Gas-assist & recycling were focus of structural plastics meeting.
Emphasis on recycling, gas-assist molding, structural foam, and new materials was evident at April's annual SPI (1) (Stateful Packet Inspection) See stateful inspection.
(2) (Service Provider Interface) The programming interface for developing Windows drivers under WOSA. Structural Plastics Conference in Washington, D.C. New developments in gas injection are likely to ease the task of designing and molding gas-assist parts. In recycling, a cost-effective method for recycling PPE/nylon car bumpers back into fresh bumpers or other exterior automobile parts without paint removal was presented. New FR-ABS and ABS/PC grades, as well as a new blowing agent, were also introduced at the conference.
FOCUS ON GAS-ASSIST
Several new developments in gas-assist molding promise to help de-mystify design and processing aspects of the process. What may be the first guide to using engineering thermoplastics in gas-assist applications has been developed as a service to customers by GE Plastics, Pittsfield, Mass. The guide gives basic rules on gas-assist part design, tooling, and process control.
GE Plastics has also developed software to help predict the structural performance of gas-assisted injection molded parts. The software first calculates the amount of material left behind in a gas-assist channel (which is also done by commercial gas-assist simulation software Simulation software is based on the process of imitating a real phenomenon with a set of mathematical formulas. It is, essentially, a program that allows the user to observe an operation through simulation without actually running the program. ), and then goes on to calculate stiffness or other structural properties of the hollow section and the overall part.
In another paper, GE Plastics presented an approach to optimizing processing conditions for gas-assist injection molding injection molding
A manufacturing process for forming objects, as of plastic or metal, by heating the molding material to a fluid state and injecting it into a mold. . The technique, which reportedly is applicable to any type of machine or processing license, uses a piezo-electric pressure transducer Pressure transducer
An instrument component which detects a fluid pressure and produces an electrical, mechanical, or pneumatic signal related to the pressure. in the gas feed line, plus one or more mold cavity-pressure transducers, to reliably determine the actual gas-injection pressure and gas-flow rates. GE found that some control settings on a gas-injection machine produce "choked" gas flow in which the pressures in the machine exceed the actual pressures in the mold. The new technique allows the three main phases of gas-assist molding--plastic/gas filling, packing, and holding--to be clearly distinguished and analyzed separately, offering molders a better understanding of which phase is being controlled at a given time. Ability to determine the effective upper limits on processing conditions and to identify the start and finish of each the three main cycle phases reportedly will increase molders' proficiency with the process.
GAS-ASSIST AIDS COMPLEX JOB
An account of how gas-assist succeeded in an unusually complex molding job was reported at the conference by Tohoku Munekata, a Japanese molder. Munekata produced a 29-in. tv cabinet with molded-in speakers--a part that reportedly is not feasible with conventional molding. The cabinet was molded without flash in the speaker grilles, which contained 40,000 0.13-in. holes, and without damage to the core pins.
Several steps contributed to this successful result: At the design stage, flow analysis using software from Mold-flow Australia Ltd. (U.S. office is in Shelton, Conn.) was conducted to achieve proper cavity-pressure distribution and appropriate gate location. In addition, the molder and Japanese resin supplier Showa Denko Showa Denko K. K. (昭和電工株式会社 together developed a "super-high-flow" HIPS material (30 MFR MFR,
n See myofascial release. ) that's said to have the same level of practical strength as currently available HIPS.
When it came to molding, a cavity-pressure sensing device with feedback control to the injection molding machine Injection molding machine (also known as injection press) - a machine for making plastic parts. Manufacturing products by injection molding process. Consist of two main parts, an injection unit and a clamping unit. maintained consistent pressure during filling. Finally, gas-assist molding, under license from Gain Technologies, Sterling Heights Sterling Heights, city (1990 pop. 117,810), Macomb co., SE Mich., on the Clinton River; platted 1835 as Jefferson Township, renamed 1838, inc. 1968. Largely rural until the mid-20th cent., the city grew as a suburb of Detroit, 19 mi (31 km) to the northeast. , Mich., was used to reduce pressure during the holding phase. Munekata says it reduced the required cavity pressure to one-fifth that of conventional molding; the required press tonnage was reduced by haft (to 650 tons) and the tool size by 30%.
RECYCLING DURABLE GOODS durable goods
Goods, such as appliances and automobiles, that have a useful life over a number of periods. Firms that produce durable goods are often subject to wide fluctuations in sales and profits. Also called consumer durables.
Several papers at the conference revealed successful efforts to recycle both post-consumer packaging and durable goods (auto bumpers and business-machine parts) into new structural parts.
Painted auto bumpers were recycled back into fresh bumpers without the need to remove paint during the recycling process, according to according to
1. As stated or indicated by; on the authority of: according to historians.
2. In keeping with: according to instructions.
3. a paper by Nissan Shatai Co. Ltd. of Japan and GE Plastics Japan Ltd. The material involved was GE's Noryl GTX GTX Gore-Tex
GTX Global TeleExchange
GTX Grand Tourisme Extra 6011 PPE/nylon alloy, which has been used on the Nissan Avenir The Nissan Avenir is a line of station wagons beginning production in 1990 by Nissan of Japan, aimed primarily at the commercial market. It replaced the long-serving Nissan Bluebird wagon. and AD wagon. Painted bumpers were ground up whole, mixed with impact modifiers and varying ratios of virgin material, pelletized, and then remolded. The recycled material was found to have a melt index similar to that of the virgin material with a negligible difference in surface quality. Mechanical strength depended on the ratio of recycle to virgin, but was within the acceptable range.
GE and Nissan concluded that the PPE/PA alloy could be recycled back into painted bumpers using up to 20% recycle. Recycled material could also be successfully used at a 100% level in small automobile exterior parts such as radiator grilles.
In addition, three projects of Xerox Corp., Rochester, N.Y., focused on closed-loop recycling of PS business-machine housings and parts. In one study, Xerox and BASF BASF Bar Association of San Francisco (since 1872; San Francisco, California)
BASF Badische Anilin und Soda Fabrik (German chemical products company)
BASF Builders Association of South Florida Corp., Parsippany, NJ., found that glass-reinforced, flame-retardant impact PS could be recycled up to five times and in concentrations up to 100% and still maintain sufficient physical properties (tensile strength tensile strength
Ratio of the maximum load a material can support without fracture when being stretched to the original area of a cross section of the material. When stresses less than the tensile strength are removed, a material completely or partially returns to its and modulus, flexural strength and modulus, Izod impact strength, and Vicat softening temperature) to be used in computer and business equipment applications over the long term.
A second Xerox study of flame-retardant HIPS copier cartridges found that the material suffered minimal property losses after being recycled up to five times, and that up to 1.5% by weight of residual toner would not affect the material's recyclability.
A third study--in which Xerox teamed with Dow Plastics, Midland, Mich., and Camoplast Inc., Richmond, Que.--found that flame-retardant HIPS structural-foam copier door panels can be recycled twice and still maintain acceptable physical properties.
Another example of recycling transformed post-consumer packaging waste into industrial parts. Collapsible, returnable material-handing containers molded by Perstorp Xytec, Inc. of Tacoma, Wash., contain 40% post-consumer HDPE HDPE
high-density polyethylene milk jugs. Molded by the low-pressure structural foam process, the containers are said to have improved performance over their all-virgin-material predecessor.
AUDITING INJECTION PRESS PERFORMANCE
A practical approach to quantifying an injection molding machine's performance has been developed by RJG RJG Arctic Skate (FAO fish species code) Associates, Traverse City, Mich., in collaboration with the Ford Motor Co. According to RJG's John Bozzelli, common molding problems such as short shots, warpage, and flash often have causes that cannot be clearly attributed to problems with the machine, mold, resin, or method of processing.
Bozzelli says the key to statistical process control is in controlling four key variables:
1) Plastic flow rate, which is critical because the melt changes viscosity as the fill rate changes.
2) Actual melt temperature, which is important to understanding the material's initial viscosity.
3) Injection-pressure profile, which determines the part weight, sinks, voids, warpage, and other characteristics.
4) Cooling rate and time, which establish a part's dimensions, molded-in orientation and stresses, and post-molding dimensional stability dimensional stability,
n See stability, dimensional. .
Bozzelli developed a series of 11 tests by taking each of the variables and translating them into machine requirements and limits of acceptable function.
* The key tests of a machine's ability to control flow rate or fill time reproducibly are load sensitivity, fill-time consistency, position-cutoff consistency, and shot-size consistency.
* The tests used to check a machine's ability to control temperature are melt temperature, nozzle temperature, plasticating-time consistency, and backpressure back·pres·sure
Residual pressure opposing the free flow of a gas or liquid, as in a pipe or an exhaust system. consistency.
* Three tests of pressure control are transfer time and consistency, second-stage pressure consistency, and cushion size.
* Finally, the principal test to audit for control of cooling is cycle time.
This battery of 11 tests is said to provide a tool for molders to evaluate the machine's process capability--the reliability of its mechanical and hydraulic components--independent of mold and auxiliaries, and to establish comparable values for different machines, old or new.
NEW RESINS & FOAMING AGENTS
A new flame-retardant PC/ABS PC/ABS Polycarbonate/Acrylonitrile Butadiene Styrene blend for blow molding and extrusion has a balance of properties that until now has been available only in resins designed for injection molding, according to its supplier, Miles Inc., Pittsburgh. New Bayblend DP2-1500 is said to have uv resistance, high impact strength at ambient and low temperatures, color stability, and a generous processing window. Key properties include a flexural flexural
pertaining to the flexure of a joint.
fixation of joints in flexion. In the newborn called contracted calves or foals. modulus of 341,000 psi, notched Izod impact of 14 ft-lb/in., HDT HDT Heat Deflection Temperature (plastics)
HDT High Dose Therapy
HDT Heatpipe Direct Touch (Xigmatek)
HDT Heat Distortion Temperature (plastics)
HDT Henry David Thoreau at 264 psi of 225 F, UL 94 ratings of V-0 at 0.062 in. and 5V at 0.125 in., and uv resistance of 300 hr (ASTM ASTM
American Society for Testing and Materials 4674) with a delta-E less than 1.5. In addition to excellent weld-line strength, the resin offers the melt strength necessary for blow molding large parts with uniform wall thickness and for extruding complex profiles, says Miles. Price is 82.21/lb.
A new addition to the Magnum 4400 series of ignition-resistant ABS resins was introduced by Dow Plastics. Grades in this series do not contain polybrominated diphenylether flame retardants (see PT, Oct. '92, p. 33). New Magnum 4425 can be injection molded, extruded, and thermoformed into computer and business-equipment housings. It's said to provide good processability, excellent uv stability, and improved practical toughness and heat stability when compared with other Magnum ABS resins.
Magnum 4425 features a flexural modulus of 310,000 psi, notched Izod impact of 3.5 ft-lb/in., and UL 94 ratings of V-0 at 0.062 in. and 5VA at 0.0975 in. The new grade reportedly offers 5-10% shorter cycles than competing PC/ABS blends; its melt-flow rate of 7.3 g/10 min at 446 F reportedly allows the material to easily fill molds requiring long flows and/or thin-wall sections with lower pressures and processing temperatures.
A new "hybrid" chemical foaming agent from a relatively new source is said to combine the best properties of both endothermic endothermic /en·do·ther·mic/ (-ther´mik) characterized by or accompanied by the absorption of heat.
en·do·ther·mic or en·do·ther·mal
1. and exothermic exothermic /exo·ther·mic/ (-ther´mik) marked or accompanied by evolution of heat; liberating heat or energy.
ex·o·ther·mic or ex·o·ther·mal
1. products for structural foam. EPI EPI
exocrine pancreatic insufficiency. Environmental Products Inc., Conroe, Texas, says its new Polycor-267 is a hybrid of a proprietary "acid-based" endothermic component combined with an azodicarbonamide exothermic agent.
The product was tested in a head-to-head structural-foam molding comparison with EPI's own straight endothermic and exothermic blowing agents. PPE-alloy business-machine housings were molded with each of the three blowing agents at FM Corp., Rogers, Ark. With Polycor-267, degassing degassing
adj related to degasification, the process by which dissolved gas is removed from water or other liquid solutions. time was equal to or better than the others. Painting was conducted just 2 hr after molding with no blistering, as compared with the five days' degassing required with an exothermic agent. Polycor-267 gave the greatest density reduction of the three blowing agents. Parts molded with Polycor-267 and with the exothermic product showed the least amount of sink. Polycor-267 gave the best surface appearance and a fine, uniform cell structure (about 100 microns). Price range of Polycor-267 is $3.00-3.50/lb.