PTFE – ASTM & AMS Grades of Molded Sheet and PTFE - Rod
Molded PTFE, polytetrafluoroethylene, more commonly known as PTFE, is one of the three fluorocarbon resins in the fluorocarbon class composed wholly of fluorine and carbon. Molded PTFE is compressed granular ASTM D4894 resin that is heated in a thermal bonding and annealing process called Sintering, at 800 degrees F and with a controlled cooling program that controls the thermal shrinkage from the mold to a stress-free room temperature condition. Large mass rod or disc shaped moldings have better success if a center cooling hole or tubular Inside Diameter can be utilized in the design to help control the cooling and thermal shrinking from the center from these sintering temperatures.
Molded sheets begin at .250” thickness. For thickness below .250”, a thickness skiving process is utilized from a large mass molded and sintered Tube that is mounted with a large turning blade that literally peals or skives off thin layers off the tube in a continuous skived sheet. Early on in the development of PTFE specifications all these were combined as one under the single AMS 3651 specification which was cancelled in December of 1994 and separated into Specifications that were created for the different PTFE manufacturing processes.
In 1994 The AMS 3651 specification was split into:
AMS 3652 & AMS 3662 for thin sheets and films
AMS 3667 for molded sheet
AMS 3656 for Extruded rods and tubes
AMS 3660 for Molded rods and tubes
Other AMS and ASTM Specifications have followed and continue to be revised, please contact Polymer Plastics Co. about these other specifications for current availability. For these and other AMS and ASTM specifications is the question of whether actual batch test reports or ‘Typical’ test reports are required for certification at substantial extra testing costs that needs to be defined in advance of ordering. The other fluoropolymer resins in this group, also referred to as Dupont or Chemours PTFE Teflon, are PFA and FEP and is reviewed under those headings.
Molded PTFE is post sintered combining the forces binding the fluorine and carbon together provide one of the strongest known chemical linkages in a compact symmetrical arrangement of atoms. The result of this bond strength plus the chain configuration is a relatively dense, chemically inert, thermally stable polymer.
Molded PTFE material resists attack by heat and virtually all chemicals. It is insoluble in all organics with the exception of a few exotics. Its electrical properties are excellent. Although it has high impact strength, its resistance to wear, tensile strength and creep resistance are low in comparison to other engineering type thermoplastics. Mechanical properties can be improved by adding fillers such as glass fibers, bronze, carbon, and graphite.
PTFE Rod, Sheet and Tube exhibits the lowest electric constant and lowest dissipation factors of all solid materials. Because of its strong chemical linkage, PTFE Sheet rod and tube shows very little attraction for dissimilar molecules. This results in a coefficient of friction as low as 0.05. Once again, because of this chemical bonding, PTFE resins are virtually insoluble.
