Theory vs practice in the adhesives process

2nd April 2020
Alex Lynn

“It works in practice, but does it work in theory” is a phrase commonly used to describe situations in economics. But the same can be applied to adhesives processes, where the datasheet may not always give the same insights as your practical observations and tests.

Here Peter Swanson, Managing Director of adhesives specialist Intertronics, explains why developing an adhesives process requires more than just the datasheet.

Every adhesives application is unique. Specifying materials and equipment for an adhesives process requires detailed discussions and testing to establish what works for your application. The datasheet offers some insight ― but may not tell you everything.

Looking past the datasheet

The data for an adhesive or coating mostly comes from laboratory test procedures, which are well understood, usually in the public domain, universal and repeatable. That means this information is great for characterising the material for properties like how hard or soft it is, whether it is rigid or elastic, how much force will it take before it breaks, and how much it will stretch before it does so. However, in many cases, this data needs interpretation and extrapolation to fit with your circumstances.

A survey of product datasheets may allow you to narrow down the candidate list from many thousands to, hopefully, a handful. This selection can then be put forward to practical testing for your specific application. Testing your production parts provides you with the assurance that what you specify will meet your unique and distinct requirements

So, while datasheets and specification documents are useful when deciding on what material or equipment to consider for your application, we would rarely recommend the selection of a product based on the datasheet alone ― there may be factors you haven’t considered.

Our approach is always “this material would be a good candidate for you to test”, or “lets evaluate this proposed process with some trials”. This doesn’t mean we don’t know what we’re talking about ― it’s quite the opposite; years of experience has shown us that what might appear simple is often complex.

Unanswered questions

One reason your adhesives process may not work in theory is because datasheets are not exhaustive ― they may not answer all your questions. For example, the datasheet may say that the adhesive bonds to ABS and PC, but not mention the bond strength to PMMA or glass. This may be that the adhesive is not recommended for those substrates, or perhaps alternatively that the adhesion to those substrates has not been tested, or if tested, published. Good suppliers may be able to fill in those datasheet gaps from experience.

You may have other questions: How does the published pot life relate to the working life I need for my process? The stated intensity of that UV curing lamp looks strong, but is it the correct wavelength for my material? How will the published cure time differ with mass? With temperature? With humidity? The performance of that adhesive looks like it will more than meet my needs, but how will my production manager fit it into our assembly process?

It’s not unusual that the cost of applying and curing the adhesive ― the process ― is more significant than the cost of the material itself. To keep the process simple, you may want to consider automation, single part materials with no requirement for mixing, fast in-line cure and process friendly packaging. Keeping the process simple will reduce costs and help you make productivity gains.

A good supplier will be able to add significant knowledge to the facts on the datasheets, using their experience of successful implementations. They could clarify whether, from their experience, the adhesive does bond to glass, even if it’s not mentioned. Or, whether the UV curing lamp will cure your coating, even though the datasheet mentions another wavelength. They may recommend a different adhesive, which won’t cause a bottleneck in your production.

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