New autoprofile system costs less.

A leading supplier of nuclear film-thickness gauges this month came out with a simple blown-film autoprofile control system for retrofit use. Like some other designs, the APC System from NDC Inc., Irwindale, Calif., controls thickness around the circumference of the bubble by adjusting a segmented air ring, which selectively heats or cools regions of the bubble. Unlike most after-market profile-control systems, APC employs a nuclear sensor rather than a capacitance gauge. The gamma gauge rides in a newly designed scanning frame located just above the stabilization cage. "We can make a control action every minute or so," says NDC v.p. Yudie Fishman. "That's about 8 or 10 times faster than in cases where our gauge has been positioned on the layflat." That speed increase has been apparent at Orange Plastics, a major blown-film processor in Orange, Calif., and the system's first user.

Orange recently installed the new APC system on two of its 80-mm Battenfeld-Gloucester HDPE lines. According to co-owner Carmelo Piraneo, the NDC system sits about 12 ft from the die versus well over 50 ft on his previous autoprofile systems. "The speed increase has been tremendous," he says. Speed matters when it's time for a die-bolt adjustment - such as during start-ups or when the film has strayed too far out of tolerance for the air ring to work. In the past, feedback from the layflat-based system sometimes took long enough that making die-bolt adjustments could take all day, Piraneo says. "Now the film doesn't have to travel 50 ft before you learn you need to make a change."

Aside from the speed enhancement, the new NDC system has held thickness variation to the 3-10% range - versus up to 25% on lines without auto-profile control. Piraneo attributes some of that accuracy to two things: First, the bubble-based sensor measures one layer of film rather than the layflat's two layers, providing a more accurate measurement. Second, Orange Plastics became involved in the system's development process by helping NDC accurately map the die bolts to the bubble segments.

A STAND-ALONE SYSTEM

The APC differs from other retrofit systems in that it works as a "stand-alone" system - one that can control profile and average film thickness without supplemental gravimetric-feeding and width-control systems. Fishman explains that nuclear gauges provide absolute thickness measurements - as compared with the relative readings furnished by capacitance sensors. Capacitance readings, he says, make sense only in relation to the film's average thickness as determined by gravimetric-feeding and width-control systems. Nuclear gauges' absolute readings have no such limitation. "Because of its sensitivity to temperature and composition, stand-alone capacitance gauging is problematic, which is why other retrofit systems are sold as an entire concept, including gravimetrics and film-width control," Fishman states.

APC's a la carte approach to auto-profiling allows users to forego the expense of a central computer capable of controlling the whole line. Instead, the APC gauging software runs on the same 32-bit processor used by the company's standard gamma gauge. "Central computerized control of the whole line is great for those who need it," says Fishman, citing coextrusion as a good example. "But centralized computer control can be expensive, especially for processors wanting to upgrade an older line."

READY TO UPGRADE

With prices starting as low as $55,000 for users with a suitable air ring - one having enough segments - the system will most likely cost less than competing autoprofile controls, Fishman says. Even starting from scratch on a line with no air ring at all, the complete system will cost under $100,000 for profile and average-thickness control. Fishman believes the system will appeal to processors who bought film lines before autoprofile and gravimetric systems became widely available. "Some of these lines from pre-1990 are still good lines just waiting for an upgrade," he says.

Right now, NDC's system is available mainly as a retrofit for older Battenfeld Gloucester lines, many of which already use NDC gamma gauges. NDC is also seeking to work with other air-ring and blown-film equipment manufacturers in order to offer the system more broadly.