by Bob Jeter, Applications Engineer, Amacoil, Inc.

Fig. 1 Jennings extrusion machine with operator at the controls (below)

Fig. 1a

Fig. 2 In-line oven system vaporizes the lubricant from the PTFE extrudate

Jennings International, Norristown, PA, USA, is a manufacturer of semi-custom polytetrafluoroethylene (PTFE) fine powder paste extrusion equipment. The company's product line includes specialized machinery for extruding PTFE-insulated wire, PTFE hose and tubing and PTFE film and tape.

Adding value to the PTFE extrusion process
The chemical and physical properties of PTFE derive from the material's fluorocarbon structure. PTFE possesses virtually universal chemical inertness, insolubility in solvents below 300°C (572°F) and good thermal stability. PTFE's electrical insulation properties include low dielectric loss, low dielectric constant and high dielectric strength.

Using Teflon® brand precursors, Jennings patented its first extruder in 1953. The process has been modified over time to accommodate the more advanced PTFE material which enters the process as a fine powder resin. The PTFE resin is stored in a temperature-controlled room where it is mixed with a lubricating solvent. The resin and lubricant mixture is then solidified in a preform press.

The resulting PTFE preform is then loaded into the extruder. It is pressed through a die and extruded as a tube, tape or insulation over wire. An in-line oven system vaporizes the lubricant from the PTFE extrudate. A sintering oven is used to cure the product where temperatures up to 850°F (1562°C).

After cooling, the product is wound onto a take-up spool for distribution. The wire take-up procedure is where Jennings International saw an opportunity to add value and strengthen its CRM (customer relationship management) policies. To improve time-to-market capability for its customers, Jennings International began to design a linear traverse assembly into the extrusion line. The linear traverse assembly guides the PTFE-insulated wire directly onto take-up spools thus eliminating the need for the customer to design and fabricate their own take-up systems.

Most Jennings customers have selected this added-value option. Jennings had to develop a manufacturing plan to build in the traverse unit without adversely affecting selling price, or their own product development costs.

Fig. 3 Linear traverse take-up system on Jennings extruding machine

Adding value without adding costs
PTFE extrusion lines can represent a significant capital investment depending on the size and stroke length of the extruder and auxiliary equipment. Naturally, production machinery carrying a large capital investment pays for itself only if the production process is operated at peak, or near-peak, efficiency rates - as close to non-stop as possible. That meant Jennings had to provide a traverse solution that was both reliable and essentially maintenance-free. Their choices were to build such a system or use a supplier capable of designing and fabricating the assembly. They chose the latter, selecting Amacoil/Uhing rolling ring linear motion systems.

"We knew we needed a simple design for the traverse," said John Porta, Jennings International VP. "Even though the traverse is a very minor part of the machine, if it breaks down or requires frequent maintenance, valuable production time is lost."

Should the traverse system fail, an even larger problem exists for Jennings customers. Porta explained that since the Jennings machine is used in a batch process operation, successful production requires complete consumption of any given batch. If the traverse system breaks down, it is feasible that the remaining batch would be lost resulting in a serious drop in production revenues.

The simplicity of the rolling ring operating principle met Jennings' needs. The type of rolling ring assembly Jennings International uses in its take-up system provides automatic reversal without clutches, cams or gears. It is not necessary to reverse the drive motor - the linear traverse direction is controlled by purely mechanical means.

Fig. 4 Comparison of rolling ring (left) and screw-based (right) drive systems

The rolling ring design enabled Jennings International to use a single motor in the traverse system, instead of one each to drive the take-up spool and the linear traverse. This is possible because rolling ring engineering permits the use of a simple pulley system to synchronize the rotational motion of the take-up spool with the traversing motion of the linear drive. Had a separate motor been required for the traverse, reversing the traverse system would have required the drive motor be slowed, stopped and reversed. The motor would have had to be a variable speed motor capable of rotating in two directions. By avoiding this, Jennings also eliminated the need for a traverse motor encoder and controls. The total savings for Jennings International is about US$1,000 per machine.

Said Porta, "The system can be free of complex electronic controls. This keeps our cost down so we can offer the added value of the traverse without adversely affecting the selling price of an extrusion line. Our customers like that we can offer a take-up solution with minimal operator training requirements because it further controls the costs to acquire the Jennings machine."

Also influencing Jennings' decision to use a rolling ring drive is the fact that the system runs on a smooth, unthreaded shaft. Thread clogging in the traverse assembly posed a problem for some customers. Designing and fabricating a shaft bellows assembly to keep the threads clean was a slight additional cost. The smooth shaft solution works better. According to Porta, "Rolling ring technology has proven itself as a reliable and maintenance-free solution."

Since the linear drive supplier is experienced in building wire winding traverse assemblies, Jennings encourages its customers to deal directly with Amacoil for any concerns with the traverse. "Our partnership with Amacoil has worked very well," said Porta. "When they have questions about the traverse assembly, our customers appreciate dealing directly with Amacoil."

Conclusion
Adding the traverse assembly option to its extruding machines has enabled Jennings International to significantly strengthen its customer relations. The rolling ring linear motion solution proved inexpensive and effective. It enabled Jennings to meet its objective of adding value without significantly increasing its product development costs.

For more information about Jennings: www.jenningsinternational.com

TEFLON® is a registered trademark of E. I. du Pont de Nemours and Company.