The differences between a new truing method using the corner end of a polycrystalline diamond (PCD) rotary truer and conventional methods utilizing a diamond rotary truer were investigated from the viewpoint of contact behavior between the truer and CBN grains.Theoretical analysis indicated that the PCD rotary truer makes uniform contact with the CBN abrasive grains, whereas the contact area between the truer and CBN grains is much smaller than that of the conventional rotary truer, because the PCD rotary truer has a markedly sharp corner end. The contact behavior of the new truing method is close to the single-point dresser, and micro-cutting edges are formed by transferring the sharp corner end of the PCD truer. Micro-cutting edges formed by the new truing method achieve low grinding force and a fine ground surface.
To improve wear resistance of titanium in short time, we propose a new surface nitriding method. Commercially pure titanium was nitrided using a vacuum atmospheric-controlled induction heating fine particle peening (AIH-FPP) treatment system, and its surface properties were evaluated. The treatment system is able to blow a gas and shoot fine particles at high speed in a controlled atmosphere with an oxygen concentration of less than 10 ppm. In this treatment, the substrate is heated to a higher temperature by high frequency induction heating. In this study, the treatment was performed under a nitrogen atmosphere at 900°C for 3 minutes. The formation of the nitrided layer on the titanium surface was accelerated by nitrogen gas blow and the wear resistance was improved. Specimens treated with peening showed a reduced thickness of the nitrided layer as a result of erosion.
On cleaning of dental implants, conventional air blasting to remove dental biofilm may increase the surface roughness of titanium abutments. Therefore, we have examined a method for cleaning using calcium carbonate particles and white fused alumina particles applied by air blasting to remove the biofilm on titanium surfaces. Calcium carbonate particles and white fused alumina particles are widely used in dental application. The test piece consisted of a rectangle of JIS type 2 pure titanium. The initial surface roughness, Ra, of the test piece was approximately 0.050 μm. Air blasting was performed for 5, 10, or 30 s at a distance of 50 mm from the test piece with an air pressure of 0.5 MPa and particle feed rate of 5 g/s. Permanent marker was applied to the test piece to simulate tooth staining. All particles peeled the marker from test piece, thus confirm the cleaning capability. However, Ra was increased and the glossiness was markedly decreased following air blasting with each type of particle.
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