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Buyer's guided to oscillating film hauloffs.

Buyers' Guide to Oscillating Film Hauloffs

They may or may not be ideal for all blown films, but there are several factors to consider when choosing among the available designs.

During the last three years, oscillating film hauloffs have become available from virtually all blown film equipment suppliers. By distributing gauge variations back and forth across the face of a web, oscillating hauloffs are said to improve overall roll quality for subsequent off-line converting operations.

Oscillating hauloffs are neither brand-new nor the only viable way of distributing film imperfections. There's an ongoing debate among blown film equipment suppliers on their merits relative to alternative methods of randomizing gauge variations.

Without attempting to resolve this larger issue, this buyers' guide will focus on key questions of operation, technical limits, and cost for processors who are considering this approach. What are some basic differences between "vertical" and "horizontal" hauloff assemblies? Is either one recommended for all resins? What are the limits on web width? How do they affect cooling? The article will also touch on some pros and cons of oscillating hauloffs versus other methods of gauge distribution.

SUPPLIERS ARE DIVIDED

Although oscillating hauloffs are widely available, some equipment suppliers favor them more than others. Supporters point out that the oscillating hauloff, because of its location high on the tower, distributes gauge imperfections caused by ambient temperature changes on the bubble.

Others minimize the importance of this advantage. Sano, for example, goes on record as saying it does not recommend an oscillating hauloff, although it will make it available to customers who request it. "It's a buzzword," according to Sano's technical sales manager, Rick Knittel, who adds that the company generally favors a rotating die as an alternative, and will supply an enclosure to protect the bubble from ambient drafts.

The key to Sano's position is that it claims to offer a rotating die that does not leak. Knittel points to the rotating die's lower cost, and adds that it imparts less stress to the bubble because it confines its action to the molten portion of the polymer.

One potential source of gauge distortions is the collapsing frame, says Knittel, adding that because the collapser oscillates with the film in an oscillating hauloff, those imperfections are not distributed by such a system. He claims that part of Sano's approach has been to focus "investigative work on collapsing to understand what it does to gauge variation in film."

Other suppliers have done so as well. Robert Krycki, president of Future Design, which offers a horizontal-type oscillating hauloff, says the unit is sensitive to differences in film quality, such as air entrapment and wrinkles coming from the collapser. Rotating dies are more forgiving of differences in film quality, he adds. In the next few months, Future Design plans to introduce an improved air ring that Krycki claims may eliminate impurities that in turn can cause film distortions in the collapser.

Notwithstanding such criticisms, advocates claim that oscillating hauloffs offer an effective and practical way of randomizing gauge variations. Battenfeld Gloucester Engineering, for one, claims that oscillating hauloffs overcome problems inherent in other configurations. In Gloucester's view, rotating winders on the tower call for expensive provisions to return rolls to the floor; a rotating extruder and die limits the size of the extruder to be used. And, as noted before, rotating the die only fails to take into account bubble imperfections induced by ambient air after the die and may also be a source of leakage. Al Chrisbacher, v.p./general manager of Alpine American, agrees that oscillating hauloffs provide the simplest alternative by allowing extruders and winders to be fixed in one position on the floor.

HOW THEY WORK

Oscillating hauloffs can be divided into two basic types--horizontal and vertical. Primary patents are actually held by only a handful of companies: Windmoeller & Hoelscher, Alpine American, Macro Engineering, and Battenfeld Gloucester. Despite some similarities of operation, there are significant differences between each of these systems.

* Windmoeller & Hoelscher, the first blown-film equipment supplier to offer an oscillating hauloff back in 1973, sells a unit that feeds the film through a series of two horizontally arranged turning bars and two idler rolls after the primary nip and collapsing frame. After being collapsed, the film may pass through an additional cooling section above the nip. Each of the turning bars and oscillating nip are angled in a scissor-like arrangement to turn a total of 360 [degrees] in one direction, and then back 360 [degrees] to a closed, or 0 [degree], position. The turning bars move in relative motion to the collapsing frame, oscillating the tube and randomizing gauge variations as the film exits the tower.

The turning bars and nip are geared together by a direct drive to steer the web to the outgoing point in the tower. Proper gear ratios in the oscillating section are critical to prevent wandering, according to W&H extrusion sales manager Andrew Wheeler. The turning bars are pneumatically pressure-loaded and PTFE-coated to minimize friction. He adds that proper tension control is also important to prevent fluctuations as the film is being drawn off.

This type of hauloff is not inexpensive. Prices can typically range between $120,000 and $320,000, says Wheeler. The cost of a W&H unit, including nip section, turning bars, and collapsing frame, for a 60-80 in. wide web could run $200,000.

W&H recently developed a hauloff that uses one turning bar that oscillates only 180 [degrees]. This unit is recommended for use only with W&H's Optifil P die and high-quality films, and is not part of the company's standard line at this time.

* Alpine American Corp. manufactures an oscillating hauloff that works on a similar principle to the W&H unit. It also provides air-loaded turning bars, and includes an extra cooling section between the nip and collapser.

One difference is that Alpine's system uses three turning bars instead of two. Each of the turning bars is independently positioned and controlled by servo drives. The advantage of this, according to Alpine's Chrisbacher, is that they can compensate for inconsistencies in film thickness that can cause the web to drift to the left or right as it exits the tower. Turning bars can be positioned just slightly differently from one another as the need arises, based on the position of the web, thus keeping the web centered.

Chrisbacher adds that the collapser can be made to combine wood slats and rollers into one assembly, to handle either tacky films or HDPE. The collapser is motorized on four sides, so that positioning, angling, and width variation can be adjusted from an operator station.

Alpine has installed seven oscillating hauloffs, and has taken orders for three more, says Chrisbacher. It is available in working widths from about 57 in. to 100 in. Prices can vary from $75,000 to $130,000, depending on width and options such as type of collapsing hardware and additional cooling. Cost of a typical "mid-range" system for a monolayer line is about $130,000, he adds.

* Macro Engineering has taken a different, "vertical" approach, where by the web is stood up on end (see PT, Feb. '88, p. 57). In this version, the tube of film passes through the collapsing frame and is drawn by the primary nip. It then passes through a slot in a round oscillating table, and wraps around a 45 [degrees]-angled roller that changes its position from horizontal to vertical, or standing on one end. The platform oscillates through 360 [degrees] powered by a variable-speed d-c drive. As it rotates, a series of vertical rollers guide the web toward a second 45 [degrees]-angled stationary roll mounted on the tower framework, so the film exits the tower in a normal horizontal position for winding.

The unit is said to have a numbered features that minimize gauge variation. The four-sided collapser uses side stabilizers to prevent bubble movement that may cause wrinkles. Two air-flotation turning bars prevent wrinkling and edge wandering, and a gear-rack drive system provides smooth, steady movement.

The gear-rack system driving the platform is said to require less maintenance than a chain-and-sprocket drive. Power and pneumatic systems are connected with flexible couplings instead of power rings and brushes, which is also said to lower maintenance needs. In addition, both turning bars have independent blowers, so plant air is only required to close the nip rollers.

Low-friction, segmented rollers can be substituted for hard maple slats in the collapsing frame to decrease friction. Adjustable air-flotation turning bars can substitute for stationary ones in the oscillating platform to prevent wrinkling and edge wandering of very slippery or thin films.

Price of a 64-in. takeoff system, including collapsing frame and oscillating platform, is in the $110,000 to $130,000 range, depending on options, according to Mirek Planeta, Macro president.

* Battenfeld Gloucester Engineering offers its Traversanip, which has a similar basic operating principle to that of the Macro unit. Here, too, the web is stood up on end by a slanted, stationary turning bar after the film passes through the primary nip. The film then travels around the framework of the oscillating platform, over a second turning bar, which returns it to the horizontal plane, and down the tower.

One difference is that the nip is mounted at the top of the assembly, which product manager Bill Hellmuth says maximizes the effective cooling height of the tower while simultaneously requiring less headroom than other designs. "If a building has a 50-ft ceiling, we can set the nips at 45 ft."

Another difference is 720 [degrees] oscillation: 360 [degrees] in one direction, in which the film totally surrounds the framework, back to the "home" position, another full turn in the opposite direction, and back again to the home position. Hellmuth claims that the double rotation introduces less instability into the bubble because the hauloff makes fewer directional changes in the course of winding a roll; this also puts less strain on the reversing mechanism. He adds that it makes possible more gradual control of acceleration and deceleration, thus avoiding a jerking motion of the bubble. However, 720 [degrees] oscillation does not in itself apparently do any better job of distributing film variation across the web than does a 360 [degrees] version.

Hellmuth says Gloucester Engineering has installed around two dozen oscillating hauloffs, primarily in the U.S. and Canada, and supplies them in web widths from 54 to 104 in. Price of an 84-in. Traversanip with standard maple collapser is about $105,000.

A few additional suppliers manufacture oscillating hauloffs, or plan to.

* Filmaster manufactures a vertical-type system with eight rolls and lead-in and lead-out idlers, which is in the $40,000 to $45,000 range for web widths of 54-84 in. It has offered the unit for about two years and has two units in the field, according to Frank Goffrieda, v.p. of sales and engineering.

* Sano Corp. has also supplied units in the past, for which it has paid Windmoeller & Hoelscher fees. It will offer its own version after this month, following the expiration of remaining patents, according to Rick Knittel.

Most other blown film equipment manufacturers contacted for this article second-source oscillating hauloffs--several from Klaus Reinhold of Lengerich, West Germany, which reportedly has licensed technology from Windmoeller & Hoelscher. Some, such as Kiefel, acquire a basic unit and add on their own nips and drives. Other manufacturers buy oscillating hauloffs from a number of outside suppliers. Polysystem Machinery Mfg., for example, sources oscillating hauloffs from Macro, Gloucester Engineering, and Reinhold, according to sales manager Jim Ley.

TECHNICAL LIMITS

Several suppliers point to potential difficulties in using oscillating hauloffs. According to Hector Marchand, manager of blown film systems for Reifenhauser-Van Dorn Co., which offers a horizontal-type unit, "there are limits on the technology. With the right films and the right widths, there is no better way to distribute gauge variation. However, there are liabilities in the approach." The following are some of the specific areas of limitation.

* Tacky or stiff materials: Reifenhauser, for example, advises against running certain resins on an oscillating hauloff. Two potential problem areas are extremely tacky materials or very stiff film, says Marchand. Film with very high EVA content may "hold onto" guide rollers or retain a memory of stress conditions; stiff materials such as nylon may tend to wrinkle as they pass through the turning bars.

Tony Klein, manager of blown film systems for Davis-Standard, which offers a horizontal-type oscillating hauloff, calls tacky and soft materials a "gray area" that could be a problem if taken to the extreme. He claims that high tension levels that hold the web straight as it passes down the tower may introduce blocking, which can cause difficulties at the slitter station.

One crucial factor for good roll quality is alignment of the turning bars. In that sense, at least, extensible materials such as LDPE may be more forgiving than stiffer films, according to Klein. "The geometry of handling the web, in tolerances relative to trimming, makes it difficult to handle a truly non-extensible web without wrinkling."

On the other hand, Hellmuth of Gloucester Engineering claims that customers are running films with up to 18% EVA loading successfully on its Traversanip. He adds that the unit is particularly suitable for running HDPE. One advantage here is mechanical simplicity: there are only two stationary air-flotation bars, which reduce the possibility of misalignment, he says. Unlike its horizontal counterparts, the assembly does not use reduction gears.

Other suppliers, such as Alpine, say it's possible to compensate for extremely tacky or stiff materials by mechanical means. Chrisbacher sees no limits on the types of materials that can be run through an oscillating hauloff. He suggests that the same methods of dealing with "difficult" materials are as effective with oscillating takeoffs as with their stationary counterparts. On the collapsing frame, PTFE coatings or felt can be used to reduce friction against the film. Turning bars on the oscillating unit can also have PTFE coatings and air flotation to minimize sticking.

* Wide webs: A second possible limiting factor for oscillating hauloffs is the width of the web. W&H's Wheeler says his company has successfully supplied oscillating hauloffs for 120-in wide webs. On the other hand, Marchand of Reifenhauser-Van Dorn, which supplies a similar system, concedes that "the challenges of mechanically dealing with these systems gets greater as the widths get wider." One disadvantage of very wide units is that they can impart stresses to the film that can show up on the roll, he explains. On narrow webs, the stresses are minimal, but as the web gets wider, its easier for the film path to get out of line and introduce stresses. He points out that a good edge guide is an important component to prevent wander.

He adds that a 120-in.-wide web requires a large assembly to be to be installed 30-35 ft above the ground, regardless of the type of oscillating hauloff used. A vertical-type assembly, in which the web is stood up on end, would add another 10 ft to the tower, he says. He claims that a horizontal-type unit would reduce this added height to about 3 ft.

Gloucester Engineering's Hellmuth, on the other hand, does not see limits on web width. He says the company is building a 104-in.-wide unit, and can provide for 124-in. webs. "The basic restriction is how to ship it," he remarks, adding that the use of stationary turning bars is better suited to wide webs.

* Light gauges: Owen Kellet of O/K International, which represents Kuhne GmbH in the U.S. and supplies a horizontal-type oscillating hauloff with its units, points to potential limits with thin-gauge film. He claims that wide webs (greater than 60 in.) of light-gauge HDPE, run at high speeds, can encounter problems if the film is not of good quality. "As it wraps around the nip rolls in an S-curve, it undergoes a lot of tension. If there is any weakness in the film, at a light gauge, it will be accentuated."

On the other hand, Bill Hellmuth reports that Gloucester Engineering has successfully run 64-in.-wide HDPE of 0.3-mil gauge at 300 ft/min through an oscillating hauloff in its lab.

ADVANTAGES FOR COEXTRUSION?

Several suppliers, although not all, say that oscillating hauloffs may have their greatest impact in coextrusion. For example, Future Design president Robert Krycki sees their primary advantage in coextrusion lines, where they can replace complex rotating die assemblies. It's here also that the six-figure price-tags of some oscillating hauloffs may appear less daunting. Krycki points out that a six-layer rotating die can run $100,000. Other suppliers add that easier maintenance requirements of oscillating hauloffs further narrow the gap in upfront costs.

On the other hand, Wheeler of W&H does not view coextrusion as a driving force, saying that gauge variation is no more common on coextrusion lines than on monolayer ones. He adds that his company provides an oscillating hauloff for nearly all of its systems.

PHOTO : The oscillating hauloff offered by Macro-Engineering stands the web on end by wrapping it

PHOTO : around a 45 [degrees] angled turning bar. The platform oscillates 360 [degrees], sending

PHOTO : the film through vertical rollers.

PHOTO : Gloucester Engineering's Traversanip turns the web to a vertical position. The nip is

PHOTO : mounted near the top of the assembly, which is said to maximize cooling, and the platform

PHOTO : oscillates 720 [degrees].

PHOTO : This horizontal-type oscillating hauloff, offered by Reifenhauser-Van Dorn, is said to

PHOTO : require less height than its vertical counterpart and has an extra cooling section near

PHOTO : the nip.
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Title Annotation:plastics machinery
Author:De Gaspari, John
Publication:Plastics Technology
Date:Oct 1, 1990
Words:2939
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