Global Processing

Plastics extruder makes a fluid transition to a new heat transfer fluid

May 24, 2004

Polyvisions Inc. is a specialty plastics company that has a wide range of extrusion and mixing capabilities. Because the company processes over 25 generic resin products with a wide variety of custom additives, they need a heat transfer fluid with consistent thermal stability and minimum impact from oxidation. They selected Paratherm NF and have continued to use this non-fouling, non-toxic heat transfer fluid ever since. The current manufacturing facility in Manchester, Penn., was opened in 1996. There are 13 employees and the company generates annual revenues of $2 million from its production of more than one million pounds of polyolefin and polyester compounds. These specialty additive compounds are supplied to a wide range of manufacturers of end use articles to enhance production processability and product properties. Specialty additives are supplied in pellet concentrate form. The exceptional performance of these specialty pellets stems from the intimate, intensive mixing of ingredients. The company is able to integrate additives evenly into plastic raw materials, as well as develop additives that have multiple applications. Polyvisions will also convert compounds from a light powder form into pellets, or process compounds that contain light powder ingredients in order to help control dust problems in customer production facilities. Among the additives that Polyvisions uses are pigments, nucleating agents (which accelerates crystallization of plastic compounds), lubricants, surface modifiers that enhance appearance and impact modifiers that make plastic compounds more durable. Polyvisions'' capital inventory includes a variety of temperature control equipment manufactured by Advantage, Delta T, TUC, and other companies that circulate Paratherm heat transfer fluids to processing machines at a precise temperature. Among these processing machines is a Readco continuous mixer, originally designed for food processing but adapted for Polyvisions'' plastic compounds. Polyvisions President and CEO, Larry Bourland, said that the mixer''s large throat opening, deep flighted screw elements and large diameter barrels are particularly useful in blending compounds that include light, powdery ingredients.
"Traditional extruders are designed for high-density materials, such as pellets," Bourland says. "The Readco can handle fluffy, low bulk density materials that are a problem for other extruders."
Bourland first encountered the equipment at Penn State University in 1990. Even though it was designed to mix food formulations such as pasta and candy, he recognized the design was ideal for blending the powdery ingredients that Polyvisions uses in its compounds.
Polyvisions adapted the unit by reconfiguring parts, such as segmented screws, internal elements and the drive train. The unusually deep flights of the Readco screw elements have large internal volumes that can accommodate light and fluffy shredded materials from recycled sources more effectively.
"Feeding these low bulk density feedstocks, mixing in the molten state, and then converting the materials into traditional solid pellets is simply not a problem," Bourland says. In fact, he was recently called in to help another company adapt a similar piece of equipment to convert recycled telephone books into kitty litter.
The lab extruder has a closed-loop thermal fluid system that circulates Paratherm NF maintaining the extruder barrel at a pre-set temperature. Over the years the Paratherm fluid has proven reliable, durable, and hazard-free. In addition the Paratherm fluid resists oxidation better than competitive fluids so there is a lot less accumulated carbon residue in the equipment.
"If that residue is permitted to accumulate on the surface of heating elements, heat control becomes crippled," Bourland adds. "The same thing will happen if residue coats the pumps or the surfaces of the cooling apparatus."
Polyvisions uses Paratherm NF for temperature control of applications of up to 550 degrees F. For even higher temperature applications, heating is controlled electrically with metallic bands as heating elements. However, this direct heating method has the potential that an electrical arc around airborne powdery substances would instantly create a hazardous situation. With Paratherm NF the heated fluid is externally circulated to the equipment removing the risk of electrical arcs.
"Removing excess heat from thermal oil is also is never a problem. The temperature control units are equipped with heat exchangers that efficiently remove excess heat generated during melt processing," says Bourland.
In addition to the Readco extruder, Polyvisions regulates the temperature of other mixing equipment by closed loop circulation of Paratherm NF heat transfer fluid. The other types of mixing equipment, a jacketed ribbon blenders, mix materials in the solid state but often the mixing is more effectively conducted at temperatures slightly elevated above ambient temperatures to promote even integration of all components. In this application, Paratherm NF circulated from the control mechanism to the blender is maintained at temperatures up to 350 degrees F.
"These tend to be long production runs," Bourland says, "so the thermal oil can become exposed to air. If the thermal fluid we used were vulnerable to oxidation it would quickly discolor and thicken. Sooner of later this would compromise thermal performance.
"Paratherm is good but that doesn''t mean we can skip routine maintenance. If you don''t perform routine maintenance, it doesn''t matter whose products you use. Eventually, your production will come to a halt."

For more information, contact Paratherm Corporation at 800-222-3611 or email