TPT January 2010

122

anuary

2010

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system developed by SMS Meer has become a widely known and

applied system. The system task consists of ensuring a high level of

product yield and quality in the tube manufacture. Smaller diameter and

wall thickness variations result in metal saving and cost reduction both

in the course of production and during subsequent tube processing.

At present, the problem of application of on-line tube dimension

control systems is of high urgency. Obviously, practically all processing

units will be furnished with systems for measuring tube wall thickness

and diameter in the near future. Multichannel sensors measuring

linear dimensions and allowing not only recording of the mean wall

thickness variation during the tube travel along the process line

but also determining the character of cross-sectional wall thickness

variation will be given preference despite their relatively high price.

Successful development of a number of base branches of

economy depends on the achievements in the field of production of

cold-worked tubes.

A special place in the pipe and tube industry is taken by cold tube

rolling and drawing processes. Application of cold working methods

ensures higher dimensional accuracy in tubes, improvement of surface

quality, structure and properties of the tube material and expansion

of the tubular product range. Manufacture of high-quality cold worked

tubes is a multicyclic process including machining and chemical

preparation of mother tube surfaces, rolling and/or drawing, thermal and

chemical treatment and a number of other process steps.

The method of cold pilger rolling invented by Newbert (USA) in

1927 as alternative to drawing of low-plastic materials has eventually

become a basic method in making tubes of major metals and alloys.

The main advantages of this method are its high mobility, considerable

reductions (up to 70-85% per pass while the highest achievable

reduction in drawing does not exceed 30-40% without intermediate

annealing), and comparatively small in-process metal loss.

In the 1930s, cold tube rolling was only used in Germany,

USSR and USA. At present, this method is used in all industrially

developed countries. The method of warm pilger rolling invented in

the 1960s has made it possible to achieve much higher reductions

as compared with the cold rolling due to a lower resistance to

deformation and a higher plasticity of a number of metals at

temperatures around 350°C. At present, this method is used in

Russia, Ukraine, Italy, Sweden and Japan.

The further development of cold (warm) rolling technology is

of rather high importance and it first of all should be directed to

improvement of the tube quality, raising of mill productivity and

reliability, through increase in reduction per deformation cycle through

a maximum utilisation of metal plasticity reserves. At the same time,

the most important task is getting lower production costs to increase

competitiveness of cold-rolled tubes. Cold rolling perfection proceeds

in two directions:

bettering manufacturing techniques including working out of

optimum rolling schedules, application of the warm rolling

process, and improvement of roll and tool designs;

improvement of equipment to raise mill output and prolong life of

mill assemblies and components.

Cold drawing is a very old and universal method of metal

forming. Drawing was first used around 3000 to 4000 BC in working

non-ferrous metals. The drawing process was first industrially used

in USA in 1886 for cold working of steel tubes (in production of

bicycles). At present, 0.2 to 765mm diameter tubes of steel and

alloys are manufactured with various wall thicknesses (smallest

achieved wall thickness in capillary tubes is 0.015mm).

The largest cold drawn tube producers are countries with the most

highly developed ferrous metallurgy (USA, Japan, China, Germany,

England, South Korea, France, Russia and Ukraine), whose share

in the world production of these products comes to 70%. The tube

drawing process in England, USA and Japan is at a higher stage of

development than the cold rolling process. In Russia and Ukraine,

cold drawn tubes are mostly produced using sink drawing method and

fixed plug drawing method. In England, the basic method of making

cold worked tubes is floating mandrel drawing. Unlike other countries,

floating plug drawing is prevailing In USA. Bull-block drawing of small

size tubes is widely used in Germany, USA, England and a number

of other countries.

At the present stage, development of the drawing processes

is aimed at the growth of cost effectiveness and intensification of

speed parameters. It can be achieved by decreasing the process

cycle number and enhancing quality of the produced tubes using

the following measures:

a) increase in total deformation (between thermal treatment

operations) and deformation per pass;

b) use of multiple continuous drawing simultaneously in several dies;

c) increase in the number of simultaneously worked tubes (from 2

to 10) in straight drawbenches;

d) use of liquid lubricants sublimating during thermal treatment and

lubricants and coatings sustaining several drawing passes.

It can be presumed with a great likelihood that fundamentally

new manufacturing processes will find their commercial application

(or will be used on a larger scale than today):

a) warm drawing;

b) core drawing;

c) drawing combined with expanding;

d) drawing with tube twisting;

e) drawing with hydrodynamic feed of lubricant to the deformation

zone;

f) drawing with ultrasonic tool oscillation;

g) back-pull drawing;

h) rotary drawing (rotary swaging combined with drawing) in various

versions.

To realise new manufacturing processes, it is necessary to

develop efficient designs of drawing mills and tools and build new or

reconstruct existing shops and equipment. Such activities are under

way in USA, Germany, Japan, Russia and other countries.

The growing demand for thin-walled stepped tubes, tubes with

a variable wall thickness and longitudinally variable cross-sectional

shape, bimetal and multilayer tubes will require application of new

methods and processes of cold drawing in mills of special designs

in the coming years.

Taking into consideration toughening requirements to the product

quality, still wider use of processes of thermal treatment of tubes in

a protective atmosphere can be expected.

Commercial use of welded tubes as mother tubes for their

subsequent cold processing is a rather promising trend of development

of the drawing technology. This assertion is confirmed by the fact that

electric welded tubes subjected to working at deformation ratios of

30-40% meet requirements to seamless tubes but they cost 10-30%

lower compared to the seamless tubes of the same size.

References

1. J. Perc Boore. The Seamless Story. – Los Angeles, The Commonwealth

Press, 1951. – 286 p.

2. Manufacture of Steel Tubular Products. – Pittsburgh, United States

Steel, 1966. – 64 p.

3. The bulletin “Metal – Expert. Steel Pipes” (Ukraine). January 2002 –

August 2009, vol. 73 – 160.

4. H.G. Müller, M. Opperer. Das Stahlrohr. – Düsseldorf, Verlag Stahleisen,

1974. – 370 s.

5. V.M. Drujan, Yu.G. Gulyayev, S.A. Chukmasov. Theory and Technology

of tubes production. – Dnepropetrovsk, Dnepr – VAL, 2001. – 544 p.

pecial

eport