【正文】 s t h e g r i n d i n g t i m e i n c r e a s e s . Thus, it is easier to remove surface material from the hardest of the 濟(jì)南大學(xué)畢業(yè) 設(shè)計外文資料翻譯 8 three kinds of the ceramic tiles (Table 1). However, as the final surface roughness of ceramic tile A500 is the same as that of ceramic tile C500, the hardness of theceramic tile does not have a direct relationship with the final surface quality. In the 3 grinding wheel step, all craters and cracks on the surface of ceramic tiles caused by the 2 grinding wheel must be removed. If residual cracks and craters exist, it will be impossible to get a high surface quality in the next step. The surface roughness obtained by the 2 grinding wheel will also affect the surface Figure 1. Surface roughness of several ceramic tiles as a function of grinding time for 2 grinding wheel. quality of next grinding step by the 3 grinding wheel. In Fig. 2, the actions of the 3 grinding wheels are given using the ceramic tiles with different initial Ra, which were ground by the 2 grinding wheel for 180 sec. The curves of surface vs. grinding time rapidly decrease in 60 sec. Asymptotic behavior essentially bees constant after 60 sec. In general, the larger the initial surface roughness, the worse the final surface roughness. For example, for ceramic tile B5001, the initial Ra was , the finial Ra was after being ground by the 3 grinding wheel. When the initial Ra was for ceramic tile B5002, the finial Ra was . In Ref. [8], we studied the relations between abrasive mesh size and evaluation indices of surface quality, such as surface roughness and surface glossiness. In rough grinding, the ground surface of ceramic tile shows fracture craters. These craters scatter the light, so that the surface glossiness values are almost constant at a low level. It is difficult to improve the surface glossiness after these steps. Figure 3 shows the slow increase in surface glossiness with time by means of the 3 grinding wheel. It can be seen that the glossiness of ceramic tile B5001 is the highest. The surface glossiness of ceramic tile A4001 is better than that of A5001 because the effective grinding times per unit area for former is longer than for latter. These trends are similar to those for surface r o u g h n e s s i n Fig. 2. 濟(jì)南大學(xué)畢業(yè) 設(shè)計外文資料翻譯 9 Wear of Grinding Wheels The wear of grinding wheels is one of the factors controlling the machining cost. As shown in Fig. 4, the wear of grinding wheels is proportional to grinding Figure 2. Surface roughness of several ceramic tiles as a function of grinding time for 3 grinding wheel. Figure 3. Surface glossiness of several ceramic tiles as a function of grinding time by 3 grinding wheel. time for both the grinding wheels and the three types of ceramic tiles. The wear rate of the 3 grinding wheel is larger than the 2 grinding wheel. It implies that the wear resistance of the 3 grinding wheel is not as good as 2 for constant grinding time of 180 sec. When the slope of the 濟(jì)南大學(xué)畢業(yè) 設(shè)計外文資料翻譯 10 curve is smaller, life of the grinding wheels will be longer. Comparison of the ceramic tiles hardness (Table 1) with the wear resistance behavior in Fig. 4 does not reveal a strong dependency. Therefore, the hardness of the ceramic tile cannot be used to distinguish the machinability. The difference of Figure 4. Wear of grinding wheels of several ceramic tiles as a function of grinding time for 2 and 3 grinding wheels. initial surface roughness of ceramic tile will affect the wear of grinding wheel. In Fig. 4, the wear of the 3 grinding wheel for ceramic tile B5001 is smaller than that for ceramic tile B5002. The initial surface roughness of the latter is higher than that of the former so that additional grinding time is required to remove the deeper residual craters on the surface. Improvement of the initial surface roughness can be the principal method for obtaining better grinding quality and grinding wheel life during rough grinding. Effects of 4 Grinding Wheels and 0 Polishing Wheels Surface Quality The bination and the performance of 4 grinding and 0 polishing wheels show different results for each ceramic tile. The grinding quality vs. grinding (polishing) time curves are presented in Fig. 5, where all the ceramic tiles were previously ground by 2 and 3 grinding wheels to the same surface quality. The surface glossiness is used to assess surface quality because the surface roughness is nearly constant as finishing or polishing time increases[8]. In this test, the ceramic tile A400 were fast ground by 4A and 4B grinding wheels [Fig. 5(a)]. The surface glossiness increased rapidly during the initial 90 sec and then slowly increased. The surface glossiness by grinding wheel 4B is higher than by 4A. Afterwards, polishing was done by four different binations of finishing wheel and polishing wheel. By means of polishing wheels 0A and 0B, we processed the surface finished by 4A grinding wheel (described as 4A–0A and 4A–0B in Fig. 5), and the surface 濟(jì)南大學(xué)畢業(yè) 設(shè)計外文資料翻譯 11 f i n i s h e d b y 4 B g r i n d i n g w h e e l (described as 4B–0A and 4B–0B in Fig. 5). The curves of surface glossiness vs. polishing time show parabolic behavior. After 60 sec of polishing, the surface glossiness reaches to ,508, then slowly increases. The polishing wheel 0B gives a better surface quality than 0A. In Fig. 5(a), the maximum surface glossiness of ceramic tile A400 is about ,75 by 4B–0B. The relation between initial surface glossiness and the final surface quality is not strong. The effect of prepolishing surface glossiness can be observed by 0B polishing wheel as polishing ceramic tile A500 [Fig. 5(b)]. The maximum surface glossiness that can be achieved is 748 in 240 sec by 4A–0B or 4B–0B. This value is lower than