问题 问答题 简答题

什么是润滑?润滑油的指标是什么?其含义是什么?

答案

参考答案:

所谓润滑就是在相对运动表面形成油膜,防止两个零件直接接触产生摩擦。

润滑油的重要指标:

(1)粘度:它表示液体在流动时,液体各薄层互相间内摩擦力的大小。

(2)粘度比:是同一油品在50℃的运动粘度,与100℃运动粘度的比值,这个比值越小说明润滑油粘度特性越好,允许使用范围越广。

(3)凝固点:油品失去流动性时的温度称为凝固点,在使用时应比此温度高若干度。

(4)残碳:指润滑油受热分解缩合形成的焦炭占润滑油质量的百分比,它是控制润滑油精制程度的一个指标。

(5)闪点:加热润滑油,使其表面的蒸汽与空气混合后刚能点着火又立即熄灭时的温度,一般要求油的工作温度低于闪点20~30℃。

(6)抗乳化性:在规定的条件下,使润滑油与水分离的时间叫抗乳化度,时间越短抗乳化性越好。

(7)抗氧化安全性:在加热和有金属存在的情况下,润滑油抗氧化作用的能力称为润滑油的抗氧化性安全性,它表现了油的化学性质。

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根据短文内容判断正误,正确的用"T",错误的用"F"

     Many teenagers feel that the most important people in their lives are their friends. They belive that their

family members, and in paticular their parents, don't know them as well as their friends do. In large families,

it is quite often for brothers and sisters to fight with each other and then they can only go to their friends for

advice.

     It is very important for teenagers to have one good friend or a cirle of friends. Even when they are not

with their friends, they usually spend a lot of time talking among themselves on the phone. This communication

is very important in children's growing up, because friends can discuss something difficult to say their family

members.

     However, parents often try to choose their children's friends for them. Some parents may even stop their

children from meeting their good friends. The question of"choice" is an interesting one. Have you ever thought

of the following questions?

     Who chooses your friends? Do you choose your friends or your friends choose you? Have you got a good

friend your parents don't like? Your answers are welcome.

( )1. May teenagers think their friends know them better than their parents do.

( )2. When teenagers stay alone, the usual way of communication is to have a discussion with their

        family by phone.

( )3. Parents often try to choose their Children's friends gor them.

( )4. Friends can discuss something difficult to say to their family members.

( )5. The sentence"your answers are welcome" means"your answers are always correct".

单项选择题