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Cooperation proves critical in tube manufacturing

In this Q&A, Mel O’Leary, Jr., president and CEO of Meredith-Springfield Associates, describes how copolyester resin and supplier cooperation helped make the Artegraft tube.

Pw 7610 Mel O Leary Sidebar

PW: Meredith-Springfield is a plastic molder of technical hollow containers and custom bottles. How does Eastman Chemical’s Eastar Copolyester MB002 resin help your company extrusion/blow-mold the Artegraft tubes?

O’Leary: PET was the obvious choice of resin because it has great clarity and other physical properties supportive of the needs of this application. While PET is largely stretch/blow-molded, the most practical way to mold Artegraft’s tube with its particular cross section and length was extrusion/blow-molding. Eastman’s resin is specifically designed for extrusion/blow-molding. It is more like an engineering resin that accommodates specific equipment requirements and a narrower processing window as compared to resins like HDPE or PVC. The 20-inch-plus length of the tube makes it a challenge.

PW: Describe the extrusion/blow-molding process on the equipment used for the Artegraft tubes.

O’Leary: We receive Eastman’s resin in pellet form, in 1,400-lb Gaylord boxes. Vacuum draws resin from the box into a desiccant dryer. PET is very hydroscopic and must be dried to a -40ºF dew point. From the drier, the material is vacuum-loaded into an extruder hopper that keeps the material dry and warm. The plastic pellets fall by gravity to the extruder screw and are melted. At the end of the extruder is a die head. The tooling in the die head forms the hot taffy-like plastic mass coming off the screw into a centerless tube called a parison. The parison free falls out of the die head. The process is continuous, so the parison never stops coming out. The mold is shuttled back and forth from under the die head, where it captures a length of parison and then transfers away from the die head to the blowing position. A pin is inserted into the tube and compressed air from this pin blows the hot plastic out into contact with the metal mold cavity. The mold is a reverse of the Artegraft tube. The mold is refrigerated to rapidly cool the plastic and stabilize the shape and dimensions of the blown tube. The mold opens and drops out a molding and then shuttles back to get another parison. This process is repeated in an ongoing, automatic cycle.

PW: What are the specific molding challenges with Artegraft’s long tube?

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