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Structural Adhesives for Structural applications

Today’s structural adhesives are an alternative to traditional joining technologies, such as mechanical fasteners.

As times change and structural assemblies become more sophisticated, manufacturing techniques must be refined to accommodate new needs in structural applications. Mechanical fasteners and welding are traditional joining methods that many manufacturers are comfortable with; however, these methods are not always the most practical solution for modern assembly. Mechanical fasteners can drive up costs, limit options for materials, and cause fatigue, metal distortion or tearing.

Solutions for structural applications are strong adhesives or tapes that can outperform mechanical fasteners and provide a clean, durable design. Industrial adhesives are an alternative that solves the problems presented by traditional joining methods.

A strength comparison between industrial adhesives and tapes and traditional mechanical fasteners when bonding aluminum to aluminum under extreme conditions.

PROBLEMS WITH MECHANICAL FASTENERS

Traditional joining methods can present difficulties in the assembly process. Metal distortion and tearing under heavy loads, or fatigue, reduce reliability and longevity of assembly parts. To address this issue, manufacturers may try and decrease the gap size between rivets or bolts, inflating the number of needed fasteners and associated purchasing and labor costs.

Welding can damage metals, by causing heat distortion or burn through, especially with lighter weight substrates. Also, energy and labor are often needed for post processing work to return the welded parts to a condition suitable for painting.

Sustainability in production is a hot button issue that is only going to escalate. Many manufacturers face pressure to decrease fuel use, energy consumption, and contaminant emissions. The best way to do that is to reduce the weight of materials being produced, and use the lighter weight materials in lieu of traditional heavier metals.

Reducing weight for sustainability’s sake becomes a difficult task because traditional joining methods usually aren’t as effective as adhesives when joining lighter-weight materials. Lighter composite or plastic materials cannot always be easily welded, and thin sheet metal parts are prone to distortion and tearing at the concentrated points where throughpart fasteners like rivets and bolts are placed.

While mechanical fasteners can often provide structural strength, the level of holding power that they provide can be overkill for many common applications. In this way, mechanical fasteners are used out of convenience rather than necessity, when there are simpler and more effective joining options available.

3M industrial adhesives and tapes are strong, but how do they stand up to a raging river? A kayak made of hard-to-bond, low-surface-energy plastic is tested.

CHOOSING ADHESIVES

Selecting industrial adhesives for structural applications opens the door to opportunities that would not be possible when relying on mechanical fasteners or welding options.

Where mechanical fasteners may rip though and damage a thin substrate, an adhesive bond provides even load distribution across the surface area of the joint. This reduces the potential for fatigue damage, lengthens the life of the bond and product, and drastically reduces replacement or repair costs. Thinner and lighter materials can be cheaper to manufacture than heavy metals, as well.

Adhesives allow manufacturers to diversify the materials used in their assemblies in ways other than using different metals. Using adhesives opens up options for more composite and plastic use, which can help manufacturers decrease material costs and improve the aesthetics of the end product.

Epoxy adhesives are tested by lifting this 14,550 pound shipping container for 18+ hours.

Where mechanical fasteners can limit design options for structural applications, adhesives expand them. Adhesives can be applied in that are inaccessible to mechanical fastening during final assembly, allowing new designs that further reduce weight, costs, and labor. From an aesthetics standpoint, adhesives can reduce and eliminate unsightly screw and rivet points and weld lines, leaving a smooth, uninterrupted surface without grinding after welding.

Bonding dissimilar materials, such as different kinds of metals or metal to composites or plastics, opens up a multitude of design options, and allows manufacturers to diversify their products and make them much more functional. Mechanical fasteners would not be a good option for joining metal to many composites. For example, drilling holes for fasteners would likely crack plastic material. When joining plastics to metal, thermal cycling can lead to fractures within the plastic.

Despite extraordinary advances in adhesive technology, many manufacturers continue to doubt adhesive strength. In this video from 3M Assembly Solutions, adhesives and tapes are shown to outperform metal fasteners in a test of strength and durability.

The video shows that adhesives and tapes such as 3M’s VHB Tapes can out-perform mechanical fasteners for applications with lighter weight substrates through their load-distribution capabilities. Adhesive sealants provide high elongation, flexibility and gap filling. Toughened epoxies are suited for applications that need a more rigid solid combination of impact resistance and strength. 3M’s provide impact load resistance on thin substrates.

When put to the test against mechanical fasteners and rivets, 3M adhesives and tapes emerge victorious with superior hold, even stress distribution and seamless design.

Tape allows for construction from panels to windows as it allows for high holding power and long-term reliability. Die-cut tape from 3M allows for easy assembly.

ADHESIVE SOLUTIONS TO BONDING CHALLENGES

If a manufacturer were to choose substrates in lieu of traditional metals for a particular project, the right adhesives can be solutions for hard-to-bond materials.

Low surface energy (LSE) plastics like polyethylene, TPO, HDPE, PP and some powdercoats can be hard to bond because of their chemical composition. Typically, these materials will require extensive surface preparation processes before even beginning the joining process.

Adhesives can join dissimilar materials including different metals to plastics and other composites.

Thermal methods like friction or ultrasonic welding are considered solutions for LSE plastics. However, these methods are typically expensive and require ongoing tooling, which is not ideal for products that have short runs or need frequent design changes.

Even adhesives don’t always solve the surface preparation issue, however some specialty adhesives, like 3M Scotch-Weld Structural Plastic Adhesive DP8010 Blue, can bond LSE materials and even reduce or eliminate the surface preparation steps, such as is seen in this video.

Adhesives can be used for a variety of uses, such as for panel-to-frame applications.

Another challenge is trying to bond oily metal. Oily metals often require extensive preparation and cleaning, which creates extra work. Unfortunately, these steps are necessary because the oil can interfere with robust bond formation.

That said, two-part structural acrylic adhesives are able to absorb most oils from metal surfaces, allowing the metals to bond without first undertaking extensive cleaning procedures. This eliminates those tedious steps, saving the manufacturer time and money.

Adhesives can eliminate the problems of metal distortion and tearing.

Though many manufacturers are comfortable with traditional fastening methods, modern design and sustainability factors render mechanical fasteners and welding to be less effective than alternative joining methods for many applications.

Adhesives are extremely effective to remedy the issues presented by mechanical fasteners, including metal distortion and tearing, and expensive repairs or replacements. Not only do adhesives provide a more effective alternative to traditional joining methods, they also allow manufacturers to choose from a wider variety of substrates,bond dissimilar or hard-to-bond substrates, and explore different design avenues to create unique and superior products.

Many people continue to misjudge the strength of adhesives. How could glue be suitable for a huge application? People may think that way, but an adhesive bond is not to be underestimated. In this video, a thin layer of adhesive holds thousands of pounds:

Imagine what adhesives could do for you and your design.