Powder coating is an electrostatic process run inside a mechanical system. The chemistry and the gun settings get most of the attention, but on a production line the conveyor decides whether the process works. If the carrier cannot hold the part at earth potential, if the part swings as it crosses the gun, or if the track feeds a fine rain of dust into the booth, no amount of parameter tuning will recover the coating quality.

This article concentrates on the design decisions that are specific to powder lines rather than to finishing lines in general. It is a companion to the main guide on industrial coating line conveyor systems.

1. Why a powder line is not simply a wet paint line

Fourteen litres of solvent evaporate; powder does not. That single difference drives the whole engineering distinction, because powder is applied dry, is charged, is recoverable, and is finally melted into a film. Practically, it means:

The part must be electrically earthed, because adhesion before cure depends on electrostatic attraction rather than on a wet film bonding to the substrate.

Overspray is a reusable raw material, so the booth is a closed-circuit material system with recovery equipment - not a spray area with extraction.

The film forms only at cure temperature, so anything that disturbs the powder layer between the gun and the oven leaves a permanent defect.

Fine powder behaves like a dust, and dust travels along any open path - including a conveyor track.

Each of those points converts into a hardware requirement on the conveyor: continuous grounding, tight booth openings, a track that does not shed particles, and a smooth drive with minimum carrier movement.

2. Zone-by-zone demands on the conveying system

A powder line loops through five distinct duty zones. Hardware chosen for one is frequently wrong for another.

Wash and dry-off. Warm aqueous chemistry and moisture are present. Corrosion-resistant wheels, pins and brackets belong here, together with drainage detail that prevents rinse water travelling along the rail toward the booth.

Transfer into the booth. This is the contamination boundary. Every kilogram of powder that escapes the booth area through the conveyor slot is lost material and a housekeeping burden.

Booth and recovery. Powder-laden air, occasional impact from a mis-hung part, constant static charge. The track running over the booth should be shrouded, and the shroud needs a form that powder cannot build up inside.

Cure oven. Sustained elevated temperature. Bearings and lubricants selected for ambient duty will not survive repeated passes; the rail requires provision for thermal movement.

Cool and unload. The part is handled by people again, so carrier stability, hook condition and operator reach all matter. This is also the zone where grounding deterioration first becomes visible as rejected parts.

3. Designing the earth path into the conveyor

Grounding on a powder line is a mechanical circuit, and it has to be designed rather than assumed. The current path runs from the workpieces, through the hooks, into the carrier frame, through the trolley wheels, onto the running rail, and out to a verified plant earth. Nothing in that route is self-maintaining.

Design consequences:

Treat hook and contact surfaces as consumable. Cured powder, oxide and burn marks accumulate on the points where hooks touch carriers and where wheels touch rail. Resistance rises steadily. Either budget for periodic stripping of hangers, or select contact geometry that is easy to clean without dismantling carriers.

Do not rely on the drive chain. A moving chain is a load path with variable contact resistance. Current carried through pins and bushes produces arcing that pits surfaces and accelerates wear, so the earth return must be independent of the chain.

Provide a deliberate rail earth connection. At a minimum, the rail should be bonded to plant earth at intervals, with the bond points protected from powder and corrosion. Where the process is sensitive, a sliding earth shoe or a dedicated earthing trolley gives a controlled path rather than incidental wheel contact.

Instrument the result. A ground-monitoring relay that measures resistance from the part to earth while the line runs converts an invisible variable into an alarm. On a line coating thousands of parts per shift, this device usually pays for itself the first time a contaminated hook is caught within minutes rather than after a day of rejects.

4. Booth interface design: openings, airflow and containment

The conveyor opening at the booth wall is the largest uncontrolled aperture in the powder enclosure. Three design rules reduce the loss.

Match the opening to the carrier envelope, not to convenience. The slot should be as narrow as the carrier, load bar and part swing actually require, with the geometry arranged so that the opening is at the top of the booth where the powder concentration is lowest.

Energise the interface deliberately. Extraction at the entry and exit slots, arranged to pull air into the booth rather than out of it, keeps powder inside the enclosure. Passive slots let the booth breathe powder into the plant.

Avoid horizontal ledges above the opening. Any flat surface on the booth roof or on the conveyor shroud becomes a powder shelf. Sloped or curved surfaces shed material back into the booth or onto a removable tray.

5. How recovery equipment changes conveyor layout

Powder recovery is a mechanical plant in its own right - cyclone, cartridge or combination, with ducting, fans and a return path for reclaimed material. Two layout implications follow, and both are habitually discovered late.

First, recovery equipment needs service access: filter changes, cyclone cleaning and duct inspection are routine, and the conveyor must not run through the space those tasks require. Second, ducting should be routed so that it does not pass directly above freshly coated parts between the booth and the oven, because condensation and dust from ductwork find their way onto wet powder.

Where a booth is fed by a power-and-free system, the transfer zone between booths also draws recovery demand, because moving carriers carry airborne powder with them. Enclosure of the transfer reduces both losses and cross-contamination between colours.

See the matching hardware in the power and free conveyor range and the enclosed rail conveyor range.

6. Transfer efficiency: the conveyor's share of the result

Transfer efficiency is normally discussed as a gun property, yet the conveying system sets the ceiling. The mechanisms are straightforward:

Distance stability. Film build depends on gun-to-part distance. A carrier that drifts a few centimetres toward or away from the gun changes the deposited thickness, and the part either fails a thickness check or consumes more powder than necessary.

Repeatability of attitude. Parts hung consistently present the same surface area, so the gun recipe stays valid and the operator is not adjusting for every carrier.

Grounding quality. Poorly earthed parts attract less powder, so more of it ends up in the recovery system. This is the single largest conveyor-related loss on most lines.

Swing elimination. A rocking part scatters powder around the intended target area, raising recovery load and reducing first-pass yield.

The practical objective is to make every carrier identical from the gun's point of view: same distance, same angle, same speed, same earth resistance.

7. Part presentation for complete coverage

Powder has limited wrap-around compared with wet electrostatic paint, so presentation strategy matters more. Choose load bars for orientation, not for convenience.

Where parts have large flat faces, present them at an angle to the gun so that edges are not shadowed. Where parts are three-dimensional or have recessed features, rotation in front of the gun is the reliable answer; a rotary hanger turns the part so that every face passes through the spray pattern at a comparable distance. Where a part is heavy, double hanger brackets distributed across two attachment points keep the carrier level and reduce the swing that causes edge build-up and misses.

Two presentation faults are worth checking during commissioning. Parts hung with the heaviest mass above the running rail amplify swing, and parts hung with a large horizontal surface facing upward collect falling powder and produce a rough finish.

8. Colour change and its effect on the mechanical system

Colour changes are a conveyor design issue because they determine how much apparatus must be cleaned and how much powder must be purged. On a line with frequent changes:

Booth interiors, gun bodies, ducting entries and conveyor shrouds are all cleaning surfaces. Fewer horizontal surfaces and more removable panels reduce changeover time directly.

If carriers are not fully emptied before a colour change, residual powder on hooks and load bars migrates into the new colour and shows as specks.

Where two booths are installed to allow rapid switching, a power-and-free system allows carriers to be routed to the booth that is ready, which typically converts a line stoppage into a routing decision.

Dedicated hangers per colour family, or a hook-cleaning station before the reload point, are simple and inexpensive measures compared with the cost of colour-contaminated rejects.

9. What the conveyor must tolerate inside the cure oven

Powder systems cure by heating the substrate until the powder flows and cross-links, which means the conveyor is heated along with the part. Three requirements follow.

Temperature-rated motion components. Wheel bearings and any lubricant in the hot section must be rated for continuous duty at the oven's metal temperature, not merely for a peak. Where a suitable lubricant is not acceptable in a plant, dry-running bushings are the alternative.

Controlled expansion of track. The hot section grows as it heats. Sliding hangers at the oven ends, a fixed mid-point anchor and expansion joints at the boundaries let that growth occur without misaligning the wheel path or squeezing the chain.

Adequate clearance at entry and exit. The oven slot is dimensioned cold but operates hot. Slots must clear the carrier, the load bar and the swinging part in the hot condition, which is a wider envelope than the cold one.

Site notes on high-temperature track are collected under the industrial thermal rail category.

10. The return leg is not a dead end

The return run from the unload station back to the load station is where most lines accumulate problems because it is the least supervised part of the loop. It carries the chain, the empty carriers and the residue of the previous cycle.

Three items belong in the design: a hook or hanger inspection position where operators can see and remove damaged hangers, a cleaning or stripping station where contact surfaces and shrouds are cleared before parts are rehung, and drip protection anywhere the return leg passes over process equipment. On a line where the return leg is simply a straight run back to the loader, contamination carried out of the booth is reintroduced at the next carrier cycle.

11. Common mistakes found on existing powder lines

A ground path designed only on paper. Resistance was never measured after installation, and transfer efficiency quietly declined over two years.

Booth slot dimensioned generously to avoid interference, creating a permanent powder escape route.

Ordinary grease in the hot section, leading to carbonised deposits that drop onto parts after a few months of production.

Load bars hung for workshop convenience rather than for spray geometry, leaving shadowed edges that are corrected by increasing powder output instead of fixing presentation.

Recovery ducting crossing above the booth-to-oven transfer.

Track running directly above the booth without a removable shroud, so overspray cures onto the rail and sheds onto product.

Each of these is inexpensive to correct before installation and expensive to correct afterwards.

12. Data to collect before ordering a powder line conveyor

Prepare the following so that a supplier can size the system rather than estimate it: maximum and typical part mass with the hanging axis; parts per hour required at unload; number of parts per carrier and carrier pitch; total process dwell time and the dwell required in the booth, dry-off and cure stages; oven metal temperature and cure time; available headroom and column positions; expected number of colours and change frequency; required grounding resistance; and whether accumulation or indexing is needed.

With those inputs a supplier can select the track, chain series and carrier arrangement, calculate drive and take-up duty, and confirm that the layout suits the building. The general specification checklist for coating lines appears in the complete coating line conveyor guide.

Frequently asked questions

1. Does a powder coating line need a different conveyor from a wet paint line?

Yes. It needs a more reliable earth path, tighter booth openings to contain reclaimable powder, and hardware with equal or greater heat resistance, since powder cure temperatures are high and the powder layer is dry and easily disturbed before the oven.

2. Can a closed track conveyor be used for powder coating?

It is normally the preferred arrangement. The closed profile keeps wheel contact and lubricant inside the track, where they cannot fall onto parts, and it protects the wheel path from powder ingress in the booth area.

3. How often should hangers be cleaned to maintain grounding?

There is no universal interval; the determinant is how quickly resistance rises above the level at which transfer efficiency falls. Measure carrier-to-earth resistance on a sample of carriers at fixed intervals and clean when it exceeds your quality threshold.

4. Is a rotary hanger always necessary for powder coating?

No. It is necessary when part geometry creates shadowed areas that a fixed orientation cannot expose. Simple flat parts coat satisfactorily without rotation.

5. What happens if parts are not properly earthed in a powder booth?

Charged powder is less strongly attracted to the part, so transfer efficiency falls, wrap-around and edge coverage deteriorate, and a much larger proportion of the sprayed powder is captured by the recovery system instead of being deposited.

6. How can powder loss at the booth entrance be reduced?

Reduce the conveyor opening to the actual carrier envelope, position it at the top of the booth, arrange extraction so that air flows into the booth at the slots, and eliminate horizontal ledges where powder can settle.

7. Will a power-and-free system improve powder line productivity?

It does when booth dwell time differs from cure dwell time, when multiple colours are run, or when carriers must be buffered between stages. It adds complexity in return, so the benefit has to be real for the specific product mix.

8. What temperature should a powder line conveyor be rated for?

The rating should be based on the metal temperature the hardware actually reaches in the cure oven and the duration of each pass, not on the oven's set point alone. Confirm the figure with the equipment supplier.

9. Can an ordinary overhead conveyor be converted to powder line duty?

Often yes, if the earth path can be established reliably, the booth area can be shrouded, and the hot section is provided with correctly rated bearings, lubricant and expansion provision. The conversion must be assessed against the same criteria as a new installation.