Dynamics and instabilities of coating liquids in 3-roll coating processes for automotive pre-coating application
- 주제(키워드) roll coating , paint
- 발행기관 고려대학교 대학원
- 지도교수 정현욱
- 발행년도 2012
- 학위수여년월 2012. 2
- 학위구분 석사
- 학과 일반대학원 화공생명공학과
- 원문페이지 82 p
- 실제URI http://www.dcollection.net/handler/korea/000000033132
- 본문언어 영어
- 제출원본 000045698133
초록/요약
Roll coating process is distinguished by the direction of rotating rolls, e.g., forward roll coating and reverse roll coating. Dynamics and stabilities of each roll coating process have been elucidated by changing the operating conditions. Roll coating technology has been widely incorporated to steel coating industries. Recently, studies about new automotive coating process using roll coating have been further developed. Current automotive coating process is involved in coating primer, basecoat and clearcoat paints in series after forming a car body through the procedure of the cutting and assembling of the steel sheet, giving rise to excessive equipment and labor due to complex and various processing stages. Also, environmental problems can occur because of use of spray coating. Therefore, studies about automotive pre-coating process using roll coating which is capable of remarkably resolving these problems have been exploited. In this study, experiments using 3-roll full reverse operation which is expected to be suitable for automotive pre-coating process have been performed. Primer paints which have a function of anti-corrosion are selected as coating liquids. Shear viscosity of primer is measured using AR2000 for determining optimal operating conditions. Relationship between dynamics of coating liquids and operating conditions are correlated with capillary number, gap between metering roll and pick-up roll (metering gap), and ratio of metering roll and pick-up roll speeds. In uniform coating region, dried coating thickness increases with increasing metering gap or decreasing speed ratio. Ribbing and cascade instabilities are observed at each low speed and high speed ratio, respectively. It is revealed that lower speed ratio makes wavelength and severity of ribbing increase, aggravating flow instability in coating systems. Applying the same methodology, the comparison of results by 3-roll full reverse and 3-roll natural reverse operations is scrutinized using another primer. It turns out that it is difficult to acquire the stable region for automotive pre-coating process under 3-roll natural reverse operation in contrast to 3-roll full reverse mode.
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Contents
Abstract …………………………………………………………………. i
Contents ……………………………………………………………….... iii
List of tables ……………………………………………………………. vi
List of figures …………………………………………………………… vii
1. Introduction ………………………………………………………….. 1
1.1. Coating process ……………………………………………………. 1
1.2. Roll coating process ……………………………………………….. 6
1.2.1. Forward roll coating ………………………………………… 11
1.2.2. Reverse roll coating ………………………………………… 12
1.3. Roll coating process for automotive pre-coated metal sheets … 13
2. Experiments …………………………………………………………. 20
2.1. Roll coating equipment …………………………………………..... 20
2.2. Coating liquids ..…………………………………………………….. 22
2.3. Measurement of rheological properties ………………………….. 22
2.3.1. Shear viscosity ……………………………………………… 22
2.3.2. Surface tension ……………………………………………... 23
2.4. Coating experiments ………………………………………………. 23
2.4.1. 3-roll coating ………………………………………………… 23
2.4.2. 3-roll full reverse operation (RRR mode) ………………… 26
2.4.3. 3-roll natural reverse operation (FRR mode) ……………. 28
2.5. Measurement of dried coating thickness and analysis of ribbing instability …………………………………………………................
31
2.5.1. Dried coating thickness ……………………………………. 31
2.5.2. Ribbing instability …………………………………………… 31
3. Results ………………………………………………………………... 32
3.1. Rheological properties …………………………………………….. 32
3.1.1. Shear viscosity ……………………………………………… 32
3.1.2. Surface tension ……………………………………………... 32
3.2. 3-roll full reverse operation for primer (Y) ……………………...... 34
3.2.1. Coating windows ……………………………………………. 34
3.2.2. Dried coating thickness in uniform region ……………….. 40
3.2.3. Wavelength of ribbing ……………………………………… 42
3.2.4. Severity of ribbing …………………………………………... 42
3.3. Comparison of 3-roll full reverse operation and 3-roll natural reverse operation for primer (G) ..………………………………...
49
3.3.1. Coating windows ……………………………………………. 49
3.3.1.1. 3-roll full reverse operation ………………………….. 49
3.3.1.2. 3-roll natural reverse operation ……………………... 49
3.3.2. Dried coating thickness in uniform region ……………….. 52
3.3.2.1. 3-roll full reverse operation ………………………….. 52
3.3.3. Comparison of wavelengths of ribbing under 3-roll full reverse and 3-roll natural reverse operations …………...
52
3.3.4. Comparison of severities of ribbing under 3-roll full reverse and 3-roll natural reverse operations …………
58
4. Conclusions ……………………………………………………….… 61
5. References ………………………………………………………..….. 64
