DN Staff

February 1, 1999

11 Min Read
The rubber band of materials

'Magic' wand collects data

In fairy tales, the Good Fairy waves her magic wand and wishes are granted. In the real world, another wand makes possible almost fairy-tale-like happenings with a helpful assist from elastomers.

Today, radio-frequency identification (RFID) is fast displacing bar-code technology as the magic wand for collecting and tracking data on everything from gas bottles and valves to livestock. The wands prove especially valuable where it may be impossible to get the line-of-sight scan required in traditional bar-code systems.

Instead of using light reflected off printed bar-code labels, RFID uses low-power radio signals to read data stored in a small radio transponder. Since RFID does not require a direct line of sight, tags can be read through nonmetallic materials. This makes the technology ideal for grimy, wet, or harsh environments, especially reading through dirt, grease, and even cement. Moreover, RFID tags have proved virtually impossible to copy, and unlike the case with read-only bar codes, you can change and read data in RFID tags many times over.

An RFID system has two major components--the reader and the tag. The reader performs several functions, one of which is to provide an RF magnetic field that powers the RFID tag. Another is to receive the RF signal from the tag and convert it into a digital signal recognizable by the host computer. The tag contains a coil antenna and an integrated circuit (IC). When a tag enters into a magnetic field produced by the reader, the recovered energy powers the IC, with the memory contents transmitted back to the reader.

The WavePointTM RFID Reader/Writer Wand from Brady Corp. (Milwaukee, WI) testifies to this technology. Scheduled to enter the marketplace early this year, the handheld wand with a tapered nose operates at 125 Hz, and features single-button operation reading or programming of RFID tags. The data it automatically transmits to the host computer manage inventory of equipment, assets, process components, and other valuable property.

Designing the wand took just 12 months from concept to market. The device features a solid housing of polypropylene combined with a Santoprene(R)-based overmolded elastomer specially modified by RTP Co. (Winona, MN). In addition to providing a protective seal from the environment, the elastomer gives the wand a tactile hand grip that makes it easy to use in all types of weather.

"We worked with Injection Technologies Inc. (Cokato, MN) to select the right materials," says Aleks Nikolich, engineering manager at Brady. "They had previous experience with overmolding polypropylene and knew it was chemically inert. That, along with its bondability to elastomers, proved important."

At first, Injection Technologies tried overmolding the polypropylene with a pure, precolored Santoprene. However, the material was too viscous and caused deformities in the rigid plastic part. RTP solved the molding problem by modifying Santoprene for higher flow. "The new material performs much better at lower pressures," Nikolich adds.

The molder conducted several technical conferences with RTP to identify the right base material and what needed to be modified to give the wand the required rigidity. This also included blending in the correct electrostatic dissipative properties to prevent sparking and accidential fires, and also making certain the two materials would bond properly.

The WavePoint could prove to be especially popular with farmers in countries comprising the European Economic Community. "Careful livestock management practices are a must in Europe to prevent the spread of mad cow disease," Nikolich explains. "For everyone's safety, it's critical that cattle raisers and slaughterers can trace their livestock inventory. Imagine how difficult it would be to bar-code cows and pigs, who are frequently covered with mud and grass. RFID helps these producers keep track of animals as they are shipped within or across country borders."

Laser tag scores big with elastomers

You're fighting off aliens with your laser weapon. ZAP, ZZZT, ZAP! Your adrenaline is pumping; your heart is racing. The reason for all the excitement: a high-tech game of "laser tag" at an amusement park that offers the LaserTrek LDD-1 Acrade Game System from Heads Up Technologies (Carrollton, TX).

Chances are you're not thinking about the equipment that makes the game possible while zapping your enemies. However, the game has to be functional, rugged, and fun. Heads Up Technologies says it has found the right combination of strength, impact resistance, looks, and heat resistance in PRISM(R) and Bayflex(R) polyurethane reaction injection molding (RIM) systems from Bayer Corp.'s Polymers Div. (Pittsburgh).

"Players wear a vest, carry a handheld laser gun, and shoot at each other with harmless laser beams to score points," explains Rob Harshaw, CEO of Heads Up. "It's a lot like our old childhood games, but the system is microprocessor-based, and, as an arcade version, has more special effects and capabilities. Instead of playing in a virtual world you're playing in a live world."

Major components of the LaserTrek system--vest, belt extender, and laser pistol--are made for Heads Up by RIM Inc. (Irving, TX). The vest frame measures just more than 11 inches wide, 16 inches long, and half an inch deep; wall thicknesses range from 1/8 to 1/2 inch. Molded in right and left halves, the frame weighs about 4 lb. The belt extender, weighing about half a pound, measures 737 inches and is 3/4 inch deep. Wall thicknesses range from 1/8 to 1/4 inch. Both parts are made with Bayer's Bayflex 110-80 polyurethane RIM system.

The laser pistol consists of two sections produced using Bayer's PRISM system. They weigh about 3 lb and measure 9316 inches. Each 2-inch-deep half has a wall thickness that ranges from 1/16 to 7/8 inch.

"We needed toughness, durability, and heat resistance for the parts," says RIM President Steve Harms. "Yet they had to have a great appearance, as well as strength."

Harms chose the Bayflex system for the vest and belt extender to take advantage of its toughness, durability, and the surface quality it produced. For the laser gun, the need for heat resistance and toughness led to the use of the PRISM solid polyurethane RIM system.

Manufacturing factors also played a key role in the selection of the Bayer products. The challenges: parts with deep recesses and varying wall thicknesses and, for the vest frame in particular, molding to tight tolerance due to mating it with a thermoplastic injection-molded part.

Use of the two systems enabled RIM Inc. to fill cavities, avoid sink marks, and keep short cycle times--about four minutes each for the vest and belt extender and 31/2 minutes for the laser pistol. Equally important, RIM produced the nearly reject-free LaserTrek parts using its existing manufacturing system.

"You're talking about giving the players a laptop to wear, so the vest and the gun had to be strong enough to withstand people dropping the gun, bumping into obstacles, or rolling on the floor," adds Heads Up's Harshaw. "Parks like Universal, Disney, and Paramount say we've got the best-looking equipment out there. In fact, the site we have at Universal Studios in Japan is the highest-grossing attraction in the park--two million people in its first year."

Felt and leather sax pads give way to urethane

By replacing the traditional cup/pad construction on saxophones with a cellular urethane, musician Wolf G. Codera (Markneukirchen, Germany), one of Germany's top 10 saxophone players, added a new level of resonance to this versatile instrument. The switch also reduced maintenance of the closure fixture and keywork.

In traditional saxophones, a felt and leather pad adheres to the underside of the key that closes the tone hole of the instrument. The pad seals the hole when the key is in the closed position. Although felt and leather are soft materials that form a good seal, they absorb some of the sound generated by the instrument. To reduce this effect, saxophone builders stick a small metal disk in the center of the leather to reflect sound back into the saxophone cavity.

Codera reasoned that if the entire underside were metal, the sound quality of the instrument would improve. So, after years of experimentation, he came up with the resoblade(R) system. In this system, the rim portion of the new blade is crimped (see diagram). To date, he has incorporated the design into the five lowest notes (low Bb/B/C#/C/Eb) found on a sax.

Enhancing the design is a ring of cellular urethane 5-mm wide and 1-mm thick inserted into the crimped channel around the metal disk. The material: PORON, supplied by Rogers Corp. (Rogers, CT). The ring seals the tone hole, but does not absorb sound. When the hole closes, the underside of the blade lies flush with the walls of the saxophone cavity, resonating with the rest of the instrument.

"We selected PORON for its sealing properties and its long life," says Michael Hoos, Codera's event coordinator and agent. "In one test, we closed the tone holes and put them under pressure for 14 days. When we opened them, we were amazed to see that there was no impression left on the PORON material. If we had done the same thing with felt and leather, the materials would have been in pieces by the end of the experiment."

Obsessed with making the perfect saxophone, Codera left his medical studies 16 years ago to do materials testing and experiment with instruments construction. Among his other innovations: flat positionable key adapters for interchangeable blades, adjustable palm keys, a ball-in-felt octave mechanism, and a spring-controlled G# bridge. All of these can be found in his new alto and tenor saxophones: the B&S Codera modeld ATR1 and TTRI built by Vogtlaendische Musikinstrumentenfabrik.

An elastomers primer

Scott Koberna, Business Management Group, RTP Co.

How can an elastomeric material expand a company's design opportunities? The following should help any design engineer discover what makes elastomers such a versatile materials:

Q: Why use an elastomer?

A: An elastomer combines the speedy, efficient, and economical processing of a thermoplastic with the functional performance and properties (soft touch, flexibility, and colorability) of thermoset rubber.

Q: Are there other advantages of elastomers over rubber?

A: Rubber processing consists of three steps: mixing, shaping, and vulcanizing. Each step is very capital, labor, and energy intensive. Thermoplastic elastomer (TPE) processing has fewer steps and faster throughput, resulting in lower part costs. Moreover, TPE can be recycled/reground, results in lighter-weight parts, and, through compounding, can be modified to meet demanding structural, conductive, precolored, flame retardant, and wear-resistant needs.

Q: What are some common types of elastomers?

A: Olefinic elastomers (TPVs) are generally a blend of polyolefin (PP or PE) and fully vulcanized rubber having a Shore Hardness of 45A to 50D, excellent chemical and environmental resistance, and good tear strength.

Styrenic (SEBS) materials are low-cost elastomers with a high degree of flexibility. They consist of block copolymers of hard styrene segments with a soft rubber midblock and contain unsaturated or saturated rubbers.

Urethane (TPUR) materials consist of hard segments of urethane and soft segments of either polyester or polyether. Polyester segments feature increased tear strength, abrasion resistance, and toughness. Polyethers have better resilience, low-temperature flexibility, and lower specific gravity.

Q:What are some common applications for TPEs?

A: Elastomers can provide highly conductive/low resistance contact points for switches, grounding straps for shoes/wrists and shoe soles/heels for ESD-sensitive environments. The also can add a soft-touch overmold for garage door openers and keyboards and can produce electrostatic, paintable parts for such applications as airbag door covers.

In the structural arena, elastomers can provide a heavy or light specific gravity material for bumpers, cushions, seals, stoppers, wheels, industrial housings, and float valves.

The flame-retardant properties of elastomers can provide tremendous flexibility to meet UL specifications for strain relief for electrical cords, wiring cable jacketing, and fuel-line covers.

Q: Are elastomers easy to color?

A: All elastomers permit precoloring for critical product color matches. They can even match unusual/new colors, such as metallics, fluorescents, and neons. And they are laser markable for keycaps, appliance knobs, and automotive dash buttons.

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