Appliance Design - January 2008 - (Page 46)

PLASTICS Get the Lead Out Ever since the European Union’s Restriction of Hazardous Substances Directive (RoHS) went into effect in 2006 — with stricter guidelines approaching in 2010 — OEMs have been scrambling for ways to remove banned substances such as lead from their products. Since 2001, Thogus Products, a custom injection molder in Avon Lake, Ohio, has been developing a process to replace lead with tungsten-filled polymers for shielding certain specialized applications. Lead, which can block electromagnetic energy waves, can also block radiation energy. That is why lead is so often used with X-ray and CT scan machines to protect the patient as well as the caregiver. Working with compounder PolyOne of Cleveland, and more recently GE Plastics (now SABIC), Thogus Products has integrated the tungsten material into several plastic materials including Nylons (6, 66, and 12) and certain TPEs and are working to incorporate the material into higher heat resins, says Matthew Hlavin, vice president of sales and marketing for Thogus. Tungsten-filled polymer has the same specific gravity as lead, 11.0 specific gravity, and it shields radiation at the same attenuation, Hlavin says. Thogus has been able to hold tolerances of the injection moldable material to +/- 0.002 in., and has made wall sections of about 1/2-in. thick. The smallest part molded by Thogus has been 20 g and the largest was 26 lbs. The ability to mold the component can reduce the number of overall parts needed, reduce secondary machining operations, and other costs related to making products from lead, according to Hlavin. This helps to offset the additional costs of tungsten. Typically, lead sells for under $1 per pound, whereas tungsten can cost between $30 and $80 per pound depending on purchase quantities, he says. Tungsten is also an abrasive material that will wear on tooling. Hlavin says that because of the toxic nature of lead and the cost of recycling the non-RoHS compliant material out of discarded equipment, the next couple years will see growth in the use of the tungsten based material in finished products. The tungsten-filled polymers can often be directly substituted for lead in applications such as collimators, X-ray tube housings, and other medicalshielding applications. To date, the company has used the technology on more than 50 different applications. One early application was the lining of a collimator for a CT scan machine where a tungsten-filled polymer part replaced an aluminum fabricated housing that was lead. Thogus worked with GE Plastics’ (now SABIC) LNP Thermocomp HSG (high specific gravity) high-density compounds on the collimator for GE Healthcare’s OEC 9800 X-ray machine. Collimators absorb stray radiation and limits X-ray exposure. According to Clare Frissora, market director, Healthcare, GE Plastics, the transition from machined and stamped lead to injection-molded engineering resins enabled tighter tolerance specifications and greater part consistency, enhancing the performance and safety of the X-ray equipment. It also helped avoid secondary operations required with lead. Also, combining multiple components into one part helps reduce manufacturing time, system cost, and complexity, she says. < For more information, enter: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310 Or email: info@thogus .com 46 applianceDESIGN January 2008 Antennas from the Centurion Wireless Technologies company use RTP compounds. ing material to block electrical fields from escaping or entering the barrier from either side. The traditional shield is a fabricated metal barrier, which is considered an effective way to achieve shielding. The downside can be added weight, cost and cycle time to the product. Shielding by dispersing conductive fillers into compounds is an option offered by suppliers such as RTP and SABIC. According to Jiang, moldable plastics with shielding properties can improve cycle times, logistics and overall system cost can be improved when the enclosures are made from inherently shielded thermoplastics. Available EMI shielding thermoplastics fillers include those based on the dispersion of stainless steel fiber, carbon fiber, graphite, nickel-coated carbon fiber, and silver-based additives and other fillers in a thermoplastic. It is the inherent conductivity, volume percentage and dispersion of the shielding additive in the thermoplastic that affects the part's volume conductivity. In inherently shielding thermoplastics the volume conductivity determines the overall shielding effectiveness. Typically, with this technology shielding values ranging from 40 dB to 60 dB can be obtained under far field conditions, which is sufficient for most consumer applications, says Jiang. Carbon filler is often used, especially when color is not important, because of cost. Carbon filler will color most plastic black or grey. While carbon-based polymer additives are cheaper than other fillers, and do provide increased shielding effectiveness, Rupprecht says that carbon cannot compete with the metal and metalized additives. The metal fibers, he says, reflect and shield wave energy better than carbon. Metal fibers also work better than powders and particulates, he says. A metal coating provides a metal skin as a shield for reflecting and absorbing. A metal-additive filled plastic makes use of an internal matrix of overlapping shields to accomplish the reflecting and absorbing actions. This internal matrix is more effectively formed with high aspect-ratio fibers as compared to metal powders or particulates. The lower loading of high aspectratio fibers provides an economic advantage versus higher loadings of low aspect-ration powders and particulates, says Rupprecht. An issue when adding additives to plastics is that some of the material’s properties can be www.applianceDESIGN.com http://www.appliancedesign.com

Table of Contents Feed for the Digital Edition of Appliance Design - January 2008

Appliance Design - January 2008 Contents Editorial Shipments/Forecasts News Watch Makers of Commercial Refrigeration Equipment Turn to Variable-Speed Motors to Improve Energy Efficiency. New Motor Design and Control Scheme Makes Brushless Motors More Economically Feasible for a Wider Range of Applications. External Gas Molding, a Relatively New Technique, Solves Many of the Challenges Associated with the Injection Molding of Large Plastic Parts. Plastic Housings Offer Many Benefits: EMI Protection Isn't One of Them. But, New Materials and Techniques are Solving that Problem. Choosing the Optimal Strategy for Effective EMI Shielding Depends on Both Mechanical and Electrical Requirements Ethernet-Enabled Microcontroller Makes Networking Schemes Easier and More Cost Effective to Implement The Ever-Changing Array of Microcontroller Memory Options Makes it Imperative to Keep Abreast of What's Available to Determine the Optimal Choice for an Application. A Vast Range of Components and Finished Products will be Exhibited at the Country's Preeminent HVAC/R Show, AHR Expo, which is Scheduled for Jan. 22-24 in New York. Advertiser's Index Association Report: PRBA

Appliance Design - January 2008

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