Hollow Bar in POM H 3000 mm natural

A hollow bar in POM H is an extruded tubular blank format where the center bore is already there. For you who turn bushings, sleeves, spacer tubes or rotationally symmetric parts, that means less chip volume, shorter machining time and less material waste than starting from solid round rod. On larger series the time saved at setup and rough turning can be significant.

The material is acetal in homopolymer form, one of the stiffest and most dimensionally stable engineering plastics. The density sits at 1.42 g/cm³, the continuous service temperature goes up to 105 degrees and the material handles down toward -50 degrees without losing toughness. Water absorption stops around 0.85 percent, which holds the tolerances even when the humidity varies. The flammability rating is HB per UL 94. The higher crystallinity of the homopolymer also gives slightly higher creep strength under static loads, which is worth taking along when the part has to stand under constant pressure.

POM H gives a glossy, smooth machined surface with small tolerances. The coefficient of friction against steel is low, the wear resistance high, and the material turns, drills and mills about as easily as brass. The chips are short and clean, which makes the material rewarding to run in automatic lathes and sliding head machines. Use sharp tools, a positive rake angle and plenty of compressed air or emulsion to evacuate the chips and keep the heat down in the cut.

In hollow bar form the material goes straight into making slide bushings, bearing housings, spacer tubes, slide rings, shims, roller sleeves and guide elements in pumps, valves and cylinders. In food and packaging machinery, POM H hollow bars are used for rollers, wheel sleeves and guide rollers where quiet running, low friction and dimensional stability matter. In medical technology and precision mechanics the ability of the material to hold its shape over time without post curing or stabilization is put to use. In hydraulics and pneumatics the material works as bearing sleeves and guide elements in cylinders where an oiled mating surface gives a long service life.

Count on a thermal expansion of around 0.11 mm per meter and degree. So allow generous tolerances if the part is to be press fitted against steel or aluminum, especially if the temperature swings in operation. The hollow bar can be bonded after surface activation, but in series production ultrasonic welding or hot gas welding is more common. For assemblies in positions that take force or torque, mechanical mounting with a screw or a snap fit is recommended.

POM H is not UV stable in natural color, and for longer outdoor exposure a black variant or a protective surface treatment is recommended. Chemically the material handles most organic solvents, mineral oils, fuels and weak acids. Strong acids, concentrated bases and oxidizing agents such as chlorine solutions should be avoided in longer contact. When choosing the mating surface in a plain bearing, hardened steel or brass works best; aluminum and stainless give higher friction and a shorter service life.

The difference between POM H and the copolymer POM C in hollow bar format is worth thinking about when choosing. The homopolymer gives slightly higher stiffness, a better turned surface and somewhat higher tensile strength. The copolymer handles contact with hot water and chlorinated media better and has slightly higher impact strength. For precision bushings in a dry environment POM H is often a good choice; for parts in contact with hot water the choice leans toward POM C. With large tensile stresses or a constant static load the creep strength of the homopolymer is an advantage.

The hollow bars are supplied in natural color as standard, with a combination of outer and inner diameter that matches common final dimensions on a finished part. Lengths are cut as needed. The standard length is around one meter; for larger production runs the bars are cut in lengths that match the handling dimensions of the machine, which saves cutting waste and setup time. If you have a specific bushing or sleeve on a drawing, we are glad to help pick the right blank so that cutting waste and machining time are kept to a minimum.

When choosing the right blank it is often the function of the final product that decides. For precision bushings with small tolerances and dry running we like to pick pure POM H. For sliding contact without lubrication a PTFE filled or internally lubricated POM variant can be better, and the material is then available in the same hollow bar format. Send over the drawing or the dimensions and we will come back with a suggestion on grade, dimension and cut length that matches the final part.