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Apr 13, 2001 12:00 AM
While web offset presses today are more efficient and productive
than presses of the recent past, many exciting emerging
technologies may have a significant impact on web offset press
operation and maintenance in the coming years.
Today, manufacturers are building presses driven by multiple AC servo motors timed digitally through fiber-optic technology, while highly sophisticated automation features, including closed-loop color control, are becoming standard equipment. Heatset press dryers can now approach nearly perfect energy efficiency due to extraordinarily effective thermal emissions control systems. The press’ electronic systems can now be remotely monitored and maintained from anywhere in the world, reducing maintenance costs.
There are also some promising technologies in R&D that will likely be available in the near future, including electrostatic-aided drying and single-fluid inks (SFI).
High-end commercial web offset presses are beginning to be manufactured with automation features that significantly decrease makeready time while reducing the required training time for new press operators. These technologies, including automated plate changing, register, blanket washing, web-ups and folder changeovers, are enabling web presses to more effectively compete in markets previously served by sheetfed presses. This is mainly because shorter, high-quality color runs can now be cost-justified.
Automation on the rise
While automated-register and blanket-washing have been common on web presses for years, semi- and fully automatic plate changing are just now becoming standard in all size classes of commercial web presses. The mammoth 64-page Heidelberg Sunday 4000, for example, comes with fully automatic plate changing—the manufacturer even claims that eight plates can be changed in only three minutes. The equally large MAN Roland (Westmont, IL) Lithoman press features semi-automatic plate changing with plate-lifting devices to aid in handling the 79-inch-wide plates. The Komori (Rolling Meadows, IL) System 20 (narrow-web) and 38 (full-size web) presses include auto-plate technology, as does the highly automated Mitsubishi (Lincolnshire, IL) Diamond BTS.
In addition to plate changing, there’s automated “web-up,” a technology patented by Heidelberg that describes the automatic webbing of a new roll through the press. The Heidelberg Sunday press features automated web-up from splicer to slitter running at 150 fpm.
Fully and semi-automatic push-button folder changeovers are also becoming more common, appearing on the MAN Roland Lithoman, Mitsubishi Diamond BTS and the Heidelberg Sunday presses, as well as others.
The use of closed-loop color automation is also spreading quickly among web offset printers. The first of these systems was introduced at Drupa ’95, and more press manufacturers are offering the technology on their press lines today than ever before. Web printers are now buying into the technology in significant numbers. For example, Quad/Graphics reportedly recently invested $25 million to retrofit all of its web presses with closed-loop systems.
These systems employ an online densitometry-based CCD video camera or a combo video/spectrophotometry system, each capable of scanning and measuring a color bar on the moving web, continually feeding data to the ink-control console for ink film thickness compensation. Printers using these systems today find they are useful not only for maintaining consistent color quality, but also as an efficient means of real-time data collection for statistical process control and customer quality assurance. There are a number of manufacturers offering closed-loop color technology for the web market, including Perretta Graphics Corp., Graphics Microsystems Inc., QTI and Web Printing Controls. (For more information, see “Closing the color-control loop,” p. 34.)
Where are the gears and belts?
Take off the side cover of most web offset presses manufactured today and many of the traditional gears, belts and pulleys will be conspicuously missing. With continued developments in synchronized AC servo-motor technology from companies like Rexroth Indramat (Lohr, Germany), presses without drive shafts are fast becoming the standard.
Power designs on traditional drive-shaft presses require a central motor to drive a mechanical line shaft that runs the length of the press. Each section of the press is mechanically synchronized using gears, chains, clutches, belts and pulleys, all connected end-to-end. Today’s shaftless designs eliminate the drive shaft and mechanical timing devices, instead making use of multiple AC servo motors, each driving separate components of the press. These separate motors have to be timed to one another within tremendously tight tolerances, made possible by fiber-optic lines running from each motor to a central digital controller. The timing data are fed in a loop, relayed from the motor to the control box, and back to the motor for compensation adjustments, ultimately allowing synchronization with other motors to within one arc minute (or .008 degrees). The result is a press with extremely tight machine stiffness.
Shaftless technology is not entirely new. It was first introduced more than two decades ago in the printing industry to allow inline folders to operate independently, reducing timing problems. Servo-motor technology has only recently advanced to the point where manufacturers are attaching individual, independent AC servo motors to each driven element in the press, including each printing couple, the reel stand, the chill rolls and the folder. In some designs, such as that used with KBA’s (Würzburg, Germany) Compacta 215 (introduced at Drupa ’95), an AC servo motor is used to drive each individual cylinder within the printing couple.
Shaftless presses boast a number of important advantages over presses with traditional line shafts. Unit-to-unit gear backlash is eliminated. This is a wear-and-tear problem caused by play in the gears that can worsen over time, adversely affecting unit-to-unit register. Shaftless presses also have the potential of maintaining a tighter level of overall web tension control, because the speed of each unit is controlled independently. The motor driving each unit can run at a fixed percentage above or below overall press speed. This allows a positive draw of almost any amount to be established between any two nip points on the press, resulting in a high level of tension control.
Another key advantage of shaftless technology is that each press unit can be operated independently. This expands the number of production options available to printers. Consider a six-unit press with the web running at full production speed through four of the units. While the press runs, a plate change can be made on the fifth unit. When the plate change is complete, the fifth unit can be brought up to press speed, synchronized with the other units, and then be placed on impression. While the five units are engaged, the sixth unit can be plated and then engaged when the portion of the run using the fifth unit is complete. Multiple sections of the run can be customized without ever stopping the press.
Finally, shaftless presses can be modified more easily than drive-shaft presses to meet new production requirements. When adding a new component, there is no drive train to tie into and no gears to align. A new section can be tested and installed, and then electronically synchronized to all other press sections.
Thermal emissions control
New developments are making web presses more fuel-efficient and environmentally friendly. At Drupa 2000, MEGTEC (De Pere, WI) introduced the Dual Dry Omega System, an integrated dryer and thermal oxidizer with the potential for zero fuel-cost operation. The system’s emission control technology is said to achieve 95 percent thermal recovery, far above traditional thermal oxidizing technology, which operates at about 65 percent thermal recovery. The system also reduces carbon monoxide and nitrogen oxide by up to 80 percent above today’s systems, while maintaining a 99 percent volatile organic compound (VOC) destruction rate.
Because of its high efficiency rate, this technology uses significantly less fuel than traditional integrated dryer/oxidizers. The technology also closely approaches a completely closed-loop emissions control system, where the energy released by ink solvents during oxidation is enough to furnish all the heat required to destroy VOCs and dry the web, requiring no added fuel to the system. This technology will result in lower operating costs and lower press emissions.
Presses today can be tied into the global network and monitored from anywhere in the world. With high levels of digital electronics incorporated into new press designs, many printers are dependent on software solutions for their presses. Downtime due to software maintenance, including upgrades and debugging, can be very expensive.
One way to maintain these systems is by implementing remote diagnostics. These systems employ a dial-up modem connection that allows a technician anywhere in the world to diagnose and fix problems.
QTI’s (Sussex, WI) Color Control System (CCS) comes with a remote diagnostics application, which includes remote detection, monitoring and operation control capabilities. Remote monitoring allows engineers to check and operate all aspects of the CCS in real time, including the ability to view exactly what the color system’s camera sees. It also can monitor parts of the hardware status.
If a problem persists, a customer can call an engineer and have him or her take control of the press remotely, using an application called PC Anywhere. With a modem connection, the engineer can start or stop the job, and make any necessary adjustments to the system in real time from anywhere in the world.
It is likely that web printers will see more options for remote diagnostic capabilities as digitally based web systems increase in number. With costs of service potentially reduced and downtime minimized, these types of systems are bound to see a sharp increase in utilization over the coming years.
On-press plate imaging took off years ago in the sheetfed litho market, and the web offset market is now seeing some of this technology as well. MAN Roland showed its DICOweb press at Drupa 2000. This press features a technology that allows imaging, erasing and re-imaging directly to a plate-like cylinder, which the company calls a “form” cylinder.
The technology involves the use of an on-press CreoScitex thermal imaging head to image a thermotransfer ribbon. The transferred image is then heated to give the ink-receptive substance durability, and the form-cylinder surface is conditioned to make it water receptive. This imaging process takes only 10 minutes. After the press run, the ink and thermotransfer material are wiped off, making the form cylinder ready for the next job.
The recommended run length for the DICOweb is between 1,000 and 30,000 impressions, making it suitable for short-run color applications. The press also has the added benefit of variable cut-off capabilities.
Other web manufacturers are beginning to develop on-press imaging technology as well. Didde Web Press (Emporia, KS) recently announced an alliance with Presstek (Hudson, NH) to develop a direct-imaging (DI) UV web press for direct mail. The assumption is that the new press will use one or more of Presstek’s on-press plate technologies. Reports say that the web offset press will be a hybrid, with variable digital imaging capabilities and inline finishing.
Didde also plans to provide the DI unit as a field upgrade to its current press lines. Although this technology is only at its genesis in the web offset market, the obvious benefits of on-press imaging for direct-mail marketing will make it more common in years to come.
There are a number of technologies at the R&D stage that will likely make an impact on web offset in the coming years. Eltex GmbH (Weilam Rhine, Germany) is researching the use of static energy to improve the efficiency of web offset heatset dryers, calling the technology “e-field drying.” The research focuses on the use of static energy to break up the solvent-laden laminate air that attaches itself to the moving web of paper as ink solvents are released in the dryer.
As the technology continues to be developed, new dryers that accommodate this technology will be shorter, will operate at lower temperatures and with reduced airflow, and will operate with higher energy efficiency than current dryers. An added benefit is that paper dried with e-field drying shows less damage.
Another emerging technology is in ink. Flint Ink (Ann Arbor, MI) has had SFI technology in R&D for more than seven years, but the technology was only recently demonstrated for the first time at Drupa last year. This ink technology eliminates the need for the dampening system, because the ink acts as an emulsion containing both an ink and dampening component. Flint Ink reports that the ink can be used with standard litho plates and unmodified ink systems. Though successful trials of SFI have been run with black ink for web heatset runs, the vendor indicates that additional R&D is needed before marketing the product.
SFI technology has the potential for enormous impact on web printers. Without ink/water balance to worry about, makereadies will likely be faster, consistent quality may be easier to maintain and paper waste may be reduced.
Web offset technology continues to develop in many ways, becoming more energy-efficient and productive. More automation, more consistent high-quality color and shorter, less-expensive makereadies have begun to increase competition between sheetfed and web printers for short- to medium-length color printing.
At the same time, the development of larger, faster and highly automated 64-page presses is helping web offset printers move to markets traditionally served by gravure. With all of these technological advancements, web offset continues to flex its muscle in the printing industry.