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Sally Sinai of ITW Devcon argues that methacrylate adhesives should be used to perform bonding applications in place of traditional thermal joining or mechanical fastening.

Methacrylate adhesives have been used in a number of industries to bond a variety of metals, plastics, composites and dissimilar substrates for many years, but what are the risks attached and can you be sure of their long-term performance? Devcon has built a blueprint that it uses to minimise risk and maximise the successful outcome of each adhesive project.

Traditional jointing methods are undisputedly well proven.

Having said that, the bonding of metals has now been successfully undertaken for many years.

Thermal joining is relatively low cost, but the two chief disadvantages are that stress is set up in the components (with the resultant risk of corrosion) and that metals can only be joined to metals.

In the case of rivets and other mechanical fastenings, when these are used the substrates have to be drilled and once again there are two down sides – stress is set up around the holes and the aesthetic appearance is compromised due to the protrusion of the fastening.

When adhesives are used, the problem of stress is eliminated, smooth surface contours can be achieved and the finish is aesthetically more pleasing as the surfaces do not discolour.

Weld spatter is avoided and the surface will have no unsightly protrusions.

The bond strength is higher and there is no need to drill holes or specially prepare the substrates.

Adhesives will bond dissimilar materials – like steel to ABS for example – and in most cases without the use of primers.

The process becomes lower cost and the joints can normally be bonded more quickly.

Devcon’s methacrylate adhesives (MMAs) are designed to give exceptional performance.

The products provide tough flexible bonds for aluminium, stainless steel, exotic and coated metals, as well as hard-to-bond plastics, composites and dissimilar substrates.

MMAs offer high load-bonding strength, are tough and flexible, can be rapid curing and are resistant to weather, humidity and wide temperature ranges.

They offer high-tensile, impact, peel and shear strengths, high fatigue resistance and UV resistance, and can be formulated to gap fill.

The exact performance of each MMA is determined at the design and development stage by the formulating chemist and product manager.

The choice of adhesive is dependent upon many factors, especially the customer’s substrates and end-use application.

Consequently, it is important to liaise with your adhesive supplier at an early stage in the project.

The cost of getting the choice of adhesive wrong could be high but, provided your supplier has the required knowledge and formulating expertise, it will take next to no time to select the most appropriate grade of MMA for your application.

The selection depends on several factors, chief of which are substrate type, joint design, production process and in-use durability requirements.

One also has to consider the service temperature encountered by the end user, together with potential exposure to any specific chemicals.

With regard to the user’s production process, we have to take into account the adhesive working time, fixture time, rheology (sag and flow characteristics) and part-handling after assembly.

Three Devcon products in particular have proved to be very popular with a large number of existing customers.

These three adhesives, each with its own unique properties, all offer the combined benefits of epoxy and polyurethane products: Metal Welder I – this two-part MMA product offers the end user the ability to bond ferrous and non-ferrous metals, and other difficult substrates without priming and with only the minimum of surface preparation; Metal Welder II – this is a two-part MMA having a medium fixture time designed for the primerless bonding of dissimilar metals; Devweld 530 is a rapid-curing, multi-purpose, toughened, load-bearing MMA suitable for bonding a range of metals, plastics, ceramics and other difficult substrates.

Devweld 530 was chosen by Birmingham Garage and Industrial Doors (BGID) to bond steel sections into the steel frames used for its security doors.

The company said that the chief reason for selecting Devweld 530 was that it offers excellent load-bearing qualities and exceptional shear, peel and impact strengths while offering a robust bond that can withstand the high temperatures encountered through the powder-coating booth.

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