A rotary wheel machine that sets a new standard for high-volume blow molding of motor-oil bottles was one of the major announcements at the recent SPE Blow Molding Conference in Toledo. Other news from the conference includes an easy way to monitor screw and barrel wear without extended downtime and an innovative cooling fixture that significantly reduces cycle time. Meanwhile, a 1-lb preform has been developed to stretch-blow one of the world’s largest oriented PET parts—a pressurized gas tank for cars.
Wheels get bigger
The Mighty 11, developed by Graham Machinery Group for Warren Oil in Dunn, N.C., is an 11-station wheel machine with 44 cavities for molding quart motor-oil bottles. It more than doubles the output of a standard shuttle machine and is said to have the highest cavitation of any wheel on the market for products in this size range. It utilizes dual-parison extrusion and a neck-to-neck molding system to produce 14,500 oil bottles/hr. Graham says shuttle machines for quart bottles typically are limited to about 10 cavities while up to now, wheel machines topped out at 28 cavities on 14 stations or 24 cavities on 24 stations.
The Mighty 11 has six extruders and makes multilayer HDPE bottles with an inner regrind layer, a 20% virgin outer layer, and a view stripe. A special takeout system positively removes the bottles from the mold, permitting longer cooling at the same wheel rpm.
To handle the higher output, Graham developed a novel trimming solution. A patented rotary deflasher and spin trimmer handles 240 “logs” (pairs of parts) per minute. The mechanically driven trimmer first deflashes the neck-to-neck logs and then spin-trims the bottles. Using one trimmer instead of two saves cost and floor space.
Meanwhile, HDPE supplier Equistar Chemicals developed a new resin produced with a modified catalyst system to lightweight the bottle from 50 g to 46 g. The change in the molecular weight of the new material, called Petrothene LR7657-01, allowed for a stiffer yet lighter part. With a density of 0.957 g/cc, the resin reportedly exhibits good impact and stress-crack resistance.
Graham says other potential applications for this machine include commercial packaging for bulk restaurant and food-service distribution, bulk household cleaning chemicals, lawn/garden product containers, and nursery pots.
Measure screw/barrel wear
Glycon Corp. introduced an innovative and easy method to measure screw and barrel wear without extended downtime to pull the screw. The SmartBarrel system, aimed initially at extrusion and blow molding, includes a digital indicator that is inserted through small ports in the extruder barrel to take exact measurements of the distance between the tips of the screw flights and the barrel wall.
“Processors no longer have to operate in the dark,” says Jeff Kuhman, president of Glycon. “Screw and barrel wear can be determined so that diminishing production rates can be flattened out.” According to Glycon, the growing radial gap between the screw and the barrel eventually reaches a point where productivity declines almost exponentially. The time to repair or replace components is when wear reaches this critical transition between linear and exponential degradation.
The SmartBarrel is installed on a new machine or when a screw and barrel are being repaired. Monitoring ports (similar to pressure-transducer ports) are drilled in the barrel at one or more locations where the worst wear can be expected. A plug, machined from material similar to that of the barrel, is installed in the hole.
Baseline measurements are taken before production begins. The plugs are removed from the barrel and a digital indicating fixture is mounted over the holes to measure the distance through the barrel to the flight surface. Then the plugs are placed in a fixture to check their starting dimensions. These measurements are repeated periodically to check for wear.
Measurements can be taken in minutes, even while the machine is near processing temperature. By correlating wear measurements with process data, processors can determine when wear is having a serious impact on productivity and energy costs. Glycon is generating data to correlate wear and energy loss. Power meters have been installed to measure energy consumption of drives and heaters and to determine their relation to screw and barrel wear.
Glycon sells the SmartBarrel kit, including digital indicator and other hardware, for about $1279. Each monitoring port costs about $700-$800. The company has about 14 systems ready to be installed on blow molding and extrusion machines in the next month. An automated electronic version that ties into the machine controls and monitors an offsite production line is expected to be rolled out at NPE 2006 in June.
Faster post-mold cooling
An innovative, patent-pending cooling fixture for a multilayer blow molded gas tank was shown by Fast4M, Troy, Mich., developer of a new laminated tooling process. The company’s Fast4M (“Fast-form”) process is a laser-based technology that laminates thin layers of flat steel or aluminum sheet to make molds or—in this case—cooling fixtures for heavy-gauge parts. In a procedure analogous to rapid prototyping, a 3D CAD model of the tool or fixture is “sliced” and the shape of each slice is cut out of a sheet of metal with a laser. Then all the slices are bonded together and the laminated assembly is machined to final dimensions (see Learn More box).
These fixtures are claimed to be an industry breakthrough because of their ability to cut cycle times by more than 30% and boost productivity compared with methods currently used. The aluminum fixture reportedly extracts heat quickly and uniformly without hot spots, says Rob Isling, v.p. of development. Heat extraction is enhanced by building continuous, open water channels into the fixture (an advantage of the laminating technique) to facilitate turbulent water flows and increase heat-transfer area. (Similarly, Fast4M can build large conformal cooling channels into molds.)
Fast4M also announced an advance in making molds for blow molding and RIM using its technology. In applications where aluminum molds are required, its new patented oven bonding system uses special alloys with thermal properties similar to those of the base aluminum to adhere the aluminum sheets. It offers a tighter seal than the previous system, which relied on an epoxy bonding agent. A blow molded car spoiler will be the first commercial use of the new system.
A whopper of a preform
R&D consulting firm Sabel Plastechs has produced one of the largest stretch-blown PET parts for the fuel tank of a developmental car powered by pressurized gas. The 10-gal tank is 10 in. in diam. and 32 in. high. It is made from a 1-lb preform with a wall thickness of 0.467 in.
Fifty tanks have been molded on a prototype two-stage machine, reports Sam Belcher, president of Sabel Plastechs. A novel preform design and the speed of the stretch rod were key elements in attaining a uniform wall thickness of 0.022 to 0.025 in. The tank was molded of a PET with higher I.V. than standard bottle resins.
The PET tank will be reinforced by filament winding over it with a 0.25-in. shell of glass and thermoset resin. Belcher says the containers have already passed pressure tests. An automaker is assessing the concept, which Belcher says has a potential volume of 16 million units/yr.