Hollow Bar in PEEK MD 3000 mm gray

A hollow bar in PEEK MD is extruded tube stock with an outer and inner diameter matched for turning out finished sleeves, bushings and tubular elements. The centered hole saves both chips and turning time compared with boring out a whole round rod, which shows clearly in the price per part when you produce series. For larger inner diameters around 40 mm and up, the saving in material and machining time becomes significant, which makes the hollow bar the standard choice at turning shops that produce bushings in PEEK.

PEEK MD is the PEEK base polymer with molybdenum disulfide blended in. The additive gives lower friction against metal, somewhat higher wear resistance and a slightly darker gray shade than pure PEEK. The density sits at 1.49 g/cm³. Parts from the hollow bar handle 260 degrees long term and 300 degrees short term, so the material choice also fits applications around hot engines, pumps and process equipment. The thermal conductivity of 0.27 W/(m·K) is not high, so the part evens out thermal gradients slowly, which is worth counting in if you design bushings against machine elements that cycle hard thermally.

Common uses are slide bushings in hot water or steam, sleeves in pumps, distribution rings, guide sleeves and shaft seal housings. The material handles wet environments, the water absorption is a low 0.03 percent and the hot water resistance is good across the whole recommended temperature range. Chemically it does well against oil, hydraulic fluid, aliphatic and aromatic solvents, alkaline and weakly acidic media. Concentrated sulfuric acid and similar super oxidants are borderline cases. The flammability rating is V-0 without flame retardants, which is valuable offshore and in applications with UL requirements.

Mechanically you get a tensile strength around 111 MPa and a ball indentation hardness of 260 N/mm². The impact strength is good, about 72 kJ/m², but keep an eye on sharp internal radii, because PEEK is, like most engineering thermoplastics, sensitive to notch effects. For turning, carbide tools with sharp edges and moderate depths of cut are used. Preheat blanks that are to be finish turned to tight tolerances, so that inherent stresses do not cause dimensional drift after the chips come off. Polishing works well, the material takes a fine surface without fuzzing. When drilling side holes or channels in the finished sleeve, use peck drilling with good flushing so that the chip does not melt and stick.

When you order a hollow bar it is smart to figure the outer and inner diameter against the finished dimension of the part, plus 1.5 to 2 mm of radius on each side for machining stock. The bars can be cut to a defined length so that you minimize offcuts. The natural color is beige gray, a shade darker than pure PEEK. To pick the right hollow bar we need the outer diameter, inner diameter and length, plus the wanted bearing wall on the finished element. In series production there is often time to be gained by going up one stock size and cutting several blanks from the same bar, rather than chasing exactly the right dimension.

For sliding pairs against metal, the PEEK MD part is especially suitable when there is no lubricant or it is impractical to maintain one, for example in applications handling food, pharmaceutical products or high purity water. A lower coefficient of friction against steel, better wear resistance and the ability to run dry at high temperature mean a PEEK MD sleeve often lasts considerably longer than the equivalent part in POM or PA in the same application.

When fitting into a metal housing it is smart to count in that the plastic expands slightly more with heat than the metal does, so that the fit holds both at room temperature and in operation. A PEEK MD bushing that is press fitted into a steel housing and then has to work at 150 degrees needs to be dimensioned so that the clearance does not disappear entirely in operation, or so that the press fit does not let go in the cold. Short calculations with thermal expansion data do the job, and we are glad to help. For parts that have to work at really high temperatures, around 250 degrees and up, PEEK MD is usually the choice because most other engineering plastics either soften or break down.

The hollow bar in gray MD at 3000 mm is a pre-bored bar to turn rings, sleeves and liners out of, without having to bore out solid stock. The material is metal detectable, so a broken off piece is found by the detector in a food line. The long length gives several blanks per bar.

If you need help choosing between PEEK MD, PEEK MG or pure PEEK for a specific sliding pair application, say so and we will go through the mating body, load and temperature together.