问题 问答题 简答题

钢粒钻头应满足哪些要求?

答案

参考答案:

钢粒钻头不仅仅起到传递轴向压力和回转力的作用,还要把钢粒压向孔底的岩石面以破碎岩石。良好的钢粒钻头应满足以下要求:

a、能够很好地压住钢粒,并能带动钢粒沿孔底滚动,以便有效地破碎岩石;

b、能顺利地流通冲洗液,排除岩粉;

c、钻头应耐磨,并且在磨耗中能保持良好的补砂和导砂性能,以保证钻进正常进行。

阅读理解

阅读理解。

      Ann loves the underground (地铁) in London. She always prefers to travel on the underground

because it is fast. She doesn't find it difficult now, as she has got used to (逐渐习惯) it. Ann knows

the underground map very well. Each line has its own color. For example, the Central Line (主干线)

is red, the Piccadilly Line (皮凯德里干线) is blue, and so on. Londoners always call the underground

"the tube" (meaning "underground") When you see the long tunnels (隧道) under ground, it isn't hard

to understand why. Yesterday Ann went home on the underground at about five o'clock in the afternoon.

She got a surprise. Since everyone was going home from work, the train was full.

      This was the "rush-hour", and it was a new experience (经历) for Ann. There were a lot of people,

but trains came every minute. Everyone waited and didn't push. As the train was full, Ann had to stand,

but she didn't mind. In the train she saw a sign. It said: "Keep away from the Rush Hour." "I will, next

time." Ann thought.

1. Travelling in London _______.

A.Ann prefers the underground to buses

B. Ann prefers buses to the underground

C. Ann prefers bike to the underground

D. Ann prefers to walk under ground

2. It's easy for Ann to take London's underground because _______.

A.she lives near the underground in London.

B. she has a good knowledge of the underground map

C. each line has its own color.

D. there are signs everywhere in London

3. Why do Londoners call the underground "the tube"?

A. Because Londoners like to use the tubes?

B. Because London's underground has too many lines.

C. Because Londoners think the underground looks like the tube

D. Because London's underground is straight and long

4. The"rush hour" here means _______.

A. 冲刺时间

B. 忙碌时间

C. 高峰时间

D. 休闲时间

5. Ann decides _______.

A. that she will take a bus instead next time

B. that she will no longer take London's underground

C. to take the underground at this time next time

D. not to take the underground at this time next time

判断题