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March 7, 2004

12 Min Read
Compounding technology is coming back

The technology for direct processing of long-fiber- reinforced thermoplastics (D-LFT) was jointly developed by RKT Kunststoffe and Coperion Werner & Pfleiderer. In a D-LFT plant (top), a ZSK 70 Megacompounder produces a homogenous melt from gravimetrically fed raw materials and additives. Glass fibers are then pulled in from rovings by the screw rotation, impregnated by the melt, cut to length, and dispersed.The compound is extruded as a flat strand into a heated confectioning unit and cut into individual blanks, which are stacked and then picked up by a robot with gripping needles and placed into the press mold. The end product, in this case a polypropylene fitting frame for a Volkswagen Golf A4 (below), weighs 3.8 kg.

The Model DSP dual-slide-plate continuous screenchanger from Conair fits standard extruder sizes from 1.75 to 12 inches and handles throughputs up to 12,000 lb/hr. Polymer flow is split evenly between two screen packs, so when one screen moves offline for replacement the other screen accepts the full flow without disrupting material flow or pressure. The screenchangers are manufactured in partnership with BD Plast Filtering Systems Srl (Ferrara, Italy).

The new line of ?Laboratory Ready? (19 to 50 mm) Wayne Yellow Jacket co-rotating twin-screw extruders are packaged with auxiliary equipment and delivered as working systems. They are made to handle mineral, glass, and other fillers; color; modifiers; masterbatch; alloys; flame retardants; liquid modifiers; and more. Gravimetric feeders are included, and a liquid-metering pump allows precise addition of oils, stabilizers, and liquid color.

Conair increased the top end of its T200 Series of pelletizers to handle higher throughputs. It has also developed cutting blades to handle the extremely hard and often abrasive and corrosive materials used in high performance compounds for tough applications.

A special welding technique wraps stainless steel pelletizer rotors in durable Stellite 12. Reduction Engineering says the Wraptor rotors stay sharp up to 30% longer than conventional rotors.

The rotor of Conair?s Model T216 pelletizer is 16 inches wide and 8 inches in diameter. It handles up to 70 strands and 4000 lb/hr of throughput, with rotor designs specific to different materials.

Mounted on the same rotor, conventional carbide blades (top) and Reduction Engineering?s new Accu-Bide blades (bottom) processed 5 million lb of glass-filled compound. The new blades are expected to last up to 50% longer than previous types.

The compounding sector did not escape the recent economic downturn. But suppliers and compounders are talking rebound, albeit cautiously. Improving end-use markets and specialized technology are pointing the way.

In compounding, as in most plastics processes, it is important to grasp both the specific events and the general trends. A large PP compounding plant planned for Poland is a specific event that is illustrative of a general trend in the compounding industry. Coperion Werner & Pfleiderer (Stuttgart, Germany) will build a line for compounding and pelletizing polypropylene in Plock, Poland that it says will be the biggest system of its kind. Scheduled to go on line in early 2005, the system is designed for a throughput rate of 55 to 60 tons/hr. Basell Orlen Polyolefins, a joint venture of Basell Polyolefins (Hoofddorp, The Netherlands) and PKN Orlen (Plock, Poland), a Polish chemical company, will operate the new PP line on a site described as Poland?s largest petrochemical complex. The system is based on a twin-screw Megacompounder ZSK 380 (380-mm) extruder from Coperion Werner & Pfleiderer with a motor exceeding 14 MW. There is an automatic nonstop screenchanger and a PP-specific underwater pelletizer with an intensively heated die plate.

The melt stream from a ZSK twin-screw extruder is conveyed radially through cylindrical screen elements in a chamber and then to the pelletizer. As impurities build on the filter surface, flow resistance rises, and when a certain melt pressure drop over the screens is achieved, the slide plate shifts horizontally across the melt stream, and the clogged screen pack is replaced by a clean one. Since this screen pack change is performed in less than a second, no interruption of production is necessary.

No gear pump is used for building the pressure for screening and pelletizing the melt. That task will be done by the screws of the extruder, which is intended to eliminate the risk of overshearing any of the various PP grades to be processed. To support the wide viscosity range planned, a Suprex super-positioning planetary gearbox adds the speed and power of a fixed-speed motor to the variable-speed motor used. This supports the wide variety of operating speeds needed for stress-free processing of various PP grades and viscosities with low energy consumption and high throughput rates.

Nimble Compounding Works

Wayne Marquis, president of ECM Plastics, a custom compounder in Worcester, MA, is seeing business generally up, but is also looking over his shoulder. One of his partners in the company recently said he used to feel better about a bad month a few years ago than he does about a good month now. Marquis said ECM?s business was pretty good in the first half of 2003 and okay in the second half. January 2004 was a great month, and Marquis is hopeful for the rest of the year, though still looking over his shoulder.

ECM does only custom work. It has 14 compounding lines evenly split between twin- and single-screw systems. The twins, all from Leistritz, range from 34 to 75 mm, and all systems are located within one 130,000-sq-ft facility. The company started with three lines in 1996, quickly added a fourth, and though still primarily serving New England markets, is seeing more business coming from farther away.

Marquis is concerned about China and would like to have ?a more level playing field,? especially since the China phenomenon is unique and thus hard to predict. But he is paying more attention to the business he sees around him, which is a fair description of ECM?s business approach. Marquis says the company is very customer-oriented and then describes how that works. Two of the four founders come from sales backgrounds, he says, but everyone is working for the customer, and he means every one of ECM?s 100 people.

The company?s broad range of markets includes a lot of packaging, cosmetic, and personal-care clients. Big enough to offer a very broad range of compounding services, it is particularly active in colors and creating appearance materials with special finishes. Pearlescent, phosphorescent, variable color, granite, and a lot more are on the menu. At the same time, Marquis stresses that the company is also small enough to react quickly when servicing customers.

Commentary about the compounding industry on a broader scale comes from Saul Ludwig, a financial analyst with McDonald Investments (Cleveland, OH), who follows the tire and specialty chemicals industries, including several of the larger compounding businesses such as A. Schulman (Akron, OH) and PolyOne (Avon Lake, OH). His analysis of those compounding businesses is largely based on conditions in the markets they serve. If the end-user market is healthy, generating demand, this reverberates upstream to the suppliers. In a recent conversation, Ludwig said that, like the rest of the economy, the compounding sector is a mix of plus and minus factors; however, at the moment the positives somewhat outweigh the negatives, and 2004 should be an improvement over 2003.

Ludwig says the industry is riding some good tailwinds from recovering end-user markets in housing and other construction, aerospace, computers, and a variety of consumer goods, including appliances. Other positive factors he sees include the U.S. GDP being up about 3% to 4% during 2004, continuing low interest rates, and strength in the housing and technical sectors. On the minus side, he mentions such factors as the shift of manufacturing work to China and the high natural gas prices that can affect raw material costs.

Positive but Guarded

Sandy Guthrie, president of single-screw extruder producer Merritt Extruder (Hamden, CT) is among the guardedly positive, and he sees recovery signs in many of the single-screw markets. Technology, he says, has been improving during the slowdown and is ready to kick in now that it?s needed. Many other suppliers echo that sentiment about technology, and have evidence to back up the claim. Guthrie points, for instance, to the generally longer screws entering the single-screw market these days, as well as to screw design.

Much has been said about barrier screws for increased plastication and throughput, and rightly so. But Guthrie is talking less about that and more about how a distributive design in the mixing section of a nonbarrier screw creates a solid advantage over traditional dispersive designs. Distributive designs are not new technology, to be sure, but combined with longer L/D ratios, they give the single-screw machines a lot more capability, which gives the compounder a lot more flexibility. Since the resin has more time to prep for actual mixing, the mixing can be more thorough. Guthrie says most of the ?cleaning up? that resin previously needed has been eliminated by the screws and L/D ratios. Even with high additive and solids content, the extrudate is much more homogenous and benefits from lower shear forces in the barrel.

Short, traditional L/D screws usually left single-screw extruders without much devolatilizing capability. Materials, particularly the more hydroscopic ones, could not be sufficiently cleaned up, and pellet quality often suffered. As a result, such jobs usually went to twin-screw extruders. Today?s longer screws mean devolatilizing can be moved further downstream, to 21 or even 23 diameters from the previous 17. This technology has only recently begun appearing in the market, and it has interesting company.

Charlie Martin, general manager of extruder supplier Leistritz (Somerville, NJ), is also seeing promising activity in the area of inline compounding, mostly for film and sheet applications. He too sees the overall market turning up, but also not in a big way. A number of smaller items are adding up to a possible recovery. Martin mentions strength in natural fibers, and not only wood. He also sees a lot of activity in the packaging sector, particularly foodstuffs, as end users seek increasingly complex combinations of properties for esthetic, marketing, and performance reasons. Combining high barrier with high clarity is the most mentioned, but there are many others, and complexity can increase dramatically depending on the material.

Activity in the Labs

Regarding inline compounding, Martin describes a gradual process of discovery for processors. Initially, a pipe or sheet extrusion specialist or a veteran injection or compression molder, looks at compounding as something very different?a world apart. It is different, but one needs to get over that mindset. Martin says the processors he has seen take the time to analyze the advantages for their own operations discover many economic and production advantages. Using reclaim is but one example, and a rather basic one. The ability to fine tune compounds that become proprietary products with market advantages is usually seen over time, as is the increase in control and flexibility.

Wood-fiber composites immediately come to mind when discussing growth segments. But Martin says that business is actually in somewhat of a comeback phase. When wood fiber was the center of much attention a few years ago, a number of compounders ordered systems to serve the variety of applications then being envisioned. The result was more capacity than this promising but still emerging segment could absorb. Demand, driven by an expanding applications base led by decking and fencing, is now catching up with supply.

Joe Scuralli, president of Wayne Machine and Die (Totowa, NJ), says his company is seeing good activity in lab lines, both domestically and abroad. Whether in private industry, universities, or research firms, labs tend to be less coupled to the ups and downs in the production marketplace. The company?s newly introduced Wayne Yellow Jacket corotating twin-screw extruders (see photo p. 17) are packaged with auxiliary equipment as working systems that allow a wide range of experiments with glass fiber, master batching of color, fillers, modifiers, flame retardants, impact modifiers, liquid modification, and other variations.

Conair says it is changing pelletizer technology incrementally in response to challenges posed by various additive combinations along with the higher throughput rates compounders are running. Cutting blades illustrate the point.

Conair?s John Bell, regional sales manager, says Conair and Reduction Engineering worked closely with a carbide producer to develop new cutting-blade materials. They say even very subtle changes in the carbide and how it is used can have a big effect on blade performance. As well, the grinding technique used on the cutting blades can be changed to optimize performance with certain materials. In one case, cutting chamber walls were changed to 316 stainless to handle the corrosive effect of a high-chlorine FR. In another, the upper feed rolls were converted from vulcanized rubber to a proprietary material that resisted the very high processing temperature.

The juiced-up throughput of high-speed, high-torque extruders led Conair to extend the size range of its T200 Series pelletizers. The rotor of the newest Model T216 is 16 inches wide and has an 8-inch diameter. It handles up to 70 strands and 4000 lb/hr of throughput, with rotor designs specific to different materials. Reduction Engineering is also offering advanced cutting blades and rotors on new Conair pelletizers or for retrofit to existing units in production. A very hard proprietary material in Reduction?s Accu-Bide carbide blades is said to offer 20% to 50% longer time between sharpenings, and, when sharpened, only about half as much material is ground away compared to conventional carbide. Wraptor rotors, so named because the stainless steel rotor is wrapped in a layer of cobalt-based, extra hard Stellite 12, reportedly stay sharp up to 30% longer than previous models. They also lose about 50% less material when resharpened.

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