问题 问答题 简答题

磨削冷却液的要求有哪些?

答案

参考答案:

①冷却性能良好,也就是冷却作用大,能在短时间内带走和散发磨削区域内产生的大量热量。磨削液的冷却性能,主要是降低磨削区温度,防止工件表面烧伤裂纹,减小工件热变形;

②有很好的清洗性能,流动性大,以便及时冲洗掉磨屑和碎磨粒;

③有适当的润滑性能,以减少砂轮与工件表面之间的摩擦,改善砂轮的切削性能,以获得较高的表面光洁度;

④成分要纯,不应含有毒性物质,不损害工人的身体健康。同时,不应有腐蚀机床和工件;

⑤冷却润滑液不应侵蚀砂轮结合剂,以免破坏粘结剂的粘结性能,而使砂轮受到腐蚀(陶瓷结合剂不受任何冷却润滑液侵蚀;而树脂粘结剂则易受碱性冷却液侵蚀;橡胶砂轮耐油性差,不能用油作冷却液);

⑥冷却润滑液应能与水均匀混合,在水箱内不起泡沫,并且不易燃烧,价格低廉;

⑦冷却润滑液中不应含有过多的润滑物质,更不能含有脏物及粉尘铁屑,要保持清洁;

⑧某些精加工中,希望冷却液是透明的,以便观察工件。以上各种要求,往往难以全面满足,应按磨削具体要求择要考虑。

阅读理解
Do teenagers in small villages do chores at home? How about the teenagers in big cities? Here is a survey. We asked 4,000 teenagers in China several questions. Half of them come from big cities like Beijing, Shanghai and Guangzhou.The others are from small villages. We made a diagram of the result of our survey. Let’s have a look at it.We found out that teenagers from small villages do more chores than those from big cities. Maybe it is because they live a harder life. Our advice to parents in big cities is that parents should give their children some chores to do. Doing chores teaches teenagers to take care of themselves.
Chores
2000 teenagers in small villages
2000 teenagers in big cities
Take out the trash
1600
1000
Sweep the floor
1200
850
Make the bed
1400
750
Do the dishes
1100
600
Fold the clothes
900
1500
小题1:They surveyed ______ teenagers from small villages.
A.1,000B.2,000C.3,000 D.4,000
小题2:There are 1,000 teenagers from the cities who ______.
A.take out the trashB.do the dishesC.make the bedD.fold the clothes
小题3:Fewer than ______ teenagers in big cities sweep the floor and make the bed.
A.500B.1,000C.1,500D.2,000
小题4:The number of teenagers ______ in big cities is bigger than that in small villages.
A.making the bedB.taking out the trash
C.folding the clothesD.doing the dishes
小题5:Why did they make the survey?
A.Because they don’t want teenagers in China to do chores at home.
B.Because they thought it’ll help teenagers to take good care of themselves to do chores at home.
C.Because they wanted to know if teenagers in China do chores at home.
D.Because they thought it’s not necessary for teenagers to look after themselves.
问答题