Silicon Carbide Wheel Research Articles

Unidirectional and opposing deep grinding of titanium alloy with periodic wheel adjustment

The grinding of slots of different length in VT8 titanium-alloy blanks by means of a highly porous silicon-carbide wheel is investigated. The formation of the components of the deep-grinding force is investigated as a function of the direction of table supply and the length of the blank, in all stages of the process. The edge stability of the highly porous wheel is considered. The operation of the wheel with blunting, self-sharpening, or mixed conditions is studied.

Influence of the components on the hardness and strength of highly porous silicon-carbide grinding wheels

Influence of the components on the hardness and strength of highly porous silicon-carbide grinding wheels

Prediction of Surface Quality for Silicon Carbide Wheel Grinding of Silicon Nitride

The experimental results for silicon carbide (SiC) wheel with fine grit size grinding of silicon carbide (Si3N4) revealed that the grinding parameters affect not only the ground silicon nitride surface roughness, but also the degree of surface damage. There exists complex non-linear relationship between the grinding parameters and surface quality. Better surface roughness doesn’t surely mean less surface damage. A method of prediction of grinding quality based on support vector regression is then presented according to the condition of small samples. The result shows the prediction accuracy based on this method is obviously higher than neural network, which provides an effective way for optimizing the grinding parameters to ensure the grinding quality as well as grinding efficiency while grinding of silicon carbide using conventional abrasive.

Wear of Metal-Bonded Diamond Tools in Different Abrasive Processes

In this present work, an experimental study was carried out to investigate the wear of metal-bonded diamond tools (specimens) in five abrasive processes – stirring diamond specimens in rock slurries and surface grinding the specimens with a vitrified alumina wheel as well as circular sawing of refractory bricks, vitrified silicon carbide wheels and natural granite with segmented diamond blades. Three diamond specimens of different hardness were fabricated by hot pressing. In addition to following the worn morphologies of the diamond tools, forces and power were also monitored in four abrasive processes. During stirring and surface grinding, the wear of the diamond specimens decreased with increasing specimen hardness, whereas the vertical force in surface grinding increased with the specimen hardness. In sawing of granite, however, the wear of the blades was closely related to the vertical force generated in sawing rather than the hardness of the diamond segments. The trends of force changes in sawing of refractory bricks were comparable to those in sawing of granite. But the force ratios in sawing of the SiC wheel were found to be much higher than those in sawing of other two materials.

Mechanisms of abrasive wear in the grinding of titanium (TC4) and nickel (K417) alloys

The present investigation was dedicated to elucidate abrasive-wear mechanisms during surface grinding of a titanium alloy (TC4) and a nickel-based superalloy (K417) by using silicon carbide (SiC), alumina (Al 2O 3), and cubic boron nitride (CBN) wheels. The temperature at the wheel–workpiece contact zone was measured using a workpiece–foil thermocouple. SEM and EDS were used to examine the morphological features of ground workpiece surfaces and worn wheel surfaces. It is shown that the grinding with either SiC or Al 2O 3 is characterized by the high temperatures reached in the grinding zone since either of them is easily worn during the grinding processes. Along with the presence of high temperatures, strong adhesion was found between the abrasives and workpieces, which might be attributed to the chemical bonding between the abrasives and workpieces at the elevated temperatures. The increasing ductile deformation of both TC4 and K417 at the elevated temperatures may also be a factor. Therefore, the wear of SiC or Al 2O 3 is both chemical and physical. In the grinding with CBN wheels, however, the wear of abrasive grits is mainly physical since CBN is more stable to higher temperatures. At extremely high temperatures, CBN was found to undergo dislodging prior to being gradually worn. In order to reduce the grinding temperatures, a segmented wheel was incorporated into the grinding with CBN wheels.

Torsional behaviour of tungsten heavy alloys made from mechanically alloyed powders: D.K.Kim et al. (University of Science and Technology, Pohang, Korea.) J. Korea Inst. Met. Mater., vol 37, no 1, 1999, 33–41. (In Korean.)

Zirconia is the preferred material used in many applications including biomedical implant. The zirconia in its sintered form is the most preferred one to manufacture a near net shaped implant material with minimal work. But it is very difficult to shape as the material chip away during the machining or grinding process. Hence zirconia in a pre-sintered form is used to achieve the required shape and size for a specific application. Then it is sintered and used. In this work, the grindability of the presintered zirconia was evaluated using a dense vitreous bond silicon carbide wheel. The grinding parameters such as wheel speed, radial depth of cut and feed rate are varied to investigate its grindability in terms of force ratio, specific energy, surface finish, G-ratio and ground surface under both wet and MQL cooling conditions. The forces produced during the grinding of pre-sintered zirconia was observed lower in the MQL (Minimum Quantity Lubrication) technique due to the reduction of friction, when compared to the wet cooling condition. The calculated specific energy was less in MQL cooling condition, due to the reduction in heat generation and friction. The surface finish of the workpiece obtained from the wet cooling condition was better due to the reduction in wheel loading. The percentage difference of the G-ratio between both the wet and MQL cooling conditions was observed to be 24 percent. This was due to the active participation of grains and less wheel loading in wet grinding condition. The ground surfaces obtained from the wet cooling condition were smooth and regular, compared to the MQL grinding condition.

SUBSURFACE DAMAGE IN GRINDING TITANIUM ALUMINIDE

This paper reports on an experimental investigation of grinding-induced subsurface damage in gamma titanium aluminide (γ-TiAl). Grinding was carried out with resin-bond diamond wheels having the same concentration but different grit sizes, and with a vitreous-bond silicon carbide wheel using various depths of cut. The extent of the subsurface damage was determined by a bonded interface technique and optical microscopy. The grinding-induced damage beneath the ground surfaces was found to consist of plastic deformation and microcracks. The severity and depth of the subsurface damage zone increased with an increase in the abrasive grit size and the depth of cut. Microcracks were observed when grinding was performed with the silicon carbide wheel at a depth of cut of 100 and 125 μm.

The abrasive wear of borosilicate glass

The abrasive wear of borosilicate glass was studied. Under dry wear conditions, the weight loss of borosilicate glass was not found to be a linear function of the sliding distance. The debris from the worn glass areas was observed to consist of glass particles, silicon carbide particles from the abrasive wheel and agglomerates of glass and silicon carbide. This showed that the wear of borosilicate glass by silicon carbide wheels is mainly abrasive but also adhessive to a lesser degree.

Internal pressure test for characterizing fast-fracture reliability of grinding wheels

A constant danger associated with the use of most grinding wheels (vitrified-bond alumina and silicon carbide wheels) is the possibility of fracture during operation. A standard practice is to subject newly manufactured wheels to a spin test and accept wheels that survive. We propose an internal pressure test which offers a simpler, more economical alternative to the spin test for testing grinding wheels. Probabilities of failure in the internal pressure test are correlated with failure probabilities in the spin test using probabilistic fracture mechanics. Results indicate a reasonably good correlation between the two tests, thus demonstrating their equivalence. A scheme for the easy implementation of the internal pressure test to detect damage in grinding wheels is outlined.

Factors affecting surface finish when grinding titanium and a titanium alloy (Ti-6Al-4V)

Under conventional grinding conditions redeposition which degrades surface finish occurs when grinding titanium and a titanium alloy (Ti-6Al-4V). To prevent redeposition and hence to obtain optimum surface finish the following grinding conditions are required: a soft grade (H) silicon carbide wheel running at 10 m s −1, a sulphur-chlorinated cutting oil grinding fluid and a relatively high table speed (0.2 m s −1), and the wheel should be re-dressed prior to taking the finishing passes (about ten) at a wheel downfeed of 2.5 μm.

砥粒切れ刃の破砕強さについて

A new method for measuring the fracture strength of cutting points on a grinding wheel is presented. With this method, a wheel surface is scratched by a diamond chisel with a slight depth of cut, when fracture forces from individual cutting points are measured by a piezoelectric dynamometer. The fracture strength is given as the mean fracture force divided by the corresponding fracture area which is theoretically calculated. The main results obtained are as follows : (1) The larger the dressing lead and dresser depth of cut, the smaller will be the fracture strength.(2) The fracture strength is smaller with a grinding wheel dressed by a dull dresser than with one by a sharp dresser.(3) The softer the grinding wheel, the smaller will be the fracture strength.(4) The fracture strength may be nearly independent of the grain size of the wheel.(5) The fracture strengths of white aluminum oxide (WA), green silicon carbide (GC) and black silicon carbide (C) wheels are smaller in the order of them.

Grinding of Glass: The Mechanics of the Process

An investigation of the material removal process in grinding glass and the effects of the grinding process on the surface structure and fracture strength of the finished product is reported in two papers. This first paper is concerned with the mechanics of material removal for grinding a large number of glasses and some glass-ceramics over a wide range of operating conditions with both silicon carbide and diamond grinding wheels. Experimental results indicate that the specific grinding energy generally increases with the softening temperature of the glass, and is an order of magnitude smaller for grinding with diamond wheels than for grinding with silicon carbide wheels. From observations of individual grinding scratches and an analysis of the experimental results, it is concluded that virtually all of the grinding energy is expended by viscous deformation. Material removal occurs by flow into chips with silicon carbide abrasive and by brittle fracture preceded by viscous deformation with diamond abrasive. The specific grinding energy with diamond is much less than with silicon carbide, since a much smaller volume of material undergoes viscous deformation when grinding with diamond.

Grinding of Glass: Surface Structure and Fracture Strength

An investigation is described of the surface structure and fracture strength for grinding of glass under various conditions. The surface structure of finished glass surfaces was examined by scanning electron microscopy. Surfaces ground using a silicon carbide wheel exhibited extensive flow over the surface, while surfaces ground with diamond wheels appeared to have been generated by brittle fracture with some evidence of localized flow. The relative amounts of flow and fracture on the diamond ground surfaces for various grinding conditions are related to the number of cutting points per unit area of finished surface. Grinding conditions resulting in relatively more flow were generally found to lead to higher fracture strengths.

Wheel variables in electrolytic grinding

This paper highlights the performance of electrolytic metal bonded aluminium oxide, silicon carbide, and diamond wheels during grinding of tungsten carbide. The metal removal rate and current density were evaluated against grinding force. The process efficiency and the Faraday efficiency were evaluated for the three types of wheels.

Machine for Fabricating Axially Symmetric Concave Aspherics

A machine has been constructed for fabricating concave aspheric surfaces of diameter up to 200 mm and reference radius from 20 mm to 150 mm. The principle is to use a plastic-bonded silicon carbide wheel with a convex cutting surface, which is continually dressed by a diamond form dresser. The cam used for directing the grinding wheel is cut on a numerically controlled jig borer with a tool of the same diameter as the cam follower. In operation, the location of the diamond dresser is used to provide feedback corrections for the grinding wheel.

硬ぜい材料の超仕上げに関する研究 (第2報)

The superfinishing process of ferrite and soda glass was investigated experimentally. In this experiment, the stock removal, the superfinishing resistance and the surface roughness were measured.The main results of experiments are as follows.1) Under light loads the shape of scratched traces on ferrite and soda glass is similar to that on metal.2) Silicon carbide wheels are more suitable for grinding of ferrite and soda glass than aluminum oxide wheels.3) The superfinishing resistance of ferrite and soda glass is expressed as the sum of two terms, ploughing and frictional. The ploughing force is proportional to the stock removal. Under the conditions used, the experimental constant C' of ferrite and soda glass is about 0.4 and 3 respectively, where C' is equivalent to the coefficient of piling-up in metal superfinishing.4) The value of surface roughness of ferrite and soda glass roughly superfinished is about 1μ Hmax and the value finely superfinished under about 1μ Hmax.5) The mean value of surface roughness is proportional to (M/N1/2) 2/3, where M is the stock removal per unit area and N the load per unit area.6) Superfinishing process of ferrite and soda glass is performed successfully in place of ordinary lapping process.

Grinding cermets with diamond wheels

1. It is shown that the chromium-carbide-base cermets cannot be machined by grinding with white corundum wheels or green silicon carbide wheels since this produces an unsatisfactory surface finish and reduces the bending strength of the material by 29%. 2. It has been found that this type of material can be satisfactorily ground with diamond wheels at the usual peripheral speeds with cooling and at increased speeds (to 35 m/sec) without cooling. The bending strength of ground specimens remained the same as the strength of specimens obtained by the powder metallurgy methods while the quality of surface finish reached the 8-th class (GOST 2789-59). 3. If no high efficiency of machining is required the chromium carbide parts can be satisfactorily machined by the electrospark method. In this case the strength of specimens can even slightly increase owing to the removal of the defects produced in the surface layer by compacting and sintering.

硬ぜい材料の超仕上げに関する研究 (第1報)

The superfinishing process of ferrite and soda glass was investigated experimentally. In this experiment, the stock removal, the superfinishing resistance and the surface roughness were measured.The main results of experiments are as follows.1) Under light loads the shape of scratched traces on ferrite and soda glass is similar to that on metal.2) Silicon carbide wheels are more suitable for grinding of ferrite and soda glass than aluminum oxide wheels.3) The superfinishing resistance of ferrite and soda glass is expressed as the sum of two terms, ploughing and frictional. The ploughing force is proportional to the stock removal. Under the conditions used, the experimental constant C' of ferrite and soda glass is about 0.4 and 3 respectively, where C' is equivalent to the coefficient of piling-up in metal superfinishing.4) The value of surface roughness of ferrite and soda glass roughly superfinished is about 1μ Hmax and the value finely superfinished under about 1μ Hmax.5) The mean value of surface roughness is proportional to (M/N1/2) 2/3, where M is the stock removal per unit area and N the load per unit area.6) Superfinishing process of ferrite and soda glass is performed successfully in place of ordinary lapping process.

Direct Assay for Molybdenum and Ruthenium in Uranium Alloys by X-Ray Emission Spectrometry

AbstractIt has been found possible to determine quickly the concentrations of molybdenum and ruthenium in non-radioactive alloys representative of high burn-up reactor fuels by the method of X-ray emission spectrometry. Preliminary steps of chemical dissolution and separation are not required. The alloys, essentially ternaries of molybdenum and ruthenium with uranium, are being studied because they are considered to typify the alloys which will result from cycling uranium fuel elements through the sequence of fabrication, use and pyro.metallurgical processing.The analytical procedure involves sampling of the ingot by slicing with a silicon carbide wheel at the plane of interest and reducing the surface to the flatness and finish obtained by a five-minute grinding and polishing operation. In the X-ray spectrograph the flat surface is examined for the intensities of its molybdenum and ruthenium K emission lines, with counting times of one to eight minutes. Calibration plots of intensity versus chemically determined weight per cent are established and used for subsequent sets of analyses.

SURGICAL CUTTING INSTRUMENTS TIPPED WITH TUNGSTEN CARBIDE

Tools tipped with tungsten carbide have the following advantages: 1. They can be produced at a nominal cost by any good machinist; 2. They can be autoclaved thus ensuring quicker and more through sterilization; 3. They retain their cutting edge for years without being sharpened; 4. They can be sharpened on an inexpensive readily obtainable, silicon-carbide grinding wheel; they need no honing. However, they do have the disadvantage of chipping easily if they are ground to fine-feather edge. If they are properly ground, the tools will not chip unless they are dropped or are grossly mishandled.