Getting PTFE to stick to metal is harder than most people realize. The coating needs to go through a sintering process above 327°C before it forms a permanent metallurgical bond with the substrate. Skip that step and your non-stick coating flakes off.
Two methods dominate industrial practice: dip coating and spray coating. Different strengths, different limits, different use cases. This guide covers both from a practical engineering standpoint — the steps, the numbers that actually matter, and the applications that come up on the shop floor.
Surface Preparation: Where Most Jobs Are Won or Lost
The coating method you pick matters, but the final result is largely decided before the first drop of PTFE touches the part.
The substrate has to be clean enough and able to take high sintering temperatures. For metal parts, sandblasting with quartz abrasive in the 0.125 to 0.3 mm range does double duty. It strips oil and dirt while microscopically roughening the surface. A rougher surface gives the PTFE more mechanical grip.
Parts get washed and dried right after sandblasting. No lingering contaminants allowed.
One exception worth noting: copper and copper alloys. They oxidize fast at sintering temperatures and form a loose oxide layer that kills adhesion. Copper-based parts need an oxygen-free inert gas environment during sintering.
Dip Coating: Every Surface, No Exceptions
The workpiece goes into a tank of PTFE emulsion and gets pulled back out at a controlled speed. The liquid coats everything it touches. After drying and sintering, you get a uniform protective layer.
The main advantage is coverage. No blind spots, no corners the spray can’t reach. That makes dip coating the natural choice for complex geometries — filter media, screws, double-sided circuit boards, conveyor belts, parts with internal cavities.
The Process in Four Steps
1. Surface prep. Degrease with alkaline cleaners or organic solvents. Roughen the surface to Ra 1.6 to 3.2 μm. Some materials like aluminum-magnesium alloys get an additional silane coupling agent treatment for activation.
2. Immersion and withdrawal. This is the critical step for thickness control. The emulsion bath stays at 20 to 25°C. The workpiece goes in at 50 to 100 mm per minute and comes out at 100 to 300 mm per minute. Target pick-up rate by weight is 150% to 250%. For porous or precision parts, a vacuum assist around -0.092 MPa forces the emulsion into every pore.
3. Drying and sintering. Drying uses a stepped ramp: 80°C to 120°C to 180°C. This prevents flash-boiling that would blister the coating. Then sintering at 360 ± 5°C for 15 to 25 minutes. The PTFE particles melt and recrystallize into a continuous film. Heating rate should stay at 5 to 10°C per minute. Faster rates cause thermal expansion mismatch and the coating delaminates.
4. Quality check. Final coating thickness runs 20 to 100 μm. Adhesion gets tested per ASTM D3359 cross-cut test, target Class 0 (clean edges, no peeling). Salt spray and chemical immersion verify corrosion resistance. Food-grade parts get their own safety inspections on top of that.
Spray Coating: Directed Application, Less Waste
Spray coating atomizes the PTFE and puts it where you want it. Two variations: wet (emulsion spray) and dry (electrostatic powder spray).
Emulsion Spray
PTFE dispersion with particle sizes in the 5 to 15 μm range gets atomized through an air spray or airless spray gun. Water-based or solvent-based, either works.
Key parameters: spray distance 15 to 25 cm, gun pressure 0.3 to 0.5 MPa, two or three passes. Each pass builds a wet film thickness of 20 to 50 μm.
This is the budget option. Good for large flat surfaces, spot repairs on existing parts, and medium to low volume runs.
Electrostatic Spray
PTFE powder gets electrostatically charged at the nozzle — 60 to 80 kV — and the grounded workpiece attracts the charged particles. The powder wraps around complex shapes and reaches internal features.
Single-pass dry film thickness is 10 to 25 μm. Build up layers with multiple passes. Powder utilization runs 80% to 90%, so overspray waste is low.
This is the method for precision mechanical parts, complex 3D geometries, medical devices, and aerospace components where coating uniformity and density are tightly specified.
| Parameter | Emulsion Spray | Electrostatic Spray |
|---|---|---|
| Cost per part | Lower | Higher |
| Material utilization | 40-60% | 80-90% |
| Best fit | Large flat areas, low volume | Complex shapes, tight specs |
| Typical thickness per pass | 20-50 μm (wet) | 10-25 μm (dry) |
| Coverage on complex shapes | Moderate | Excellent |
Choosing Between Dip and Spray
No universal answer here. It depends on what you’re coating and what you need from it.
Dip coating for small parts with complex shapes and internal cavities that need protection on every surface. Threaded fasteners, porous filters, multi-sided brackets.
Electrostatic spray when you need a smooth, uniform finish on complex external surfaces — bakeware molds, food processing tools, surgical instruments. The electrostatic wrap effect gives coverage that emulsion spray can’t match on intricate shapes.
Emulsion spray when the geometry is simple, the surface is large and flat, and cost per part matters. Sheet metal panels and equipment housings.
Real Applications
Food processing. Bakery molds and meat processing conveyor belts get electrostatic food-grade PTFE coatings compliant with FDA 21 CFR 177.1550 or GB 4806.10. Low surface energy means baked goods release cleanly. Mold release rates can hit 99%. Cleaning intervals stretch much further than uncoated steel.
Chemical equipment. Reactor vessels and pipe fittings exposed to aggressive chemicals get dip-coated with a thick PTFE liner, typically 0.5 to 1.0 mm. Service life jumps from months to years compared to unprotected metal.
Medical devices and electronics. Surgical tools that go through repeated autoclave cycles benefit from high-purity electrostatic PTFE coatings that resist wear and prevent tissue adhesion. PCB handling fixtures and semiconductor carriers get thin PTFE insulating layers against solder splash and chemical attack.
Three Trends to Watch
PFAS regulations are forcing a rethink. Both the EU and China (through the updated GB 4806.10-2025 standard) are tightening restrictions on persistent fluorinated compounds. Alternatives are emerging: polysiloxane-based anti-icing and release coatings, alumina-chitosan composites, and engineering polymer options like igus’s iglidur series.
Nanocomposites are raising the performance ceiling. Adding graphene, nano-silica, or nano-alumina to PTFE formulations keeps the classic non-stick properties while improving wear resistance and hardness by 50% or more. Friction coefficients have dropped to 0.03 in some formulations.
Smart manufacturing is taking over the coating line. Lidar scanners map part geometry in real time. Robotic sprayers adjust trajectories and flow rates on the fly. Bake curves get optimized from logged process data rather than operator intuition. The result is coating consistency that manual processes simply couldn’t deliver.
PTFE coating isn’t a solved problem. But the tools available today give engineers more control over the outcome than ever before. Match the process to the part, and remember that surface preparation is where most jobs are won or lost.