Tips for Selecting Adhesives

Tips for selecting an adhesive

Whether your goal is to achieve a unique design, implement process improvements, or improve the quality of your product, there are many potential benefits to using adhesives. In order to achieve your desired outcome, the adhesive you choose must be up for the task.

The Thomasnet database indicates there are >250 manufacturers and distributors of industrial adhesives in North America. Each company might have multiple products and distributors sometimes offer private label products, so there are potentially thousands of products to choose from. How, exactly, do you choose the right adhesive for your needs?

Maybe, if you have a large enough business opportunity to get the attention of the supplier’s or distributer’s sales rep, you go with their top recommendation.

Maybe you pour over technical data sheets or interactive selection guides and pick the best match for your application.

Maybe you read a product review online.

Maybe you just use the same product you’ve always used, no matter the application.

Whatever your selection process, asking the following questions about your application will help you find the best candidates for sampling, trialing, and ultimately achieving your goals.

What are the substrates?

Substrate compatibility can be thought of as the foundation for achieving the expected performance of the adhesive. Most technical data sheets and adhesive selection tools provide substrate compatibility guidelines which can be very helpful in identifying a class or type of adhesive (e.g., epoxy, cyanoacrylate, polyurethane, acrylic) for your application. Keep in mind that these guidelines are rarely based on exhaustive testing and exceptions sometimes exist. An adhesive must also be compatible with both process chemicals used upstream of the bonding operation and any contamination not removed before bonding. Some substrates change with age and in some cases, this affects the quality of the bond. Testing is often the best way to confirm compatibility.

How strong of an adhesive is needed?

This question is best answered by design or engineering-focused team members. Often the tensile strength of the bulk adhesive or shear strength of bonded coupons is known or can be measured and used to guide selection. Modulus is another property that can help you select the right adhesive. For example, a high modulus adhesive can provide a stiff joint while a low modulus adhesive might allow some compliance to dissipate stress or provide damping. When evaluating supplier data for tensile strength and modulus, keep in mind that these properties can sometimes be affected by curing conditions and could lead to different results if your process differs significantly from those used by the supplier in generating test data.

What conditions will this joint experience in use?

Depending on the end use of the bonded part, the adhesive might be exposed to a wide range of conditions. A few examples include high or low temperatures, constant or cyclical loading, weathering, corrosive environments, and chemicals. Each of these exposures can lead to a change in the properties of the adhesive and this in turn can lead to a change in the performance of the joint during use. Selecting products compatible with the conditions expected during use will set you up for success. Keep in mind that the combined effect of various exposures on performance is often difficult to predict and testing is often used to determine the response from individual types of exposure.

How will the adhesive be applied?

Consider how the adhesive will be physically applied to parts. For example, will the adhesive be applied using automated pumping and dispensing systems? Or will it be applied manually by an operator using a hand-powered gun? How much will ambient temperature change during production? Answers to these questions might narrow down options based on viscosity, recommended plant conditions, and available packaging sizes.

What is the desired cycle time?

Thinking about how quickly (or slowly) your production processes moves will also help you narrow down options. Small parts can typically be bonded and joined more quickly than large parts and can accommodate adhesives with shorter “work life” or “open time.” Large parts typically require longer open times and work life to allow part coverage and joining. “Fixture time” or “time to handling strength” is another factor to consider and indicates how long clamps or fixtures are necessary to hold the assembly together while the adhesive cures. “Time to full strength” is exactly what it sounds like and can be selected relative to how soon parts are put into service. Often a balance must be struck allowing enough time for application and joining while minimizing the time a part sits in an assembly fixture. Fortunately, suppliers often indicate these properties on the technical data sheet and packaging. 

Are there any Environmental, Health, and Safety Concerns?

Some adhesives contain toxic chemicals that can be harmful to human health and the environment. When selecting an adhesive, it's important to consider the toxicity of the adhesive and its impact on the environment. Supplier Safety Data Sheets (SDS) should disclose known hazards and describe handling, storage, and emergency response measures. Hazard reviews are a great tool for communicating safe operating procedures related to your bonding process.

What is the cost?

Cost is also an important factor to consider when selecting an adhesive. The cost should be weighed against its performance, durability, and other factors. In some cases, a more expensive adhesive may be more cost-effective in the long run, as it may last longer and require fewer repairs.

Putting it all together

Trying your best to answer these questions will go a long way in helping you choose the right adhesive for your application. Answers might be found in technical data sheets, supplier test reports, and adhesive selection apps and can help you identify potential candidates for further evaluation. Keep in mind that the parameters used to generate the test data in a data sheet often differ from your specific application and, in practice, might give different results. Depending on the consequences of part failure, planning and performing your own tests to answer these questions can be a great risk management strategy.

If you have questions about how to choose the right adhesive or how to develop and execute your own test plan for your application, contact Digital Glissade to schedule a consultation.