How to Choose the Right Adhesive for Your Application
If you read our previous blog, you discovered some of the many ways in which adhesive bonding can be more effective, more efficient and more reliable than bolts or other assembly solutions.
If you’ve decided to explore a switch to adhesives, the next step is understanding your options. There are pluses and minuses to each chemistry, so be sure to consider your needs before researching a solution.
What is the size of the gap I need to fill (small or large)?
Are there any environmental factors that the bond will face (polar or nonpolar solvents)?
What temperatures will the bond face?
Is fixture and cure time important?
Is flexibility important?
We test our adhesives in virtually every application out there. Tests are developed based on customer needs and applications, and chances are, we’ve tested our products in a comparable environment or application to yours. If we haven’t, let us know and we’ll perform the test for you, or give you our advice for performing the test on your own.
Still, it’s good to have a base knowledge of the kinds of adhesives available to better understand if they can help in your application. Here’s a quick overview.
If any adhesive can be called “all purpose,” it’s cyanoacrylates (CAs). In the consumer market, they’re better known as “super glue.” CAs are great because they can bond almost anything, and they’ll do it very quickly. The one material we don’t suggest using CA’s for is glass. Other than that, they can be effective for bonding polymers, rubbers, wood products, metals, painted metals, and more. Common applications include gasket bonding and speaker component bonding.
CAs do have their limitations, though. We don’t recommend using them for joints that require large gap filling, and they tend to have poor impact resistance. CAs also have a shorter shelf life once opened than other adhesives, so if you won’t be using them regularly, that’s something to consider.
Light cure solutions are commonly used in the optical industry and in medical technology, in applications like needle and catheter bonding. They’re ultra-fast, cure on demand, and are particularly well suited for glass due to high transparency and exceptional stability.
Because these are light cure solutions, however, one transparent surface is necessary for light to pass through in order to bond the two substrates, and additional equipment is required.
Epoxies are known for their high strength, chemical and heat resistance, excellent mechanical properties, and very good electrical insulating properties.
The computer and electronics industries often use epoxies for things like encapsulating printed circuit boards. Other applications include the construction of aircraft, automobiles, bicycles, boats, golf clubs, and many other applications where strong bonds are required.
Epoxies are not always as convenient as other adhesive products, however, as they require a mixing of a hardener and resin, or heat curing. Epoxies are also not recommended for many plastic types, or assemblies where flexibility is required.
The high shear strength and durable impact and peel resistance of two-part acrylics make them a popular choice for difficult environments exposed to moisture and harsh elements. The marine industry uses these solutions for FRP boat bonding, and as an alternative to spot welding and rivet replacement in panel bonding.
But, as with epoxies, there is a mixing step required (in this case a resin with an activator). These solutions also have a strong odor, so they should be used only in facilities with good ventilation.
With a two-step acrylic, no mixing is required, so there is an advantage over two-part acrylics. These adhesives also score high on the toughness and durability scale. Applications include magnet bonding in electric motors or speakers, and name plate bonding.
An activator is still necessary, however, and these acrylics are limited in their gap filling ability.
Since the 1980s, silane-modified polymers (SMPs) have been used to formulate sealants and adhesives. Flexible and paintable, this polymer type combines the most desirable properties of silicones with those of polyurethanes. Applications for SMPs include truck and trailer bonding and seam sealing.
They have limited gap-filling capability (1K), however, as well as limited high temperature resistance.
Flexible, paintable urethanes are another of the more prominent adhesive options for industries ranging from automotive (window glazing) to clean energy (wind turbine blade bonding). (2K)
Challenges for urethanes are the same as those for SMPs – limited temperature resistance and gap filling. (1K)
Silicone adhesives are renowned for their sealing qualities on windows, and in gaskets for oil pans and differentials. This is one of the more flexible adhesive options and one that provides excellent temperature and UV resistance.
Where they can fall short, however, is adhesion capability. Silicones are also non-paintable, which limits them in certain applications.
Also known as machinery adhesives, anaerobics typically augment the seal or holding force of a mechanically joined assembly. They’re used for threadlocking, retaining, thread sealing and flange sealing. Anaerobics prevent loosening from vibration, and also protect joints from corrosion or rust that can result from moisture. They cure in the absence of air and in the presence of metal.
Anaerobics have high shear strength, but low peel strength.
For specific applications such as filter bonding or low-pressure molding, hot melts are a fast, effective and economical solution. They work with a range of part sizes, but are not as adaptable as other adhesive types due to their limited temperature resistance and poor adhesion to metals.
Making the Right Choice
With so many options, it can be challenging to pick the right adhesive for the job. Testing is the most important step you can take to ensure the adhesive you choose works well in your application. It’s even possible that more than one candidate can be found to do the job. If that’s the case, economical and infrastructural aspects come into play.
Do you have any questions about the different types of adhesives? Let us know in the comments!