Hollow Bar in PTFE MG 45/28x1900 mm natural

Hollow bars in PTFE MG are thick walled tubes of unfilled, sintered polytetrafluoroethylene, intended as turning blanks for hollow parts. The point is simple: if you are making rings, sleeves or seats with a through hole, you start with a blank that already has the hole, instead of turning away large volumes of material from a solid rod. That saves machine time, tool wear and material; the larger the hole diameter, the bigger the gain.

The material is the same unfilled PTFE as in our sheets and round rods. Continuous service temperature from minus 200 °C to 260 °C, density around 2.15 g/cm³ and a V-0 flammability rating per UL 94. The chemical resistance covers in practice the whole scale from concentrated acids to strong bases and solvents; that is why valve and pump makers count PTFE as the standard material for seals. The friction against steel is around 0.05 to 0.10, entirely without lubrication, and the material takes up no moisture, so the dimensions hold regardless of season and humidity.

Valve seats, stuffing box rings, support rings, slide bushings in mixers and dosing pumps, insulating sleeves in electrical equipment and liner sleeves where media pipes pass through an aggressive environment are all turned from the hollow bars. The chemical process industry, paper mills and the energy sector are typical homes; anywhere the medium is hot, aggressive or both. The natural grade is unpigmented and turns up often in food and pharmaceutical equipment, and which approvals apply to your application you read in the TDS for the material.

In short: if the part has a hole, start with a tube.

Pick a blank where the dimensions of the finished part fit with a machining allowance on both the outer and the inner diameter; the surfaces of the tube are rough and have to be cleaned up to the finished dimension. Think also about the wall that is left, because a ring with a very thin wall is hard to clamp without deforming it. A common rule of thumb is to go up one step in outer diameter rather than being stingy with the machining allowance; what you lose in material cost you win back in fewer scrapped parts and a calmer setup.

The design advice is the same as for all PTFE. The material creeps under a constant load, so rings that have to hold a preload over time need a spring element behind them or a filled grade. The thermal expansion is large compared with steel; a seal working from a cold start up to process temperature needs the clearance calculated across the whole range, not only at room temperature.

At the lathe the same recipe applies as for PTFE in general: sharp tools, a high cutting speed and a low feed. Tubes with a thin wall deform easily from the clamping pressure in the chuck; clamp with moderation, use soft jaws or a mandrel in the hole, and the part keeps its roundness. The material forms tough chips that like to wind up, so break the chip at regular intervals. With tight tolerances it pays to rough machine, let the blank rest and take the finishing cut last; then both roundness and diameter end up where you want them.

If you want the blanks cut to part lengths, we arrange that; add CTS to the cart and state the length per blank.

The dimensions are given as outer diameter/inner diameter times length, all in millimeters. In the 1900 mm length we stock one dimension, 45/28 mm. With an 8.5 mm wall it is a well sized blank for rings and sleeves that fit within a 45 mm outer diameter.

Not sure whether a hollow bar or a solid rod is the right starting point for your part? Call us and we will work it out.