🧪 PEEK
PEEK Machining and Component Supply in Appleton, WI — Precision Polymer Parts for Fox Valley Industry
PEEK — polyether ether ketone — is the polymer engineers reach for when everything else has already failed: continuous service at 260°C, chemical resistance to virtually every industrial fluid, and mechanical properties at 150°C that exceed most metals at room temperature. In Appleton's manufacturing corridor, PEEK parts appear in hydraulic system insulators, bearing cages, valve seats, and structural components on industrial machinery where the combination of heat, chemical exposure, and load rules out nylon, acetal, and even PTFE. This page covers what Fox Valley buyers and engineers need to know to source PEEK effectively.
ISO 9001ISO 13485AS9100
Three PEEK Grades and Where Each Belongs in Fox Valley Applications
Unfilled PEEK — natural tan/beige color, virgin resin with no filler additions — offers the purest combination of the material's signature properties: continuous service temperature of 260°C, tensile strength of 100 MPa at room temperature, near-universal chemical resistance, and FDA/USP compliance for food contact and pharmaceutical applications. Unfilled PEEK is the grade for electrical insulation, medical device components, and fluid-contact parts where extractables from fillers are a concern. In Appleton's industrial market, unfilled PEEK is specified for pump impellers, valve seats, and bearing retainers in chemical-process equipment where nylon or acetal would swell or degrade.
Glass-filled PEEK (typically 30% short glass fiber by weight) trades the pure chemical and electrical properties of unfilled PEEK for a significant improvement in stiffness and reduced thermal expansion. Tensile strength rises to approximately 165 MPa, flexural modulus increases from 3.6 GPa to 9.5 GPa, and the coefficient of thermal expansion (CTE) drops substantially — from 47 ppm/°C for unfilled to around 20 ppm/°C for 30% glass-filled. This CTE reduction is critical for structural components that mate with metal: a PEEK housing bolted to a steel frame will rack and crack at temperature if the CTE mismatch is too large, and glass filling closes that gap. Appleton shops machine 30% glass-filled PEEK for pump housings, manifold blocks, and structural brackets in industrial equipment.
Carbon-filled PEEK (30% carbon fiber or carbon-graphite blend) is specified when the dominant requirements are tribological: low friction, high wear resistance, and dimensional stability under sustained bearing loads. The carbon fiber reinforcement raises compressive strength above 200 MPa and provides inherent lubricity — a carbon-filled PEEK bearing running dry against a steel shaft has a coefficient of friction as low as 0.10, compared to 0.35–0.45 for unfilled PEEK. This makes carbon-filled PEEK the standard grade for bushings, thrust washers, and wear pads in heavy-equipment hydraulic systems and industrial gearboxes where lubricant contamination is a concern. It is electrically conductive, which eliminates it from electrical insulation applications but makes it suitable for anti-static components in flammable-vapor environments.
Machining PEEK at Appleton CNC Shops: Key Process Considerations
PEEK machines cleanly with sharp carbide tooling and produces short, manageable chips — a significant advantage over flexible polymers like PTFE. Cutting speeds for PEEK typically run 500–800 SFM with carbide, and aggressive feeds produce better surfaces than the timid feeds that work on softer polymers. Flooded coolant (water-soluble or clean water) or compressed air is recommended to evacuate chips and prevent heat buildup; dry cutting is possible on short operations but risks surface melting on longer passes.
The critical process challenge with PEEK is stress relief and dimensional stability. Unfilled and filled PEEK bar stock contains residual internal stresses from the extrusion or compression-molding process. Tight-tolerance parts machined without stress relief may move dimensionally during the first 24–48 hours after machining as residual stresses relax. Appleton shops running high-precision PEEK components — ±0.001" bore tolerances, close-clearance bearing fits — anneal the stock at 200–220°C for 4+ hours before finish machining. This adds a day to the schedule but eliminates post-machining dimensional drift.
Fixturing PEEK requires attention to clamping force. Excessive jaw pressure distorts bore dimensions on thin-wall cylinders, and the distortion springs back when unclamped — leaving a part that passes in the chuck but fails in the gauge. Soft jaws bored to match the workpiece OD, or collet-style fixtures that distribute clamping load evenly, are standard practice for bore-critical PEEK work at Appleton precision shops. For flat parts, vacuum fixture tables work well and eliminate the distortion risk entirely.
Comparing PEEK to Alternatives for Industrial Applications in the Fox Valley
Buyers encountering PEEK for the first time typically have three questions: why not use nylon, why not use Delrin, and why not use aluminum? Each comparison has a different answer depending on the application conditions. Versus nylon 6/6 (the cheapest engineering polymer): PEEK is appropriate when service temperature exceeds 130°C, when exposure to hot water or steam is continuous, or when dimensional stability in humid environments is critical. Nylon absorbs moisture (up to 8% by weight) and swells proportionally; PEEK absorbs effectively zero. In a hydraulic system or steam-environment fitting, nylon's dimensional change from moisture absorption is a disqualifying failure mode that PEEK avoids entirely.
Versus Delrin/acetal: PEEK is specified when temperature exceeds 120°C or when chemical resistance to strong acids, bases, or hydrocarbons is required. Acetal decomposes in strong oxidizing agents and chlorinated solvents; PEEK resists both. Acetal is substantially cheaper per pound and easier to machine, so it retains its position in moderate-temperature, moderate-chemical-exposure applications. The cost premium for PEEK over acetal is roughly 10–15x on a per-pound basis — a premium that must be justified by a performance requirement that acetal cannot meet.
Versus aluminum: PEEK is lighter (1.32 g/cm³ vs. 2.70 g/cm³ for 6061 aluminum), electrically insulating, and thermally insulating — properties that matter in specific Appleton applications like isolator brackets in hybrid-electric powertrain test equipment, polymer bearing housings where electrical isolation prevents shaft current damage to bearings, and low-thermal-mass fixture components in precision measurement equipment. PEEK's lower strength and modulus than aluminum are real tradeoffs; structural calculations for PEEK components in loaded applications must account for creep under sustained load, particularly above 150°C.
Sourcing PEEK Stock and Finished Components Through ManufacturingBase in Appleton
PEEK rod, plate, and tube in unfilled and 30% glass-filled grades are stocked by industrial plastics distributors serving the Midwest, with delivery to Appleton typically in 3–7 business days. Carbon-filled PEEK and specialty grades (glass-carbon hybrid, bearing grade with PTFE and graphite) are less commonly stocked and may require 2–4 week lead times from specialty polymer distributors. Extruded rod is the most common stock form; compression-molded plate has better through-thickness properties for flat parts and is preferred for high-load structural components.
For machined PEEK components, Appleton precision shops quote 2–4 weeks for prototypes and 4–8 weeks for production quantities with first-article inspection. Buyers should supply a PDF drawing with all critical dimensions tolerance-called and material grade specified — 'PEEK' alone is not sufficient when the application may benefit from a filled grade. ManufacturingBase profiles identify shops with documented polymer machining experience and stress-relief protocols, separating them from general shops that can cut PEEK but lack the process controls for tight-tolerance aerospace or medical-grade work.
Material certifications for PEEK should include the manufacturer's certificate of compliance with applicable material standards (ASTM D6262 for unfilled PEEK is the standard reference), batch number, and composition confirmation for filled grades. For aerospace and medical applications, buyers should request that the shop maintain traceability from certified PEEK stock to finished part, with documentation retained per the program's quality plan requirements.
Frequently Asked Questions
Unfilled PEEK has a continuous service temperature rating of 260°C (500°F) and a short-term peak tolerance above 300°C before thermal degradation begins. For Appleton buyers, this temperature capability unlocks applications that would destroy competing polymers: valve seats in steam systems operating at 200°C, structural insulators in furnace ancillary equipment, bushing and bearing components on machinery with oil bath temperatures exceeding 150°C, and pump internals handling hot process fluids. The practical comparison: nylon 6/6 softens and loses structural integrity above 130°C; acetal begins to creep and dimensionally distort above 110°C; PTFE handles temperature but lacks structural strength; PEEK combines temperature resistance with genuine load-bearing capability. In the Fox Valley's industrial machinery market, this combination drives specification of PEEK in bearing housings and manifold components on hot-oil lubrication systems and high-temperature process equipment.
The 30% short glass fiber addition to PEEK changes the material's behavior in several ways that buyers and machinists need to understand. Mechanically: flexural modulus increases from 3.6 GPa to 9.5 GPa, tensile strength increases from 100 MPa to 165 MPa, and CTE drops from 47 ppm/°C to around 20 ppm/°C. This CTE reduction is the primary reason glass-filled PEEK is specified for components bolted to metal structures — it dramatically reduces the differential thermal expansion stress that would crack an unfilled PEEK housing. In machining: glass-filled PEEK is significantly more abrasive on cutting tools than unfilled; carbide insert life decreases and PCD (polycrystalline diamond) tooling is used in high-volume production for cost-effectiveness. Surface finish on glass-filled grades is slightly rougher at equivalent machining parameters. Glass-filled PEEK is NOT electrically insulating in the same class as unfilled — the glass fibers reduce conductivity but do not maintain the 10^16 ohm-cm resistivity of unfilled PEEK. Electrical isolation applications should specify unfilled grade.
With proper stress relief and fixturing, Appleton precision shops hold ±0.001" on machined PEEK bores and ODs as a standard capability, with ±0.0005" achievable on critical fits with dedicated fixturing and temperature-controlled measurement. Unfilled PEEK is slightly easier to hold tight tolerance than glass-filled due to its more homogeneous microstructure. The keys to achieving these tolerances are stock annealing before finish machining (4+ hours at 200°C for large cross-sections), avoidance of excessive clamping force that distorts thin walls, and inspection in a temperature-controlled environment — PEEK's CTE of 47 ppm/°C means a 10°F temperature change shifts a 3" bore by 0.00024", which matters when chasing ±0.001" tolerances. Surface finish on turned PEEK typically achieves 32–63 Ra µin; with fine finishing passes and sharp tooling, 16 Ra µin is achievable and sufficient for most sealing and bearing surface requirements.
Carbon-filled PEEK (30% carbon fiber, or a carbon-graphite-PTFE bearing compound) is an excellent bearing material for heavy-equipment applications where the operating conditions fall within its capability envelope. Its compressive strength exceeds 200 MPa, its PV limit (pressure times velocity) runs to 0.3 MPa·m/s in continuous dry running, and its coefficient of thermal expansion is low enough to maintain bearing clearance across temperature cycles. For lightly lubricated applications — oil-mist or periodic grease — the carbon-graphite compound grades from specialty suppliers achieve even better PV performance. The application limitations to check: carbon-filled PEEK should not be used against soft aluminum shafts because the carbon fiber can abrade the shaft surface; hardened steel (50+ HRC) or hardened stainless (440C) is the ideal mating surface. Carbon-filled grades are also electrically conductive at approximately 10^2–10^4 ohm-cm, which disqualifies them from electrical isolation bushings but makes them suitable for anti-static bearing applications in powder-handling equipment.
PEEK stock material runs roughly $80–$150 per pound in rod and plate form, compared to $4–$8 per pound for Delrin/acetal and $3–$5 per pound for nylon 6/6. On a finished machined part basis, the premium compounds because PEEK requires more careful process control (stress relief, dedicated tooling, slower speeds for filled grades) which adds to labor cost. The premium is justified when one or more of the following conditions apply: continuous service temperature above 130°C (eliminates nylon and acetal), exposure to strong solvents or oxidizing agents that degrade acetal (chlorine, strong acids), requirement for FDA/USP compliance with no extractables from plasticizers or stabilizers, dimensional stability in wet environments (PEEK absorbs <0.1% moisture vs. 8% for nylon), or an electrical isolation requirement at elevated temperature. For most room-temperature, dry, moderate-chemical-exposure applications, Delrin is the economically correct choice and PEEK is overspecified. Appleton buyers who see PEEK on a drawing should confirm with the engineer that one of these justifying conditions actually applies before accepting the specification.
Last updated: July 2026
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