Bonding assembly: materials and good practices for application
Glue and adhesive strips are 2 alternatives to traditional joining methods such as welding or screwdriving. Find out why bonding is a versatile joining solution, and learn some good practices for applying it.
What materials can be assembled through bonding?
Bonding and material surface energy
The easiest materials to bond are those with a very high surface energy, i.e. metals.
Materials with a very low surface energy are the hardest to assemble because they prevent the glue from spreading. These are mainly:
- Fluorinated polymers (PTFE, PVF)
- Polyethylene (PEHD)
Adhesives for just about any material
Thanks to the progress made in recent decades by adhesive manufacturers, it is now possible to bond almost any material, whether flexible or rigid, with low or high surface energy.
The advantages of bonding
Like adhesive strip assembly, bonding has the advantage of being discreet, allowing for virtually invisible assemblies.
Bonding has the added benefit of allowing for extremely strong structural assemblies. The adhesives used are generally epoxy, acrylic, or urethane based.
As an example: LED road signs, which have to withstand extreme weather conditions (wind, cold, heat, etc.), can be assembled through bonding.
Bonding: an industrial-scale solution
The use of adhesives has evolved considerably in recent years. The bonding process can now be automated and is compatible with industrial robotics.
How should you properly apply an adhesive strip?
Clean the surfaces to be glued
This step is necessary in applying any adhesive in order to remove pollutants. The products to be used vary according to the materials to be cleaned. It is therefore imperative to use compatible products. In general, cleaning includes:
- Dust removal with a cloth or wipe;
- One or more degreasing steps.
Air bubbles are the sworn enemy of bonding, because their presence reduces the cohesion of the adhesive joint.
What’s more, for assemblies meant to withstand high temperatures, warming can generate air bubbles that burst on the surface.
Therefore, the presence of air bubbles is synonymous with weakening of bonded assemblies.
Respect application constraints
Adhesives are highly complex chemical products, whose properties vary according to several factors. It is therefore imperative to respect adhesion constraints, including:
- Application temperature;
- Holding time at a particular temperature, placing the material in an oven if necessary;
- The humidity of the room (steaming may be required).
How can you optimize bonding?
For structural applications, when bonding must guarantee a very high shear strength (7 to 40 MPa), additional steps might be required to optimize the bonding. Here are a few examples:
- Surface treatment (flaming, corona discharge, chemical treatments) to increase the surface energy of low-energy materials
- Application of an adhesion primer to improve material cohesion, increase surface energy, and block capillary rise
- Vacuuming to eliminate bubbles in porosities
- Bonding under pressure, to ensure better adhesive penetration
Bonding: a complex mechanism
The strength of a bonded assembly is based on 3 properties: bond strength, cohesion strength, and tack.
- The adhesive cohesion is determined by its chemical composition and depends on the nature of the adhesive.
- Adhesion is what happens when glue adheres to a surface, and is thus a parameter that depends as much on the nature of the materials and the adhesive as on the surface properties.
- Tack is a 3rd force, which depends on applied pressure and contact time. The higher the tack, the faster the adhesive will react.
While there is no such thing as a miracle glue, bonding allows you to join all kinds of materials, whether for structural applications or not. We’re experts in adhesives and application procedures
Do not hesitate to contact an ADDEV Materials expert for help choosing your adhesive strips.