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Surface cracks in wire rod rolling
KTH, Superseded Departments, Production Engineering.
2004 (English)In: Steel Research International, ISSN 1611-3683, Vol. 75, no 12, 818-828 p.Article 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.

Place, publisher, year, edition, pages
2004. Vol. 75, no 12, 818-828 p.
Keyword [en]
artificial surface cracks, wire rod, working range, roll pass design
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-8842ISI: 000225979100008Scopus ID: 2-s2.0-10944240571OAI: oai:DiVA.org:kth-8842DiVA: diva2:14305
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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