JPS6234450B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to the improvement of a mold material for casting titanium or a titanium alloy, and is used for casting dental castings and precision machine casting parts. (Prior art) Gold alloys, silver-palladium alloys, nickel-chromium, cobalt-chromium alloys, etc. have been widely used in the casting of precision castings such as dental castings. It is usually cast using a silica-based gypsum-based mold material or a high-temperature phosphoric acid-based mold material. However, the gold alloys and silver-palladium alloys have problems in terms of price and corrosion resistance (especially silver alloys), and the cobalt-chromium alloys have problems in terms of stable supply of chromium and cobalt due to underground resources. In addition to the problems, it also has the disadvantage that it is too hard for metals such as crown bridges. Furthermore, nickel
Regarding chromium alloys, the biotoxicity of nickel has been pointed out in recent years, and the use of chromium alloys has been viewed as a problem. Therefore, in recent years, titanium and titanium alloys, which are relatively abundant underground resources and have excellent biocompatibility, have been attracting attention as metals for casting in the dental field and the like. In other words, titanium (a) has excellent corrosion resistance and biocompatibility, (b) mechanical properties (strength, hardness) are optimal as a dental metal, etc., and (c) titanium is a nickel-chromium alloy. It has excellent properties such as being lightweight with a specific gravity of approximately 1/2 compared to other alloys, and (d) considering its specific gravity, it is cheaper than nickel-chromium alloys, etc. In the dental field, etc., there is a strong desire for its practical application and widespread use. However, titanium has a high melting point (approximately 1720℃),
It is easily oxidized at high temperatures, has extremely high high-temperature activity, and has the characteristics of a considerably large amount of shrinkage of the cast body, so conventional mold materials, such as high-temperature phosphate mold materials based on silica and magnesia-based mold materials, cannot be used. With mold materials, it is impossible to cast a cast body with desired dimensional accuracy. Therefore, various experimental studies are being conducted to develop new mold materials for titanium or titanium alloys. The inventor of the present application also uses (a) magnesia (MgO) as a mold material for casting titanium or titanium alloy.
(b) Aggregates mainly composed of magnesia (MgO) to which alkali metal hydrogen carbonate, alkaline earth metal carbonate, etc. are added as hardening accelerators, and (b) aggregates mainly composed of magnesia (MgO). We have developed and published a mold material in which alkali metal hydrogen carbonate, alkaline earth metal carbonate, etc. are added as hardening accelerators, and fine aluminum powder is added as an expansion accelerator. By the way, a mold material made by adding a hardening accelerator and an expansion accelerator (fine aluminum powder) to the aggregate mainly composed of magnesia has the following properties: (a) The solidification of the mold material mixed with water is promoted, and mold manufacturing is facilitated. (b) When the mold material (green mold) mixed with water is cured, the green mold expands by about 0.7 to 0.8%;
The mold expands by 0.5 to 0.7% during casting (approximately 700 to 800°C), resulting in an overall mold expansion of approximately 1.5%, and (c) the compressive strength of the mold is improved by the action of the hardening accelerator. It has excellent practical utility. (Problems to be Solved by the Invention) However, the mold material still has many problems to be solved as described below. (1) The maximum mold expansion obtained by adding aluminum powder is about 1.5%, which is far from the optimal mold expansion of 1.8% required for titanium or titanium alloys, and as a result, it is not sufficient. dimensional compensation cannot be achieved. (2) Hydrogen gas generated when aluminum and water react causes the mold to expand (approximately 0.8%) during green mold hardening (mold condensation). Because it is hardened, expansion in the lateral direction is restricted, resulting in an imbalance between expansion in the vertical direction and expansion in the lateral direction, which may cause deformation of the wax pattern in dental castings, etc. be. (3) It is quite difficult to control the amount of hydrogen gas in the mold material during curing to a desired value, and it is not always possible to obtain a constant expansion rate even if the mixing ratio of aluminum is the same. Further, if hydrogen gas remains in the mold, various problems occur when the mold is heated. The purpose of the present invention is to solve the above-mentioned problems with conventional mold materials. At least one of an alloy powder containing Zr as a main component and Sn powder is mixed in advance, the metal powder is oxidized during mold heating, and the expansion caused by the oxidation is utilized.
That is, when the molten metal cools to room temperature, its dimensions shrink more than when it was molten. However, if the mold expands by the amount of shrinkage during casting, it is possible to obtain a cast body that matches the original shape (e.g. wax pattern).
Full dimensional compensation will be achieved. The present invention has the following advantages: (a) When melt casting titanium or titanium alloy, the shrinkage rate (approximately 1.8%) of the cast product can be almost completely compensated for the dimensions, and (b) the expansion of the mold is It is obtained when the mold is heated rather than during curing, and as a result (c) it is possible to cast extremely high-precision castings without causing any deformation of the original model (wax pattern) and with almost no dimensional errors. The purpose is to provide mold materials. (Means for Solving the Problems) The present invention adds a metal powder that does not generate gas during curing and heating of the mold material into the mold material, and utilizes the expansion of the metal powder due to oxidation. The basic structure is to expand the mold by an appropriate amount during heating. (Function) The metal powder added into the mold material is oxidized by heating the mold, and the volume of the oxidized metal powder increases. As a result, the mold as a whole expands in volume, and the volume of the casting space after dewaxing also increases at a constant rate. In addition, with the mold stored in the metal mold frame,
Even when the mold is heated together with the mold, the metal mold itself expands due to heating, so there are no inconveniences caused by restricting expansion in the radial direction, such as expansion when the mold hardens. Does not occur. (Example) Various experiments regarding the mold material according to the present invention and their results will be described below. In experiments related to the present invention, as a mold material,
Magnesia mold material (MD) manufactured by Taihei Shoji Co., Ltd.
-105) is used, and the composition of the magnesia-based mold material is shown in Table 1.

[Table] In addition, in the present invention, Zr, Fe, Si, and Sn powders manufactured by Hanui Chemical Industry Co., Ltd. and Cu, Ni, and Cr powders manufactured by Nippon Powder Metallurgy Co., Ltd. are used as metal powders, respectively. has been done. Furthermore, among the above-mentioned metal powders, the one whose free energy of oxide formation is smaller than that of titanium or titanium alloy is Zr powder, and as described later, this Zr powder is the most suitable for carrying out the present invention among these metal powders. It turned out to be a suitable metal. In this example, the magnesia mold material and metal powder were used to measure (a) dimensional changes during mold hardening, (b) dimensional changes during mold heating, and (c) casting and conformance. A sex test was conducted. The above test methods and test results are as follows. (b) Measurement of dimensional changes during mold hardening As shown in Figure 1, inner diameter D = 25mmφ, height L =
A 30 mm metal tube 1 is lined with Kao wool 2 and fixed on a plastic plate 4 with wax 3. Next, a mold material slurry is poured while being vibrated with a vibrator, a plastic plate (floating plate) 5 is placed on top of the slurry, and a differential transformer 6 is used to measure dimensional changes in the vertical direction. Note that the load caused by the differential transformer 6 is approximately 5 gr. (b) Measurement of dimensional changes during mold heating The mold material slurry is poured into silicone rubber split molds 7a and 7b as shown in Figure 2 a and b while being vibrated, and when green strength is obtained (from pouring to about 18
After an hour), the molds 7a and 7b were taken out, heated at a rate of 5° C. per minute, and the amount of dimensional change was measured. In addition, the sample made from the split mold shown in Figure 2a (5mmφ×
20mm) was measured using a thermal expansion analyzer (Thermoflex) manufactured by Rigaku Denki Kogyo Co., Ltd.
Sample using the split mold shown in Figure b (4mm x 6mm x 10mm)
The dimensional changes were measured using a thermomechanical analysis device (TM-20) manufactured by Shimadzu Corporation. The load measured by the measuring device, etc. is approximately 5g.
It is. (c) Casting test and suitability test for cast products Add the specified amount of water to the mold material and first mix it in advance. The amount of water was kept to a minimum without impairing operability, and preliminary kneading was carried out by hand kneading for a few seconds. After that, it was kneaded for 2 minutes using a vacuum automatic kneader (CONEL) manufactured by Towa Giken Co., Ltd., and the sunken mold material buried with the wax pattern was dried at room temperature for about 16 hours while being vibrated with a vibrator. After that, it is heated in an electric furnace under various heating conditions (with or without a heating ring, heating speed, heating temperature, etc.), and then casted using an argon arc melting casting machine (CASTMATIC) manufactured by Iwatani Sangyo Co., Ltd. and carried out casting. Pure titanium KS-50 (purity of 99.8% or more) manufactured by Kobe Steel, Ltd. was used as the casting metal for compatibility tests, casting surface roughness, and seizure tests. The form of the buried wax pattern is as follows:
As shown in FIGS. 3a to 3d, a mold 9a,
There were four types: bMOD-inlay 9b, c-clinical pattern 9c, and d-bridge 9d. Castings of each pattern were investigated for casting surface roughness, seizure, etc. (d) Compatibility test for cast products The compatibility of cast products is determined by the amount of uplift A between the abutment tooth 8 and the cast body 9, as shown in Figures 4a to 4c.
was investigated by measuring it using a sliding microscope. Incidentally, the measurement point for the amount of uplift is shown by A in FIG. 4, but the amount of uplift is not measured for the bridge because the measurement point is complicated. Next, the results of each of the above tests will be explained. (1) Preliminary test regarding casting and compatibility First, tests were conducted using the magnesia molding material MD-105 as a base material and adding 5% by weight of various metal powders to it. The test results are shown in Table 2.

[Table] (2) Measurement results of dimensional changes during mold hardening From the results of the casting and compatibility preliminary tests,
In the case where zirconium powder was added, which gave relatively good test results, dimensional changes were measured using the amount added as a parameter. The result is the fifth
As shown in the figure, curve _C1 contains 3wt% Zr, and curve _C2 contains 3wt% Zr.
4wt%, _C3 is 5wt%, _C4 is 6wt%, _C5 is 6.54wt%
In addition, C ₆ shows the case where Zr=0wt%. There is no correlation between the amount of Zr powder added and the dimensional change during curing. In conclusion, M.D.
- When Zr powder is added to 105, the maximum shrinkage during curing is about 0.2%, excluding the influence of the measurement load (about 0.2%). (3) Measurement results of dimensional changes during mold heating The measurement results of dimensional changes during heating are shown in Figure 6. In addition, in Figure 6, curve D ₁ has Zr of 3wt.
%, _D2 is 4wt%, _D3 is 5wt%, _D4 is 6wt%, _D5 is
The case of 6.54wt% is shown respectively. As is clear from FIG. 6, the dimensional change during heating is approximately proportional to the amount of Zr powder added. When adding 5wt% of Zr powder, the dimensional change rate at 900℃ is +2.25%, and considering the shrinkage (about 0.2 to 0.4) during mold hardening, the total expansion is about 1.85%.
(900℃). That is, by adding 5wt% of Zr powder,
The required mold expansion will be achieved. (4) Results of casting and compatibility test (1) Tests were conducted by changing the heating conditions during casting and the use or non-use of a ring during heating. This is because there is a close relationship between the degree of oxidation of the Zr powder and the compatibility of the cast body. Table 3 (a) is the result of the compatibility test.
(b) shows the heating conditions, and in any case, no seizure or roughening of the casting surface occurs on each cast body.

【table】

【table】

[Table] (1) and (2), (2) and (3), (5) and (6) in Table 3 are the cases in which a ring is fitted into the mold when heating mold materials of the same composition. This is a comparison of whether it is better to heat the product as it is or to heat it without a ring. In either case, using a ring improves compatibility than not using a ring. are doing. In addition, (7), (8), and (9) examine the difference in oxidation depending on the buried position of the wax pattern, and
As shown in the figure, the temperature range for Zr oxide formation is about 600 to 700°C, so this temperature range was heated at a low heating rate. As a result (7), it was found that the surface side was well elongated, but the center side was less elongated, causing considerable distortion. There was almost no difference between molds (8) and (9) when they were wide horizontally and when they were long vertically. In other words, if the embedded wax pattern is fixed at the center of the mold, a cast body with almost no distortion can be obtained. Finally, regarding (10), (11), (12) and (13),
We investigated whether there is a difference between ring and ringless materials when slowly heated to Zr oxide formation temperature range (approximately 600 to 700 degrees Celsius). The temperature range for slow heating was 600 to 750°C for safety reasons, and the temperature increase rate was 0.8°C/min. In (12) and (13), the ring is clearly a better fit than the ringless one. Comparing (10) and (11), it seems that the ringless one has better compatibility, but the cast body of (11) had air bubbles on the inside of the cup due to poor burial, so the air bubbles were removed. This is thought to have caused a poor fit during fitting. Therefore, in this case (slow heating between 600 and 750℃),
It was found that using a ring was more effective than using a ringless method. Furthermore, when comparing (1) and (13), in which 5 wt% of Zr was added, (13) has considerably better compatibility. From this, it was found that in the Zr oxide formation temperature range (between 600 and 700°C), slow heating improves compatibility. To summarize the above results, in order to completely oxidize the Zr powder in the mold material without deforming the cast body, the heating rate should be slow (especially between 600 and 700℃), a ring should be used, and the inside of the Zr powder should be oxidized slowly. Since the method of spreading Kao wool seemed to be optimal, subsequent heating was performed using this method. (5) Results of casting and compatibility test (2) As shown in Figure 7, stainless steel ring 10a
After fixing the wax pattern 11 to the truncated cone 13 with the spool 12 and pouring the molding slurry into it, it is dried for about 16 hours. . Thereafter, the stand 14 and the truncated cone 13 were removed and heated as they were in an electric furnace to 900° C. according to the schedule shown in FIG. 8, and various wax patterns were cast. Incidentally, the casting results are as in the case of the first example.
No roughening or burning of the casting surface is observed in any of the cast bodies. Next, a compatibility test was conducted for each cast body cast by the above method. Table 4 shows the results.

[Table] In the clinical pattern compatibility test, the compatibility improved as the amount of Zr powder added increased. However, with Zr5wt% addition and Zr6wt% addition,
Since the difference is only 0.02 mm and the mold is disposable, taking economic aspects into account, it seems appropriate to add Zr powder at about 5 wt%. In clinical applications, the lifting amount is approximately the same as the alloy currently in use (approximately 0.06 mm).
This is because there seems to be no problem. In addition, in a compliance test using a MOD-inlay with 5wt% Zr powder added, the lifting amount was 0.44mm.
It may not seem like a good fit, but even when conventional dental alloys are used, this level of lifting is achieved. This is because MOD inlays do not fit into the abutment teeth if the cast is too large or too small.
From the MOD-inlay compliance test, it seems that the amount of Zr powder added is approximately 5wt%. Compatibility testing with Bridge also shows that the compatibility is comparable to that of conventional dental alloys. As mentioned above, in this example, by adding Zr powder of 2 to 7 wt%, preferably 5 wt%, to MD-105, which is a magnesia-based molding material, a cast body without roughening of the casting surface or seizure was created. and nearly perfect dimensional compensation can be achieved. In addition, in this example, high purity (purity 99.8% or more)
The cast metal is titanium, but it is possible to obtain almost the same results as in each of the above embodiments even with titanium with a lower purity than this, or with an alloy of titanium and other metals. can. For example, in the case of an alloy containing 50 to 60 wt% titanium, Zr powder is
It has been confirmed that the desired purpose can be sufficiently achieved by adding ~3%. Moreover, although high-purity Zr powder is used in this example, even low-purity Zr powder, Zr-based alloy powder, and Sn powder can be used to achieve the desired results. can achieve the objectives of Furthermore, in this example, the above-mentioned mold material was used.
MD-105 is used, but the mold material is MD-105.
Of course, the material is not limited to 105, and other types of mold materials may be used. (Effects of the Invention) In the present invention, an appropriate amount of metal powder is added to the mold material and the expansion due to oxidation is utilized, so that an extremely high expansion coefficient of the mold can be obtained during heating. , almost perfect dimensional compensation can be easily achieved, and casting can be performed without roughening of the casting surface or seizure. Further, in the present invention, unlike the prior art, the mold is not expanded by the generated gas, so there is no adverse effect caused by the gas, and a cast body that substantially matches the original mold can be obtained. Furthermore, in the present invention, the mold expands only when it is heated, and no expansion occurs when the mold hardens, so there is no adverse effect on the wax pattern compared to the prior art, and extremely high precision casting can be achieved. You can get a body. As mentioned above, the present invention has excellent practical utility.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a method for measuring dimensional changes during mold hardening. FIG. 2 is a perspective view of a silicone rubber split mold used to measure dimensional changes during mold heating. FIG. 3 is a perspective view of various wax patterns used in casting tests. FIG. 4 is an explanatory diagram showing locations where the amount of lifting of various wax patterns is measured. FIG. 5 shows the rate of dimensional change during curing of the mold. FIG. 6 shows the rate of dimensional change during heating of the mold. FIG. 7 is a perspective view of the casting apparatus in another casting test. FIG. 8 is a heating schedule curve of the mold. 1...metal tube, 2...kao wool, 3...wax,
4... Plastic plate, 5... Floating plate, 6... Differential transformer, 7a, 7b... Split mold, 8... Abutment tooth, 9... Cast body, A... Floating amount.

Claims (1)

[Scope of Claims] 1. Titanium, which is made by adding at least one of zirconium powder, zirconium-based alloy powder, and tin powder to the main mold aggregate as a mold expansion accelerator. Or mold material for casting titanium alloys. 2. The mold material for casting titanium or titanium alloy according to claim 1, wherein the main mold aggregate is a magnesia-based mold aggregate. 3 Adding zirconium component from 2% by weight to 7%
A mold material for casting titanium or a titanium alloy according to claim 1 expressed in weight %.