For engineers who already know the math—but still lose projects. For the last few years, I’ve been sharing technical guides here on Mechanical Design Handbook —how to size a motor, how to calculate fits, and (as you recently read) how to choose between timing belts and ball screws. But after 25 years in industrial automation, I realized something uncomfortable: Projects rarely fail because the math was wrong. They fail because: The client changed the scope three times in one week. A critical vendor lied about a shipping date (and no one verified it). The installation technician couldn’t fit a wrench into the gap we designed. University taught us the physics. It didn’t teach us the reality. That gap is why I wrote my new book, The Sheet Mechanic . This is not a textbook. It is a field manual for the messy, political, and chaotic space between the CAD model and the factory floor. It captures the systems I’ve used to survive industrial projec...
Figure 1: PEEK fasteners offer chemical resistance where steel would corrode.
The "Supercar" of Plastics: PEEK
PEEK (Polyetheretherketone) is not your average plastic. Sitting at the very top of the polymer pyramid, PEEK is a semi-crystalline organic polymer that offers a combination of mechanical strength and chemical resistance that rivals metals.
It is often the "material of last resort"—when Nylon melts, Acetal degrades, and metals are too heavy or corrosive, engineers turn to PEEK. Because of this, it commands a premium price, often costing 10x to 20x more than standard engineering plastics.
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Why is PEEK Special? Key Properties
1. Extreme Thermal Performance
PEEK has a continuous service temperature of 250°C (480°F) and can handle short-term spikes up to 300°C. Unlike other plastics that soften and lose strength, PEEK retains its mechanical stiffness even near its melting point.
Application: Under-the-hood automotive connectors and aerospace engine components.
2. Hydrolysis Resistance (Steam Proof)
This is a critical differentiator. PEEK is unaffected by continuous exposure to hot water and high-pressure steam. It is virtually insoluble in all common solvents.
Application: Autoclave trays in hospitals and downhole connectors in the Oil & Gas industry.
3. Biocompatibility (Radiolucency)
PEEK is biologically inert and does not trigger immune responses. Furthermore, it is Radiolucent, meaning it does not block X-rays (unlike Titanium implants). This allows doctors to inspect bone growth through the implant.
Material Grades: Choosing the Right Blend
Just like metals, PEEK comes in various "alloys" or filled grades to enhance specific properties.
1. Virgin PEEK (Unfilled)
The standard grade. Naturally tan/beige in color. It offers the best toughness and impact resistance.
2. Glass-Filled PEEK (30% Glass)
Adding glass fibers significantly increases stiffness and reduces thermal expansion. However, it is abrasive to mating surfaces and machine tools.
Best for: Structural insulators and housing rings.
3. Carbon-Filled PEEK (30% Carbon)
Carbon fibers boost the compressive strength and thermal conductivity significantly. This grade is lighter than aluminum but offers comparable tensile strength in certain directions.
Best for: Aerospace brackets and high-load wear rings.
4. Bearing Grade PEEK (HPV)
A specialized blend containing Graphite, PTFE (Teflon), and Carbon Fiber. This formulation is designed for Low Friction and High Wear Resistance.
Best for: Bushings and slide pads where lubrication is impossible.
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Machining & Processing PEEK
Machining PEEK is similar to machining hard steels, but with unique challenges.
- Annealing is Mandatory: PEEK builds up internal stress during extrusion. If you machine it without stress-relieving (annealing) the stock first, the parts will warp or crack days after machining.
- Coolant: Use water-soluble coolants to manage heat. PEEK does not melt like Nylon, but heat buildup can cause surface micro-cracking.
- Tooling: Carbide tooling is required. For Glass or Carbon-filled grades, Diamond-coated (PCD) tools are recommended to prevent rapid tool wear.
The New Frontier: 3D Printing PEEK
Historically, PEEK parts had to be machined from wasteful blocks. Today, FFF (Fused Filament Fabrication) allows for PEEK printing.
Warning: You cannot print PEEK on a standard hobby printer. It requires:
- Nozzle Temperature: > 400°C
- Bed Temperature: > 120°C
- Heated Chamber: Essential to prevent layer delamination.
Typical Industrial Applications
- Oil & Gas: Subsea connectors and valve seats (due to resistance to sour gas/H2S).
- Semiconductor: Wafer handling wands (PEEK does not outgas or contaminate vacuum chambers).
- Medical: Spinal cages and dental implants.
- Aerospace: Cable clamps and interior fasteners (Low Smoke/Toxic Gas emissions).
Summary Table
| Property | Virgin PEEK | 30% Carbon PEEK |
|---|---|---|
| Density | 1.32 g/cm³ | 1.44 g/cm³ |
| Tensile Strength | 95 MPa | 130 MPa |
| Max Temp (Short Term) | 300°C | 315°C |
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