Changing the sequence of color layers in multilayer coextruded sheet is costly in terms of labor, material and downtime. This can be especially problematic as the industry trends toward shorter production runs.
Processing Technologies International (PTi) has developed the FastSelect online system to make changes in the layer sequence almost instantaneously, while eliminating the need for purging before making the changeover. The device is used for real-time color changes, by flipping material layers on the fly. For instance, two extruders running resin into the feedblock and die to create the A and B layers of an A-B-C structure can be reordered, so that the resulting sheet has layers B-A-C. With the FastSelect device, the two extruders producing the affected layers operate without interruption.
The change is effected via a diverter valve with a proprietary piston that is moveable in the body of the device. The device is added onto a coextrusion sheet line immediately upstream from the feedblock, said PTi President Dana Hanson.
An operator pulls a lever, which changes the diverter piston position from a straight flow to
a crossover flow path, changing the extrudate positions while the extruders continue to run at full speed.
The device streamlines a process that is time-consuming and costly for sheet extruders.
"One of the greatest challenges faced by processors of coextruded product is managing color change," Hanson said. Traditionally, color changes involve purging the machines offline and then restarting the machinery. Significant scrap and downtime are generated with this approach.
FastSelect allows operators to flip color layers without shutting the machinery down, Hanson said. "It literally occurs in seconds versus tens of minutes."
PTi has an exclusive ongoing agreement with Nordson Extrusion Dies Industries to manufacture the system. FastSelect is installed at Nordson's research and development center.
Sam Iuliano, senior technical manager for Nordson, said the key is that the new system is designed so that as one flow path begins to close, the other opens and the pressure doesn't fluctuate. "All flow paths remain flowing, so there's no dead material," he said.
Sheet extruders often change colors multiple times a day. In the course of a year, that can add up to many days of lost production. "So, on an annualized basis, the savings is tremendous," Hanson said.
FastSelect offers significant savings in terms of both downtime and lost productivity. Assuming three color changes a day, with extruders producing 3,500 pounds per hour, the conventional method can generate as much as 1.7 million pounds of scrap annually. That compares to less than 29,000 pounds of scrap with the FastSelect system. Under those parameters and assuming 30 minutes of downtime for a conventional color change, the conventional method produces 21 days or more of lost productivity per year; FastSelect averages about a third of a day.
PTi said the most practical applications to benefit from FastSelect are those that require routine color changes. An example would include the production of a four-layer disposable beverage cup that has a white inner layer and an out- side layer featuring one of a variety of colors. In a conventional process, an extruder is dedicated to each layer – an inner color layer, a regrind layer, an exterior color layer and a clear layer.
With every change in the exterior color layer, the processor generates scrap until color is fully transitioned. For an inline application, the line is shut down, the machines are purged and then restarted. These steps are avoided using FastSelect.
Iuliano said that in this application, the new color is fed into the extruder that is making the regrind layer a few minutes before it's time to change colors. "You start to prime it with the new color and then fill the valve. Let's say in a minute you purged out the die and feedblock. So, you're making one minute's worth of scrap cups as opposed to 40 minutes' worth of scrap cups. So, that's the concept, the application that PTi is initially marketing this for," he said.
The system also can be used to change the sequence of film layers in multilayer cast film. Iuliano said in certain stretch film applications, for example, a processor might have a four-layer structure and want to switch from the clear layer being on top to it being on the bottom. "So, you already have the extruder, you just pull a lever on the FastSelect device, and you can move the clear from one side to the other side."
FastSelect's features include a locking pin that ensures correct alignment at each layer sequence position. The spool coatings are lubricated to allow for smooth rotation. Each spool can be designed for two different three-layer structures. And the adaptor is easily disassembled for routine cleanings and spool replacement. While FastSelect currently operates manually, a powered version is feasible, Iuliano said.
Allan Gerlat, correspondent
For more information
Nordson Extrusion Dies Industries LLC,
Chippewa Falls, Wis., 715-726-1201, www.extrusiondies.com
Processing Technologies International LLC,
Aurora, Ill., 630-585-5800, www.ptiextruders.com
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