PEEK is the stronger choice for elevated-temperature lead screw service, while acetal remains practical for moderate heat, clean dry-running mechanisms and easy machining.
The comparison depends on nut load, screw speed, continuous exposure, lubricant compatibility and chemical environment, not on polymer name alone.
Acetal and PEEK limits at a glance
Acetal should be treated as the lower-temperature option. A practical machining reference places its melting temperature at 338°F, or 170°C, while noting that working-temperature limits are load dependent because acetal softens under stress [S5]. A separate fabrication discussion recommends acetal below 200°F, approximately 93°C, for harsh operating conditions [S3].
PEEK appears in the same dry-running polymer nut family as acetal, polyester, Torlon, Vespel, PVDF, UHMW and Ertalyte, but the research does not assign a universal PEEK temperature limit. The correct comparison is therefore grade-specific: obtain the supplier's continuous-use rating, short-term limit, creep behavior and chemical compatibility data, then test the actual nut, screw and lubricant combination.
For reference, the polymer-nut discussion defines maximum continuous temperature as the level a material can withstand for a prolonged period without substantial property change, and maximum short-term temperature as a level that softens the material enough to accept only small loads for a few minutes [S4]. That distinction prevents a brief excursion from being mistaken for continuous service capability.
Selection criteria for high-temperature nuts
Load is the first screening criterion. Acetal has limited static-load capability, so a nut that runs hot while carrying substantial thrust cannot be specified from temperature rating alone [S5]. Its engineering utility lies in low- or moderate-load sliding contact, where a self-wiping polymer can reduce screw wear and avoid the lubrication demands of metal-on-metal contact [S5].
Speed and duty cycle are equally important because frictional heat rises with sliding speed and continuous operation. A practical acetal installation advises machining in small stages and using oil to avoid friction heating the nut [S5]. If the screw runs continuously at elevated speed, a lower surface temperature does not compensate for prolonged exposure above the nut's load-dependent deflection limit [S3].
Lubrication separates the design paths. Bronze against a steel or stainless-steel screw requires lubrication because the PV relation does not fully represent wear in a lubricated sliding pair; modified PV charts add duty cycle and lubrication conditions [S1]. Dry-running PEEK or acetal can avoid that constraint, but the selected polymer grade must still be compatible with the ambient chemistry and any accidental process fluid.
Acetal versus PEEK by application
Against temperature, PEEK has the better case because acetal is tied to a melting point of 338°F and is commonly limited below 200°F in harsh service, while the PEEK grade remains the higher-temperature polymer option [S3][S5]. Against machining cost and ease, acetal is easier to machine, and filled acetal is described as tougher under harsh conditions [S3].
Against load, neither polymer should be treated as a universal substitute for metal. Bronze nuts offer higher load capacity, better impact and shock resistance, and better resistance to high or low temperatures than most plastics [S1]. PEEK is normally the polymer of interest where elevated heat matters, but a high-thrust application still requires manufacturer load, PV and creep limits rather than an assumption based on polymer family [S2].
Against chemical exposure, acetal, PEEK and other thermoplastics must be checked against the actual process. A published compatibility scale uses A for excellent continuous service, B for minor effect, C for softening, swelling or loss of strength, D for severe effect, NA where data is unavailable, and temperature codes 1 and 2 for use up to 72°F and 120°F respectively [S2]. This scale also underlines why a generic chemical-resistance claim is inadequate.
Operating conditions that can disqualify a polymer nut
Excess load is the clearest failure mode. Acetal can thermoform as temperature rises, increasing heat transfer to the nut; at roughly 250°F under a load of a few hundred psi, the material begins to deform, and continued heating drives it toward flow at the 338°F melting point [S5]. In a powered axis, this combination of load and softening can turn a stable nut into a high-friction interface.
Frictional heating is the second failure mode. During machining, the screw should be heated in small stages with oil used to limit overheating [S5]. In service, a high-speed, high-duty-cycle screw can create a similar heat input even when ambient temperature is moderate, which means cycle time and speed belong in the thermal calculation.
Chemical attack and moisture are the third constraint. The acetal reference includes softening, loss of strength and swelling under moderate chemical effects, while continuous exposure is not recommended for that rating [S2]. The referenced PEEK, acetal, polyester and other polymer nuts are designed for self-lubrication, quiet operation and reliable dry-running performance, but that benefit does not create immunity to incompatible chemicals [S2].
Best-fit applications by material class
Choose acetal for moderate-temperature, low-to-medium-load axes that benefit from dry running, low noise and straightforward machining. The material can provide a self-wiping action that limits screw wear, and a fitted acetal nut has achieved approximately 0.0005 inch backlash in a machine-tool application with hundreds of operating hours [S5]. That field example supports use, not a universal life or load rating.
Choose PEEK when continuous service temperature is the controlling requirement and the manufacturer provides a suitable continuous-use and short-term rating for the exact grade. The research identifies PEEK as a self-lubricating plastic nut material, but it does not establish a universal load, PV or temperature specification [S2]. Use a lead screw nut datasheet and application testing to verify creep, wear and dimensional stability.
Choose bronze when thrust, shock, corrosion or extreme temperature outweigh the higher friction and lubrication requirements. Bearing-grade SAE 660, also identified as C93200, is a typical bronze nut material, and a bronze nut with a stainless-steel screw is used for corrosion resistance in many food and beverage applications [S1]. For very high thrust, compare a metal nut against a ball screw, because rolling contact removes much of the sliding-friction heat problem.
Procurement and verification checklist
Specify the nut as a system, not as a polymer coupon. Record the screw material, diameter, lead, nut geometry, axial load, speed, duty cycle, ambient and surface temperature, lubricant, contaminant and cleaning chemicals. Then require continuous and short-term temperature ratings, load or PV data, creep allowance, wear rate and chemical ratings for the exact nut grade [S1][S2][S4].
Use a short verification sequence: confirm fit and backlash, run at the intended speed and load, monitor nut and screw temperature, inspect for flattening, creep and wear, and repeat under actual lubricants and cleaning cycles. The research explicitly recommends testing products in their actual conditions because a chemical compatibility table is only a selection aid and does not guarantee performance [S2].
The traceable decision is therefore: acetal for moderate heat and accessible machining, PEEK for the higher-temperature polymer envelope when its grade-specific limits fit the load, and bronze when load, shock or temperature exceed the defensible polymer range. The next procurement checkpoint is the supplier's signed continuous-temperature, PV, creep and chemical-compatibility data for the final screw-nut-lubricant combination.