Joining technology reaches new frontiers

Tom Shelley reports on the latest innovations in fastening and joining

Whether it is by mechanical fasteners, adhesives, or electrical connectors, speed of application and long term reliability are the main goals when joining items together. An extreme example is the need to quickly and cleanly join blood vessels to synthetic grafts during major surgery. Surgeons at Papworth Hospital have come up with a grooved plastic connector which is placed inside the blood vessel. A metal band with lugs on the outside secure it in place. The device is made of tightly woven polyester impregnated with collagen. It is passed over the blood vessel and secured in place, pressing both the graft and blood vessel into the groove. The devices are currently being tested on pig hearts. When fastening sheet metal, Profil (UK) says its range of RSD self piercing nuts are 30% lighter than the company's RND series and provide a flush finish on the outside of the panel. They have a shorter installed length than competitive products, allowing the use of shorter screws and reduced storage space for stacked components. They provide vibration resistant and watertight fixings with a positional accuracy of ±0.2mm in a wide variety of coated and uncoated materials. The alternative is to use adhesives which are continually improving their properties. Master Bond, for example, has brought out formulations both for very low and high temperature use. The company's Supreme 10HTFL is a one component flexible epoxy adhesive/sealant that stays flexible even at very low cryogenic temperature. It can be used over the range 4K to 450K. It has high resistance to severe thermal shock and vibration, and is suited for bonding substrates with wide variations in thermal expansion coefficients. It also has excellent chemical resistance to water, salts, oils and fuels and has unlimited life at room temperature. It cures at temperatures of 120ºC to 150ºC in 45 to 90 minutes. Tensile lap shear strength was more than 13.8MPa when bonding aluminium. For slightly less arduous applications, Tesa UK has introduced three double sided adhesive tapes with closed cell PE foam backing and acrylic adhesive for the permanent mounting of signage, emblems, panels and trims. Working in a different direction, Henkel has brought out two threadlocking adhesives, Loctite 2400 and 2700, which carry no hazard symbols, risk or safety phrases, and contain no declarable carcinogenic, mutagenic or reproductive toxins.