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Extrusion in the '90s: quality at your fingertips.

Extrusion In the '90s: Quality at Your Fingertips

What can processors expect in extrusion machinery design, productivity, and product quality in the 1990's? Answers vary widely among major machinery suppliers and screw designers interviewed over the last several weeks, although some definite trends are already taking shape. Even the most divergent predictions tend to come together on the ultimate benefits that processors may eventually reap in the 1990's: a better match between process controls and machinery; improved quality control without sacrificing output; new screw designs more precisely matched to the expected new crop of materials. Overall - but particularly in the area of controls and gauging - suppliers emphasize that machinery will become easier to use as it performs increasingly complex functions.

The neat consensus of where extrusion processing is headed seems to come apart as manufacturers consider how to get there. A host of equipment options - gear pumps, brushless d-c drives, "intelligent" controls, and "screwless" extruders, to name a few - will pose hard choices for processors deciding just where to place their investment dollars during the next 10 years, a period that is sure to see increased demands on both quality and productivity. As one supplier puts it, "Quality is going to be a more important issue for everyone. Although people will want to increase quantity, they will not want to do it necessarily with sacrifices to quality."


Screws of the '90s will see more demanding applications as new "high-performance" resins, blends, and alloys are introduced to the market. According to Hassan Helmy, v.p. of engineering for Egan Machinery Div. of John Brown, Inc., Somerville, N.J., some of these materials may not melt in the conventional way, creating surging problems, or might exhibit poor dispersion during mixing, requiring operation at high temperatures. He says these challenges will require more carefully designed conventional screws, barrier screws, grooved extruders, and dynamic mixing devices.

Several screw designers and extruder manufacturers pointed to a trend toward more application-specific screws, for which precision will play an increasingly important role as polymers grow more sophisticated. Use of new gear pumps, grooved feed sections, or particular dies may also prompt specific screw designs.

Helmy is one who foresees a trend toward application-specific screws. "There are some task-oriented screws that are being looked at for certain outputs and lower melt temperatures," he says, adding that since changing screws is usually not a problem, the better performance gained from using a specific screw is worth the effort.

New devices for controlling the backpressure on the screw while it is running will be an alternative to changing screws to get top performance, suggests Robert Dray, president of R. Dray Manufacturing, Hamilton, Texas. "We have found that there are very narrow ranges for screws to run optimally," he says. The addition of regrind, or even the use of the same material from two different suppliers, can lead to less-than-optimum performance. Dray claims to have achieved better performance through his recently patented add-on adjustable dam device (see PT, Feb '89, p. 13), which allows for micrometer adjustment of the flow restrictors within the screw flights. The company is now reportedly testing an automatic version of the mechanism that will sense temperature or pressure variations through a PID loop, and then adjust the dam to its optimal position to maintain setpoints for those values.


Precise tailoring of material properties to a specific application may be the driving force behind another trend: blending of polymers in the process extruder. Screw designer Robert Barr, president of Robert Barr, Inc., Virginia Beach, Va., says that there will be more and more blending - and in some cases, copolymerization - taking place inside the extruder while producing a finished product. The benefits of this are two-fold: cost savings, because it eliminates precompounding the material or work done in a polymer reactor, and the ability to customize material for a specific purpose.

"It means a lot more emphasis on distributive mixing and shear mixing rather than just on melting," says Barr. "It's a challenge to get out of a single-screw machine what a twin-screw does."

In blown film, better quality will be achieved with improved screw designs and better thermal homogenization and mixing in the extruder, according to Al Chrisbacher, v.p./general manager of Alpine American Corp., Natick, Mass. "We're doing some things in screw designs, in the types of mixing units, the overall screw geometry, and the heating required in that area of the barrel. These are interrelated subjects and all areas of ongoing work."

Some expect that use of efficient mixing sections will rise as processors move toward higher outputs while trying to achieve improved quality at the same time. Although some of these devices are not new, they could spark renewed interest, according to screw designer Dr. Chris Rauwendaal, president of Rauwendaal Extrusion Engineering, Los Altos Hills, Calif. He points to Du Pont's Saxton distributive mixing section, which he claims is efficient because it splits and reorients the flow, achieving good mixing without sacrificing significant output.

Dr. George Kruder, consultant for HPM Corp., Mt. Gilead, Ohio, and the designer of HPM's Double Wave screw, expects to see more intricate screw patterns that will broaden the range of what can be done with single-screw extruders. As an example, he says that the Double Wave screw will become more important because it meters and mixes at the same time. "The mixing gives faster melting, so it makes possible running at higher output ranges as well as providing better mixing."


More processors will be using barrier screws in the '90s, several extruder manufacturers predict. Jim Johnson, manager of sheet lines for Davis-Standard Div. of Crompton & Knowles Corp., Pawcatuck, Conn., says that about 70% of the screws he sells are already barrier types, and applications where they are not yet used will continue to change over. One reason is that barrier screws reportedly help provide more stability and control. Wayne Tibbs, v.p. of sales for Akron Extruders Inc., Canal Fulton, Ohio, agrees and adds that he already

sees more use of barrier designs in profile applications.

Egan's Hassan Helmy, on the other hand, does not see universal use of barrier screws. "You can't just put a barrier screw in and run at full speeds with all types of resins and expect to get optimum performance," he says. On materials such as PP and engineering resins, processors will have to be selective, he says.


Helmy does see, however, more use of special screw materials that can handle engineering resins at melt temperatures of 800-900 F, especially in sheet and cast film lines. And Robert Barr expects that one area of continuing development will be the application of some high-performance wear metals on the screw.

Others caution that use of the hardest materials for all applications may not always be cost-effective. According to Bob Dray, there is a middle ground. Depositing very expensive hard-facing materials on a screw may extend its service life, but the screws may not be able to be rebuilt. "In glass- or mica-filled applications, it's often better to back off a bit on hardness so you can allow repeated rebuilding of a screw so that its more cost-effective. We rebuild screws for major suppliers 40 or 50 times." He feels that one thing that should be addressed in this decade is the lack of expertise in both metallurgy and screw design in the machinery industry.


Use of twin-screw extruders will rise for certain applications, according to some suppliers. A major potential area here is compounding in-line with shape extrusion, where the use of twin-screw extruders can eliminate a processing step. One such application currently is in carpet coating, where at least one processor is using a twin-screw machine to compound highly filled material in-line reports Egan's Helmy. He also predicts more lines equipped with both single-and twin-screw extruders to produce coextruded shapes for demanding applications, particularly automotive parts that combine the strength of a filled resin and a smooth, unfilled outside surface.

Yet others predict less dominance of twin screws outside of compounding. One is Robert Barr, who says, "Smaller extruders for profiles and things of that nature - even rigid PVC - are moving back toward the single screw." Lower initial cost, greater output capacity per investment dollar, and simpler operation and maintenance are among the reasons he gives for the continued prevalence of single-screw extruders in other applications in the 1990's. He adds that use of gear pumps is making single screws competitive with twin screws' positive displacement and uniform delivery.


Use of grooved feed sections will expand beyond its traditional area of high-molecular-weight HDPE, say several suppliers. Al Chrisbacher of Alpine says his company is already supplying grooved feed sections for LLDPE and MDPE, as well - a trend he expects to continue into the new decade. Dave Smith, chief engineer of Battenfeld Gloucester Engineering Co., Gloucester, Mass., agrees: "We see them as great machines for the future." Advocates of grooved feed sections say they provide higher output rates for the same film quality, as well as space savings and lower capital costs because smaller machines can be used.

Use of tougher alloys will reduce the amount of wear associated with grooved feeds. Gunther Hoyt, v.p. of sales and marketing for Xaloy Corp., Pulaski, Va., sees an increase in the use of tungsten carbide. In addition, Xaloy is offering a new iron-chrome alloy called Xaloy 102 that will reportedly offer wear and corrosion resistance at a more economical price (see PT, Jan. '90, p. 102).


Quality is the name of the game in blown film in the 1990's, say equipment suppliers, and some feel that the automatic gauge-correcting die is the way to get it. Windmoeller & Hoelscher Corp., Lincoln, R.I., and Reifenhauser-Van Dorn Co., Danvers, Mass., recently introduced the first automatic dies for blown film (PT, Jan. '90, p. 73). Dr. Werner Feistkorn, W&H's director of extrusion R&D, predicts that automatic dies for blown film will become universally accepted during the next decade.

Others are a bit more tempered in their predictions. Without doubting that automatic dies will become important for blown film, Alpine's Chrisbacher points out that there are other ways in which to control final film gauge. He says Alpine is working on some alternatives that he expects to be introduced early in the decade, but declined to give details.

In sheet and flat film, Frank Nissel, president of Welex Inc., Blue Bell, Pa., expects that automatic dies will expand beyond their current high-performance uses - such as biaxially oriented film and barrier sheet lines - to become standard. Jim Johnson of Davis-Standard agrees: "There are probably three or four different auto-die controls now on the market. I see more in that area, and the cost will come down, so they will become more attractive for smaller lines."

One possibility for coextrusion applications is more widespread use of multimanifold dies. According to Egan's Hassan Helmy, the advantage of the multimanifold die is that it is a simpler approach to the complexities of coextrusion than a feedblock in which all materials are combined before being spread out to final product dimensions in the die.


How widely used computer simulation will be in extrusion in the '90s - and for what applications - is still unclear and a source of disagreement among suppliers. Ron Klein, market manager of Scientific Process & Research, Somerset, N.J., expects screw simulation software (which his firm markets) to find wider appeal. "The cost involved is very low compared with the `poke and hope' method of extrusion process design," he says, adding that some processors that have a unique market niche may be apt to get more involved in screw design on their own with the aid of simulation software rather than depending on hardware suppliers.

Chris Rauwendaal points out that screw simulation programs have become much more widely available. He sees more widespread use of finite-element analysis, "where you can get complex calculations of flow, temperature, and complex geometries on extrusion dies and extrusion screws."

One drawback of these programs - the need for substantial computer time - he sees as temporary. "As computers themselves get less expensive, the trend will grow rapidly. In a few years, people will buy very substantial finite-element analysis capabilities. Before long - within one to two years - you should be able to buy a PC for quite substantial modeling," he predicts.

In fact, one such commercial simulation software package for fluid dynamics, called FIDAP (see PT, Feb. '87, p. 12), has recently been made available to run on PC's. Simon Rosenblat, managing director of Fluid Dynamics International, Evanston, Ill., reports interest from both equipment suppliers and processors in modeling flow in all types of extrusion dies, and expects their numbers to increase. Rosenblat predicts that a major development during the next decade will be to interface simulation software and CAD packages. "A company will be able to do the design on a CAD package and take that picture and put it into an analysis program like ours," he says.

Yet others in the industry remain skeptical of the value of simulation for screw design. One major reason, they say, is that there are too many variables involved. Robert Barr, for one, views screw simulation as limited to establishing trends, rather than exact predictions, in melt temperature and through-put.

Robert Dray says, "In the past, people have taken theory out in the field and tried to match reality to the theory, rather than the other way around." He claims to be re-deriving some of the original equations for screw simulation by taking actual data from a lab extruder and trying to adapt the theory to the actual data, rather than the reverse. He speculates that some day there may be a simple program for a PC that might be of use to a processor or designer, but adds that no such program exists today.

Neither these experts, nor any of the machinery manufacturers interviewed, see much of a trend toward more processors designing their own screws. According to Bob Dray, it's difficult for an individual processor to get a broad understanding of what is competitive screw performance in the market as a whole. "A processor may develop a design that works for his operation, but is that design in fact competitive with other modern designs that are available? It's very difficult for him to know that."

But that's not to write off the value of computer simulation as it becomes available to more users. SPR's Ron Klein argues that the recently developed PC version of the company's "Extrud" extrusion process simulator goes beyond just screw design. It reportedly can also be used for training, giving insight into the workings of the extruder. As a process-analysis device, it can help solve extrusion problems by simulating barrel temperature, screw speed, and other parameters on over 20 processing factors, including output, quality, and melt temperature. The software, which contains over 1500 polymers in its data-base, can be used for resin evaluation as well.


More accurate temperature-measuring devices will be an important issue in the '90s, according to several equipment suppliers. One possibility is increased use of RTD's, a temperature-measuring device that senses by resistance, explains Chris Rauwendaal, who claims that RTD's are more accurate than thermocouples.

Steve Fox, president of Normag Corp., Hickory, N.C., also foresees the growing importance of accurate melt-temperature measuring devices. To that end, the company introduced a product called the Autoprobe - a motor-driven, retractable melt thermocouple (PT, July '88, p. 33). It can make a plot of the temperature profile across the melt stream, and commonly reveals variations of an unexpected magnitude, owing to insufficient melt homogenization. A less expensive version of the unit will be introduced this year, says Fox.

Look for more "intelligent" temperature controls, i.e., microprocessor-based multi-zone controls that can communicate with a host computer, says Lou Faillace, marketing v.p. of HES/Davis-Standard. The intelligent interface will lead to more diagnostic capabilities, such as detection of heater burnout, thermocouple break, or a problem in cooling, he says. "There's a lot of information that can be derived from just sensing the temperature in an intelligent way."

Faillace also sees a trend toward controls that are stable under various conditions. To this end, he foresees growing acceptance of HES's Dual Sensor system, utilizing deep and shallow thermocouples in each zone to control barrel temperature. It reportedly achieves stability to [plus or minus] 1 [degree]F under various conditions. An important aspect of the dual sensor is that it is an instantaneous auto-tuning device, he says.


More sophisticated feedback controls and highly integrated controls are on the horizon. However, on the top of some "wish lists" is for controls software to be better matched to the extrusion lines it is supposed to be controlling.

Lou Faillace says that controls manufacturers and machinery OEM's must "stay closer to the processor's needs and translate those needs into features that would make their lives a lot easier." This means focusing on maintaining quality at high throughput rates and maximizing uptime. Process controls should provide diagnostics that give the operator better tools to identify problems quickly, he says. He sees a need to get away from buzzwords such as "artificial intelligence" and take a more practical approach that is affordable and practical with today's software.

Faillace also predicts that controls in the 1990's will be easier to use, using more features such as interactive graphics and touch screens. Truly sophisticated controls are easier to operate, not more complicated, he points out.

Dana Darley, extrusion product manager of Luwa Corp., Charlotte, N.C., says that one trend in the '90s will be to integrate various microprocessor-based process controls on an extruder. Today it is possible to get different microprocessors on one extrusion line to communicate with each other on some level, he says. During the '90s, that trend will be taken a step further, where one microprocessor will control several different systems on a line. The burden, he says, will fall on OEM's to integrate their auxiliary equipment into their microprocessor controls.

Egan's Hassan Helmy predicts wider application of sophisticated feed-back- type control algorithms for optimizing dynamic process parameters. Today this technology - the ability to model a process to predict cause and effect - is being used in automatic dies, he says. During the next decade, this modeling may be applied to controlling melt temperature as well as mixing quality, says Helmy.


Precise speed control made possible by digital-drive circuits will be seen in the '90s, according to Alpine's Al Chrisbacher. These control circuits provide zero speed variation, and thus eliminate one of the variables that may contribute to lower product quality. Given the next decade's emphasis on quality, he expects digital drives to become universal within the next decade.

How popular will brushless d-c drives, currently supplied only by Wertec Corp., Charlotte, N.C., become in this decade is an open question. Although these drives are still relatively new to the industry, several equipment suppliers say that they will have a place in the '90s. At least three extruder manufacturers - HPM, Killion Extruders, Cedar Grove, N.J., and Cincinnati Milacron Plastics Machinery Systems, Cincinnati - have recently made them standard on their machinery (PT, Nov. '89, p. 120; Dec. '89, p. 58).

According to Wertec president Walter Rudisch, brushless d-c drives are competitively priced vs. conventional d-c motors. He expects his motor to become standard in the industry in five years, especially in the 5- to 300-hp range, currently the limit for brushless drives. Acceptance in larger horsepowers will take longer, he says.

Cincinnati Milacron recently made brushless d-c drives standard on its twin-screw extruders. Al England, marketing manager of extrusion systems, sees the main benefit of the drives in PVC processing. Because the Wertec drives operate from a digital speed loop, there are no brushes that are normally subject to corrosion from HCL gas emitted during PVC extrusion. He claims that the brushless d-c drives add little or no cost to the machines.

Killion vice president of sales Charles Martin claims that his customers are generally satisfied with the brushless drives, which are standard on his machines for 5 hp and above. The drives are said to provide speed ranges of 100:1, vs. the 10:1 usually possible, as well as full torque over the full speed range. They are also said to provide improved speed regulation over the entire 100:1 operating range.

Normag's Steve Fox also reports that his company has had "quite a bit of success" with brushless d-c drives, which are offered as a standard option. He estimates that 25-40% of his mid-sized drives are now brushless, and he expects that share to increase over the next few years, especially in the below-50 hp range.

Some of those interviewed are more hesitant to predict wide-scale success for brushless d-c drives. Tim Womer, process engineer of NRM Corp., Columbiana, Ohio, for example, says these drives will have their place in the '90s, although for the most part their use will be limited to particular applications. "In one application where we tried brushless drives for a sheet line, we were not convinced they were ideal. They don't have the speed range that is sometimes needed."

Others interviewed are downright skeptical. According to Welex's Frank Nissel, speaking of his specialty in sheet extrusion, "Digital speed regulation has no value at all because the extruder motor today is controlled by the gear pump. The precision of the motor is of no consequence when you have a gear pump and a gravimetric system."

Egan's Hassan Helmy claims that brushless d-c drives are expensive. He adds that they may be applicable for smaller machines, but are not available in ranges to cover larger extruders. He also questions what the drives offer for the money: "If rpm is so critical at that low level - which I don't think it is - then in most cases, maybe adding a melt pump at the end of an extruder may be a better answer."

One possibility for the future is a-c drives, says Wayne Tibbs of Akron Extruders. "I think they are more efficient than d-c drives. Right now they are expensive compared with the d-c drive, but once the cost problems are overcome, that may be something that people will look at." Davis-Standard's Lou Faillace agrees that a-c variable-speed drives are more energy efficient than d-c, a factor that he thinks could be significant in the '90s (PT, Jan. '90, p. 63).


The '90s will certainly see more use of use of gear pumps, say many equipment manufacturers, but opinions differ on just how far they'll go.

Normag's Steve Fox sees wide application in multilayer sheet and oriented sheet, as well as certain profiles, wire and cable, and difficult-to-process materials, such as urethanes, elastomers, and polyesters. He also sees some application in blown film, especially for coextrusions and more exotic materials. Another area of big potential for gear pumps is recycling, Fox says, where a variety of melt indexes and viscosities are encountered.

Dana Darley of Luwa says that the gear pump's efficient pressure-building capability and predictable output give it great versatility. "Any screw designer will tell you that a properly designed screw will do anything that a gear pump can do - and they're right. But the problem comes when changing parameters. With a gear pump, you will probably get 95% optimum performance on anything you run."

Rigid PVC or other thermally degradable products are a potential new application for gear pumps. Luwa's new Corex gear pump is designed specifically for heat-sensitive thermoplastics and elastomers. According to Darley, the Corex pump is streamlined to prevent dead spots where material can degrade; its jacketed design is said to eliminate hot or cold spots; and it bleeds out polymer used for lubrication rather than recirculating it back to the suction site, where it may cause degradation problems. Darley claims that the pump has run 1500 hr with rigid PVC with no damage or wear. He says that the Corex can provide [+ or -] 0.5-1% gauge control with rigid PVC. The price of the unit is reportedly double that for a standard gear pump.

Gear pumps certainly have their strong supporters in the industry. Among the staunchest is Welex's Frank Nissel, who expects gear pumps - along with gravimetric controls and static mixers - to become universal on sheet lines during the 1990's. With those three devices, he says, "Sheet extrusion has reached a peak of performance where it is going to be very difficult to think of anything else that people can desire."

Others see more use in selective areas, such as coextrusion, high-precision medical tubing, or thermoforming, where an unusual amount of trim waste is recycled.

Robert Barr doesn't expect gear pumps to be universal, although he admits that there are many cases in which gear pumps offer a real advantage because of their uniform delivery. "The best-designed single screw can get near 1% variation; gear pumps can get down to 0.2%. If you need the kind of delivery accuracy that gear pumps can give you, it's well worth it." On the other hand, he says if that kind of accuracy is not needed, "Don't go near it." He points to added maintenance problems, as well as up to 50-70 [degrees] higher melt temperature due to added shear.

Egan's Hassan Helmy predicts that gear pumps will be used with more discretion during the next decade. "Today, when people use melt pumps, they just tag it on the end of an extruder. In the '90s, we will make the melt pump an integral part of the screw - it will replace the pumping function of the screw." This will allow the use of shorter screws, or perhaps deeper screws to give more output, he claims.

One interesting variation on the gear pump is a "conversion-cavity" melt pump - essentially a piston pump - that is said to offer completely positive displacement. The unit, which is being developed by Sidney Levy & Associates, Laverne, Calif., reportedly can handle a wide range of materials at melt temperatures up to 750 F. The pump sells for about $12,000 without the drives.

Another variation of the gear pump, recently introduced by Harrel Inc., E. Norwalk, Conn., may well find a place in the '90s. Called the Geartruder, the unit is a gear pump and extruder designed into an integrated system, including controls and digital drives. Its main advantage reportedly is that it integrates each element into a smoothly operating system. In addition, this system's screw is said to be designed to take full advantage of the pump.


Most equipment suppliers agree that gravimetric controls will have a place in extrusion during the next decade. In blown film, Alpine's Chrisbacher feels that gravimetrics will definitely become standard, especially in more elaborate processes that use blending. "There are many more people blending today and many more companies advocating blending of material for improved product performance. This will only force others to go to gravimetrics as well, because control of these blend ratios will become much more critical."

Others see big potential in coextrusion. Gravimetric controls will become standard on barrier coextrusion lines during the first part of the decade, and will gradually work their way down to coextrusion lines in general, according to Luwa's Dana Darley. He says the trend is basically driven by material cost savings. He also expects the price of gravimetric controls to drop by 25-50% as manufacturers recoup their development costs.

Still others say that gravimetric controls will only occupy a specific niche. One equipment supplier points out that gravimetric controls have limits in that they are not particularly good for short-term variations. "The readings of most gravimetric systems take as much as 4 min to come to a new setpoint. So if you have a process where you are looking for short-term or small changes in a relatively stable process - just to tweak it for screen-pack pressure build-up, for example - gravimetrics will just complicate things." On the other hand, gravimetrics are useful in controlling long-term changes due to lot variations in resins, he points out, adding that they are especially useful in controlling layer thickness in a coextrusion line.


Although gear pumps and gravimetric controls provide more stability and control in coextrusion, most equipment suppliers do not consider them a total replacement for thickness gauges. Al Chrisbacher of Alpine points out that while gravimetric controls provide average thickness calculations, customers are concerned about product performance, which is usually dependent on the thinnest spot in the film. On the other hand, some suggest that gravimetric controls and gear pumps can supplement, or even simplify, the gauging system that is used. Nevertheless, one thing expected in the 1990's is more reliable on-line thickness measurement.

Look for development of what Dave Williams, marketing v.p. of Kineron Gauging Systems Div. of Eurotherm International, Reston, Va., calls a "true thickness gauge." Common beta gauges, he points out, do not provide a direct measure of thickness, but rather an inference based on mass. He expects new technologies that use direct non-contact thickness measurement, such as laser techniques, to evolve rapidly. One obstacle is the necessity to scan the sheet, he says, because the mechanical motion of the gauge can cause an error in the thickness measurement.

John Rogers of TopWave U.S.A., Roselle, N.J., sees more interest from processors in better indication of the precise thickness of individual layers in a coextrusion. The TopWave thickness gauge, which is said to do a better job of this than infrared-absorption instruments, is based on a white-light interferometer that scans the interference pattern of a light beam reflecting from the material to be measured; layer thickness is then calculated from the separation of the interference pulses, and similarities or differences between material composition of the layers is not a factor. Unlike infrared absorption gauges, the interferometer can separately measure two layers of the same material in a coextrusion.

Kineron's Williams sees a number of techniques being explored for measurement of individual coextruded layers, including infrared scanning, optical interference, and adding fluorescent dyes to polymers that go into coextruded layers. Although they may be promising, each has limitations, he says.

Simplified thickness gauges and self-diagnostics are trends for the future, according to Williams. "Processors aren't interested in having a degree'd engineer on staff just to maintain a gauging system, and in a lot of cases today, that's what we have to deal with."

TopWave, too, is now reportedly redeveloping its gauge to simplify setup and operation. The new version is expected to be on the market in mid-1990.


In blown film, internal bubble cooling still has significant output improvements yet to be realized, according to Alpine's Al Chrisbacher. The most significant area of improvement, he says, is in die design to allow higher volumes of air into the bubble and out again. He expects to see continued blown film productivity improvements in the next decade in the area of 3-4% per year.

In lines devoted to continuous production of the same product, he expects to see more machinery - such as additional air rings - offered for additional external bubble cooling, as well.

A third area of improvements tied to quality is oscillating nip systems. Chrisbacher estimates that 1-2% of all machines in North America use this technology today; during the next decade, he expects it to become universal. The improved flatness made possible with oscillating hauloffs leads to higher quality converting operations, as well as 25-50% higher speeds, he says. Flatter film will also facilitate the use of bigger winders.

Frank Nissel of Welex expects to see some breakthroughs in downstream equipment for sheet. "We'll see improvements in capacity, because people seem to want larger and larger lines." That could mean more and bigger rolls - "huge cooling rolls, additional cooling rolls behind the primary cooling rolls."

Cincinnati Milacron is working on increasing the length of contact between the puller and extruded profiles, in order to decrease the force the puller puts on the part. This should benefit processors who run thin parts.

John Rupert, sales manager of American Maplan Corp., McPherson, Kans., predicts that output rates for rigid PVC siding will climb from the present 800-1500 lb/hr range to 1200-1800 lb/hr. He says the limiting factor to running at high speeds is downstream product. One answer in the PVC siding market, he says, is automated packaging, which is inevitable as speeds pick up.


There will also be a place for unconventional extruders, according to a number of experts. Egan's Hassan Helmy, for example, sees the so-called "screwless" extruders that have been on the market for last several years coming to occupy a niche in the 90's. He expects to see such alternatives providing some competition for single- and twin-screw extruders. But he also points out that the flexibility of single-screw machines makes it unlikely that newer type machines will occupy more than a niche.

The main commercial example of these "alternative" extruders is the InstaMelt Rotary Extrusion System, from InstaMelt Systems, Midland, Texas. It has no screw or flights, but uses a smooth, fat rotor in a short, eccentrically bored barrel to create compression and shear. Because of a shorter residence time, it is said to impart less heat history and reduced degradation. The unit is also said to be an efficient converter of mechanical horsepower, resulting in reduced energy costs. In running copolymer PP at 1000 lb/hr, the InstaMelt is said to result in energy savings of 27% over a conventional extruder. Maintenance is claimed to be simplified because there are no thrust bearings.

According to project engineer Doug Horton, InstaMelt has sold seven of these units, three in joint ventures. He claims that the machine has been successfully used in all types of extrusion applications. Because the machine can extrude 100% regrind, he expects it to assume a major role in the reclaim market.

Another alternative is the Diskpack processor from Farrel Corp., Ansonia, Conn. Although Farrel expressed great hopes for the system in the early '80s, its commercial impact was slight. A company spokesman asserted that the device will have a place in the '90s but would not elaborate at presstime.


There are also a number of developments that, although not yet widely used, may bring real improvements in the future. For complex profiles, on-line video inspection, marketed here by Krauss-Maffei Corp., Florence, Ky., is a new possibility (see PT, July '89, p. 69).

Some experts say that video inspection still needs further development before becoming widely implemented. One potential problem is changes in contrast: Computers reportedly have no sliding scale to adjust themselves from daylight to mixed light to artificial light. In addition, dust generated on a shop floor may cause problems on video lenses.

Other high-tech solutions, such as the quick-tool changing system recently developed by Krauss-Maffei for window-profile extrusion lines (see PT, Dec. '89, p. 13), may also have a place in the next decade. For the present, however, a company spokesman sees slower growth for such a system in the U.S. than in Europe.

An interesting innovation for wire and cable extrusion is a new rapid color-change head from Davis-Standard, for scrap-free instant color changes (p. 76 of this issue). According to a company spokesman, the material and time-savings made possible could lead to wider implementation.

PHOTO : Some experts predict that automatic dies will play a more important role in the next decade, especially in coextrusion applications, such as in the cast film line pictured above. Others predict that controls will be easier to use, as features such as touch screens become common.

PHOTO : Simulation may not be limited to screw design. Scientific Process & Research's Extrud-PC simulator reportedly can be used for training and process improvement. SPR's Ron Klein calls simulation "as essential to the plastics industry as a flight simulator is to aviation."

PHOTO : Several experts predict that twin screws will see wider use in compounding applications - especially in-line with shape extrusion to eliminate a processing step. Another possibility is more lines equipped with both twin- and single-screw extruders for coextruded shapes. (Photo: Xaloy)

PHOTO : Gear pumps will gain wider use with the help of new designs, like Luwa's new Corex pump for extrusion of PVC and other heat-sensitive thermoplastics and elastomers.

PHOTO : Wider use of special auxiliaries, such as additional air rings around the bubble for enhanced cooling capacity, can be expected in some blown film applications, particularly for 24-hr continuous production of the same product. (Photo: Alpine America Corp.)

PHOTO : Output rates in blown film will continue to increase at a rate of 3-5%/yr during the next decade, according to one source. Improved dies can be expected to allow more air flow into and out of the bubble.

PHOTO : One of a number of "alternative" extruders, the InstaMelt machine has no screw or flights. Instead, it uses a smooth rotor housed inside an eccentrically bored barrel to create pressure to achieve melting.
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Author:De Gaspari, John
Publication:Plastics Technology
Date:Feb 1, 1990
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