JPH07314078A - Molding material - Google Patents

Abstract

PURPOSE:To make it possible to freely change the coefft. of expansion of a casting mold by compounding a specific ratio of tungsten metallic powder with a binder. CONSTITUTION:The tungsten metallic powder is compounded at 5 to 40wt.% of the binder with the binder of the molding material for a titanium alloy consisting of the binder, such as alumina cement or zirconia sol, and aggregate, such as zirconium oxide or magnesium oxide as basic components. The tungsten metallic powder is oxidized to form tungsten oxide which expands to compensate the casting shrinkage of the titanium alloy. The tungsten metallic powder having purity >=95wt.% is more preferable and its grain size is adequately 3 to 50mum. An increase of a calcination speed is attained if the tungsten metallic powder is used as an expanding material. The coefft. of expansion is adjustable in a range of 0.1 to 7%. The molding material which does not roughen casting surfaces is thus obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a casting material for casting titanium or titanium alloy, and provides a casting material whose expansion coefficient can be freely changed.

[0002]

2. Description of the Related Art In recent years, titanium or titanium alloy having good biocompatibility has been used in place of conventional alloys such as nickel, chromium and cobalt.

However, titanium or a titanium alloy has a high melting point and is easily oxidized, and a conventional silica-based or phosphoric-acid-based template material is cast on a wax pattern of a model, cured, and lost wax is performed, and then titanium is dissolved. When cast, the titanium surface is easily oxidized and becomes hard and brittle, so precise dimensional accuracy and good casting surface cannot be obtained.

In order to solve these problems, Japanese Patent Laid-Open No. 60-18250 discloses an aggregate containing an oxide such as magnesium oxide and calcia as a main component and a zirconium oxide compound such as zirconium alkoxide and zirconia sol. The use of a binder is disclosed. Further, JP-A-4-75744 discloses the use of colloidal zirconium oxide powder, alkaline zirconia sol and calcium oxide, carbonate and hydroxide. Further, Japanese Patent Laid-Open No. 5-246818 proposes a mold material containing a binder of alumina cement and an aggregate as main components and further containing a carbonate of an alkaline earth metal as a hardening aid.

However, these mold materials have a problem that when molten titanium metal is cast into a solid state, it shrinks. In order to compensate for this shrinkage, Japanese Patent Application Laid-Open No. 61-9940 proposes a method in which metal powder such as Zr, Fe, Si, Sn, Cu, Ni and Cr is added and the expansion of the metal due to oxidation is used. Similarly to this, JP-A-61-213459
Proposes a mold material composition containing fine powder of Ti metal.

[0006]

In the method utilizing expansion of metal due to oxidation, a metal having an oxide formation free energy equal to or lower than that of titanium oxide is preferable, and zirconium and titanium are most preferable. It is noted to be a suitable metal.

However, the zirconium oxide metal powder is easily oxidized, and cracking is likely to occur in the mold material when heated rapidly from room temperature and fired. Therefore, it is necessary to slow the firing rate for the mold material containing the zirconium metal powder.

An object of the present invention is to provide a mold material that can be fired at a high rate, has an appropriate expansion coefficient, and is easy to handle without seizure of titanium or titanium alloy.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies to achieve the above object, and as a result, by using a tungsten metal powder as an expansive material, it is possible to increase the firing rate and to obtain an appropriate expansion coefficient. The present invention has been completed by finding a mold material which has no deterioration in the casting surface and has no rough casting surface.

That is, the present invention relates to a casting material for titanium or titanium alloy containing a binder and an aggregate as basic components,
Further, the above-mentioned casting material is characterized in that 5 to 40% by weight of tungsten metal powder is mixed with the binder.

The method of producing the tungsten metal powder used in the present invention is not particularly limited, and the purity may be 70% by weight or more, but 95% by weight or more is preferably used.

The particle size of the tungsten metal powder is preferably 1 μm to 100 μm, and particularly preferably 3 μm to 50 μm. The smaller the particle size, the more easily it is oxidized, but if the particle size is too small, it tends to be difficult to knead. If the particle size is too large, tungsten is not sufficiently oxidized, and it tends to be difficult to obtain an appropriate expansion coefficient.

The content of the tungsten metal powder in the mold material is determined by the casting shrinkage ratio of titanium or titanium alloy, the ratio of the binder in the mold material, and the water content, and is 5 to 40% by weight based on the binder. Range is mandatory. By including the tungsten metal powder in this range, the expansion coefficient is 0.
It can be adjusted in the range of 1 to 7% and can compensate for the casting shrinkage of titanium or titanium alloy. It is considered that this expansion coefficient is due to the generation of tungsten oxide by the oxidation of the tungsten metal powder. If the proportion of the tungsten metal powder is less than 5% by weight with respect to the binder, the shrinkage of titanium or titanium alloy after casting cannot be compensated. On the other hand, when the proportion of the tungsten metal powder exceeds 40% by weight with respect to the binder, the tungsten metal powder expands excessively and cracks easily occur in the mold material, which is not suitable for practical use.

By the way, in casting, a part of the casting material should not be seized on the surface of the cast body due to the reaction between the casting material and the metal to be cast. If such seizure occurs, the casting surface becomes rough and a cast body with high dimensional accuracy cannot be obtained. No seizure is seen in titanium or titanium alloys cast using the mold material of the present invention containing tungsten metal powder. Although the reason for this is not clear, tungsten oxide has a higher melting point despite the higher free energy of oxide formation than that of titanium oxide, so it is difficult to react even if it comes into contact with molten titanium or titanium alloy. it is conceivable that. Further, particularly when magnesium oxide is used for the aggregate, a composite oxide composed of tungsten oxide and magnesia oxide is generated, and since the oxide formation free energy of this composite oxide is lower than that of titanium, it is even more It is considered that the reaction with titanium or titanium alloy hardly occurs.

In the casting material of the present invention, known binders and aggregates can be used as long as they are used for casting titanium or titanium alloy.

Specific examples of the binder include alumina cement and zirconia sol. Of these, alumina cement is particularly preferably used because the strength of the cured product of the obtained template material is high.

As the alumina cement, CaO.Al ₂
A known material containing O ₃ as a main component is used without any limitation. Specific examples thereof include powdery alumina cement manufactured by a dissolution method using white bauxite and limestone as raw materials, and powdery alumina cement manufactured by a dissolution method using red bauxite and limestone as raw materials. Alumina cement has an average particle size of 0.1 to 10
Those having a thickness of 0 μm can be preferably used.

When alumina cement is used, the proportion of alumina cement in all components of the casting material is usually 5 to 80% by weight, preferably 10 to 70% by weight. If it is less than 5% by weight, the strength is weak, and if it exceeds 80%, the strength after casting tends to be too high and indexing tends to be difficult, which is not practical.

When zirconia sol is used as the binder, examples of the zirconia sol include zirconia acetate sol and ammonium zirconium carbonate sol. In particular, zirconia acetate sol is particularly preferably used because the mold shrinkage is small. The ratio of zirconia sol to the total components of the casting material is usually 5 to 50% by weight.

As the aggregate used in the casting material of the present invention, any material having fire resistance can be used without limitation. Specific examples of the aggregate include aluminum oxide, magnesium oxide, zirconium oxide, zircon, mullite, titanium oxide, spinel, silicon carbide, silicon nitride and silica.
Of these, zirconium oxide is particularly preferable because it is a compound that is stable with respect to titanium oxide. Furthermore, magnesia oxide is more preferable because it forms a stable complex metal oxide with tungsten metal. These can be used alone or in combination of two or more. In particular, a combination of zirconium oxide and magnesium oxide is more preferable because seizure hardly occurs. These aggregates are made of a binder 100.
Usually, 70 to 900 parts by weight is blended with respect to parts by weight.

In the present invention, when alumina cement is used as the binder, a lithium compound can be used as a hardening aid. As the lithium compound, inorganic lithium salts such as lithium chloride, lithium nitrate, lithium sulfate, lithium fluoride and lithium carbonate, organic lithium salts such as lithium acetate and lithium tartrate, lithium hydroxide and the like can be used.

Among these lithium compounds, after firing,
Organolithium salts are preferred because they decompose organic components, burn off, do not form unstable oxides, and do not adversely affect the equipment such as electric furnaces without the generation of inorganic acids, especially lithium citrate. Has an operation allowance time, and has fluidity of a slurry composed of a mold material and a kneading liquid,
It is preferably used because it cures quickly.

The content of these lithium compounds is preferably in the range of 0.05 to 5% by weight with respect to the alumina cement. If the content is less than 0.05% by weight, curing will not be rapid, and if it exceeds 5% by weight, the melting point will be lowered and seizure with a metal will tend to start.

The lithium compound may be coated with a higher alcohol in order to adjust the operation allowance time. When a lithium compound is coated with a higher alcohol, this higher alcohol can be used without limitation as long as it has 4 or more carbon atoms. Specific examples are butanol, 2-ethylhexanol, heptanol tridecanol, n-octyl alcohol, and n.
-Decyl alcohol, lauryl alcohol, cetyl alcohol, oleyl alcohol, stearyl alcohol and the like.

When the higher alcohol is liquid at room temperature, the lithium compound is coated with the higher alcohol so that the lithium compound is placed in the higher alcohol and dispersed and mixed with stirring to retain the higher alcohol on the surface of the lithium compound. Then, it is taken out and used as a powder or paste whose surface is wet with higher alcohol. Further, when the higher alcohol is solid at room temperature, the lithium compound is put into a liquid higher alcohol by applying a temperature, and the lithium compound is dispersed with stirring to coat the surface of the lithium compound with the higher alcohol. If the lithium compound coated with higher alcohol is powdery, it is used as it is, and if it is lumpy, it is powdered using a crusher such as a mortar, a rocking mixer and a ball mill. Further, if necessary, it is also possible to coat with a solution in which a higher alcohol is dissolved in an organic solvent having a low boiling point.

The amount of higher alcohol to be coated is preferably in the range of 20 to 100% by weight based on the lithium compound. By changing the amount of this higher alcohol, the timing of dissolution of the lithium compound in water can be changed, and the time during which the fluidity of the kneaded mold material can be maintained, that is, the operating margin time can be changed. The larger the coating amount of the higher alcohol, the longer the operation allowance time can be made, but normally, the coating amount is determined so that the effective operation allowance time is in the range of 2 minutes to 5 minutes. The coating amount of higher alcohol is 10
When it exceeds 0% by weight, higher alcohols remain as organic substances in the cured product, and after baking, they remain as cavities, the surface of the baked cured product is roughened, and the empty firing strength tends to decrease, which is not preferable. On the contrary, when the coating amount is less than 20% by weight, the lithium compound cannot be sufficiently coated, and the effect of controlling the operation allowance time is not sufficiently exerted.

Further, when using alumina cement as a binder, by adding a curing retarder such as citric acid, sodium citrate, sodium carbonate, tripolyphosphoric acid, sodium humate, ligninsulfonic acid, dextrin or carboxymethylcellulose. You can also adjust the operating margin. These hardening retarders are usually used in the range of 0.1 to 10 parts by weight with respect to the alumina cement.

The mold material of the present invention may be prepared by mixing a binder, an aggregate, a tungsten metal powder and, if necessary, a hardening aid, a hardening retarder and the like in any order. Also,
There is no limitation on the mixing method. However, in a mode in which a lithium compound coated with a higher alcohol is used as a curing aid, when the amount of the lithium compound coated with a higher alcohol added to the template material is small, it is necessary to use an aggregate component such as magnesium oxide or zirconium oxide in advance. A high-alcohol-coated lithium compound is first mixed in a high concentration in a mortar or rocking mixer to form a masterbatch, and the required amount is taken from the masterbatch, and further, alumina cement, aggregate, tungsten metal powder and, if necessary, An adjusting method of mixing with a curing retarder or the like to form a mold material is suitably adopted.

In the casting material of the present invention, alumina cement, zirconium oxide and / or magnesium oxide,
A mold material containing an organic acid lithium salt and a tungsten metal powder, wherein the organic lithium salt is 0.05 to 5% by weight with respect to the alumina cement, and the tungsten metal powder is 5 to 40% by weight with respect to the alumina cement. But,
It is particularly preferable because the firing rate can be increased, the firing has an appropriate expansion coefficient, the strength is sufficient, and the casting surface is not roughened.

The kneading liquid used for curing the template material of the present invention can be used without limitation as long as it is an aqueous solution which does not affect the basic properties of the template material. For example, water, colloidal silica aqueous solution, alumina colloidal aqueous solution, zirconia colloidal aqueous solution and the like can be mentioned. The mixing ratio of the template material and the kneading liquid may be in a range such that the kneaded product obtained has suitable fluidity and does not affect the physical properties. Generally, the ratio of the mold material to the kneading liquid is used in the range of 10/1 to 1/1. The casting material of the present invention and the kneading liquid are mixed and poured onto the wax pattern, and then baked to dissolve the wax and further increase the strength and expand the wax. The firing temperature is usually in the range of 500 to 850 ° C. This firing temperature is higher than that of 500 to 700 ° C. when zirconia metal powder is used.

When the template material of the present invention is used, the firing rate can be 5 to 15 ° C./min, which is considerably faster than the firing rate of about 2 ° C./min when zirconium metal powder is used. Can be fired at. The reason for this is not clear, but tungsten metal is less likely to be oxidized than zirconium metal, is hardly oxidized from room temperature to 400 ° C., does not generate oxidation heat, and does not expand, so that it can be rapidly heated. On the other hand, when zirconium is rapidly heated from room temperature, it is considered that the heat of oxidation is rapidly generated and the mold material is cracked.

[0032]

EFFECTS OF THE INVENTION The mold material of the present invention can obtain an appropriate expansion coefficient by containing the tungsten metal powder. Moreover, there is an advantage that firing can be performed at a high firing rate in order to obtain stable expansion. As a result, it can be easily baked and is economical. Furthermore, when titanium or a titanium alloy is cast using the casting material of the present invention, a cast body having a clean casting surface without seizure can be obtained.

In addition to the fact that zirconium metal powder is easily ignited in air and difficult to handle, tungsten metal powder has an advantage that it is easy to handle because it is relatively stable at room temperature.

[0034]

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. The test methods shown in the examples are as follows.

1. Curing time According to the Japanese Industrial Standard T6601 coagulation time test method, a mixed sample was filled into a metal cylinder with an inner diameter of 30 mm and a height of 30 mm, and when mixing was started, a Vicat needle with a load of 300 g (needle diameter The time until 2 mm) does not enter the sample is the curing time.

2. Flowability The mixed sample was filled in a frame having an inner diameter of 40 mm and a height of 30 mm, the frame was removed 2 minutes after the mixing was started, and the spread of the sample after curing was used as a measure of the fluidity. Flowability is expressed as the value of the diameter of the spread sample.

3. Operation allowance time The mixed sample is filled in a container having an inner diameter of 40 mm and a height of 30 mm, the container is tilted at 90 degrees, and the time from the start of kneading until the sample does not flow out is the operation allowance time.

4. Fracture resistance According to the Fracture resistance test method of Japanese Industrial Standard T6601,
Fill a mixed sample in a metal cylinder with an inner diameter of 30 mm and a height of 60 mm, and after solidifying to the extent that it can be handled, remove it from the mold, leave it at room temperature, and use a compression tester 24 hours after the start of mixing. The crosshead was measured at 1 mm / min, and the value was used as the green strength of the casting material.

For the strength after air-baking, a sample was prepared by the same method, heated to a predetermined temperature in an electric furnace at 10 ° C./minute, and
After mooring for 0 minutes and allowing to cool to room temperature, the compressive strength was measured and the value was taken as the dry firing strength.

5. Expansion coefficient Measured according to the thermal expansion test method of Japanese Industrial Standard T6601. The sample size is 1 x 10 cm in diameter, 8
After heating to 50 ° C. or 1000 ° C. and cooling, the length increased from the original length was measured, and the rate of increase from the original length was determined to obtain the expansion coefficient.

6. Burn-in Regarding burn-in roughness, a wax pattern of 20 × 10 × 2 mm is buried in a mold material, and after curing, firing is performed to a predetermined temperature, casting is performed, and the roughness on the metal surface after indexing is visually observed and the following three stages It was evaluated by.

◯: Almost no seizure Δ: Partial seizure ×: Whole seizure Note that the metal is pure titanium “Citadent” (Ti purity 99.5%, Towa Giken Co., Ltd.) or titanium alloy “Citadent II”. (Ti 90%, Al 6%, V4%, Towa Giken Co., Ltd.) was used, and casting was performed using Mycast (manufactured by Towa Sangyo Co., Ltd.).

Example 1 Alumina cement (Asano Cement No. 1,
100 parts by weight of Nippon Cement Co., Ltd., 100 parts by weight of alumina (average particle size 20 μm), 150 parts by weight of zirconium oxide (average 100 μm), 40 parts by weight of tungsten metal powder (manufactured by Wako Pure Chemical Industries, purity 99) 0.9% by weight, average particle size 10 μm), and 5 parts by weight of lithium citrate were sufficiently mixed to obtain a powder component.

The ratio of this powder component and the kneading liquid (water) (P /
L) was mixed in an amount of 100: 20 by weight, and the curing time, fluidity, operating margin, crushing resistance, and expansion rate were examined according to the method described above. The firing temperature is 850 ° C.
As a result, the curing time was 13 minutes, the green strength was 18 MPa, the dry firing strength was 8 MPa, the fluidity was 115 mm, the operation margin time was 5 minutes 30 seconds, and the expansion coefficient was 2.4%, indicating a sufficient expansion coefficient. Further, the mold material did not crack. The expansion coefficient was 2.4% even when the baking temperature was 1000 ° C., and a low baking temperature of 800 ° C. to 850 ° C. was sufficient to obtain a stable expansion coefficient. The firing rate was 10 ° C./minute.

Next, when casting was performed and the seizure was examined, there was almost no seizure. Examples 2 to 10 and Comparative Examples 1 to 4 As shown in Table 1, the type of tungsten metal powder or the binder and the aggregate in Example 1 were changed, and the case where the tungsten metal powder was not used and the zirconium metal powder were used as Comparative Examples. Using. Except for this, the same procedure as in Example 1 was performed, but when acetic acid sol was used as the binder, lithium citrate was not used. The results are shown in Table 2.

In the case of using the zirconium metal powder of Comparative Example 3, when the firing rate was set to 10 ° C./minute, cracks were generated during firing, so that the expansion coefficient, blank firing strength and seizure could not be measured. With the casting materials of Examples 2 to 10, there was almost no seizure, and it was determined to be “◯”. Among them, in Examples 2 to 5 and Examples 7 and 8, the seizure was extremely small and a good casting surface was obtained. In Comparative Examples 1 and 2 containing no tungsten metal powder, expansion did not occur, but rather contraction occurred. In Comparative Example 4, when the content of the tungsten metal powder was 50 parts by weight, the expansion rate was too large and a crack was generated during firing, so the expansion coefficient, the blank firing strength and the seizure could not be measured.

The acetic acid sol shown in the table was zirconyl acetate from Daiichi Rare Element Chemical Industry Co., Ltd., and the alumina cement was Asano Cement No. 1.

[0048]

[Table 1]

[0049]

[Table 2]

Example 13 300 parts by weight of lithium carbonate was added to 100 parts by weight of stearyl alcohol by heating to dissolve it, and the mixture was thoroughly mixed and returned to room temperature to obtain lithium carbonate covered with stearyl alcohol which became solid. Obtained. This was further pulverized to a powder of about 500 μm, and 1 part by weight of this powder and 99 parts by weight of magnesium oxide (average particle size 5 μm) were sufficiently mixed. The stearyl alcohol-coated lithium carbonate diluted with magnesium oxide was used as a masterbatch of lithium carbonate.

100 parts by weight of alumina cement (Asano alumina cement No. 1: Nippon Cement Co., Ltd.) as a binder, and magnesium oxide (average particle size 5 μm) as an aggregate.
150 parts by weight, 150 parts by weight of zirconium oxide, 4 parts by weight of the above lithium carbonate master batch (0.3 parts by weight of lithium carbonate, 0.1 part by weight of stearyl alcohol), and 20 parts by weight of tungsten metal powder (average particle diameter 10 μm). It was thoroughly mixed to obtain a powder component. 100 g of this powder component was mixed with 30 ml of a 20% colloidal silica aqueous solution (Cataloid SI40: Catalysis Co., Ltd.), and the curing time, fluidity, operation margin time, dry firing strength and expansion coefficient were examined in the same manner as in Example 1. As a result, the curing time is 11
Min, fluidity 69 mm, operation allowance time 4 minutes 30 seconds, dry firing strength 7.1 MPa and expansion rate 2.0%. The firing rate was 8 ° C./minute, but no cracks were found in the mold material. When the baking was examined, the baking was scarcely observed, and the result was evaluated as “◯”.

Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display area C04B 14:34)

Claims (1)

[Claims] 1. A mold material for titanium or titanium alloy containing a binder and an aggregate as a basic component, further comprising 5 to 40% by weight of a tungsten metal powder with respect to the binder, said mold. Material.