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12/1/1999 | 6 MINUTE READ

Mold & Machine Automation Highlight Rotomolding Conference

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The first process-simulation software for rotomolding and the industry's first automatic mold-opening/closing device both made their debut at the recent 24th annual fall conference of the Association of Rotational Molders (ARM) in Cleveland. The conference, which drew a record attendance of 730, was held along with the third Rotoplast exhibition, which drew 2300 people to the 108 exhibits. Other news included automatic mold-charging devices and what's said to be the first HDPE that meets UL 94V-0 at 1/8 in. thickness. There was also a rotomolding unit with triple air lines that provide added heat, vacuum, or cooling assistance.

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'Virtual' rotomolding

A new computer process-simulation tool in development at Queens University in Belfast, Northern Ireland, will help molders see how material flows and builds up in a mold. The software accepts CAD files of a mold. Then the user selects the machine type (like biaxial rotation or rock-and-roll) and type of rotation (continuous, intermittent, or reverse). Next, users specify shot weight, rotation speed, oven temperatures, and cooling rates (by still-air, forced-air or water-spray cooling). The program can be stopped at any stage of the cycle for analysis and can define the wall thickness developed at that moment for any point in the mold.

The tool can be used to optimize process parameters or train new employees without losing productive machine time. The software reportedly runs very fast on a PC. The system is currently in beta testing to assess its predictive accuracy. A material database is also in development.

Less handling of molds

The first automated mold-opening and closing unit was demonstrated in prototype form by Norstar Aluminum Molds Inc., Cedarburg, Wis. The bolt-less and clamp-less Norstar System positions the wheel-shaped spider horizontally under a hydraulic arm, which descends and actuates an unlocking cylinder that holds two or more molds shut. Springs then push the upper mold halves away from the lower halves, and the arm lifts them free so that parts can be demolded. After the molds are prepped and recharged, the hydraulic arm descends, pushes the molds shut and then actuates the locking device to hold them closed after the arm withdraws. The spider then indexes the next group of molds into place. This method is said to save time, labor, and mold damage.

Three new mold-clamping devices from Wheeler Boyce Co., Stow, Ohio, are said to make for easier handling of molds and mold components. First, the new Roller Guide system is said to save large, complex, multi-part molds from being damaged during part removal. Each mold section is attached to a rollaway support that is permanently mounted on the machine arm. The guide system prevents molds from being dropped, and it maintains alignment of the mold to prevent parting-line damage during mold closing. The system raises initial tooling costs but reduces mold maintenance as well as labor for parts trimming and touch-ups caused by flashing from worn multi-piece molds.

Second, a new Swing Clamp design attaches to the mold frame and secures multiple pull pins, core pieces, threaded caps, fill ports, or other pieces. The device is said to reduce labor compared with conventional clamps.

Third is the new Rapid Mount system, which quickly installs single molds, multi-cavity spider molds, and universal-grate spider molds. It consists of a base mounted permanently on the machine arm and a universal mold plate that is welded to the mold frame. A dovetail locking jaw on the base, operated by a single hex-head bolt, clamps or releases the mold.

Wheeler Boyce also offers a new series of parting line clamps that mount directly on the parting line instead of the spider frame. The change in clamp position virtually eliminates witness lines on the part, the company says.

Machinery update

Swing arms on any new machine from Ferry Industries Inc., Stow, Ohio, can now be equipped with triple inner air lines capable of bringing hot air, nitrogen, or vacuum into a mold during heating or pressurized air during cooling. Two lines were previously the maximum.

New hexagonal ovens with angled oven doors on Ferry machines reportedly reduce the dead air space inside the oven by 20% and lead to faster mold heating. The new shape conforms better to the mold and also shrinks oven dimensions 20%.

Ferry has introduced a balanced exhaust system that removes heated air from the cooling chamber at the same rate that cool air is being pumped in. Instead of merely letting hot air escape through an opening, Ferry has put a high-speed fan atop the oven to draw out the hot air. Faster cooling is said to result. In addition, the cooling-air capacity has been upgraded by 20%. Floor space is reduced by means of two-piece telescoping doors.

Ferry also commercialized its IRT system, which uses an infrared thermometer to monitor the mold's outer temperature. This permits optimizing the process by controlling the machine cycle based on temperature and time rather than time alone.

Next year, Ferry plans to introduce its biggest five-station, three-arm machine to date, the RS-600. The unit will have a 236-in. swing radius.

Caccia Engineering S.p.A. of Italy (represented by E.A.P. Machinery Systems Inc., Erie, Pa.) updated its entry-level model 2300 shuttle machine with new PLC controls and 20% smaller oven burners that operate at 480-700 F. The former Rotobox unit has been renamed First Step. Overall size of the single- or dual-sided unit has been reduced 25%, yet it still has a 90-in. swing radius and molds 528-gal containers.

A 30% increase in productivity over conventional two-arm shuttle machines is estimated for the new XS series two-arm linear shuttle model from STP Equipment Inc., Bromptonville, Que. The unit has a newly designed heating and cooling system that reportedly results in shorter cycles. A low-fire heating system stays warm when idle and heats up quickly when molding begins. A new cooling system draws 36,000 cfm of air--twice as much as the firm's ZS models. Also featured are an automatic mold positioning system and a Windows-based touchscreen controller.

STP also introduced the entry-level Lab-40 shuttle unit, outfitted with one offset arm, a test mold, a mold-temperature logging system, and internal air and gas injection lines. The oven can use either natural gas, liquid propane, or electricity. The model has a PC-based touchscreen control. The system has a spherical diameter of 40 in. and takes up 138 sq ft.

Automated mold filling

Ferry offers a new way to cut labor costs and eliminate over- or under-charging the mold. Its new Gravimold system automatically and precisely dispenses up to four material components into a mold. Gravimold is a loss-in-weight feeder that dispenses up to 6 lb/sec with a reported accuracy of ±0.02 lb. The feeder reads a barcode on the mold that is matched to a dispensing recipe, then supplies the required amounts of color and resin powder. The system holds over 65,000 recipes. A top-mounted digital display shows the set amount and actual amount dispensed.

A system to reduce colored resin inventory by mixing resin, color, and additives at the machine is new from STP. The Flexicolor system combines high-intensity mixing and dispensing of up to four colors and resins simultaneously. It mounts on the workstation. It uses four batch mixers, each with 44-lb capacity, mounted on four "silos" or hoppers that hold 264 lb each. The batches are mixed in 5 min. The silos are mounted on weigh scales and dispense gravimetrically into molds that are placed underneath.

New PE materials debut

FR-RF53 is the first flame-retardant HDPE that meets UL 94V-0 at 1/8 in., says Stephen Copeland, president of Jericho Plastic Industries, Inc., Akron, Ohio. The 5-MI, 1.1-density material is offered in pellets or powder and in natural, black, or custom colors.

Jericho also has a new HDPE with high-impact (60 ft-lb/in. ARM low temperature impact) and high-stiffness (100,000 psi flex modulus). SL9435 has a 4-5 MI and density of 0.943.

Improved sintering characteristics, good impact strength, and 33% faster cooling are claimed for the first Elite metallocene LLDPE resin for rotomolding from Dow Plastics, Midland, Mich. The new 5-MI, 0.940-g/cc material reportedly forms good parts faster at a lower temperature (600 F for 18 min) and with less warpage and shrinkage than standard resins of similar MI and density.

HM-335 is a new HDPE compound from Muehlstein Compounded Products, Houston. It is designed for outdoor products like kayaks or boats that require stiffness and toughness. The 3.5-MI, 0.948-g/cc resin provides 126,000 psi flexural modulus and Gardner impact of 280 in.-lb at -40 F. It comes in pellets or powder, in black or standard colors.

Rotomolding Rides in Front

The sophisticated new look of rotomolding is epitomized by the Smart Bar passenger-vehicle frontal-protection device by Team Poly Pty Ltd. in Lonsdale, Australia. The part took ARM's Product of the Year award and Innovative State-of-the-Art award. The bumper system mounts on the vehicle's bumper-support beam to protect against run-ins with large wild animals. It uses a proprietary polyethylene from Courtenay Polymers of Victoria, Australia.