JPH0372371B2 - - Google Patents

Description

[Detailed description of the invention]

Various methods have been used to bond particles of refractory material (generally sand) together to form foundry cores and sometimes molds. Some binders solidify spontaneously after some time in the presence of a catalyst. There are also binders that are hardened by passing through the refractory mixture a suitable reactive gas, for example carbon dioxide, sulfur dioxide or more complex gases based on amines. Some of the latter gases are extremely unpleasant to handle, require extensive venting of the core making plant, and are even toxic. To date, the most satisfactory gas to use has been carbon dioxide, which is non-toxic and fairly inexpensive. It is primarily used to harden binders in the form of sodium silicate, and upon reaction with sodium silicate, dissociates the silica as hydrozolo, forming sodium carbonate and forming bonds between sand particles. Sodium silicate is attractive as such because it is inexpensive and does not rely on organic materials derived from petrochemistry. On the other hand, the bonds it forms are not as strong as those that can be obtained by using more complex organic resin binders based on phenol formaldehyde or furan resins. Moreover, sodium silicate melts with sand particles at high temperatures to form a relatively hard glass;
Problems can arise when separating the casting from the core material. Most other known gas curing methods use an organic binder and cure the organic binder by passing it through a gas that is toxic or at least unpleasant to handle. Therefore, gas that is inexpensive and easy to handle,
For example, it uses carbon dioxide and does not require heat or long curing times, and at the same time is as resistant to handling as silicate-bonded cores during placement and casting, but breaks down after casting and It forms clumps that are easy to remove. There is a strong need for an improved gas curing process that produces cores. In recent published UK Patent Application No. 2037787, a binder which is cold curable by the action of carbon dioxide is prepared using alcohol-soluble phenolic resins, polyvalent metal hydroxides (e.g. calcium hydroxide) and/or oxides. , it has been suggested that it can be composed of an organic solvent (eg alcohol or acetone) and an alkali metal hydroxide (eg sodium hydroxide) and some water. A specially developed phenolic resin is used to produce an insoluble phenolic resin formulation that forms the main binder. A wide range of possible starting materials is suggested and the resins can be based on resols, novolacs, resorcinols or high phenols such as cresols or butylphenols. It is acknowledged that in U.S. Pat. . Suggested copolymers are copolymers of acrylic esters with ammonium acrylate and sodium acrylate. Its disadvantage is that the core or mold takes time to develop its strength after passing the gas, and moreover, ammonia is liberated and pollutes the environment. The novel process proposed in the aforementioned patent specification consists of using copolymers selected from the cited range of such materials and neutralized with alkali together with sodium hydroxide. Suggested copolymers are copolymers of maleic anhydride and alpha olefin or styrene or methyl vinyl ether. The possibility of adding polyvinyl alcohol, calcium oxide and certain other metal hydroxides is mentioned. The purpose of the alkali is to render the copolymer water soluble by reaction with one or more carboxyl groups in the copolymer to form a soluble metal salt of the carboxylic acid, such as a sodium or potassium salt. It is. German Published Application No. 2814357, which corresponds to the aforementioned US patent application, describes the simple use of carboxyl group-containing homopolymers, without necessarily using copolymers, together with polyvalent metal hydroxides and polyvinyl alcohol resins. Possibilities are mentioned. It is stated that when this homopolymer is water soluble, it is unnecessary to add alkali. Finally, GB 1568600 discloses a carbon dioxide process in which binders are prepared from aqueous solutions of sodium salts of copolymers of carboxylic acids, such as copolymers of styrene and maleic acid. The known methods described above are not easy to implement and are believed to be sensitive to factors not fully identified during the disclosure of the problem. Moreover, the range of possible materials is not differentiated between those that are effective and those that are not. In particular, in the aforementioned US Pat. No. 4,269,256, various binary and ternary copolymers based on esters and organic acid salts are described as prior art, but they are said to have drawbacks. Reaction products of poorly soluble or insoluble polymers with caustic alkalis have been suggested, but these are hydrolyzed esters;
It's probably not salt. Therefore, foundry molds or cores, i.e. carbon dioxide gas (or There remains a need for a method of forming foundry cores or molds that are gassed with other acidic gases) and that are resistant to handling (and gain strength quickly) and that are easily disintegrated after casting. According to the present invention, a binder consisting of (a) an alkali metal salt of a polyvalent organic acid or an alkali metal salt of a polymerized monovalent organic acid is added to the refractory particles, and (b) a hydroxide of an alkaline earth metal is added to the refractory particles. and (c) water (and optionally (d) polyvalent metal oxide), and the organic acid has a pK of 2.5 or more and the alkali before adding the alkaline earth metal hydroxide. Metal salt solution is 5.7
The foundry mold or core has a pH of ~12.5, the total amount of alkaline earth metal hydroxide is 25-400% by weight of the salt of organic acid, and involves passing acid gas through the resulting object. A method of forming is provided.
The present invention also relates to a foundry mold or core formed by such a method. Such compositions can be gassed with sulfur dioxide or carbon dioxide, the latter being preferred for the general reasons set out above. The alkali metal salt, which is one of the essential requirements of the present invention, is preferably a sodium salt, for reasons of availability and cost, and is formed by the reaction of an acid (or its anhydride or ester) with sodium hydroxide. Ru. Also, according to an important feature of the invention, this is a PH of 5 or higher, preferably 5.7.
Amounts are used to produce a solution with a PH of ~12.5, most preferably 5.7-6.6. It is believed that the PH of alkali metal salts of carboxylic acids has been previously recognized to be important when obtaining effective results. In particular, the solution should contain residual sodium hydroxide to make it significantly alkaline, and later alkaline earth metal hydroxides such as calcium hydroxide, which are one of the other essential requirements of the invention. This will be done even when mixed with. A preferred alkali metal salt is sodium polyacrylate. It is not readily available in solid form, but can be prepared and obtained as an aqueous solution. Instead of preparing it in advance, it can be prepared in situ by adding its various components to an aqueous solution and allowing them to react together during mixing. Instead of reacting the polymerized acid with sodium hydroxide, another method is to make sodium acrylate monomer and polymerize it. The organic material should preferably be such that it has a high molecular weight, preferably an average value greater than 50,000. The binder components are reacted in the presence of gas and liquid. The liquid may conveniently be a solvent or carrier for the organic component. Preferably this should be a polar liquid; water is easy to use and its presence facilitates the reactions that occur during gas treatment. Gas treatment is carried out in seconds by injecting carbon dioxide into the mold or core using techniques well known in the industry. The binder mixture is homogeneously mixed with sand or other refractory material to form a flowable mass that can be poured into a mold or core box. In some cases, a portion of the alkaline earth metal hydroxide can be replaced by one or more polyvalent metal oxides and/or other polyvalent metal hydroxides. The relative proportions of the components can vary within a very wide range. Preferably, the total weight of the alkaline earth metal hydroxide and metal oxide (if present) is 25 to 400% by weight of the organic acid salt, and the metal oxide can form no more than 80% of the non-organic component. .
oxide or mixture of oxides in small amounts (e.g. 10
%) of polyvalent metals, such as aluminum sulfate, is also advantageous, although not essential. In a typical example, the sand mixture contains 0.2 to 6% by weight organic component, i.e. 10% by weight in the liquid carrier.
~70% alkali metal salts, added as a solution. Add to this a quarter of the weight of the organic component.
10% to 100% alkaline earth metal hydroxide (e.g. calcium hydroxide) and the remainder consisting of one or more oxides of polyvalent metals, in four times the amount without
% of additional ionic salts of other polyvalent metals. The amount of liquid present in the sand mixture should be 0.5-5% by weight of polar liquid, which can be added as a carrier for organic salts or by other means. The organic component preferably accounts for the total weight of the sand mixture.
present in the range of 0.5-1.5%, and inorganic components
It is present in the range of 0.5-2%. 1.5-4% water may be present and the weight of carbon dioxide used for gas treatment is 0.3-2% of the total weight. As is clear from the test results described later, the resulting core and mold have excellent strength;
After casting, it is easy to remove from cold castings. They also have the advantage that they can be removed by vibration or by washing with water at relatively low pressures. They are easily removed from aluminum castings as well as from castings made from higher melting point metals. It will be appreciated that when the organic component is a salt of a polymerized monobasic acid rather than a polybasic acid, the molecules of the polymer must not lack a certain number of free carboxylic acid groups. The action of the curing gas is to form a polymeric cement formed from an insoluble polyvalent metal salt of an acidic gas, a polybasic (or polymerized monobasic) acid and a polyvalent metal;
It is to disturb the chemical equilibrium of a mixture of organic and inorganic components in such a way as to produce a chemical reaction (which together act as a binder system for the sand). The preferred material, sodium polyacrylate, is believed to be more effective than other polymer-based or polymerized monomer-based alkaline salts of acids. Sodium carbonate is formed when the carbon dioxide gas reacts with some of the sodium ions of the salt, and an increase in the ionic strength of the binder mixture causes precipitation of the polyacrylate as a gel. The action of this gel as a binder agent increases the (gas-treated) strength of the sand compared to other polymer-based or binders based on alkali metal salts of polymerized acids.
The reaction between the calcium ions in the binder and the polyacrylic acid causes an even stronger build-up over 24 hours. The salts of the other substances investigated apparently do not precipitate as easily or as completely as sodium polyacrylate. However, salts of closely related substances,
It is possible that such polymethacrylic acids or mixtures thereof with polyacrylic acids act in the same way. The invention will be illustrated with reference to a number of example compositions and the results of tests carried out on these compositions, as well as tests demonstrating the importance of ensuring the correct PH value of sodium polyacrylate. In the tests whose results are described below, Chelford 60 silica sand was used throughout and the organic component was a solution of sodium polyacrylate prepared by adding sodium hydroxide solution to polyacrylic acid. Ta. The theoretical amount required to neutralize the acid was added as a 20% aqueous solution. Except where stated, polyacrylic acid
A 25% aqueous solution is used, and its average molecular weight is
It was 230,000. A stock solution with the following composition was prepared: Polyacrylic acid (25% solution) 600 g Sodium hydroxide 83.4 g Water 400 g The inorganic component is calcium hydroxide throughout, with commercially available fine powders such as magnesium oxide. , magnesium hydroxide, zinc oxide,
Fondue cement, iron () salt,
and ammonium salt were added. Sand Preparation and Test Methods A sand mixture was prepared by mixing a quantity of polyacrylate solution with sand for 1 minute. The inorganic ingredients were then added and mixing continued for an additional minute. The mixed sand was placed in a sealed container before use. Prepare a standard 5cm x 5cm AFS compression test piece,
It was then cured by gassing with carbon dioxide at flow rates ranging from 2.5/min to 10/min and gassing times from 1 to 60 seconds. After gas treatment, the specimens were used for strength testing, some were used immediately and the measured compressive strength was recorded as “immediately after gas treatment”, while others were stored for up to a period of one week and the compressive strength was Measurements were taken at appropriate intervals within that time. Sand failure after casting was evaluated by making test castings using 5 cm x 5 cm AFS compression specimen specimens as cores. The test casting used had dimensions of 254 mm x 176 mm x 78
mm, and weighed 25Kg. Six cores were placed in each casting, for which a green sand mold was used. The castings were made from gray iron, poured at 1400°C. When cooled, the casting was carefully removed from the mold. The extent of core failure was evaluated using a BCIRA impact penetration tester (31.75 Kg load), which essentially measures the resistance of the sand to a sharp probe. The number of impacts required to penetrate each centimeter of core depth remaining in the casting was recorded as a measure of failure. Lower values indicate better destruction and higher values indicate poorer destruction. Example Test Results 1 A mixture containing the following ingredients was prepared: Chelford 60 seconds 1.5Kg Sodium polyacrylate solution 54g Calcium hydroxide 20g The mixed sand was free-flowing and compacted well during ram processing. And it had a bench life of over 3 hours. Compressive strength results for cores prepared from this mixture are shown in Table 1. For comparison, Table 2 shows the results obtained for _CO2 -silicate cores under similar conditions. As is clear from these results, cores can be produced with excellent handling strength in very short gas treatment times. The “fresh gassed” strength of 180 lbs/in2 (12.7 Kg/cm ² ) is comparable to a conventional cast sodium silicate binder, but the equivalent gassing time for silicate is 30 seconds. exceeded - see Table 2. When stored, the cores continue to harden within 24 hours and achieve exceptional strength, which is generally superior to CO ₂ -silicate cores and is now commonly used in core manufacturing. Comparable to the strength achieved from most cold-curing resin binder methods in use.

【table】

[Table] Example 2 - Showing the use of the addition of mixed powders A sand mixture was made from the following ingredients: Thielford 60 seconds 1.5 Sodium polyacrylate solution 54 g Sodium hydroxide 10 g Magnesium oxide 10 g) Added together to obtain The mixture is free-flowing, and Example 1
has a drier consistency than about
It gave a very well compacted core and had a long hench life (longer than 4 o'clock). Cores made from this mixture had an excellent surface finish, excellent strength, and an excellent edge and 'smooth' skin. The compressive strength results are shown in Table 3.

[Table] Examples 3 to 10 See Table 4 The effect of the composition of the sand mixture on the compressive strength is
This can be understood from Table 4. The most effective composition is
The content of calcium hydroxide is relatively high, and small amounts of magnesium oxide and fondue cement or zinc oxide are added.

【table】

[Table] Example 11 Core Destruction Test A sand mixture containing the following ingredients was prepared: Thiel hood 60 seconds 1.5Kg Sodium polyacrylate solution 54g Calcium hydroxide 15g Magnesium oxide 5g A 5cm x 5cm AFS compression specimen was The mixture was made up and gassed with _CO2 at 2.5/min for 10 seconds. Six specimens were subjected to the core breaking test described above. Table 5 shows the results. These results indicate that the CO ₂ -silicate core and special breaking additives contain
Comparable to the results for CO ₂ -silicate cores.

[Table] Destructive additives
As can be seen, this new binder has excellent fracture properties for iron casting. Example 12 Similar experiments were carried out on aluminum castings and fracture was found to be equally good. Test casting and knockout
out) method is different from that used for iron casting,
Comparative experiments were conducted using cores bonded with the novel binder material and cores bonded with a _CO2 -silicate binder. The results were as follows.

[Table] Example 13 In order to produce a good defect-free surface finish on the casting, it is often necessary to apply a special hardening coating to the core before fixing it in the mold. be. Such coatings can be water-based and require oven drying or are spirit based, with excess spirit burning off after coating. water-based coatings and spirit-based coatings.
This new binder has been applied to cores made with satisfactory results. The core was not damaged by the coating, drying, or combustion procedures required to produce a superior film barrier. The coated core was used successfully in the production of a number of different test castings and produced an excellent surface finish. Example 14 The addition of certain silane compounds (e.g. gamma-aminopropyltriethoxysilane) to a sand mixture containing an organic resin binder can have a beneficial effect on the strength properties of the bonded sand. Are known. Such silane modification can be carried out on this binder system to great effect and can substantially improve the tensile strength. Silane modification can be accomplished by treating the formulation prior to mixing with the sand or by separately adding the silane compound directly to the sand mixture during preparation. Effect of PH on Binder Properties The following tests illustrate the importance of achieving the correct PH. In each case 1.5Kg
of Thieford sand was mixed with 20 grams of calcium hydroxide and an amount of sodium polyacrylate solution made from each of the ranges listed in Table 5 below. It will be seen that the PH ranges from just above 4 to 13.0. In each case,
The sodium polyacrylate solution was mixed with the sand for 1 minute, then the calcium hydroxide was added and mixing continued for an additional minute. The polyacrylic acid used in making sodium polyacrylate had an average molecular weight of 230,000 and was in the form of a 25% aqueous solution.

【table】

[Table] A standard AFS compression test piece of 5cm x 5cm was made,
These were then cured with carbon dioxide gas at a flow rate of 2.5/min with a gas treatment time of 10 seconds. The core compressive strength was measured immediately after removal from the core tube (“immediately after gas treatment”), and then at 1 hour after the test piece was manufactured.
Measurements were made after 4 hours and 24 hours, and the test pieces were
Stored at a temperature of 22-24°C and a relative temperature of 50-60%. After 24 hours, an indirect tensile test was also performed in which a cylindrical section of a 5 cm x 5 cm AFS compression specimen was placed between the jaws of the testing machine and a compressive load was applied diametrically. The specimens were fractured along the loaded diameter line and the load required to rupture was divided by 4 and the value was converted to indirect tensile strength (lbs/in²). This test is
Report, F. Hofmann, Giesserei.50, 815−822
(1963). The results are listed in Table 6 below. It is clear from these results that the properties of the bound sand were influenced by the pH of the sodium polyacrylate solution. 6
Sands with pH values below had relatively short bench lives and were not ideally suited for use in applications where gas-cured binder castings are commonly used. At all PH values above 6, bench life exceeded 2 hours.

【table】

[Table] As the compressive strength results show, a PH of 5.7 to 6.6 is desirable for high "freshly gassed" strength, and in this PH range, strength is achieved in 1 hour.
The 24 hours were also very good. At PH values above 6.6, a constant decline is observed in the gas hardening rate, and finally in very alkaline conditions, the specimens do not have sufficient handling strength after gas treatment, and after a period of 1 hour Even then, it was still relatively weak. However, the 24-hour compressive strength of the sand in the PH range approximately 6.8-12.5 was very high. Therefore, in order to form a material with excellent strength immediately after gas treatment, it is preferable that the pH at the initial stage (formation of the first binder component) is within the range of 5.7 to 6.6. That is, when the mixture is slightly acidic, a product with excellent strength immediately after gas treatment is obtained, and even if the mixture is made highly alkaline by adding alkaline earth metal hydroxide afterwards, the result is not affected. do not have. However, on the other hand, PH
In the range of 6.8 to 12.5, extremely high compressive strength after 24 hours of gas treatment can be obtained. In this case, the strength immediately after gas treatment is reduced to about 30 pounds per square inch, but even this value is sufficient for practical use. From the above, it can be concluded that the superior advantages of the present invention are achieved with a pH within the range of 5.7 to 12.5. Based on this information, the preferred carboxylic acid is polyacrylic acid, although other acids can be used. But when the acid is a strong acid at the start,
It is believed that less satisfactory results are obtained, and for this reason tartaric acid can give results but are less acceptable than acrylic acid. Maleic acid and maleic anhydride are too strong acids. In practice, the starting material should have a pK value of 2.5 or higher. Part or all of the polyacrylic acid can be replaced and this will improve flow and reduce consistency, but will reduce strength somewhat. Finally, especially when the composition is used to form a foundry core by blowing,
Certain known additives to improve flowability,
For example, it may be beneficial to add 1% paraffin (added just before transferring the mixture from the mixer to the sand blower) or 0.1-1% Anuni oil at an early stage. Other additives that can be used are 1% finely ground graphite or fly ash, which can be added to the mixer.

Claims (1)

[Claims] 1. A binder consisting of an alkali metal salt of a polyvalent organic acid or an alkali metal salt of a polymerized monovalent organic acid is added to refractory particles together with an alkaline earth metal hydroxide and water. In addition, the organic acid has a pK of 2.5 or more, and the solution of the alkali metal salt before adding the alkaline earth metal hydroxide has a pK of 5.7 to
has a pH of 12.5, and the total amount of the alkaline earth metal hydroxide is 25 to 400% by weight of the salt of the organic acid;
A method of forming a foundry mold or core comprising passing an acid gas through the resulting object. 2. The method according to claim 1, wherein the gas is carbon dioxide. 3. The method according to claim 1 or 2, wherein the polymerized organic acid is polyacrylic acid. 4. The method of claim 3, wherein the salt is sodium polyacrylate. 5. The method according to any one of claims 1 to 4, wherein the alkaline earth metal hydroxide is calcium hydroxide. 6. The method according to any one of claims 1 to 5, wherein the salt of the organic acid is added to about 0.2 to 6% by weight of the total weight of the refractory mixture. 7. The method of claim 6, wherein the salt of the organic acid is added in an amount of about 0.5 to 1.5% by weight of the total weight of the refractory mixture. 8. A binder consisting of an alkali metal salt of a polyvalent organic acid or an alkali metal salt of a polymerized monovalent organic acid is added to the refractory particles together with an alkaline earth metal hydroxide and water, and the organic acid is has a pK of 2.5 or more, and the solution of the alkali metal salt before adding the alkaline earth metal hydroxide has a pK of 5.7 to
has a pH of 12.5, and the total amount of the alkaline earth metal hydroxide is 25 to 400% by weight of the salt of the organic acid;
A foundry mold or core formed by a method comprising passing an acid gas through the resulting object. 9 A binder consisting of an alkali metal salt of a polyvalent organic acid or an alkali metal salt of a polymerized monovalent organic acid is added to the refractory particles together with an alkaline earth metal hydroxide, water, and a polyvalent metal oxide. In addition,
The organic acid has a pK of 2.5 or more, the solution of the alkali metal salt before adding the alkaline earth metal hydroxide has a pH of 5.7 to 12.5, and the alkaline earth metal hydroxide and the A method of forming a foundry mold or core, wherein the total amount of polyvalent metal oxide is 25 to 400% by weight of the salt of the organic acid, and the method comprises passing an acid gas through the resulting object.