PVC window profiles: how high can output go?

In the past two years, many processors have doubled output rates, first by hiking line speeds, then by extruding two strands instead of one. How much faster can they go? We may soon be seeing 2000 lb.hr - double what's considered 'high output' today.

The market figures look good for vinyl window-profile extruders. PVC window sales are growing by 7-8% annually, according to Steven Senzer, president of Sabre Associates, a market-research firm in West Cornwall, Conn. He says PVC now accounts for roughly 75% of yearly sales of double-hung replacement windows and 30% of single-hung windows for new homes. And vinyl profile extruders are eyeing new markets in light commercial windows.

But the more processors rev up output, the more the competition grows. Big European processors are looking to the U.S. for growth. Plunging resin prices also squeeze domestic processors' margins.

It all adds up to intense pressure to boost extruder power, streamline dies, multiply strands, add extra calibrators and water tanks, lengthen cooling sleeves, automate takeoff and handling, and speed tool changes on shorter production runs. For example, Mikron Industries in Kent, Wash., which claims to be the largest PVC profile extruder in the U.S., runs window and door profiles 10% faster now than a year ago and 45% faster than three years ago, says president Paul Warner.

How much faster can they go? Some of the fastest profile lines may be bumping up against the limits of today's dies and downstream equipment. But a few ambitious processors may be willing to risk untried technology to hike rates again in the very near future (see sidebar).

Heading for a ton an hour

The limiting factor in the push for ever-higher outputs keeps changing. "A few years ago it was extruders, but that's been fixed," says Sean Kelly, regional sales manager of Technoplast International, which supplies PVC window-profile lines. As we have reported over the past two years, virtually all major machine builders have launched new higher-output parallel twin-screw extruders with higher horsepower and longer L/Ds of 25-28:1 for better mixing at high rates. Among them are new models from American Maplan, Davis-Standard, Krauss-Maffei, Milacron, and Technoplast.

Next, calibration was the hold up. Processors at first simply added more dry calibrators to cool at higher rates. But three or four dry calibrators in a row - at $65,000-100,000 a pop for a complex profile - put a drag on profits. They also put a frictional drag on the dry surface of a profile. Pullers couldn't haul the load, so takeoffs were beefed up. At K'98, Vobau in Germany, a maker of profile downstream equipment, showed a new high-output puller with two AC drive motors on the top belt and a third on the lower belt. The first line, delivered six months ago to Koemmerling GmbH in Germany, pulls single PVC profiles at 18 ft/min and dual strands at 13 ft/min.

Pulling harder can create another problem: It can deform the soft core of a heavy profile, building in stresses that could cause unacceptable shrinkage later. In response, some suppliers coated calibrators with PVDC to reduce friction. Processors also tried adding more surface slip agent to the PVC formulation.

Die designs also evolved to permit higher outputs. Internal flow channels in the die were elongated so material would flow in straighter paths. "But that built up pressures and would overheat the material," says David Murdock, product manager for PVC profiles at Davis-Standard. So after first getting longer, now dies are getting shorter again to keep from building up pressures, he says.

Cooler tools

The latest trend in profile cooling is to use one short dry calibrator made of stainless steel or a sleeve-type calibrator made of aluminum with a removable liner of harder stainless steel. They are followed by two to five more sleeve-type calibrators. Vinyl Tech in Youngstown, Ohio, pioneered economical dry-sleeve technology, in which most of the space between the outer box and inner sleeve is filled with cooling water. The sleeve is only 0.01 in. thick, so cooling is very efficient at high output rates. Sleeve-type dry calibrators may cost $30,000-50,000 and are lighter and quicker to hook up than traditional solid tools with multiple water lines. Sleeve calibrators are also sequenced a few inches apart, with pressurized cooling water impinging directly on the profile in the gap between calibrators. Vinyl Tech president Rick Amato says this approach requires shorter cooling tables, typically 18 ft instead of 40 ft for a mainframe profile running 13 ft/min.

An alternative is two or three longer calibrators instead of five standard 12-in. units. Processors are also adding extra water tanks. Actual Maschinenbau in Austria says its customers are now using 18-ft cooling tables to run dual strands at up to 1000 lb/hr. In the U.S., Acro Extrusion Corp., Wilmington, Del., today runs 36-ft-long water tables, compared with 16-ft tables two years ago.

Processors of dual small strands might run both through one line of calibrators and water tanks. Veka Inc. in Fombell, Pa., which runs dual complex profiles, separates them at the die and runs them through two separate cooling lines.

Greiner Extrusionstechnik in Austria (represented here by Uniplast International) builds dies in Europe with cooled core-pins to cool profiles from inside, but this doesn't work on typical U.S. profiles, Greiner says. Cooling can also be improved by adding turbulence to water tanks, the subject of a patent dispute between Greiner and Technoplast. But turbulent cooling has the limitation that it doesn't allow preferential cooling of one side of a profile to correct a bow.

Mastering quick changes

Setting up a window-profile line often takes 2-4 hr, during which a prodigious amount of scrap can be generated by high-speed systems. "A lot of companies run at medium speeds - 7-9 ft/min - and aren't ready for high outputs of 13 ft/min or more because the scrap is so much higher on start-up," notes Uniplast sales representative Thomas Herrick. But some companies have worked around the problem. Silverline Building Products Corp. in North Brunswick, N.J., reports that it accomplishes complete changeovers in about an hour using preheated dies and quick-change calibrators with single water and vacuum disconnects. In Germany, Veka AG reportedly has slashed times for complete changeovers down to 20 min with the aid of quick-set-up tools.

Holder of a world speed record may be The Wire Mold Co. in West Hartford, Conn., which makes PVC profiles for wire raceways, which are very similar to window profiles in shape and downstream cooling. Wire Mold does complete changeovers in as little as 10 min and averages 30 tool changes a day on 12 extrusion lines, says extrusion team leader, Greg Stepeck. The firm's raceway profiles run as fast as 100 ft/min, depending on the complexity of the profile.

Coextrusion at high output - e.g., of soft black seals on white window frames - is tricky because it means high volumes of start-up scrap that can't be recycled. One solution is to separate the two extruders and not coextrude through one die. This lets operators get the rigid PVC running before introducing a second material or color.

No limit?

For companies already running at high output rates, it gets harder and harder to save money by going faster. "We went from 2 meters a minute to 4 meters and then to 6 meters, first with single and then dual strands," says Oliver Beer, technical manager of Koemmerling. "But now it's getting much more difficult to get any significant economic benefit. Going to 8 meters a minute isn't enough. You have to go to 10 meters." Is there a speed limit out there for PVC? Vinyl Building Products' Cangialosi doesn't think so. "You can always go faster," he says. "That's the future."

RELATED ARTICLE: Who's Ahead in the Profile Race

Window-profile wall thickness varies greatly in different housing markets, and therefore so do standards of what constitutes high output. U.S. double-hung frames typically weigh 0.7-1.0 lb/ft. Single-hung types weigh slightly less. Most European frames run up to 1.4-1.5 lb/ft, while U.K. and Canadian frames fall somewhere in between. Today's state of the art in speed is to extrude lighter U.S.-style profiles at 13-18 ft/min. High output of heavier European profiles means anything over 10 ft/min. In pounds, high output is considered anything over 800 lb/hour in either market.

A pacesetter among domestic window-profile makers is Veka Inc. in Fombell, Pa., the U.S. unit of Germany's Veka AG, which is the world's largest producer of PVC window profiles. The Fombell plant runs six super-high-output lines, most of them with dual strands of big profiles. "Those six machines do the work of 16 regular lines," says general manager Charles Spaulding. Since 1995, these lines have been converted to more powerful parallel twin-screw extruders and dual strands. Output first doubled, then tripled from 375-500 lb/hr to 1000-1500 lb/hr. "We're trying to get up to 2000 lb/hr by year end," Spaulding says. He says it will be two strand, but no current two-strand die can handle that volume.

Veka is also pushing harder on outputs of its smaller-volume profile products. The company is replacing its workhorse Milacron CM 55 twin-screws, which produce 300 lb/hr, with bigger CM 80s that produce up to 800 lb/hr.

On the fast track abroad is Koemmerling GmbH in Pirmasens, Germany. Just this year it commercialized new high-output technology that pumps out window profiles at 1700 lb/hr.

Not all window-profile makers are pushing the speed limit yet. Vinyl Building Products, a large producer in Oakland, N.J. (half owned by Thyssen Polymer of Germany since 1995) is looking to boost its current top speed of 10 ft/min for dual-strand profiles, says company president, Nick Cangialosi.

At Silverline Building Products Corp. in North Brunswick, N.J., the nation's largest integrated manufacturer of PVC windows, 10 ft/min is also the top speed for single- and dual-strand window profiles.

Dayton Technologies in Monroe, Ohio (acquired last year by Deceuninck Group of Belgium) runs dual frames and quad sashes. Deceuninck runs multi-strand profiles at up to 900 lb/hour, says William Uhl, director of corporate development and planning at Dayton.