CRUX
LIKE WATER OFF A DUCK'S BAK
Crux is the third generation of Camelbak’s reservoir efforts and we are proud to have been instrumental in the development of both the Crux and the previous generation’s Antidote. The hydration reservoir is Camelbak’s flagship product that originally established the company. Crux is revolutionary for Camelbak in that the cap seal is a thermoplastic elastomer overmolded to the polypropylene substrate cap body; a first for the company.
The Camelbak Crux reservoir cap was full of challenges. Sealing hydration fluids against leakage in hostile environments - whether it be for the avid recreational backpacker at Zion National Park, or for US troops stationed in Afghanistan - is a very difficult task. Couple this with the need to constantly and easily access the fill port for replenishing and the challenge begins.
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SELF-ENERGIZED SEAL
Bertuccelli Design detailed four different sealing profiles for testing that were molded in prototype injection molding tooling. The results of pressure testing revealed two clear candidates, one of which was a self-energized seal. Self-energized seals resemble a tongue profile that seals stronger with more pressure against it. Yet the real beauty of that design in this application is the low force required to screw on and off the cap. The seal itself offers almost no resistance, lacking the stiction created with conventional gasket seal profiles.
OVERMOLD GATING
Unfortunately, the disadvantage of a self-energized seal is that it is very tolerance sensitive and this proved to be maddening as leaks began to develop during further testing. Fortunately, Camelbak is dedicated to thorough scrubbing of new products and after exhaustive analysis we were able to pinpoint the leaks to knits on the sealing surface where the polymer flow fronts come together. Indiscernible by the eye, even under a scope, the knits trapped the smallest amount of air which eventually became leak paths for the water.
By gating the overmold from the outside of the part and clever tunneling inside, out, and back inside again, we were able to direct the TPE polymer flow by:
(1) gating from the outside of the cap and tunneling through the substrate to create the seal...
(2) flowing around the perimeter until the seal knits to itself...
(3) tunneling back to the outside of the cap thus pushing and pulling the trapped air away from the seal and filling the cosmetic ribbon emblazoned with the Camelback logo and finally...
(4) tunneling back inside the center of the cap to a small button of material with no other function than a landing pad for the trapped air and gasses.
This was an amazing effort. Directing trapped air and gasses for a part is unusual at this level of detail. But in this case it was functionally necessary to perform at the expectations for a Camelbak product.