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Understanding the role of snout contamination in the formation of an oxide based defect in hot dip galvanised coating / Lewis J. Berry; Craig H. Phillips; David Penney

Surface and Coatings Technology, Volume: 306, Pages: 397 - 407

Swansea University Author: David, Penney

Abstract

Due to increased demand for defect free, quality critical outer panel material for the automotive sector, continued focus on zinc coating quality is required. The snout area of a continuous galvanizing line is often a major source of coating issues with various surface defects arising from poorly un...

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Published in: Surface and Coatings Technology
ISSN: 0257-8972
Published: 2016
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URI: https://cronfa.swan.ac.uk/Record/cronfa26470
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spelling 2017-07-10T09:55:58.4211681 v2 26470 2016-02-19 Understanding the role of snout contamination in the formation of an oxide based defect in hot dip galvanised coating 869becc35438853f2bca0044df467631 0000-0002-8942-8067 David Penney David Penney true false 2016-02-19 EEN Due to increased demand for defect free, quality critical outer panel material for the automotive sector, continued focus on zinc coating quality is required. The snout area of a continuous galvanizing line is often a major source of coating issues with various surface defects arising from poorly understood and uncontrolled snout practices. This paper investigates the formation of a snout defect termed ‘the arrowhead defect’, named after its characteristic arrowhead shape. Defective samples have been characterised with the use of SEM/EDX and XRD and compared with contaminated sources collected from within the continuous galvanizing line snout. It is common practice to inject wet HNx into the snout in order to inhibit the production of zinc vapour. The wet HNx promotes the for- mation of a ZnO layer on the surface of the liquid zinc bath, preventing vaporisation and thereby reduces zinc dust contamination. The presence of ZnO, deliberately formed through the injection of wet HNx into the snout was observed within the arrowhead defect and can be identified as the root cause of this defect. Discrete contam- ination particles were entrained within the tail of the defect. XRD patterns of both the defect & snout contamina- tion have been presented to discern the nature of the contamination entrained within the zinc coating. Characteristic ZnO peaks were observed at θ = 32° for both surface contamination and at increasing penetration depths within the coating in the region of the arrowhead defect. The inclusion of the arrowhead defect in Full Finish material led to an increase in the rate of corrosion 2.5× that of the corrosion rate on non-defective mate- rial, highlighting the need to produce defect free galvanized steel for both aesthetic and corrosion purposes. Whilst the injection of wet HNx as a method of suppressing the formation of zinc vapour is a long standing pro- cess for automotive Full Finish production, due to the nature of these oxide-based defects, this process is in fact a “double edged sword” in that it solves one problem but can create another. Alternative techniques to suppress zinc vapour formation should be investigated to further drive up the quality of zinc coatings for automotive applications. Journal Article Surface and Coatings Technology 306 397 407 0257-8972 Zinc, XRD, GI, Full Finish, Coating quality, Continuous hot dip galvanizing 25 11 2016 2016-11-25 10.1016/j.surfcoat.2016.02.009 http://ac.els-cdn.com/S0257897216300718/1-s2.0-S0257897216300718-main.pdf?_tid=a404fc26-33af-11e6-83ca-00000aab0f26&amp;acdnat=1466074194_4e62c4a142dc6744784d6b5a7661c27a COLLEGE NANME Engineering COLLEGE CODE EEN Swansea University RCUK 2017-07-10T09:55:58.4211681 2016-02-19T14:04:17.2991133 College of Engineering Engineering Lewis J. Berry 1 Craig H. Phillips 2 David Penney 0000-0002-8942-8067 3 0026470-19022016140522.pdf BerryUnderstandingTheRoleOfSnoutContamination2016AAM.pdf 2016-02-19T14:05:22.6800000 Output 1815485 application/pdf Accepted Manuscript true 2017-02-09T00:00:00.0000000 true
title Understanding the role of snout contamination in the formation of an oxide based defect in hot dip galvanised coating
spellingShingle Understanding the role of snout contamination in the formation of an oxide based defect in hot dip galvanised coating
David, Penney
title_short Understanding the role of snout contamination in the formation of an oxide based defect in hot dip galvanised coating
title_full Understanding the role of snout contamination in the formation of an oxide based defect in hot dip galvanised coating
title_fullStr Understanding the role of snout contamination in the formation of an oxide based defect in hot dip galvanised coating
title_full_unstemmed Understanding the role of snout contamination in the formation of an oxide based defect in hot dip galvanised coating
title_sort Understanding the role of snout contamination in the formation of an oxide based defect in hot dip galvanised coating
author_id_str_mv 869becc35438853f2bca0044df467631
author_id_fullname_str_mv 869becc35438853f2bca0044df467631_***_David, Penney
author David, Penney
author2 Lewis J. Berry
Craig H. Phillips
David Penney
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container_volume 306
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publishDate 2016
institution Swansea University
issn 0257-8972
doi_str_mv 10.1016/j.surfcoat.2016.02.009
college_str College of Engineering
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hierarchy_top_title College of Engineering
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hierarchy_parent_title College of Engineering
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url http://ac.els-cdn.com/S0257897216300718/1-s2.0-S0257897216300718-main.pdf?_tid=a404fc26-33af-11e6-83ca-00000aab0f26&amp;acdnat=1466074194_4e62c4a142dc6744784d6b5a7661c27a
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description Due to increased demand for defect free, quality critical outer panel material for the automotive sector, continued focus on zinc coating quality is required. The snout area of a continuous galvanizing line is often a major source of coating issues with various surface defects arising from poorly understood and uncontrolled snout practices. This paper investigates the formation of a snout defect termed ‘the arrowhead defect’, named after its characteristic arrowhead shape. Defective samples have been characterised with the use of SEM/EDX and XRD and compared with contaminated sources collected from within the continuous galvanizing line snout. It is common practice to inject wet HNx into the snout in order to inhibit the production of zinc vapour. The wet HNx promotes the for- mation of a ZnO layer on the surface of the liquid zinc bath, preventing vaporisation and thereby reduces zinc dust contamination. The presence of ZnO, deliberately formed through the injection of wet HNx into the snout was observed within the arrowhead defect and can be identified as the root cause of this defect. Discrete contam- ination particles were entrained within the tail of the defect. XRD patterns of both the defect & snout contamina- tion have been presented to discern the nature of the contamination entrained within the zinc coating. Characteristic ZnO peaks were observed at θ = 32° for both surface contamination and at increasing penetration depths within the coating in the region of the arrowhead defect. The inclusion of the arrowhead defect in Full Finish material led to an increase in the rate of corrosion 2.5× that of the corrosion rate on non-defective mate- rial, highlighting the need to produce defect free galvanized steel for both aesthetic and corrosion purposes. Whilst the injection of wet HNx as a method of suppressing the formation of zinc vapour is a long standing pro- cess for automotive Full Finish production, due to the nature of these oxide-based defects, this process is in fact a “double edged sword” in that it solves one problem but can create another. Alternative techniques to suppress zinc vapour formation should be investigated to further drive up the quality of zinc coatings for automotive applications.
published_date 2016-11-25T03:36:14Z
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