Adhesives & Sealants in Transportation

Posted on 9/6/2012 8:46:32 AM By Sandy Niks

Hello - and welcome to the transportation blog! This is the first in a series of semi-monthly posts. First, some background.

I am retired, having spent over 32 years working for one of the automotive manufacturers. While there,  I worked on many aspects of adhesion, including adhesion theory, formulation, testing, plant trials, and writing test methods and specifications. Also as part of my responsibilities, I worked on adhesive related standards at ASTM International  and Society of Automotive Engineers (SAE) International and continue to do so today. I will be writing about these experiences as well as researching the latest information available on adhesives in the transportation industry.

Adhesives in transportation covers a large territory. Automotive applications include structural metal bonding, structural fiber reinforced plastic bonding, exterior trim, interior trim, and glass bonding. Some applications supplement the adhesive with primers, mechanical fasteners, or spot welds.

As with other adhesive sectors, adhesives come in various forms, such as two-part gunnable adhesives, one-part gunnable adhesives, liquid adhesives, tapes, hot-melt adhesives, or warm-melt adhesives. They can be 100% solids or solvent-borne, although most solvent-borne adhesives are actually water-borne adhesives to reduce any volatile organic compound (VOC) concerns. Cure mechanisms can be instant anaerobic cures, heat-activated, ultraviolet radiation, evaporation, cooling, or several other mechanisms. Some do not cure but remain tacky to maintain contact with the substrate. Chemistries are just as varied  - epoxies, urethanes, acrylics, cyanoacrylates, etc., as well as combinations. Properties are further modified by the addition of fillers and other ingredients to meet the requirements of a specific application.

Performance requirements are defined by the user, the automotive manufacturer, and are usually published within the company and to the supplier community as material specifications. These specifications will include requirements from the joint design for the application and the manufacturing requirements for assembly. The adhesion requirements start with the bond strength needed for the application, then expands into durability - what strength is required initially, then what level of strength needs to be retained after exposure to temperature, humidity, radiation, chemicals (such as salt spray), and other conditions meant to simulate end user situations. The chemical content of the adhesive is examined to ensure compliance with safe handling practices and hazardous material concerns. New requirements regarding sustainability are beginning to appear, although they haven't been fully defined and may provide an opportunity for those affected to participate in the development to ensure that the requirements can be met.

The test methods used to evaluate adhesive candidates as to their ability to meet the requirements may be authored and published by the automotive manufacturer, but the test methods are more often the common ground between manufacturers. Voluntary or industry standards are used, such as SAE, ASTM, or ISO.

Of course, the use of adhesives is not limited to cars and trucks in transportation, but also includes aerospace, marine, and motorcycle applications. I intend to elaborate on all of the topics touched on today in future blogs.

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