E-Thesis 246 views 54 downloads
The development of surface treatments on galvanised steel products for the automotive industry utilising a chemcoater / JAMIE WILLIAMS
Swansea University Author: JAMIE WILLIAMS
DOI (Published version): 10.23889/SUthesis.64906
Abstract
This thesis investigates the development of coatings to be applied via a two-roll roller coating system, a Chemcoater. Novel coatings were investigated to enhance a substrate’s performance and add overall value to the hot-dipped galvanised steel product, by adding fuctionalities such as improved cor...
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Swansea, Wales, UK
2023
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| Institution: | Swansea University |
| Degree level: | Doctoral |
| Degree name: | EngD |
| Supervisor: | Jewell, E. and Challinor, C. |
| URI: | https://cronfa.swan.ac.uk/Record/cronfa64906 |
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| Abstract: |
This thesis investigates the development of coatings to be applied via a two-roll roller coating system, a Chemcoater. Novel coatings were investigated to enhance a substrate’s performance and add overall value to the hot-dipped galvanised steel product, by adding fuctionalities such as improved corrosion resistance, enhanced surface passivation and increased surface lubricity. Historically, hexavalent chromate was a common component of coatings for hot-dipped galvanised steel to provide corrosion protection during material storage and transportation. However, REACH law within the European Union prohibited its use due to its intrinsic toxicity and detrimental environmental effects. This legislation accelerated industry and researchers’ attention toward developing alternative, more environmentally friendly processes. Initial investigations included the analysis of current coatings, PrimeCoat and PLT. Both coatings were shown to have similar rheological characteristics and similar thermal stabilities with PLT performing well as a dry film lubricant. A common laboratory polishing unit was adapted to create a novel Pin-on-Disk tribometer, providing an effective and reliable method for measuring the dynamic coefficient of friction of coated substrates. The adapted unit was designed, built, and commissioned according to ASTM G99-17, and it was able to produce repeatable results for measuring the coefficient of friction. An additional investigation showed that sulphate-based treatments could reduce the coefficient of friction of zinc-coated steel substrates. Tests indicated that a neutral ammonium sulphate solution improved lubricity by 15-10%. Ammonium and sodium sulphate treatments were deemed suitable for coil coating, improving the capacity to reduce oil volume and overall production costs. A systematic study was conducted to improve the processability of a one-step hydrophobic coating. The best-performing coating had a contact angle of 146° with a reduced processing time of ~67%, using IPA as the solvent, 2% wt. 1 M NaOH (aq), 0.2 M stearic acid and micro-SiO2 (0.2–0.3 μm). This method significantly reduced processing time and fewer health and safety risks, avoiding the use of toxic chemicals. On further analysis, the coating was shown to be relatively formable and durable, with no significant reduction in hydrophobic performance after 30% strain was induced. Several corrosion analysis techniques showed increased performance in comparison to uncoated hot-dipped galvanised steel samples. These results suggested that the coating could be a viable option for some industrial applications and showed a potentially positive alternative to banned hexavalent chromate options. The chemical constituents of the newly proposed coatings have significantly less toxicity and pose a reduced negative effect on the wider environment and its users. |
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| Keywords: |
Functional coatings, galvanised steel, corrosion resistance |
| College: |
Faculty of Science and Engineering |
| Funders: |
Tata Steel UK, EPSRC |