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Roll pass design for improved flexibility and quality in wire rod rolling
KTH, Superseded Departments, Production Engineering.
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
Keywords [en]
Materials science, wire rod, roll pass design, working range, productivity, swedish wire rod mills
Keywords [sv]
Materialvetenskap
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-53ISBN: 91-628-6232-4 (print)OAI: oai:DiVA.org:kth-53DiVA, id: diva2:14308
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
List of papers
1. Working range for sequences and series of two-symmetrical grooves in wire rod rolling
Open this publication in new window or tab >>Working range for sequences and series of two-symmetrical grooves in wire rod rolling
2006 (English)In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 174, no 1-3, p. 250-257Article in journal (Refereed) Published
Abstract [en]

A calculation procedure has been developed to determine the working range for series of grooves including "oval", "round", "false round", "square" and "diamond" shapes. The minimum and maximum roll-gap setting and corresponding bar areas are calculated for all grooves. Flatter ovals increase the flexibility in false round-oval series and low rolling geometry factors reduce the working range. The working range is smaller for pass sequences designed for high reductions. To evaluate the model, laboratory tests for passes in "round"-"oval"-"false round"-"oval" sequences were carried out. Samples from a square-oval series were examined and it was shown that this series was insufficient for stainless steel wire rod rolling. The fitting factors were too high and the square grooves were slightly overfilled. It is shown that "false round"-"oval" series give the largest working range and thus enable the rolling of a wide range of different stainless steel grades.

Keywords
roll pass design, wire rods, working range, flexibility
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-8840 (URN)10.1016/j.jmatprotec.2006.01.007 (DOI)000237817700032 ()
Available from: 2004-11-30 Created: 2004-11-30 Last updated: 2017-12-14Bibliographically approved
2. Flexibility and utilization of roll pass sequences in some Swedish wire rod mills
Open this publication in new window or tab >>Flexibility and utilization of roll pass sequences in some Swedish wire rod mills
2005 (English)In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 76, no 9, p. 635-643Article in journal (Refereed) Published
Abstract [en]

A computer program has been developed to calculate the working range for series of two-symmetrical grooves including oval, round, false round, square and diamond shapes. Eight different pass designs are compared. The geometry of rolling or entry bar height over roll radius is in the range 0.09-0.26 for squares, 0.10-0.23 for false round and 0.06-0.21 for ovals. Square-oval and round-oval have similar flexibility, but in the round-oval sequence, the flexibility can be extended by opening up the gaps and run the rounds as false rounds. In the square-oval sequence the flexibility can be improved by making the squares with larger corner radii but the reduction capability will be reduced. The false round-oval sequence has the best flexibility and the working range can be extended by making "flatter" ovals. Improvement of the roll pass design in Fagersta Stainless AB has made it possible to roll wire rod with higher flexibility and better quality.

Keywords
Flexibility, Roll pass design, Swedish mills, Wire rods, Working range
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-8841 (URN)000232488400004 ()2-s2.0-25444499707 (Scopus ID)
Available from: 2004-11-30 Created: 2004-11-30 Last updated: 2017-12-14Bibliographically approved
3. Surface cracks in wire rod rolling
Open this publication in new window or tab >>Surface cracks in wire rod rolling
2004 (English)In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 75, no 12, p. 818-828Article in journal (Refereed) Published
Abstract [en]

Surface defects in wire rod and bar rolling are common and well-known to mill people. Nowadays, surface defects are not accepted on high-alloyed steel wire rods. The steel making, casting and rolling processes give rise to defects. Also, the final handling of the wire and bar can destroy the surface. In this work, artificial V-shaped cracks in the longitudinal direction were investigated for different reduction series. The false round-oval series are known as a series for high quality steels and are usually better than square-oval series. Experiments confirmed that in the false round-oval sequences a surface crack in the groove bottom may open up during rolling at the same time as its depth is reduced, which is a beneficial situation. Surface cracks found at 45degrees to the rolling direction, at groove "corners" and on free surfaces will be closed or reduced in depth. The closing of cracks is detrimental since the cracks usually hide rolled-in oxides beneath the bar surface. The experiments showed that for the subsequent oval-false round sequence the visible crack at the groove bottom will be closed and become shallower. The cracks at 45degrees and on the free sides will also be closed, but deeper causing a serious surface defect. An FE-analysis was carried out, explaining the experimental results. Flat oval grooves are better than round ovals and false rounds are superior to square for opening and decreasing the depth of a longitudinal crack. It is difficult to eliminate a surface defect constituting a closed crack.

Keywords
artificial surface cracks, wire rod, working range, roll pass design
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-8842 (URN)000225979100008 ()2-s2.0-10944240571 (Scopus ID)
Available from: 2004-11-30 Created: 2004-11-30 Last updated: 2017-12-14Bibliographically approved
4. Working range of roll pass sequences in wire rod rolling with interstand tensions
Open this publication in new window or tab >>Working range of roll pass sequences in wire rod rolling with interstand tensions
2004 (English)In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 31, no 1, p. 81-92Article 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.

Keywords
wire rod rolling, roll pass design, computer programs
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-8843 (URN)10.1179/030192304225011016 (DOI)000222387200011 ()
Available from: 2004-11-30 Created: 2004-11-30 Last updated: 2017-12-14Bibliographically approved
5. Ultra high speed rolling of stainless steel wire rod by means of interstand tensions
Open this publication in new window or tab >>Ultra high speed rolling of stainless steel wire rod by means of interstand tensions
2005 (English)In: Berg- und Huttenmännische Monatshefte (BHM), ISSN 0005-8912, E-ISSN 1613-7531, Vol. 150, no 1, p. 5-11Article in journal (Refereed) Published
Abstract [en]

By introduction of an interstand tension in the order of 10% of the actual yield stress of the rolled material in the intermediate stage of wire rod rolling, it is possible to increase the intermediate reductions without excessive increase of energy supply for rolling. Thus, an eight passes finishing block can be replaced by two intermediate stands and a four stand finishing block of a module type. This configuration gives two improvements on the productivity in a wire rod mill for stainless steel. First, the finish rolling speed can be increased from typically 60 m/s up to 80 m/s, meaning 33% higher rolling rate. Second, the modern twin module block system gives the possibility to introduce a single family rolling system, which gives a reduction of the downtime for roll and groove changing in the order of 20% of the production time, depending on the product mix in the mill.

Abstract [de]

Durch Einführen eines 10%igen Längszugs im Knüppel während des Streckwalzens ist es mögllich, die Dickenabnahmen ohne Erhöhung des Energieverbrauchs zu vergrößern. So kann ein achtgerüstiger Fertigblock ersetzt werden durch zwei Zwischengerüste und einen viergerüstigen Fertigblock. Durch eine solche Anordnung lassen sich Produktivitätsverbesserungen des Walzwerks erzielen: Erstens kann die Endwalzgeschwindigkeit von typischen 60 m/s auf 80 m/s erhöht werden, was ein 33%ige Erhöhung der Walzleistung bedeutet. Zweitens eröffnet der moderne Endwalzblockmodul die Möglichkeit, eine einzige Kaliberfamilie zu installieren, wodurch sich eine Totzeitverminderung von 20% beim Walzenwechsel erzielen lässt.

National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-8844 (URN)10.1007/BF03165142 (DOI)
Available from: 2004-11-30 Created: 2004-11-30 Last updated: 2017-12-14Bibliographically approved

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