Alumina (Al2O3) bubble particles were added into the mixture of CBN abrasive grains, Cu-Sn-Ti alloy and graphite particles to prepare the composite blocks for porous CBN abrasive wheels. The specimens were sintered at the temperature of 920°C for the dwell time of 30 min. The bending strength of the composite blocks was measured by the three-point bending tests. The fracture surface of the blocks was characterized. The results show that, the content of alumina bubble particles does not take significant effect on the mechanical strength of the composite blocks. Even the lowest strength of the composite blocks, 98 MPa, is higher than that of the vitrified CBN abra-sive wheels. Cu-Sn-Ti alloy has bonded firmly alumina particles and CBN grains by means of the chemical reaction and corresponding products. Finally, the chip space was formed through the re-moval of the ceramic wall of the alumina bubble particles within the CBN abrasive wheel during dressing.
Abrasive composite bulks consisting of polycrystalline cubic boron nitride (PCBN) grains, Cu-Sn-Ti alloy and graphite particles were sintered at the heating temperature of 920 °C for the dwell time of 30 min. The bending strength of abrasive composite bulks was measured. The interfacial microstructure and the phases were characterized. In addition, the dressing experiment was carried out to detect the self-sharpening behavior of the composite bulks. Results obtained show that the abrasive composite bulks in this investigation give higher bending strength than that of the vitrified abrasive wheels. The compounds of TiN, TiB2were formed and the PCBN grains were embedded firmly. Strong fixing of the bulks to the PCBN grains led to the breakage of the PCBN grains when the abrasive composite bulks fractured. The intergranular fracture mode of the PCBN grains ensured the self-sharpening effect of the grains.
Based on the kinematic analysis of the double sided polishing process, the equation of
relative velocity (the workpiece to the polishing plate) is established. According to the Preston’s
equation, the function of stock removal uniformity is presented. By computer simulations of the
machining process, the effects of rotating speed ratios (the carrier revolution speed to plate rotating
speed, carrier rotating speed to plate speed) on the stock removal uniformity are discussed in this
paper. At last, some experiments have been done for validating the theoretical study of stock
removal uniformity. The results show that, the computer simulation can estimate and conduct the
experiment result in double-sided polishing process.
In this study, we explore whether auditor experience has an effect on stock price crash risk. Using a sample of Chinese firms, we find a negative association between auditor experience and stock price crash risk, especially in firms with high client importance. The path analysis shows that accounting information transparency plays a mediating role in the relationship between auditor experience and stock price crash risk. And the effect of auditor experience on clients' stock price crash risk is dominant when auditor tenure is short and when the firm is audited by non‐Big Four audit firms.
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