机械密封摩擦副材料在选用方面应注意那些问题？常用的材料有哪些？
参考答案：
1.在化学性能方面，抗密封介质腐蚀、磨蚀、溶解和溶胀的性能。
2.在物理性能方面，要有高弹性模数、强度值较低的滑动摩擦系数，优良的耐磨性和自润滑性，以及良好的不渗透性和湿附性能。
3.在热力性能方面，要有良好的导热性、耐热性、耐寒性和耐温度的急变形。材料来源要方便。加工容易，成本较低等。摩擦副常用的非金属材料：纯石墨、浸渍石墨、聚四氟乙烯和填充聚四氟乙烯、酚醛塑料、陶瓷以及喷镀陶瓷等。常用的金属材料：铸铁、碳钢、青铜、铬钢、铬镍钢及硬质合金等。
Directions: Complete the following passage by using the words in the box. Each word can only be used once. Note that there is one word more than you need.
Many kinds of stones are used as building materials. Stones and marbles are ____小题3:__ for important monuments because they are not burnable and can be expected to __小题4:____. Stone architecture was often blended with stone sculpture. The use of stones has declined, however, because a number of other materials are more ____小题5:__ to industrial use. The complexity of modern life calls for a variety of buildings. More people live in ____小题6:____ housing and go to work in large office buildings, send their children to many different kinds of schools, and when they are sick they go to ___小题7:___ hospitals and clinics. All these different types of buildings ____小题8:____ experiences needed by their designers. By the middle of the 20th century, modern architecture, which was influenced by new technology and mass production, was dealing with ___小题9:__ complex social needs. Important characteristics of modern architectural works are expanses of glass and the use of reinforced concrete. Advances in elevator technology, air conditioning, and electric lighting have all had important effects. |
