D Jianxin et al./ Materials Science and Engineering A 444(2007)120-129 Fig. 3. Schematic diagram of the sand blasting machine tool(1, air compressor, 2, control valve; 3, filter; 4, desiccator; 5. press adjusting valve; 6, dust catcher, 7, blasting gun: 8, abrasive hopper: 9, ceramic nozzle). 851115K沁总;:mm nozzle entry with the compositional distribution changing from the entry layer to the exit layer with the lowest volume frac Fig. 5. SEM micrograph of the SiC abrasives used for dry sand blasting ion of SiC(see Fig. 2(a)). While in Fig. 2(b), the compositional istribution of the laminated ceramic nozzle is symmetrical, the trolled by the valves and regulators. The abrasive air jet is formed layer with the highest volume fraction of Sic was put both in in the blasting gun using a suction-type process as schematically the entry layer and in the exit layer. The homologous stress-free illustrated in Fig. 4. The gas flow rate is controlled by the com- nozzle with no compositional change is shown in Fig. 2(c).The pressed air, and the abrasive particle velocity through the nozzle ceramic nozzle laminated only in entry area is named GN-2, the is adjusted to 60m/s ceramic nozzle laminated both in entry and exit area is named The erodent abrasives used in this study were of silicon GN-3. while the stress-free nozzle is named CN-2. carbide(Sic) powders with 50-150 um grain size. The SEM Six Sic/(w,Ti)c composite powders of different mixture micrograph of the SiC powders used for the dry sand blasting is ratios were prepared by wet ball milling in alcohol with shown in Fig. 5. As these abrasives are more durable and create cemented carbide balls for 80h. Following drying, the mixtures less dust than sand, and typically are reclaimed and reused. composite powders with different mixture ratios were laminate Nozzles with internal diameter mm and length 30 mm made into the mould in turn. The sample was then hot-pressed in flow- from SiC/(W, Ti)C laminated structure(GN-2 and GN-3)and ing nitrogen for 40 min at 1900C temperature with 30MPa stress-free structure(CN-2)were manufactured by hot-pressing as can be seen in Fig. 6. The mass loss of the worn nozzles was measured with an accurate electronic balance(minimum 2.2. Sand blasting tests 0. 1 mg). All the test conditions are listed in Table 1. The erosion rates(W) of the nozzles are defined as the nozzle mass loss(mD) .. Fig. 3 shows the schematic diagram of the abrasive air-jet divided by the nozzle density (d) times the mass of the erodent chine tool(GS-6 type), which consists of an air compressor, abrasive particles(m2) a blasting gun, a control valve, a particle supply tube, a filter, a desiccator, an adjusting press valve. a dust catcher, an abra- W= ml (1) sive hopper, and a nozzle. The dust catcher was used to prevent fugitive dust emissions. The air and grit flow adjusting was con- where the Whas the units of volume loss per unit mass(mm/g) Abrasive flow orifice Fig. 4. Schematic diagram of blasting gun structure(1, gun support; 2, air flow nozzle; 3, adjusting gasket; 4, ceramic nozzle; 5, plastic jacket for the nozzle).122 D. Jianxin et al. / Materials Science and Engineering A 444 (2007) 120–129 Fig. 3. Schematic diagram of the sand blasting machine tool (1, air compressor; 2, control valve; 3, filter; 4, desiccator; 5, press adjusting valve; 6, dust catcher; 7, blasting gun; 8, abrasive hopper; 9, ceramic nozzle). nozzle entry with the compositional distribution changing from the entry layer to the exit layer with the lowest volume frac￾tion of SiC (see Fig. 2(a)). While in Fig. 2(b), the compositional distribution of the laminated ceramic nozzle is symmetrical, the layer with the highest volume fraction of SiC was put both in the entry layer and in the exit layer. The homologous stress-free nozzle with no compositional change is shown in Fig. 2(c). The ceramic nozzle laminated only in entry area is named GN-2, the ceramic nozzle laminated both in entry and exit area is named GN-3, while the stress-free nozzle is named CN-2. Six SiC/(W,Ti)C composite powders of different mixture ratios were prepared by wet ball milling in alcohol with cemented carbide balls for 80 h. Following drying, the mixtures composite powders with different mixture ratios were laminated into the mould in turn. The sample was then hot-pressed in flow￾ing nitrogen for 40 min at 1900 ◦C temperature with 30 MPa pressure. 2.2. Sand blasting tests Fig. 3 shows the schematic diagram of the abrasive air-jet machine tool (GS-6 type), which consists of an air compressor, a blasting gun, a control valve, a particle supply tube, a filter, a desiccator, an adjusting press valve, a dust catcher, an abra￾sive hopper, and a nozzle. The dust catcher was used to prevent fugitive dust emissions. The air and grit flow adjusting was con￾Fig. 5. SEM micrograph of the SiC abrasives used for dry sand blasting. trolled by the valves and regulators. The abrasive air jet is formed in the blasting gun using a suction-type process as schematically illustrated in Fig. 4. The gas flow rate is controlled by the com￾pressed air, and the abrasive particle velocity through the nozzle is adjusted to 60 m/s. The erodent abrasives used in this study were of silicon carbide (SiC) powders with 50–150 m grain size. The SEM micrograph of the SiC powders used for the dry sand blasting is shown in Fig. 5. As these abrasives are more durable and create less dust than sand, and typically are reclaimed and reused. Nozzles with internal diameter 8 mm and length 30 mm made from SiC/(W,Ti)C laminated structure (GN-2 and GN-3) and stress-free structure (CN-2) were manufactured by hot-pressing as can be seen in Fig. 6. The mass loss of the worn nozzles was measured with an accurate electronic balance (minimum 0.1 mg). All the test conditions are listed in Table 1. The erosion rates (W) of the nozzles are defined as the nozzle mass loss (m1) divided by the nozzle density (d) times the mass of the erodent abrasive particles (m2): W = m1 (d × m2) (1) where the W has the units of volume loss per unit mass (mm3/g). Fig. 4. Schematic diagram of blasting gun structure (1, gun support; 2, air flow nozzle; 3, adjusting gasket; 4, ceramic nozzle; 5, plastic jacket for the nozzle).