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September 1, 2005

14 Min Read
Auxiliaries matter: Reducing costs means re-thinking basic assumptions

The rise in resin costs is driving new thinking at every stage of the manufacturing process, and not just in big machinery. From recycling, to blending, granulating, and pelletizing, greater efficiency is something processors can''t afford to ignore.

For inexpensive raw material, look to your shop floor

Plastics processors on average generate about 3% scrap. For some processes, such as extrusion of bioriented PET (BOPET) film, scrap rates jump much higher-as much as 15% to 20%.

With the increase in resin pricing probably being the single biggest issue facing processors today, it is little surprise that many are looking to these scrap rates and seeing potential savings. What is surprising, though, is that recycling machinery manufactures say their levels of sales are not actually driven much by plastics pricing. For instance, at Erema (Ansfelden, Austria), a firm that specializes in systems for plastics recycling, Gerhard Wendelin, managing director, says plastics pricing is probably third on the list of factors driving customer purchases.

The biggest factor driving purchasing decisions for Erema customers remains the local economic situation, says Wendelin, followed by any legislative decisions that push recycling. Plastics pricing plays a part. too, of course. "The higher the price, the more processors call us," he notes.

Wendelin, citing the 3% scrap figure, notes that if a processor brings recycling in-house, at a cost including machine depreciation of about e.20 to e.30/kg, then that scrap rapidly becomes an inexpensive source of new material. "That''s our main argument. If a processor has enough scrap to run a recycling unit at least two shifts per day, it generally pays for itself within six months," he says. Erema''s largest customer group is made of processors handling their in-house scrap, followed by recyclers of post-consumer waste.

Recycling machinery developments have included changes to help users streamline their processes. For instance, plastics recycler Ambiente Recuperagao de Materiqis Plásticos, based in Leiria, Portugal, is one of the early adopters of a T-DD (tangential-double disc) extrusion system for recycling plastic, introduced by Erema at last October''s K show. Ambiente has been an Erema customer since 1990 but upgraded to the T-DD unit in 2004.

The upgrade has allowed Ambiente to continue using an older wash line with low drying capacity (which Ambiente owner Paulo Pires says he is now upgrading). T-DD units have about double the drying power of a standard Erema recycling system, an important consideration, notes Pires. He says the unit allows him to maintain high throughput almost regardless of the level of moisture in the washed recyclate. Ambiente exports about 90% of its output to processors in North Africa, Asia, and Europe.

Wendelin adds that systems to dry washed plastics scrap are energy and maintenance intensive. He says the T-DD works well even with hydroscopic materials such as PET or polyamide, and with moisture levels up to about 20%-or about 40 times the level of moisture a standard extruder-even with degassing-can accept.

Ambiente recycles about 15 to 20 tonnes of plastic per day-purchasing post-consumer recyclate (PCR) or industrial waste from processors, washing it, and then drying and granulating it using the Erema unit. Most of the material is LDPE or LLDPE film. The largest customer segment for the granulate is extrusion processors of films for trash bags, though some is sold to pipe processors and injection molders. Peter Pauli, manager, after-sales service at Erema, says it took about one week to install the T-DD unit at Ambiente. The machine occupies about 30 sq m of floorspace.

Though Ambiente has a long history of success, many entrepreneurs are lured to the recycling industry without doing their math, says Wendelin. "Many of them see the plastic bottles and bags on the roadside and think it''s easy to make money in this business, but they often don''t have enough PCR supply to support a business." Erema, he says, has taken a consulting role in many instances to break that hard truth to these potential recyclers. "We now have literally hundreds of people in Russia and Eastern Europe contacting us for recycling of PCR PET, but likely only a few have a chance," he says. MD

Automotive prosperous for recycler

With more than 200,000 tonnes of recyclate-based polypropylene (PP) compound sold, AKG Polymers is an experienced hand in the recycling market. Demand from automotive parts processors has driven growth.

AKG purchases industrial regrind, or grinds scrap in-house, and also has agglomeration capacity to densify film, nonwovens or raffia tape to agglomerate. Material is then loaded into one of the compounder''s six 80-tonne silos and blended, explains Ian Cleveley, the U.K.-based commercial manager of the firm (Vroomshop, the Netherlands).

From silos, material is transferred to one of AKG''s 10 single-screw or four twin-screw (for filled compounds) extrusion compounding lines, for filtering, addition of additives, and degassing, says Cleveley. The product is then post-blended in 80-tonne silos to ensure full homogenization.

Though AKG markets compounds based on other recycled material, PP is its specialty. Cleveley says its PP compounds for the automotive market (including unfilled, talc, and glass fiber filled homopolymer and copolymer black compounds) see use in under-the-hood and under-the-wheel arch applications. In late April the compounder was invited to GM Opel''s Rüsselsheim, Germany headquarters to present its materials during the OEM''s in-house fair.

Increasingly, says Cleveley, customers want to incorporate more recyclate into (visible) interior parts as well, making color matching more important. For such applications, he says, the compounder typically uses a recipe incorporating virgin and recycled material.

The price recyclers can demand has climbed in concert with virgin plastics pricing, and Cleveley says that typically compounds based on recyclate can sell for 80% to 90% of prime price. The automotive market pays on the upper end as its specifications limit the number of recyclers able to supply it, he says. Last year AKG raised its compounding capacity to 28,000 tonnes/yr, putting it in position to continue profiting from demand from automotive parts and other processors. MD

Holding the line on costs via gravimetric blending

With raw material costs skyrocketing, waste is unacceptable. In fact, profits can quickly erode when color concentrates and other additives required for molded parts are not measured and blended accurately.

Stephen Buckley, VP of project engineering and marketing, for Process Control Corp. (Atlanta, GA), says that many processors believe that simple metering accuracy will result in good parts. However, notes Buckley, "You need to have a good consistent mix, not just good metering, to ensure good products."

Most blender suppliers talk only about metering accuracy-how accurate they can dose. Many processors, particularly blowmolders and injection molders, do custom jobs for particular customers that require various levels of dosing, but few understand how overdosing by just a small amount of colorant or additive can result in big losses.

Buckley offers the case study of a blowmolding company that was using older, volumetric technology with a combination of regrind, virgin resin, and color concentrate. This company had a contract with its customer that specified a 4% letdown ratio for color, and part price was based on this.

"Anything more than the agreed-upon 4%, the processor pays for," says Buckley. "As far as the customer is concerned, they could care less. This blowmolder realized they were spending a lot of money on color concentrate because to get a consistent color with their current feeding system, they had to overdose on the color."

Typically, up to a 12% letdown ratio can be used to still produce the same color. If less than a 4% letdown ratio is used, color "shading," or variations, can occur. "This blowmolder was overdosing on the color," says Buckley. "They were using an 8% to 10% letdown ratio. You can make product with any system, but what is it costing you?"

Mixing accuracy-not just metering-is key to eliminating "dead zones" in color or additives, and getting good products. When the blowmolder began testing new equipment using specific criteria to determine which metering/mixing equipment gave it optimum products, it performed tests in batches.

This is key, says Buckley, because your process is not seeing this material as a batch. "You might have 25 lb of material in the batch, but the molding machine only takes a small percentage of the batch to make a part," he explains. "We convinced this blowmolder to use the metering test as it planned [measure each component to ensure the same weight and see how accurate the machine metered each part], but to also add mixing the batches and blowing the bottles, then check for consistency in the finished product."

Batch-to-batch inconsistency can be a problem, as spiking can occur between batches. The blowmolder tested the equipment using three consecutive batches, blowmolding 30 bottles with each batch. It collected the bottles from each batch and checked for opacity, performed an "ash" test (burning the bottle) to test how much color was in each bottle; then tested for how low it could go on the letdown ratio of color concentrate and still make a consistent bottle.

The original setpoint for the product was 4%, but it was using an 8% to 10% letdown ratio in order to compensate for inaccurate metering and mixing. During the test, the company slowly reduced the amount of color concentrate from 4% to 2.4% and still made bottles with consistent color. It finally increased the letdown ratio to 3% and that''s where the product continues to run.

It''s not just processors who are concerned with profitability and competitiveness. The color companies are just as eager to gain a competitive edge. "These companies approach us to ask if they can supply the color at different loadings," explains Buckley. "What they do, due to inaccurate metering, is dilute the pellet, putting less color per pellet, so that in order to get a consistent color more pellets must be used. They do that because the feeding technology typically used can''t accurately blend and disperse the color. Their idea is to be able to supply the pellet at a higher loading, which reduces the poundage of pellets required to get consistent color, but processors have to have a system that can feed it and mix it properly or it doesn''t work."

In order to get a 4% letdown ratio, color companies can double-load color into the carrier pellet so it has twice the color. For the customer to make the same color it only uses a 2% letdown ratio, but still gets the 4% in the finished product. "Color companies typically charge more for the loaded pellet-about 20% to 25% more-but processors are using 50% less material. It''s another way for processors to lower their costs," says Buckley. CG

Plenty of pelletizing innovations help processors

Operator ease, quick-change cutting heads to reduce downtime between product changes, and compact footprints are elements that masterbatchers and compounders are looking for in today''s pelletizing units, says Horst Müller, product manager, at auxiliaries manufacturer Reiter Automatik (Grossostheim, Germany).

"Quick-cutting head exchange in less than five minutes has become a must for large-size strand pelletizing equipment," Müller says. The reason for this is that standby equipment and its handling are seen by many processors as too staff-intensive and an unwanted expense.

Other trends that Müller says have taken hold are digital line-speed displays and pellet length adjustment on the fly. Also, pelletizing equipment is being adapted more and more to process new compounds and product shapes. These include long-fiber-reinforced thermoplastics with pellet length up to 50 mm, micro pellets to aid in producing easy-flow color concentrates, wood plastics, natural fiber granules, and nanocomposites.

Müller points to an interesting new application his company has just delivered to an Asian polymer maker producing general-purpose polystyrene compounds. To accommodate the volume of this application, Rieter delivered three individual large-sized M-USG1200V strand pelletizers, which are being grouped into a sophisticated production unit. Two pelletizers are always in production while the third is on standby to meet production spikes. Each unit handles up to 228 strands and offers an output of 14,000 kg/hr. Cutting-head exchange takes five minutes, says Müller. This fully automatic strand pelletizer includes a classifier to screen out over-lengths and fines. Very low vertical acceleration avoids standup of the over-length pellets on the screening area.

Today there is a wide range of units available from which masterbatchers and compounders can select. The X-class series strand pelletizers from Scheer Bay (Bay City, MI) move on casters for shopfloor ease, and the compact form measures only 32 by 26 by 73 inches (81 by 66 by 85 cm). It includes a 32-tooth Stellite-tipped rotor and a four-edge solid tungsten carbide bed knife. Both strand pelletizers from AEC (S. Attleboro, MA; the standard and ER Series) and Sterling (Milwaukee, WI; the BP Series) include synchronized feed roll and rotor speeds, which provide accurate pellet-length control as well as quick-change gears to produce a variety of pellet lengths. The helical cutter operates at slow speeds to reduce power consumption and decibel levels.

IPS (Grssosheim, Germany), a part of Kreyenborg (Münster, Germany), came out at K 2004 with a small-quantity production strand pelletizer, ips-SGE30, designed for quick changes or small-lot masterbatches. It offers throughput up to 150 kg/hr, a small footprint, a-c motor, and the ability to cut up to five strands in granule sizes from 1.5 to 5 mm at throughputs of up to 80 m/min, says Gerald Weis, managing director.

Kreyenborg''s other unit, BKG Bruckmann (Münster, Germany), covers a similar market segment with the UG30, introduced in January, for processors who prefer spherical pellets produced by underwater pelletizers (UWP) rather than cylindrical strand-cut granules from a strand-cutting unit. Competitor Dynisco Europe (Heilbronn, Germany) says that with its WRP12i inline UWP pelletizer there is no problem with water flow timing, the hot die-face cutting is insensitive to melt-flow interruptions, and the flexible blade design eliminates difficult knife adjustments.

Conair (Pittsburgh, PA) says its Vortex Spray Pelletizer system combines the performance features of an underwater and water-ring pelletizer for what it says is better quality and easier handling. Its straight-line flow path minimizes shear and reduces material hangups for fast cleaning between batches. The company also says the vortex cooling design removes polymer heat up to 50% faster than conventional pelletizers.

Michael Eloo, technical manager at auxiliary equipment manufacturer Gala (Xanten, Germany), says UWP units provide more advantages than strand units, pointing to comparative tests his company made at facilities with American, English, and German customers using both types.

"The situation is particularly critical for color masterbatchers [using strand pelletizers] who are finding increasing difficulties when the pigment portion in the melt is increased. The result is often poorer strand quality and higher shear rates, resulting in higher melt temperatures combined with poor strand cooling," Eloo says. An alternative would be to reduce speed and output, but that leads to higher costs.

Eloo says one customer found a significant difference in costs during color batch changovers and cleaning of the pelletizers. The units were coupled to a 50-mm extruder. More (25 kg) purge material was needed by the strand unit than the UWP, which required about 25% less purge for the same job. Annual savings were €8000.

Processor Polyplast Müller (Straelen, Germany), a color masterbatcher, says that during color change of organic color masterbatches, its operators cut downtime to a maximum of 40 minutes for cleaning of the die plate, adaptor, and water chamber. Its strand pelletizer took two hours. A comparison of annual maintenance also came out in UWP''s favor says Eloo. Grinding and polishing the rotor knives of a strand pelletizer came out to €1880/yr, compared to €1106/yr for a six-blade cutting set with a UWP. RC

Breaking it down

In part targeting processors interested in reclaiming material for reuse, at K 2004 Wittmann Inc. (Torrington, CT) introduced its new Master MC series of central granulators featuring conveyor feeding, a tunnel sound enclosure, and a metal detector. The Master MC replaces the MS granulator series and has six sizes for use in reclaiming material processed via injection, extrusion, or blowmolding. With motors up to 99 kW, the granulators have average throughput ranges of 150 to 1500 kg/hr. Bob Harrison, Wittmann''s granulator product sales manager, says high resin costs have prompted more processors to investigate reclaiming material, but not at the levels one might expect.

"The culture or stigma of using regrind has to be overcome," Harrison says. "Too many think of regrind as a problem to process. They either haven''t used regrind in years, or are using old high-speed granulators. They don''t seem to realize how far technology has advanced." TD

Contact information

AKG Polymers  

AEC, Inc.  

BKG Bruckmann & Kreyenborg Granuliertechnik Conair  

Dynisco Extrusion  

Erema  

Gala Industries, Inc.  

GmbH  

IPS  

Kreyenborg GmbH  

Polyplast Müller  

Process Control  

Rieter Automatik GmbH  

Scheer Bay Co. Pelletizing Systems  

Sterling  

Wittmann Inc.  

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