Tài liệu Ktf_4_oberflächenbehandlung stbo

Adhesive Manufacturing Processes Chapter 4: Surface Treatment Methods Univ.-Prof. Dr.-Ing. Prof. h.c. Stefan Böhm Department for Cutting and Joining Manufacturing Processes (tff) University of Kassel, Germany Quelle: Wikipedia Agenda  Introduction  Surface Preparation  Surface Pre-Treatment  Surface Post-Treatment 2 Introduction Adhesion (Interface Adhesion) ● Molecular bond of the adhesive layer with the material ● Surface of the material must be clean ● High adhesion through large joining area Cohesion (Cohesive Power) ● Cohesion of the internal adhesive molecules ● The higher the cohesion, the higher the strength ● If the applicaion of a too thick layer is avoided, then it can be used optimally 3 www.uhu.de Introduction  Aims of the Surface Treatment: ● Even and very good wetting of the joint contact areas with the adhesive ● Improvement of the bond between the joint contact surfaces and the adhesive layer ● Reproducible, longlasting adhesive bond The creation of a surface that is suitable for adhesion is the basic prerequisite for the development of the best possible bonding forces between the joint elements and the adhesive. This is defined through the geometry of the surface and the physical-chemical characteristics of the joint surfaces. Bonding forces at interface layer Adhesive Bonding forces at inrerface layer Joint Element Source: Habenicht 4 Wetting  A good wetting is the prerequisite for an optimal adhesion.  Wetting is the approach of the adhesive to the joint contact area  Prerequisites for a good wetting are ● sufficient and low viscosity of the fluid adhesive ● the difference between the surface tension of the (fluid) adhesive and the surface energy/tension joint material The surface energy of the joint material must be higher than the surface tension of the used adhesive, otherwise the wetting is not sufficient ! 5 Wetting  Selected surface energies/tensions Material Surface Energy [mN/m] Iron 2550 Titanium 2050 Copper 1850 Gold 1550 Silver 1250 PA 49-47 Epoxy Resin 47 PVC 40 PMMA 33-44 PS 33-35 PE 31 PP 29 PTFE (Teflon) 19 Typical adhesives have a surface tension of at least 35 mN/m Source: Bond it, S.25 6 Wetting  Test Ink – The Examination of the Surface Energy of a Solid Material ● The test ink, whose surface energy has been defined, is used to define the surface energy of a solid object (either bigger or smaller than the test ink). ● The ink is painted onto the surface which is to be examined and then the period in which the wetting continues is measured. ● If the wetting stays for more than 2-3 seconds, then the surface energy of the solid object is higher than that of the ink. Good Wetting Bad Wetting http://www.plasmatreat.de/ 7 Wetting Good Wetting G σFG σKG α α Adhesive σKF Joint Element Joint Element Wetting Surface Bad Wetting σFG = Surface Energy of the joint element σKG = Surface tension of the adhesive σKF = Tension in the boundary layer of bonding element/adhesive α = Wetting angle G = Air (i.e. gas atmosphere of the environment) α Joint Elementl Wetting Surface 8 Surface Layers of Metaic Joint Elements Oxide Layers Slag Layer Oil Grease Varnish Dirt, Dust 9 Introduction Wetting is decisive for adhesion. Range of forces ~ 1/10 nm 10 Introduction  Classification of the Surface Treatments Surface Treatment Surface Preparation Surface Pre-Treatment Surface Post-Treatment Cleaning Mechanical Prep. Climatisation Making Fit Physical Prep. Application of Bonding Agents Degreasing Chemical Prep. Application of Primers (Conservation) Source: Habenicht 11 Agenda  Introduction  Surface Preparation  Surface Pre-Treatment  Surface Post-Treatment 12 Surface Preparation  Cleaning ● Removal of adherent, visible layers, i.e. dirt, scale, rust, colour… ● Removal mainly mechanical: i.e. through blasting, grinding, brushing Source: Habenicht 13 Surface Preparation  Making Fit ● To achieve an evenly distributed layer thickness ● i.e. through: – Deburring of smaller joint elements – Adjusting of bigger joint elements ● Goal is a parallel gap  thus an even force distribution Source: Habenicht 14 Surface Preparation  Degreasing ● Is the most important step among the preparations ● Prior degreasing is necessary even for mechanical surface pretreatments (fat molecules could otherwise enter into joint contact area) ● Choice of degreasing method depends on: – Number of pieces – Geometry of the joint contact areas – Necessary degree of absence of grease Source: Habenicht 15 Surface Preparation  Degreasing ● Simple Degreasing – Wiping of the surface with solvent-soaked cloth – Immersion of the joint elements  Disadvantage: uncontrollable grease residue ● Steam Degreasing – Condensated solvent degreases  Advantage: very free of grease Source: Habenicht 16 Surface Preparation Steam Degreasing Suction Feed Cooling zone for steam condensation Pieces that are to be degreased (big pieces loosely, smaller pieces in baskets) Heating 17 Surface Preparation  Degreasing ● Ultrasonic Degreasing – Degreasing baths can be supported by ultrasound (20-40KHz) Source: Habenicht 18 Agenda  Introduction  Surface Preparation  Surface Pretreatment  Surface Post-Treatment 19 Surface Pretreatment Surface Treatment Surface Preparation Surface Pretreatment Surface Post-Treatment Cleaning Mechanical Prep. Climatisation Making Fit Physical Prep. Application of Bonding Agents Degreasing Chemical Prep. Application of Primers (Conservation)  Goal: - Cleaning and increasing of the surface - Increasing the surface energy Source: Habenicht 20