---
type: process
name: "Powder Coating"
category: "Finishing"
subcategory: "Additive"
materials: ["Metal"]
tolerances: "Adds 2–4 mils (50–100 µm) per surface; budget 2× film thickness on a bore diameter and roughly 4× on thread pitch diameter, or mask"
volumes: "1 to millions of parts; conveyorized lines are most economical above a few hundred parts per run"
lead_time: "3–7 business days at a job shop; 24–48 hours expedited on stock colors; 2–3 weeks for a custom-matched powder"
url: https://manufacturingprocesses.org/processes/finishing/powder-coating
---

# Powder Coating

Powder coating sprays electrostatically charged dry polymer powder onto an earthed part, then bakes it into a tough continuous film.

- **Category**: [Finishing](https://manufacturingprocesses.org/processes/finishing.md)
- **Family**: Additive
- **Materials**: Metal
- **Typical tolerances**: Adds 2–4 mils (50–100 µm) per surface; budget 2× film thickness on a bore diameter and roughly 4× on thread pitch diameter, or mask
- **Surface finish**: Smooth gloss through heavy texture depending on powder; the film smooths but does not fill substrate defects
- **Typical volumes**: 1 to millions of parts; conveyorized lines are most economical above a few hundred parts per run
- **Lead time**: 3–7 business days at a job shop; 24–48 hours expedited on stock colors; 2–3 weeks for a custom-matched powder

## Overview

Powder coating applies a dry thermoset polymer powder to an electrically grounded part with an electrostatically charged spray gun, then fuses and cures it in an oven into a single continuous film. There is no solvent, so film builds that would sag in liquid paint are routine: a typical single coat runs 2–4 mils (50–100 µm) against roughly 1–2 mils for a sprayed liquid topcoat. Cure is typically 10–20 minutes at 350–400 °F (177–204 °C) part metal temperature.

The economics come from reclaim — overspray that misses the part is collected and re-sprayed, so material utilization can exceed 95% against 30–65% for conventional liquid spray, and VOC emissions are essentially zero. The constraints follow from the same physics: the part must conduct to hold a charge and must survive the bake, deep recesses starve from Faraday-cage shielding, and 2–4 mils lands on every reachable surface including threads and bores.

## How it works

1. **Clean and pretreat.** Degrease, then either chemically convert the surface or blast it. Iron phosphate is the common commercial pretreatment; zinc phosphate gives markedly better corrosion performance under the film. On structural steel the alternative is abrasive blasting to an SSPC preparation grade with a 1.5–3 mil (38–75 µm) anchor profile. Pretreatment, not the powder, determines how the finished part performs in salt spray.

2. **Dry off.** A dry-off oven drives water out of seams, weld joints and blind holes. Trapped moisture flashes during cure and blisters the film.

3. **Apply.** A corona gun charges powder to 30–100 kV as it leaves the nozzle; the charged particles follow field lines to the grounded part and cling electrostatically until cured. Tribo guns charge by particle-to-wall friction instead and penetrate recesses better because they produce no free-ion cloud. Fluidized-bed dipping — preheating the part and immersing it in aerated powder — is the alternative route for heavy builds of 10–40 mils (250–1000 µm), used mainly for electrical insulation.

4. **Cure.** The part passes through a convection or infrared oven. The powder melts, flows out, and the thermoset chemistry crosslinks. Schedules are quoted as part metal temperature, not air temperature: 10–20 minutes at 350–400 °F (177–204 °C) is typical, and heavy sections need extra oven time simply to reach temperature. Low-temperature powders cure near 250–300 °F (121–149 °C); UV-cure powders melt thermally and then crosslink under UV in seconds, which is what makes powder coating of MDF and some plastics possible.

5. **Cool and inspect.** Film thickness is verified with a magnetic or eddy-current gauge, adhesion by cross-hatch tape test to ASTM D3359. Reclaimed overspray from the booth cyclone is sieved and blended back into the feed.

### Which powder chemistry?

Epoxy is the toughest and most chemically resistant but chalks quickly in sunlight, so it is an interior and primer material. Polyester — TGIC and TGIC-free — is the standard exterior choice. Polyester-urethane gives a smoother, thinner-looking film for appearance parts. Superdurable polyester and fluoropolymer powders serve architectural work specified to AAMA 2604 and AAMA 2605.

## Design guidelines

### Budget 2–4 mils on every reachable surface

The film goes everywhere the powder can reach. On a 0.250 in bore, 3 mils per wall closes the diameter by about 0.006 in. On a 1/4-20 thread the pitch diameter grows by roughly 4× the radial build — 3 mils becomes about 0.012 in, which no thread class accepts. Mask threads with silicone plugs or caps, or chase them after cure.

### Break every sharp edge

Molten powder pulls away from a sharp edge by surface tension, so an unbroken edge ends up with a fraction of the film thickness of the adjacent flat and becomes the site where corrosion and chipping start. Break outside edges to at least a 0.020 in (0.5 mm) radius; 0.030–0.060 in (0.75–1.5 mm) is better on parts that must pass a long salt-spray requirement.

### Design around the Faraday cage

Electrostatic field lines terminate on the nearest grounded surface, so powder starves in inside corners, deep pockets, channel interiors and slots. As a working rule, a recess deeper than its opening is wide will coat thin. Open up internal corners, provide gun access, or accept a thinner film in the recess and state it on the drawing.

### Provide a hanging point, drainage and venting

The part hangs from a hook that must make bare metal-to-metal contact, so at least one location will carry a mark: add a dedicated hanging hole, typically 0.20–0.38 in (5–10 mm), in a non-cosmetic area. Cups, box sections and blind pockets trap pretreatment solution that boils out during cure and ruins the film, so add a drain hole at the low point in the hanging orientation and vent enclosed volumes.

### Check that everything in the assembly survives the oven

Cure at 350–400 °F (177–204 °C) rules out most thermoplastics, elastomeric seals, bearings, adhesives, electronics and some pressed-in inserts. Coat before assembly, or move to a low-temperature or UV-cure powder.

### Do not expect powder to hide the substrate

A 2–4 mil film smooths but does not fill. Weld spatter, deep tool marks, casting porosity and blast profile telegraph through. Textured and wrinkle powders exist specifically to disguise a poor substrate.

| Feature | Recommended | Limit | Why |
| --- | --- | --- | --- |
| Single-coat film thickness | 2–4 mils (50–100 µm) | 1.5 mils (38 µm) minimum | Below ~1.5 mils coverage becomes discontinuous |
| Outside edge radius | 0.030 in (0.75 mm) | 0.020 in (0.5 mm) | Molten powder pulls back from sharp edges |
| Bore diameter allowance | 2 × film thickness | — | Film builds on both walls |
| Thread allowance | 4 × film thickness on pitch dia. | Mask instead | Thread geometry multiplies radial build |
| Recess depth vs. opening width | ≤ 1 : 1 | — | Faraday cage starves deeper recesses |
| Hanging hole | 0.20–0.38 in (5–10 mm), non-cosmetic face | — | Grounding contact always leaves a mark |
| Component temperature rating | Above cure temperature | 350–400 °F (177–204 °C) | Seals, bearings and plastics fail in the oven |

## Variants

- Electrostatic Spraying
- Fluidized Bed Powder Coating

## Cost drivers

Powder coating is priced per part or per rack over a lot minimum, and the powder itself is rarely the dominant cost.

- **Racking and line density.** Cost tracks how many parts fit on a linear foot of conveyor. A part that hangs flat and nests closely runs at a fraction of the cost of a bulky weldment.
- **Pretreatment level.** A five-stage zinc phosphate washer or an abrasive blast to a specified SSPC grade is a separate operation with its own labor and consumables — and it is the single biggest determinant of corrosion performance.
- **Color changes.** Reclaim booths must be blown down and cleaned between colors, so a short run in a non-stock color pays for that cleanout.
- **Masking.** Silicone plugs, caps and high-temperature tape are applied and removed by hand, twice per part.
- **Rework rate.** Powder cannot be spot-repaired the way liquid paint can. A defect usually means chemical or burn-off stripping and a full recoat.

Cost-reduction tactics:

1. Consolidate to a single stock color — black and white are the cheapest almost everywhere.
2. Design in a hanging hole and orient the part so it drains, which eliminates rework for runs and trapped solution.
3. Replace masked threads with post-cure thread chasing where the thread is accessible.
4. Break edges during machining or deburring rather than paying for hand work at the coater.
5. Release in full-line-load batches — the oven and booth cost the same whether the conveyor is full or half empty.

## FAQ

### How thick is powder coating?

A typical single coat is 2–4 mils (50–100 µm), roughly double a sprayed liquid topcoat. Below about 1.5 mils (38 µm) coverage becomes patchy. Fluidized-bed dipping is used when a much heavier build of 10–40 mils (250–1000 µm) is needed, mainly for electrical insulation.

### What temperature does powder coating cure at?

Most thermoset powders cure at 350–400 °F (177–204 °C) part metal temperature for 10–20 minutes. Low-temperature powders cure near 250–300 °F (121–149 °C), and UV-cure powders melt thermally then crosslink under UV light in seconds, which is what allows MDF and some plastics to be powder coated.

### Will powder coating close up threads and bores?

Yes. At 3 mils per surface a bore loses about 0.006 in on diameter, and a thread's pitch diameter grows by roughly 4× the radial build, or about 0.012 in — enough to bind any standard thread class. Mask threads with silicone plugs and caps, or chase them after cure.

### Can plastic be powder coated?

Only with a low-temperature or UV-cure powder, and only if the part can be made conductive — typically with a conductive primer, because electrostatic application needs a ground path. Standard thermoset powders cure at 350–400 °F (177–204 °C), which destroys most thermoplastics.

### Why does powder coating come out thin on sharp edges?

Molten powder pulls away from a sharp edge by surface tension during flow-out, leaving a fraction of the film thickness found on the adjacent flat. That thin spot is where chipping and corrosion begin. Break outside edges to at least a 0.020 in (0.5 mm) radius, and 0.030 in or more for demanding corrosion requirements.

### Is powder coating more durable than liquid paint?

For impact and abrasion resistance, generally yes — the film is thicker and fully crosslinked. But corrosion performance is set mostly by pretreatment: zinc phosphate under the powder outperforms iron phosphate by a wide margin. Liquid paint still wins where a Class A automotive appearance, field touch-up or a heat-sensitive substrate is required.

### Which powder chemistry should I specify?

Epoxy for interior and primer use — tough and chemically resistant, but it chalks in sunlight. Polyester for general exterior work. Polyester-urethane for appearance parts. Superdurable polyester or fluoropolymer for architectural aluminum specified to AAMA 2604 or 2605.

## Alternative processes

- [Spray Painting](https://manufacturingprocesses.org/processes/finishing/spray-painting.md): Spray painting atomises liquid coating onto a prepared surface, building a film that cures into a decorative and protective layer.
- [E-Coating (Electrophoretic Deposition)](https://manufacturingprocesses.org/processes/finishing/e-coating-electrophoretic-deposition.md): E-coating deposits paint electrically from a bath so it plates evenly into every recess, then cures to a uniform film.
- [Anodizing](https://manufacturingprocesses.org/processes/finishing/anodizing.md): Anodizing grows a hard porous oxide layer on aluminum electrochemically, which can then be dyed and sealed for wear and corrosion resistance.
- [Cerakote Ceramic Coating](https://manufacturingprocesses.org/processes/finishing/cerakote-ceramic-coating.md): Cerakote sprays a thin ceramic-filled polymer coating onto a prepared part and cures it, giving wear and corrosion resistance in a very thin film.
- [Electroplating](https://manufacturingprocesses.org/processes/finishing/electroplating.md): Electroplating deposits a metal coating from solution onto a conductive part by passing current through an electrolyte bath.

## Related processes

- [E-Coating (Electrophoretic Deposition)](https://manufacturingprocesses.org/processes/finishing/e-coating-electrophoretic-deposition.md): E-coating deposits paint electrically from a bath so it plates evenly into every recess, then cures to a uniform film.
- [Spray Painting](https://manufacturingprocesses.org/processes/finishing/spray-painting.md): Spray painting atomises liquid coating onto a prepared surface, building a film that cures into a decorative and protective layer.
- [Abrasive Blasting](https://manufacturingprocesses.org/processes/finishing/abrasive-blasting.md): Abrasive blasting propels media at a surface with compressed air to clean it, strip scale, or produce a uniform matte texture.
- [Chemical Conversion Coating](https://manufacturingprocesses.org/processes/finishing/chemical-conversion-coating.md): Chemical conversion coating reacts the metal surface with a chemical bath to form a thin protective, conductive or paint-adhering film.
- [Galvanizing](https://manufacturingprocesses.org/processes/finishing/galvanizing.md): Galvanizing coats steel with zinc, usually by hot dipping, so the zinc corrodes sacrificially and protects the steel beneath it.

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*Source: [Manufacturing Processes](https://manufacturingprocesses.org/processes/finishing/powder-coating)*

*Last updated: August 11, 2026*