MIG technology is out of date and inefficient, but until the advent of new polymer technology products, the alternatives haven’t been very effective.
A MIG (Metal Inert Gas) welder uses a wire electrode along with shielding gas which are passed to a welding gun, in a “metal to metal” welding operation. This way of joining metals has been used for many years.
Epoxies – slow, rigid and not particularly strong
Epoxy resin adhesives were touted as a solution that would enable you to bond metals without welding. However, they have not lived up to their promise. They are tricky to use, because their two ingredients have to be mixed in exactly the correct proportion, otherwise they fail. They are also slow in curing – up to seven days in some cases. Even after that, their performance can best be described as just about adequate.
Light alloys, for example aluminium, are particularly difficult to join with metal bonding adhesives, because of the high oxide content. Once cured, these bonds can be completely inflexible, which is a drawback given metal’s fluctuating response to temperature changes.
The new world of hybrid polymers
There has recently been a step change in polymer technology, with the advent of the hybrid polymer. This amazing new material combines the advantages of both polyurethane and silicone. The result is a product with very low viscosity. That means it doesn’t need to have solvents, plasticisers or catalysts added to it. It’s a high strength but very flexible adhesive.
The best example is Power Grab ‘N’ Bond, a unique hybrid polymer adhesive for joining metals. It makes an incredibly strong bond, but remains flexible so it doesn’t fail when the two metals move (http://www.ct1ltd.com/en/metal-to-metal-adhesive.html).
It’s not affected by high oxide content and it can bond metal to a range of other materials such as brick, wood and plastic. This will revolutionise fixing applications because it removes the need for drilling.
The good news is that it’s far more environmentally friendly than the old epoxy resins. It contains no solvents, so it’s safer and doesn’t give off the strong smell that is associated with conventional adhesives.
Strong, fast, effective, flexible – it certainly looks like hybrid polymers are going to make a big impact.
Choosing the right metal bonding adhesive
Bonding metal is harder than bonding wood or plastic because metal is usually smooth and non-porous, which is why welding and soldering were traditionally used. Modern adhesives remove the need for heat, making the job safer, and they create strong joints with more even stress distribution, a neater finish, good corrosion resistance and less wasted material. The trade-offs are that surfaces need preparing, some products need time to cure, some cannot cope with extreme temperatures and they can be expensive.
Epoxy adhesives are usually two-part, mixing a resin and hardener, and they produce very strong, durable bonds that resist chemicals and extreme temperatures. Cyanoacrylates dry very quickly and clear, leaving joins barely visible. Polyurethanes are versatile and resist water, heat and chemicals, while silicones stay flexible and handle high temperatures. Acrylics cure quickly and bond metals such as aluminium and steel especially well.
These adhesives are used to join car panels and windscreens, aircraft wings, flooring and tiny electronic components.
Why hybrid polymers outperform epoxy
Epoxy resins were long the main alternative for joining metal, and they have real drawbacks. They must be mixed in exact proportions, which is hard to judge by eye, and some take up to seven days to cure fully. That is impractical for a repair to something used every day. Even then, the joins are not especially strong, and because epoxies are rigid they can crack when metal expands and contracts.
Hybrid polymer adhesives solve many of these problems. They combine a strong adhesive with other ingredients that improve performance, so the bond is both strong and flexible. They can join metal to metal and also metal to wood, plastic, PVC and other materials.
In a bathroom, for example, the same adhesive can seal around a bath, bond wood to aluminium fittings or fix metal to plastic. Glass-friendly versions are ideal for mirrors, because they will not cause the black spots that some adhesives create over time, and many can be used in wet rooms or even underwater.