Lean, Green, and Reliable Manufacturing Practices
Manufacturing engineers must carefully address several elements when adhesively bonding different surfaces, such as low surface energy polymers, thermoplastics, and composites –particularly regarding optimizing surface cleanliness and chemistry. In this regard, bonding interfaces define a boundary between a material and its surrounding environment. Bonding interfaces exhibit high chemical reactivity, and, in many cases, modifying a surface can lead to a surface with properties different from those of the bulk structure. Manufactured substrates may exhibit one or a combination of bonding challenges, including surface contamination, such as hydrocarbon films and particles and non-wettable or nonpolar surface chemistry. Solvent-based surface preparation methods employed to address these challenges are labor-intensive, cannot be replicated consistently, and are unreliable.
An exemplary application is the preparation of surfaces for adhesively bonding rivetless fasteners used in aerospace, defense, marine, automotive, rail, energy, and industrial sectors. Conventional surface preparation methods for this application typically utilize manual organic solvent wiping techniques. Wiping the contaminated surface with a solvent tends to smear oily contaminants and is inefficient for cleaning rough surface topography.
In this regard, this conventional surface preparation technique employs an abrasive pad such as Scotch-Brite containing superhard aluminum oxide particles to remove the contaminated surface, followed by solvent wipe cleaning to remove abraded surface and Scotch-Brite particles (i.e., oxides, metal, and polymer) and contaminants. Abrading a contaminated surface tends to infuse carbonaceous substances into the surface. Given this, it is best practice to clean the surface before and after ablation, increasing manufacturing waste. In this regard, solvent wipe cleaning techniques produce manufacturing waste such as increased time, labor, and materials and cannot be automated.
A CO2 Composite Spray is a superior alternative to solvent-based surface preparation for adhesive bonding. A CO2 Composite Spray uses a combination of micronized CO2 particles entrained in a compressed air jet to selectively and consistently produce chemically and physically clean surfaces, removing organic, ionic, and particulate contamination.
Moreover, if required, atmospheric plasma complements a CO2 Composite Spray cleaning process (Particle-Plasma™) by physicochemically restructuring bonding interfaces. An atmospheric plasma contains many beneficial treatment agents – excited and ionized particles, photons, radicals, electrons, and heat – in a gaseous medium such as Air, CO2, N2, Ar, and other gases and admixtures. These energetic agents catalyze numerous chemical reactions that create and graft various oxygen, carbon, and nitrogen-based surface functionalities onto CO2-cleaned surfaces, increasing surface wettability and enhancing adhesive bondability.
The CO2 Composite Spray and Particle-Plasma processes provide consistent and broad-spectrum surface preparation capability while eliminating environmental health and safety hazards. They may be performed manually or automatically. Manufacturers of high-reliability products should consider our CO2 surface preparation expertise and technology for reliable adhesive bonding.
