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1、Investigation of the air boundary layer around a rotating grinding wheel,Advanced Manufacturing Technology Research Laboratory General Engineering Research Institute Liverpool John Moores University,07 November 2008,2,Content of presentation,Introduction and review Experimental arrangement and metho
2、d Experimental results and discussion Further results from CFD simulation Conclusions,3,Introduction and review,Problems in grinding process:,High specific energy, which is converted to heat in the grinding zone High temperature causes thermal damage to the workpiece - burning, phase transformations
3、 - softening surface layer with possible re-hardening - unfavourable residual tensile stresses - cracks, and reduced fatigue strength - accelerate wheel wear Contribute to inaccuracies and distortions in the final product,4,Introduction and review,Problems in grinding process:,Grinding fluid is appl
4、ied in order to limit the high temperatures and thermal damage and wheel wear.,Role of grinding fluid: lubrication, bulk cooling and transport of debris.,5,Introduction and review,Problems in fluid delivery in grinding :,Grinding fluid must be delivered to the grinding zone in sufficient volume. (fo
5、r effective lubricating and cooling) Air boundary layer develops around the periphery of the wheel surface in grinding, which may prevent the fluid reaching the wheel surface. Two main methods of grinding fluid delivery: low pressure nozzle (flood) high pressure nozzle (jet) Fluid delivery at high p
6、ressure (jet) leads to increased friction and wastage of power. Fluid delivery via a low-pressure system may be insufficient to penetrate this air boundary layer, especially in high-speed grinding.,6,Introduction and review,Interest on air boundary layer investigation:,The air boundary layer flow ha
7、s sufficient energy to prevent the fluid reaching the wheel surface and the grinding contact zone. This has aroused interest that has led to the studies of the air boundary layer flow around the rotating grinding wheels. The air velocity distribution has been measured by some researchers.,Cutting fl
8、uid backing up due to boundary layer effects S. Ebbrell etal (1999),7,Introduction and review,Problems in previous measurement of air boundary layer:,Most of the previous measurements were intrusive measurement method (not sensitive enough to measure the low velocity air flow) Most previous research
9、ers only measured the tangential component velocity of the air boundary layer (one component velocity) Different measurement methods and experimental parameters led to conflicting results Therefore, a comprehensive understanding of the air boundary layer flow has not been obtained,8,Introduction and
10、 review,Review of previous measurements:,V. N. Serov (1965): air velocity changes along the wheel width reaching a minimum value in the middle section. Method: unknown,V. Radhakrishnan (1977): Similar to Serovs results Method: Pitot tube and hot-wire,9,Introduction and review,Review of previous meas
11、urement:,J. Shibata (1982): Two peaks around the sides of the wheel close to wheel surface, but tend to shift to the center of the wheel width with the distance to the wheel surface Method: Hot-wire anemometer,Sven Alenius (1996): Air central peak along the wheel width Method: Pitot tub,10,Experimen
12、tal arrangement and method,LDA measurement:,Laser Doppler Anemometry (LDA) represents a most effective tool in the fluid velocity measurements. Advantages of the LDA: non-intrusive measurement with high temporal and spatial resolution Ideal measurement technique for the investigation of air flow vel
13、ocity.,(a ) Laser system generator,(b) Burst Spectrum Analyzer (BSA),(c) PC,LDA measurement system,11,Experimental arrangement and method,Experimental arrangement:,Grinder: Abwood Series 5020 surface grinding machine LDA: Argon+-ion LDA system (two-component dual-beam LDA , back-scatter mode) Seedin
14、g particle: Smoker generator,12,Experimental arrangement and method,Experimental arrangement:,Schema of the configuration,Wheel Parameters: Material: Alumina Diameter: 182.5mm Width: 25mm Surface roughness: Rt=2mm,13,Experimental arrangement and method,Experimental Method:,Measurement coordinate sys
15、tem and the measurement area,Lattice of measurement points,14,Experimental arrangement and method,Experimental works presented:,Air tangential velocity contour map with different wheel speed (Vs) Air radial velocity contour map with different wheel speed Effect of the wheel speed on air velocity Eff
16、ect of the wheel roughness on air velocity Tangential and radial velocity turbulent value map,15,Experimental results,Air tangential velocity contour maps:,(Vs = 20m/s),(Vs = 30m/s),(Vs = 40m/s),The air tangential velocity has its highest value close to the wheel surface. The highest tangential air velocity is always in the wheel middle section along the wheel width. Close to the wheel edges, the gradient of Vt is high.,16,Experimental results,Air radial velocity co
