The three principal types of rolling mills used for the rolling of steel are referred to as "two-high", "three-high", and "four-high mills". As the names indicate, the classification is based on the manner of arranging the rolls in the housings, a two-high stand consisting of two rolls, one above the other; a three-high mill has three rolls, and a four-high mill has four rolls, arranged similarly. When rolling is in one direction only on two-high mills, and the piece is returned over the top of the rolls to be rerolled in the next pass, the mill is known as "a pull-over" or "drag-over mill". This type of mill formerly was used mainly for production of light sheets and tin plate; it still is used for rolling of tool and high-alloy steels. On two-high reversing mills, the direction of rotation of the rolls can be reversed, and rolling is alternately in opposite directions, with work done on the piece while travelling in each direction. The reversing two-high type of mill occupies an important position in the industry and, with the use of manipulators, it is possible to produce on it slabs, blooms, plates, billets, rounds, and partially-formed sections suitable for later rolling into finished shapes on other mills. In all three-high mills, each roll revolves continuously in one direction; the top and bottom rolls in the same direction and the middle roll in the opposite direction. The piece is lifted from the bottom pass to the return top pass by mechanically-operated lift tables. Usually the large top and bottom rolls are driven, while the smaller middle roll is friction driven. This latter roll is about two-thirds the size of the other two rolls in order to permit removal through the housing windows. Four-high mills are used for rolling flat material, like sheets and plates, and represent a special type of two-high mill for both hot and cold rolling, in which large backing-up rolls are employed to reinforce the smaller working rolls. The use of four-high mills resists the tendency of long working rolls to deflect and permits the use of small-diameter working rolls for producing wide plates, and hot- or cold-rolled strip and sheets of uniform gage. These mills often consist of a number of stands spaced closely together in one continuous line and are known as "tandem mills": the product passes in a straight line from one stand to the next. A continuous mill consists of several stands of rolls arranged in a straight line (in tandem). Each succeeding stand operates with roll surface speed greater than its predecessor. Reduction takes place at the same time until the piece emerges as a finished shape from the last roll stand. In cluster mills, each of the two working rolls is supported by two (or more) backing-up rolls. This latter type of mill is used for rolling of thin sheets.
Many of the accessories of rolling mills are common to all types of mills, differing in design and operations to conform with the conditions in a particular mill. In addition to the rolls, essential parts include the mill drive, lead spindle, pinions and their housings, spindles and coupling boxes, chock bearings, screws, edges, front and back mill tables, manipulators etc. The newer mills may be equipped also with various control devices, such as pressure meters and automatic roll-setting devices.
Дополнительные слова и словосочетания:
1) chock bearing – направляющий подшипник
2) a two-high (three-high, four-high) mill – двухвалковый стан (трех-,
четырехвалковый стан)
3) a pull-over or a drag-over mill – дуостан с приспособлением для
перекидки прокатного изделия
через верхний валок
4) a two-high reversing mill – двухвалковый реверсивный стан
5) backing-up rolls – опорные валки
6) tandem – тандем (последовательно
расположенный)
7) roll surface speed – скорость прокатки
8) a cluster mill – многовалковый стан
9) control devices – контрольные приборы
10) automatic roll-setting devices – автоматическая установка валков
VII. Прочитайте текст и изложите основное содержание в 5-ти предложениях.
VIII. Укажите предложения, которые соответствуют содержанию текста.
1. This type of mill formerly was used mainly for production of light sheets and tin plate.
2. The quality of continuous cast material appears to be slightly superior to that produced by normal methods.
3. The newer mills may be equipped also with various control devices, such as pressure meters and automatic roll-setting devices.
4. Electrodes may be either graphite or amorphous carbon.
5. A continuous mill consists of several stands of rolls arranged in a straight line (in tandem).
IX. Вставьте подходящие по смыслу слова.
1. The piece is lifted from the … pass to the return … pass by mechanically-operated lift tables.
a) bottom; top;
b) furnace; electric current;
c) rockers; roof.
2. Reduction takes place at the same … until the piece … as a finished shape from the last roll stand.
a) place; of cast material;
b) age; cast ingot;
c) time; emerges.
3. Usually the large top and bottom rolls are …, while the smaller … roll is friction driven.
a) discarded; slabbing mill;
b) driven; middle
c) offers; billet.
4. The newer mills may be … also with various control devices, such as pressure meters and …. roll-setting devices.
a) rolled; process;
b) tapped; important;
c) equipped; automatic.
5. The use of four-high mills resists the … of long working rolls to deflect and permits the use of small-diameter … rolls.
a) process; casting;
b) tendency; working;
c) trace; sand casting.
X. Выберите из текста предложения в которых описывается двухвалковый реверсивный стан.
XI. Составьте план к тексту на русском языке.
XII. Прочтите данный текст и переведите его без использования словаря.
The original method of reducing the size of a piece of hot steel was by use of a hammer, which has long been the symbol of a blacksmith. In some of the early forges an enormous hammer head, fixed on a wooden shaft, was raised by water power and allowed to fall on the steel, which rested on a heavy anvil.
The first stage in the modern rolling mill is the rolling of white-hot ingots between special forged steel rolls. A huge piece of steel is brought to the shaping rolls over small power-driven rollers, and is carried through. The rolls are then made to rotate in the opposite direction, and the steel drawn back through them. The distance between the rolls must be carefully adjusted so as to reduce the thickness of the ingot as quickly as possible but without cracking or tearing it.
The steel at this stage is fairly soft, but can nevertheless be cracked if the reduction at one pass through the rolls is too great. When a certain amount of reduction has been achieved, say to 6-in. square or round pieces of steel, it is chopped into lengths (known as "billets") by means of a powerful guillotine, and then set on one side or immediately reheated for further processing.