PAI Rod - Torlon 5030, 30% Glass, Extruded

Polyamide-imide, PAI, is the highest-performing melt-processable thermoplastic there is. It holds more strength and stiffness at 500F than most plastics have at room temperature, it creeps almost not at all, and it machines to tight tolerance. It is also expensive and slow to make - every stock shape goes through a multi-week cure cycle before it ships - which is why it is specified only where nothing cheaper survives.

This is the strongest and stiffest of the four, and the one to specify when a metal part has to come out and the replacement has to hold load at temperature. Published stock-shape figures: tensile strength 23,000 psi, flexural strength 30,000 psi, flexural modulus 980,000 psi, tensile modulus 1,000,000 psi, compressive strength 40,000 psi at 10 percent deformation, notched Izod 1.0 ft-lb/in, Rockwell E90. Specific gravity 1.60. Tensile strength is still 18,000 psi at 300F.

Do NOT specify it for bearings or bushings. The 30 percent glass fiber that makes it strong is abrasive, and it will wear the mating surface. 4301 is the wear grade. Equally, a buyer who picks 4301 for a structural part gets 15,000 psi tensile where this gives 23,000.

One important qualification on the headline thermal number. The coefficient of thermal expansion of 0.9 x 10-5 per F is measured ALONG the extrusion direction, where the glass fiber aligns. Across it, properties and expansion differ by 10 to 25 percent. If you are machining a precision plate out of extruded rod and the tolerance has to hold at temperature, the axis you cut it on matters - that is precisely why the compression-molded 5530 grade exists.

One disclosure about the numbers on this page, because it is the single biggest trap in PAI copy. Polyamide-imide is published twice: once by the resin producer, measured on injection-molded test bars, and once by the shape makers, measured on specimens machined out of actual extruded stock. The two sets do not agree and the shape figures are lower - for the 30 percent glass grade the resin tensile is 32,000 psi against the shape's 23,000, a 39 percent difference. Everything quoted here is the stock-shape figure, because stock shape is what you are buying. If you have been designing to a resin datasheet, check your margins.

Temperature, which is the reason to buy it: glass transition is 527F and it is the same for every grade, because it is a property of the polymer rather than the filler. Long-term continuous service in air is 500F. Heat deflection at 264 psi runs 520 to 532F depending on grade. Note that PAI is amorphous - it does NOT melt at 527F, and a datasheet row reading "melt point 527F" is a mislabeled glass transition.

Machining notes. Positive-geometry ground-periphery inserts, fine-grain C-2 carbide for short runs and polycrystalline diamond for production, tight tolerance or any of the reinforced grades - all four grades are abrasive and will move your tool offsets over a long run. Unlike most of the laminates, PAI DOES want flood coolant for single-point threading, for drilling holes under an inch, and for tapping; deep-hole drilling without enough coolant cracks the part. Use 360 degree chuck pressure and soft or pie jaws on thin-wall tube. Excessive tool rubbing tears material out and looks exactly like localized porosity on an inspection report.

Torlon is a registered trademark of Syensqo and we are not affiliated with or endorsed by them. The generic name is polyamide-imide, PAI - not polyamide, which is nylon, and not polyimide, a different family.