One of the product categories that can be considered to make up the industrial market is those infrastructure products that support the booming electronic and telecommunications industry. This year's SPI Structural Plastics Conference and Design Competition focused on some of these interesting applications.
An eye-catching example from the industrial telecommunications perspective was the award-winning Alcoa Fujikura splice box, molded and submitted by Mack Molding (see opposite page). The part represents a metal-replacement trend in this market that's been under way for several years and is now reaching critical mass.
Unless you've been in a coma for the last five years, you know that the digital revolution is well underway. Baby Bells, AT&T, MCI Worldcom, Sprint, British Telecom, and a host of other mega-companies are positioning themselves to build and cash in on new and improved telephone, cable, and mobile communications networks. These networks have an infrastructure being built by the likes of Lucent, Nortel, and Motorola.
Joel Fouquart, technical manager at GE Plastics, says the Alcoa/Mack splice box is the best example of the trend occurring in the outdoor infrastructure arena. The Alcoa box replaces a diecast aluminum predecessor that weighed 65 lb and was a beast to install. But with a switch to GE's Valox PBT and structural foam molding, Alcoa suddenly had a lighter, equally durable, less expensive box that could be produced in volumes. That, says Fouquart, is the key-producing in high volumes to accommodate the new and improved networks under construction.
Indoors, Fouquart says the central office is the scene of the most changes. Not happy producing simple computer and electronics cabinets and housings, many manufacturers are looking to plastics and injection molding to create a more striking identity, similar to the job Silicon Graphics has done with its standout colors and contours. Fouquart says many OEMs struggle to determine the break-even point between plastic and metal.
The economic advantages of plastics increase with part complexity. Plastics allow designers to incorporate unique features that are often difficult to impossible to produce in sheet metal. GE and Fouquart conducted a study using a standard 6-ft cabinet panel with moderate contours and complexity, and compared the cost of producing it via structural foam vs. metal. The sheet metal, he says, has an initial tooling cost ranging from $10,000 to $90,000, where an injection mold ranges from $100,000 to $275,000.
However, downstream welding and shaping of the metal ballooned the per part cost to $550 for metal compared to $350 for plastic. Not only that, but the break-even volume for the plastic part is 1000 units annually.
The Best Paper winner at the Structural Plastics Conference was written and presented by Michael Caropreso, who, with Hewlett-Packard, devised a system for molding plastic panels to replace a large metal door on a peripheral computer rack system. The metal door H-P was looking to replace cost $40 to make and $150 to ship because of its size, and was often damaged in transit.
The series of smaller plastic panels would prove less expensive to make, and ship, and easier to use for service personnel who need to access cabinets. But what made the project particularly interesting was the rare combination of gas-assist molding and sequential gating.
The panels are 35 inches long and 16 inches wide, with a nominal wall thickness of .140 inch, unpainted and with no visible sink marks or weld lines allowed. Two gates were used in the mold, both fed by a hot manifold system with hydraulic valves.
To establish production parameters, the mold was filled through one gate in a series of short shots that were used to determine the ram position at which the flow front reached the second gate. This position was used to trigger the second valve, which finished filling the part. This overlap in flow fronts rendered weld lines invisible.
Gas filling begins after both gates close. A series of carefully guided gas bubbles help pack out different sections of the panel, provide strength, and eliminate sinks. The entire cycle runs in just over a minute, with no secondary operations. The molder produces the parts at facilities in California and Dublin, Ireland.
|The Freedonia Group (Cleveland) has projected material use for molded products in the industrial market, which it has defined as gears, pinions, valves, fasteners, meter boxes, and other mechanical transmission components. HDPE is still the dominant material, but its use is expected to decline through the early part of the next century. Nylon, on the other hand, is expected to increase 4 percent annually through 2006. Overall growth is expected to be a modest 1.3 percent. Go to www.freedoniagroup.com for more information.
Metal-to-plastic conversion takes the weigh off
Replacing its eight-part diecast aluminum predecessor, this structural foam molded splice box weighs less than half as much and greatly reduced the total part count. The splice box, manufactured for Alcoa Fujikura Ltd. by Mack Molding (Arlington, VT), is mounted on utility poles and buildings and is used to house and protect spliced fiber optic connections.
"An excellent metal replacement application, this splice box previously weighed 65 lb," says Brian Sumpter, new business development director at Mack's southern division. "We've reduced that to 29 lb, which is a tremendous relief to field service personnel who are hoisting these units up telephone poles to install them." The 10-by-30-inch box consists of two primary parts: one is a drawer in which lines are spliced; the other is the enclosure into which the drawer slides (see photo). The drawer accommodates up to 360 fiber splices and up to six individual cables of various types and sizes. The gasketed drawer can be easily opened for periodic maintenance.
Called the Opti-Guard splice box, it's high-pressure structural foam molded of Valox PBT from GE Plastics at Mack Molding's Inman, SC facility. The material was chosen to meet requirements of UV exposure, ballistic resistance, impact resistance of 100 ft-lb or more at -40F, and temperature resistance ranging from -40F to 176F. Also, Alcoa's internal tieoff system resists more than 100 lb of tension per cable.
The part was an award winner at the Structural Plastics '99 Conference and Design Competition, an annual event hosted by the Society of the Plastics Industry.
For more information:
GE Plastics, Pittsfield, MA
Phone: (800) 845-0600; Fax: (800) 433-2925
Rare-earth compound, plastic unite for speedometer part
All the plastic parts you see in this Bitorque speedometer, designed for some models of Harley Davidson motorcycles, are molded by Thomas G. Faria Corp. But the two parts below the speedometer required a special material. Called bobbins, the parts hold a pin that connects to a magnetic source on the back side of the speedometer. That magnetic source emits a varying electrical charge based on how fast the engine is running. The bobbin, connected to the pin and a meter, rotates according to that charge, thus telling the driver the vehicle's speed.
Faria needed a moldable, highly filled, high-temperature polymer that could be insert molded and then magnetized as part of the inner electrical workings of the speedometer. It hired custom compounder Foster Corp. (Dayville, CT), which developed a compound from a nylon and a rare-earth material called ferrite (an iron-based material). Specifics of the material were not released, but according to the molder, the plastic version is equal in quality to the chrome-plated, hand-finished instrument made for other Harley motorcycles.
Faria runs 40 or so injection molding machines ranging from 15 to 200 tons at its Uncasville, CT plant.
For more information:
Foster Corp., Dayville, CT
Phone: (860) 848-9271
Fax: (860) 848-2704
Regenerative pump housing benefits from PPS
Designed to house regenerative pumps for use in soft drink dispensing systems in the U.S. and the U.K., this part is required to withstand up to 30 bar of pressure and must operate in temperatures ranging from -4F to 212F. Chemical resistance is required to withstand periodic purging with cleaners. Good surface hardness and dimensional stability are also required. Chosen to mold the part: 40 percent glass-filled Fortron PPS from Ticona.
The critical component in the housing design is the back plate. Stress analysis conducted during the design phase indicated that unacceptably high stress levels in key areas around the connecting points could cause the part to fail. A new design was submitted in which the overall wall section was increased, ensuring greater strength and dimensional stability, with cored-out sections to minimize material use.
Tests on the new design showed a reduction in strain levels around the connecting points by a factor of three. Tests also predicted that the design would be able to meet the stress requirements as well as maintain the .05 mm flatness required for the pump's impeller. The housings are made in the U.K. by Electromag-Neil, which insert molds the stainless steel threads for connecting pipes.
For more information:
Ticona, Summit, NJ
Phone: (800) 235-2637
Fax: (908) 598-4165
Polypropylene wheel unit endures heavy weight
This four-caster wheel unit, called the Universal Gondola Skate, is designed to facilitate safe and easy movement of heavy, fully loaded shelves during renovation of retail stores. The wheels are placed under the shelves so that during a store's off hours, the shelves can be moved out of the way to make room for renovation and construction. Then, they can be easily rolled back to their place during regular store hours. They are designed to hold up to 2000 lb and reportedly cost up to 50 percent less than comparable products.
The idea was co-developed by Cozza Harris Design (San Diego) and Co-Mack Technology (Vista, CA). Co-Mack molds the part in a structural foam molding process on a 385-ton Battenfeld. Up to 700 wheel units can be produced in a day on the single-cavity mold. The part is made from a 10 percent glass-filled polypropylene from RheTech Inc. that doesn't have to meet tight tolerances, but must offer strength. The casters are purchased out of house and assembled at Co-Mack.
For more information:
Whitmore Lake, MI
Phone: (734) 769-0585
Fax: (734) 769-3565
Tension knob gets lubed with switch to acetal
The knob on the Ovation 2 thermal transfer printer is used to adjust ribbon tension each time a different width label is used. The printer produces labels up to 4 inches wide and is used to make bar codes, tags, and other products. The tension knob is used intermittently, but not continuously. For Orlando-based manufacturer Datamax, this was a problem with the material used previously, which tended to bind up if the knob was not frequently used.
"The binding," says Ken Colonel, director of mechanical engineering at Datamax, "was due to the fact that the knob is a part that is not in constant operation. The lubricated material we previously used would have worked fine had this been the case. Frequent use would have brought the internal lubricants to the surface and allowed for better performance."
For help, Datamax switched to Fulton 441D, a silicone lubricated acetal composite produced by LNP Engineering Plastics. Because of the silicone's limited compatibility with the base acetal material, it migrates to the surface of the tension adjustment knob. The result is a continuous generation of silicone film, which serves as a boundary or lubricant.
For more information:
LNP Engineering Plastics
Phone: (610) 363-4500;
Fax: (610) 363-4749
Encapsulated solenoids endure with PET
Solenoids manufactured by Caterpillar Inc. are designed to operate hydraulic valves on heavy-duty equipment used in construction, mining, and agriculture. The key to the solenoid's durability is the encapsulation, which blocks moisture and insulates the unit from sudden temperature changes.
Previously overmolded with a thermoset or other thermoplastic, the solenoid is now encapsulated with 30 percent glass-filled Rynite PET from DuPont. More durable than previous designs, the encapsulated product meets Caterpillar's standards for resistance to heat, thermal shock, vibration, moisture penetration, fuel, and lubricants. The company rates solenoids for service at ambient temperatures from -40F to 250F. The PET is also used to mold a coil bobbin that is part of the assembly.
John Hoffman, an engineer for Caterpillar, says the new design and the switch to Rynite PET makes the new units less expensive to produce than the ones they replace. Also, the addition of an integrated electrical receptacle into the encapsulation shell saves the cost of an additional part. The solenoids are installed on bulldozers, wheel loaders, motor graders, agricultural tractors, and off-highway mining trucks.
For more information:
DuPont Engineering Polymers
Phone: (800) 441-0575
Fax: (302) 999-2311
TPE rubber used in electrica plugs, connectors
Electrical products maker Leviton Mfg. in Little Neck, NY makes this watertight locking plug and connector assembly for indoor and outdoor industrial electrical applications. Called the Wetguard, the unit is used to connect two flexible cords in order to supply power to electrical appliances, tools, and machines in a safe and simple installation procedure. The guard shields the connection from threatening environmental elements, providing protection from moisture and dust.
Leviton molds the Wetguard with a Capron nylon 6 from AlliedSignal Plastics and overmolds it with a Santoprene thermoplastic elastomer from Advanced Elastomer Systems. Santoprene not only gives a tactile feel, it also provides resistance to harsh environments, insulation, and good part uniformity and sealability. Levitron specified nylon-bondable grades of Santoprene because they chemically bond well with Capron, thus eliminating any possibility for leakage in the area where the two parts meet. The combination also reportedly resists crushing, impact, and abrasion.
The plugs and connectors, which are available in 15A, 20A, and 30A Nema ratings, feature a tongue-and-groove design, meaning when the male and female parts of the plug and connector are put together, it seals itself. It also has a locking indicator that gives the user visual confirmation that a seal has been obtained.
The Wetguard enclosure consists of two parts that are insert injection molded on a 150-ton press in a two-cavity mold. Previously, enclosures for the 15A devices were designed as a two-part assembly, which, according to Leviton, was a slow operation that often provided an unsatisfactory seal.
For more information:
Advanced Elastomer Systems
Phone: (330) 849-5000
Fax: (330) 849-5599
Phone: (201) 455-5010
Fax: (201) 455-3506
Multimeter features one-shot overmolding of TPU resin
Tektronix Inc. wanted to improve the durability of its TX-DMM family of true RMS digital multimeters, and ease the manufacturing process at the same time. Handheld DMMs are the most common of all electrical and electronic test instruments. Tektronix used film insert molding to improve the bezel and display window of the DMM but the back cover presented some design molding challenges.
The back cover, which is injection molded with Bayer's Bayblend FR110 PC/ABS resin, requires three additional parts molded with an elastomer resin: a water-resistant gasket that seals the DMM's electronics from moisture, dust and other elements; a mechanical connection that holds a metal electromagnetic interference shield inside the back cover; and four no-skid pads on the outside of the back cover. Poly-Cast (Tigard, OR), which molds the front and back covers, wanted the three parts to be molded from the same material in just one shot. It chose Bayer's Desmopan KU2-8651 TPU resin, with a 75 Shore A hardness, because it offers good flexibility, resilience, and compression-set properties.
After the Bayblend PC/ABS back covers are molded, Poly-Cast inserts them and an EMI shield into the press. The Desmopan resin is shot onto the back cover through two gates. The resin flows around the lip of the back cover to form a watertight gasket. It then continues through an opening on each side of the part's interior and flows into separate lines over the EMI shield. Finally, the resin flows through openings in the EMI shield and back cover to form four capsule-shaped feet on the outside diameter of the DMM's back cover.
According to Steve Lyford, mechanical engineer for Tektronix, it was less expensive to overmold the parts using this process than to perform a secondary operation by hand. Tektronix had previously used a custom-made gasket, but preferred the overmolding operation even though the mold was tougher to build because the resin has to run a long flow path. The complex mold was built by Bestco of Hillsboro, OR.
For more information:
Bayer Corp., Polymers Div.
Phone: (800) 622-6004
Fax: (412) 777-5585