Economic factors revive compression..

Tag : Phenolic Resin

Compression molding was one of the original plastics processingmethods developed at the dawn of the commercial plastics industry.As the inherent cost/performance advantages of this process gainedacceptance in the marketplace, the resins in the compressionmolders gamut gradually expanded  from the early thermoset resins(phenolic, epoxy, melamine and urea) to unsaturated polyester (theideal material for glass fiber-reinforced composite parts). Withthe development of PE & PP in the 1950s, compression moldingprocess was modified to accommodate these low-cost commoditythermoplastics as well.

Yet as the North American economy grew, hiking the correspondingdemand for engineering materials, manufacturing industryincreasingly sought fast-cycling plastic materials and processingmethods to accommodate their mass-production methods. Compressionmolding and other thermoset processing methods fell into disfavorin comparison to thermoplastics molding methods that advanced. Thecompression molding business underwent massive corporateconsolidation as players determined to remain in the businesssought economies of scale. By 2000 the number of companies withcompression molding operations had been drastically reduced, manylong-term players in machinery manufacturing had exited thebusiness, and the share of compression molding in total plasticsproduction ebbed close to 1%. Then came the recession of 2001 andthe events of 9/11, and the compression molders, like all otherplastics processors, experienced a further production downturn.
The compression molding business, driven by a range of domestic andglobal economic pressures, has seen a revival since 2001. Energy aswell as resin prices have soared. The impact on thermoset resinpricing has been more benign relative to the pricing ofthermoplastics. Moreover, compression molding has beenrediscovered as a highly cost-effective production process withlow-cost molds and low-maintenance machinery. The car and heavytruck OEMs are intensifying their search for lightweight materialsto produce exterior, interior and under-the-hood parts to enhancevehicle fuel efficiency. Builders and homeowners are convertingfrom steel to lightweight and creative composite-skinned exteriorresidential doors. And although much of US electrical component andelectronic equipment industries has gone offshore, the OEMscontinue to regard compression molding as a critical component oftheir operations.

Compression molding as a plastics processing method has undergonenumerous advances: In the 1990s, Minnesota based processorComposite Products Inc. (CPI) unveiled a new process forcompression molding automotive and other structural composites fromlong-glass-reinforced thermoplastics which offered advantages ineconomics, processability, and part quality over processes usingglass-mat/thermoplastic (GMT) sheet. This novel molding techniqueinvolved compression molding an extruded "hot log" ofreinforced compound. The hot log compound was produced directlyfrom glass and resin in a single step thereby eliminated theexpense of buying pre-compounded material. CPI process offeredseveral advantages over GMT sheet, including ability to mold morecomplex parts. Superior flow inside the mold resulted in moreuniform distribution of fibers and got rid of resin-rich areas incomplex parts. The process could result in substantial scrapreduction and enabled to reuse scrap material, much like ininjection molding. The inherent cost advantages over GMT, resultingfrom scrap reduction and the elimination of the value-added step ofsheet preparation, were to be drivers for future applications andlicensees. The two most proprietary aspects included the extrusioncompounding system and the preform accumulator. The compoundingsystem needed a single-screw extruder built to CPI's proprietaryspecifications while the preform accumulator was designed and builtby CPI. The control package also included a variety of dedicatedmicroprocessor-driven software systems and monitors.

Most recently in K 2007 show in Dusseldorf, Italian company SacmiImola S.C. unveiled a new continuous compression molding processcalled Preform Advance Molding (PAM) for making PET bottle performswhich resulted in cost reduction, higher quality and productivity,and the potential for weight reduction. The PAM system was anoutgrowth of the companys established machinery for continuouscompression molding of beverage-bottle caps and other closures,which now can turn out up to 100,000 caps/hr. The PAM starts withan extruder. The system uses a 120-mm model with the processingcapacity of 1760 lb/hr of PET. It continuously extrudes acylindrical parison, which descends from a vertical die and is cutby a knife into a slug. The gob is grabbed by an insertion carouseland dropped into one of 48 mold cavities on a spinning carousel. Asit turns (9.5 to 10.5 rpm), the cavities rise to meet the cores andthread splits and mold each preform under 2 tons of force. Themolding carousel processes standard 0.5L carbonated soft-drinkperforms (23 gm weight, 120 mm long, PCO 1810 neck finish) at up to450 to 500/hr. After a 6.5-sec molding cycle (approx. 90% of whichinvolves actual pressing), the core and neck splits lift thepreform out of the cavity and another robot transfers the preformsto a post-cooling carousel. The carousel has 256 sleeves in whichpreforms are air-cooled inside and out for the equivalent of 5.3molding cycles. The preforms leave the system aligned on aconveyor, which permits integration of 100% vision inspection ordirect delivery to a stretch-blowing machine. PAM system will becompetitive with a preform injection system of similar outputcapacity. Molding at lower temperature and tonnage saves energy,Sacmi notes. But the biggest savings come from reduced scrap andpotential lightweighting.

In 2003, Swiss manufacturer of aerospace, automotive, and medicalparts - Icotec AG developed a novel compression molding processcalled Composite Flow Molding (CFM) that delivered net-shapethermoplastic composites with strength per unit weight reportedlycompetitive with those of machined steel, aluminum, and titanium.This process transferred up to 62% by volume of carbon fiber into athermoplastic, yielding high-strength and abrasion-resistantscrews, bolts, inserts, studs, anchor nuts, and other fasteners.CFM composites were increasingly being used to make medicalimplants and small (up to 0.5-in long) structural bearings andother parts. The favored matrix polymer was PEEK, supplied byVictrex PLC. The CFM process started with a pultruded PEEK/carbonfiber rod made by one of the German suppliers who employed aproprietary method of incorporating high levels of carbon-fiber towinto PEEK with virtually no damage to the integrity of thereinforcements. Icotec then cuts the PEEK rod into a blank whosevolume is precisely equal to the volume of the final part. Theblank was transferred by robot to a heating chamber where the PEEKmelted and wets-out the continuous fibers, minimizing voids. Theblank is then transferred to a compression mold cavity where it ispressed at precise speed, temperature, and pressure to form a partwith a predictable fiber orientation to enhance part strength. Thevibration-resistance of CFM fasteners had immense appeal for marineapplications like rig fittings and the like. The company thenworked to broaden the capability of CFM processing with additionalresins such as nylon 6 and PBT and then to permit fibers other thancarbon to be used, in particular ceramic, glass, and tantalum.
After this, Greenerd built the highly customized, up-actingcompression molding press for filled urethane polishing pads usedin semiconductor manufacturing. It had