KR100530313B1 - Magnesia-Phosphate bonded Investment - Google Patents

Abstract

The present invention relates to a magnesia-phosphate-based investment material for precision casting of non-noble metal alloys including dental gold alloys, using magnesia and monobasic ammonium phosphate salts as a binder, quartz, cristobalite, aluminum oxide (Alumina) And zirconium oxide (Zirconia) as a refractory material, and the phosphate content is limited to 8% or less with respect to 100 parts by weight of the refractory, and in order to reduce the coma ratio, quartz sand (Quartz Sand) mixed in a fixed proportion for casting metal to be.

Description

Magnesia-Phosphate Bonded Investment}

The present invention relates to investment materials for precision casting of non-noble metal alloys, including dental gold alloys, and more particularly, to raw materials and production of investment materials, which are irregular refractory materials required for casting dental casting alloys by wax disappearing.

Many medical devices, including dental prostheses, require dimensional accuracy and are often manufactured by casting because of their complex shape. Since the introduction of the first lost-wax practice by Taggart in the UK in 1907, several methods have been tried to obtain satisfactory casting bodies.

Casting refers to a method of making a cast body in a desired size and shape by taking advantage of the fact that the metal is melted at a high temperature and flowable, and such a casting method can easily produce a shape difficult to process. There are many casting methods, but the dentist mainly uses a casting method using a wax disappearing method. The wax disappearing method is one of precision casting methods. A wax pattern is made of wax, and when it is cured after being buried using a buried material, the wax is discharged by heating to a high temperature. At this point, the wax is lost and the molten metal is filled in the remaining cavity.

In the dentistry, the casting method is used to repair the missing hemorrhoids, but when a cast body having poor dimensional accuracy is made, the cement is not suitable for hemorrhoids, or it is excessively expanded to use excess cement, so that the plaque ( plaque) easily deposits, which leads to secondary caries, resulting in restoration failure. Successful fabrication of prosthetics or castings requires the proper investment methods for each investment material, as well as pretreatment such as eliminating undercuts or oblique hemorrhoids, proper impression acquisition, modeling, and use of low shrinkage wax. And choice are important.

The investment material is classified into gypsum-based, phosphate-based, ethyl silicate-based, etc. according to the constituents, which are classified according to the binder which binds the refractory. Generally, all investment materials use silica such as quartz or cristobalite as refractory materials, and gypsum or phosphoric acid-magnesia compounds (MgO-NH ₄ H ₂ PO ₄ ) or ethyl silicate and hydrochloric acid (HCl) as binders. do. Gypsum-based castings are most commonly used for casting alloys with high casting temperatures. In order to cast metals with high melting temperatures such as non-noble metals and titanium, phosphate-based compounds having strong bonding strength are used.

The requirements of the investment material should be easy to mix and easy to operate, and should form a smooth surface and excellent flowability to reproduce fine part precision and margin. In addition, it should not emit harmful gas when heated at high temperature, have no sintering reaction with the alloy surface, and have a porous structure so that air or gas can escape into the investment material during casting. And the investment material should not be destroyed at high temperatures, and after the casting is completed, the investment material should be easily removed from the metal surface. It should also have sufficient hardening and thermal expansion to compensate for shrinkage of the wax and solidification shrinkage of the metal. These properties are common to all types of investment materials.

Among the requirements of such investment materials, the most necessary properties for the production of precise castings are expansion ratio and gas permeability.

Expansion of investment material includes curing expansion, hydration expansion and thermal expansion. Cure expansion occurs as the binder grows or bonds, with an average 0.5% expansion. Hydration expansion can be obtained by adding a small amount of water after curing, mainly by the method used in gypsum-based. Cure expansion and hydration expansion are dependent on the binder, while thermal expansion can be obtained using a refractory material.

The expansion of the magnesia-phosphate-based investment material is made possible by changing the content of magnesia and phosphate used as the binder and controlling the ratio of quartz and cristobalite used as the refractory material. Theoretically, quartz undergoes about 1.4% expansion at phase transformation from 573 ° C. to α → β and cristobalite at 1.6 ° C. at 200-270 ° C. as well. Therefore, by controlling the ratio of these binders, refractory materials and additives, it is possible to produce investment materials to compensate for shrinkage of the metal and wax.

As for the investment casting material for high temperature casting, the phosphate-based investment material disclosed in Korean Patent Publication No. 2000-0020333 is known. By the way, in the Korean Patent Publication, the content of the phosphate is 9-12% with respect to 100 parts by weight of the refractory, and there is a problem of causing sintering reaction with the metal due to extra phosphorus which is not consumed during high temperature casting. On the other hand, the phosphate-based investment material imported and used in Korea has a problem in that it is difficult to manufacture a large casting due to lack of strength at high temperature and has excessive expansion.

The present invention has been made to solve the above problems, the object of the present invention is to reduce the sintering reaction due to the excess phosphorus (phosphorus) that can occur at high temperatures to form a casting material that can produce a smooth and metallic color reproduction To provide.

It is another object of the present invention to provide a buried material which can reduce the content of coma ratio and cristobalite to prevent excessive swelling, reduce the reaction product by sintering with molten metal and enhance the high temperature strength.

The investment material according to the present invention for achieving the above object, including magnesia and monobasic ammonium phosphate salt, containing 5.5-8 parts by weight of the ammonium phosphate monobasic salt, and 9-13 parts by weight of magnesia relative to 100 parts by weight of the refractory It features.

At this time, by including 20 to 40 parts by weight of quartz sand with respect to 100 parts by weight of the refractory, it is possible to prevent the shrinkage of the investment material due to the dehydration of water.

Further, by further including 1-5 parts by weight of aluminum oxide and 1-3 parts by weight of zirconium oxide with respect to 100 parts by weight of the refractory, it is possible to obtain the surface stability and strength enhancing effect at a high temperature.

In addition, by further comprising 0.02-0.05 parts by weight of nano-sized aluminum oxide as an additive with respect to 100 parts by weight of the refractory, it is possible to give a viscosity at the time of mixing the buried material and increase the high temperature strength.

Hereinafter, the specific features of the present invention will be described in more detail.

The greatest feature of the present invention, in preparing a magnesia-phosphate-based investment material, is to mix the magnesia and ammonium monophosphate salt, but to limit the content of ammonium phosphate monobasic salt to 8 parts by weight or less, preferably from 5.5 to 8 parts by weight Restrict. Ammonium phosphate monobasic is not specifically limited, A well-known thing was used. At this time, the content of magnesia is preferably 9 to 13 parts by weight based on 100 parts by weight of the refractory.

In addition, a second feature of the present invention is to use a quartz sand, specifically, using 40-40 parts by weight of a quartz sand having a size of 100-300 μm with respect to 100 parts by weight of a refractory material.

In addition, a third feature of the present invention is to add aluminum oxide and zirconium oxide to the refractory to contribute to surface stability and strength enhancement at a high temperature. Specifically, aluminum oxide 1-5 to 100 parts by weight of the refractory. By weight, 1-3 parts by weight of zirconium oxide is added.

In addition, the fourth feature of the present invention is to add nano-sized aluminum oxide as an additive to impart viscosity when mixing the buried material and to increase the high temperature strength, specifically, 100-200nm aluminum oxide powder based on 100 parts by weight of the refractory material. 0.02-0.05 parts by weight is added.

According to the present invention, in the magnesia-phosphate investment material for precision casting of metal, magnesia and monobasic ammonium phosphate salt were used as binders, and quartz, cristobalite, aluminum oxide, and zirconia oxide were used. In particular, the content of phosphate is limited to 8% or less with respect to 100 parts by weight of refractory.Quartz Sand is mixed in a fixed ratio to eliminate the quenching reaction with metal and increase the strength after summoning to increase the casting pressure. It provides an investment material that withstands.

By limiting the phosphate content to 8 parts by weight or less as the investment material, the ammonium phosphate monobasic is decomposed as NH ₄ ⁺ + PO ₄ ^3- + 2H ⁺ by water contained in the colloidal silica solution added when the investment material is cured. In detail, the buried material is cured by combining the decomposed PO ₄ ^3- ions and Mg ²⁺ dissociated in Mg (OH) ₂ . At this time, not all of the added phosphate is decomposed, but excess phosphorus remains and reacts with the final metal casting to cause sintering reaction on the surface. Therefore, when more than 8 parts by weight of phosphate is added, the solubility of the phosphate is limited, which causes excess phosphorus (phosphors) to cause sintering reaction with the cast metal.

The addition amount of the monoammonium phosphate salt used for this invention is 5.5-8 weight part with respect to 100 weight part of other refractory components. The resulting magnesia is 9-13 parts by weight with respect to 100 parts by weight of the other refractory components. Although the amount of each additive is not absolute, if it greatly exceeds the above range, it causes sintering reaction on the surface of the cast and the surface is not smooth due to incomplete hardening.

In addition, by adding the quartz sand as in the present invention, when only the quartz powder is added, an excess water is required to maintain a proper mixing ratio, and the investment material may be prevented from shrinking due to dehydration of water. In addition, it is also effective to reduce the proportion of the pores in the investment material by mixing the powder of various sizes. If the amount of quartz sand is excessively added, the cristobalite content in the investment material is reduced, thereby reducing the expansion. On the contrary, if the amount of sand is reduced, excess water is required for sufficient mixing, causing shrinkage.

In addition, in the present invention, the nano-sized aluminum oxide and zirconium oxide added to impart high temperature strength and improve high temperature heat resistance have improved high temperature heat resistance and strength as their amount is increased, but if excessively added, the price of the final product increases. If the amount is too small, the effect can not be exhibited. Specifically, in the case of nano-sized aluminum oxide, it reacts with magnesia added at high temperature (850 ° C) as well as its thermal stability, thereby forming a spinel structure oxide (MgAl ₂ O ₄ ) and contributing to strength enhancement. Zirconium oxide has excellent heat resistance and is not reactive with molten metal at high temperature, thus contributing to surface improvement. However, when a small amount is added, the effect is difficult to expect.

Therefore, if the mixing ratio of magnesia and ammonium phosphate, quartz, quartz sand, cristobalite, aluminum oxide and zirconium oxide is properly adjusted, there is no sintering reaction during casting at high temperature, it has strength to withstand casting pressure, and sufficiently expands casting shrinkage. It can be given to the investment material.

Although not particularly limited, in order to eliminate the high temperature sintering reaction of the precious metal alloy for precision casting currently used and to obtain strength to withstand expansion and casting pressure to compensate for casting shrinkage, the mixing ratio of the binder is 15 to 20% by weight. %, Quartz is 5-20% by weight, quartz sand is 20-40% by weight, cristobalite is 10-30% by weight, aluminum oxide is 1-5% by weight and zirconium oxide is 1-3% by weight. When the mixing ratio in the investment material for precise casting of the dental alloy of the general composition greatly exceeds the above range, the strength of the investment material is lowered, the dimensional accuracy of the casting is lowered, and a lot of surface defects of the casting are generated.

Features and other advantages of the present invention as described above will become more apparent from the following experimental examples. The present invention is not limited to the following experimental examples.

Experimental Example

As shown in Tables 1 to 5 below, a buried material was prepared by varying the mixing ratio of quartz, cristobalite, aluminum oxide and zirconium oxide, and nano-sized aluminum oxide as a refractory material and a binder, and at room temperature curing expansion, thermal expansion, The compressive strength and cast surface characteristics were tested. At this time, in order to prepare a slurry for investment material, 30 wt% colloidal silica liquid was mixed as a softening liquid at a rate of 20 ml per 100 g of investment material powder, and the size of the hardening expansion measurement specimen was 100 mm in length and 30 mm in top width. The amount of linear curing expansion was measured for 2 hours by pouring into a V-type mold, and the thermal expansion was cured for 2 hours with a specimen size of φ6 × 12 mm, and then heated to 900 ° C. at a temperature rising rate of 5 ° C./min at room temperature. After maintaining for 20 minutes at 900 ℃, it was measured by cooling to room temperature.

Tables 1 to 5 show the characteristics of the ammonium phosphate salt, quartz sand, aluminum oxide, zirconium oxide, and nano aluminum oxide, respectively.

The compressive strength for each case was tested. 60 g of the material was mixed and 60 minutes after the start of mixing, the specimen was removed from the mold and stored at 23 ± 2 ° C. and a relative humidity of 30 ± 10%. The specimen was placed in the axial direction under the load of the test instrument (Instron 6022, U.K.) and no packing was used between the specimen and the plat. At 120 ± 5 minutes after the start of mixing, the pressure began to be applied at a cross-head speed of 0.5 mm / min and the force was recorded until breakage occurred.

Casting characteristics for each example were tested. At this time, the casting characteristics test was carried out by casting experiments of the non-noble metal alloy by the wax disappearing method, in order to prepare a slurry for the investment material 30% by weight colloidal silica was mixed in a ratio of 20 ml per 100g of investment material as a softening liquid. A wax-made model was placed in a metal mold and the investment material slurry mixed with distilled water was filled into the metal mold and cured for 2 hours. The mold containing the cured investment material was heated to 850 ° C. at a temperature rising rate of 10 / min at room temperature and maintained at 850 ° C. for 30 minutes, and then casting experiments were conducted by dissolving the alloy.

Example 1

When the refractory was fixed at 82 parts by weight and the content ratio of magnesia and monobasic ammonium phosphate was changed, the cure expansion rate, thermal expansion rate, and surface quenching reaction of the real casting were observed. The surface was shown and sintering reaction was observed. In addition, it was observed that as the weight part of ammonium phosphate salt decreased, surface properties were improved and the cure expansion rate gradually increased. However, when the ammonium monophosphate salt dropped below 6 parts by weight, it was observed that the surface properties were lowered again and the curing expansion was also reduced. The results of this example are shown in Table 1 and FIGS. 1 to 4.

[Table 1] Changes in the amount of ammonium phosphate added

Component Test No. MgO (% by weight) NH4H2PO4 (% by weight) Refractory (% by weight) Cure expansion rate (%) Thermal expansion rate (%) Casting surface (sintering reaction) One 9 9 82 0.4 1.2 × 2 11 7 82 0.6 1.3 ● 3 12 6 82 0.7 1.4 ○ 4 12.5 5.5 82 0.2 1.2 ◎

×: sintering reaction, ●: rough surface, ○: normal surface, ◎: smooth surface

Example 2

Example 2 was intended to determine the effect on the coma and the strength and thermal expansion by using the same binder and by changing the proportion of quartz sand in the refractory. The results are shown in Table 2. As the amount of quartz sand increased, the coma ratio decreased and the thermal expansion rate gradually decreased. In particular, when the quartz sand is added at 30 parts by weight or less and when added at 50 parts by weight or more, physical properties of the material may be observed to decrease.

[Table 2] Change of physical properties according to the change of quartz sand

Component Test No. Binder (wt%) Quartz Sand (wt%) Other Refractory (wt%) Proper Coma Ratio (%) burglar(%) Thermal expansion rate (%) 5 20 20 60 0.3 or more × × 6 20 30 50 0.26 2.5 1.4 7 20 40 40 0.22 3.0 1.3 8 20 50 30 0.18 2.0 0.9

X: Not mixed

Example 3

Table 3 shows the results of varying the weight ratio of aluminum oxide to improve high temperature strength and surface properties. When the content of aluminum oxide was increased, both surface properties and strength were improved. However, the effect of improving the strength did not change significantly at 3 parts by weight or more, and at about 0.5 parts by weight, it was difficult to expect the effect.

[Table 3] Change according to the change of aluminum oxide

Component Test No. Binder (wt%) Alumina (% by weight) Zirconia (% by weight) Nano alumina (wt%) Other Refactory (wt%) burglar(%) Casting surface (sintering reaction) 9 20 0.5 0 0 79.5 2.50 × 10 20 3 0 0 77 3.65 ◎ 11 20 5 0 0 75 3.80 ○ 12 20 6 0 0 74 3.20 ○

×: sintering reaction, ●: rough surface, ○: excellent surface, ◎: smooth surface

Example 4

Example 4 was tested for improvement of sintering reaction with molten metal at high temperature. When the content ratio of zirconium oxide was increased, the surface was gradually improved, but it was observed that the strength was increased by a very large difference rather than the improvement of the surface properties. The addition of 0.5 parts by weight of zirconium oxide alone showed a large increase in strength.

[Table 4] Physical Properties of Zirconium Oxide Addition

Component Test No. Binder (wt%) Alumina (% by weight) Zirconia (% by weight) Nano alumina (wt%) Other Refactory (wt%) burglar(%) Casting surface (sintering reaction) 13 20 0 0.5 0 79.5 3.4 × 14 20 0 1.0 0 79.0 3.7 ○ 15 20 0 2.0 0 78.0 3.6 ◎ 16 20 0 3.0 0 77.0 3.8 ○

×: sintering reaction, ●: rough surface, ○: excellent surface, ◎: smooth surface

Example 5

Example 5 was carried out to verify the effect of enhancing the strength according to the addition of nano-sized aluminum oxide. In particular, although not particularly limited, the addition of nano-sized aluminum oxide showed a large increase in strength.

[Table 5] Properties of Nano Aluminum Oxide Added

Component Test No. Binder (wt%) alumina (% by weight) Zirconia (% by weight) Nano alumina (wt%) Other refractory (% by weight) Hardening expansion (%) Compressive strength (MPa) 17 20 0 0 0.02 79.08 0.6 3.6 18 20 0 0 0.05 79.05 0.6 3.4 19 20 0 0 0.10 79.90 0.6 3.6 20 20 0 0 0.50 79.50 0.5 4.5

In the accompanying drawings, Figures 1 to 4 are the component test No. 1 of Table 1 showing the characteristics according to the change amount of the ammonium phosphate monobasic. The casting according to the composition according to 1 to 4 is shown, and FIGS. 5 to 8 are the component test Nos. 9 to 12 shows the casting by the composition, Figures 9 to 12 show the casting by the composition of Table 4 showing the physical properties according to the change in the amount of addition of zirconium oxide.

As described above, according to the present invention, by using magnesia and monobasic ammonium phosphate as a binder, using quartz, cristobalite, aluminum oxide, zirconium oxide as a refractory material, casting pressure by changing the amount of addition of nano-sized aluminum oxide as an additive The mixing ratio can be obtained to obtain the proper expansion amount to compensate for the casting shrinkage of the cast metal, and the investment material blended with the mixing ratio can be used to obtain the dimensional accuracy of the casting and the beauty of the cast surface. By improving the marketability can be greatly improved.

Although the above has been illustrated and described with respect to the preferred embodiment of the present invention, the present invention is not limited to the above-described specific embodiment, those skilled in the art will be various within the scope not departing from the gist of the present invention. Modifications are possible, of course, such modifications will fall within the scope of the claims of the present invention.

1 to 4 is a view showing a casting by the composition of varying the amount of ammonium phosphate monobasic;

5 to 8 show castings with compositions of varying aluminum oxide, and

9 to 12 are diagrams showing castings having compositions with varying amounts of zirconium oxide added.

Claims (5)

As a magnesia-phosphate investment material for precision casting of cast metal, 9 to 13 parts by weight of magnesia, 5.5 to 8 parts by weight of ammonium phosphate salt, 20 to 40 parts by weight of quartz sand, 1 to 5 parts by weight of aluminum oxide, and 1-3 parts by weight of zirconium oxide, based on 100 parts by weight of refractory. As an investment material, characterized in that it further comprises 0.02-0.05 parts by weight of nano-sized aluminum oxide. delete delete delete delete