问题 问答题 简答题

车外圆时表面上有混乱的波纹(振动)缺陷与机床的哪些因素有关?

答案

参考答案:

精车外圆时,造成外圆表面上有混乱的波纹(振动)的有关因素有:

(1)主轴上的滚动轴承滚道磨损间隙过大。

(2)主轴的轴向窜动太大。

(3)用卡盘夹持工件切削时,因卡盘法兰松动使工件夹持不稳定。

(4)床鞍和中、小滑板的滑动表面间隙过大。

(5)使用尾座顶尖夹持工件。切削时,顶尖套不稳定;活顶尖中轴承滚道磨损,间隙过大。

阅读理解

C

Last Sep.11 was an important day too. After unknown gunmen attacked aid workers from the Nobel Prize-winning Medecins sans Frontieres at a roadblock on that day , most of the international aid groups helping Darfur’s 6 million people stopped using the roads . On Dec.18 , unknown gunmen attacked the southern town of Gereida. More than 70 aid workers then pulled out of the refugee(难民) camp there—Darfur’s largest, with 130,000 people —leaving only 10 Red Cross employees behind. Yet at the time no one said what had really caused the sudden pullbacks.

Damaging has become surprisingly common in Darfur, where 200,000 Africans have been killed and a third of the population have been sent fleeing into camps in three years of war. But the attacks on international aid workers suggested a dramatic and dangerous start—to attack on purpose those helping to keep Darfur’s millions of refugee alive. A dozen people from foreign NGOs (non-governmental organizations) have been killed in just the past six months , more than previous years. There are about 14,000 aid workers in Darfur now , the majority of them Sudanese, working for foreign NGOs and U.N. agencies and delivering $1 billion a year in aid . Just a few more terrible attacks could throw that into jeopardy. Last week 14 U.N. offices working in Darfur made a clear warning that “the humanitarian (人道主义) organization cannot possibly make certain the survival of the population Darfur if aid workers don’t feel safe. ”

64.What made Sept.11 an important day according to the passage?

A.Two World Trade Center buildings were destroyed in the USA.

B.International aid workers were attacked in Darfur.

C.A fight happened between the international aid workers and some unknown gunmen in Darfur.

D.International aid groups stopped their help to Darfur.

65.Which of the following shows a picture of Darfur?

A.Darfur has been in war since the last Sept.11.

B.Many people in Datfur are homeless because of the war.

C.Darfur will not get help from organizations including the UN.

D.International aid groups have never been attacked before.

66.The underlined word“jeopardy”in the last paragraph most probably means     

A.light                   B.practice              C.danger            D.effect   

67.Which of the following can be the tide of the passage?

A.People in        Darfur        B.International Aid Groups in Danger

C.War in Darfur                D.International Aid to Darfur

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