Laser and other cleaning procedures for aerospace moulds and a study of mould release agents.

317 Pages·2017·53.7 MB·English

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Laser and other cleaning
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moulds and a study of mould
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,I
LASER AND OTHER CLEANING PROCEDURES FOR AEROSP ACE
MOULDS AND A STUDY OF MOULD RELEASE AGENTS
By
Robert E. Litchfield
A PhD Thesis
Submitted in partial fulfilment of the requirements for the award of
Doctor of Philosophy at Loughborough University
December 2003
Institute of Polymer Technology and Materials Engineering
Supervisor: Dr.G.W.Critchlow, Institute of Surface Science Technology
I
ABSTRACT
A selection of cleaning procedures are discussed which may be used to remove
epoxide resin flash contamination bonded on metal and carbon fibre reinforced
composite mould tooling that is used in the aerospace industry.
Laser ablation, dry ice blasting and chemical cleaning using sodium hydride are
three cleaning procedures studied in depth and have been used to treat a range
of industrially sourced and model substrates, and contaminants. The
effectiveness of the different cleaning regimes have been evaluated using
Scanning Electron Microscopy, Atomic Force Microscopy, Auger Electron
Spectroscopy, X-ray Photoelectron Spectroscopy and other analytical
characterisation techniques.
The necessity to clean aerospace tooling arises when moulded parts cannot be
easily released from mould tooling and this is associated with mould release
residues that have built up over a number of moulding cycles and eventually
cause the moulding to stick. A comprehensive literature review of non-stick
coatings is given and alternative mould non-silicone based release coatings are
evaluated using the above analytical techniques. Coatings investigated include;
fluoroalkylsilane, fluoropolymers and metal-fluoropolymer composites and the
problems and merits associated with each are discussed.
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Acknowledgements
I would like to take this opportunity to thank all the people who have supported
me and helped me in achieving this thesis.
Firstly, I would like to thank my supervisor Dr.G.W.Critchlow for giving me the
opportunity to work for this degree. He was always available to help, support
and to guide me through any difficulties I faced relating to the thesis.
Secondly I would like to thank Professor D.C.Emmony for finding the time to
discuss different aspects of laser cleaning with me and for guiding me through
some of the complexities of the subject.
My final thanks go to all the staff and students of the Institute of Surface Science
for their support and encouragement during my work and also to the staff of the
Institute of Polymer Technology and Materials Engineering, and especially,
Mr.John Bates who greatly assisted me in respect of electron microscopy.
IV
LASER AND OTHER CLEANING PROCEDURES FOR AEROSPACE
MOULDS AND A STUDY OF MOULD RELEASE AGENTS
Contents
CHAPTER 1: INTRODUCTION
1.1 Aims and Outline of work 1
CHAPTER 2: MOULD CLEANING TECHNOLOGIES
2.1 Introduction to Cleaning Methods 5
2.2 Introduction to Laser Cleaning 6
2.2.1 Laser Paint Stripping 9
2.2.2 Laser Ablation Processes 13
2.2.3 Interactions of lasers with materials 16
2.2.3.1 Refraction, Reflection and Absorption 19
2.2.3.2 Heat Flow Theory 24
2.2.3.3 Thermomechanical Effects 28
2.2.3.4 Laser Shockwaves 32
2.2.4 Laser Cleaning ofParticulate Surface Contamination 33
2.2.4.1 Interaction Forces in Interfacial Systems 33
2.2.5 Operation and characteristics of TEA COzlasers 38
2.2.6 Operation and characteristics ofNd:YA G lasers 42
2.3 Mould Cleaning using dry ice pellet blasting 46
2.3.1 Principles of dry ice pellet blasting 48
2.3.2 Advantages and Disadvantages of the process 51
2.3.3 Mould metallurgy and temperature effects 52
2.3.4 Other carbon dioxide and related blasting technologies 53
2.3.4.1 Carbon dioxide "snow" cleaning 53
2.3.4.2 Solvent Properties of Supercritical carbon dioxide 53
2.3.4.3 Blasting using ordinary ice 55
2.4 Dry ice and ultra-violet light cleaning methods 55
2.5 Mould Cleaning using a fused alkali bath 56
v
2.6 Ultrasonic Cleaning of mould tooling 58
2.7 Plasma Cleaning 59
2.8 High Pressure Water Jet Cleaning 61
2.9 Summary of Surface Cleaning Technologies 61
2.9.1 Laser Cleaning 62
2.9.2 Dry ice blasting 62
2.9.3 Sodium hydride cleaning 62
2.9.4 Other Cleaning Methods 63
CHAPTER 3: MOULD RELEASE AGENTS AND NON-STICK POLYMERS
3.1 Introduction 64
3.2 Mould Release Agents 64
3.2.1 Internal Mould Releases 66
3.2.2 External Mould Releases 67
3.3 Mould Fouling 72
3.4 Theories of Adhesion 73
3.5 Non-stick Polymers 75
3.5.1 Polytetrafluoroethylene(PTFE) 75
3.5.1.1 Teflon AF 78
3.5.2 Polydimethylsiloxane(PDMS) 79
3.5.3 Non-stick Coatings for Cooking and Baking 81
3.5.4 Non-stick Coatings to Prevent Marine Fouling 83
3.5.5 Silicone Release Coatings 85
3.5.6 Hydrophobic Coatings 88
3.5.7 Fluoroalkylsilanes 91
3.6 Electroless NickellPTFE Composite Non-stick Coatings 93
3.7 Mechanical Tests for Non-Stick Polymers 95
3.7.1 The Blister Test Method 96
3.8 Analytical Techniques 98
3.8.1 Scanning Electron Microscopy & X-Ray Microanalysis 99
3.8.2 Atomic Force Microscopy 101
3.8.3 Interference Microscopy 104
3.8.4 ElIipsometry 106
VI
3.8.5 Auger Electron Spectroscopy 108
3.8.6 Secondary Ion Mass Spectrometry 113
3.8.7 X-Ray Photoelectron Spectroscopy 113
3.8.8 Contact Angle Analysis 116
3.8.8.1 Quantitative Contact Angle Analysis 119
3.8.9 Infrared Spectroscopy 122
3.8.10 Differential Scanning Calorimetry and Thermogravimetric Analysis 124
3.9 Summary 126
CHAPTER 4: EXPERIMENTAL
4.1. Introduction 127
4.2. Materials 127
4.2.1 Industrially sourced substrates 127
4.2.2 Model substrates 129
4.2.3 Model contaminants 131
4.2.3.1 Pre-treatment cleaning of substrates 132
4.2.3.2 Application of resin 132
4.3 Surface cleaning procedures 134
4.3.1 TEA C02 laser cleaning 134
4.3.2 Nd:YA G laser cleaning 134
4.3.3.Liaison with extemallaser laboratories 135
4.3.4 Dry ice cleaning 136
4.3.5 Sodium hydride cleaning 137
4.4 Application conditions for mould release coatings 137
4.4.1 Frekote 137
4.4.2 Zyvax 139
4.4.3 Fluoroalkylsilane 140
4.4.4 Oxsilan 141
4.4.5 Oxsilan and fluoroalkylsilane coating 141
4.4.6 Fluoropolymers - Xylan 8080 and Xylar 2020 142
4.4.7 NilPTFE composite coating 143
4.5 Surface Analytical Procedures 144
4.5.l.SEM 144
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