TALAT Lecture 4704: Surface Preparation and Application Procedures
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TALAT Lecture 4704: Surface Preparation and Application Procedures

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This lecture describes the important aspects of surface preparation and pretreatments for adhesive joining of aluminium parts; it illustrates the methods and equipment necessary to obtain good ...

This lecture describes the important aspects of surface preparation and pretreatments for adhesive joining of aluminium parts; it illustrates the methods and equipment necessary to obtain good adhesive bonds. General background in production engineering and material science, some knowledge of mechanics and polymer science is assumed.

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    TALAT Lecture 4704: Surface Preparation and Application Procedures TALAT Lecture 4704: Surface Preparation and Application Procedures Document Transcript

    • TALAT Lecture 4704 Surface Preparation and Application Procedures 12 pages, 13 figures Basic Level prepared by Lutz Dorn, Technische Universität, Berlin Objectives: − to describe the important aspects of surface preparation and pretreatments for adjesive joining of aluminium parts − to illustrate the methods and equipment necessary to obtain good adhesive bonds Prerequisites: − general background in production engineering and material science − background in mechanics and polymer science Date of Issue: 1994  EAA - European Aluminium Association
    • 4704 Surface Preparation and Application Procedures Table of Contents 4704 Surface Preparation and Application Procedures...............................2 4704.01 Surface Preparation of Metallic Parts to be Joined............................... 2 Surface layers of metallic parts to be joined ............................................................2 Surface treatment processes .....................................................................................3 Methods of surface pretreatment..............................................................................4 Surface pretreatments for aluminium.......................................................................4 Correlation between adhesive strength and surface roughness................................5 4704.02 Application Procedures ............................................................................ 6 Methods of applying adhesives................................................................................6 Equipment for working adhesives ...........................................................................7 Correlation between adhesive joint strength and adhesive layer .............................8 Methods of applying pressure ..................................................................................8 Correlation between adhesive joint strength and applied pressure ..........................9 Correlation between hardening temperature, hardening time and adhesive ..... joint strength...................................................................................................................10 4704.03 Literature/References ............................................................................ 11 4704.04 List of Figures............................................................................................ 12 4704.01 Surface Preparation of Metallic Parts to be Joined • Surface layers of metallic parts to be joined • Surface treatment processes • Methods of surface pretreatment • Surface pretreatments for aluminium • Correlation between adhesive strength and surface roughness Surface layers of metallic parts to be joined The surfaces of parts which have to be joint are treated prior to joining in order to have an optimal adhesion force between joint part surface and the adhesive layer. For this purpose it is absolutely necessary to first remove impurities in an undefined layer thickness (i.e., dust, dirt, oil, grease, fat, water) and the inactive adsorption layer created by foreign molecules (i.e., water, gases) (Figure 4704.01.01). TALAT 4704 2
    • Surface Treatment Impurities Absorption Layer ( ~1·10-7 to 1·10-6 mm ) Reaction Layer ( ~ 1·10-6 to 1·10-5 mm ) Cold Worked Interface Layer ( ~ 2 to 5·10-3 mm ) Base Material alu Surface Layers of Metallic Parts to be Joined 4704.01.01 Training in Aluminium Application Technologies Surface treatment processes The whole surface treatment can be subdivided into a preparation, pretreatment and after-treatment operation. In general, an active surface for adhesives can be created by cleaning and increasing the surface area, creation of lattice defects on the surface and changing the chemical structure of the surface. Surface Treatment Processes Surface Treatment Surface Surface Surface Preparation Pretreatment After-Treatment Cleaning Mechanical Conditioning Process Chemical Application Fitting Process of Primer Electrochemical Degreasing Conservation Process Source : Kaliske alu Surface Treatment Process 4704.01.02 Training in Aluminium Application Technologies In cases where a longer time-lapse is expected between the surface treatment and the adhesive joining, the surface of the joining parts should be conserved, using for example, a primer (Figure 4704.01.02). TALAT 4704 3
    • Methods of surface pretreatment Because of current ecological reasons, there is an increasing tendency to replace wet chemical surface pretreatment processes by mechanical, electrical and dry chemical pretreatment methods (Figure 4704.01.03). Methods of Surface Pretreatment Thermo Grinding Corona Brushing Plasma Gun Mechanical Electrical Pretreatment Pretreatment Blasting Corona Low-Pressure Thinning * Plasma Electrochemical Flaming Pretreatment ** Thermal Pretreatment Radiation Silicoater Pretreatment With Reactive Coating Chemical Gases Pretreatment * only for Plastics With Chemical Process Source: Dorn, Wahono ** only for Metals alu Methods of Surface Pretreatment 4704.01.03 Training in Aluminium Application Technologies Surface pretreatments for aluminium The list in Figure 4704.01.04 and Figure 4704.01.05 depicts processes, including their parameters, which have proven to be successful for use with aluminium materials. Surface Pre-Treatments for Aluminium 1. Degrease and Roughen with Griding Cloth or Fine Blasting or Brushing or 2. Degrease and CSA Etch ( Pickling Process ) Solution for approx. 1l: 650 g H2O ( Distilled ) 75 g Na2Cr2O7 275 g H 2SO 4 ( Conc. ) Pre- Etching: Addition of 0.5 g/l Aluminium + 1.5 g/l Copper Sulphate Etching: Temp. : 60 - 65 °C ( Replace Steam Loss ) Time: 30 min Rinsing: Under Running Cold Water and Final Rinsing with Deionised Water Drying: At max. 65 °C or 3. Degreasing and FPL Etching Solution for 1l: 650 g H2O ( Distilled ) ; 50 g Na2Cr2O4 * 2 H2O ; 300 g H 2SO 4 ( Conc. ) Top up with Distilled Water to be Dissolved Pre- Etching: 1.5 g AlCuMg 2pl/1l Etchant to be dissolved Etching: Temp. : 65 °C ( Replace Water lost at Steam ) Time: 10 min Rinsing and Drying: see CSA Etching alu Surface Petreatment for Aluminium I 4704.01.04 Training in Aluminium Application Technologies TALAT 4704 4
    • Surface Pre-Treatments for Aluminium or 4. Degrease and CSB Etching and Chromic Acid Anodising ( CAA ) Solution for Approx. 1 l: 40g CrO 3 Cathode: Stainless Steel ( V2A ) o o Temp.: 40 C ( + 2 C) - Time: from 0 to 40 V in 10 min (replace water losses) 40 V 20 min Rising: 10 min in distilled H2O from 40 to 50 V in 5 min at 40 oC 50 V 5 min Drying: at max. 40 oC or 5. Degrease and FPL Etching and Phosphoric Acid Anodising ( PPA ) Solution for Approx. 1 l: 129g 85% H3PO 4 / 1 l H2O Cathode: Stainless Steel ( V2A ) Temp.: RT Time: from 0 to 40 V in 10 min 40 V 20 min Rising: 22 min in distilled H2O from 40 to 50 V in 5 min o at 40 C 50 V 5 min Drying: at max. 40 oC alu Surface Pretreatments for Aluminium II 4704.01.05 Training in Aluminium Application Technologies When used as the only surface pretreatment method, FPL-etching is inferior to the CSA- etching. A CAA or PAA anodisation which follows, improves the long-term stability of the adhesive joint. Compared to the oxide layer created by the CAA process, the PAA oxide layer is thinner and more sensitive to mechanical damage, making it necessary to use a protective primer. It must be stressed here, that etching solutions must be handled and later deposited with great care, especially since these may contain dangerous (partly cancerogenic) substances and the used solution may be dumped only in so-called "special" dumps. Correlation between adhesive strength and surface roughness In view of the attainable strength of the adhesive joint and the notch sensitivity of most aluminium materials, the mechanical surface pretreatment should deliver only a low maximum roughness (Figure 4704.01.06). TALAT 4704 5
    • Strength of Adhesive Metal Joints Adhesive Joint Strength TB 50 100 150 !m Max. Surface Roughness R max Correlation Between Adhesive Strength alu 4704.01.06 Training in Aluminium Application Technologies and Surface Roughness 4704.02Application Procedures • Methods of applying adhesives • Equipment for working adhesives • Correlation between adhesive joint strength and adhesive layer • Methods of applying pressure • Correlation between adhesive joint strength and applied pressure • Correlation between hardening temperature, hardening time and adhesive joint strength Methods of applying adhesives The possible application processes, depending on the consistency (solid or fluid) of the adhesive and on the application method used (manual or mechanised), have been listed in Figure 4704.02.01. TALAT 4704 6
    • Working with Adhesives Manual Application Application Methods MechanicalApplication Solid Fluid Application Type Fluid Solid Adhesives Adhesives Adhesives Adhesives Coating Immersion Flowing Rolling Spraying Sintering Spreading Melting Placing alu Training in Aluminium Application Technologies Methods of Applying Adhesives 4704.02.01 Equipment for working adhesives A large variety of equipment (including robots) is available for working with the adhesives. The working principle of a 2-component dosing and application machine is illustrated in Figure 4704.02.02. Pneumatic drive Comp. "A" Comp. "B" Pump "A" Pump "B" By-Pass By-Pass Mixing Block Mixing Pipe Rinsing Medium Blowing Air Outlet alu Equipment for Working Adhesives 4704.02.02 Training in Aluminium Application Technologies TALAT 4704 7
    • Correlation between adhesive joint strength and adhesive layer Generally, an adhesive layer thickness of about 50 to 200 µm should be strived at (exception: CA adhesives). It should be remembered that the adhesive layer thickness depends, to a large extent, on the pressure applied during setting (curing) (Figure 4704.02.03). Strength of Metal Adhesive Joints Adhesive Joint Strength τΒ 1 2 3 0 0.05 0.2 0.5 [mm] Adhesive Layer Thickness d alu Correlation Between Adhesive Joint Strength Training in Aluminium Application Technologies and Adhesive Layer Thickness (Schematic) 4704.02.03 Methods of applying pressure The possibilities of applying pressure during the hardening of the adhesive are illustrated in Figure 4704.02.04 and Figure 4704.02.05. Most adhesives require only a contact pressure (about 0.1 N/mm2). Adhesives, which react chemically and produce by-products during the curing (setting) process (i.e., PF adhesives), are an exception. TALAT 4704 8
    • Working with Adhesives Methods of Applying Pressure - I Wrong Right Pressure Application Spot Weld, Weight-Loading Spring Loading Screw, Rivet alu Methods of Applying Pressure - I 4704.02.04 Training in Aluminium Application Technologies Working With Adhesives Methods of Applying Pressure - II Autoclave Method Tension Band Pressure-Bag Method Vacuum Method alu Training in Aluminium Application Technologies Methods of Applying Pressure - II 4704.02.05 Correlation between adhesive joint strength and applied pressure The method of applying pressure from all sides, like in the autoclave method, should be used preferably (Figure 4704.02.06). TALAT 4704 9
    • Working with Adhesives tB tB Adhesive Joint Strength Adhesive Joint Strength 1 2 Pressure p Pressure p Correlation Between Adhesive Joint Strength and Applied Pressure Curve 1: Pressure Applied from All Sides Curve 2: Pressure Applied from Two Sides alu Correlation Between Adhesive Joint Strength 4704.02.06 Training in Aluminium Application Technologies and Applied Pressure Correlation between hardening temperature, hardening time and adhesive joint strength Usually a functional correlation exists between hardening time and hardening temperature (Figure 4704.02.07). Especially in the case of cold-hardening adhesives, the strength can be increased by hardening at higher temperatures or by tempering (after the cold-hardening). It should be noted that the temperature, pressure and time recommendations of the manufacturer apply for the adhesive layer. Heating times for the joining parts and for the adhesive equipment must be determined and considered. TALAT 4704 10
    • Working With Adhesives [h] [Nmm²] 40 30 B 20 25 T 22 Adhesive Joint Strength Time t 10 20 8 6 15 4 3 2 10 1 20 40 60 80 [°C] 100 Temperature T Source: Schlegel Correlation Between Hardening Temperature, alu Hardening Time and Adhesive Joint Strength 4704.02.07 Training in Aluminium Application Technologies 4704.03 Literature/References 1. Brockmann, W., Hennemann, O.-D. und Kollik, H.: Surface properties and adhesion in bonding aluminium alloys by adhesives. Int. J. Adhesion and Adhesives 2 (1982) pp. 33-40. 2. Kollek, H.: Adhäsionsmechanismen beim Kleben. Tagungsband Fertigungssystem Kleben, S. 210-222, TU Berlin, 1984. 3. Comyn, J.: Kinetics and mechanism of environmental attack. In: Durability of structural adhesives, Applied Science Publishers New York and London, 1983, pp. 85-131. 4. Kollek, H.: Die Beständigkeit von Metallklebverbindungen. Adhäsion 36 (1986) H. 6, S. 17-24. 5. Steffens, H.D. und Brockmann, W.: Die Alterungsgeschwindigkeit geklebter Leichtmetallverbindungen unter Berücksichtigung neuer Oberflächen- vorbehandlungsverfahren. Adhäsion 15 (1971) H. 10, S. 330-338. 6. Brockmann, W., Dorn, L. und Käufer, H.: Kleben von Kunststoff mit Metall. Springer Verlag Berlin-Heidelberg - New York 1989 7. Schlegel, H.: Technologie der Metall-Verklebung. Plaste u. Kautsch. 5 (1958), S. 327-330 TALAT 4704 11
    • 8. VDI-Richtlinie 2229: Metallkleben. Ausgabe Juni 1979. VDI-Verlag Düsseldorf 1979. 9. Schmitz, B.H.: Auswirkungen der Feuchtigkeit auf das Atlerungs- und Langzeitverhalten von Metallklebverbindungen. Dissertation RWTH Aachen, 1989. Schweißtechnische Forschungsberichte 28, DVS Verlag Düsseldorf 1989. 10. Matz, C.: Alterungs- und Chemikalienbeständigkeit von strukturellen Klebverbindungen im zivilen Flugzeugbau. TUB-Dokumentation (1984) H. 21, S. 307/318. 11. Kollek, H.: Untersuchungen der Einflüsse auf die Festigkewit von geklebten Verbindungen. Maschinenmarkt 91 (1985) H. 75, S. 1479-1482. 4704.04 List of Figures Figure No. Figure Title (Overhead) 4704.01.01 Surface Layers of Metallic Parts to be Joined 4704.01.02 Surface Treatment Process 4704.01.03 Methods of Surface Pretreatment 4704.01.04 Surface Pretreatments for Aluminium I 4704.01.05 Surface Pretreatments for Aluminium II 4704.01.06 Correlation between Adhesive Strength and Surface Roughness 4704.02.01 Methods of Applying Adhesives 4704.02.02 Equipment for Working Adhesives 4704.02.03 Correlation between Adhesive Joint Strength and Adhesive Layer 4704.02.04 Methods of Applying Pressure - I 4704.02.05 Methods of Applying Pressure - II 4704.02.06 Correlation between Adhesive Joint Strength and Applied Pressure 4704.02.07 Correlation between Hardening Temperature, Hardening Time and Adhesive Joint Strength TALAT 4704 12