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Working range of roll pass sequences in wire rod rolling with interstand tensions
KTH, Superseded Departments, Production Engineering.
2004 (English)In: Ironmaking & steelmaking, ISSN 0301-9233, Vol. 31, no 1, 81-92 p.Article in journal (Refereed) Published
Abstract [en]

In the high speed rolling of wire rod in blocks, interstand tensions are utilised in order to keep the process stable. However, interstand tensions influence the rolling process, and especially the spread and forward slip, which are dependent of tensions between the stands. By the influence on spread, the tolerances of the rolled product depend on the tensions and usually the interstand tensions are kept as low as possible in order to obtain required tolerances. A narrow spread technology is used to utilise interstand tensions in order to increase the working range of a pass sequence and move the product range towards smaller sizes. By adapting a certain amount of interstand tensions, smaller sizes can be rolled by a given roll pass schedule. A practical problem in this method is the fixed gearings in the common blocks, which require a certain and given level of interstand tensions and corresponding reductions. In the latest generation of blocks, where the stands are arranged in units, two by two, with each unit driven by a dedicated electrical motor, it is possible to introduce 'inter unit' tensions, and by this method extend the working range of the pass sequence. A special computer program for analysis of interstand tensions has been developed by combining a program TENSION, developed at the Royal Institute of Technology in Stockholm, dealing with the basic principles of rolling with interstand tensions, with the recently published program WORKRAN, which analyses the working range of any roll pass sequence built up by common two-symmetrical grooves. From the analysis and experimental data it is shown that interstand tensions at the level of 10% of the yield stress of the material increase the working range in a six stand block by 2% and reduce the lower limit of the exit section area by about 15%. Higher tension levels have a larger effect both on the extension of the working range and on the reduction of the minimum exit area but it becomes more difficult to control the tolerances at higher tension levels. The influence of interstand tensions on the reduction and on the working range of the pass sequence is mainly obtained by the influence on the round passes, while the oval passes have a counteracting effect on the influence of interstand tensions.

Place, publisher, year, edition, pages
2004. Vol. 31, no 1, 81-92 p.
Keyword [en]
wire rod rolling, roll pass design, computer programs
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-8843DOI: 10.1179/030192304225011016ISI: 000222387200011OAI: oai:DiVA.org:kth-8843DiVA: diva2:14306
Available from: 2004-11-30 Created: 2004-11-30 Last updated: 2011-08-31Bibliographically approved
In thesis
1. Roll pass design for improved flexibility and quality in wire rod rolling
Open this publication in new window or tab >>Roll pass design for improved flexibility and quality in wire rod rolling
2004 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The thesis treats roll pass design in wire rod rolling of stainless steel for sequences and series built up by two-symmetrical grooves. It is focused on predicting rolling flexibility, also called working range, as well as product quality. For analysing the flexibility a computer program has been developed. The minimum and maximum roll gap and corresponding bar areas for series of grooves including "oval", "round", "false round", "square" and "diamond" shapes are calculated. Six pass designs used in Swedish mills are analysed. Full-scale rolling is compared with laboratory experiments for the square-oval and false round (round)-oval series. The false round-oval series offers the largest working range and that the flexibility is smaller for pass sequences designed for high reductions. The false round-oval series are also acknowledged as a series for high quality steels and are usually better than the square-oval series having a tendency for defect formation. The thesis also includes high-speed rolling of wire rod in blocks. Here interstand tensions are utilised in order to keep the process stable. For obtaining the required dimensional tolerances of the product they are kept as low as possible. However interstand tensions could be used in order to increase the working range and move the product range towards smaller wire cross sections. For analysing this possibility, a narrow spread technology is utilised. At present time a practical problem is referred to the fixed gearings in the common blocks, which require a certain and given level of interstand tensions and corresponding reductions. This problem can however be solved by means of new block design and modern process control technology. Roll stands can be separately driven and controlled at very high speeds. Thus the eight stand blocks can be subdivided into four plus four passes blocks with a cooling line between enabling also higher productivity without violating the product quality because defect formations caused by a too high rolling temperature. The true working range of a series for a specific steel grade is however not only dependent on the possible spectrum of wire dimensions that can be obtained but might also depend on its ability to decrease or eliminate defects such as surface cracks. Thus, the behaviour of artificial V-shaped cracks in the longitudinal direction has been investigated and compared for the square-oval and false round (round)-oval series mentioned above. In agreement with other research works it was established that efficient rolling conditions for reducing the cracks are obtained when the cracks open up at the same time as their depth is reduced. If the V-shaped crack is closed by contact between its oxidized side surfaces the rolling schedule is not optimal for getting a high quality product. A deeper understanding of the experimental results was obtained by means of an FE-analysis

Place, publisher, year, edition, pages
Stockholm: Industriell produktion, 2004
Series
Trita-IIP, ISSN 1650-1888 ; 04:13
Keyword
Materials science, wire rod, roll pass design, working range, productivity, swedish wire rod mills, Materialvetenskap
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-53 (URN)91-628-6232-4 (ISBN)
Public defence
2004-11-19, Sal M311, KTH, Brinellvägen 68, Stockholm, 10:00
Opponent
Supervisors
Available from: 2004-11-30 Created: 2004-11-30 Last updated: 2012-03-20

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