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Structural adhesive used to assemble a hovercraft

11.08.2021

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Internationally renowned Griffon Hoverwork, the developer and builder of hovercrafts, has partnered with Scigrip, the manufacturer of structural MMA adhesives, to streamline the production process. The two-component MMA bonding adhesive was successfully tested and is now being used to bond the 12000TD aluminum floor to the aluminum upper structure.

The 12000TD is a 22 meters long passenger ship carrying 12 tons with a seating capacity of 80 passengers and is operating in the most varied and difficult areas of the world, from the southern jungles of South America to the cold seas of the Baltic and the Arctic. Therefore, it was critical that the Scigrip adhesive solution chosen was capable of withstanding the rigors of the harsh and demanding environment.

Griffon Hoverwork has used traditional techniques of using welding to assemble the key elements of its vessels. But this method can cause Thermal Deformation, resulting in other problems, including localized stress points [1].

The Structural MMA Adhesives was specially designed for marine conditions and has undergone all the necessary tests. The adhesive application operation was performed using air-powered dispenser guns by a team of operators that were trained in the field. This application method allowed access into difficult and confined areas. The manufacturer was also able to use varying joint thickness, which also gives workers greater flexibility during the application. The glue has a tensile strength of 21-24 MPa, meaning it is ideal for structured adhesives in many applications which require not only the strength of the joint, but the ability to resist high stress fatigue loads as well.

“The tests we conducted in humid and corrosive conditions, such as saline water or salt spray, demonstrated the acceptability and longevity of these bonding compounds. That the product was endorsed by Lloyds adds another confidence level and was a major factor in the selection process,” said Mark Downer, chief engineer at Griffon Hoverwork, when commenting on the results of the tests.

Selection of an epoxy in an application where dynamic loads are being continually applied is considered to be highly influenced by the mechanical bonding properties, to include shear, peel and compression strengths. Two component epoxy glues are well known as very durable binders with high resistance to ambient conditions. Two component acrylic glues are well known for their resistance to vibrations and shocks. The combination of both technology with cyanoacrylate chemistry has enabled scientists to design versatile structured binders. It is used to ensure high attachment speeds while retaining the longevity of epoxy and the vibration stability of acrylics.

Researchers have tested the durability and the fatigue of adhesive metal-to-metal connections [2]. For the test, a maximum limit of 36 million shear cycles was set. The tests demonstrated that a higher shear resistance does not correspond straightforwardly to a component’s extended service life. Altogether, Structural MMA Adhesives from Henkel had the highest endurance rating, showing high shear strength and enduring long-term shock loads. The lowest performance was found in the 5-minute epoxy. The hybrid adhesives were lacking in their initial bond strength, but generally worked better than high performance epoxy, which is usually regarded as very strong.

In general, the methyl methacrylate (MMA)-based adhesive is quite strong and is the most fatigue resistant of all the glues tested. After millions of loads, this glue retained about 48% of its ultimate strength, while the epoxies only retained 7% of their initial strength. For this reason, this adhesive type is used for joining Avial e-Bikes frame elements made of aircraft aluminum alloys.

Detailed information:
[1] SCIGRIP TRANSFORMS 12000TD HOVERCRAFT ASSEMBLY PROCESS WITH SG230HV STRUCTURAL ADHESIVE – https://compositesuk.co.uk/communication/news/scigrip-transforms-12000td-hovercraft-assembly-process-sg230hv-structural
[2] FATIGUE RESISTANCE OF STRUCTURAL ADHESIVES – https://www.ellsworth.com/insights/white-papers/fatigue-resistance-of-structural-adhesives/