Fasteners and Sealing
Fig. 3. Figs. 3, 4 and 5. Shear, peel and cleavage forces.
selecting the adhesive that will deliver the best performance for that particular construction.
Adhesive technologies
Compared with traditional assembly methods, adhesive bonds are superior in the presence of dynamic stress, thanks above all to their flexible nature. Rivets or bolts can only transmit forces over a very localised area (point loads), whereas in an adhesive bond, the stress distribution or force transmission is spread over the entire area of the bond. The low heat build-up is another key criterion when
joining parts that already have their final surface finish, for example chrome-plated steel. As non-conducting materials, cured adhesives also have an insulating effect, thus preventing contact corrosion. The substrates involved and the demands made on the final construction are deciding factors when selecting the adhesive to be used. Depending on the field of application, various adhesive technologies with specific product properties are available for structural bonding.
Epoxies
The most widespread class of adhesives used for structural bonding are the epoxies. They are found in automotive and aircraft manufacturing as well as in the building and
construction industry. Their big advantage is that they can bond both metals and plastics. Moreover, they are extremely durable, show a low tendency to creep, and only minimal shrinkage on curing. Depending on the type, they can withstand continuous
exposure to temperatures ranging up to 100–200˚C. A further advantage is their very good chemical resistance, although they are generally rigid. Epoxy adhesives offer a broad potlife range of five minutes up to two hours. A long potlife can be an advantage when the parts to be joined require some time to manoeuvre or when they have to be repositioned after they have been assembled. Epoxies are available as one-part or two-part systems. In
one-part systems, the resin and hardener components are already mixed in the correct ratio during production and only begin to react with each other when exposed to heat. Two-part systems consist of separate resin and hardener components which are only mixed directly before application. When using two-part systems, it should be remembered that the chemical curing reaction begins immediately after mixing.
Polyurethanes
Polyurethane adhesives are also available as one-part or two-part systems. They come in a large variety of viscosities,
Nut designed for use in applications with a minimum sheet thickness of 1mm
T
R Fastenings is to introduce the new K-Series nut, a versatile product which can be used for sheet steel and some plastic applications too thin to be tapped by conventional methods. The K-Series nut has been specially designed for use in applications with a minimum sheet thickness of 1mm. The nut, which offers a permanent female thread, can be installed
36
www.engineerlive.com resistance.
K-Series nuts are manufactured in a case hardened carbon steel, plated and tested to ISO898, stainless steel can be supplied to order. Sizes range from M2.5-M16, with three different spigot lengths, the body of the product is hexagon with a serrated spigot. ●
without the need for specialist tooling. Once fixed, the product offers a permanent thread with a high prevailing torque and pullout
For more information, visit
www.trfastenings.com
Fig. 4.
Fig. 5.
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