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End-Use Case Study
- Customized Elastomeric Compound Solves Molding Dilemma
They turn heads as quickly as they turn their operators. They quietly and efficiently cover ground with the balance and grace of a ballerina. They are Segway™ Human Transporters (HTs), the world’s first electric, self-balancing transportation device.
Conceived to replace short car trips and as an industrial productivity tool, the Segway HT is quickly becoming recognized for its ability to allow people to safely, quickly, and easily move farther and carry more. Especially useful in large factory and distribution facilities, the Segway HT makes use of an advanced system of electronics and gyroscopes to mimic the balance system of the human body. Riders can concentrate on task completion while the Segway HT takes care of both movement and balance over varied terrain.
Capable of speeds up to 12.5 mph (20 kmph) and operator weights to 250 pounds (113 kg), the Segway HT requires rugged protection for its finely tuned components. The cover over the motors, battery and gyroscopes also functions as a rider platform. Fabricated of aluminum, the platform also incorporates part of the system that detects the presence or absence of a rider. To provide both grip and cushioning, a softer material was desired for overmolding onto the aluminum, creating a mat that provides both comfort and safety.
Mack Molding shot prototypes with a general-purpose thermoplastic elastomer. After adjusting conditions to facilitate encapsulating a large 12 inch x 15 inch (30 cm x 38 cm) section of metal, Mack produced geometrically and cosmetically acceptable parts. It didn’t last. Thom McMahon, business development manager for Mack, noticed a “greenish residue, a kind of blooming effect” on the parts occurring, invariably, after about twenty shots.
Mack approached RTP Company as an alternative material source. An analysis by RTP Company engineers revealed that the flame retardant package was incompatible with the elastomer, and would separate during processing. “Quickly,” McMahon said, “RTP Company was able to customize a material that allowed us to enjoy long production runs with no trace of blooming.”
The RTP Company solution was a RTP 2800 Series polyolfin thermoplastic elastomer compound, optimized for overmolding that met the 55 Shore A hardness, UL V-0 flammability rating, and UV stability requirements. It perfectly matched the custom gray color in the Segway HT specifications as well. The compound features a tear strength of 65 pli (11 kN/m) and tensile elongation of over 400%. Combined, these properties provide a soft but tough and abrasion-resistant surface.
“RTP Company’s experience with the intricacies of flame retardants really paid off. They recognized the problem and solved it, enabling us to go from a puzzling prototype to a smooth production with very little delay. A supplier with that expertise, who is also able to provide the color, processing, and mech-anical performance we needed, is invaluable,” said McMahon.
Segway, LLC manufactures and markets the Segway™ Human Transporter from their headquarters in Manchester, NH. For more information, visit their website at www.segway.com.
Mack Molding Co. is one of the largest custom injection molders in the U.S. They serve medical, industrial, business equipment, and telecommunications markets from 12 locations in Europe and the Americas. For more information, visit their website at www.mack.com.