Sticking up for adhesives
July 16th 2007 Involving the adhesives supplier at an early stage can help design engineers, says Bob Goss, of Henkel, maker of Loctite brand products.
Ask some design engineers why they seem reluctant to specify adhesives and you’ll likely get one of two main reasons. First, they believe the performance of adhesives is not always predictable in advance. And secondly, a previous bad experience has led them to suppose glue simply doesn’t work.
The truth is the performance can be ascertained and, providing the right adhesive is used, there is no reason why the joint or seal cannot be as effective – if not better – than other methods. So there's some myths that need to be dispelled.
Predicting performance
Those adhesive manufacturers that have invested in appropriate laboratory facilities can replicate, with great accuracy, the actual process that will be used in the production environment. That enables designers not only to test out their designs before costly production runs are started, but also to seek expert advice about a number of issues involving the use of adhesives.
So, just what kind of advice can you expect from an adhesives supplier? Alongside the selection of the right kind of adhesive technology, perhaps one of the most important areas is that of joint design.
Bonded assemblies must uphold a multiplicity of forces. To achieve maximum strength (and therefore, reliability), adhesive joints should be designed such that cleavage and peel stresses are, wherever possible, avoided. In addition, the substrate material in question, its thickness and the type of adhesive should be evaluated to establish the optimum area of overlap.
On a simple lap shear joint the highest stress points are at the leading and trailing edge of the joint. The length of the overlap increases strength - but by diminishing amounts. On the other hand, expanding the width of the overlap creates a proportional increase in strength.
Where a butt joint has been used as a previous assembly design, a simple bevelling of the two mating surfaces can produce the area required for an effective bonded joint.
Again, seeking advice from an adhesives manufacturer will prove invaluable.
However, that supplier could go one step further and take the various anticipated joint designs and put them to the test in a laboratory situation.
There are several other ways in which involving the adhesive supplier at an early stage can help, including: trials and tests, selecting the right product, applying the solution and enhancing designs. To learn more see this month's issue of IP&E.
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