by Douglas Craig, Technical Application Engineer & Collision Industry Liaison, Structural Adhesives Tech Service, LORD Corporation
Aluminum’s light weight makes it an ideal autobody substrate as an environmentally-friendly, cost-effective method for increasing performance, boosting fuel economy and reducing emissions while maintaining or improving safety and durability.
Auto OEMs are using crash durable adhesives in the manufacturing process, and will be recommending similar type adhesives for repair operations to return vehicles to pre-accident condition.
Two-component crash-durable adhesives for repair have been formulated to replace all OEM one-component crash-durable adhesives. The crash-durable adhesives allow you to duplicate the original vehicle right down to the adhesive.
Reference is often made to one-component and two-component, or 1K and 2K, materials. This designation refers to how many materials are applied as a bead or are mixed to be applied as a bead. A one-component material is applied as received from the supplier, whereas a two-component material is mixed together during the application.
Most of the vehicles produced today, whether aluminum- or steel-bodied, are assembled with a one-component crash-durable adhesive, whereas the repair version of the crash-durable adhesive is a two-component formulation. Here’s the reason for the differences:
When OEMs assemble cars with crash-durable adhesives, the vehicles go through a heat-curing process for the adhesive, along with drying processes for the paint and/or e-coating. The one-component crash-durable adhesive is made to withstand temperatures up to 400° F. All of this heat allows the chemistry in the one-component adhesive to cure.
In the collision repair shop, it is not possible to place a repaired vehicle into such high temperatures for the curing process. The two-component epoxy formulation allows repairs to be made to vehicles that match the original adhesive application.
Crash-durable adhesives not only have the strength of structural adhesives, they also provide exceptional toughness. This is why they are sometimes referred to as “impact-toughened” adhesives. Crash-durable adhesives are extremely flexible, with the ability to stretch without losing their effectiveness.
Flexibility is especially crucial in crash mode situations. Crash-durable adhesives will not “micro-fracture” in a “crush-and-crash” mode as with standard structural adhesives. Therefore, joints will hold together better and not lose their strength during a crash. This is especially important when considering that thinner substrates, such as aluminum, tend to “move around” more during a crash, and the flexibility of the adhesives helps to hold the joints together.
Crash-durable adhesives, for repair procedures, are used to replace all the original equipment locations of OEM-applied crash-durable adhesives. Typically, these areas are between all the metal panels and in sections such as A-, B- and C-pillars, and other locations including roof joints and engine box joints. They can be used for panel bonding, weld bonding and rivet bonding of aluminum panels.
Though application methods for these adhesives are similar to conventional structural adhesives, technicians might be “startled” by their appearance. Crash-durable adhesives are highly pigmented and come in colors such as purple, orange, red, and blue.Offering both strength and sealing functions, crash-durable adhesives provide a sealant to the vehicle‘s body structure and a bonding method. If there is any doubt as to whether the OEM adhesive is crash durable, use a crash-durable adhesive in the repair.
For repair, it is important to understand that colors do not need to be matched. For example, a purple OEM adhesive can be replaced with a blue repair adhesive as long as that repair adhesive meets the OEM requirements.