Blown-film controls lead the way to automation

Advancements in blown-film extrusion controls have enabled the automation of complex lines to help suppliers reduce labor costs, and more importantly, improve the quality of their products by creating a repeatable, automated process.

In the blown-film sphere, control has never been more attainable. Advances in remote control, sensors, temperature monitoring, and user interfaces have demystified the blown-film process, and in doing so have reduced waste and cut back on labor costs.

Harinder Tamber, extrusion and R&D manager of The Packaging Group (TPG; Concord, ON), a blown-film manufacturer, can attest to this. The company manufactures forming and nonforming webs based on nylon, EVOH, LLDPE, and ionomer with a film thickness range of 2 to 10 mm; and currently, the company is using an eight-layer blown-film line from Brampton Engineering Inc. (Brampton, ON) with the Brampton?s Italycs control system technology. The output on the machine ranges from 450 to 660 lb/hr depending on the width and gauge of the final film or sheet.

Tamber says that the control systems have changed for the better. ?In the past few years, there were manual controls and trivial display units, which were very labor intensive for the operator because he had to view all of the parameters individually. Now, the control system provides most of the process parameters or variables on a single screen, which makes it easier for the operator.?

According to Bud Smith, president and CEO of Brampton Engineering Inc., the newest version of Italycs, yet to be released, will allow operators to monitor temperature, pressure, extruder speed, film width, thickness, extruder throughput, blend throughput, and line speed.

?With the increasing complexity of structures and operating parameters, the system reduces the guesswork in producing blown film and relies on data and recipes. The system can store thousands of recipes,? says Smith. On a 16 GB hard drive there is room for over 150,000 recipes.

These ?recipes? contain saved parameters for a certain process. The company believes that processors will find the historical information and trend data most useful for quality control purposes and for solving process problems. The historical data, including all process values, all alarms, and software events, is kept for 60 days. However, if you?d like to keep the data for the long term, the files can be exported to another computer.

Blown-film manufacturer Liqui-Box Canada (Whitby, ON) also uses the Italycs control system. The company employs 225 people and manufactures polyethylene monolayer film and polyethylene/EVOH/polyethylene coextruded film, primarily for the food industry. According to process engineer Steve Skopitz, the company has seven blown-film lines, extruding film with layflat ranging from 800 to 2200 mm; the typical output of each machine is 300 to 600 kg/hr. ?The most beneficial feature of the Italycs system is how it integrates all of the control loops into a human machine interface (HMI). Italycs has the ability to be customized to integrate other monitoring devices if we choose to add them to the machine,? says Skopitz.

The benefit of using Italycs is not only the reduction of labor, but also detecting problems in a process early on, before too much damage is done to the product, according to Skopitz. ?We design our machines so that they can be run with minimal man power, without increasing the risk of off-standard product going out the door,? he says. ?However, the most important aspect of our control system is to detect when a key variable has gone out of control. This increases the probability of detecting off-spec material immediately, and assures our customers that everything they receive is first grade.?

Eliminating the Black Art

Davis-Standard (Pawcatuck, CT) has been working to take the guesswork out of the blown-film process with its control system, Epic. Epic is an open-architecture operating system. It?s made with commercial software and hardware, which according to Rick Keller, director of marketing at Davis-Standard, doesn?t require the customer to come back to them for proprietary parts or software. ?This also simplifies the interface for operators, so you don?t need to get highly skilled workers to man the process,? he says.

As with Italycs, the Epic provides recipe storage for product consistency and quality. Other key features include gravimetric layer thickness and blender control, thickness profile measurement and control, temperature control, drive speed and web tension control, drive logic control, alarm and event recording, and SPC reporting and production reports.

Another important aspect of today?s control systems is remote control and diagnostics. Because the Epic is on a Windows 2000 platform, it is possible for a user in a remote location to connect via modem and a dedicated phone line to the plant-floor Epic controls. However, while the user can view the process remotely, he can?t make any changes to set points or recipes.

Support for the systems is very important to customers, according to Keller. ?Many of our customers are reducing their staff to stay competitive, so providing support is very important. The trend has been to have more data as well as support to link into higher-level systems.?

Blown-film extruder Mid South Extrusion (MSE; Monroe, LA) uses the Epic controls on two of its three-layer blown-film lines. ?We decided that we needed an advanced control system when we made the decision to install three-layer co-extrusion blown-film systems. We knew we needed better control systems to assist us with control of the many variables necessary for the more complicated coextrusion blown-film lines,? says Ron Mason, COO of MSE.

Mason says controlling the many heat/cool zones of multiple extruders, the large number of heat zones on multilayered dies, and the multiple resin hoppers and gravimetric blenders settings with simple discrete controls would have been too difficult, which is why they decided on the Epic system. ?The Epic system gives a centrally located operating medium that is user friendly and allows our operators to easily monitor and control many aspects of the process from one location,? he says.

Although the controls are designed to make life easier for the operators and reduce the need for skilled laborers, Mason says acquiring the advanced controls has also increased the company?s need for well-trained information-systems and PC-maintenance personnel.

The higher complexity of control technology does produce a need for a more dedicated support. Tim Fisher, owner of Facts Inc. (Cuyahoga Falls, OH), says that support is definitely a driving factor in control systems; standardizing the technology is at the top of the list as well. The company continues working to provide a system that basically runs itself. ?We are making a steady progression toward near lights-out operation,? says Fisher.

The result of that objective is the Facts Inc. Total Line Control (TLC) system, which uses a high-resolution touch screen for operator input and graphics display. It offers temperature control, speed control, closed loop control, pressure monitoring, melt pump control, alarming for out of tolerance, data acquisition/archiving, trending, recipe support, touch screen, and easy installation. The company says that it has more than 500 control systems installed in 250 plastics and rubber manufacturing facilities?80% of Facts Inc. customers are plastics processors.

In 2003, Facts Inc. entered into an exclusive agreement with Equitech International Corp. to incorporate its newest blown-film control technology, the Color Analyzer color measurement system, into its process control systems. The technology offers continuous monitoring, closed loop control, and eliminates the need for sampling and laboratory measurement.

Hosokawa Alpine?s (Natick, MA) latest control technology relies on connectivity and data acquisition to improve quality control. Jay Ragusa, VP of engineering, says that the company has focused its technology around high quality and flexibility, while improving production rates. ?We?ve got an open architecture-based system that?s easy to maintain, and easy to integrate in plants? networking systems. Our long-term goal is to take the ?black art? out of the blown-film process.?

Total Control

?Labor is a large part of the manufacturing cost in blown-film processes. Today everybody pays about the same prices for resin and energy in North America; so now they want to changeover the line from order to order quickly, with as little scrap as possible,? says Robert D. Krycki, president of Future Design Inc. (Mississauga, ON).

Krycki says that the air ring was the last product in blown-film really in need of controls. The company supplies Saturn air ring technology, the newest of which is the Genie. The Genie provides more control over process variables than the other air rings, and can be customized to meet the producer?s needs.

Currently, there are six Genies running in the field. There are 40 models of the Genie and each model has specific designs that can be changed for each die. For instance, Future Design can tweak the lipset to suit the manufacturer.

?It?s always been up to the operator to tweak that process to suit the conditions. The Saturn Genie can recall any successful recipes from a history file. And we?ve been able to motorize four major adjustments that we?ve patented on the Genie,? says Krycki.

These include digital pressure and temperature gauges for the air ring chamber in a localized box for signal feedback, probes located near the inlet of the blower to measure relative room humidity, and probes to determine ambient room temperature of the factory. All of these settings can be saved as recipes, so that an operator can recall successful settings from the history file and the temperature and humidity of the plant. ?It really improves the time it takes to set up a machine and reduces scrap for most processes,? he says.

The next step in controls is to combine the air ring controls with the overall extruder control systems. ?Companies like Davis Standard have been able to computerize the film line itself. The air ring is the only solo part that?s been left out of that equation by all manufacturers,? says Krycki.

Flexibility is Paramount

Flexibility is a key issue for Eurotherm, part of Invensys plc, (Leesburg, VA). The company offers the EM-3 (extrusion master) control system that uses a ?building block? architecture, which offers versatility for blown-film processors for future upgrades. The EM-3 combines the company?s PC-based operator station, application specific I/O blocks (ASBs), and terminal I/O blocks (TBs). The operator interface is a touch screen that offers multiple windows, online documentation, animated objects, statistical process control, online trending, and recipe management. Eurotherm also offers the ability to remotely control the technology through a modem or local network.

The control system for the Varex blown-film lines from Windmoeller & Hoelscher Corp. (W&H; Lincoln, RI) accommodates the lines? modular designs to simplify updates or changes. ?In theory, if a company is looking to go from a monolayer film line to a seven-layer line, they just have to change the die and add six extruders and gravimetric blenders,? says sales manager Jim Ciolino. W&H?s system saves recipes that include gravimetric settings, extruder temperatures, die temperatures, haul-off settings, oscillation rates, and winder settings.

The controls systems were developed with processors? basic needs in mind. ?It boils down to what customers want from controls. They want operator-friendly interfaces, reduced labor costs, and flexibility.?

Controlling the Future

It seems the answer to future development of control systems is just a more automated offshoot of what?s being offered today. Skopitz of Liqui-Box Canada explains what the company expects for its lines in coming years. ?We strive for a machine that is intelligent enough to know when our product is off-standard, and alert the operator so that he can correct the problem immediately. We want the machine to be as automated as possible, and we want all of the key operating conditions continually monitored and stored.?

Tamber of TPG hopes that eventually controls will provide better individual layer control in coextrusion, specifically for thin layers such as tie resin or EVOH, and says that ?really the most important aspects of control systems are the reduction of waste and labor.?