Polyketone POK / PK: friction, chemical contact and stable geometry

Polyketone POK / PK should be evaluated through the operation of a specific assembly. In this group of applications, part service life is determined by the contact pair, the working fluid, moisture, a stable micro-clearance, shape repeatability after cycles and the stability of the moulded geometry.

POK is worth considering for parts that simultaneously combine friction, contact with industrial media, a requirement for a stable fit and predictable behaviour after series moulding. This is exactly the logic behind the Exablend® POK range from Material Wizard.

The Material Wizard range includes grades for different scenarios: unreinforced POK for moving assemblies and fluid contact, glass-filled compounds for rigid parts, a mineral-filled option for surface and warpage control, and a carbon-filled compound for precision assemblies in chemically aggressive environments.

Why POK is assessed through the assembly

In many technical parts, the problem does not start with instant failure. First the micro-clearance changes, noise increases, smoothness of motion deteriorates, wear particles appear, and the fit changes after contact with water or an industrial fluid. The part may still be intact, but the assembly already operates differently.

Under such conditions, value is determined by how the material behaves under a combination of factors: the contact pair, humidity, fluid, temperature, part geometry, load mode, surface roughness and moulding quality.

On the Material Wizard Exablend® POK page, this platform is presented for gears, rollers, valves, dosing units, pump elements, and fuel and chemically loaded components. This set of applications clearly illustrates the POK logic: a moving element, contact with the medium, control of the working surface and stability after cycles.

Polyketone is particularly attractive in parts where service life is simultaneously affected by friction, fluid, moisture, geometric stability, cyclic loading and repeatable mechanism travel.

The material basis of POK

Polyketone is a semi-crystalline aliphatic polymer based on carbon monoxide and olefins. The regular chain structure, polar carbonyl groups and dense morphology create a combination of properties important for moving parts: wear resistance, hydrolytic stability, low moisture dependence, resistance to industrial media and barrier behaviour towards a range of hydrocarbon and gas media.

In practice, this means a lower risk of the assembly geometry changing after conditioning and a lower risk of losing the initial contact-pair regime due to water, fuel, oil or another fluid.

For the design engineer this has a direct consequence: POK must be verified by the behaviour of the specific part after operating cycles. For the process engineer, what matter are moulding stability, shrinkage, weld lines, mould temperature, filler orientation and dimensional repeatability in series production.

Where POK properties deliver the greatest effect

POK's strongest zone is assemblies that simultaneously combine friction, an industrial fluid, moisture and a requirement for a stable clearance. Under such conditions, the material is judged by how well the part retains its function after operating cycles.

Friction and wear

In gears, bushings, rollers, guides, valve and dosing assemblies, wear affects more than the service life of the working surface. The contact patch, noise, smoothness of motion, backlash and local heating all change.

That is why the behaviour of the contact pair matters in such parts: counterface material, pressure, sliding speed, lubricant, temperature, roughness and the geometry of the working zone.

Water, steam and cleaning media

For POK, low water absorption is directly linked to fit stability. If a part operates in a humid assembly, even a small dimensional change can affect the clearance, noise, actuation force or sealing.

This is exactly why POK is worth evaluating for bearing elements, valves, pump parts, plumbing fittings, dosing units and moving components in contact with water, steam or cleaning media.

Fuel, oils, glycols, industrial fluids

For Exablend® POK M330A, operation in contact with fuel, coolants and glycols is specifically stated. For Exablend® POK CF20 TRM, low water absorption, dimensional stability and resistance to fuel, oils and industrial fluids are also highlighted.

In these modes, the value of the material lies in the part retaining its shape, contact surface and function in the working environment.

POK compared with other materials

Comparison with PA, POM, PBT, PPA or PPS is needed to define the boundaries. POK should not be specified automatically in place of each of these materials. It becomes justified when a standard material creates a risk due to moisture, fluid, wear, noise or an unstable fit.

For Exablend® POK M330A, the product page states practically zero water absorption of up to 0.5% compared with saturated PA66, operation in hot water and steam up to 100°C, a low coefficient of friction, use in gears and bushings, and contact with fuel, diesel, glycols, brake fluids and oils.

Specifying POK automatically for every part would be a technically weak decision. If the assembly runs dry, with no moisture, no fluid and no strict fit-stability requirements, POM or PA may remain the more rational choice.

The Exablend® POK range

Material Wizard's strength lies in the ability to match a grade to the specific risk driver in the part. The range includes an unreinforced option, glass-filled grades for rigidity, a mineral-filled option for geometry and surface, and a carbon-filled compound for precision assemblies.

Exablend® POK M330A

A general-purpose injection moulding grade for parts in contact with aggressive media and under cyclic loading. M330A is highlighted for practically zero water absorption, operation in hot water and steam, a low coefficient of friction, use in gears and bushings, and contact with fuel, diesel, glycols, brake fluids and oils.

Exablend® POK GF30 G2

A 30% glass fibre content provides pronounced reinforcement without moving to the more rigid GF50 scenarios. This grade emphasises balance: rigidity, strength, impact toughness, stable geometry and resistance to industrial media.

Exablend® POK GF30 NC

A grade for parts where, in addition to rigidity, contact with fuel, glycols and oils and low moisture dependence are important. It is a logical candidate for testing in chemically and water-loaded assemblies.

Exablend® POK GF50 F4

A highly filled compound for moulded parts requiring high rigidity, stable geometry, low shrinkage and operation in contact with industrial media.

Exablend® POK GF50 S4

A grade for precision structural parts requiring high rigidity, low shrinkage and a stable shape after moulding. The page lists a tensile modulus of 17 000 MPa, flexural strength of 220 MPa, HDT of 205°C at 1.8 MPa and shrinkage of 0.1–0.3% in the flow direction.

Exablend® POK MF25 S2

A mineral-filled option for parts where wear resistance, surface quality, predictable friction behaviour and warpage control are important. The grade's strong zone is more uniform shrinkage and lower anisotropy compared with glass fibre.

Exablend® POK CF20 TRM

A carbon-filled compound for parts requiring rigidity, dimensional stability, low water absorption and resistance to fuel, oils and industrial fluids. The grade is appropriate where precision, weight and controlled behaviour in a chemically aggressive environment matter.

Typical products where the POK logic is especially clear

Charging connector and port cover

Such an assembly combines a precise fit, contact with the external environment, moisture, cyclic opening, and insulation and structural requirements. That is why it works well as the main visual image of this article.

Dosing units and pumps

In such parts, small-scale mechanics, fluid contact, a sliding pair, repeated travel, stable geometry and a clean surface are important. Here POK helps to consider the operating stability of the entire assembly.

Gears, rollers, bushings

In these parts, wear, noise, working-surface stability, backlash and the contact regime are critical. POK is particularly attractive when fluid, oil or a humid environment is added to friction.

Valve and fuel elements

For such components, chemical contact, dimensional stability, fit precision and predictable behaviour in an industrial environment are important.

Limitations to take into account

POK has clear application boundaries. If the assembly runs dry, with no moisture, no fluids and no strict micro-clearance stability requirements, POM or PA may remain the more rational choice. If the primary requirement is continuous operation at temperatures above 130°C, PPA or PPS often become the first candidates.

For GF50, MF25 and CF20 compounds, moulding behaviour must be verified separately. The filler changes shrinkage, orientation, weld-line sensitivity, warpage and the directional distribution of rigidity. This is especially important for precision parts and housing elements.

The material is evaluated in the real assembly: the contact pair, temperature, lubricant, fluid, part geometry, weld lines and load mode are often more important than a single value from the TDS.

A practical verification matrix before selecting POK

Practical conclusion

Polyketone POK / PK should be included in the selection process when a part operates under friction while simultaneously in contact with water, fuel, oil or another industrial fluid, and the service life of the assembly depends on a stable micro-clearance, predictable geometry and repeatable travel after cycles.

For Material Wizard, this topic is particularly strong thanks to the complete Exablend® POK range: from M330A as the base injection moulding grade to GF30 G2, GF30 NC, GF50 F4, GF50 S4, MF25 S2 and CF20 TRM. This structure makes it possible to match a specific grade to the risk driver in the part.