A flip-flopping good time
New color concentrates give plastic parts an intriguing iridescent look. Light reflection, refraction, scat-tering, and transmissions interact and produce different colors when parts are viewed from different angles. The Tek-PEARLite FlipFlop concentrates are formulated for homopolymer polypropylene (PP), clarified PP, polyethylene, transparent poly-styrene and flexible PVC. They are suited for injection or blow molding and conventional extrusion.
Leco Plastics Inc., Hackensack, N.J., extruded decorative belts made from the concentrates. Company president Barry Schwartz says that a resin-to-concentrate ratio of 25:1 gave an extrusion color match that was highly reproducible. Complex geometries yield the most dramatic effects, he notes, especially those with multiple curves, recesses, and sharp angles.
Teknor Color Co., 505 Central Ave., Pawtucket, RI 02861, (401) 725-8000.
The mother-of-pearl brilliance imparted by TekPEARLite concentrates is generated without the use of heavy metals. They are available in red, gold, blue, green, orange, and violet.
New Teflon extends valve life
Conventionally lined Teflon (PTFE) valves in DuPont Dow Elastomers' Pontchartrain plant, La Place, La., were prone to failure when 18°C liquid chloroprene permeated the Teflon lining and made it swell. But new butterfly valves made with Teflon NXT resist absorption of chloroprene and a whole host of other caustic chemicals and extend valve service life by nearly eightfold.
Teflon NXT is said to have higher creep resistance and stiffness than conventional PTFE as well as a smoother surface. In addition, the inherent lubricity of the NXT material lets the valve operate smoothly unlike metal valves which often see their lubricants washed away by chloroprene and other harsh fluids.
Gar-Seal butterfly valves by Garlock Inc., Newtown, Pa., have a minimum seal lining 0.125-in. thick and vary in size from 2 to 42 in.
Information for this article was provided by DuPont Fluoroproducts, Wilmington, Del.
MINIATURE HAND EXTRUDER
The WeldMax miniature hand extruder contains a plasticizing unit, hot-air blower, rod feed, and electronics in one package.
The compact tool from the Swiss firm Leister Process Technologies and distributed in the U.S. by Uneco Systems Inc., Romeoville, Ill., requires no additional booster and weighs only 2.8 kg. PTFE welding shoes and blanks are available for all weld structures. The WeldMax can extrude PE-HD, PE-LD, PP, PPS, PVC-U, and PVDF materials.
Small framed 3,000-ton press packs a big punch
Textron Automotive, Athens, Tenn., fit a 3,000-ton press into floor space designed for a conventional 1,500-ton machine. The new press also helped the manufacturing cell boost line speeds and shrink cycle times, or TAKT times, by nearly 15%. The Milacron Maxima is said to balance cell or operator time with the 61-sec TAKT time requirements and requires no additional work in process when compared to conventional 3,000-ton presses.
The two-platen injection machine produces 1,200 GM instrument panels per day. The material of choice for the
The Maxima two-platten machine from Ferromatic Milacron North America, has a 44 15.75-ft footprint and a height of about 12 ft.
The more-compact 3,000-ton press fits into a manufacturing cell designed for a unit half its tonnage. The machine's two-platen design also helped beat previous cycle times by 15%.
HIGH-VOLUME GASKETING MATERIALS Loctite Corp., Rocky-Hill, Conn., has added four FastGasket materials to its line of high-volume, cured-in-place (CIP), silicone gaskets. All the materials are nonsolvent and applied robotically in precise and consistent beads onto metal, aluminum, ceramic, or plastic flange surfaces. FastGasket 5963 is a gray, one-component material with high fluid and heat resistance for sealing transaxle pans, valve covers, water pumps, radiators, and other parts used in demanding power-train environments. The brown, one-component FastGasket 5964 features low durometer and high elongation for applications in antilock-brake modules, timing-belt covers, and connectors. FastGasket 5965 is a black, one-component, water-resistant foam that doubles in size during microwave cure. The material fills large gaps and provides dampening in plastic housings. The red, two-component 5966 resists fuel on cam covers, fuel injectors, intake manifolds, fuel lines, and other aromatic fuel environments.
GM panel is a 16% glass-filled SMA styrenic. The shot is 8.5 lb and is drawn from a central system/silo and is shot in a short stroke using a direct-acting hydraulic ram. This is said to eliminate the double-platen deflection common to machines that build tonnage through tie rods. The ram's maximum travel is 1.37 in. The Maxima also has a dry-cycle time of 8.1 sec (30-ips clamp speed at 50% stroke).
Milacron Inc., Plastics Technologies, 4165 Halfacre Rd., Batavia, OH 45103, (513) 536-2428.
Bonding low surface energy plastics
Adhesion is a surface phenomenon. A surface's texture, porosity, and flexibility affect the adhesive strength of a plastic joint. Ditto for any contaminants such as mold release agents, plasticizers, or other resin formulations that migrate to the surface.
Surface energy also influences adhesion. It defines the ability of adhesives and pressure-sensitive adhesive (PSA) tapes to "wet out" plastic surfaces to allow adhesion. Surface wet out refers to how well a liquid or viscoelastic solid flows and intimately covers a surface. Maximum adhesion develops when the adhesive or viscoelastic PSA tape thoroughly wets out the surface to be bonded. The greater the wet out, the better the surface coverage and the greater the attractive forces between adhesives and plastic surfaces. Surfaces with high surface energy bond more readily because they are easier to wet with conventional adhesives and tapes than are low-energy surfaces.
Surface energy is a relative phenomenon. To gauge the effects of surface energy on adhesion, one must compare the surface energy of a liquid or viscoelastic solid to that of a solid surface. A liquid or viscoelastic solid possessing a lower surface energy than a solid surface will spontaneously wet out the solid surface.
High surface energy plastics such as ABS and polycarbonate bond well with standard conventional adhesives and tapes possessing lower surface energy (LSE). But wet out becomes a challenge when using these same adhesives and tapes to bond LSE plastics such as polypropylene, TPOs, and polyethylene. Conventional adhesives and tapes can't wet them out properly resulting in minimal contact with the plastic surface and unsatisfactory bonds.
Traditionally, these LSE plastics have been primed, flame treated, or corona treated to raise surface energy and make them more suitable for bonding with conventional tapes and adhesives. As design and production engineers shift to LSE plastics, they need better and more efficient ways of attaching LSE plastics to themselves, metals, or other materials.
NEW ADHESIVES AND TAPES FOR LSE PLASTICS
The most recent advance in adhesive technology allows structural bonding (in excess of 1,000 psi in overlap shear)
of LSE plastics without priming or other pretreatment steps. It is based on a two-part solvent-free acrylic adhesive technology. This room-temper-ature-curing adhesive saves cost, time, oven-curing space, UV lamps, and heaters. It also resists many chemicals, water, humidity, and corrosion.
Another adhesive technology that bonds LSE plastics without pretreatment involves sprayable hot melt adhesives. They combine high heat resistance with high strength and low creep and are pressure sensitive when first applied. These adhesives handle light to medium- weight bonding and can be used in making furniture or transportation interiors manufacturing to bond fabric with polypropylene or polyethylene foams or foam to foam.
Acrylic pressure-sensitive adhesives often provide the best balance of adhesion and performance properties for
3M Scotch-Weld Structural Plastic Adhesive DP-8005 bonds thermoplastic composites such as this hollow railing. The railing is said to be stiffer than most woods.
Surface wetting affects contact area and the degree of adhesion between adhesives and bonding surfaces.
many applications, but generally do not bond to LSE plastics. Historically, some acrylic PSAs have been formulated to bond to LSE plastics. But they've often had to compromise performance at high heat and with chemicals to better wet out the LSE surface. A relatively new acrylic PSA technology now bonds to a wide variety of LSE plastics while maintaining excellent high-temperature and chemical resistance and high-peel strength. This technology is available as an adhesive transfer tape and as a double-coated tape. It works in light to medium-weight bonding applications, as for bonding nameplates to LSE plastic parts or bonding carpet onto polypropylene door panels.
New tape and adhesive technologies that bond to LSE
plastics without a pretreatment step offer increased efficiency, reduced costs, and improved design flexibility to manufacturing operations.
New acrylic PSA suitable for bonding carpeting to unprimed polypropylene door panel.
Information for this article was contributed by Dr. Barry W. Kostyk, 3M Bonding Solutions, St. Paul.
Chile peppers repel pests
There's now a process that molecularly bonds the natural "heat" (capsaicin) of the Habañero chile pepper into plastics, paints, stains, and other rubberized materials. The capsaicin successfully repels a variety of destructive pests including termites, mice, fire ants, and woodpeckers. Researchers at New Mexico Tech, Socorro, N.M., invented the process which is said to be powerful, inexpensive, and provide an effect that remains active for the life of the treated material.
Potential uses include rodent control for fiber optic or traditional cabling runs. Maritime coatings could benefit both freshwater and saltwater vessels. Another possibility is as a termite or woodpecker deterrent for wood products. Other potential pests such as beaver, deer, and gophers find the chile repellent distasteful as well.
MEDD4 LLC, 6542 Prairie Dunes Dr., Houston, TX 77069, (281) 895-7999, fax (281) 895-7788, www.medd4.com
The natural oils of the chile pepper allow capsaicin to be molecularly bonded into various materials. It can be compounded into plastics or included in a coating prior to application.
Real-time composition information via dielectric analyzer
Adielectric analyzer measures solvent, filler, and additive concentrations of polymer resins, compounds, and chemicals. Though aimed at polymer makers, users of lubricants and industrial fluids benefit from the device as well. The Proceptor in-line analyzer also keeps watch over air, water, and contaminant concentrations.
The analyzer measures concentrations of additive and fillers such as alumina, calcium carbonate, silica, clay nanoparticles, and polystyrene microballoons in molten polymers and thermosetting molding compounds. It helps control evaporators by measuring individual concentrations of water and methanol in polymers for flexible printing plates. And it accurately measures air in automotive lubricants.
The Proceptor's sensor is a ceramic ring with electrodes on its inside surface. Electric fields extend into process material which flows through the sensor. The system measures relative permittivity, or dielectric constant, and electrical conductivity over a broad frequency range.
The composition of two component mixtures, with significantly different dielectric constants, can quantitatively be determined using published mixing rules. The system's conductivity mea-
The Proceptor sensor system presents no obstructions to the process flow and includes an easily installed bolt-in housing.
A steel housing contains the dielectric analyzer sensor and facilitates attachment to application equipment and electronics. Standard sensor diameters are 12 and 45 mm (0.5 and
1.77 in.) but up to
300 mm (12 in.) devices are available.
surements are often used to quantify three component mixtures. The system also promptly detects composition changes for materials having more than three independently variable components. The Proceptor in-line analyzer also works with insulating materials having conductivities less than about 0.1 Siemens/m.
The dielectric analyzer measures opaque, abrasive, viscous, and hot materials. It is rugged with no moving parts or flow obstructions, and is drift-free and impervious to vibration.
Chemical ElectroPhysics Co. Inc., 705 Yorklyn Rd., Hockessin, DE 19707, (302) 234-8206.
The cutting edge
Snowboarders now have something that virtually every other sport, including roller skating, has — shock absorbers. The shock sits between the snowboard and the binding and gives not only a smoother ride, but also better edge control. Called Snoshox, it gives these qualities by letting the binding move vertically.
Verton MFX, a polypropylene composite reinforced with long glass fibers, lets the shock absorption system add just over 2 lb to board weight. But the boost in performance makes the added weight a nonissue for many athletes.
Verton MFX composite has a high strength-to-weight ratio and is said to maintain good impact resistance at subzero temperatures.
LNP Engineering Plastics, 475 Creamery Way, Exton, PA 19341, (610) 363-4500, www.lnp.com.
Incline Inc., Portland, Oreg., chose Verton MFX because the long-fiber-reinforced composite was lighter and less expensive than polycarbonate and carbon-fiber-reinforced nylon candidates.
ACRYLIC ATTACHMENT TAPES
Norcryl solid-acrylic attachment tapes from Saint-Gobain Performance Plastics, Wayne, N.J., feature high internal strength and can reduce or replace conventional fasteners, rivets, liquid adhesives, and welds. Norcryl K-2000 is translucent so the tape blends in with the background to maintain product appearance, and K-1000 is clear and nearly invisible once applied. Norcryl comes in thicknesses from 0.01 to 0.06 in. and roll widths from 0.25 to 18 in.
New resins make their debut at NPE 2000
SPEEDING YOUR WAY TO FAST COLOR MATCH
A new family of thermoplastic-metal composites, Polymetals, are poised to replace lead and other high-gravity metallics. Potential uses include radiation shielding for nuclear medicine, medical imaging, and radiation therapy; weighting and ballast applications for industrial machinery, sporting goods, and instrumentation; and nontoxic projectile inserts for small-caliber ammunition.
The high-density composite, called Ecomass, con-A new system lets M.A. Hanna turn a color-matching job around in 24 hr, compared to manual industry-standard methods that often take up to seven days. The system, called Speedecolor, consists of a portable, benchtop spectrophotometer and color-matching software. Repeatable and consistent colorimetric techniques let the customized software search Hanna's database of formulations to get the best color match.
The system builds on expertise gained from the more than 22,000 custom color matches the firm conducts each year. The majority of formulations currently in the database are opaque and nonspecial-effect colors for olefinic, styrenic, and acrylonitrile-butadiene-styrene (ABS) materials. With color data or a fingerprint captured from a sample, the Speedecolor system uses a laptop computer to identify and sort through candidate formulations, while taking into account needed engineering attributes.
The resulting summary includes the nearest color matches with corresponding formulation numbers, data, FDA compliance status, light-and heat-stability data, let-down resins and ratios, and product form (concentrate, dry color, etc.). The technical center in Suwanee, Ga., typically turns around color chip orders in 24 hr.
Air-intake ducts are now made from Forprene, a PP/EPDM TPV. The TPVs were developed in Italy by So.F.teR, but are now available in the U.S. through a joint venture with M.A. Hanna Co.
sists of powdered tungsten dispersed in a thermo-plastic matrix. The composite provides a high level of radiation shielding and dense mass comparable to lead without the negative health effects and environ-mental concerns over toxicity. Currently, eight Eco-mass compounds are commercially available, ranging in specific gravity from 6.0 to 11.0 gm/cc. A special radiation-shielding formulation is said to provide shielding efficiency comparable to lead with approximately only two-thirds the density.
Another resin system crosses the Atlantic after a successful 15-yr run in Europe. Forprene, a thermo-plastic vulcanate (TPV) elastomer, expands M.A. Hanna's Co., Cleveland, portfolio of thermoplastic elastomers (TPEs). The Forprene TPV compounds consist of a polyolefin phase with a cross-linked ethylene-propylene-diene monomer (EPDM) rubber phase dispersed throughout. The TPV has rubberlike properties such as softness, elastic memory, and flexibility, but is melt processible.
The Forprene product line covers a broad hardness range extending from Shore 35A to 60D. Resins are tailored for injection and blow molding, extrusion, and calendering. Special grades are stabilized against heat, copper, and UV degradation, while others are flame resistant, high-flow, and antifogging.
Hanna also debuts a new line of thermally conductive composites under the Edgetek family of high-performance compounds. Called Therma-tech they sport a high coefficient of thermal conductivity and target thermal management applications. Custom-molded
Speedecolor matching system searches through an extensive color formulation database for an equivalent hue and displays the formulation number and other necessary data to make a good color match for plastic parts.
heat sinks on circuit boards, and innovative heat exchangers in appliances, telecommunication devices, business machines, and other related industrial equipment are possible.
The easily recyclable compounds are designed to replace metal and nonrecyclable metallized plastics in shrouds, heat sinks, thermostats, heat exchangers, and radiant heating coils. Thermal qualities are said to rival those of commonly used metals such as steel, tin, and aluminum. Other formulations combine both thermal and electrical conductivity, permitting both heat dissipation and electrical management in a single part.
M.A. Hanna Co., 200 Public Square, Suite 36-5000, Cleveland, OH 44114,
(216) 589-4000, www.mahanna.com.
Flexible thermoplastic bearings
Thermoplastic rolling-element bearings are flexible enough to let pulleys, rollers, precision gears, and fixing clips integrate into the bearing races. Most of the bearings from Sarnatech BNL (USA) Inc., Foxboro, Mass., are POM (acetal), a semicrystalline material that forms a thin surface layer of ultrafine crystals when injection molded. Bearings can be manufactured with up to 150-mm OD. The bearings target applications needing high speed and precise motion control.
Specifying elastomer footpads
Footpads had their origins in the 1920s when felt on the feet of furniture kept scuff marks off wooden floors. Later, rubber pads on telephones helped eliminate mars on desktops. Custom-blended urethane materials dominate the footpad market today, with molded solid urethane with an adhesive backing top-ping the list. More recently, diecut footpads made from cellular urethane materials offer designers a new option.
Selection of these cellular or foam footpads relies on factors which include footpad loading, thickness requirements, whether the device will be stationary or slide around, and the level of material "cleanliness" the application demands.
STEP ONE: DETERMINING APPLICATION PARAMETERS
The performance of a footpad depends on loading, compression, material properties such as density, firmness, and pad thickness.
Fortunately, these properties interrelate and are captured on load-compression graphs. Three different grades of Poron cellular urethane help illustrate the selection process. As a hypothetical example, a 20-lb computer monitor needs four circular footpads in
1 /16-in. recesses on the monitor base. Each 1-in.-diameter pad has an area of 0.785 sq in. and experiences a force of 6.4 psi.
First examine load-compression graphs at 25% deflection or strain. Deflection of 25% is considered the standard because urethane at this compression level provides its best protection, maximum longevity, and vibration damping. At the juncture on each graph where 6.4 psi stress meets 25% strain the material stress/strain curve that comes closest to the intersection is Poron 470-40.
Second, a pad thickness must compensate for 25% compression plus the
1 /16-in. recess. Obviously the selection hinges on getting a pad thick enough to accommodate the recess when compressed.
The Poron cellular urethanes don't take a permanent compression set under load and retain over 90% of their original thickness when tested under ASTM D3574 guidelines at room temperature. It is important to note however, that compression set test methods for foams don't apply to solid elastomers. Solid materials deform or creep over time and often take on a permanent compression set. They also don't compress as much as foam, often reaching only an upper limit of 15% of their total thickness.
STEP TWO: "SLIP" OR "GRIP"
Material gripping power is described by coefficient of friction. COF is a measure of the relative difficulty
Compressive load-deflection cures help designers select the best footpad for their application.
with which the surface of one material will slide over another. High COF denotes a better grip.
It is always best to consult with your materials supplier when selecting the COF of a material. However, you can use the following rule of thumb: if the application sees occasional use, such as a kitchen appliance or a battery charger, select a material with a coefficient of friction of 0.4 or less. In cases where the device should remain stationary, select a COF of 1.0 or greater.
STEP THREE: FOOTPAD CLEANLINESS
Many elastomers contain plasticizers for better flexibility at low temperatures. Often, these plasticizers over time migrate to the surface. Stains, contamination, and even surface corrosion may arise depending on plasticizer formulation. Poron polyurethanes contain no plasticizers and re-main flexible to 40°F.
Information for this article was provided by Fred Seidel, Applications Engineer, Rogers Corp., One Technology Dr., Rogers, CT, 06263 (860) 774-9605.
NEW RESIN BRINGS 15-GBYTE OPTICAL DISC
Polycyclohexylethylene (PCHE) resin will make possible 15-Gbyte data densities for next-generation optical media. The new resin is said to have higher light transmittance with lower birefringence, water absorption, melt viscosity, and specific gravity than traditional polycarbonates. The refractive index of PCHE is 1.51 and its light transition spreads across a full spectrum, extending down to the ultraviolet range of 300 nm.
The 300-nm transmittance range lets next-generation, high-density optical media technologies switch from red lasers to much shorter wavelengths — violet, blue, and green. The shorter wavelengths can read more densely spread pits on the disc surface. PCHE layers are ultimately expected to surpass the 15-Gbyte capacity obtained by U.K.based Plasmon Data Systems Ltd. during molding trials.
PCHE also has low inherent moisture, less than 0.01%; an important factor in maintaining extreme flatness during disc manufacturing. The new resin may help thwart disc piracy as well. Materials currently used to replicate optical media are often unmonitored. MediaShield, Dow Plastic's PCHE/anitpiracy program, involves creating an independent legal entity to track the PCHE supply and secure its use for legitimate replication only.
Dow Plastics, Box 1206, Midland, MI 48674, (800) 441-4369, www.dow.com.
Poron cellular urethane goes into footpads, crash stops, or bumpers for electronic equipment, household appliances, and kitchen cabinetry. The material will not stain surfaces it touches.
HDPE MILK BOTTLE WORKS LIKE A PITCHER Uniloy Milacron, Manchester, Mich., offers a pour-friendly HDPE milk jug with an off-center neck and handle that replicates a pitcher's balance for easier handling and control.
The jug can be produced with neck finishes that meet dairy-industry standards and incurs no cycle-time penalty on standard reciprocating blow-molding machines. Sizes are available from 2 to 5 liters.
New carbon fibers from petroleum
Houston. . . . Conoco Inc. has developed a new pitch-based carbon fiber for use in plastics, carbon composites, carbon-carbon systems, batteries, and cement structures. The material is intended for automobiles, telecommunications, electrical systems, and construction material. Twelve years in the making, the carbon fiber will be manufactured using several Conoco carbon-upgrading processes. Carbon upgrading takes lower-value feedstocks and engineers them into higher-value products such as lubricants, specialty graphite, and now, carbon fibers.
Other types of carbon fibers such as Rayon and PAN (polyacrylonitrile) are made from higher-cost chemical intermediaries — primary polymers. Others are made from isotropic pitch that comes from lower-cost petroleum or coal-tar feedstocks. In the past, more economical isotropic pitch fibers did not provide a sufficiently broad range of properties.
The Conoco carbon fiber is made from a higher performing petroleum pitch called mesophase. The word "mesophase" means liquid crystal. The ordered, molecular liquid-crystal structure, fossilized in fiber form, is said to yield fibers with higher performance than isotropic pitch.
Much the way different grades of steel perform depending on structure and
New pitch-based carbon fibers are said to have higher modulus or stiffness than conventional carbon fibers.
heat treatment, pitch and PAN carbon fibers have properties that suit different applications. The most common carbon-fiber type is PAN. It is primarily for structural reinforcement because of its high tensile strength. Mesophase pitch fibers, on the other hand, offer designers a different profile. They are easily customized to meet specific applications. They often have a higher modulus, or stiffness than conventional PAN fibers, are intrinsically more pure electrochemically, and have higher ionic intercalation. Mesophase pitch fibers also are said to possess higher thermal and electrical conductivity, and different friction properties.
Conoco Carbon Fibers, Box 2197, Houston, TX 77252, (281) 293-4002, ww.carbonfiber.conoco.com.
SINGLE-SIDED BLOW-MOLDING MACHINE
The H-111S is a single-sided blow-molding machine from Bekum America Corp., Williamston, Mich. The machine features a compact footprint, integrated control cabinet, and a smooth barrel-extrusion system for material flexibility. It can produce up to a 3-liter container with single-cavity molds and up to 1 liter in two cavities. Three cavities are possible for smaller bottles.
The right plastic for rotationally molded designs
Theoretically, any plastic material is rotationally moldable. But candidate plastics must meet two primary requirements. First, the plastic must flow well enough to evenly coat the cavity of the rotating mold. Second, the materials must be thermally stable at the oven temperature and corresponding cycle time.
Most plastics for rotational molding are special formulations. They include both thermoplastics and thermosets. Thermoplastics melt or soften and flow when heated, then harden during cooling. Thermosets cross link or cure when heated and can't be remelted. Rotationally moldable plastics generally need high flow, superior thermal stability, and narrow molecular weight distributions for the best physical properties. Most bulk resins typically melt at a rate between 3 and 10 gm/10 min. Engineered resins are the exception. Their melt rates span both above and below this range. Most resins for rotational molding are fine powders, 35 mesh, instead of more typical liquid or micropellet forms.
Key physical properties are melt index, molecular weight distribution (MWD), and density. Gloss improves as melt index rises, but is accompanied by drops in heat resistance, breaking tensile strength, and low-temperature impact. Resins with a narrow MWD have better physical properties and processibility. Stiffness, heat-deflection temperature, warpage, and shrinkage all generally increase with material density.
LLDPE (linear low-density polyethylene) — The most widely used material for rotational molding. Its stiffness ranges from flexible to medium and it has high resistance to impacts, chemicals, and environmental stress cracking. LLDPE is easy to process and commonly available with UV stabilizers. Most grades meet FDA, USDA, NSF, and UL ratings. It is most widely used for tanks, containers, toys, and playground equipment.
HDPE (high-density polyethylene) — These are the stiffest of all polyethylenes. They have good chemical and impact resistance, are easy to
Pawnee Rotational Molding Co. L.P., Maple Plain, Minn., simplified the Panda 6080 Power Sweeper Frame design by converting 120 steel parts to a single rotationally molded unit made from LLDPE. The weight of the frame dropped from 100 to only 45 lb.
ARM UPCOMING EVENTS Association of Rotational Molders (ARM) Design seminars: July 10-12 — Hands-on advanced seminar in rotational molding. Equistar Chemicals LP, Cincinnati.
August 21-22 — Design seminar for rotational molding. Hyatt Regency on Capital Hill, Washington, D.C. October 13-14 — Design seminar for rotational molding. Hyatt Regency, Atlanta.
October 15-17 — 25th annual Fall meeting. Hyatt Regency, Atlanta.
process, and most are available with UV stabilizers. As a whole, they meet FDA, USDA, NSF, and UL standards. Applications for HDPEs include tanks, ducting, and parts needing maximum rigidity.
XLPE (cross-linked polyethylene) — XLPE resins contain a cross-linking agent which reacts with the material during molding. They exhibit a cross-linked molecular structure similar to that in thermoset resins. Properly cross-linked resins provide good impact, environmental stress crack resistance, and weatherability. They also stand up well to the cold. Common applications include gas and oil storage, trash containers, as well as parts requiring minimum toughness. However, most XLPEs don't meet FDA, USDA, or NSF requirements.
Ducting junction boxes used underground are now made with 50% postconsumer regrind material. Manufactured by Rototek Ltd. in the U.K., the boxes are used for street lighting, traffic signals, telephone cables, and cable television junctions.
Flame-retardant additives help PEs pass the stringent UL vertical burn test.
PE parts can also mold in a one-step process that produces an outer skin of PE and a foam-filled core, thanks to foaming or blowing agents compounded into pellets and used in conjunction with powder. Flotation, insulation, and sound-reducing parts benefit from this system.
Chemical modification of PE lets the material bond to metal and other polymer systems. Commonly known as rotolining resins, they provide corrosion and chemical resistance to metal vessels. Rotolining resins also serve as a bonding or tie layer when two dissimilar resins are joined in a process called corotational molding.
PVC compounds come in either liquid or powder form. The liquid plastisols are fluid suspensions of fine-particle resins in a plasticizing liquid. PVCs are moderate in cost and easy to process. Different formulations produce parts ranging from flexible to semi-rigid. Durometer of these resins vary from 60 Shore A to 65 Shore D. Balls, doll heads, teething rings, and flexible bellows are typically PVC.
NYLON Type 6 — Good stiffness, tensile, and impact strength as well as high heat resistance are common traits of nylon 6. The moderately priced resins offer good chemical resistance and are used for military fuel tanks, hydraulic oil and solvent containers, grain buckets, and air ducts.
Type 12 — Moisture absorption, melting point, and mechanical properties are lower than nylon 6, but nylon 12 is more easily processed. Applications include heating and air conditioning ducts along with gasoline and chemical tanks.
PCs are said to have the highest impact strength of all rigid plastics. In addition, they have good mechanical properties such as stiffness, tensile strength, and creep resistance. They also mold clear. Applications needing high heat resistance and toughness are good candidates for these resins. Examples include light fixture globes, snowmobile hoods, and shipping containers.
Generally PP materials are stiffer than most PEs and have higher heat-distortion temperature. They also have good environmental stress crack resistance and are autoclavable. But, PP powder must be ground cryogeni-
cally which may boost price. Biochemical vessels, solar panels, and medical storage containers are common applications.
Pressure from environmental groups, both government and private, is leading some rotational molders to use postconsumer resins (PCR).
Most commercially available PCRs come from HDPE blow-molded containers. These HDPE PCRs have a much lower melt index than typical rotational molding resins. It is common practice, therefore, to blend 10 to 20% PCR with virgin resin.
How these PCR/virgin resins are blended will affect the inner surface of the part. Parts rotationally molded from dry blends may have rough inner surfaces.
Parts from HDPE PCR/virgin resin extrusion blends exhibit smooth inner surfaces. Color of PCR/virgin resins is dictated by the recycled HDPE and is either off-white, slightly tinted green, or gray with black specks.
Compared to virgin LLDPE resin, the toughness of
HDPE PCR/virgin resin blends is much lower, dropping as HDPE PCR content increases.
The Invinca road sign rotationally molded by Rototek Ltd., Newark, England, features a patented process that produces a one-piece seamless part from two different colored resins, HDPE and LLDPE
Association of Rotational Molders, 2000 Spring Rd., Suite 511, Oak Brook, IL 60523, (630) 571-0611, fax: (630) 571-0616, www.rotomolding.org
Dip-molded tabs have more to grab
Harman Corp., Rochester, Mich., has added grab tabs to its line of dip-molded tabs for industrial applications. The grab tabs feature additional surface area for more grab-and-pull strength, and the ergonomic finger-tab version provides comfort for continuous-removal and installation processes. The grab tabs come in diameters from 0.215 to 1.25 in. and lengths from 0.25 to 2 in. Lengths can be adjusted in 0.0625-in. increments. The tabs are said to be a timesaver for thread protectors, masks during painting, shipping caps, dust caps, and other applications that protect parts from unwanted substances.
New resins target specific needs
Suppliers of engineered materials are increasingly working directly with customers to develop products that meet specific needs. Rather than seeking a onesize-fits-all solution, resin manufacturers are tailoring materials to the exact application with the goal of increasing performance and processing efficiency while lowering costs.
For instance, DuPont, Wilmington, Del., is introducing a number of new resins at NPE 2000 to give its customers a competitive edge in both existing and new products. These new offerings target a range of industries, including automotive, electronics, office automation, and recreation equipment. Here's a quick overview:
Replacing metal. New Zytel HTN resins, for example, have been developed to replace metal structural parts. Zytel HTN is a high-performance polyamide with low moisture absorption, compared with nylon 66 and 6. Thus, moisture and humidity have little effect on properties and dimensions. It also maintains mechanical integrity at significantly higher temperatures than standard nylons.
One area DuPont is targeting with the new Zytel HTN 53G and 54G resins is structural components for automotive power trains, chassis, and interiors, such as pedal boxes, reinforcement brackets and plates, dashboard frames, and seat parts. Similar applications are envisioned in industrial equipment.
The new resins, containing 50% glass-fiber reinforcement, combine strength, stiffness, and toughness at high temperatures. At 100°C, the 54G resin has a tensile modulus of 11.5 GPa and elongation of about 3%. Zytel 53G is stronger and stiffer at ambient temperatures, although it loses more strength and stiffness at high temperatures, compared to 54G.
Precision parts. The company is also developing new applications for Zenite LCP, a family of glass-and-mineral reinforced liquid-crystal-polymer resins used for injection molding precision parts. They combine high-temperature performance with excellent dimensional stability, chemical resistance, and flame-retardant properties without additives.
It is suitable for parts as thin as 0.015 in. and can be molded in long, thin sections. Zenite LCP is currently used
for electrical and electronic components, fiber-optic connectors, and film guides for laser and inkjet printers. Under development are lighting components, ignition parts and blow-molded ducting for automotive engines, and extruded structures such as fuel tanks. In the latter case, LCP serves as the barrier in a multilayer structure with other thermoplastics. Such constructions block fuel permeation while lowering costs.
Electronic shielding. To meet growing needs for
EMI/RFI shielded housings, DuPont is introducing new conductive grades of
Zytel DMX modified nylon resins. They combine built-in shielding with good flow characteristics, dimensional stability, toughness, and strength, providing design flexibility for housings of laptops, hard drives, and other electronic devices. Compared with the magnesium housings used for many cell phones, for example, Zytel DMX parts reduce molding costs and eliminate painting. They can mold housings with 0.05-in. walls, providing parts thinner than possible with conductive grades of polycarbonate/ABS alloys while maintaining strength, toughness, and shielding.
Conductive Zytel DMX is formulated with various types of carbon fibers that provide both conductivity and reinforcement. The modified-nylon polymer matrix absorbs less moisture and has better dimensional stability in humid conditions than standard nylon 66 or 6 resins.
A number of developmental grades of Zytel DMX offer different combinations of conductivity, attenuation, flame-retardant and mechanical properties. EMI shielding values range from 25 to 75 dB tested at frequencies into the 4-GHz range.
Static dissipation. Auto manufacturers are considering a move to antistatic plastics in fuel systems to reduce
Zenite LCP resin is used in miniature balun connectors for digital transmission lines.
corrosion, improve fire safety by dissipating electrostatic charges, and help avoid radio interference caused by static buildup.
New grades of Delrin acetal and Zytel nylon resins contain conductive fillers or other proprietary ingredients to provide sufficient conductivity for static dissipation. Each is tailored to meet specific needs. For instance, one Zytel grade is engineered for fuel-line fasteners, tank caps, and other parts that require good toughness. A new grade of Delrin has been developed for parts submerged in fuel, and another with good toughness for parts like fuel modules and filler pockets.
Tougher gears. Two new grades of Delrin acetal resin are said to extend gear life. One is tailored for printers and other office machines. In lifetime tests, spur gears made of the new material lasted at least 15% longer than two other low-wear grades of Delrin. The resin also features excellent dimensional stability with low shrinkage and low post-molding shrinkage. This allows gears to be molded within a narrow tolerance range and maintain dimensions throughout assembly and their useful life. The resin features low wear and friction without PTFE, so molders avoid productivity and tool-maintenance problems associated with PTFE plate-out.
Another new Delrin grade promises longer life for highly loaded gears. Applications include gears in small automotive electric motors for window lifts, seat adjusters, and windshield
wipers, for example. A key factor is that the resin achieves a uniformly high level of crystallization on all surfaces of the gear teeth. Operating temperatures are 5 to 10°C higher than general-purpose Delrin.
Parts that shine. DuPont is adding new Surlyn Reflection Series supergloss molding alloys to broaden performance, ease processing, and improve color. The bright, colorful alloys eliminate the need to paint thermo-plastic parts, which reduces costs. The tough, high-gloss material is used in automotive fascia, ice-skate boots, snowmobile hoods, and motorcycle body parts. One new formulation improves scratch and mar resistance, making it suitable for indoor appliances. A new higher melt-flow grade processes at lower temperatures so mold cavities fill more easily with less flashing.
Information for this story was provided by DuPont Engineered Polymers. For more information, call (800) 441-0575 or visit www.dupont.com/enggpolymers.
New Zytel HTN resins feature good stiffness and toughness at elevated temperature.
Mmm mmm good
A temperature-sensing infant spoon changes color when food is too hot. The bowl of the spoon is formed by a multishot injection-molding process using thermoplastic elastomers (TPEs) overmolded onto a polypropylene handle. Special additives blended into the TPE, called Dynaflex, give the spoon bowl its heat sensitivity.
The resin is said to have good optical clarity which makes it easy to color the spoon into its dark, vibrant hues. The TPE used by the molder Questech International Inc., Tampa, Fla., has a hardness of 40 Shore A and is said to contain no harmful additives, plasticizers, or carcinogens sometimes found in other infant products made from latex or PVC.
GLS Corp., 833 Ridgeview Dr., McHenry, IL 60050, (815) 385-8500.
The infant "Too Hot" Spoon turns color when food is dangerously hot. The colored bowl of the spoon made from a temperature-sensing TPE comes in red, blue, raspberry, and teal. The soft and flexible TPE also gives added safety during feeding time.
BONDING TECHNIQUE YIELDS INTRICATE MANIFOLDS Eastern Plastics Inc. (EPI), Bristol, Conn., offers diffusion-bonded Ultem manifolds that withstand harsh chemicals, high temperatures, and other stresses. Diffusion bonding creates complex, close-tolerance, three-dimensional fluid manifolds without using adhesives, solvents, ultrasound, or vibration. Flat layers are fused together with a combination of heat, time, and pressure. The clean process produces clear, obstruction-free internal tracks, chambers, and other features.
Ultem is a polyetherimide, and multilayer Ultem manifolds can be used where metal and other materials are incompatible.
MODELING AND MACHINING SOFTWARE
New features on Mastercam Version 8 from CNC Software Inc., Tolland, Conn., include full toolpath/geometry associativity, better surface control and solid machining, and high-speed motion control. Full associativity is said to simplify programming and changes to milling operations including pocketing, contouring, drilling, multisurface roughing and finishing, and multiaxis machining. Geometry and toolpath are linked so one mouse click updates a toolpath to reflect changes to the model or tooling. Users can drag and drop parameters, toolpaths, and tool definitions from one operation to another, as well as create a library of common operations to apply to new models. The software has methods for running standard toolpaths in high-speed format and toolpaths specifically for high-speed machines.
MIXHEAD FOR SPRAYING POLYURETHANE The MiniRim Spray Head is a recirculating mixhead for spraying polyurethane in RIM applications. The mixhead from Gusmer-Admiral Inc., Akron, Ohio, is self-cleaning and specifically designed for open pour. The nozzle mechanism eliminates mixed urethane resins from the chamber and cavity automatically, reducing waste and shortening cycle times. The spray head disperses the foam material in a fan pattern that can be widened or shortened.
HEAT-TRANSFER LABELS FOR AUTOMOBILE INTERIORS HeatSeal is a printed film that combines patent-pending materials and processes to produce warning and information labels. The film from the Industrial Products Div. of Avery Dennison Corp., Strongsville, Ohio, is recommended for interior labeling as on automotive visors and other fabric-coated surfaces. It consists of three layers: a clear PET liner, printed HeatSeal film layer, and heat-activated adhesive bottom layer that provides a permanent bond.
HIGH-PRESSURE IMPINGEMENT MIXING MACHINE The Micro-Innovator from Linden/EMB, Cuyahoga Falls, Ohio, is a high-pressure impingement mixing machine that replaces solvent flushing typically associated with equipment operating at low flow rates. The environmentally friendly machine has closed-loop flow control and throughput range from 10 to 100 gm/sec.
ULTRAHIGH-SPEED COMPOUNDING SYSTEM
The Gelimat Compounder from Draiswerke Inc., Mahwah, N.J., is an ultrahigh-speed thermokinetic mixing, fluxing, and compounding system for processing virgin and recycled polymers, as well as highly loaded compounds and masterbatches. An electronic temperature sensor automatically ejects compounded material through a dis-charge door. The ejected material is fed into a melt pump, short-barrel extruder, calender, molding system, or other stamping device. Users can change process parameters with a touch of a finger, and the process control logs and graphically displays the parameters as they occur. Systems are available from laboratory to large-scale production sizes.