A Light in the Dark

December 1, 2004
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Araldite® epoxy adhesive-bonded magnetic-force flashlight operates in tough environments

The NightStar magnetic force flashlight provides long-lasting performance, using Araldite 2015 epoxy adhesive-bonded repulsion magnets to support its operation.
A state-of-the-art flashlight, powered by a magnetic charging system rather than batteries, is now being used by soldiers, mariners, miners, outdoor enthusiasts and emergency responders worldwide for reliable lighting in challenging situations. Manufactured by Applied Innovative Technologies Inc., Fort Lupton, CO, the NightStar magnetic force flashlight produces more than 20 minutes of high-brightness light after it is shaken for only 30 seconds. The magnetic charging system uses zinc-plated, rare-earth ceramic magnets that are bonded in either end of a polycarbonate (PC) housing with Araldite®* 2015 structural epoxy adhesive. Supplied by Huntsman Advanced Materials, Los Angeles, the toughened epoxy maintains its bond strength even when exposed to extreme temperatures, shocks and vibration.

Steve Vetorino, vice president and R&D director of Applied Innovative Technologies, says, "As we developed the NightStar flashlight, we tried many different magnet and adhesive combinations. Huntsman's Araldite epoxy adhesive was the only material that provided the required performance. In fact, in shear tests, the ceramic magnets tore apart before bonds broke. The epoxy has the added benefits of being cost effective and easy to handle."

* Araldite is a registered trademark of Huntsman LLC or an affiliate thereof in one or more, but not all, countries.



How NightStar Works

One of the toughest flashlights on the market, NightStar has only one moving part - a high-strength, neodymium charging magnet. When the flashlight is shaken, the charging magnet rebounds between Araldite epoxy adhesive-bonded repulsion magnets, generating electrical energy as it repeatedly passes back-and-forth through a wire coil. The energy in the coil is then stored in a high-energy capacitor that, unlike batteries, is corrosion-resistant, able to operate in extreme hot and cold temperatures, and can be recharged several hundred thousand times. When charged, the capacitor powers a light emitting diode (LED). A specially designed acrylic lens and reflector project light from the LED into a concentrated, uniform beam measuring 12 feet in diameter at a distance of 50 feet. The virtually unbreakable LED has a lifetime of tens of thousands of hours and is available in three colors - bright white, super-bright green or red - to meet the needs of military personnel and hunters.

The flashlight also features a unique switch design that uses an on/off slider containing a magnet in combination with an internal reed switch. When the reed switch is activated, energy from the capacitor flows into the LED. The switch is non-sparking and watertight, permitting the flashlight's use in mines, military installations, and fuel depots where explosive materials are present.

Product Assembly

During assembly, a PC housing is placed in a holding fixture, and a repulsion magnet in another jig, to ensure its precise orientation. Bond surfaces require no pretreatment, but care is taken to handle magnets with gloves to prevent fingerprint contamination. To prepare for bonding, technicians install a 50-ml dual-barrel cartridge containing pre-measured amounts of Araldite 2015 epoxy resin and hardener in a dispensing gun. A static mixing nozzle is added to the cartridge front, adhesive is mixed in the nozzle and technicians apply a small amount of mixed epoxy to magnet surfaces. The housing is then brought down onto the magnet so that it is securely seated in a small pocket in the bottom of the PC tube.

"The magnet is pressed into the housing so that adhesive spreads across the bottom and up around the sides, increasing the bonded surface area for greater strength," Vetorino explains. The Araldite 2015 epoxy adhesive is well suited for this process because its viscosity allows the material to easily flow into and fill gaps.

Technicians follow the same process to bond the second magnet in the top of the flashlight. Flashlight sections then cure at room temperature for about eight hours before moving into final assembly. The cured epoxy has a lap shear strength of 3,150 psi at 77°F (25°C) and maintains its high-bond strength even at elevated temperatures. It also exhibits good peel strength with a roller peel of 25 pli.

"Araldite 2015 epoxy adhesive plays a significant role in the reliable performance of our NightStar flashlight, supporting its use in the most demanding environments and applications," Vetorino says.

For more information on Araldite, contact Huntsman, 500 Huntsman Way, Salt Lake City, UT 84108; phone (801) 584-5700; or visit http://www.huntsman.com .

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