TPT January 2010

S pecial R eport

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.

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 a) 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 b) 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

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J anuary 2010

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