the invention is more appropriate when attempting to rejoin reclaimed sand from this source. Many smelting operations can use more than one binder system, so that reclaimed sand can be derived from a number of processes. Alternatively, a foundry can be selected to add a proportion of new sand to the reclaimed reclaimed sand, or both practices can be applied. According to these circumstances, the cohesion force can be significantly better when the recovered sand is re-united only from molds and nuclei joined with silicate or a phenolic resin, cured with ester. In general, cohesive forces increase with increasing amounts of new sand or sand recovered from other processes. Observable improvements in the cohesion forces are obtained by the incorporation of the inorganic additive when the majority of the refractory aggregate is recovered from the molds and cores made with phenolic binders cured by ester or silicates cured by ester or C02. According to a preferred embodiment, the present invention provides a method for preparing a particulate refractory composition for use in the manufacture of casting molds and cores from cast molds and worn cores, formed of a refractory material and a binder , selected from an ester-cured phenolic resin binder, an ester-cured silicate binder and a silicate binder cured by CO2, this method comprises the steps of breaking the spent casting molds or cores and mixing the resulting broken material with a particulate clay, which has a smaller particle size 0.5 mm and, optionally, water. Preferably, the mixture is then subjected to a heat treatment at elevated temperature.

The above method is especially useful in the case where the refractory material of the spent molds and cores is sand. The heat treatment, when employed, is preferably carried out under thermal recovery conditions, for example at a temperature of 400 to 1000 ° C, preferably 500 to 900 ° C, and typically of about 800 ° C, for 1 to 12, typically 1 to 4. hours. The method, in accordance with this preferred embodiment, further preferably comprises the step of removing the powder and / or fine particles during and / or after the heat treatment. Traditionally, this is achieved by the application of suction to the particulate refractory material to remove the lighter particles that can be collected in a cyclone for discharge. The amount of fine particles removed can be controlled by controlling the degree of suction applied. The mixture of the particulate refractory aggregate containing the eluble alkali and the particulate clay, prepared as described above, with or without any subsequent heat treatment, or the material obtained after the heat treatment, with the fine particles removed or not, can be used as part or all of the particulate refractory material in the casting molding composition, together with a curable binder system. Alternatively, the aggregate containing eluble alkali, the particulate clay and, optionally, the water, may be incorporated without the above mixture into a casting molding composition together with the binder. Thus, the present invention provides a casting molding composition comprising a mixture of a particulate refractory aggregate containing eluble alkali, a liquid curable binder, in an amount of 0.5 to 5% by weight, based on the weight of the refractory aggregate , and a particulate clay, which has a particle size of less than 0.5 mm. The particulate clay, typically, is present in an amount of 0.05 to 5%, preferably 0.05 to 2%, by weight of the refractory aggregate. The binder system of the foundry can be any of the usual systems known in the art and the details of such systems will not be provided here. However, for practical purposes, greater benefits are achieved when the casting binder system used is one selected from the alkaline phenolic resin cured with an ester, liquid or gaseous curing agent, or a mixture thereof, the silicate cured with a liquid ester or a silicate cured with carbon dioxide. Alkaline phenolic resin binders are well known in the art and typically comprise an aqueous alkaline resin produced by the condensation of a phenolic compound, usually the phenol itself, with an aldehyde, usually the for-maldehyde, at a molar ratio of the phenol: aldehyde from 1: 1.2 to 1: 3, in the presence of a base, such as NAOH or KOH. These alkaline phenolic resins are known to cure or harden by reaction with an ester, such as a carboxylic acid ester, an organic carbonate or a lactone or a mixture of any two or more of them. The details of such materials and the manner of their use in the production of casting molds and cores are well known in the casting art. For example, reference can be made to the patents EP-A-027333 and EP-A-085512. In general, a casting mold or core can be obtained by preparing a mixture containing the particulate aggregate, the particulate clay, the ester curable binder and at least one liquid ester curing agent for the binder, which forms the mixture in the desired configuration and which allows the binder curable with ester to undergo curing. The curing of an ester curable binder can also be accomplished by gassing with a gaseous or vaporous ester, typically the methyl formate. The details of the healing technique with the gaseous ester are given in EP-A-086615. In generalA casting mold or core can be produced using a gasification technique by forming the mixture of the aggregate, particulate clay and ester-curable phenolic resin, in the desired configuration, and then gasifying the mixture formed with the steam methyl format. As is well known in the art, there are some circumstances where a gasification technique can be combined with the use of a liquid ester / lactone / organic carbonate curing agent. Silicates, as is well known in the art, can also be used to bond aggregates, such as sand, to produce casting molds and cores. They can be cured by reaction with a liquid ester, a lactone, an organic carbonate or a mixture of two or more of them, or they can be cured by gasification with CO2. In view of the wide knowledge of the use of these binder systems, it is not considered necessary to provide additional details here. Beneficial results are achieved by using a particulate clay with a mechanically recovered sand, without subjecting the two materials together to a subsequent heat treatment prior to mixing with the binder. Although the improvements obtained in this way do not correspond to those obtained in the case where a subsequent thermal treatment is used, they are significant in enabling the realization of adequate resistance achieved with the use of reclaimed sand, without the expense of thermal recovery. Obviously, by melting the metal in a mold / core produced from the compositions described herein, a proportion of the sand will have a relatively high temperature and the presence of the particulate clay additive will act to trap any free alkali in the sand. An additional, unexpected and notable feature of the invention is that the thermal treatment of the sand before the addition of the particulate clay additive was observed to give high cohesive forces, although it is unlikely that a chemical reaction has occurred. The small amount of the inorganic reaction product, formed by the reaction of the particulate clay with the eluble alkali, has no role in the bonding process, except to prevent the detrimental effects of the alkali metal free salts. The use of particulate clay additives to improve the cohesive forces, obtained with the sands recovered from the molds and cores, prepared with the use of phenolic resins cured with ester and the silicates cured with ester or CO2, was not known in the prior art. Additions of inorganic dusts were actually considered to be detrimental in the performance of ester-cured phenolic resins or liquid organic binder systems, generally due to the reduced mobility of the binder system and the problems of "intense drying", which would adversely affect to the adhesive and cohesive strength of the binder. In fact, such problems can be overcome in either of two ways. First, when the powder additions are made to the sand to which the liquid resin is to be added directly, a further addition of the water can be made to maintain a degree of mobility and prevent "intense drying". Second, the addition can be made after the mold or core has been manufactured, but before the recovery and recycling of the sand for subsequent re-adhesion. A further facet of the invention is that the treated sand can be thermally recovered without fear of glass formation or "sintering", thus reducing the organic contaminants in the sand, which could also adversely affect the characteristics of the re-adhesion. EXPERIMENTAL TEST Materials 1. Alkaline Phenolic Resins 1.1 Alkaline Resin Phenolic Resin 100% phenol was dissolved in 50% aqueous KOH, in an amount corresponding to the KOH: phenol molar ratio of 0.78: 1. The solution was heated to reflux and 50% aqueous formaldehyde was added slowly, while maintaining the reflux, in an amount corresponding to a molar ratio of formaldehyde: phenol of 1.9: 1. The initial reaction was carried out at a temperature of 80 ° C and then the temperature was raised to 95 ° C and maintained until it reached a viscosity in the range of 100 to 120 cP (cone viscometer and ICI plate, cone of 5 Poises). to 25BC). The temperature was lowered to 802C and maintained once more until the viscosity reached a value of 130 to 140 cP (tested as before). The resin, thus obtained, was then diluted with water and methanol was added at 2.3% by weight (in the resin solution), 1.0% by weight of urea and 0.4% by weight of silane. The final viscosity was 80 c St (U-tube, size G at 250C). 1.2 Phenolic Resin Alkaline B 100% phenol was dissolved in 50% aqueous KOH in an amount corresponding to a molar ratio of KOH: phenol of 0.68: 1. The solution was heated to reflux and 50% aqueous formaldehyde was added slowly while refluxing was maintained in an amount corresponding to a 2.0: 1 formaldehyde: phenol molar ratio. The initial reaction was carried out at a temperature between 75 and ßoac and the temperature was then maintained at 802C until reaching a viscosity in the range of 170 to 180 cP (cone viscometer and ICI plate, cone of 5 Poise at 252C) . The resin was then cooled rapidly and 1.8% by weight of urea, 0.4% by weight of silane and 3.8% by weight of phenoxyethanol was added. The final viscosity was about 130 cP (measured as before). 2. Silicate resin 2.1 Silicate resin A Sodium silicate solution, characterized by the following composition: Si02 25% Na20 12% Na2C03 0.55% Dry solids = 43%, viscosity = 350-400 cP, Specific Gravity. § 20SC = 1.45. 3. Ester Hardeners 3.1 Ester Hardener A (for use with Resol Alkaline Phenolic Resin) Composition: Triacetin 95% Resorcinol 5% 3.2 Ester Hardener B (for use with Alkaline Resin Phenolic Resin B) Methyl Format - from BASF. 3.3 Ester Hardener C (for use with Silicate Resin A) Propylene Carbonate 4. Carbon Dioxide 4.1 Hardener D (for use with Silicate Resin A) Carbon Dioxide Gas, from L'Air Liquide . Additives 5.1 Silane A? -amino-propyl-silane 5% water 95% 5.2 Meta-kaolin A Powder Geopolymite PS2, from Geopolymere, 60700 Ste Maxence, France 5.3 Meta-kaolin B Metakaolin, from AGS Laboratory, France Particle size: 0 -20 mieras 5.4 Meta-kaolin C Metakaolin, from AGS, France Particle size: 0-100 microns 5.5 kaolinite A Kaolin KP, from Morbihen, 56270 Leurean Ploemeur 5.6 kaolinite B Clay GTY, from Hoden Davis, Newcastle-under-Lyme, Staffordshire, United Kingdom 5.7 Halolsita A New Zealand Halloysite, Premium, from New Zealand China Clays Ltd., Northland, New Zealand. . 8 Calcium Montmorillonite A Berkbond No. 1, Steetley Minerals Ltd., Milton Keynes, United Kingdom. 5.9 Ben o ita A Bentonite L 1001D, by Hoben Davis, Newcastle-under-Lyme, Staffordshire, United Kingdom. 5.10 Atapulauita A Attagel 50, from Lawrence, United Kingdom 5.11 Vepniculita A Exfoliated DF, from Dupre, Hertford, United Kingdom. Particle size: 1 - 2 mm. 5.12 Vermiculite B Supra Vermiculite L862D, by Hoben Davis, Newcastle-under-Lyme, Staffordshire, United Kingdom. Particle size < 0.5 mm.

TEST METHODS LOSS OF IGNITION: Loss of weight after 45 minutes at 900SC ALLCALI ELUIBLE (see below) FINE PARTICLES Percentage passing a sieve of 0.1 mm SOLUBLE POTASSIUM AND SODIUM IN WATER (see below) MEASUREMENTS OF FLEXIONAL RESISTANCE (see below) POTASSIUM HYDROXIDE / ELUIBLE SODIUM HYDROXIDE Method Exactly about 50 g of the sand under test was weighed into a clean laboratory beaker, with magnetic stirrer. 50 ml of distilled water was added and stirred for 10 minutes with the magnetic stirrer. The pH was checked and then 50 ml of 0.05M sulfuric acid was added by means of a pipette. A watch glass was placed on the laboratory beaker and then heated to the boiling point with the use of a Bunsen burner with tripod and gauze. Immediately after the contents of the laboratory beaker begin to boil, remove the heat and add 50 ml of distilled water, to cool them to room temperature.

Holder with the pH meter, with stirring, with a 0.1 M NaOH solution at a pH of 7.0 Title at pH 7.0 (mi) x 0.56 KOH content Weight of the sand sample (g) Title at pH 7.0 (mi) x 0.40 NaOH Content Sand weight Measurement of potassium and soluble sodium in sand samples recovered by flame photometry Equipment Flame photometer, EEL (Corning) Material Standard Potassium Solution: A solution containing 10 ppm potassium was prepared, of Analar Potassium Chloride, carefully dried at 110ac. Standard Sodium Solution: A solution containing 10 ppm of sodium, of Analar Sodium Chloride, carefully dried at HOSC was prepared. Sample Preparation The sand sample, 10 g, was loaded into a 250 ml conical flask to which 250 ml of deionized water was added. The flask was shaken and allowed to stand for 2 hours. The solution was filtered through a Buckner funnel, with the use of Shatman filter paper No. 1. A 10 ml sample was then diluted with 100 ml deionized water in a volumetric flask to bring the concentration within the 10 ppm range of potassium or sodium. Sand Treatment The mechanically recovered sand (50 g), the mineral additive (0.15 g) and the water (0.15 g) were mixed in a 100 ml plastic laboratory beaker, using a spatula, for three minutes. A control sample was prepared using mechanically recovered sand (50 g) and water (0.15 g) in a similar manner. The sand mixtures (20 g) were loaded in a 50 ml silica crucible and placed in an oven at the required temperature for 3 hours. The sand was allowed to cool before sample preparation.

Method for Determination of Flexural Strength-Phenolic Resins and Silicates Cured with Liquid Ester a) Mixing Procedure 2500 g of sand were loaded into a mixing bowl of a Kenwood Chef mixer and the temperature was adjusted to 22se by mixing in dry. The required amount of additive was loaded into the sand and mixed for 2 minutes to achieve a homogeneous mixture of sand / additive. If required, water is added and mixing is continued for one more minute, followed by the hardener and mixed for another minute. The resin was loaded into a disposable syringe and added to the sand mixture, while operating the mixer, for a period of 10 seconds. The mixer was then operated at a maximum speed (300 revolutions / minute) for 2 minutes, before the preparation of the test specimens.

Determination of the flexural strength The binder / sand mixture was packed in two boxes, each containing six molds measuring 22.4 x 22.4 x 177.8 mm. The sand mixture was evenly distributed between the two boxes and packed in the corners of each mold manually. The sand was rammed using a wooden shaving bar. The excess sand was removed by the action of a steel sheet through the top of each box. A small amount of the binder / sand mixture was then placed along the middle of each box and carefully pressed using the steel sheet. This is to ensure a consistent smooth surface through the middle of each bar at the point of pressure where the test instrument is in contact with the test bar.

The measurements were made using a Howden Tensometer tension measuring device equipped with flexional test jaws. Three test pieces were broken in time intervals after mixing and the average resistance measurements were calculated.

Method for the Determination of Flexural Resistance - Phenolic Resins and Silicate Cured with Liquid Ester a) Mixing Procedure 2500 g of sand were loaded into a mixing bowl of a Kenwood Chef mixer and the temperature was adjusted to 22QC by the dry mix. The required amount of additive was loaded into the sand and mixed for 2 minutes to achieve a homogeneous mixture of sand / additive. If required, water is added and the mixture is continued for one more minute. The resin was loaded into a disposable syringe and added to the sand mixture, while operating the mixer, for a period of 10 seconds. The mixer was then operated at a maximum speed (300 revolutions / minute) for 2 minutes, before the preparation of the test specimens. b) Determination of the flexural strength The binder / sand mixture was packed into a mold measuring 22.4 x 22.4 x 177.8 ram. The sand mixture was evenly distributed in the mold and packed in the corners of each mold manually. The sand was rammed using a wooden shaving bar. The excess sand was removed by the action of a steel sheet through the top of each box. A small amount of the binder / sand mixture was then placed along the middle of each box and carefully pressed using the steel sheet. This is to ensure a consistent smooth surface through the middle of each bar at the point of pressure where the test instrument is in contact with the test bar. The mold is gasified by passing steam until this mold is completely cured.

Gasification Conditions for Alkaline Resins Phenolic Resins; Saturated vapor of methyl formate was passed in a stream of nitrogen gas at a pressure of 0.1 bar, through the mold for 15 seconds.

Gasification Conditions for Silicate Resins Carbon dioxide gas was passed from a cylinder at 0.1 bar, through the mold for 60 seconds. The measurements were made using a Howden Tensometer tension measuring device equipped with flexional test jaws. Three test pieces were broken in time intervals after mixing and the average resistance measurements were calculated.

EXAMPLES THAT DEMONSTRATE THE PREVIOUS TECHNIQUE 1. PHENOLIC RESIN CURED WITH LIQUID ESTER The typical resistances obtained with Resol Alkaline Phenolic Resin with Ester Hardener A, on a new and untreated reclaimed sand, are given in Table A TABLE 1 Analysis of the Arena: 2. FESOLIC RESIN CURED WITH ESTER VAPOR The typical resistances obtained with the Resol Phenolic Alkaline Resin B, with the ester Hardener B, in new and untreated sand, are given in Table 2. The figures are included where the water additions and silane have been made, according to the prior art (patent EP130584) TABLE 2 Analysis of the Arena: Treated at 800 ° C for 12 hours and separated from the powder to remove fine particles The resistances of alkaline phenolic resin binders in sand contaminated with residual sodium salts vary depending on the temperature at which the sand has been heated. Table 3 gives typical figures for the Resol Alkaline Phenolic Resin, cured with the Ester Hardener A.

TABLE 3 Sand Analysis The effect of the binder produced by the clay and the free alkali is minimal, as evidenced by the examples given in Table 4. The addition of extra alkali to the Resol Phenolic B, when cured with Hardener B of Ester results in a poor cure of the phenolic resin. When alkali and clay are used alone, no binder effect of the sand is evident.

TABLE 4 Analysis of the Arena 3. SILICATE CURED WITH LIQUID ESTER The typical resistances obtained with the Silicate Resin A and the Ester Hardener C, supplied to the reclaimed sand, are shown in Table 5.

TABLE 5 Analysis of the sand: 4. SILICATE CURED WITH CARBON DIOXIDE VAPOR The typical resistance values for Silicate Resin A, cured with Hardener D, in new and reclaimed sand, are given in Table 6.

TABLE 6 EXAMPLES DEMONSTRATING THE INVENTION 1. PHENOLIC RESINS CURED WITH LIQUID ESTER The results of the re-adhesion of the mechanically recovered sand, as described in Table 1 (after adding the additive and the heat treatment) with the Alkaline Phenolic Resin A and the Ester Hardener A, they are given in Table 7.

TABLE 7 Analysis of the Arena: When comparing with the results given in Table 1, it can be seen that the resistances are as good as those obtained with new sand. 2. FENOLIC RESINS CURED WITH ESTER VALUE The results of the re-adhesion of the mechanically and thermally recovered sand, as described in Table 2, when it is treated after adding the additive with the Resol Phenolic Alkaline resin b and Hardener B of Ester, are given in Table 8.

TABLE 8 Table 9 illustrates the effect of the different levels of addition of Meta-kaolin B additive to the mechanically recovered sand.

TABLE 9 Analysis of the Arena: The same materials shown have a significantly greater resistance improvement when the mechanically recovered sand is heat treated. The results are shown in Table 10.

TABLE 10 LAARENA ANALYSIS: It can be seen that an addition level of 0.05% and above, gives a significant improvement in resistance. Table 11 shows that many different types of clay can be used as a pre-treatment before heat treatment, to give improvements in the cohesion forces. The examples, which do not contain additives and the additive of 'Vermiculite A', do not form part of the invention, but are included for comparative purposes. Examples using Vermiculite A and Vermiculite B demonstrate that the size of the particles is a factor in determining whether the additives are useful for the invention. The particle size of >0.5mm is considered too large to be effective. However, for minor particles, no significant differences in performance characteristics are seen at different particle size ranges, as is evident from the results of Meta-kaolin B and Meta-kaolin C, which have particle size distributions. 0 to 20 microns and 0 to 100 microns, respectively. A relationship between the cohesive force (Flexional Resistance in kg / cm2, after 0 minutes) and the amount of water-soluble potassium is shown (see Figure 1).

TABLE 11 Analysis of the Arena: The sand contaminated with sodium salts can be treated with an additive, in this case Meta-kaolin B, to provide significantly better results than those obtained from the additive. The results given in the following Table 12 show the resistances obtained with the use of the Alkaline Phenolic Resin A cured with the Ester Hardener A and incorporating the Meta-kaolin B and compared with the results given previously in Table 3, where applied the same heat treatment, but without using additive.

TABLE 12 Sand Analysis: 3. CORATED SILICATE WITH LIQUID ESTER The results of the re-adhesion of the mechanically recovered sand, as described in Table 5, but with the addition of Meta-kaolin A, are shown in Table 13. The binder system used was Silicate Resin A and C Hardener.

TABLE 12 4. CARBON DIOXIDE CURED SILICATE Improvements in strength were obtained when the mechanically recovered sand was re-bonded, as described in Table 6, but with the addition of Meta-kaolin A, as shown in Table 14. The binder system used was Silicate Resin A and Hardener D.

TABLE 14 NOVELTY OF THE INVENTION Having described the present invention, it is considered as a novelty and, therefore, the content of the following is claimed as property:

Claims (29)

1. CLAIMS 1. A particulate refractory composition, for use in the manufacture of casting molds and cores, which comprises a mixture of a particulate refractory aggregate, containing eluble alkali, with, as an additive, a particulate active clay, which has a particle size less than 0.5 mm.
2. 2. A particulate refractory composition, according to claim 1, in which the particulate refractory aggregate containing eluble alkali is sand recovered from cast molds or spent cores.
3. 3. A particulate refractory composition, according to claim 2, wherein the sand that has been recovered from cast molds or spent cast cores contains an ester-cured phenolic resin binder, an ester-cured silicate binder or a binder of silicate cured with carbon dioxide.
4. 4. A particulate refractory composition, according to claim 2, wherein the sand and the particulate clay additive are subjected together to a heat treatment at an elevated temperature.
5. 5. A particulate refractory composition according to any of claims 1 to 4, in which the particulate clay additive is one or more substances selected from kaolins, heat-treated kaolins, smectites, montmorillonites, bentonites, vermiculites, etc. litas, atapulguitas, serpentinos, glauconitas, illitas, alí-fanas and imogolitas.
6. 6. A particulate refractory composition, according to claim 5, in which the additive of the particulate clay is a kaolin or a heat-treated kaolin.
7. 7. A refractory composition, according to any of claims 1 to 6, wherein the particulate clay additive is added such that it is present in an amount of 0.05 to 5%, preferably 0.05 to 2%, by weight, with particle size less than 0.5 mm, based on the weight of the particulate refractory aggregate.
8. 8. A particulate refractory composition according to any of claims 1 to 7, which additionally contains water.
9. 9. A method for preparing a particulate refractory composition, for use in the manufacture of casting molds and cores from spent casting molds or cores formed of refractory material and a binder, selected from an ester-cured phenolic resin, a silicate cured with ester or a silicate cured with carbon dioxide, this method comprises the steps of breaking the spent casting molds or cores and mixing the resulting broken material is a particulate clay, having a particle size of less than 0.5 mm and , optionally, water.
10. 10. A method according to claim 9, wherein the mixture of the broken material and the particulate clay is subjected to a thermal treatment at elevated temperature.
11. A method, according to any of claims 9 or 10, wherein the refractory material in spent molds or cores is sand, where the particulate clay is one or more substances selected from kaolin, heat-treated kaolin, smectite, montmorilloni-ta, bentonite, vermiculite, atapulguite, serpentine, glauco-nite, illite, allophane and imogolite, and in which the heat treatment is carried out at a temperature in the range of 400 to 1000 ° C, preferably 500 to 900 ° C.
12. 12. A method, according to any of claims 10 or 11, which further comprises the step of removing the powder and / or fine particles, during and / or after the heat treatment.
13. 13. A particulate refractory composition, prepared by the method claimed in any of claims 9 to 12.
14. 14. A casting molding composition, which comprises a mixture of a particulate refractory aggregate, containing eludable alkali, a curable binder with liquid, in an amount of 0.5 to 5% by weight, based on the weight of the refractory aggregate and a particulate clay, having a particle size of less than 0.5 mm.
15. 15. A casting molding composition, according to claim 14, in which the particulate clay is present in an amount of 0.05 to 5%, preferably 0.05 to 2% by weight, based on the weight of the particulate refractory aggregate.
16. 16. A casting molding composition, according to claim 14 or claim 15, wherein the particulate refractory aggregate, which contains the eluble alkali, is sand obtained from cast molds or spent cast cores.
17. 17. A casting molding composition according to claim 16, wherein the sand that has been recovered from cast molds or spent casting cores contains an ester cured phenolic resin binder, an ester cured silicate binder. or a silicate binder cured with carbon dioxide.
18. 18. A casting molding composition according to any of claims 14 to 17, in which the particulate clay is a substance selected from kaolin, heat-treated kaolin, smectite, montmo-rillonite, bentonite, vermiculite, attapulguite, serpentine, glauconite, illite, allophane and imogolite.
19. 19. A casting molding composition, according to claim 18, wherein the particulate clay is kaolin or kaolin heat treated.
20. 20. A casting molding composition according to any of claims 14 to 19, which additionally contains water.
21. 21. A casting molding composition, comprising a mixture of the particulate refractory composition claimed in any of claims 1 to 8 and 13, with a liquid curable binder in an amount of 0.5 to 5% by weight, based on the weight of the particulate refractory composition.
22. 22. A casting molding composition according to any of claims 14 to 21, wherein the liquid curable binder is an ester curable phenolic resin.
23. 23. A casting molding composition, according to claim 22, wherein the ester-curable phenolic resin is an aqueous, alkaline, phenol-formaldehyde resin.
24. 24. A cast molding composition according to any of claims 14 to 21, wherein the liquid curable binder is an ester curable silicate.
25. 25. A casting molding composition according to any of claims 22 to 24, which additionally contains a liquid ester curing agent, for curing the ester curable binder.
26. 26. A method for manufacturing a casting mold or core, which comprises preparing a composition, according to claim 25, forming the composition in the desired design or configuration and allowing the ester curable binder to undergo curing.
27. A method for manufacturing a casting mold or core, which comprises preparing a composition according to any of claims 14 to 21, wherein the liquid curable binder is a silicate curable by carbon dioxide, forming the composition in the desired design or configuration and gasifying the composition formed with the carbon dioxide, to effect the curing of the binder.
28. A method for manufacturing a casting mold or core, which comprises preparing a composition according to any of claim 22 or claim 23, forming the composition in the desired design or configuration and gasifying the composition formed with a gaseous ester , to perform the cure of the binder.
29. 29. A method, according to claim 28, wherein the gaseous ester is the methyl formate. Only * Mariano ßoßí