问题 问答题 简答题

如何用砂轮进行火花鉴别黑色金属材料成分?

答案

参考答案:

火花鉴别金属材料砂轮是用手提砂轮机和台式砂轮机,砂轮一般为36~60号普通氧化铝砂轮,同时应备有各种牌号的标准钢样,以防可能发生的错觉和误差。火花鉴别时最好在暗处进行,砂轮转速以2800~4000转/分为宜。在钢材接触砂轮圆周进行磨削时,压力适中,使火花大致向略高于水平方向发射,以便于仔细观察火花的长度和部位花型特征。

阅读理解

Expo 2010 is held in Shanghai from May 1 to October 31.People all over the world are looking forward to it.Here are several golden rules on how to best plan your hip.

Rule 1:Do your homework

Read everything you call before going.Really study the maps.Know the pavilions.Arrive at the entrance nearest Io the things you want to see.Have a plan.It will make a big difference.

Rule 2:Allow plenty of time

Expo 2010 is the largest attraction event in the history of the world.It will take many days to see it.Plan to spend from five to eight days or more seeing it.

Rule 3:Pace yourself

Expo is enormous.The distances are punishing.It is better to spend a day seeing a single area than to man hack and forth all over the site.Remember to wear the most comfortable shoes.Never mind what they look like.

Rule 4:Get going in May

At many Expos the crowds are smaller in May and in early June than any other time.And beware the last two weeks.During every Expo, people delay their visits and then in early October they suddenly realize.“Expo will close soon! I haven’t seen it!’’ As a result, the last several weeks usually have the most crowded days of the entire Expo.

Rule 5:Find out what everyone else is doing-and do the opposite

If you don’t like large crowds and long lines.do the opposite.Here is all example:Most people go on Saturdays or on holidays, So avoid Saturdays and holidays.Go on weekdays when most people are at work.

Rule 6:Turn up

Expo 2010 is the largest celebration in China’s history-an amazing once-in-a-lifetime event.When it is gone and it will never be seen again.So whatever you do,don’t miss it!

小题1:Expo 2010 will last _________.

A.five to eight days

B.several weeks

C.six months

D.a year小题2:According to Rule 4,you’d bettor not go to Expo on ________.

A.May 3

B.July 5

C.September 16

D.October 20小题3:When there are lots of people waiting in line to see the most popular activations, what’s your  best choice?

A.I’ll wait in line as other people do.

B.I’ll go back and return tomorrow.

C.I’ll visit the less crowded places instead.

D.I’ll sit on a bench to have a rest for about two or three hours.小题4:In Rule 6 “turn up” here means ________.

A.don’t miss it

B.come and see

C.make the sound louder

D.never be seen again

单项选择题