Simple Steps for Adhesion Success
A correctly dimensioned bonding gap is extremely important when engineering an adhesive-friendly design. It ensures a consistent adhesive layer thickness, which enables the adhesive to fully develop its adhesion forces. It can be provided by a defined contact area with spacers integrated into the components being bonded, or by a tongue and groove joint. If the gap is too narrow, the components press the adhesive out and the bond will not hold.
While tongue and groove is a reliable and widely used method to ensure solid structural bonding, it is not feasible when bonding thin metal sheets. However, there are several other options available. If the materials are formable, bending the components and placing them one on top of the other will improve the bond strength, as this will significantly increase the bonding area. Although more complex, as it involves additional process steps, this is an excellent option where higher strength is required (figure 1).
The strength of a pipe joint leaves much to be desired if the two components are bonded at their ends (figure 2). Adding an additional interior or exterior ring enlarges the bonding area tremendously and decreases the risk of bending stress. The two components can also be overlapped by adapting the diameter of one. Because of the adhesive's sealing properties, liquids can easily flow through these pipe joints without leaking.
Structural bonding has many advantages over conventional joining technologies. However, adhesives should be considered early on in the design phase to take full advantage of their potential. The first part of this article was about how to ideally utilize these possibilities with a tongue and groove connection. The second and last part introduces further design options.
8 rules for design engineers
Provide sufficiently large bonding areas and gapsAchieve evenly distributed tensionsLimit stress to compression, tension and shear stress if possibleAvoid peel and bending stressAvoid eccentric force transmissionPrevent plastic component deformationProvide adhesive-friendly surfacesComply with the curing conditions required by the adhesive
Advantages of bonding
Different materials can be joinedTension is evenly distributedComponents are not weakened, e. g. by boreholesHigh resistance to dynamic forcesLaminar joining of thin componentsComponents are not or are only slightly subjected to heatSimultaneous bonding and sealing is possibleThe adhesive layer balances tolerancesElectrically or thermally conductive adhesives are available
Conclusion
In order to create an adhesive-friendly design, engineers should follow basic design principles such as working with sufficiently large bonding areas and eliminating the potential of peel and bending stress. By following these steps the end result will be a strong, sturdy and powerful joint.
Further design options can be found in part 1.
