问题 问答题 简答题

主梁产生下挠的原因有哪些?

答案

参考答案:

在制造天车时,按规定主梁有一定的上拱度。而天车使用一段时间后,主梁的上拱度逐渐减少,随着使用时间的延长,主梁就由上拱过渡到下挠。所谓下挠,就是主梁的向下弯曲程度。当下挠到一定程度,就要考虑主梁的修复。

主梁产生下挠的原因有:

(1)制造时下料不准、焊接不当按规定腹板下料时的形状应与主梁的拱度要求一致,而不能把腹板下成直料,然后靠烘烤或焊接来使主梁产生上拱形状,这种工艺加工,方法虽简单,但在使用上会使上拱度很快消失而产生下挠。

(2)维修和使用不合理一般主梁上面不允许气焊和气割,但有时为了更换小车轨道等,过大面积地使用了气焊和气割,这对主梁变形影响很大。另一方面不按技术操作规定,违章操作,如随意改变天车的工作类型,拉拽重物及拔地脚螺钉、超负荷使用等都将造成主梁下挠。

(3)高温的影响设计天车是按常温情况下考虑的,所以,经常在高温环境下使用,要降低金属材料的屈服点和产生温度应力,从而增加了主梁下挠的可能性。

阅读理解

Compared to the other parts of the body, our ears don’t ask for much. They don't need to be brushed once a day like your teeth. But they need some special care, especially if you like listening to music with earphones.

Maybe your mum or dad has told you, "Turn that down before you go deaf!" Well, they are quite right. Loud noise might cause hearing loss for a short time or even forever. Think that earphones are a good way to escape from your parents’ eyes? Well. It may not be as good a way as you expect. American doctors have studied a group of 44,000 people who used earphones more than 15 hours per week. The doctors found that 37,000 of them were getting hearing problems.

If you use earphones for too long a time, your ears might feel painful. You could also lose your hearing for the rest of your life.

So don’t wear your earphones too long. Use them less than one hour a day.

Want sharp hearing? Don’t forget to do the following:

Try to stay away from places where there is too much noise, like a disco. If you have to go, wear earplugs.

When swimming, remember to put earplugs into your ears to stop water from getting in.

Never put anything sharp into your ears. If you think you have too much earwax, ask your mum or dad to help you clean it out.

Keep these things in mind! Then you won't be saying "WHAT???" when you are older.

小题1:Which is the topic paragraph of the article?

A.Paragraph One.

B.Paragraph Two

C.Paragraph Five.

D.The last Paragraph小题2:Using earphones "may not be as good a way as you expect" because _______.

A.your parents know what you're doing

B.it can cause hearing problems

C.it makes your parents angry

D.most of you use them improperly小题3:If you want sharp hearing, you should _____.

A.have your ears specially trained

B.often wear earplugs and clean out the earwax

C.take good care of your ears

D.choose what you listen to carefully小题4:"WHAT???" in the last sentence is an expression showing that the speaker____.

A.has become impatient

B.speaks in a loud voice

C.is slow in understanding

D.asks for a lot of repetition

单项选择题