问题 问答题 简答题

如何防止精炼过程钢液的回磷?

答案

参考答案:

精炼过程回磷主要是因为渣中的(P2O5)被还原而进入钢液,所以必须降低入LF渣中的(P2O5),渣中的(P2O5)主要是初炼炉下渣所带来的。转炉或电炉终点炉渣中的(P2O5)较高,如出钢带入钢包内的炉渣过多,由于钢包内钢水的对流作用及造还原渣,渣中的(P2O5)会还原而进入钢液中,所以要减少下渣量,电弧炉炼钢由于采用偏心底出钢技术及留钢留渣操作,可基本做到不带下渣,即所谓的无渣出钢。而转炉下渣却难以控制,虽然采用了挡渣球、机械挡渣塞、气动挡渣及电磁感应传感器法挡渣,仍不可避免地会有下渣带入,但下渣量相比以前大幅度降低,下渣入钢包后,要立即对下渣进行处理。

单项选择题
单项选择题

Workforce is defined as the total number of people who are available to work and earn incomes. The definition includes everyone who is employed or seeking paid employment, so it includes employers and the self-employed.

Although the size of the workforce depends a great deal on the size of the total population, there are several other influences which also affect it. The age distribution of the total population has a very marked effect on the available workforce. If the population has a high proportion of very young people or of those too old to work, then the available workforce would be lower than if there were an evenly spread age distribution. If the population grows rapidly from natural increase, i.e., the number of births greatly exceeds the number of deaths, then as the total population increases, the proportion in the workforce declines

Sometimes a population is described as aging, which means that the birth rate is either falling or growing very slowly, and as people retire from the workforce, there are not enough young people entering it to replace those who are leaving it. The population is top-heavy with older people. So the percentage of the population in the workforce declines when there is either a rapid increase in births or a falling birth rate.

The age distribution of the population has several important effects on the economy. If the population is aging and there is an increase in the number of people retiring without a corresponding increase in the number entering the workforce, this raises the problem of the ability of the economy to provide a reasonable level of social services to the retired group. If the aged are to be cared for in special homes or hotels, finances must be available for that purpose. If the size of the workforce is small relative to the total population, then the government tax receipts are relatively low and either the government has less money available to it or the workforce members have to be taxed more heavily.

The last paragraph focuses on ().

A. the factors that influence the workforce structure

B. the importance of workforce distribution to the economy

C. the relationship between age distribution and economy

D. the influence of population growth on the national economy