1. Прочитайте и запомните новые термины.

size (v) - калибровать

pass (n) - калибр, ручей

sinking mill - редукционный стан

stretch-reducing mill - стан для прокатки труб с натяжением

OD - outside diameter - внешний диаметр

roll dressing - шлифовка валка

2. Прочитайте и переведите цепочки слов:

the final hot forming process, uniform tube wall, tube wall thickness, thick-wall tubes, high roll pass accuracy, roll pass dressing, hot rolled tubes, outer surface quality.

3. Просмотрите текст и скажите какую информацию вы извлекли (время 7 минут).

Tube production

Today, the final hot forming process in the production of tubes is usually performed on rolling mills with rolls reducing or rising the OD of the tube. The pass formed by these rolls is almost circular. Depending on the objective to be met, these rolling mills can be sizing mills, sinking mills or stretch-reducing mills.

In most cases, these rolling mills are of the same type of construction. To obtain a uniform tube wall, the shape of the roll pass must take into full consideration the ratio of tube wall thickness to tube diameter. Relatively thick-wall tubes require a round shape of the roll pass, while thin-wall tubing demands a more opened pass form. To cover a wide range of ratios of wall thickness to diameter with just one basic design and, thereby, obtain high reductions, multiple-roll stands are being employed, mostly stands using three rolls to form a pass.

The passes are machined into the rolls on specifically developed roll dressing machines. For machining, the rolls remain in the stands, thus assuring highest roll pass accuracy. After a pass is worn, it is remachined to suit the pass of the next larger stand position. On the basis of this procedure, the stand with the rolls therein forms a unit until the rolls are worn.

Roll pass dressing on the earlier mentioned machines assures a machining precision which is only one tenth of the permissible tolerances applicable in the production of hot roll tubes. This precision machining of the rolls in today's rigid stands directly determines and insures the OD and other outer surface quality of the finished tube.

4. Переведите текст со словарем и составьте план к тексту.

§3 ROLL SERVICE LIFE

1. Прочитайте и запомните новые термины:

damage (n) - повреждение

deterioration - порча, ухудшение

fatigue (v) - уставать, изнашиваться

maintenance - эксплуатация, техническое обслуживание

spelling - выкрашивание (валков)

Roll Service Life

Backup rolls (subsequently referred to as rolls) in 4 or 6-h mills are used to support heavy rolling loads. Compressive forces repeatedly act on the barrel of the rolls so that, in general, the roll barrel requires outstanding resistance to wear as well as to spelling. As a result, rolls with high hardness have соmе into use. In selecting rolls, however, specifications should be established which consider mill characteristics, operating conditions and accessory facilities so that optimum roll performance may be fully achieved.

Roll life is generally determined on the basis of the tote amount of the material rolled.

Wear and spelling are considered the two leading factors governing roll life. Since the roll surface layer is worn and fatigued during service, the roll is dressed and the fatigue layer is removed after a certain period of time. If the fatigue layer has not been adequately removed, spelling will occur and a large amount of dressing will be required which shortens roll life considerably. It is therefore very important to reduce fatigue damage and to prevent spelling through economically dressing the roll surface.

To prevent spelling, the manufacturer must develop rolls with good spelling resistance, while the user must be familiar with the roll characteristics and maintain the rolls in such a way that optimum performance is obtained.

Since roll characteristics vary widely with differences in hardness, roll hardness must be chosen carefully with consideration of factors such as mechanical properties, operating conditions and accessory facilities, so that optimum roll performance can be realized. In general higher hardness should be selected for hot strip mills, although backup rolls with higher hardness may cause surface deterioration of the work rolls. In such cases, the hardness of the backup rolls must be reduced. Wear resistance increases rapidly with increasing hardness indicating that higher hardness rolls should be provided to insure longer life or less frequent roll changes.

When the roll barrel contacts the work or intermediate roll its surface layer wears and fracture occurs in the form of spelling. The prevention of spelling requires both the proper selection of rolls with a high resistance to spelling and appropriate maintenance. When spelling has occurred, it is often uneconomical to dress the whole barrel to remove the spelling thoroughly. Depending on the degree of spelling it is possible to reuse the roll merely by local dressing. However, if an appropriate method of repair is used, new spelling may occur and develop into a fatal fracture.