TECHNOLOGY
Impact process reclaims PTFE scrap Powder product particles are similar in size and shape to those of virgin resin and have similar molding properties
PTFE SCRAP. Operator at Metallurgical International's New Shrewsbury, N.J., plant examines pile of reprocessed PTFE powder and various forms of scrap, including tape, shavings, and hard stock. Next to the operator is the blast chamber from which a flexible tube carries powder up to the classifier
Metallurgical International, Inc., is now reclaiming scrap polytetrafluoroethylene (PTFE) at its new industrial powders plant in New Shrewsbury, N.J. The company's patented Coldstream impact process produces a powder from scrap P T F E - D u Pont's Teflon and Allied Chemicars Halon, for example—in a much finer, irregularly shaped particle size than is presently obtained by conventional grinding or milling methods. When remolded into billets for further machining of parts, the fine powder gives a reprocessed material possessing superior physical properties to that remolded from coarser particles, MI says. Executive vice president Ira L. Friedman expects fabricators to be encouraged by the improved performance of Coldstream reprocessed PTFE to show wider acceptance of the material. Such acceptance, he says, would enlarge not only markets for reprocessed material but also for virgin resin. Presently, he estimates, total U.S. production of PTFE is about 15 million pounds a year. Of this total, 8 to 10% goes to scrap shavings and chips at the molders and fabricators. The least expensive grade of virgin PTFE costs $3.25 per pound, which makes reclamation economically attractive compared to lower-priced thermoplastics. Since PTFE does not melt-flow as do other thermoplastic resins, it cannot be injection-molded into parts. Scraps as well as virgin resin must be powdered and compression-molded into forms from which parts are then machined. But polyethylene, polystyrene, acrylic, nylon, and other thermoplastic scraps are simply granulated, blended in with feed resin, and re-extruded. Amounting to no more than 5% of a molder's production output, such scraps result from extruder startups, off-size particles from the pelletizer, and trimmings from injection-molding equipment. Reclaiming PTFE is an important new application of the Coldstream impact process, Mr. Friedman says. Originally MI developed the process for reclaiming refractory metals, such as tungsten carbide, and for preparing powdered metals and alloys. But now, two of the three Coldstream impact units at the New Shrewsbury plant are designated for processing PTFE at a design capacity of 20 tons per month. MI will operate the other unit along with its new atomization facility to convert atomized metals and alloys to
irregularly shaped, oxide-free alloy powders for its business in powder metallurgy. Versatility of the Coldstream impact process lies in its simplicity. Material to be powdered is fed into an air stream traveling at several times the speed of sound under pressures to 1000 p.s.i. As the air stream rushes through a Venturi nozzle and expands into the blast chamber, its adiabatic expansion produces an extreme cooling effect down to about 0° C. The material is blasted against the cold target, such as tungsten carbide, and swept through a particle classifier. Fines go to a dust collector, specification-size particles go to product drums, and oversizes recycle through another blasting. Cold target. "When I felt how cold the target remains even after processing a refractory metal such as tungsten carbide, I realized that the process would apply to reclaiming scrap thermoplastics, particularly PTFE," recalls J. Douglas Campbell, director of corporate development. Since the process generates no heat, the resin remains cool and crystalline for maximum shattering on impact. The real advantage of the Coldstream impact process, says Frank Sellars, general manager of the resins division, is that it produces particles similar in size and shape to those of virgin resin. The process shatters particles to irregular shapes which are as finely divided as 20 microns, slightly smaller than those available commercially at 30 microns. As a result, the Coldstream reprocessed powder can be extruded and compression-molded as readily as virgin powder. Today's conventionally reprocessed PTFE powders are coarser and smoother particles, Mr. Sellars points out. When the powder is compacted, large volumes of air voids remain in the form or billet. When compressed even at high pressures, so little cohesion develops between particles that the form disintegrates if removed from the mold for heat curing. To prevent this fragmentation, processors must heat-cure the form at about 700° F. while keeping it under high pressures in the mold housing. Mr. Sellars points out that using the Coldstream reprocessed powders reduces the molding problems and gives a molded product with improved physical and dielectric properties. Allied's plastics division finds that the Coldstream powder molds much
Availability Report:
Experimental Molybdenum Chemicals
BLAST CHAMBER. Tungsten carbide particles in air stream traveling several times the speed of sound enter blast chamber and strike cold target. This disperses the powder which is swept to the classifier. The Coldstream impact process, used to reclaim PTFE, was originally developed for reclaiming refractory metals such as tungsten carbide
Formulated by Climax to help you explore new processes and products NEW • 12-Molybdophosphoric Acid H3 [PM012O40] • x H 2 0 (A: = 5-29) NEW • 12-MoIybdosilicic Acid H4 [SiMo12O40] • x H 2 0 (x = 5-29) NEW • Sodium 12-Molybdosilicate Na4 [SiMoi2O40] • x H 2 0 {x = 10-15) D Molybdenum Tetrachloride D Molybdenum Dioxydichloride •
Molybdenum (III) Acetylacetonate
D Molybdenum Tetrachloride Dipyridine D Molybdenum Oxytrichloride D Molybdenum Oxy tetrachloride D Dimeric Ammonium 5-Molybdocobaltate(III) (NHJe [Co2Mo10O36] • x H 2 0 (x = 6-10) more like virgin resin than does conventionally reprocessed material. The company views Mi's process as a step to expanding the markets for both virgin and reprocessed PTFE. Du Pont's fluorocarbons division agrees that, for certain critical applications, today's reprocessed PTFE lacks the performance of virgin resin. Du Pont mentions that molding with a finer-particle-size powder is, indeed, essential to improving the physical properties of reprocessed PTFE. While making these improvements, the reprocessors, Du Pont cautions, must keep a close watch that no contamination enters the product. MI has taken precautions to ensure that product contamination is not a problem, Mr. Friedman emphasizes. Each of the two Coldstream impact units for processing PTFE is in a separately enclosed room with clean-room conditions. Specialized cleaning processes treat incoming scrap material. Filters and adapters purify the air stream from the compressor before it sweeps resin through the impact cycle. The system has no moving parts or obstructions to entrap particles from a previous run. Metal powders. Mr. Friedman sees great potential in the partnership of the Coldstream impact process with
the company's new 1 million poundper-year atomization facility. Atomization is an excellent way to prepare high alloys as spherical particles which then can be irregularly shaped through the Coldstream impact process, he says. Such blasted high alloys have greater point-to-point compactibility which powder metallurgists require for cold-pressing and sintering stronger parts. Other irregularly shaped alloys can be made with large surface areas exposed for maximum catalytic activity. Another advantage of the Coldstream impact process is that the blasting action strips any surface oxides from the underlying metal, Mr. Friedman points out. The brittle oxide film strikes the target and shatters before the particle's metal core does. During classification, the fine, fluffy oxide is preferentially collected in the dust bags, the shiny metal in the product drums. MI is presently negotiating licensing agreements on its Coldstream impact process internationally. The company holds patents on the process in the U.S. (3,184,169, issued to Lawrence S. Friedman, Ira L. Friedman, Kenneth C. Zagielski, and Leo A. Adams), nine European countries, Japan, and Canada.
D Ammonium 6-Molybdocobaltate(III) (NH4)3 [CoMo 6 0 24 H 6 ]. x H 2 0 (x= 5 - 7 ) D Ammonium 6-Moly bdoaluminate(III) (NH 4 ) 3 [AlMo6024H6] . J C H 2 0 ( ^ = 4 - 7 )
D Ammonium 6-Molybdochromate(III) (NH4)3 [CrMob024H6] a H 2 0 ( j c = 4 - 7 ) • Ammonium 6-MolybdonickeIate(II) (NH4)4 [NiMo 6 0 24 H 6 ]. x H 2 0 (* = 4 - 6 ) •
Molybdenyl Bis-Acetylacetonate
•
Molybdenum(VI) Oxalate H2 [Mo0 3 (C 2 0 4 )(H 2 0)] H 2 0
•
Ammonium 9-Molybdonickelate(IV) (NH4)6 [NiMo9032] • 6.5H20
D Ammonium 6-Molybdoferrate(III) (NHJa [FeMo 6 0 24 H 6 ]. JCH2O(JC = 5 - 1 0 )
Data sheets on any or all of these chemicals promptly available. Write:
CLIMAX MOLYBDENUM COMPANY An AAAA>C Division 1270 Avenue of the Americas New York, N.Y. 10020 SEPT. 4, 1967 C&EN 37
