An experimental study was carried out to quantitati ve ly evaluate the loads acting on the diamond grits during circular sawing of two kinds of typical granite with diamond segmented saw blade. Measurements were mad e...An experimental study was carried out to quantitati ve ly evaluate the loads acting on the diamond grits during circular sawing of two kinds of typical granite with diamond segmented saw blade. Measurements were mad e of the horizontal and vertical force components and the consumed power in order to obtain the tangential and the normal force components. The temperatures at the diamond-granite contact zone were measured using a foil thermocouple. T he measurement, together with the net sawing power, was subsequently used to est imate the energy partition to the granite by a temperature matching technique. B ased on the energy partition values, the temperatures at individual cutting poin ts were estimated using an analytical model. SEM was used to follow the topograp hies of worn diamond segments. The average force acting on each diamond grit was found to be only 4% of the diamond compressive strength measured by a static me thod. The strength disparity of diamond grits and the random protrusion of grits beyond bond matrix should be significant factors in accounting for the wear of diamond grits. The wear of diamond grits was also found to be closely related to the high temperatures generated at individual cutting points and the pop-outs of diamonds from the bond matrix might be mainly attributed to the heat conducte d to the segments.展开更多
Diamond grits are indispensable for sawing granite or concrete.Each year about 1 000 tons of diamond grits are consumed for such purposes.In all cases,mono crystalline diamond is used.However, polycrystalline grits(po...Diamond grits are indispensable for sawing granite or concrete.Each year about 1 000 tons of diamond grits are consumed for such purposes.In all cases,mono crystalline diamond is used.However, polycrystalline grits(polygrits) are generally better performed than mono grits as abrasives.For example,poly grits of cubic boron nitride(e.g.Borazon(?) CBN-550 of Diamond Innovations) can cut faster and they last longer than mono grits(e.g.Borazon(?) CBN-500). Polygrits of alumina(e.g.Cubitron(?) of 3M) also out perform by far glassy grits(e.g.white alumina).For diamond superabrasives,micron polygrits formed by shock waves may polish as fast as mono grits of the same size,but without causing as much scratches due to the presence of smaller sintered grains.The improved performance of poly grits is attributed to their ability to micro chipping that renews the sharp cutting corners from time to time.By contrast,mono grits tend to round off at low cutting force or macro fracture at high cutting force,so they may lose the cutting ability rapidly. For sawing granite with mesh sizes 40/50 or coarser,poly grits of diamond have not been available until recently.In this research,we have made polygrits in mini cube with sizes of 18/20,20/25,and 30/40.Turbo grinders and wire saws were made by brazing both mono grits and polygrits on steel substrates.Cutting performance on granite demonstrated that grinding speed was faster with turbo grinder,and the surface finish was smoother with wire saw for poly grits than mono ones. Polygrits and mono grits of diamond were mixed for comparison(upper left).Polygrits of mini cubes were brazed on the pearl of a wire saw(upper right).Mono diamond grits were brazed on a turbo grinder(bottom diagrams ).展开更多
The diamond wire-sawing process was developed to cut granite in both quarries and block processing plants.In this paper,swarf was collected from different areas along the sawing arc when sawing three granites.The part...The diamond wire-sawing process was developed to cut granite in both quarries and block processing plants.In this paper,swarf was collected from different areas along the sawing arc when sawing three granites.The particle size distribution and the morphology of the swarf were investigated systematically,along with the swarf formation mechanism in sawing.Granite swarf formation was dominated by transgranular fractures based on the morphology of sawn granite chips and the analysis of sawn chip size.A long cutting arc increased the movement among the swarf,tool,and workpiece,thereby inducing a secondary fracture in the sawn chip.展开更多
Four wear modes and four wear mechanisms of diamonds in sawblades are identified in a study of varied segments damaged in field operation of sawing hard stone. The four wear mechanisms are impactshearing, fatiguing, p...Four wear modes and four wear mechanisms of diamonds in sawblades are identified in a study of varied segments damaged in field operation of sawing hard stone. The four wear mechanisms are impactshearing, fatiguing, pullingout and thermal effects. Surface erosion is the result of thermal effects, while impactshearing and fatiguing lead to macro and microfracture, and pullingout results in wholesale dislodgement of diamonds provided the inequality Fn>M/(μλδ) is satisfied.展开更多
In the field of deep space exploration,the rapid development of terahertz spectrometer has put forward higher requirements to the back-end chirp transform spectrometer(CTS)system.In order to simultaneously meet the me...In the field of deep space exploration,the rapid development of terahertz spectrometer has put forward higher requirements to the back-end chirp transform spectrometer(CTS)system.In order to simultaneously meet the measurement requirements of wide bandwidth and high accuracy spectral lines,we built a CTS system with an analysis bandwidth of 1 GHz and a frequency resolution of 100 kHz around the surface acoustic wave(SAW)chirp filter with a bandwidth of 1 GHz.In this paper,the relationship between the CTS nonlinear phase error shift model and the basic measurement parameters is studied,and the effect of CTS phase mismatch on the pulse compression waveform is analyzed by simulation.And the expander error optimization method is proposed for the problem that the large nonlinear error of the expander leads to the unbalanced response of the CTS system and the serious distortion of the compressed pulse waveform under large bandwidth.It is verified through simulation and experiment that the method is effective for reducing the root mean square error(RMSE)of the phase of the expander from 18.75°to 6.65°,reducing the in-band standard deviation of the CTS frequency resolution index from 8.43 kHz to 4.72 kHz,solving the problem of serious distortion of the compressed pulse waveform,and improving the uneven CTS response under large bandwidth.展开更多
基金ProjectsupportedbytheNationalNaturalScienceFoundationofChina (NSFC ) (No .5 0 1 75 0 3 0 ) ,theEducationDepartmentofFujianProvinceinChina (No .JA0 0 2 3 6) ,andtheNaturalScienceFoundationofFujianProvinceinChina (No .F0 1 1 0 0 0 2 )
文摘An experimental study was carried out to quantitati ve ly evaluate the loads acting on the diamond grits during circular sawing of two kinds of typical granite with diamond segmented saw blade. Measurements were mad e of the horizontal and vertical force components and the consumed power in order to obtain the tangential and the normal force components. The temperatures at the diamond-granite contact zone were measured using a foil thermocouple. T he measurement, together with the net sawing power, was subsequently used to est imate the energy partition to the granite by a temperature matching technique. B ased on the energy partition values, the temperatures at individual cutting poin ts were estimated using an analytical model. SEM was used to follow the topograp hies of worn diamond segments. The average force acting on each diamond grit was found to be only 4% of the diamond compressive strength measured by a static me thod. The strength disparity of diamond grits and the random protrusion of grits beyond bond matrix should be significant factors in accounting for the wear of diamond grits. The wear of diamond grits was also found to be closely related to the high temperatures generated at individual cutting points and the pop-outs of diamonds from the bond matrix might be mainly attributed to the heat conducte d to the segments.
文摘Diamond grits are indispensable for sawing granite or concrete.Each year about 1 000 tons of diamond grits are consumed for such purposes.In all cases,mono crystalline diamond is used.However, polycrystalline grits(polygrits) are generally better performed than mono grits as abrasives.For example,poly grits of cubic boron nitride(e.g.Borazon(?) CBN-550 of Diamond Innovations) can cut faster and they last longer than mono grits(e.g.Borazon(?) CBN-500). Polygrits of alumina(e.g.Cubitron(?) of 3M) also out perform by far glassy grits(e.g.white alumina).For diamond superabrasives,micron polygrits formed by shock waves may polish as fast as mono grits of the same size,but without causing as much scratches due to the presence of smaller sintered grains.The improved performance of poly grits is attributed to their ability to micro chipping that renews the sharp cutting corners from time to time.By contrast,mono grits tend to round off at low cutting force or macro fracture at high cutting force,so they may lose the cutting ability rapidly. For sawing granite with mesh sizes 40/50 or coarser,poly grits of diamond have not been available until recently.In this research,we have made polygrits in mini cube with sizes of 18/20,20/25,and 30/40.Turbo grinders and wire saws were made by brazing both mono grits and polygrits on steel substrates.Cutting performance on granite demonstrated that grinding speed was faster with turbo grinder,and the surface finish was smoother with wire saw for poly grits than mono ones. Polygrits and mono grits of diamond were mixed for comparison(upper left).Polygrits of mini cubes were brazed on the pearl of a wire saw(upper right).Mono diamond grits were brazed on a turbo grinder(bottom diagrams ).
文摘The diamond wire-sawing process was developed to cut granite in both quarries and block processing plants.In this paper,swarf was collected from different areas along the sawing arc when sawing three granites.The particle size distribution and the morphology of the swarf were investigated systematically,along with the swarf formation mechanism in sawing.Granite swarf formation was dominated by transgranular fractures based on the morphology of sawn granite chips and the analysis of sawn chip size.A long cutting arc increased the movement among the swarf,tool,and workpiece,thereby inducing a secondary fracture in the sawn chip.
文摘Four wear modes and four wear mechanisms of diamonds in sawblades are identified in a study of varied segments damaged in field operation of sawing hard stone. The four wear mechanisms are impactshearing, fatiguing, pullingout and thermal effects. Surface erosion is the result of thermal effects, while impactshearing and fatiguing lead to macro and microfracture, and pullingout results in wholesale dislodgement of diamonds provided the inequality Fn>M/(μλδ) is satisfied.
文摘In the field of deep space exploration,the rapid development of terahertz spectrometer has put forward higher requirements to the back-end chirp transform spectrometer(CTS)system.In order to simultaneously meet the measurement requirements of wide bandwidth and high accuracy spectral lines,we built a CTS system with an analysis bandwidth of 1 GHz and a frequency resolution of 100 kHz around the surface acoustic wave(SAW)chirp filter with a bandwidth of 1 GHz.In this paper,the relationship between the CTS nonlinear phase error shift model and the basic measurement parameters is studied,and the effect of CTS phase mismatch on the pulse compression waveform is analyzed by simulation.And the expander error optimization method is proposed for the problem that the large nonlinear error of the expander leads to the unbalanced response of the CTS system and the serious distortion of the compressed pulse waveform under large bandwidth.It is verified through simulation and experiment that the method is effective for reducing the root mean square error(RMSE)of the phase of the expander from 18.75°to 6.65°,reducing the in-band standard deviation of the CTS frequency resolution index from 8.43 kHz to 4.72 kHz,solving the problem of serious distortion of the compressed pulse waveform,and improving the uneven CTS response under large bandwidth.
