JPH0579423B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a mold used for a shell mold casting die, and mainly to a mold material suitable for manufacturing a core. More specifically, the present invention relates to a molding material for shell molds that provides a core with good collapsibility and easy sand removal work after casting in the casting of low melting point light alloys such as aluminum alloys. It is. Conventional technology Conventionally, thermosetting phenolic resin, which has excellent thermal stability during casting, has been used as a binder for the main mold or core (mold) used in shell mold casting of cast iron, cast steel, aluminum alloy, etc. Widely used. However, on the other hand, the property that the core can be easily discharged and removed from the cast product after casting, that is, the easy disintegration of the core, is not always fully satisfactory, especially for aluminum alloys cast at low temperatures. In light metals with low melting points, such as, the core tends to remain in the casting without disintegrating after casting. For this reason, when manufacturing light metal castings, the castings are usually pounded with a knockout machine to roughen the core, and then heat treated in a high-temperature firing furnace for several hours. A method has been implemented to remove residual sand from castings by providing a "burning process". However, such a method has drawbacks such as consuming a huge amount of energy and requiring a great deal of labor and time. Furthermore, recent automobile castings have become thinner and lighter in order to improve fuel efficiency, and have become structurally more complex.
Alternatively, there is a trend to use light alloys such as aluminum alloys in place of conventional cast iron, and the development of technology regarding the easy disintegration of cores after casting is considered an important and urgent issue in this technical field. To address these technical issues, we have developed more techniques than before to improve disintegration, such as by incorporating potassium permanganate, a strong oxidizing agent, into shell sand, hotbox sand, and oil sand as a disintegration improver. , a method for improving mold disintegration has been proposed [Giesereitechnik, Vol. 6, p. 180 (1979).
Year)〕. According to this method, regarding the disintegration of the mold,
Although it may still be insufficient depending on the shape of the mold, it can be significantly improved. however,
Since the resulting mold bending strength is significantly reduced, it is necessary to increase the amount of resin added to maintain the strength during use, which inevitably increases manufacturing costs and furthermore, the disintegrability itself deteriorates. However, it has not yet been put into practical use. Problems to be Solved by the Invention Under these circumstances, the object of the present invention is to provide a shell mold suitable for manufacturing a casting mold that has excellent disintegrability after casting and has room-temperature strength that does not pose any practical problems. The objective is to provide mold materials for Means for Solving the Problems The present inventors have conducted extensive research in order to develop a mold material that satisfies the above requirements, and as a result, we have developed a method of heat-treating a certain type of permanganate above its decomposition temperature. It was found that the obtained decomposition product exhibited a remarkable catalytic effect in the thermal decomposition reaction of phenolic resin, and by blending this decomposition product into foundry sand as a disintegration improver together with the phenolic resin as a binder. The inventors have discovered that the object can be achieved, and have completed the present invention based on this knowledge. That is, the present invention provides a casting material for a shell mold that includes foundry sand, a phenolic resin, and a disintegration improver as essential components, and in which the disintegration improver includes an alkali metal salt and an alkaline earth metal salt of permanganate. The present invention provides a mold material for a shell mold, characterized in that it uses a thermal decomposition product of at least one salt selected from among them. There are no particular limitations on the phenolic resin used in the present invention, and examples include phenols such as phenol, resorcinol, catechol, and hydroquinone, metacresol, 3,5-xylenol, or phenolic resins having 1 to 1 to 1 carbon atoms in the ortho or para position.
Alkylphenols having 4 alkyl groups,
Bisphenols such as bisphenol A, bisphenol F, and bisphenol S, and at least one phenolic compound such as a purification residue by-produced in the production of the above phenols, alkylphenols, or bisphenols; formaldehyde; paraformaldehyde, trioxane,
Oxalic acid, hydrochloric acid, sulfuric acid, zinc acetate, zinc borate, Novolac type phenolic resin obtained using acidic substances such as zinc chloride and para-toluenesulfonic acid, resol type phenolic resin obtained using inorganic alkaline substances such as sodium hydroxide, calcium hydroxide, magnesium oxide, or ammonia. , nitrogen-containing resol-type phenolic resins obtained using amine compounds such as triethylamine, ethylenediamine, and hexamine, as well as inorganic acid salts such as zinc borate and zinc chloride, or organic carbonates such as zinc acetate and lead naphthenate. Benzyl ether type phenolic resins obtained using divalent metal salts of acids, mixed resins thereof, and modified phenolic resins modified as appropriate depending on the purpose of use,
For example, at any stage in the production of phenolic resin, thermosetting resins such as epoxy resins, xylene resins, urea resins, melamine resins, thermoplastic resins such as vinyl acetate resins, polyamide resins, acrylic resins, polyethylene resins, or urea, melamine, Modified phenolic resins made by mixing or reacting aniline, furfural, furfuryl alcohol, coconut oil, tall oil, etc. are used. These phenolic resins are produced by known production methods and are used in solid, liquid or varnish form. The amount of the phenolic resin blended into the foundry sand is usually appropriately selected within the range of 0.2 to 10% by weight, preferably 0.5 to 5% by weight. The disintegration improver used in the present invention is a decomposition product obtained by heat-treating an alkali metal salt of permanganate or an alkaline earth metal salt of permanganate at a temperature higher than its decomposition temperature. In the present invention, one type of the disintegration improver may be used, or two or more types may be used in combination. Specific examples of the permanganate include potassium permanganate, sodium permanganate, lithium permanganate, strontium permanganate, calcium permanganate, barium permanganate, magnesium permanganate, etc. In particular, potassium permanganate and sodium permanganate are preferably used because they are easily available as commercial products. When using these permanganates as the disintegration improver used in the present invention, as mentioned above, it is necessary to heat treat them at a temperature higher than their thermal decomposition temperature. Approximately 300~ considering efficiency etc.
Processing temperatures in the range of 1000°C are used. On the other hand, the processing time varies depending on various conditions such as the processing system (batch type, continuous type), heat source (electricity, gas, hot air), unit processing amount, etc., but it usually takes about 10 to 180 minutes. Selected by range. In addition, 1 of the heat-treated product obtained according to the above method
Manganate salts such as potassium manganate, sodium manganate, and pallium manganate, which are components and are produced as intermediate products in the manufacturing process of permanganate, have a disadvantage in that they are difficult to obtain as commercial products. However, it can be used in the same way as the thermal decomposition products. The amount of the disintegration improver according to the present invention is usually
The content is appropriately selected in the range of 0.5 to 30% by weight, preferably 1 to 20% by weight based on the phenolic resin. If the amount is less than 0.5% by weight, the disintegration after casting cannot be improved, and if it exceeds 30% by weight, the bending strength of the mold will drop significantly, making it impossible to put it to practical use. When producing the molding material for shell molds of the present invention, the method of blending the disintegration improver is usually (1) adding the disintegration improver to the foundry sand in advance, and then adding and mixing the resin; (2) A method of adding and mixing a disintegration improver to molding sand at the same time as the resin, (3) After mixing the resin and molding sand in advance,
A method of adding and mixing a disintegration improver is also adopted.In addition, as for the method of manufacturing the mold material for shell mold of the present invention, any of the dry hot coating method, semi-hot coating method, cold coating method, and powder solvent method can be used. It may be a method. Furthermore, in addition to the above-mentioned components, the shell mold molding material of the present invention may include any conventionally commonly used compounding agents, such as silane coupling agents such as amino-based silanes and epoxy-based silanes; Stearic acid mono or amides such as bisamide and methylolamide, aromatic carboxylic acids such as benzoic acid and salicylic acid, hexamethylenetetramine, potassium stearate, red iron sand, and the like are blended within a range that does not impair the purpose of the present invention. be able to. Further, these compounding agents are usually blended during the production of the mold material, but it is preferable that the silane coupling agent, amides, or aromatic carboxylic acids be blended during the production of the phenolic resin. Effect The thermal decomposition products of alkali metal permanganate and alkaline earth metal salts (hereinafter referred to as permanganates) contained in the mold produced using the mold material for shell molds of the present invention cause Although the mechanism of action by which the disintegrability of the mold improves is not necessarily clear, it is inferred as follows. That is, the permanganate is oxidatively decomposed by heat treatment to become a mixture containing manganate and manganese dioxide as main components. When this mixture is used as a disintegration improver, when molten metal is poured, the manganate acts catalytically on the alkaline thermal decomposition reaction of the phenolic resin, while the coexisting manganese dioxide also acts on the alkali thermal decomposition reaction of the phenolic resin. Due to this synergistic effect, conventionally known permanganates (oxidative decomposition reactions mainly due to released oxygen)
It is presumed that the disintegration of the mold is promoted and the disintegration properties are improved. Examples Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples in any way. In addition, the physical property values in each example were measured as follows. (1) Mold bending strength: Measured according to JIS-K-6910. (2) Bend: Measured according to JACT test method SM-3. In addition, bend was determined to be a curing property evaluation method, and the smaller the numerical value, the faster the curing speed. (3) Disintegrability; the first one is 40 mm wide, 75 mm long, and 25 mm thick.
A dogbone type tensile strength test piece with the shape shown in (1) in the figure was made from resin coated sand and used as a core for the collapsibility test. Furthermore, an outer mold (Fig. 1, 2) of 125 mm x 80 mm x 75 mm and a space slightly larger than the core test piece was prepared separately, and the core test piece was set in it and heated to 720 ± 5°C. Molten aluminum alloy is cast to form a casting 3, and after cooling, vibration is applied to one part of the casting 3 (Fig. 2) using an air hammer with a pressure of 0.4 kg/cm ² to reduce the diameter of the casting to 16 mm.
Measure the weight of the sand discharged from the discharge port every hour, divide it by the total weight when all is discharged,
The amount was expressed in weight% and was defined as disintegration. Example 1 5000 g of foundry sand (product name: Pearl Sand) heated to 140-150°C was put into a speed mixer (manufactured by Enshu Tekko Co., Ltd.), and novolak-type phenolic resin (manufactured by Asahi Yokuzai Kogyo Co., Ltd.) was added as a binder.
Sp690) 60g (1.2% by weight based on the foundry sand) and 200g of potassium permanganate as a disintegration improver.
Pyrolysis product obtained by heat treatment at ℃ for 1 hour
6.6 g (11% by weight based on binder) were added and kneaded in a mixer for 50 seconds. Hexamethylenetetramine (15% by weight based on the binder) was then added to water.
Pour in the entire amount of the aqueous solution dissolved in 75 g, and add about 40 to 60 g.
After continuing to mix for seconds, 5 g of calcium stearate was added as a lubricant, and after further mixing for about 15 seconds, the mixture was discharged from the mixer to obtain a mold material for a shell mold. Examples 2-6 Potassium permanganate as a disintegration improver
Same as Example 1 except that instead of the pyrolysis product obtained by heat treatment at 200°C for 1 hour, a pyrolysis product of potassium permanganate treated under the heat treatment conditions listed in the attached table was used. A mold material for shell mold was obtained. Example 7 As a disintegration improver, in place of 6.6 g (11% by weight of the binder) of a thermal decomposition product of potassium permanganate obtained by heat treatment at 200°C for 1 hour,
A mold material for a shell mold was prepared in the same manner as in Example 1, except that 3 g (5% by weight of the binder) of the thermal decomposition product of potassium permanganate obtained by heat treatment at 600°C for 1 hour was used. I got it. Example 8 As a disintegration improver, in place of 6.6 g (11% by weight of the binder) of a thermal decomposition product of potassium permanganate obtained by heat treatment at 200°C for 1 hour,
3 g of potassium manganate, a component of the thermal decomposition product of potassium permanganate (5 g per binder)
A mold material for a shell mold was obtained in the same manner as in Example 1, except that % by weight) was used. Comparative Example 1 A mold material for a shell mold was obtained in the same manner as in Example 1 except that no disintegration improver was used. Comparative Example 2 Same as Example 1 except that 1.1% by weight of binder was used based on the foundry sand in order to obtain mold bending strength equivalent to Examples 1 to 6 without using a disintegration improver. A mold material for shell mold was obtained. Comparative Example 3 A mold material for a shell mold was obtained in the same manner as in Example 1, except that potassium permanganate without heat treatment was used as the disintegration improver. Comparative Example 4 In order to obtain mold bending strength equivalent to Examples 1 to 6 and Comparative Example 2, the amount of binder was 1.45% by weight based on the foundry sand, and potassium permanganate without heat treatment was used as a disintegration improver. A mold material for a shell mold was obtained in the same manner as in Example 1 except that 11% by weight of the binder was used. Comparative Example 5 In order to obtain mold bending strength equivalent to Examples 7, 8, and Comparative Example 1, the amount of binder was increased to 1.45% of the foundry sand.
A mold material for a shell mold was obtained in the same manner as in Example 1, except that 5% by weight of potassium permanganate, which had not been heat-treated, was used as a disintegration improver based on the binder. Comparative Example 6 As a disintegration improver, a thermal decomposition product of potassium permanganate obtained by heat treatment at 100°C for 1 hour was used in an amount of 11% by weight based on the binder.
A mold material for a shell mold was obtained in the same manner as in Example 1. The mold bending strength, bending and collapsibility of the mold materials for shell molds obtained in Examples 1 to 8 and Comparative Examples 1 to 6 were investigated. The results are shown in the attached table. Further, the hydrogen ion concentration (PH) of potassium permanganate, its heat-treated products under various conditions, and aqueous solutions of potassium permanganate were measured by the following method. The results are also shown in the table. Measuring method of hydrogen ion concentration (PH) of aqueous solution of disintegration improver 1.0 g of pyrolysis product of potassium permanganate obtained by heat treatment under each condition in a 200 c.c. beaker
100 c.c. of distilled water was added thereto, and after stirring for about 20 minutes, the solution was allowed to stand and the PH of this solution was measured using a PH meter (manufactured by Toa Denshi Kogyo Co., Ltd.).

【table】

[Table] Examples 1 to 1 in which 11% by weight of the disintegration improver obtained by heat treatment at a temperature higher than the thermal decomposition temperature of potassium permanganate was used based on the binder as in the present invention.
6 has slightly lower mold bending strength than Comparative Example 1, which did not use a disintegration improver, but compared to Comparative Example 3, which used potassium permanganate without heat treatment, and potassium permanganate, which did not use heat treatment. Comparative Example 6 using a product heat-treated for 1 hour below the thermal decomposition temperature
Compared to this, the decrease in mold bending strength is very small. In addition, in order to obtain mold bending strength equivalent to Examples 1 to 6, the amount of binder in Comparative Example 2, which does not use a disintegration enhancer, is 1.1% by weight, and potassium permanganate without heat treatment is used. Comparative Example 4 required 1.45% by weight of binder. In addition, in Example 7, in which 5% by weight of the heat-treated product of potassium permanganate obtained by heat-treating above the thermal decomposition temperature was used based on the binder, the disintegration improver was not used with the same amount of binder. In the case of Comparative Example 5, which has almost the same mold bending strength as Comparative Example 1 and uses unheated potassium permanganate, in order to obtain mold bending strength equivalent to Example 7 and Comparative Example 1, the mold bending strength is 1.45. % binder by weight was required. Regarding the disintegration property, when comparing Examples 1 to 6 and Comparative Examples 2 and 4, which have the same mold bending strength, Examples 1 to 6 have a large difference compared to Comparative Example 2, which does not use a disintegration improver. The disintegrability has improved. Also,
The disintegration properties were also improved compared to Comparative Example 4, which used potassium permanganate without heat treatment.
This is also clear from the comparison between Example 7 and Comparative Examples 1 and 5. Furthermore, in Example 8, which used potassium manganate, which is a component of a disintegration improver obtained by heat-treating potassium permanganate at a temperature higher than the thermal decomposition temperature, almost the same effect as Example 7 was obtained. . Effects of the Invention As is clear from the above explanation, the mold material for shell molds of the present invention containing a heat-treated product of permanganate prevents deterioration of mold bending strength and hardens the mold when molding. This improves the mold properties, such as improving the mold properties, and also greatly improves the collapsibility of the mold after casting, which greatly reduces the time, labor, and energy costs required for mold collapse, and increases production efficiency. performance is significantly improved. In addition, the impact pressure required to collapse the mold can be reduced, which reduces damage to cast products and improves product yield. It also has many features such as lowering noise and improving the working environment. and provide industrial utility.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are cross-sectional views showing a test device for measuring disintegration described in Examples and its usage state.

Claims (1)

[Claims] 1. In a shell mold molding material containing foundry sand, a phenolic resin, and a disintegration improver as essential components, the disintegration improver is selected from alkali metal salts and alkaline earth metal salts of permanganate. A molding material for a shell mold, characterized in that it uses a thermal decomposition product of at least one salt.