Key takeaways
- At 70 µm and 1.5 g/cm³ a square metre holds about 105 g of powder; at 60% transfer efficiency the booth sprays 175 g, so 70 g/m² leaves as overspray and that is the material a recovery system works on.
- Reclaim at a 20% blend by weight cuts virgin consumption from 1.67 kg to 1.33 kg per kg deposited, a 20% saving; above 25% the fines balance and the colour consistency start to move.
- A cyclone cuts near 10 µm, so reclaimed powder is short of the fines that carry charge and give wraparound; below about 3% fines the film orange-peels and Faraday-cage areas thin out.
- Reclaimed powder is only reclaimable while it stays the same chemistry, colour and moisture content; one colour change without a full purge contaminates the hopper and the whole blend becomes general-purpose fill.
- Metallic, textured, wrinkle and class-A automotive finishes are not reclaim candidates — the effect depends on particle geometry and orientation, and recycling changes both.
A square metre of powder coating at 70 µm holds about 105 g of material, because powder goes down at roughly 1.5 g/cm³. A booth running at 60% transfer efficiency has to spray 175 g to deposit that 105 g, so 70 g leaves the part as overspray. Multiply by the surface area of a canopy program and the overspray becomes tonnes a year, which is why every serious booth has a recovery system and why most of them run it wrong.
Powder recovery is not a bin that catches what misses. It is a particle classification problem. The cyclone captures the coarse fraction, the filters take the fines, and the balance between them determines whether the reclaimed powder behaves like the virgin material or like a different product with the same label.
What can be reclaimed is set by four things: the cut point of the recovery device, the chemistry and colour history of the batch, the moisture the powder has absorbed, and the appearance standard of the part. This page works through each, with the blend ratio and the checks that keep a reclaimed film within the same specification as a virgin one.
How much powder does a booth actually waste?
Transfer efficiency is the fraction of sprayed powder that lands and stays on the part. Manual spraying with a corona gun runs 50–70% on simple panels and drops to 40% on a part with deep recesses, because the Faraday cage keeps the field out and the powder follows the field. Automatic guns on a reciprocator with a well-designed part presentation reach 70–90%.
Three variables move that number more than the operator does. Part density on the rack, because a sparse rack lets powder pass between parts to the booth walls. Gun distance, because the spray cone widens and the velocity drops beyond 200 mm. And the geometry of the part, because a hem or a channel presents a surface the field cannot reach.
| Parameter | Virgin powder | Reclaimed powder | Ganesh limit or note |
|---|---|---|---|
| Particle size range | 10–90 µm, mean 35–45 µm | 15–90 µm, mean near 30 µm | cyclone cut point around 10 µm |
| Fines below 10 µm | 8–12% | 2–5% | below 3% the wrap and texture suffer |
| Bulk density | 0.5–0.7 g/cm³ | slightly higher, fewer fines | check fluidisation at the hopper |
| Moisture content | below 0.5% | rises with storage humidity | store below 30 °C, 60% RH |
| Max blend into virgin | — | 20% decorative, 50% hidden | recorded per batch |
| Colour change purge | — | 20–30 min on a full booth | dedicated hoppers for repeat colours |
| Transfer efficiency | 60–75% manual, 70–90% auto | 55–70% | measured by mass balance, not by eye |
| Film build | 60–80 µm | 60–80 µm | DFT checked on every batch |
| Recovered fraction | — | 60–80% of overspray by weight | the remainder goes to filters |
What powder recovery captures and what it loses
A cyclone separates by mass and drag. Large particles are thrown to the wall and fall to the collection hopper; small ones stay in the airstream and go to the cartridge filters. The cut point — the size at which half the particles are captured — sits near 10 µm on a well-set booth cyclone, and it moves with airflow.
That cut is the reason reclaimed powder is not the same material it was. The virgin distribution has a deliberate fines tail: those particles charge quickly, follow the field into corners and give the film its smoothness. Reclaim has had most of that tail removed by the very process that recovered it.
The practical consequences are consistent. Reclaimed-rich blends orange-peel on flat panels, thin out inside channels, and need a higher gun voltage to coat a recess. The film still cures and still passes a DFT check, which is why the problem is often invisible until someone compares two panels side by side.
Cartridge filters capture the fines and a fraction of the coarse material that the cyclone missed. Filter reclaim is a different product again: finer, lighter and more contaminated with booth dust. Some plants blend it back at a low ratio; many send it out as waste. It should never be treated as equivalent to cyclone reclaim.
The blend ratio and how to prove it
A 20% reclaim blend by weight is the working limit for a decorative finish. It is not a rule of chemistry; it is where the fines deficit and the colour variation stay inside a normal appearance tolerance on a 60–80 µm film.
The mass balance shows why the number is modest. Depositing 105 g/m² at 60% transfer efficiency sprays 175 g and creates 70 g of overspray. If the cyclone recovers 70% of that, 49 g comes back. At a 20% blend the hopper takes 35 g of reclaim with 140 g of virgin, so 14 g of the recovered material has no home and leaves as waste. Virgin consumption falls from 175 g to 140 g per square metre, a 20% saving. Push the blend to 40% and the arithmetic allows more reclaim, but the fines and colour penalties arrive faster than the saving.
Prove the blend rather than assume it. Weigh the virgin and reclaim going into the hopper, record the ratio on the batch card, and check three things on the first article: film build across the part, gloss at 60°, and a visual comparison against the approved master under the same light. If the blend is drifting, the gloss and the texture move before the colour does.
Moisture, storage and the fluidising air
Polyester powder is hygroscopic enough that a humid week changes how it sprays. Above about 60% relative humidity and 30 °C, powder in an open hopper absorbs water, cakes at the bottom and stops fluidising. The symptom is spitting: a spit of damp powder lands on the panel, the charge holds it, and it cures as a crater with a bald centre.
Reclaimed powder is more exposed to this than virgin, because it has been through the booth air, the cyclone and the return line. Store it in a sealed container, keep it away from the oven wall, and use it inside the batch window rather than carrying it into the next quarter.
The fluidising air itself has to be dry. A dew point above 10 °C puts moisture into every hopper on the line, and the compressor that feeds it is often the same one feeding the blow-guns. A coalescing filter and a refrigerant dryer at the booth inlet are cheaper than the rejections they prevent.
Measuring recovery: the mass balance that proves it
A recovery system is judged on one figure: kilograms of virgin powder consumed per kilogram of powder deposited. Nothing on the booth display reports it, and the number a plant believes it saves is usually the number the vendor quoted at commissioning.
Measure it over a full shift. Weigh every virgin box that goes into the hopper and every reclaim container that leaves it. Weigh a sample of coated parts before and after coating, or calculate the deposited mass from area and film build, since the geometry is known. The difference between sprayed and deposited is the overspray, and the difference between overspray and recovered is the loss to filters and the floor.
Three results come out of that shift. Transfer efficiency, as deposited divided by sprayed. Recovery rate, as recovered divided by overspray. And the effective consumption, as virgin divided by deposited. Track the third number monthly; it is the one that pays for the equipment.
The measurement also exposes the leaks that flatter the other two. Powder that escapes past a worn booth seal, or that is cleaned off the floor at the end of a shift, never reaches the cyclone. A recovery rate of 80% measured at the cyclone can sit inside a booth that loses another 15% to the room.
Colour, chemistry and the batches that cannot mix
Reclaim is only valid within one powder family: same resin, same colour, same gloss level, same cure schedule. Two powders that look identical in the tin can have different gel times, and a blend of them cures to a film with a soft spot that appears only after a week in service.
Colour change is the operational limit. A booth that runs six colours a week cannot reclaim across them without a full clean-down between each, which costs more in labour than the powder is worth. The workable arrangement is dedicated hoppers for the two or three repeat colours and no reclaim at all on the occasional ones.
ISO 8130-1 covers the determination of particle size distribution and ISO 8130-6 covers gel time — the two measurements that tell you whether a reclaim batch is still the same product. A plant that checks neither is blending on trust.
The finishes that are not reclaim candidates
Metallic and effect powders depend on platelet orientation. The aluminium flakes align with the film as it flows, and the brightness comes from that alignment. Reclaimed powder has been through a gun, a cyclone and a return line, and the platelets arrive randomly oriented and partly coated, so the metallic effect flattens and the batch no longer matches the master.
Textured and wrinkle finishes depend on particle size to build the texture. Removing the fines changes the pattern, and blending reclaim into a texture powder produces a patchy surface that reads as a defect.
Class-A automotive and appliance faces have an appearance standard measured in gloss and distinctness of image. Reclaim can meet the film thickness and fail the appearance, which is a rejection with no material saving to show for it.
Food-contact and medical enclosures usually carry a specification that requires virgin material with a traceable batch. That is a documentation requirement, not a technical one, and it rules reclaim out regardless of how well the powder behaves.
What Ganesh runs
Ganesh coats in an 18 ft × 14 ft electrostatic powder booth with a wet paint booth alongside it, after a seven-tank pretreatment line and, where the surface needs it, a 16 ft × 16 ft shot blast chamber. Parts arrive from a 12 kW fibre laser with a 40 ft × 16 ft bed, presses from 20 T to 300 T, a 200 T 5-axis brake and three CLOOS robotic MIG cells, so the coating line sees flat panels, formed covers and welded frames in the same week.
The plants hold ISO 9001:2015 and ISO 14001:2015, and the environmental system treats powder waste as a monitored stream — which is exactly why the reclaim ratio is recorded rather than left to the booth operator. Film build is checked with a DFT gauge on every batch, and adhesion by cross-hatch. The paint shop page sets out the full sequence, powder coating laser-cut edges covers the edge condition that decides whether a reclaimed film covers cleanly, and the plant and quality hub collects the booth and waste records.
What to put on the coating specification
- Powder type, resin family and colour reference, with the gloss level and the appearance standard.
- Film build range, and the faces that are coated.
- Whether reclaimed powder may be used, and at what maximum blend. If the answer is no, say so; it changes the price.
- The cure schedule, especially where a component in the assembly cannot take the full metal temperature.
- First-off approval: a panel or a part compared against the master under defined light.
- Batch traceability, where the part goes into a safety-critical assembly.
- Masking: threads, earth studs, mating faces and any conductive contact.
A supplier who cannot state the blend ratio on the batch card is not controlling recovery, whatever the booth is fitted with.
When recovery is the wrong investment
A booth that runs more than a dozen colours a month will spend more on purging than it saves on powder. Below roughly 2,000 m² of coated surface a year, the capital and the cleaning labour do not repay, and a simple cartridge booth with no reclaim is the better machine.
Where the appearance standard is class-A, where the powder is metallic or textured, or where the customer's specification calls for virgin material, the correct policy is no reclaim at all. Recovery then becomes a waste-handling question, not a cost-saving one.
And a plant that cannot hold its humidity below 60% should fix the building before it installs a cyclone. Recovery returns moisture-exposed powder to the gun, and the crater rate rises with every pass through the loop.
Set the cut point, keep the blend at or below 20%, purge between colours and store the reclaim dry. Recovery then saves about a fifth of the virgin powder without changing the film the customer inspects. Send the drawing and colour reference through the RFQ and the quotation states the reclaim policy.
Related reading: the 5S on a fabrication floor: what it changes in practice and the Calibration register: how instruments stay traceable take the same problem further.
Frequently asked questions
Can all oversprayed powder be reclaimed?
No. A cyclone recovers the fraction above roughly 10 µm, which is 60–80% of the overspray by weight; the rest goes to the cartridge filters with the exhaust air. Powder that has cured, picked up moisture or mixed with another colour cannot go back.
What percentage of reclaimed powder can be blended with virgin?
Up to 20% by weight for a decorative finish, and up to 50% only on hidden or structural parts where appearance is not judged. Above 20% the fines deficit shows as orange peel and the colour drifts batch to batch.
Why does reclaimed powder cause orange peel?
Because the fines are gone. Particles below 10 µm carry charge well, fill the surface texture and follow the field into recesses. A reclaimed blend with 2–3% fines flows out coarser and covers Faraday-cage areas thinly.
How should reclaimed powder be stored?
In a sealed container below 30 °C and 60% relative humidity, away from the oven, and used within the batch window. Damp powder cakes, stops fluidising and sprays in spits that leave uncoated craters.
Does reclaimed powder cure differently?
The chemistry is the same if the powder has not seen heat. Once particles have partially cured on a hot booth wall or in a return line near the oven, the gel time shortens and the film can lose gloss and adhesion.
Sources and further reading
- ISO 8130-1 — Coating powders: determination of particle size distribution · reviewed 3 Nov 2026
- ISO 8130-6 — Coating powders: determination of gel time · reviewed 3 Nov 2026
- ISO 2360 — Non-conductive coatings on non-magnetic basis metals · reviewed 3 Nov 2026
Coating a batch with a colour-critical finish?
Send the drawing, the colour reference and the annual quantity. The quotation states the powder type, the reclaim policy and the first-off approval route.
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