TITLE:

Surface Properties of Electrochemically Buffed Titanium Casting

LANGUAGE:

in English

AUTHORS:

Okawa S, Hossain A, Kanatani M, Watanabe K and Miyakawa O Corresponding author, E-mail: sokawa@dent.niigata-u.ac.jp

INSTITUTE:

Division of Dental Biomaterial Science, Niigata Universtiy Graduate School of Medical and Dental Sciences

JOURNAL:

Dental Materials Journal Vol. 23 No. 4 504-511 (2004)

KEYWORDS: Titanium, Polishing, Surface characterization

ABSTRACT:
Electrochemical buffing, a combined process of electrochemical and mechanical polishing, was applied to titanium casting. Mixture of a-Al₂O₃ suspension (average grain diameter of 5 mm) and 5% KNO₃ solution was used as abrasive slurry. Specimen and experimental wheel buff were respectively connected to the positive arid negative poles of a DC source, whose potential ratings ranged from 0 V (MEP) to 10 V (ECB10). Surface roughness, hardness, color, and cleanness were investigated. ECB10 surface produced a gold color and attained a mirror finish, as its roughness value was only one-quarter that of MEP. High amount of aluminum was present in MEP surface. Its bond state entirely differed from that of a-Al₂O₃, hence indicating surface alteration due to chemical reactions with the abrasive material. At higher potentials, reaction products might be dissolved anodically, so that the surface was chemically clean to some extent. The surface also became rich in OH^-.

TITLE:

Pressure Behavior of the Mold Cavity in a Differential Pressure Casting Unit with Two Chambers -- Influence of Mold Temperature, Mold Size and Crucible Conditions --

LANGUAGE:

in JAPANESE with English Abstract

AUTHORS:

Okawa S, Kanatani M, Watanabe K, Nakano S, Miyakawa O

INSTITUTE:

Division of Dental Biomaterial Science, Niigata Universtiy Graduate School of Medical and Dental Sciences

JOURNAL:

The Journal of the Japanese Society for Dental Materials and Device Vol. 23 No. 1 1-7 (2004)

KEYWORDS: Casting mold, Permeability, Titanium, Casting pressure, Pressure casting .

ABSTRACT:
In a two-chamber pressure-casting system, the rate of casting pressure increase depends on the exhausting rate of argon gas in the mold. The purpose of this study was to measure the pressure change in a mold cavity after the start of casting and to investigate the influence of mold temperature and thickness on the initial rate and later value of casting pressure. Moreover, a new casting mold with an experimentally improved crucible was proposed and its influence on the casting pressure was also investigated. Regardless of crucible condition, the initial rate of casting pressure decreased with mold temperature and thickness. Although the difference in crucible condition did not significantly influence the initial rate, the improved crucible increased the later value of casting pressure.

TITLE:

Pressure Behavior in Mold Cavity during Titanium Casting — Differential Pressure Casting Unit with Two Chambers—

LANGUAGE:

in JAPANESE with English Abstract

AUTHORS:

Okawa,S., Kanatani,M., Watanabe,K., Nakano,S., and Miyakawa,O.

INSTITUTE:

Division of Dental Biomaterial Science, Niigata Universtiy Graduate School of Medical and Dental Sciences

JOURNAL:

The Journal of the Japanese Society for Dental Materials and Device Vol. 22 No. 1 37-44 (2003)

KEYWORDS: Casting mold, Permeability, Casting condition, Titanium, Casting pressure, Pressure Casting

ABSTRACT:
Since the mold cavity is exposed to the melting chamber in a two-chamber casting unit, the cavity is filled with Ar gas till casting of molten titanium. Thus, the gas evacuation rate immediately after melt casting must influence the castability and generation of internal defects. In this study, the cavity pressure was measured using a mold simulating a two-chamber casting process at room temperature and the results were converted into the casting pressure. Mold permeability and preset pressures in the melting and casting chambers were considered as factors influencing the quality of casting. The higher the mold permeability and the higher the difference between the preset pressures, the higher level the casting pressure rapidly reached.
The results suggested that the choice of investment material should be made from the perspective of mold permeability suitable to the casting mechnaism.

TITLE:

Pressure Behavior in the Cavity on Casting — An Enclosed One-chamber Casting Unit—

LANGUAGE:

in JAPANESE with English Abstract

AUTHORS:

Okawa,S., Watanabe,K., Kanatani,M., Nakano,S., and Miyakawa,O.

INSTITUTE:

Dental Materials and Technology, Faculty of Dentistry, Niigata University

JOURNAL:

The Journal of the Japanese Society for Dental Materials and Device Vol. 19 No. 1 108-114 (2000)

KEYWORDS: Casting, Titanium, Casting mold, Permeability

ABSTRACT:

This study evaluated the pressure behavior of both the casting chamber and the cavity in the mold using an enclosed one-chamber casting unit. An experimental device with a pressure sensor modeled on the casting system was attached to the casting unit. The chamber pressure rose rapidly and reached half of the preset casting pressure within 0.2s after introducing argon gas into the chamber. Both the preset casting pressure and the gas permeability in the mold strongly influenced the differential pressure between the chamber and the cavity. When a mold with a high level of rising pressure in the cavity, i.e. a mold with higher gas permeability, was used, a large quantity of argon gas penetrated the cavity through the mold wall before the cavity was filled by the molten metal. For this reason, it was thought that some casting defects, such as incomplete casting or gas inclusion, often occur. This study showed that it is desirable to use a mold with lower gas permeability in an enclosed one-chamber casting unit.

TITLE:

A New Investment Containing Stabilized Zirconia-Capsuled Quartz for Titanium Casting -- Mechanical Properties and Surface Reaction Layers of Casting --

LANGUAGE:

in JAPANESE with English Abstract

AUTHORS:

Okawa,S., Watanabe,K., Kanatani,K., Nakano,S., Miyakawa,O., and Kobayashi.M.¹

INSTITUTE:

Dental Materials and Technology, School of Dentistry, Niigata University and ¹EMX Laboratory, Niigata University

JOURNAL:

The Journal of the Japanese Society for Dental Materials and Device Vol.18 No.4 287-294 (1999)

KEYWORDS:
Titanium, Investment for titanium alloy, High-temperature casting, Surface property, Mechanical property, Capsule

A non-phosphate bonded investment including quartz capsuled with stabilized zirconia was developed for casting titanium. The mechanical properties of castings were compared between the experimental investment and a commercially available phosphate-bonded silica investment. The tensile strength values were almost the same for both castings, while the elongation was higher than that of castings from the commercial investment. Although the inner hardness was almost the same for both castings, the hardness in the surface layer was lower. The reaction layer of the casting was clearly thinner. These results suggested that the capsulizing zirconia significantly reduced the reaction of molten titanium with silica, which improved the quality of titanium casting.

TITLE:

Mechanical Properties of Titanium Casting Prepared in Different Atmospheres

LANGUAGE:

in JAPANESE with English Abstract

AUTHORS:

Okawa,S., Watanabe,K., Kanatani,M., Nakano,S., Miyakawa,O. and Kobayashi,M.

INSTITUTE:

JOURNAL:

The Journal of the Japanese Society for Dental Materials and Device 16:330-335, 1997

ABSTRACT:
Keyword. Casting, Titanium, Mechanical property
Titanium castings were prepared in two atmospheres: one was argon-arc melted and cast in the ambient atmosphere (AA) and the other was argon-arc melted and cast in the argon-replaced atmosphere (ARA). Tensile test and Vickers hardness measurement were conducted. The results were discussed in relation to the contents of oxygen and nitrogen absorbed by titanium during the melting and the casting procedures. While the tensile strength and the hardness of castings obtained in AA were higher than those of castings obtained in ARA, the elongation exhibited the reverse relation. The oxygen content was ranked from least to most: the ingot, the solidified and the cast. The oxygen content of the solidified and the cast-obtained in ARA tended to be higher than that of castings obtained in AA. On the contrary, the nitrogen content of castings obtained in AA was 13 to 15 times higher than that of castings obtained in ARA. The results of this study indicate that the nitrogen content relates to the above-mentioned difference in mechanical properties of castings obtained in AA or ARA.

TITLE:

Studies on Spinel Investment for Casting of Titanium: Part 2 Thermal Properties of Spinel Investment in Addition of Fluoride

LANGUAGE:

in JAPANESE with English Abstract

AUTHORS:

Okawa,S.

INSTITUTE:

JOURNAL:

The Journal of the Japanese Society for Dental Materials and Device 13:260-269, 1994

ABSTRACT:
Keyword. Spinel, Fluoride, Investment, Titanium casting, Thermal expansion
The present study investigated a spinel investment composed of MgO, Al₂O₃ and ZrO₂ for titanium castings. The spinel investment with added fluorides, such as MgF₂, CaF₂, had a high compressive strength and the spinel content was increased after firing. For instance, using a spinel investment containing 3% MgF₂ and 3% CaF₂, the remaining expansion was 1.2-2.5% after firing at 1,200 °C for 60 min. The compressive strength was 0.9-2 kgf/mm². The remaining expansion depended on the composition of the spinel investment, firing temperature and firing time. Finally, a spinel investment with a remaining expansion equivalent to the casting shrinkage of titanium was prepared. A hard layer in which both aluminum and oxygen were dissolved in titanium, was formed at the surface of the titanium casting. However, high quality titanium castings could be cast with the spinel investment.

 TITLE:

Studies on Spinel Investment for Casting of Titaium: Part 1 Composition of MgO-Al₂O₃-ZrO₂ Investment and Titanium-mold Reaction

LANGUAGE:

in JAPANESE with English Abstract

AUTHORS:

Okawa,S.

INSTITUTE:

JOURNAL:

The Journal of the Japanese Society for Dental Materials and Device 13:253-259, 1994

ABSTRACT:
Keyword: Spinel, Investment, Titanium casting, Reacted layers
Mold investment using a spinel investment was developed to cast full denture bases or crowns with pure titanium. The spinel investment was composed of refractory materials: magnesia, alumina and zirconia. Aluminum lactic acid was used for the mixing liquid and the liquid/powder ratio was 0.2. After firing the spinel investment at 1,200 °C, the spinel content of the mold and the remaining expansion were measured. The remaining expansion of the mold after firing at l,200 °C for 60 min was 0.3-0.7%. However, this value was not sufficient to compensate for the titanium casting shrinkage. The remaining expansion of the mold, Y (%) was evaluated as Y=-1.52+0.074X,r=0.9 (X: the spinel content, r: the coefficient of correlation). Using this investment, a reaction layer 30 mm deep was formed at the surface of the titanium casting. The hardness of the layer was greater than that of the inner part of the titanium casting. The titanium mold reaction created the hard layer in which both the aluminum and the oxygen were dissolved in the titanium.

TITLE:

Measurement of the casting time of titanium by the centrifugal system and pressure system

LANGUAGE:

in JAPANESE with English Abstract

AUTHORS:

Okawa,S., Watanabe,K.,Miyakawa,O., Nakano,S.,Honma,H., Shiokawa,N. and Kobayashi,M.

INSTITUTE:

JOURNAL:

Niigata Dental Journal 22:27-33, 1992

ABSTRACT:
Key Words : Dental titanium casting, Centrifugal casting unit, Pressure-differential casting unit, Casting time
The aim of this study was to measure the casting time of titanium casting into the coil pattern by means of thermocouple method using either the centrifugal casting unit or pressure-differential casting unit. The following results were obtained.
(l) With centrifugal casting unit, the more the spring prewinds, the shorter was the casting time. In the case of coil pattern of 4 mm in diameter and at room temperature mold , for example, the casting time was 0.03 sec at 35 spring prewinds.
(2) With pressure-differential casting unit, the casting time was scattered from 0.05 to 0.09 sec under the casting pressure of 1.4 kg/cm², for example, when pattern diameter was 4 mm and the mold temperature was about 500 to 700 °C. On the contrary, in the case of 2 mm diameter coil pattern and 500 to 700 °C mold, the higher the pressure the shorter was the casting time. In conclusion, the casting time by the centrifugal casting unit is half as short as that of the pressure-differential casting unit under the manufacture's instruction.

TITLE:

Measurements of the rotational and rise time by the centrifugal casting unit for titanium

LANGUAGE:

in JAPANESE with English Abstract

AUTHORS:

Okawa,S., Watanabe,K.,Miyakawa,O., Nakano,S.,Honma,H., Shiokawa,N., and Kobayashi,M.

INSTITUTE:

JOURNAL:

Niigata Dental Journal 22: 21-26, 1992

ABSTRACT:
Key Words: Dental titanium casting, Centrifugal casting unit, Rotational speed, Rise time
The purpose of this study was to determine the rotational speed and rise time by the centrifugal casting unit for titanium by means of the phoIcr-intemipter circuit. The following results were obtained.
(l) The rotatinal speed and rise time were influenced by either the spring prewinds or mold weight. For example, mounted the small mold (225g) on the centrifugal casting unit, the rotational speed was 20.0 rps at 38 spring prewinds. On the other hand, the large mold (500g), it was 18.2 rps. The rotational speed by the centrifugal casting unit for titanium was twice as fast as that of the ordinary one.
(2) The rise time was 0.11 sec at 38 spring prewinds with the crucible (355 g) only. When mounted the small or the large mold, the rise time was 0. 12 sec or 0. 14 sec at 38 spring prewinds, respectively. The rise time by the centrifugal casting unit for titanium was half as short as that of the ordinary one.
The centrifugal casting unit for titanium was characterized by the powerful rotation; therefore, its rotational speed was different from the ordinary one.