If the set collar end hardness is lower than HRC40, should first on the end surface again a built-up welding hard alloy, after the polish repackaging.

如果固定环端面硬度低于HRC40，则应先在端面上重新堆焊一层硬质合金，经磨光后再装配。

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"If I wore a white shirt to school, by the end of the day it would be brown, " recalls He, who was born in 1974, "and there would be a ring of black soot under the collar."

他回忆说：“如果我穿一件白衬衫去上学，一天下来衬衫就变成了棕褐色。 领子下面还有一圈黑黑的烟灰。”

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But they're hard to miss in foundering blue-collar and low-end service communities across the country.

但是在各地衰落的蓝领、低端服务行业中却十分明显。

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Instead, people worry that the great shift in social mobility that came with the expansion of higher education and of white-collar work has come to an end, leaving the people who did not benefit from it more stuck than ever.

ECONOMIST: Income inequality

His 39 years at Caterpillar protect Lierle from the current plan to shed 20, 000 jobs, but he knows many of the workers who are gone, or who will be let go over the next couple of months, and worries that a way of life in blue-collar industrial towns like Peoria is coming to an end.

CNN: Recession comes late but hits hard in Peoria

They end in hooks which would have been linked together when the collar was worn.

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