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Prevent Read-Through on Trailer Panels—Even when Using Thin-Gauge Substrates

( 03/10/2021 ) Written by: Anonymous

Today’s trailers typically use thin-gauge substrates instead of the thick-gauge aluminum or steel components that were once standard. Aluminum is the most common substrate material, with thermoset composites also being popular. While thinner materials are lighter-weight, more economical and often provide better aesthetics, sometimes assemblers run into trouble with adhesive read-through.

Read-through is a type of surface distortion in which adhesive bond lines can be seen on the exterior of the panel or skin. It is sometimes assumed that thicker substrates are needed to combat the problem, when, in fact, the issue may just be a mismatch between adhesive type and substrate. If an adhesive is rigid with high exotherm properties, or if it shrinks as it cures, it can pull at the thin, flexible metal or composite panel, creating distortion.

In addition to considering the use of thicker panels, manufacturers sometimes believe that they should use welds or rivets to bond materials where read-through is a concern. But mechanical fasteners concentrate loading and create stresses in substrates. Corrosion of welds over time can also compromise the integrity of the panel system. Adhesives, on the other hand, resist corrosion and environmental conditions while providing strength and sealing against weather. Adhesives are also ideal for bonding dissimilar materials such as steel to aluminum or aluminum to composites and plastics.

As an alternative to rigid structural adhesives and their inherent read-through problems, some manufacturers use a urethane or silicone adhesive. But these formulations have their own set of complications: silicones tend to not have the desired strength for structural applications and urethanes cannot be used on bare metals without first needing excessive surface preparation. Acrylic adhesives are a better choice because they provide the strength characteristics of a structural adhesive, without the time-consuming surface preparation required for silicone or urethane adhesives. They also prevent read-through.

Case Study: LORD 810 Low Read-Through Adhesive

LORD 810 adhesive delivers superior peel strength on a variety of metal and plastic/composite substrates and has excellent bake resistance on thin-gauge aluminum up to typical powder coating temperatures. Good peel strength is especially important on applications such as sidewalls, roof panels and front-nose panels, where wind resistance and deflection capabilities are crucial.

Fast cure times are another benefit of this acrylic adhesive. It has a handling time of as little as 20 minutes and is 90 percent cured in 30 minutes at room temperature. By applying modest heat (<150°F/<66°C), users can customize cure rates to their application. LORD 810 adhesive also offers environmental resistance to dilute acids, alkalis, solvents, greases, oils and moisture as well as provides excellent resistance to UV-exposure and weathering.

LORD 810 adhesive is a proven solution for trailer manufacturers. In one application, a utility trailer builder had been enjoying the advantages of adhesives over rivets for several years—assembly costs were lower and there were significant improvements with water-leak warranty issues—but sidewall distortion was a quality concern. The manufacturer considered increasing the panel thickness to prevent distortion. However, when they switched to LORD 810 Low Read-Through Adhesive, the distortion problem was solved.

In another example, a trailer manufacturer wanted to avoid the excessive surface preparation required for using tape and/or adhesive to bond bare aluminum and galvanized metals. Additional labor, along with heavy grinding/sanding and extra bare metal primers, was necessary, increasing the manufacturer’s costs. After trying LORD 810 Low Read-Through Adhesive, the manufacturer discovered that the adhesive bonded without fail to the substrates. Only minimal wiping was needed to prep the surfaces, saving significant work time. In addition to saving time and money, the manufacturer reaped the benefits of avoiding read-through on sidewall surfaces.

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