A design engineer usually arrives at polyketone (POK) not from a blank sheet, but with a finished drawing that already specifies POM (acetal) or polyamide. The part works, but only “almost”: somewhere the friction pair wears out, somewhere the material swells from moisture, somewhere it fails on contact with fuel or a cleaning solution. POK often closes exactly these “almosts.” Let’s look at when it makes engineering sense to redesign a part around polyketone, and when the existing material is enough.
This is not an introductory “what is POK” article — the base properties of the class are collected in the product section “Polyketone POK.” Here the angle is practical: how to make the decision at the design stage.
Three “red flags” that signal it’s time to consider POK
Picture a typical functional part — a pump gear, a bushing, a water-meter housing, a fuel-system connector. If the specification includes even one of the following three points, polyketone deserves a place on the shortlist alongside POM and polyamide.
First — wear in a friction pair without abundant lubrication. POK is known for high wear resistance; according to material producers, the abrasion resistance of polyketone exceeds acetal by a multiple (some sources cite an order of 10× and higher). The exact figure always depends on the counterface, load, and duty cycle, so it must be verified on the specific pair, but the direction is clear: where a POM gear “gets eaten away,” POK often lasts noticeably longer.
Second — moisture and hydrolysis. Aliphatic polyamides (PA6, PA66) are hygroscopic: they absorb water, change dimensions, and lose stiffness, and in hot water they also degrade through chain hydrolysis. POK has a carbon backbone and inherent hydrolysis resistance, so in systems with constant contact with water or a humid environment it holds its dimensions and properties more stably than unprotected polyamide.
Third — aggressive chemistry: fuels, oils, brake and coolant fluids, cleaning agents, weak acids and alkalis. Polyketone traditionally shows broad chemical resistance, which is why it is chosen for fuel and fluid assemblies. If your POM or PA part sits in such an environment “on the edge,” that is a reason to run the numbers on POK.
How POK differs from POM and polyamide — the short engineering logic
| Criterion | POK (polyketone) | POM (acetal) | PA6 / PA66 (polyamide) |
|---|---|---|---|
| Wear resistance | very high | high | medium–high (increases with GF) |
| Water absorption | low | very low | notable (hygroscopic) |
| Hydrolysis resistance | high | high (especially copolymer) | limited without stabilization |
| Chemical resistance | broad | good against fuels/solvents | more vulnerable to acids |
| Impact toughness at low t | usually good | moderate | good in HI grades |
| Dimensional stability when wet | high | high | requires conditioning |
The point of the comparison lies elsewhere: POK combines the strengths of both of its neighbors — wear and chemical resistance on the level of “the better acetal” with the dimensional stability that unprotected polyamide lacks. It is precisely at this intersection that it wins the material selection.
What changes in the drawing itself
Redesigning around POK is not simply “swap the material in the specification.” Polyketone is a semi-crystalline material with its own shrinkage, so the designer should recalculate several things.
Shrinkage and tolerances
Like any semi-crystalline polymer, POK exhibits oriented shrinkage; for critical dimensions it is factored in from the grade TDS and verified on the mold, rather than carried over “one-to-one” from the old POM drawing.
Wall thicknesses and ribs
Polyketone carries loads well, but the general rules of molding still apply: uniform walls, smooth transitions, ribs for stiffness instead of thickened sections that produce sink marks and internal stresses.
Friction pair
If the part works in contact with metal or another polymer, it is worth planning a test of that specific pair from the outset — the coefficient of friction and wear depend heavily on the counterface.
Limitations — without them there is no honest picture
POK is not a “silver bullet.” A few limits to keep in mind:
Temperature class. POK is not a high-temperature material on the level of PPA. If the part operates for long periods at high temperatures under load, polyketone may fall short — polyphthalamides (PPA) or glass-filled heat-stabilized polyamides are more often appropriate there.
Narrow processing window. Polyketone is sensitive to overheating: the typical melt window for the class is roughly 230–250 °C, with reluctance to cross the limit of about 260 °C to avoid thermal degradation; residence time in the barrel is kept short. This means careful settings and a clean, well-vented mold.
Grade availability. The range of polyketones on the market is narrower than for polyamides or acetal; the choice of grades is smaller, and this is worth taking into account at the stage when the part can still be designed around an available material.
Coefficient of friction. Despite high wear resistance, aliphatic polyketones may have a somewhat higher coefficient of friction than acetal — for some sliding applications this is a nuance to be verified experimentally.
When it is better to keep POM or polyamide
If the part is a simple sliding bushing with no chemical load and no moisture, and POM already performs flawlessly, switching to POK will not deliver a gain that justifies retooling. Likewise, if the key requirement is maximum heat resistance under load, the material to look at is not polyketone but PPA or a heat-stabilized glass-filled polyamide. POK comes into its own precisely at the intersection of wear, moisture, and chemistry — where each of its neighbors, taken alone, “falls short.”
What to check before serial launch
- Pellet moisture. Drying per the grade TDS (typically desiccant, moderate settings), because processing wet material spoils the surface and properties.
- Shrinkage and dimensions. On the actual mold, not from the catalog.
- Friction pair. Wear and coefficient of friction on the specific counterface under the working load.
- Chemical cycle. Immersion of samples in the working fluid (fuel, glycol, cleaning solution) with measurement of the change in mass and mechanics.
- Batch stability. Verification of incoming batches by MFR/viscosity.
- Behavior in a humid cycle. Dimensions and impact strength after conditioning.
POK grades in the Material Wizard range
Material Wizard supplies engineering polyketones under the Exablend® brand and provides technical support in selecting the grade for a specific part — from gears and bushings to housing and fluid assemblies. If you are at the design stage and hesitating between POM, polyamide, and POK — this is the case where a test of the friction pair and the chemical cycle pays off.
Exablend® POK — high-performance polyketoneHigh wear resistance · hydrolysis resistance · broad chemical resistance — for wear- and chemical-resistant partsBuy with delivery across Ukraine → Exablend® POK M330APolyketone for critical functional assemblies · dimensional stability · fluid resistance · stable batchesRequest supply terms →A full overview of the class and the available grades is in the product hub “Polyketone POK.” For specific parameters for your part, consult a specialist.
Expert breakdown: 5 questions before choosing POK
Does the part really need polyketone specifically, rather than a heat-stabilized polyamide?
If the main problem is heat resistance under load, the answer is more likely “no”: POK is not a high-temperature material, and PPA or GF polyamide are often the more rational choice here.
How will the friction pair behave on the actual counterface?
The abrasion resistance of POK is high, but the coefficient of friction and wear depend on the partner material; catalog figures do not replace testing of the specific pair.
Will the material withstand your particular working fluid?
“Broad chemical resistance” is a class-level statement; a critical part requires an immersion test in your fuel, glycol, or cleaning solution with measurement of the change in mass and mechanics.
Has the shrinkage been recalculated for POK, rather than carried over from the POM drawing?
The semi-crystalline shrinkage of polyketone is its own; carrying tolerances over “one-to-one” from the old part is a typical mistake.
Can the required grade realistically be obtained in the required volume?
The POK range is narrower than polyamides; grade availability is worth confirming before the part is locked to a single material.