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New grades of blow moldable nylon 6 from Lanxess and high-impact acetal from Ticona are offered as monolayer solutions for low-permeability fuel tanks for nonautomotive applications. (Photo: Ticona)
Parison-spreader device from Kautex stretches a tubular parison to produce large, flat parts with improved wall thickness. The part is clamped by the mold inboard of the spreader pins, and flying knives outside the mold slit the parison to free the pins for the next cycle. This device is used by Suncast to make four panels of a garden storage box in one cycle.
New tooling from Dr. Heinz Gross uses a simple, precise, and digitally repeatable tilting die to vary wall thickness in complex parts.
GWDS pin from Dr. Gross has a cylindrical instead of conical profile and an area shaved off to locally alter parison thickness.
Hesta’s HMD 310E is an all-electric shuttle machine for products up to 2.5L. The company will introduce an HE model for up to 5L containers at the K 2013 show in Germany next year.
New barrier materials for small fuel tanks, tooling developments for large, flat, and odd-shaped industrial parts, new all-electric machines for large containers, and gravimetric extrusion control for bottles are some of the topics discussed at the recent SPE Blow Molding Div. annual conference in Pittsburgh. More than 300 people attended the meeting, which presented two days of technical papers and tabletop exhibits. This report also includes in a sidebar some blow molding news from a different SPE meeting.
A continuing topic of discussion among blow molders is low-permeation materials and structures to meet stricter fuel emissions limits from the U.S. EPA and European authorities. Of particular interest are smaller fuel tanks for marine craft, motorcycles, lawn and garden equipment, and off-road and recreational vehicles. Although many alternatives are available, including multi-layer coextrusion, blending a barrier additive, and surface fluorination, the most-desired solution would be a mono-material, monolayer structure that does not need a coating that can be damaged or flake off.
One possible route to that goal is offered by Lanxess Corp., Pittsburgh. It supplies blow moldable grades of nylon 6 and 66 that combine barrier properties and low-temperature toughness. Among its newer products are two nylon 6 grades said to be tougher than HDPE: Durethan BC 700HTS and BC 550 Z. The first is an unreinforced, impact-modified copolymer stabilized against heat aging. The second is similar but boasts greater low-temperature toughness. These materials are also recommended for a related market segment that is attracting interest: compressed natural gas (CNG) tank liners.
Another monolayer material offering for fuel tanks is toughened, blow moldable acetal, or POM (polyoxymethylene). Acetal has inherently low permeability but low impact as well. Thanks to a proprietary modification of the polymer backbone, Ticona, Florence, Ky., achieved what it calls “unprecedented” toughness enhancements in its relatively new Hostaform S.
For the past two years, Ticona has been developing fuel-tank applications for this acetal family. The translucent, UV-stabilized material is compatible with high-ethanol blends. Blow molded tanks are said to withstand punishing impact tests, such as a 1.25-meter drop at -40 C and a 51-in. drop of a 2-in. steel ball at -35 C. Hostaform S can be processed with a standard HDPE screw and head on reciprocating-screw, continuous-extrusion, and accumulator-head machines. It reportedly gives up to 25% faster cycles than HDPE or nylon 6. It accommodates high blow-up ratios for complex geometries and up to 50% regrind or more.
Several tanks made from this material are commercial in the U.S. and several more are soon to be released. One user of the material is Kyodo America Industries Co., Ltd., Lawrenceville, Ga., which produces parts for lawn and garden equipment. The firm has been injection molding in the U.S. since 1996 and just opened its first U.S. blow molding facility with six Kautex accumulator-head machines; four more are on order.
Another recently introduced material is aimed at coextruded fuel tanks, where it can serve as a barrier layer. A second generation grade of Ixef polyarylamide (or MXD6 nylon) is BXT-2000/0203 from Solvay Specialty Polymers, Alpharetta, Ga. It is blow moldable, has good impact toughness, and processes more like EVOH than previous materials. It reportedly bonds well without adhesive to nylon 610 and to some other nylons and polyethylenes.
Sean Stephan, regional manager for Kautex Machines, Inc., North Branch, N.J., continued the fuel tank theme with a presentation on composite pressure cylinders for automotive CNG tanks, portable propane tanks, medical oxygen tanks, and scuba diving gear—all having blow molded liners overwrapped with filament wound epoxy and glass or carbon fibers. Liners can be of PE, nylon, or multilayer structures. The company is shipping components for a fully automated plant in India to make cylinders for cooking gas. The production line will have stations for blow molding, filament winding, and injection molding (for casings and handles). The plant uses six-axis robots and computer-controlled winding machines that can wind five tanks at once. The plant will have the capacity produce 300,000 to 500,000 tanks/yr. For the blow molded liners, Stephan said control of wall thickness is key, so the company recommends use of its PWDS (Programmable Wall Distribution System) die-flexing system.
Chuck Flammer, Kautex’s North American sales v.p., presented a novel solution for a completely different area of specialized industrial blow molding. The company developed parison-spreading and flying-knife technologies for making large flat panels with improved wall thickness, instead of the thick middle section and thinner ends that would normally result. This patented system has been used in Mexico to make rear decks for Volkswagen cars.
More recently it was used for making side panels for garden storage boxes. Suncast Corp., Batavia, Ill., purchased Kautex accumulator-head machines with a version of the parison-spreader technology to stretch the HDPE parison into a long, flat rectangle. The parison is gripped at the top and bottom before mold closing to hold air inside for needle blowing. The parison is also clamped by the mold inboard of the spreader pins. Flying knives outside the mold slit the clamped-off sides of the parison to release the spreader pins for the next cycle. Suncast uses this method under license from Kautex to mold four side panels for the garden box in one shot.
Continuing the theme of die modifications for producing difficult industrial part shapes, Dr. Heinz Gross, head of a German engineering and development firm, Dr. Ing. Heinz Gross Kunststoff-Verfahrenstechnik, proposed that a normal round die is inherently non-optimal for making flat parts, and the simple answer would be to use a flat die, so no stretching would be necessary. However, he noted, “Blow molding people have no experience in designing flat dies.”
In the meantime, he is offering two other solutions for improving part quality and reducing weight. His system for tilting the die instead of shifting it is said to accomplish what other systems lack: A simple solution to change the radial position (centering) of the pin during parison extrusion in a sensitive, precise manner, and to do it in a way that is reproducible and capable of being automated without great expense.
His new approach uses an elastic tilting joint with a tight-fitting elastomer ring. (He is also testing the concept for mandrel centering in pipe extrusion.) The die does not require high clamping forces and uses a simple bayonet closure with a single turn to lock/unlock. Die precentering is no longer necessary, due to the tight fit of the die and pin with the elastomer ring. Two linear stepper motors positioned at 90° tilt the die with pushbutton control. This method can tilt the die up to 0.5 mm and can provide centering with precision as fine as 1 micron or less, Gross claims. What’s more, the tilting movements can be stored in the controller and reproduced at will—something completely new, he says. “Now you can fine-tune the die position to the optimum degree—no more settling for just ‘close.’ And it takes only two fingers.” He adds that tilting “on the fly” is possible with a computer program for profiling the parison.
Gross says his new system is a low-cost, simple design, retrofittable to any head and safe to use, but it has limitations: The elastomer ring’s operating temperature is up to 320 C (608 F), and it’s not suited to abrasive materials. But Gross is working on a metallic tilting joint to overcome these limits.
Gross also developed the GWDS die profiling system, which can be used on its own or with the die-tilting mechanism. His system for “dynamic wall-thickness profiling” is said to be more cost-effective than expensive flexible-die-ring technologies. Unlike other profiling mechanisms, which use a conical pin to change the width of the flow channel, he uses a cylindrical flow-channel geometry at the end of the die. Gross says this means pin movement does not change the velocity of the melt and parison and cannot cause die or pin damage if the pin travels too far. Also, while a typical system increases parison thickness equally around 360°, GWDS allows shaving off part of the pin’s cylindrical profile to increase parison thickness in a selective radial zone. This is possible because the GWDS pin is built from a stack of individually profiled disks. GWDS can be retrofitted to any existing head and machine, as it requires no additional actuators or special software.
Sources at W. Muller USA Inc., Agawam, Mass., hint of one new development to be unveiled at the K 2013 show in Dusseldorf next October. The company is working on extrusion heads for automotive piping using foam for sound insulation. Details will become available early next spring.
There was also news at the meeting about equipment for blow molded bottles. Hesta Blasformtechnik GmbH of Germany plans to introduce larger sizes of all-electric extrusion blow machines at the K 2013 show. Hesta already offers all its machines in electric/hydraulic hybrid versions and all-electric is an option for its small HV (vertical extruder) machine for small (up to 750-ml) medical products and its HM and HMD (double-sided) shuttle machines for up to 2.5-liter products. K 2013 will see the debut of the single-sided HE electric shuttle with 12-metric-ton clamp force for up to 5L products (currently offered only in hybrid version). Later on, Hesta will introduce a double-sided (HGDE) model.
In this fiercely competitive economy, processors must tighten the screws on their production efficiency. One way to do this is to avoid “giving away” extra resin on overweight bottles. A way to do this is to use gravimetric extrusion control. Continuous loss-in-weight yield control has been used for decades in extrusion, but is brand-new to blow molding, according to Conair, Cranberry Township, Pa. Conair presented its TrueWeigh system, which uses hoppers with load cells that measure the amount of material being fed into the extruder per unit of time. Individual hoppers are used for each material in a coextruded bottle. Weight/time data is received by a controller, which can adjust individual extruder screw speeds to maintain uniform throughput. The system is suited to continuous-extrusion shuttle and wheel machines. On wheels, control of screw speed can be slaved to the wheel speed, or both wheel and screw speeds can be adjusted automatically to control bottle weight.
By monitoring and controlling the feed weight of each screw, the system can adjust for screen-pack blockage, temperature variations, regrind percentage variations, and screw/barrel wear. The biggest economic benefit is from allowing stable production closer to the minimum tolerance range for bottle weight and layer thickness of expensive barrier materials. Instead of running a bit heavy (or thick) to avoid variations that dip too close to the minimum spec, narrowing the variability range with gravimetric control can run a process reliably at ±0.5% of setpoint, Conair says. It also means reduced startup scrap by virtue of synchronized ramping of all extruders to achieve stable conditions faster. And it removes the operator as a quality variable. For example, if an operator tweaks throughput of one layer in a coex structure, it affects all the other layers by changing the backpressure in the die head. Gravimetric control keeps the layers in constant ratio. (For more on gravimetric control of blow molding, see our April feature article, “How Gravimetric Systems Pay Off in Blow Molding.”)
Frank Hohmann, president of FGH Systems, Denville, N.J., reported some recent achievements in blowing HDPE motor-oil bottles on B&W long-stroke shuttle machines. One customer is using a six-parison, 12-cavity system to mold oil bottles in 12 sec instead of the usual 16-18 sec. The secret is a special mold-cooling system with three temperature zones to cool the upper neck and lower tail insert faster. The upper and lower zones are at 42 F while the center body zone is at 68 F. The mold inserts are insulated to prevent condensation.
Other features include a special blow-pin design that water-cools the inside of the neck and flash and also directs a stream of recirculated blowing air over the flash to cool it. There is also leak testing inside the machine.
Another customer is blowing HDPE motorcycle oil bottles with a nylon inner barrier layer plus a clear view stripe. The latter is said to be unusual because adhesives for nylon and PE are not usually clear. In this case, the coex structure blocks the PE layer in the area of the view stripe. This system is also running on a double-sided B&W machine with six heads and 12 cavities. Hohmann adds that “view stripes tend to wander” but they are kept straight on this system by the ability to adjust the view stripe “on the fly” while running.
Rapid prototyping is gaining adherents in blow molding, according to Greg Healey, business development manager for Dynacept Div. of Spectrum Plastics Group, Brewster, N.Y. His facility specializes in rapid prototyping and quick-turn manufacturing. It has nine stereolithography machines, which can go from “art to part” in 4 hr. Dynacast can cut an aluminum tool and produce initial blow molded parts in one to two weeks.
Kautex in Germany introduced a rapid prototyping service earlier this year. It reportedly can produce blow molded samples from a 3D CAD model in 48 hr. Kautex will machine a thin-shell aluminum cavity and mount it in a special existing mold half that already has water cooling.
Monroe Mold, LLC in Monroe, Mich., recently added 7000 ft² or 30% more floor space. Besides adding additional machinery, the expansion includes a new 1000 ft² engineering center and a new inspection room with a CMM and laser scanner. Monroe Mold also added a new service—laser welding of aluminum, beryllium/copper, and steel. Although too expensive for many moldmakers, laser welding is a newer technique said to save time by requiring less cleanup afterwork, and it doesn’t affect the properties of the parent metal or cause distortion.
Gravimetric control systems offer blow molders improvements in processing efficiencies above and bey...