3. Прочитайте текст, стараясь понять его содержание; расскажите о смене валков на прокатных станах, пользуясь вопросами в конце текста.

Rapid Work Roll Changing – Past, Present and Future

Increased demand for improving gage, shape and surface quality requires more frequent roll changers. The time needed for making these roll changes considerably reduces the utilization time and production of a rolling mill. Therefore, rapid changing of work rolls is important for all rolling mills which roll steel or other metals to a finished product such as bars, shapes, plates, hot and cold strip.

In the past, work roll changes were made generally by overhead mill cranes with several different methods being employed:

- Older open-top design stands permitted the rolls to be lifted out vertically after the housing tops had been opened. This method was suited only to 2 and 3-h mills since work rolls could be lifted individually or in combination in a cartridge.

- Entire mill stands were exchanged with completely preassembled spare stands. The limitation of this method included the high cost of spare stands, the cost of large cranes and buildings to support them.

- The use of auxiliary tools. With this method normally only one roll was taken out at a time, although some units could handle a pair of work rolls together. However, they were expensive, difficult to operate arid required specially adapted cranes.

- Two work rolls were pulled by overhead crane or hydraulic cylinder with the work rolls riding on top of the bottom back-up roll. After the exchange of the work rolls, the set was transferred back into the stand in the same manner. Because of the slow speed of the back-up roll changing cylinder this method was a slow procedure, especially when several mill stands were involved.

With all four of these methods, changing one individual stand was relatively fast. Depending on the skill of the roll changing crew and crane operator, roll changes were performed within 10 to 15 min. The real time loss occurred when more than one stand of a tandem mill was changed. Losses of more than 1 hr production time were not uncommon.

Present day work roll changing devices are of various designs. All of them are, to a large extent, independent of the mill crane during roll changing. If all stands of a tandem mill are equipped with rapid roll changers, a changing time of approximately 5 to 6 min can be expected, regardless of the number of stands to be changed.

All mills have always been sufficiently different in design and layout, therefore, standardization of roll changing devices has not been developed. Optimum designs are investigated on an individual mill basis. The basic design approach is determined by its application to either a new or existing mill, and the amount of automation desired.

No new mill should go into operation without some type of rapid roll changing. In the future, computer controlled tandem mills will be built that permit rapid roll changes on the fly.

Notes: 1. on the fly - на ходу

4. Вопросы.

1.Why are frequent and rapid roll changes required?

2. In what ways were work roll changes made in the past?

3. What are present day work roll changing devices?

4. What mills will be built in the future?

5. Сделайте письменный перевод 2, 3, 4, 5 абзацев.

6. Составьте краткую аннотацию к тексту.

§9

1. Письменно переведите текст со словарем (время – 40 минут).

Experience has shown that lubrication of steel mill equipment can be a critical factor in increasing production, reducing delays and lowering operating and maintenance costs. In order to create new types of lubricants it is necessary to develop and apply new lubrication technology.

In service the lubricant is subjected to two types of changes: a change brought about by the lubricant itself, often referred to as a chemical change, and a change due to outside factors. Chemical changes resulting from oil oxidation cause increases in viscosity (вязкость), in addition to darkening the lubricants colour. The rate of oxidation depends on temperature, time and the type and quality of the lubricant.

Contamination in a steel mill environment consists of heat, air, dirt, water and other lubricants. The two types of changes are interrelated and significantly effect the service life of the lubricant.

Generally lubricant samples are submitted to the laboratory to determine whether the lubricant is in a satisfactory condition for continued service in a critical application or whether the condition of the lubricant is the direct cause of an operational problem.