Choosing glue between FRP and aluminum

[Lorens]

What should i take in to considerations when I choose a glue between aluminum and FRP (PET). What I have come up to is the following

1. tensile strength 2. coefficient of linear expansion (but for this on It vary with temperature and stress since we are working with plastic) 3. adhesive strength

Kindly Lorens

 

[wes616]

Surface treatment of the metal prior to bonding. Galvanic corrosion...

Wes C.
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[Compositepro]

Thickness of the adherands (twice as thick=twice as stiff), coefficient of thermal expansion (CTE), thermal expansion differences during cure and during use, bondline thickness, strain capability of the adhesive, surface preparation, adhesive application method, air entrapment in the bondline, flow of the adhesive during cure, fixturing of the joint during cure, joint design.

 

[rodneybennet]

Dear Lorens,

Regarding adhesive strength:

To assess whether the Aluminum sticks to an adhesive, and whether the PET frp sticks to the adhesive, the concept of surface energies and forthcoming related interfacial energy calculations are of major importance.

This will also help you to decide if an interfacial adhesive is necessary (or whether the PET has sufficient capability to stick to Aluminum... however NOT expected for most applications).

Also see Wiki: surface energy, or information at:

http://www.composite-agency.com/materials-forum.htm

Regards,
Rodney

 

[hoidap]

please look at your application 1st, then find out what the material need to stand.
Normally, peel strength should check.
PET and Aluminum are quite different adherents, so 1 adhesive may not suitable but should have primer on surface 1st, then adhesive. priming just like attaching the same hands for both substrates before bonding

 

[riff42]

Depending on your processing abilities, we have had luck using DuPont Surlyn thermoplastic with bonding materials to aluminum. We use it with Nylon as well.

 

[RPstress]

Al is usually cleaned and anodised and often primed before bonding. This is compatible (depending on primer choice) with many adhesives.

The choice of glue for bonding the PET depends somewhat on whether it's thermoplastic PET (which it usually would be with this name). Major suppliers of engineering thermoplastic such as DuPont (

http://plastics.dupont.com/

) or DOW (

http://www.dowplastics.com/

) should have a lot of online advice on compatible adhesives, and even more specific technical advice if you contact them.

The glue's coefficient of thermal expansion is largely irrelevant - there's not much glue and it's the CTE mismatch between the substrates which matters most. Most glueed joints are shear joints - if yours isn't then you might like to reconsider the design. As such it's the glue shear strength which is important. The adhesion is likely to be adequate with most adheisves; it's the adhesive properties of the substrate surfaces which is more important, which is why care is taken over surface prep. Ideally, you want a cohesive failure; that is, the glue breaks with glue left visible on each failure surface, or a substrate breaks, with only failed substrate surface visible on the failure surface (or combinations). Adhesive failure such that subsrate surface or primer surface (if applicable) is visible is generally bad.

 

[corrosionman]

Lorens, of utmost importanceis surface preparation.
We always Shotblast the Aluminium AND the GRP / FRP surface
Anything less is inferior - Our Competitor prepares by grinding the surfaces - - We have seen his failures and the joints fail very early in life leaving clearly visible grinding marks.
Regards CM