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Adhesives selection is an essential aspect of bike and component assembly. The materials must bond a variety of substrates with dissimilar coefficients of thermal expansion and produce joints strong enough to withstand exposure to vibration, temperature extremes and corrosive substances such as salt spray.
To satisfy these diverse requirements, LP Composites, White Salmon, WA, relies on Araldite 2015 epoxy to build ergonomically improved bar ends, grips and seat posts for mountain and road bikes. Before specifying the high-performance epoxy paste, LP investigated a number of adhesives from different manufacturers. Technicians found that 2015 provided the handling ease and physical properties needed to securely join braided carbon/aramid fiber components to aluminum alloy end-fittings used in bike accessories.
Similarly, Serotta Bicycles, Saratoga Springs, NY, assembles its Ottrott ST custom bikes with toughened epoxy from Huntsman. The adhesive is used to install carbon fiber tubes in polished titanium lugs, producing lightweight bikes that combine speed with comfort and responsiveness.
Serotta has more than 30 years experience in building bikes; LP has been in operation since 1995.
The ProcessBoth bike manufacturers begin with pre-formed components. At LP, carbon and aramid fiber bike accessories are resin transfer molded and then cured. The process provides precise control of composite wall thickness, optimizing strength and flex characteristics for outstanding riding performance. The resulting parts, available in black, natural carbon and hybrid carbon-and-gold braid, are also aesthetically attractive with “high-tech” appeal.
LP President Stu Fisher says, “We’ve come to rely on advanced composites and adhesives to build anatomically designed, extremely tough grips, handle bars and seat posts. The Araldite 2015 epoxy is easy to use because it’s gap filling and sag resistant. It’s also ideal for securely joining the dissimilar materials we use in fabricating bike accessories.” The epoxy attains handling strength after four hours at room temperature and produces joints with lap shear strength of 3,200 psi at room temperature.
At Serotta, carbon fiber tubes and titanium fittings are pre-welded and substrate surfaces are abraded to ensure good adhesion. The epoxy, supplied in dual-barrel cartridges, is mixed and dispensed through a disposable nozzle onto a board. The adhesive is then applied to the metal and composite surfaces using a tongue depressor. Next, carbon fiber tubes are inserted into the metal fittings until fully seated. Excess adhesive is removed, and the bonded frame is cured overnight in the prepared assembly jig.
“We manufacture each bike with a custom-designed geometry using a specially designed fixture that allows us to construct each frame according to pre-established dimensions. The Huntsman epoxy helps us in this process because it is easy to dispense from waste-free 50 mL cartridges and features the needed combination of tough physical characteristics for durable bonding,” says Jason Clark, R&D director at Serotta. Araldite high-performance epoxy is designed for outstanding performance at temperatures from -67 degrees F (55 degrees C) up to 250 degrees F (121 degrees C) and exhibits a room-temperature lap shear strength of 2,500 psi.
“Bicycling is all about movement. Cycling enthusiasts rely on high-performance equipment that will support their continuous motion on a variety of terrains and in changeable weather conditions and temperatures. Composite parts joined with advanced epoxies help us produce bikes that have the power, endurance, speed and comfort our customers demand,” Clark said.