问题 问答题 简答题

为什么铝合金浇注系统常采用底注开放式和垂直缝隙式浇注系统?

答案

参考答案:

由于铝合金密度小,不易充型,化学性质活泼,极易氧化和吸气,金属氧化物的密度与铝液相近混入液态中难以清除,因此铸造铝合金浇注系统应具有充型快、挡渣能力强、液态平稳、无涡流、飞溅和冲剂等特点。再因为铝合金凝固体收缩大,易形成缩孔、缩松、变形、甚至裂纹,因此浇注系统设臵时应考虑顺序凝固,便于冒口补缩等因素。常用的底注开放式和垂直缝隙式浇注系统是为了满足铝合金浇注系统特点和要求而设臵的。

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Editor,

     Brockingham is run by people who are more interested in tourists than its residents. The problem is that

the people running the government refuse to accept new ideas. By banning all fast-food restaurants and

discount stores, they take away all the places kids can afford to shop.

     These people forget that when they were young, they could go to the South Street Soda Fountain and get

an ice-cream soda for 25 cents. Today you can't find an ice-cream soda anywhere in Brockingham for less

than $2! Where can kids go for a snack?

     There is not a single restaurant in Brockingham where a family of four can eat dinner for less than $100.

Add a 15% tip and sales tax and you have spent nearly $125 to eat a meal you could prepare at home for

about $12. Have you noticed that Brockingham families never dine in Brockingham?

     Fast-food restaurants are also a good place for school kids to get an after-school job. Fast-food restaurants

are busiest during the early supper hours when students are able to work, whereas the fancy food restaurants

cater to late-night diners. Working in one of these establishments requires working shifts that are too late for

most students.

     The City Council claims that local merchants, rather than national chains, should benefit from the tourist

business. I agree that it is important to support local businesses, but I think the fast-food restaurants would

encourage more people to shop in Brockingham.

     Another thing that disturbs me is that we must travel 25 miles to the nearest discount store. If I need a

tire for my bike, I have a choice of buying one at Surf and Peddle Sport Shop for $15 or driving to

Parkersburg Discount Center where I can buy the some kind of tire for $9. Again, I think the ban on all food

chains and discount houses is counterproductive for our city. Wes Woodrow 9th-Grade Student at

Brockingham High School

1. Why does Wes Woodrow write this letter to the editor?

A. Because the government bans all fastfood restaurants and discount stores in Brockingham.

B. Because the writer can't find an icecream soda anywhere in Brockingham for less than $2.

C. Because a family of four can't find a restaurant in Brockingham to eat dinner for less than $100.

D. Because the writer has to travel 25 miles to the nearest discount store.

2. From the letter we can infer that _____.

A. the writer used to buy a lot of icecream soda

B. the students refuse to work in fancy food restaurants

C. the government's ban benefits local merchants much

D. discount stores usually offer a discount of 40%.

3. The underlined word "counterproductive" in Paragraph 6 of the letter probably means _______.

A. cheap, not expensive

B. surprising, not expected

C. harmful, not helpful

D. doubtful, not sure

4. One way the writer of this letter tries to convince the reader is by _____.

A. complaining that someone has to drive him to Parkersburg

B. getting an after-school job in fast-food restaurant himself

C. suggesting that many businessmen have the same opinion

D. giving specific examples of the high costs in Brockingham