Hollow Bar in PTFE CP10 2000 mm natural

Tubes in PTFE CP10 are pressed and sintered PTFE blanks where the matrix is filled with both carbon fiber and graphite. The carbon fiber provides the stiffness and the creep resistance; the graphite adds the lubricating effect that keeps friction low even when the part runs dry or half dry against the mating surface. It is a compound that suits bushings, valve seats and similar cylindrical parts particularly well, where the chemical inertness of PTFE has to be combined with higher pressure and wear than pure PTFE takes. The natural color is dark gray to black, since the carbon fiber and the graphite color the material dark.

The material handles 260 degrees long term and more than that in short peaks. Down toward cryogenic temperatures around minus 200 degrees, PTFE keeps its dimensional stability and its properties to a greater degree than most other plastics. The flammability rating is V0 per UL 94, which makes the material relevant in applications with fire requirements. Chemically CP10 is broadly resistant. Concentrated acids, bases and most organic solvents do not attack the material at normal service temperatures, and neither hot oils nor warm alkalis cause noticeable breakdown. At very high temperatures, fluorinated chemicals and alkali metals should be handled with care, but that is a marginal question in most applications.

The tubular format finds its place in mechanical designs where rotation, axial movement or pressure acts along a cylinder. Slide bushings in pumps and compressors, liner tubes in valves, seats in ball valves, guide sleeves in pneumatic and hydraulic cylinders, insulating parts at high temperature. PTFE based materials are also used in pharmaceutical manufacturing and in parts of the food industry thanks to the inert surface and the low adhesion, but formal certification always has to be confirmed per delivery batch. In stuffing boxes around pump shafts, CP10 works without a separate lubricant, which is an advantage where oil would contaminate the process medium or where food hygiene decides the choice.

Machinability is good. The material turns and drills easily with sharp carbide inserts, preferably with a diamond coating since the carbon fiber wears the cutting edge. Low feeds and sharp edges give a good surface finish. Heat generation in the cut should be kept down by not running cuts too fast; PTFE conducts heat moderately and the heat easily stays in the machining zone. Since the material cold flows it is wise to measure tolerances after the part has rested for an hour or so, not right after cutting. When finish turning sealing seats it pays to take light finishing cuts so that the surface structure comes out even.

Bonding works poorly unless the surface is chemically etched, which is down to the low surface energy of PTFE. Press fitting, bolted joints or mechanical fasteners are the usual ways to hold a CP10 part in place. Seals against the mating surface handle both dry and lubricated conditions, and the mating surface does not have to be hard if the load is moderate. At higher PV values it pays to polish or harden the mating surface so that the fiber does not wear it down. In rotating bearings a short running in window at low speed helps the material find its sliding surface before full operation is switched on.

In practice two things matter when choosing. The first is the dimensional margin. Sintered tubes have some ovality and may need to be turned both inside and outside to reach the final dimension. Count on chips. The second is the thermal expansion, which is high for PTFE compared with steel, so sliding clearances and fits need to be worked through if the service temperature varies. For seats in valves it is common to allow a slight interference in the cold state so that the seal holds even when the system heats up.

Tubes are supplied in a span of outer and inner diameters, usually in standard lengths of around one meter. The surface is matte straight from sintering and can be finished finer if needed. For short parts the tube is easily cut on a band saw or on the lathe, and the offcut can often be used for smaller packings and seal rings if the cut is made in a controlled way.

When assembling turned parts, press fitting is the most common way to hold the piece in its housing. The dimension chain has to count in that PTFE based materials expand more with temperature than metals do, so sliding clearances and press fits should be dimensioned with the operating conditions in mind. For rotating parts such as bushings it is common to give a short running in window at low speed before full operation is switched on, so that the material has time to settle in the bearing seat.

Would you like help choosing between CP10, pure PTFE, a carbon fiber reinforced or a bronze filled grade? Send over the drawing and the operating conditions and we will go through the options together.