Centrifugal Machine Research Articles

Fatigue Property of Super-Elastic Ti–Ni Alloy Dental Castings

Ti–Ni alloy is a promising material in the medical and dental fields due to its special mechanical properties, especially super-elasticity. Since dental prostheses are generally used under repetitive stress condition, fatigue properties of Ti–Ni alloy castings were investigated in this study. Ti–50.85Ni (mol%) alloy ingots were used for casting, which exhibited super-elasticity at 310 K in tensile test. Specimens were prepared with a centrifugal casting machine and a magnesia-based mold material. Fatigue test was performed at 310 K under repetitive loading condition with sine-waved load. The minimum stress was set at 0 MPa to evaluate the fatigue properties and change in residual strain. The maximum stress was set in the appropriate range considering the tensile property. Ultimate tensile strength and elongation to fracture of Ti–Ni alloy castings were 732 MPa and 10.6%, respectively, which were between those of CP-Ti and Ti–6Al–4V alloy castings. The fatigue limit of Ti–Ni alloy casting (206 MPa) was equivalent to or higher than that of CP-Ti or Ti–6Al–4V alloy. There was linear correlation between the fatigue ratios to ultimate tensile strength and the elongation to fracture for Ti–Ni alloy, CP-Ti and Ti–6Al–4V alloy castings, while Ti–Ni alloy showed high fatigue ratio to proof stress, which appears to relate to the twin deformation by stress-induced martensitic transformation. The stress-strain properties of Ti– Ni alloy castings were evaluated to be stable, and it is possible to utilize the super-elasticity in cast dental prostheses.

Improvement of Surface Layer Characteristics by Shot Lining

In the present study, lining of the metal with foils using shot peening was investigated to improve the surface layer characteristics. In the shot peening experiment, the foils set on the metal are pelted with hard particles traveling at a high velocity. The foils are bonded to the metal surface due to plastic deformation induced by the collision of the particles. The foils and the metal are heated to heighten the bondability because of the reduction of flow stress. Lining the metal with the hard powder sandwiched between two aluminum foil sheets was also attempted. In this experiment, a centrifugal shot peening machine wite an electrical heater was employed. The metals are commercially aluminium alloys and magnesium alloys, and the foils are commercially aluminum, titanium and nickel. The effects of shot speed and the heating temperature on the bondability were examined. Wear resistance was also evaluated by grinding. The foils were successfully bonded to the metal surface. It was found that the present method is effective in improving of surface layer characteristics.

Mechanical properties of cast Ti‐6Al‐4V‐XCu alloys

The mechanical properties of Ti-6Al-4V-XCu (1, 4 and 10 wt% Cu) alloys were examined. The castings for each alloy were made in a centrifugal titanium casting machine. Two shapes of specimens were used: a dumbbell (20 mm gauge length x 2.8 mm diameter) for mechanical property studies, and a flat slab (2 mm x 10 mm x 10 mm) for metallography, microhardness determination and X-ray diffractometry. Tensile strength, yield strength, modulus of elasticity, elongation and microhardness were evaluated. After tensile testing, the fracture surfaces were observed using scanning electron microscopy. The tensile strengths of the quaternary alloys decreased from 1016 MPa for the 1% Cu alloy to 387 MPa for the 10% Cu alloy. Elongation decreased with an increase in the copper content. The 1% Cu alloy exhibited elongation similar to Ti-6Al-4V without copper (3.0%). The results also indicated that the copper additions increased the bulk hardness of the quaternary alloy. In particular, the 10% Cu alloy had the highest hardness and underwent the most brittle fracture. The mechanical properties of cast Ti-6Al-4V alloy with 1 and 4% Cu were well within the values for existing dental casting non-precious alloys.

A study on corrosion resistance of the Ti–10Mo experimental alloy after different processing methods

The purpose of this work was to evaluate the microstructure and corrosion resistance of the experimental Ti–10Mo (wt.%) alloy as-cast and treated. These alloys were divided into three groups for analysis: as-cast, after solution heat treatment at 1000 °C in argon atmosphere and remelting in centrifugal machine (investment casting). The microstructure formed from each condition was studied using optical microscopy. Corrosion behavior of titanium–molybdenum alloys in fluoridated physiological serum (0.15 M NaCl+0.03 M NaF [pH=6]) was studied and compared with Ti–6Al–4V alloy. In all electrodes systems, similar electrochemical response was obtained. In naturally aerated physiological serum, the corrosion rate is mainly controlled by dissolution process of a complex passive film. This film appears to be formed by titanium species with different oxidation states. Experimental Ti–10Mo alloy exhibit the lowest passive current densities, in particular, samples after heat treatment.

Inverse Design Method for Centrifugal Impellers and Comparison with Numerical Simulation Tools

A process that enables us to improve the design of 2D centrifugal and helico-centrifugal pumps is presented. First of all, the definition of the impeller geometry as well as the analysis of its global performances are carried out starting from the mean streamline method (1D), based at the same time on ideal models and experimental correlations. A second stage of optimisation is achieved from a quasi three-dimensional (Q3D) method, by studying the meridional flow and blade-to-blade flow. Finally, 3D flow solution is performed by CFD tools. Nowadays, we have a group of tools which help the designers improve the performance of new machines. These digital tools are built around two computer programs, HELIOX developed for design and performance analysis in any centrifugal and mixed flow pumps equipped with volute or deswirl vanes, and also the module REMIX that gathers the meridional flow analysis and the simplified blade-to-blade one. To validate this procedure, a centrifugal machine with a volute (NS32) was modified and studied with it, and the results were simultaneously compared with the previous trial runs and with the software CFX-BladeGEN+ and CFX-TASCflow. The results for a machine equipped with a deswirl (VM51) are also presented.

Effects of interfacial variables on ceramic adherence to cast and machined commercially pure titanium

Statement of problem Titanium-ceramic bonding is less optimal than conventional metal-ceramic bonding, due to excessive oxidation of titanium during porcelain firing. Purpose This in vitro study evaluated the effects of porcelain firing atmosphere and gold sputter coating on titanium surfaces on porcelain bonding to machined and as-cast titanium substrates. Material and methods Eight groups of ASTM grade 2 commercially pure (CP) titanium specimens (13 mm ×13 mm ×1 mm) were prepared (n=10). A conventional Au-Pd-In metal-ceramic alloy (Orion) and an ultra low-fusing porcelain (Finesse) served as the control (n=10). Forty machined titanium specimens were prepared from 1.00-mm thick titanium sheets with a diamond band saw. Forty titanium specimens were produced in a centrifugal dental titanium casting machine. All titanium specimens were airborne particle abraded with 110-μm alumina particles, whereas the control specimens were airborne particle abraded with 50-μm alumina particles. Forty titanium specimens (20 specimens each of as-cast and machined titanium) were randomly selected for gold sputter coating before ceramic firing. An ultra low-fusing porcelain (Vita Titankeramik) was fused on the central 6-mm diameter circular area on each titanium specimen. Porcelain firing environments for the titanium specimens consisted of vacuum and a reduced argon atmosphere. Porcelain was debonded by a biaxial flexure, constant strain test at a cross-head speed of 0.25 mm/min. Specimens were analyzed by standardized SEM/EDS analysis 3 times throughout the study to determine the silicon atomic percentage (Si at %): (1) after airborne particle abrasion, before porcelain application; (2) after the application of the first layer of porcelain; and (3) after the fracture of porcelain from the metal substrate. The titanium-ceramic adhesion was characterized by determining the area fraction of adherent porcelain (AFAP). Results were analyzed by analysis of variance and the Student-Newman-Keuls test (α=.05). Results Statistical analysis showed a significant difference in the AFAP values among all the groups. AFAP value of the control group was significantly higher (135.35 ± 23.68) than those of the experimental groups ( P<.001). For the machined titanium, AFAP value of gold sputter-coated/argon group (91.38 ± 7.93) was significantly higher than the rest of the groups ( P<.001). For the as-cast titanium fired in vacuum, significantly lower AFAP values ( P<.001) were found in the gold sputter-coated group (50.2 ± 11.26 vs 66.15 ± 10.41). AFAP values between the argon groups with or without the gold coating were not significantly different ( P=.303); however, both argon groups (93.83 ± 4.65 and 98.09 ± 6.35) showed significantly higher AFAP values compared with the vacuum groups ( P<.001). Conclusion Firing porcelain in a reduced argon atmosphere significantly improved titanium-ceramic bonding for machined and as-cast titanium. The sputter-coated gold layer on titanium provided improved titanium-ceramic bonding only when combined with firing porcelain in reduced argon atmosphere. When porcelain was fired in vacuum in the presence of the gold layer, the titanium-ceramic bonding was weakened in as-cast titanium and was not affected in machined titanium. Conventional noble metal-ceramic bonding was superior to titanium-ceramic bonding regardless of the interfacial variables examined in this study.

Adhesive bonding of super-elastic titanium-nickel alloy castings with a phosphate metal conditioner and an acrylic adhesive.

The purpose of the current study was to evaluate the bonding characteristics of super-elastic titanium-nickel (Ti-Ni) alloy castings. Disk specimens were cast from a Ti-Ni alloy (Ti-50.85Ni mol%) using an arc centrifugal casting machine. High-purity titanium and nickel specimens were also prepared as experimental references. The specimens were air-abraded with alumina, and bonded with an adhesive resin (Super-Bond C & B). A metal conditioner containing a phosphate monomer (Cesead II Opaque Primer) was also used for priming the specimens. Post-thermocycling average bond strengths (MPa) of the primed groups were 41.5 for Ti-Ni, 30.4 for Ti and 19.5 for Ni, whereas those of the unprimed groups were 21.6 for Ti, 19.3 for Ti-Ni and 9.3 for Ni. Application of the phosphate conditioner elevated the bond strengths of all alloy/metals (P < 0.05). X-ray fluorescence analysis revealed that nickel was attached to the debonded resin surface of the resin-to-nickel bonded specimen, indicating that corrosion of high-purity nickel occurred at the resin-nickel interface. Durable bonding to super-elastic Ti-Ni alloy castings can be achieved with a combination of a phosphate metal conditioner and a tri-n-butylborane-initiated adhesive resin.

Grindability of cast Ti–Cu alloys

Objectives. The purpose of the present study was to evaluate the grindability of a series of cast Ti–Cu alloys in order to develop a titanium alloy with better grindability than commercially pure titanium (CP Ti), which is considered to be one of the most difficult metals to machine. Methods. Experimental Ti–Cu alloys (0.5, 1.0, 2.0, 5.0, and 10.0 mass% Cu) were made in an argon-arc melting furnace. Each alloy was cast into a magnesia mold using a centrifugal casting machine. Cast alloy slabs (3.5 mm×8.5 mm×30.5 mm), from which the hardened surface layer (250 μm) was removed, were ground using a SiC abrasive wheel on an electric handpiece at four circumferential speeds (500, 750, 1000, or 1250 m/min) at 0.98 N (100 gf). Grindability was evaluated by measuring the amount of metal volume removed after grinding for 1 min. Data were compared to those for CP Ti and Ti–6Al–4V. Results. For all speeds, Ti–10% Cu alloy exhibited the highest grindability. For the Ti–Cu alloys with a Cu content of 2% or less, the highest grindability corresponded to an intermediate speed. It was observed that the grindability increased with an increase in the Cu concentration compared to CP Ti, particularly for the 5 or 10% Cu alloys at a circumferential speed of 1000 m/min or above. Significance. By alloying with copper, the cast titanium exhibited better grindability at high speed. The continuous precipitation of Ti 2Cu among the α-matrix grains made this material less ductile and facilitated more effective grinding because small broken segments more readily formed.

Casting behavior of titanium alloys in a centrifugal casting machine

Since dental casting requires replication of complex shapes with great accuracy, this study examined how well some commercial titanium alloys and experimental titanium–copper alloys filled a mold cavity. The metals examined were three types of commercial dental titanium [commercially pure titanium (hereinafter noted as CP-Ti), Ti–6Al–4V (T64) and Ti–6Al–7Nb (T67)], and experimental titanium–copper alloys [3%, 5% and 10% Cu (mass %)]. The volume percentage filling the cavity was evaluated in castings prepared in a very thin perforated sheet pattern and cast in a centrifugal casting machine. The flow behavior of the molten metal was also examined using a so-called “tracer element technique.” The amounts of CP-Ti and all the Ti–Cu alloys filling the cavity were similar; less T64 and T67 filled the cavity. However, the Ti–Cu alloys failed to reach the end of the cavities due to a lower fluidity compared to the other metals. A mold prepared with specially designed perforated sheets was effective at differentiating the flow behavior of the metals tested. The present technique also revealed that the more viscous Ti–Cu alloys with a wide freezing range failed to sequentially flow to the end of the cavity.

Veneering technique for a Ti-6Al-7Nb framework used in a resin-bonded fixed partial denture with a highly filled indirect composite

This article presents a veneering technique for fixed partial denture frameworks made from a Ti-6Al-7Nb alloy. The fixed partial denture framework was prepared with a magnesia-based mold material and a centrifugal casting machine. An esthetic veneer was fabricated with a highly filled dual-polymerized composite material and a metal-conditioning agent. This technique can be applied as a standardized veneering procedure for the titanium alloy, for which porcelain fusing is currently difficult. (J Prosthet Dent 2002;88:636-9.)

Lining of light metals with hard powders using shot peening

A lining of light metals with hard powders using shot peening was carried out. The hard powders are bonded to the surface of the workpieces due to the collision with many shots. To fix the hard powders on the surface of the workpiece, the powder is placed on the uneven surface, and the surface is covered with a pure aluminium foil during the shot peening. To make the fixing of powders easy, the lining of workpiece with the powders sandwiched in between two aluminium foils was also tried. In this experiment, a centrifugal shot peening machine with an electrical heater is employed. The workpieces are aluminium and magnesium alloys, and the hard powders are commercially pure chromium, ceramics and cemented carbide. The effects of collision speed and the processing temperature on the bondability were examined. The wear resistance was evaluated by wear test. The hard powders are successfully bonded over the surface of workpieces by raising the processing temperature.

Mechanical properties and microstructures of cast Ti–Cu alloys

Objectives: This study evaluated the mechanical properties of cast Ti–Cu alloys with the hope of developing an alloy for dental casting with better mechanical properties than unalloyed titanium. Methods: Ti–Cu alloys with five concentrations of copper (0.5, 1.0, 2.0, 5.0 and 10.0 mass%) were made in an argon-arc melting furnace. The alloys were cast into magnesia-based molds using a centrifugal casting machine. The microstructure, microhardness profile of the specimen cross section, tensile strength, yield strength, and elongation were determined for the castings. Scanning electron microscope fractography was undertaken for the fractured surfaces after tensile testing. XRD was performed on the polished specimens. Results were analyzed using one-way ANOVA and the Student–Newman–Keuls tests. Results: The mean tensile strengths of all the cast Ti–Cu alloys were significantly ( p<0.05) higher than for cast commercially pure titanium (CP Ti). Of the Ti–Cu alloys tested, the 5 and 10% Cu alloys had significantly higher strength than the rest. The 10% Cu alloy exhibited the lowest mean elongation. CP Ti and the 0.5 and 1% Cu alloys showed higher ductility. The bulk hardness of all the cast Ti–Cu alloys, except for the 10% Cu alloy, and CP Ti was approximately the same. Significance: By alloying with copper, the cast titanium became stronger. Increases in the tensile strength (30%) and yield strength (40%) over CP Ti were obtained for the 5% Cu alloy. Elongation was approximately 3%, which was similar to cast Ti–6Al–4V. Ti–Cu alloys, such as the 5% Cu alloy, could be used for prosthetic dental applications if other properties necessary for dental castings are obtained.

Sensitivity of a disc rupture strength test to air bubble pores in phosphate-bonded investment materials at elevated temperatures

Objectives: To investigate the sensitivity of a modified disc rupture test to variables affecting the strength of four phosphate-bonded investment materials under conditions closely resembling the in-service environment. This study examined the influence of air bubble pores on the strength of phosphate bonded investment materials at a temperature of 900°C. Method: A modified disc rupture configuration was used to test a circular investment diaphragm with clamped edges, in tension, initiated by bending. A sequentially-varying molten metal mass was used to apply the load using an electronic centrifugal casting machine. The staircase method was used to determine the increase or decrease of the applied load with the standardized increment of load being no greater than 1 or 2 g. The mean load applied to 30 samples defined the transition of survival to failure of the investment disc and was taken as a measurement of investment strength. Two material handling techniques, one giving virtually no pores and one showing a wide pore size distribution were used. Results: The diaphragm clearly either failed or survived the test with the pattern of fracture indicating brittle failure. A statistically significant difference in strength ( P<0.050) of diaphragms with and without air bubble pores was demonstrated for three materials. Fewer pores resulted in increased strength of those materials and produced a much reduced scatter of strength in the fourth. Significance: The modified disc rupture test is sufficiently sensitive to identify variations in strength of phosphate bonded investment materials caused by differing pore size distributions.

Modeling of the Flow Parts of Stationary Centrifugal Compressor Machines for Compression of Real Gases. Gasdynamic Tests and Processing of Their Results. I. Theoretical Calculations

Similarity numbers of the processes of compression of real gases in the stages of centrifugal compressor machines are given. A method for setting up promptly the thermal and calorific equations of state of the mixtures of real gases for the prescribed region of operation of a compressor machine is proposed. A procedure for processing of experimental data obtained in gasdynamic tests with mixtures of real gases and for reduction of the results obtained to the nominal conditions of operation of the flow part is presented.

709 最近の材料損傷に起因する労働災害事例

This paper presents two types of resent occupational accident caused by damage of materials used in machinery. One case is that a hoist link chain used in a factory mainly recycling cathode-ray tubes failed during the cleaning process of cullet. Consequently, the worker working this process was burnt with the high-temperature cleaning solvent since the load fell in the cleaning tank. In this case, link chains were subjected to over load repeatedly due to removing the coil spring above the hock. The other case is that the molten metal leaked from the die of a centrifugal casting machine due to failure of screw threads cramping the upper die with the inner die . Four workers fell sacrifices to this accident.

Application of laser measuring, numerical simulation and rapid prototyping to titanium dental castings

Objectives. This paper describes a method of making titanium dental crowns by means of integrating laser measuring, numerical simulation and rapid prototype (RP) manufacture of wax patterns for the investment casting process. Methods. Four real tooth crowns (FDI No. 24, 25, 26, 27) were measured by means of 3D laser scanning. The laser digitized geometry of the crowns was processed and converted into standard CAD models in STL format, which is used by RP systems and numerical simulation software. Commercial software (MAGMASOFT) was used to simulate the casting process and optimize the runner and gating system (sprue) design. RP crowns were ‘printed’ directly on a ModelMaker II 3D Plotting System. A silicone negative mold (soft tool) was made from the RP crowns, then more than hundreds wax crowns were duplicated. The duplicated crowns were joined to the optimized runner and gating system. By using the investment casting process 20–25 replicas of each crown were made on a centrifugal casting machine. All castings were examined for porosity by X-ray radiographs. Results. By using the integrated scanning, simulation, RP pattern and casting procedure, cast crowns, free of porosity, with excellent functional contour and a smooth surface finish, were obtained from the first casting trial. Significance. The coupling of laser digitizing and RP indicates a potential to replace the traditional ‘impression taking and waxing’ procedure in dental laboratory, with the quality of the cast titanium prostheses also being improved by using the numerically optimized runner and gating system design.

Numerical simulation of the casting process of titanium tooth crowns and bridges.

The objectives of this paper were to simulate the casting process of titanium tooth crowns and bridges; to predict and control porosity defect. A casting simulation software, MAGMASOFT, was used. The geometry of the crowns with fine details of the occlusal surface were digitized by means of laser measuring technique, then converted and read in the simulation software. Both mold filling and solidification were simulated, the shrinkage porosity was predicted by a "feeding criterion", and the gas pore sensitivity was studied based on the mold filling and solidification simulations. Two types of dental prostheses (a single-crown casting and a three-unit-bridge) with various sprue designs were numerically "poured", and only one optimal design for each prosthesis was recommended for real casting trial. With the numerically optimized design, real titanium dental prostheses (five replicas for each) were made on a centrifugal casting machine. All the castings endured radiographic examination, and no porosity was detected in the cast prostheses. It indicates that the numerical simulation is an efficient tool for dental casting design and porosity control.

Titanium casting: the surface reaction layer of castings obtained using ultra-low-temperature molds.

To examine whether the surface reaction layer of titanium castings can be reduced by lowering the mold temperature during casting, we cast titanium at three mold temperatures, including an ultra-low temperature produced by cooling the mold with liquid nitrogen, then measured the tensile strength and elongation of the castings. The titanium was cast using a centrifugal casting machine, and the molds were incinerated according to the manufacturers' instructions. Castings were then made with the molds at 200 degrees C, 600 degrees C, and an ultra-low temperature (-196 degrees C). The castability of titanium cast in the mold at the ultra-low temperature was good. The Vickers hardness near the surface layer of castings decreased as the mold temperature decreased.

Test to evaluate countercurrent chromatographs: Liquid stationary phase retention and chromatographic resolution

Countercurrent chromatography (CCC) is a liquid chromatography (LC) technique with a special column able to retain a liquid stationary phase while the liquid mobile phase is pumped through. The coil planet centrifuge machines are made of open tube wound on spools. A simple test is proposed. The methanol–water (90:10, v/v)–heptane biphasic system is used with heptane as the mobile phase in the ascending or tail-to-head mode. The methanol–water stationary phase retention volume is measured at different flow-rates and rotor rotation speeds. After every machine equilibration, an alkylbenzene mixture is injected and the retention factors, peak efficiencies and resolution factors are measured or calculated for each solute. The wealth of information contained in the data set obtained is demonstrated. Four coil planet centrifuge machines of very different characteristics and one hydrostatic CCC machine with channels and ducts were submitted to the test. It was shown that the Sf, stationary retention factor, obtained with these machines was linearly dependent on the square root of F, the mobile phase flow-rate [Q. Du, C. Wu, G. Qian, P. Wu, Y. Ito, J. Chromatogr. A 835 (1999) 231–235]. It is shown that the slopes of the Sf versus F 1/2 lines could be related to a minimum rotor rotation, ω mini, necessary to obtain the hydrodynamic equilibrium. The Sf and F parameters give the mobile phase linear velocity, u. It is shown that u is proportional to the square root of ω, the rotor rotation speed. The slope and intercept of the latter relationship also result in an ω mini value coherent with the first one. With the peak efficiencies and chromatographic resolution factors obtained for toluene and hexylbenzene, the parameters: number of plates per tubing turn, machine volume for one plate, and tubing length for one plate, were calculated and compared for the five machines. The internal diameter of the tubing used is shown to be a critical parameter acting on the machine volume and number of tubing turns.

On the enrichment of low-abundant isotopes of light chemical elements by gas centrifuges

A brief review of the main areas for the application of the isotopes 15N and 13C is made. Separation of the nitrogen isotopes in a single gas centrifuge in the form of pure nitrogen, ammonia, and trifluoride of nitrogen as well as the carbon isotopes in the form of carbon dioxide has been studied by means of numerical simulation. The parameters of the centrifugal machine investigated were close to the parameters of the Iguassu machine. The dependence of the efficiency criterion versus the basic parameters of the separation process has been explored in the computational experiments. Comparisons of the calculated results with the experimental data have shown good agreement. The results obtained have demonstrated the possibility of using gas centrifuge technology to enrich successfully the low-abundant isotopes of light chemical elements.