Degreasing electrical enclosures before coating

An electrical enclosure that fails in service usually fails at the first 50 µm above the steel. Powder does not bond to a steel surface; it bonds to a conversion coating, and that coating only forms on metal that is chemically clean. Degreasing electrical enclosures is the stage that makes everything downstream possible, and it is the stage that fabricators who send paint out to a job worker cannot see, measure or control.

The number to keep in mind is 1–3 g/m². That is the mill oil left on CRCA from IS 513 supply, applied deliberately to stop the coil rusting. Add press lubricant from a drawn panel, anti-spatter spray from a welded corner, zinc dust from a galvanised gland plate and fingerprints from handling, and the enclosure reaches the pretreatment line carrying a film that will prevent phosphate nucleation across part of its surface.

Powder sprayed over that film looks correct. It passes a visual check, it passes a thickness gauge, and it fails a cross-hatch or a salt-spray test weeks later. This page covers what has to come off, how the seven tanks remove it, and the drawing decisions that stop an enclosure from trapping chemistry and releasing it in the oven.

What is actually on the enclosure before it is degreased?

Five contaminants, and they behave differently.

• Mill oil and rust preventive from the coil, 1–3 g/m², spread evenly. An alkaline degreaser removes it readily if the bath is in range.
• Drawing and press lubricant on drawn or formed panels, heavier at the corners and in the draw marks. It sits in the same places that will later be difficult to rinse.
• Anti-spatter and cutting fluid from welding and laser cutting. Silicone-based anti-spatter is the worst of these because it can crater powder at 200 °C even when the part looks clean.
• Laser oxide and dross on the cut edge, which is a different problem from oil but is removed in the same acid stage.
• Handling contamination, which is sweat and skin oil from gloves that have stopped being clean.

Each one has a different removal mechanism, which is why a single wipe-down with solvent does not substitute for a degrease tank. Solvent wiping moves oil around and leaves a film at the edge of the wiped area. The chemistry itself is covered in degreasing before powder coating; what changes on an enclosure is that the part is a closed box, so the same chemistry has to reach surfaces it cannot easily drain from.

The seven-tank route from oiled CRCA to a coated enclosure

The line sequence that matters for an enclosure is degrease, rinse, derust, rinse, phosphate, rinse, passivate and dry, the same seven stages set out tank by tank in the seven-tank pretreatment guide. The dwell times and temperatures below are the working range for CRCA enclosure panels.

Why a box traps chemistry, and what that costs

An enclosure is not a flat panel. It has return flanges, door hems, welded corners, gland plate openings and often a double-skin door. Every one of those is a place where liquid enters easily and leaves slowly.

The failure sequence is predictable. The part goes through degrease and rinse, the liquid enters a hem through a 2 mm gap, and the rinse cannot displace it. It then goes through the acid and phosphate stages carrying a pocket of older chemistry, which dilutes and contaminates each bath in turn. In the dry-off oven at 110–120 °C the pocket expands and weeps out through the same gap, leaving a brown stain down the face and, on a closed box, a blister where the liquid boiled under the skin.

Two drawing changes prevent most of it:

1. An 8 mm drain hole at the lowest point of every closed section. Not a 3 mm weep hole, which surface tension can bridge, and not a slot that weakens a weld.
2. A 6 mm vent hole at the highest point. A sealed box with a drain but no vent is still a bottle.

Where a hole is not acceptable for IP or ingress reasons, the alternative is to drill a temporary drain that is plugged and sealed after coating. That is a process decision that has to be agreed at quotation, because it adds an operation and a plug to the piece price.

Hems are the other trap. A folded door edge with a 1.5 mm gap wicks chemistry by capillary action and holds it. Either close the hem fully, seal it before coating, or accept that the edge will be the first place to rust and specify a sealer bead as part of the drawing.

Temperature, dwell and the mistakes that look like paint faults

Most coating defects that get blamed on the powder are decided in the pretreatment line. Four patterns cover the majority:

Blistering in a line along a hem or weld. Trapped chemistry or trapped moisture under a lap joint. The fix is the drain and vent hole, or a continuous weld instead of a stitch.

Patchy gloss and blotchy colour. Phosphate coating weight varies where oil carried over from a weak degrease stage. The fix is the bath, not the booth.

Adhesion failure at 45° cross-hatch, with the powder lifting in flakes. A residual oil film or a dry-off that left the surface damp. A water-break test after the rinse catches the oil before the phosphate tank sees it.

Rust at the cut edge within weeks outdoors. Laser oxide left on the edge, or a coating that is too thin at the edge because the spray angle favoured the face. Edges need the full derust dwell and a coat build that includes them.

Bath chemistry drifts. Free alkalinity falls as oil is saponified, temperature drops when a cold batch of parts enters, and the acid stage loads up with dissolved iron. Titration and temperature logs are the only way to know the line is doing what the specification says, and they are the records an ISO 9001:2015 audit will ask for.

Masking an enclosure so it still works

Coating an enclosure is not only a corrosion decision. Every masked zone on the drawing is a function: earth continuity, sealing, gland entry, hinge movement or thread engagement.

• Earth stud and bonding points. Powder over an earth stud leaves the enclosure isolated. Mask the stud, the washer face and about 10 mm around it, and check the bond with a low-resistance ohmmeter after assembly.
• Gland plate and door gasket faces. A gasket compresses against a flat, coated face far better than against a powder film that creeps under load. Mask the sealing land.
• Threaded inserts, standoffs and hinge pins. Cured powder in a thread is a tap and a rework ticket; on a hinge pin it is a stiff door.
• Nameplate and label areas where the adhesive is specified for bare metal.

Masking is planned before the part is quoted, because each plug and each tape zone is an operation. An enclosure with twelve masked zones is a different piece price from one with two, and the difference is not in the powder.

Coating thickness, environment and the numbers to specify

Indoor enclosures in a controlled hall generally take 60–80 µm of polyester powder over zinc phosphate. Outdoors, or in a plant room with sulphur or chloride exposure, the specification should move to 80–120 µm and the environment should be classified rather than described: ISO 12944-2 sets out corrosivity categories from C1 to CX, and a coastal installation is a different class from a dry indoor switch room.

Salt-spray acceptance belongs in the specification, not in a shop-floor promise. ISO 9227 neutral salt spray at 500 h is a common call-out for C3 service and 720 h for C4, and the result depends on the whole system: pretreatment, coating type, DFT and edge coverage. We run DFT measurement and cross-hatch adhesion in-house on every batch, and salt-spray testing is arranged to the customer's stated method when the specification requires a report.

ISO 2409 grades the cross-hatch from Gt 0, no detachment, to Gt 5. For a powder-coated enclosure over a correct conversion coating, Gt 0 to Gt 1 is the normal result on a flat face; the harder test is on a formed return, which is where the film is thinnest and where the coating actually fails first.

What Ganesh runs

Every enclosure we coat goes through the seven-tank pretreatment line, with shot blasting in the 16 ft × 16 ft chamber first where the specification calls for it and weld scale has to come off. Powder is applied in the 18 ft × 14 ft electrostatic booth and cured in the oven, with a wet paint booth available where the specification calls for a liquid system or a primer. Coating thickness and adhesion are checked with a DFT gauge and cross-hatch testing, and the effluent from the line goes through our own treatment plant under ISO 14001:2015.

The paint shop capability page sets out the full route, and the surface treatment hub collects the pretreatment, phosphating and coating articles. If the enclosure is a genset canopy or a control panel for a generator, the coating decisions are the same ones described for genset parts.

What to put on the enclosure drawing

1. Material and surface condition: CRCA grade, mill finish, galvanised, or aluminium, since each changes the pretreatment chemistry.
2. Coating system: powder type, colour, gloss and DFT range, with the corrosivity class if the enclosure is outdoors.
3. Masked zones, listed by feature rather than by note: earth stud, gland plate, gasket land, threads, hinges.
4. Drain and vent holes, with size and position, or an instruction to add them.
5. Edge and hem treatment: seal, close or accept.
6. Acceptance: adhesion grade, DFT points, and any salt-spray requirement with its method and duration.

The powder coating cost estimator is a reasonable way to see how much of a piece price sits in the finish before you decide whether the extra 40 µm is worth specifying.

When this route does not fit

Stainless steel enclosures for washdown duty do not go through the same line. Stainless is usually supplied brushed or passivated, and coating it is a choice rather than a requirement; the pretreatment for stainless is a different chemistry and we would quote it as a separate route.

Electrophoretic primer, an e-coat layer under the powder, is not part of our line. Where an outdoor enclosure specification calls for e-coat plus powder for maximum edge coverage, that is a different supplier and a different price, and it is better to know that at the drawing stage.

Parts larger than the 18 ft × 14 ft booth or the 16 ft × 16 ft blast chamber cannot be handled as a single piece, and splitting a large canopy or enclosure into coated sections changes the assembly and the sealing detail.

The one thing we will not do is coat over an unknown surface. If a customer supplies parts that have already been painted, galvanised elsewhere or stored outdoors long enough to rust, the surface has to be assessed before it enters the line. A coating over an uncontrolled substrate is the most expensive finish there is, because it fails after the assembly is built.

Send the enclosure drawing with the service environment and the finish specification through the RFQ route and the pretreatment route, masking plan and drain holes will be agreed before the part is quoted.