问题 问答题 简答题

目前钢轨焊接有哪几种?它们焊接原理是什么?

答案

参考答案:

目前钢轨焊接主要有接触焊、气压焊和铝热焊三种。(1)接触焊是将低电压大电流加在被焊钢轨上,经闪平清洁被焊钢轨端面,通过预热和烧化使之加热至表面熔化状态,然后断电并立即加压,在压力下两钢轨端面相互结晶,使两节钢轨焊接在一起;(2)气压焊是将钢轨两清洁端面紧密贴合,并对贴面用气体火焰加热,待贴合面及附近被加热至塑性状态,金属原子具有足够的“活化能”,并穿过界面互相急剧扩散时,即对贴合面加以顶锻,以达到原子间的金属键联接,完成重新再结晶,使两根钢轨焊接在一起;(3)铝热焊是把预先配制好的焊剂,用高温火柴点燃后,发生激烈的化学反应和冶金反应,使其瞬间温度达到1200~1300℃,钢水下沉,氧化铝以渣的形态浮于溶化金属上面,然后把钢水注入套在对接钢轨上、预热好的砂模铸型内,与预热温度达900℃以上的钢轨端部融合,高温钢水将铸型内的两节钢轨端部熔化,冷却后把两节钢轨焊接在一起。

阅读理解

From a young age, it was my dream to go to Africa and work with animals. Everybody laughed at me, but my mother, Vanne, told me never to give up, and that I could always find a way.

So, when I was 23, after saving up my earnings from working as a waitress, I went to wild, untamed (野性的) Africa and began my work. In 1960 I went to the Gombe Stream Chimpanzee Reserve. At that time, we knew nothing of the behavior or social structure of chimps (黑猩猩), and I was to go there and see what I could find out. Usually, when you wake up, you leave your dreams behind you, but I found myself waking up to my dream.

As the British government wouldn’t let me go without older women’s company, my amazing mother came with me and stayed for four months. We shared a second-hand army tent, and we used the stream for fresh water and washing. We could swim in the lake, although there were crocodiles.

It was beautiful there, although both my mother and I nearly died of malaria (疟疾). I was scared I wouldn’t be able to do what I had set out to, because, at first, the chimps ran away from me in fear. I spent my days watching, listening, tracking and in the evenings writing up my notes.

For my mother, who stayed back at the camp, it must have been terrifying, and very lonely. There were snakes and spiders, as well as an old leopard who would come by. But she had an amazing way with people, and would hand out medicines to the fishermen, who saw her as a witch doctor.

In my fifth month there, I finally saw one of the chimps, which I called David Greybeard, stripping (剥光) straw to “fish” for termites (白蚁). It proved that man wasn’t the only toolmaker, and that everything had to be redefined.

小题1:What does the author mean by saying “I found myself waking up to my dream” in the second paragraph?

A.She lacked sleep due to busy work.

B.She found her dream was hard to realize.

C.She had more new dreams about her work.

D.She tried to realize her dream every day.小题2:The author was afraid at the Reserve in the beginning because _____.

A.there were crocodiles in the lake

B.she could not get close to the chimps

C.it was hard to get clean water

D.the chimps attacked her sometimes小题3:The author’s mother was thought of by the local people as _____.

A.helpful and warm-hearted

B.funny and selfish

C.romantic and talkative

D.honest and hardworking小题4: Which of the following is the author’s important discovery?

A.She found a new kind of termite.

B.Chimps can communicate with each other.

C.Some other animals can also make tools.

D.Chimps can find medicines to cure themselves.

单项选择题