Forming a bond

The choices of fixing components together are numerous and varied. But while traditional methods such as screws, rivets, latches or spot welds still have a place, engineers are increasingly turning to adhesive bonding when they require a permanent join.

Modern adhesives are classified either by the way they are used or by their chemical type. The strongest ones solidify by a chemical reaction, while less strong types harden through physical change.

Adhesives include: anaerobics that harden when in contact with metal and air is excluded, often used as locking compounds; cyanoacrylates, a special type of acrylic that cures through reaction with moisture held on the surface to be bonded that is suited to small parts and rubber; epoxies, consisting of an epoxy resin plus a hardener that provides strong durable bonds with most materials; polyurethanes that provide strong resilient joints that are resistant to impacts and useful for bonding glass fibre-reinforced plastics; and modified phenolics, the first adhesives for metals which have a history of use for making high-strength metal-to-metal joints.