When it comes to producing high-quality, reproducible bonds, workpiece surface preparation and pretreatment is a vital part of the process. Depending on the field of application, intended use and the workpieces themselves, there are various pretreatment processes designed to optimize adhesion and wettability. To produce connections that eliminate the possibility of unwanted changes after joining, adherend surfaces must be able to cope with physical interactions and chemical bonds.
Surface treatment is crucial to the gluing process
There are three distinct aspects to surface treatment: preparation, pretreatment and post-treatment. As a technology provider, plant automation specialist and integrator, ATN has expertise in all three.
Types of surface treatment
The main purpose of surface preparation is to expose the surface and identify obvious flaws. This includes:
- Establishing accuracy of fit
- Cleaning and degreasing
Pretreatment changes the morphological and chemical structure of the surface to make it conducive to glue application. This includes:
- Mechanical processes such as grinding and blasting
- Chemical processes such as pickling, anodizing and fluorination
- Physical processes such as flame and plasma treatment
- Painted, ceramic or galvanized coatings
Post-treatment keeps the surface activated to prevent chemical reactions with the environment. This includes:
- Priming/adhesion promotion
- Air conditioning
ATN surface treatments
Surface preparation – cleaning and degreasing
Cleaning and degreasing a surface in preparation for the application of glue or other materials entails removing all contaminants. Key factors here are wetting the surface well and ensuring that the cleaning agent evaporates quickly and leaves no residue.
It’s also important to make sure the adherend is not damaged in the process, for example by metal corrosion or plastic swelling.
The cleaning agents applied (by wiping) in ATN processes fall into two categories:
- Solvent-based cleaning fluids (acidic cleaning agents, non-halogenated hydrocarbons)
- Water-based (acid, alkaline or neutral) cleaning fluids
Surface post-treatment – priming/activation
Applying a primer or activator preserves the surface. But external factors such as surface treatment or ambient temperatures can deactivate it again. This means that the glue or material must be applied within a certain time if it is to react properly.
Priming/activation plays two fundamental roles:
- Improving wettability for optimum adhesion (e.g. on rough surfaces)
- Improving the contact properties between the glue and the adherend if they are not an ideal chemical match
There are four types of primer for different fields of application and chemical requirements.
- Clear primer (over 90% solvent and 2–5% adhesion promoter; forms a molecular layer as an adhesion promoter once the solvent evaporates)
- Glass primer (smaller proportion of solvent, contains carbon black for UV protection; the primer needs to circulate during application to prevent the carbon from settling)
- Hydro primer (some of the solvent is replaced with water, slowing down evaporation; high-precision dispensing required when spraying)
- Activator (re-activates primed workpieces; combined cleaning and priming, similar composition to clear primer)
Surface pretreatment – flame or plasma treatment
Surfaces can also be pretreated using flame treatment or plasma penetration. ATN does not supply the technology for these particular processes but integrates them into automation plants.
As a specialist in application and automation processes, ATN has many years of experience and therefore an in-depth understanding of the relevant integration requirements.
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