Round Rod in PAI C CF30 152.4 mm black

PAI C CF30 in round rod format is the raw material for turned and milled components where no other thermoplastic is enough. The polyamide-imide is compression molded and post cured, which gives a very high base level of mechanical and thermal performance. The addition of 30 percent carbon fiber raises the stiffness further, lowers the thermal expansion and improves the tribology considerably compared with unfilled PAI. The round rod has a dark brown, matte surface that is typical of the material and should not be mistaken for surface defects.

The rod is used above all for bushings, plain bearings, piston rings, stuffing box sleeves, washers, valve seats and sealing elements where the operating temperature is high and lubrication is marginal. The carbon fiber makes the material forgiving of dry running and keeps the PV value up even when the surrounding temperature rises. Wear against steel is low and the coefficient of friction stays stable over a wide temperature range. The material also scratches softer mating surfaces less than glass fiber filled PAI does, which is a concrete advantage in designs where the mating surface is aluminum or brass.

Heat resistance sits far above PEEK in continuous service, and PAI keeps a large share of its stiffness well up into the range where other engineering plastics soften. That makes the material relevant in compressor valve components, high temperature turned shaft bushings, semiconductor equipment, motor insulators and pump housings in the chemical industry. The low thermal expansion is valuable in designs where fits against steel or aluminum have to hold through the whole temperature cycle. When the material is combined correctly with metal mating surfaces, the risk of play in the cold and seizing in the heat is minimized.

Chemical resistance is broad. PAI withstands almost all organic solvents, hydraulic fluids, oils, fuels and refrigerants. The material is well proven in contact with synthetic brake fluids, compressor oils and most hydraulic fluids used in industry and vehicles. The limit lies in concentrated acids and strong alkalis, where other materials suit better. Moisture absorption is low and does not affect the dimensions the way it does on PA grades, which is a strong advantage in precision parts that live in damp or temperature cycling environments. Keep that in mind when you compare turned PAI bushings with the equivalent in PA6 C, where the change of season can move the measurement by several tenths.

For machining, use sharp tools in carbide or PCD. The carbon fiber wears on the inserts, and tool changes come more often than when turning unfilled PA or POM. Set a moderate feed, a low depth of cut for finishing and good chip clearance. Use compressed air or cutting oil for cooling, and avoid water. The natural dark brown tone of the rods darkens somewhat after post curing, which is normal and does not affect performance. Bear in mind that the round rod is expensive per kilo and that waste during turning should be kept down through a well thought out raw size; do not start with a grossly over thick rod unless there are geometric reasons for it.

In many designs it works to start with a slightly thicker round rod and mill down toward finished size, since the large diameters are expensive and at times hard to get hold of. If you need a grade with higher dimensional stability and cheaper machining instead, the GF30 version works better, at the cost of the tribology. There are also PAI grades with added PTFE and graphite for even lower friction, but they lose structural strength and cost more. For many compressor and pump components, CF30 is the best practical compromise between wear resistance, thermal stability and machinability.

For designers approaching PAI for the first time it is worth thinking in three dimensions: operating temperature, mating surface and PV value. The material takes you considerably higher in all three than PEEK and PI do, but it is expensive per kilo and calls for more frequent tool changes. Working with a local service supplier who has experience of PAI saves both time and waste. Stocked diameters vary; the most common is the range from about 10 mm up toward 200 mm, with thinner rods more readily available than heavy ones.

Do you want help choosing diameter and grade based on your component's operating temperature, load and mating surface? Get in touch and we will go through it together.