John Griffin, plant engineer for Tex-Trude LP, Channelview, Tex. recalls the afternoon on Saturday, Nov. 8, 2008 when he received a call from the fire department informing him they needed his assistance at the plant. When the smoke finally cleared two days later once the five-alarm fire was extinguished, the film processor had lost more than 4.5 million lb of finished goods, in excess of 2 million lb of resin and its shipping, receiving, reprocessing and bag-making departments totaling 170,000 ft² .
Less than three years later, Tex-Trude has emerged from the disaster as a more efficient operation. They have installed new materials conveying in addition to recycling and blown-film technologies that have repositioned it as a leader in supplying PE and PVC films for newspaper bags, industrial bags, construction film and many other applications.
Tex-Trude uses large volumes of off-spec film scrap—some of which it generates, the rest purchased from brokers When it came time to rebuild it wanted a single vendor that could handle the integration of the feeding and pneumatic conveying systems on a soup-to-nuts basis, including management of the project from design to startup. Tex-Trude opted to go with the K-Tron Process Group, Pitman, N.J.
In the new system, reclaimed materials are pneumatically conveyed with fillers and other additives to the process area via a vacuum sequencing system. The pneumatic receivers refill gravimetric and volumetric feeders, which in turn feed into a collection screw. The collection screw then conveys materials to a recycling system supplied by Erema, Ipswich, Mass. After extrusion, the reprocessed pellets are totalized by using a weigh belt feeder, then pneumatically conveyed to indoor blend silos and finally transferred to outdoor storage tanks.
The vacuum sequencing system includes multiple receivers, with some designed specifically for handling fine powder fillers and additives. Custom units feature a large-capacity hopper, an extended cartridge filter and a feeder vent. The large capacity hopper allows the receiver to be used as a refill hopper and saves on headroom. The extended cartridge provides additional filter area and allows for the conveying of a variety of products, from plastic pellets to fine minerals. The custom designed receiver also includes a vent assembly that eliminates the need for external dust collection during feeder refill. When the loss-in-weight feeder request a refill, the discharge valve and the vent valve on the receiver simultaneously open and material flows into the feeder hopper. The displaced air in the feeder hopper is ducted back to the receiver. This allows the receiver to be used as the filter for the displaced air during feeder refill.
To ensure proper screw fill and prevent bridging in the hopper the additive feeders were equipped with K-Tron’s ActiFlow bulk solid activators. The ActiFlow is a non product contact device, bolted to the outside of the of the feeder hopper, eliminating the need for mechanical vertical agitation. The unit consists of the ActiFlow drive and the ActiFlow control unit, which continuously activates the material inside the hopper with an optimized variable frequency and amplitude.
The throughput of the extruder is measured by the K-Tron Smart Weigh Belt Feeder (SWB). This unit provides a master mass flow signal for the additive feeders to be slaved on line. The volumetric and loss-in-weight feeders dose the additives in preset ratios based on the master signal from the SWB. This is all monitored via the K-Vision line operator interface.
Griffin said that once the finished plastic pellets are pneumatically conveyed from the Erema process to the indoor blend silos, Tex-Trude wanted a way to mix multiple batches together to ensure a more uniform blend before conveying to outdoor storage tanks. K-Tron was able to achieve this by providing a custom PLC system to control the material going into the silos and adding zone blenders within one of two tanks on each system. The zone blender is mounted on the bottom of the silo and, its special geometry guides the pellets through multiple zones at different velocities and residence times. As a result, the discharged pellets are uniformly blended.
The process works as follows: Recycled pellets are conveyed from the continuous production system into a transfer silo until a specified amount of pellets is delivered by weight. At that time a second silo (blend silo), equipped with a Zone Blender , calls for material from the transfer silo and fills to a set weight. Once the set point is reached, the blend silo releases the pellets and circulates them back into the top of the blend silo. The pellets continue to circulate through the Zone Blender until a predetermined mix time expires. At that point the pellets are transferred to outdoor storage tanks. The result is a uniform blend of pellets.
Griffin stated the result of this re-engineering is Tex-Trude now runs three reprocessing lines and produces 35% more product than the five line system they had prior to the fire. It is also enhancing its film-extrusion capacity with the recent purchase of a three-layer line from Hosokawa Alpine American, Natick, Mass. for the production of films up to 80-in. wide. Tex-Trude runs 19 blown film lines in total.