Grinding Area Research Articles

Safe Operations and Friction Characteristics of Regulation Wheel in Centerless Grinding

In the centerless grinding process, it happens on rare occasions that the workpiece rotation suddenly speeds up toward the peripheral velocity of the grinding wheel and, in the worst case, the workpiece jumps from the grinding area. This phenomenon called “spinners” sometimes causes the grinding wheel to burst. In this paper, the mechanism of spinner occurrence is discussed. The existence of safe-operation zone, where there is no risk of spinners, is presented with primary set-up conditions. This paper also describes friction characteristics of the regulating wheel that are the dominant factor in determining the safe-operation zone. The test results of friction coefficients of various regulating wheels are discussed, and the set-up guidelines to avoid the spinner problem are proposed.

High quality machining of ceramics

Machining performance in the drilling and grinding of ceramics to obtain high-quality ground components has been investigated experimentally. Ultrasonic vibration was applied in the operation of core drilling the ceramics, a considerable decrease of the normal grinding force (up to 70%) being observed for the drilling of a 10 mm diameter hole in silicon nitride. The relationships between the voltage and the machining rate of electrical discharge machining in electrolyte were investigated for the drilling of holes of small diameter (0.5 mm) in non-conducting ceramics. A newly developed electrolytic/electro-chemical in-process dressing method was applied to very fine grain-size wheels for finishing to a mirror-like surface in the contour grinding of a blade-shaped silicon nitride with a machining center. The in-process dressing enabled a fine grain-size wheel to keep almost constant normal force during grinding. The relationship between the grain size and the surface roughness of the ground ceramics was determined. A high-quality surface ( R a = 0.0050 μ m ) could be accomplished with silicon nitride by using a 1000-mesh metal-bonded diamond wheel. The ground surfaces of the ceramics were also investigated by SEM. The ratio of the ductile-mode grinding area to brittle fracture-mode area on the ground surface was found to increase with finer grain size of the wheels. X-ray diffraction measurement showed that the surface compressive residual stresses increased with increasing feed-rate or with decreasing wheel speed. It was found, however, that there was no effect from the normal grinding force during grinding. It is concluded that the residual stresses decrease with decreasing chip cross-sectional area.

Size distribution of airborne particulates in monazite dust

A six-stage cascade impactor was used to collect airborne dust particulates in the grinding area of a monazite separation plant. The samples were analysed using particle-induced X-ray emission (PIXE) to determine the elemental concentrations, with special attention to thorium and uranium concentrations. The particle size distribution of the samples containing thorium and uranium were determined. The mass median aerodynamic diameter (MMAD) obtained was 1.15 μm for both elements. The activity median aerodynamic diameter (AMAD) was estimated based on the MMAD. The results are compared with ICRP recommendations for derived air concentrations (DAC) for thorium and uranium in restricted areas.

Evaluation of a Grinding Booth for Medium-Size Castings

A research program was undertaken to design, build, install, and test a new type of grinding booth for moderate-size castings at a small foundry. Testing was conducted under a variety of operating conditions. The central question was whether a booth could reduce the quantities of respirable, crystalline free silica in the portable grinding area of the foundry to levels within OSHA standards.

Crash Repair Program to Control Serious Pitting Corrosion on Process Tanks

Abstract Describes serious pitting corrosion attack in autoclaves at plant where uranium ore is treated by leaching with sodium carbonate-bicarbonate solution. Serious pitting began after plant was on-stream for only six months. Attack was on mild steel vessels above liquid level. Crash repair and corrosion protection program was begun while investigation was underway. Inconel strips were welded to froth line levels where pitting had occurred, but these patches also corroded. Coatings also were used in crash repair program: baked phenolics, epoxy-phenolic combinations, epoxies and vinyls. None of organic coatings tested was completely resistant to attack in vapor and liquid phase or pulp cones of vessels. Stainless steel belts then were welded to autoclave shells where pitting had occurred. Later, more rapid corrosion rates were encountered, no longer confined to froth line of the autoclaves. Corrosion spread to classifier shafts in the grinding area, pitting of filter drums and even affected clarifier fr...

The Deep-Basined Metate of the Southern California Coast

Deep-basined metates are frequently found in early sites on the southern California coast, but the faces of the accompanying manos usually are only moderately convex. Mano faces examined by the writer never have been sufficiently excurvate to make contact with the grinding surfaces of the deeply ground metates. This presents an interesting problem: how were the manos manipulated on the metates?An examination of specimens from Oak Grove sites 7, 21, and 79 (Rogers, 1929) and the Smithsonian Institution River Basin Surveys’ sites 4SBa477 and 4SBa485 in Santa Barbara County, California, reveals the following associations and characteristics. Slab, shallow-basined, and deep-basined metates are found in association. The first two types exhibit an unbroken grinding area, but specimens of the latter almost invariably have a slight shoulder running at least a part of the way around the basin, the transition between a slightly concave ground area and the deeply ground cavity.