PAI Rod - Torlon 4301, Bearing and Wear Grade

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.

Read this before you specify it. TORLON 4301 IS NOT AN ELECTRICAL INSULATOR. It carries 12 percent graphite powder and 3 percent PTFE, which drops surface resistivity to around 1E13 ohm against 1E16 for the unreinforced 4203, and raises dielectric constant to 6.0 against 4.2. If the part insulates, order 4203 / 4203L. This grade is for sliding contact and nothing else.

What it is for: bearings, bushings, thrust washers, seal and wear rings, spline liners and valve seats, running non-lubricated or marginally lubricated. Limiting PV is 40,000 psi-ft/min against 12,000 for the unreinforced grade - better than three times - and the wear factor is about a third. Dynamic coefficient of friction against steel is around 0.20 dry.

Published stock-shape figures: tensile strength 15,000 psi, flexural strength 23,000 psi, flexural modulus 800,000 psi, compressive strength 22,000 psi at 10 percent deformation, compressive modulus 950,000 psi, notched Izod 0.8 ft-lb/in, Rockwell M106. Specific gravity 1.45. It is stronger in compression than the unreinforced grade but far less tough - 0.8 ft-lb/in against 2.0.

The wear numbers come with a condition attached that is easy to miss: the published wear factor and limiting PV are both measured WITH a post-machine cure. Without re-curing, wear can be roughly ten times worse and limiting PV about half. The published guidance is to re-cure above 100 feet per minute surface speed or above 10,000 psi-ft/min PV. Low-speed high-pressure applications gain little. Ask us and we will arrange it.

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.

The honest limits. PAI is not universally chemical resistant: strong bases such as sodium hydroxide attack it, and so do saturated steam and some high-temperature acids. Steam service is a common and expensive mistake. It absorbs water and grows - thin unreinforced stock at high humidity and 110F picked up about 4 percent water and grew half a percent over a hundred days - so a tight-tolerance part needs that planned for. And cured PAI cannot be recycled: your chips and remnants are scrap, which matters when you cost out machining yield on material this expensive.

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.