Laser-Markable Compound Adds Extra Detail

02 July 2004

When designing a new control unit for its adjustable suspension system, SRAM Corp needed to find specialised materials to make the concept a reality.

In the sport of cycling where weight reduction is at a premium, SRAM Corporation, the second largest bicycle component manufacturer in the world, has pioneered the use of injection moulded engineering thermoplastic compounds supplied by custom compounder RTP Company to provide lightweight strength for many of their products.

When designing the new PopLoc control for its RockShox adjustable suspension system, specialised materials were needed to make the concept a reality.

Rather than placing the PopLoc adjustment lever on the suspension system itself, SRAM decided to place it on the handlebar to provide easy access for the rider. The lever includes an integrated readable setting scale that permits the rider to quickly and confidently adjust damping for upcoming terrain and provide a reliable positioning reference.

SRAM chose an RTP 200A Series glass-fibre-reinforced nylon 6 compound for the control lever.

According to finish manager Patrick Brady, SPRAM already knew that the material would meet the project's structural requirements of strength, rigidity, and impact resistance.

He had specified the same material with great success in previous applications. ""This material has served us well in other components and, structurally, we knew it would perform here"", he said. Highly reinforced, the compound exhibits a tensile strength of 165MPa and flexural modulus of 11,713MPa, meeting the needs for strength and rigidity.

A notched Izod value of 214J/m provides the necessary impact resistance. Incorporating the fine gradations of a scale, however, proved a challenging task. Part geometry precluded moulded-in markings, and pad printing lacked the necessary durability.

Laser-marking would be the ideal method, but real success in marking reinforced nylon has been, at best, elusive.

""We were prepared to offer the product without the gradations, if necessary"", said Brady.

RTP Company worked with SRAM to modify the compound to offer improved laser-marking characteristics.

""We've come to depend on RTP Company to meet our structural needs, but what really helped this project evolve was their support capabilities"", Brady said.

Making use of in-house development equipment, RTP Company engineers provided moulded samples with test laser-marking patterns for Brady's review and approval. Brady continued: ""This was all accomplished in a very satisfactory time frame and left no doubt as to the success of the project"".

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