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Tech Tips – Bonding Dissimilar Materials with Industrial Adhesives

Using industrial adhesive is an ideal method of bonding dissimilar materials e.g. metal to plastic. Joining techniques (such as welding, brazing, solvent welding, friction welding etc.) are all quite fussy and dictate that you can only join similar materials (e.g. metal to metal or plastic to plastic).  Adhesives are far less dictatorial and let you bond a whole multitude of substrate materials to virtually anything you like!

Problems joining dissimilar materials

Different substrate materials have different coefficients of thermal expansion. This means when materials warm up, they expand – but different materials do this at different rates. If you imagine a long aluminium profile bonded to glass that is expanding and contracting there could be quite a lot of difference between the two materials – potentially the glass could shatter as a result of thermal shock.

Graph below shows a selection of common materials and their coefficients of thermal expansion.

Differential expansion

 

Tech Tips for bonding dissimilar engineering materials

  • Make sure surfaces are properly prepared before bonding to maximise bond strength
  • Choose a toughened or flexible adhesive, this will allow components to expand and contract more easily.
  • Keeping a thicker glue line can help dissipate stress into the adhesive layer rather than into the substrate materials. We recommend 0.25mm – 0.3mm (0.008” – 0.012”) glue line thickness. This can be controlled by placing wire of this thickness in the joint or sprinkling microscopic glass beads of this diameter onto the surface of the adhesive before closing the joint.
  • Curing the adhesive at the temperature at which the assembly will normally be operating at helps create a zero stress joint between the two substrates.

For further assistance and advice, please contact the Permabond technical team.