High-end adhesives are designed to meet specific application criteria. Are you evaluating your application and asking the right questions before choosing a product?
We often see these terms used interchangeably. While true that there are some sealants and adhesives that can be used in similar applications, and many sealants have adhesive qualities, they are not the same. As explained by Mario van Leeuwen, sealants SEAL spaces between surfaces to make them air and water-tight, while adhesives are used to BOND materials together. That is an important distinction as it relates to this article, which focuses specifically on adhesive applications.
From household glues to complex technologies required for critical aerospace applications, the uses of adhesives run a wide gamut of significance.
Reducing the weight of their end product while maintaining or improving structural integrity, as well as reducing production costs, are important to OEM’s in transportation and industrial markets. This is why adhesives are used extensively in truck/trailer, automotive, marine, and many other applications.
As explained at adhesives.org, the need by aircraft manufacturers to reduce weight has “…provided the key technology impulse for modern bonding technology.” The website continues, “The basic need for weight saving was the driving force for new design and construction methods. In modern Airbus aircraft, for example, about 30% of all components are joined using bonding technology.”
Adhesives manufacturers go to tremendous lengths to consider the many factors that might be at play in a given application when developing products. Just a few of the questions they ask include:
- Is the application structural (weight-bearing) or non-structural?
- What substrates are involved?
- What are the environmental conditions for the application and end-use of the product?
- What physical stresses must the adhesive tolerate?
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Here are a few examples of applications in which adhesives can be used standalone or as a complement to other joining methods.
The bonding of glass, primed and painted metal panels, and other structures to a variety of substrates is very common in the transportation industry
Important characteristics of an adhesive for these types of applications include:
- Ability to bond and seal simultaneously
- Very high shear-thinning property (thixotropy) for good gap-filling properties
- Non-staining curing process
- Non-corrosive
- Over-paintable with many coatings
- Shock/Impact resistant
- Vibration and sound-damping properties
Sika’s Sikaflex-255 FC is a high-strength, elastic polyurethane adhesive that can be used in many 
applications. It is a high-performance, fast-curing, flexible 1-component polyurethane used for direct glazing and has excellent gap-filling capabilities. It offers extremely high initial bond strength with initial load-bearing capacity, increasing the rigidness of the final assembly. Its fast cure rate results in rapid strength development and shorter service times.
The product is moisture-cured, requiring only atmospheric humidity to form a durable elastomer. It begins to cure and exhibit excellent green strength right out of the package.
Welding is a simple way of bonding two pieces of metal together. It’s an efficient process that offers versatility and strength. However, there are drawbacks to welding, including the cost of required skilled labor and equipment. The heat of welding can degrade the base materials, and unbalanced heat can lead to residual stresses.
Epoxy-based tacky structural adhesive tapes provide an excellent alternative, or complement, to welding for companies with heat-activating capabilities. These tapes have the ability to provide a bond in areas where there is limited weld accessibility, varying design gaps, and requirements to join dissimilar substrates. In different substrate applications, substrate separation is maintained to prevent galvanic corrosion while also accounting for the expansion of materials due to temperature change (coefficient of thermal expansion).
L&L Products L5001 F and L5773 epoxy tapes offer highly consistent bonding and can be used to replace or augment manual MIG welding. Applied upstream, it can reduce the welding cycle time by approximately 40%.
Use of these tapes can also:
- Reduce witness marks caused by welding
- Improve durability and corrosion resistance
- Reduce gaps often created in welded applications
Structural bonding of metals without primers and engineered thermoplastics and composite assemblies with little-to-no surface preparation can be difficult. ITW Performance Polymers Plexus MA205HV does a superb job of handling this situation. It is an advanced non-conductive two-part methacrylate adhesive designed for the structural bonding of various electronic assemblies. Combined at a 10:1 ratio by volume, MA205HV has a working time of approximately 3 to 5 minutes and achieves a handling strength of 50 psi in approximately 8 minutes on polycarbonate. This product provides a unique combination of high strength, excellent fatigue endurance, outstanding impact resistance, and superior toughness.
If you have a bonding application you believe could be made more efficient or effective through the use of structural or non-structural adhesives, contact your Austin Hardware rep or our nearest location. Our trained professionals will evaluate your needs and make the best recommendation to help you achieve your goals.
