Powder Coating

Start here: ten words every newcomer needs

Overheard on the job

Real-sounding lines from the floor, translated into plain English.

• Inside corners are caging again, drop the kV and shoot the recesses first before the recip gets them.

  TranslationPowder is not reaching the inside corners because of the Faraday cage effect, so lower the gun voltage and hand-spray those areas before the automatic guns coat the rest.

• PMT on the thick flanges never got past 360, so they failed MEK, send them back through and slow the line.

  TranslationThe heavy parts never reached cure temperature and the solvent rub test shows they are undercured, so run them through the oven again at a slower conveyor speed.

• Second coat is all starbursts, you're back ionizing, back off the gun and turn down the micro-amps.

  TranslationThe recoat is pitted because the powder layer is overcharged and repelling new powder, so increase gun distance and reduce charging current.

• Castings are gassy, give them an hour pre-bake and hot flock them or we'll be pinholed again.

  TranslationThe cast parts release trapped gas when heated, so bake them first and spray them while still hot to avoid holes in the finish.

• Cleaner's down to 3 points and the panels are water-breaking, that's why the adhesion went.

  TranslationThe washer's cleaning bath is weak, parts are still oily after cleaning, and that oil is the reason the coating is not sticking.

• Bad ground on the crossbar, half the rack is light and the reclaim is going through the roof.

  TranslationCured powder on the rack is blocking the electrical path to earth, so parts are coating thin and much more powder is missing the parts.

• White came out cooked and yellow, the line sat with that load in the oven through break.

  TranslationThe white parts were overbaked and turned yellow because the conveyor stopped while they were inside the cure oven.

Powder types, resins, crosslinkers, special effects and the material facts that drive coverage and storage.

• Bonded metallicalso bonded metallic powder
  Metallic powder in which the flake is fused onto the base particles so it sprays and recycles evenly.
• Candyalso candy color, tinted clear
  A tinted transparent topcoat sprayed over a bright base so the color glows with metallic depth. Shop talk
• Crosslinkeralso curing agent, hardener
  The hardener in a thermoset powder that reacts with the resin to tie it into a network.
• Dry blendalso dry-blended metallic
  Powder in which additives such as metallic flake are mixed in loose after milling rather than fused on.
• Epoxy powderalso epoxy
  Powder based on epoxy resin, prized for chemical and corrosion resistance but weak in sunlight.
• FBEalso fusion-bonded epoxy, fusion bond
  Fusion-bonded epoxy, a fast-curing epoxy powder applied to preheated pipe, rebar and valves for corrosion protection.
• Finesalso dust, fine fraction
  The smallest particles in a powder, roughly under 10 microns, which fluidize, charge and recycle poorly.
• HAAalso TGIC-free polyester, Primid polyester
  Hydroxyalkylamide, the TGIC-free crosslinker used to cure carboxyl polyester powders.
• Hybridalso epoxy-polyester hybrid, epoxy-polyester
  Powder that cures an epoxy resin and a polyester resin together, trading some outdoor life for low cost and good flow.
• Low-cure powderalso low-bake powder, LTC powder
  Powder formulated to cure at lower oven temperatures, used to save energy or coat heat-sensitive parts.
• Polyester powderalso polyester
  Powder based on polyester resin, the standard choice for outdoor parts because it holds color and gloss in sunlight.
• Reclaimalso reclaimed powder, recovered powder
  Oversprayed powder collected from the booth and fed back into the system for reuse.
• Shelf lifealso storage life
  How long boxed powder stays sprayable and reactive when stored cool and dry.
• Superdurablealso super durable, SD polyester
  Describing polyester powders built with weather-stable acids that hold gloss and color several times longer outdoors.
• TGICalso TGIC polyester, triglycidyl isocyanurate
  Triglycidyl isocyanurate, the classic crosslinker that cures carboxyl polyesters into weather-resistant films.
• Theoretical coveragealso coverage, sq ft per pound
  The area one pound of powder covers at one mil if every particle lands on the part.
• Thermoplastic powderalso thermoplastic coating
  Coating powder that simply melts and solidifies on cooling, with no chemical cure, so it can be remelted.
• Thermoset powderalso thermosetting powder
  Coating powder that melts, flows and then chemically crosslinks in the oven, so it cannot be remelted.
• Urethane polyesteralso polyurethane powder, urethane
  Hydroxyl polyester powder cured with a blocked isocyanate, known for smooth, thin films.
• Wrinkle finishalso wrinkle, wrinkle texture
  Textured powder that cures into a fine wrinkled pattern, hiding substrate flaws and fingerprints.
• Zinc-rich primeralso zinc primer
  Epoxy powder primer loaded with zinc dust to give steel extra corrosion protection under a topcoat.

Washers, conversion coatings, blasting, stripping and every step that gets metal ready to hold powder.

• Anchor profilealso profile, surface profile
  The peak-to-valley roughness that blasting cuts into steel, giving the coating something to grip.
• Blastalso sandblast, media blast
  To strip and roughen a part with abrasive media before coating, or as a noun, the blast room itself. Shop talk
• Blow-offalso air blow-off, air knife
  Blasts of compressed air used to clear water from pockets or dust from parts before they are coated. Shop talk
• Burn-off ovenalso burn-off, pyrolysis oven
  A high-temperature oven that burns cured powder off racks, hooks and rejected parts.
• Conversion coatingalso conversion coat
  A thin layer formed by chemically reacting the metal surface, which improves adhesion and slows corrosion under powder.
• DI rinsealso deionized rinse, DI water rinse
  Deionized water rinse, the final stage that washes salts off the part so they do not end up trapped under powder.
• Dry-off ovenalso dry-off, drying oven
  The oven after the washer that drives off rinse water before parts reach the powder booth.
• Five-stagealso five-stage washer, 5-stage
  Shop name for a spray washer with five tanks: clean, rinse, conversion coat, rinse and final seal or DI rinse. Shop talk
• Flash rustalso flash rusting
  A thin orange rust bloom that forms within minutes on wet, freshly cleaned steel.
• Iron phosphatealso iron phos, iron phosphating
  A thin, amorphous phosphate conversion coating on steel, the economical standard for indoor and light outdoor parts.
• Pointsalso titration points
  The titration reading for a washer bath, given in milliliters of titrant and used to judge bath strength. Shop talk
• Pretreatmentalso pretreat, prep
  The cleaning and chemical conditioning a part gets before powder, which decides most of its adhesion and corrosion life.
• Seal rinsealso final seal, post-rinse
  A final pretreatment rinse that fills pores in the conversion coating and boosts corrosion resistance.
• Smutalso etch smut
  A loose dark film left on metal after alkaline etching or acid pickling that must come off before coating.
• Stripalso stripping
  To remove cured powder from a rejected part or rack so it can be recoated. Shop talk
• Thin-film pretreatmentalso zirc, zirconium pretreatment
  A zirconium- or titanium-based conversion coating only nanometers thick, run in place of phosphate on many lines.
• Washalso washer, the washer
  Line slang for the spray pretreatment washer, or for the pass a part makes through it. Shop talk
• Water-break testalso water break, water-break-free test
  Quick cleanliness check: a clean surface holds an unbroken sheet of water, an oily one makes it bead and split.
• Zinc phosphatealso zinc phos
  A heavy crystalline phosphate conversion coating that gives steel top-tier corrosion resistance under powder.

Guns, charging, booths, recovery, hoppers and the electrostatic effects that decide where powder lands.

• Back ionizationalso back ion, electrostatic rejection
  Tiny electrical discharges inside an overcharged powder layer that repel new powder and pit the finish.
• Bad groundalso no ground, poor ground
  A hook or rack contact too crusted with cured powder to carry charge away, so powder will not stick properly. Shop talk
• Boilalso simmer
  To bubble gently and evenly like simmering water, the way a properly fluidized hopper of powder should look. Shop talk
• Cagealso caging
  Shop shorthand for a recess resisting powder because of Faraday cage effect. Shop talk
• Color changealso color change-over
  Cleaning the booth, guns, hoses and recovery system so a new color can run without contamination.
• Corona gunalso corona charging gun
  A powder gun that charges particles with a high-voltage electrode at the tip, the most common gun type.
• Cyclonealso cyclone separator, cyclone recovery
  A cone-shaped separator that spins booth exhaust so the powder drops out for reclaim and the air goes to filters.
• Dustingalso dust coat, dust it
  A light, quick pass of powder that barely covers, or the first thin pass before building film. Shop talk
• Electrostatic sprayalso electrostatic application, electrostatic powder spraying
  Spraying charged powder at a grounded part so electrical attraction pulls it on and holds it until cure.
• Faraday cage effectalso Faraday cage, Faraday effect
  The tendency of charged powder to avoid inside corners and recesses because the electric field bunches on nearby edges.
• Feed hopperalso hopper, fluidizing hopper
  The fluidized container that holds powder and supplies it to the gun pumps.
• Fluidized bedalso fluid bed
  A tank of powder kept airborne by air blown up through a porous floor, used to dip preheated parts.
• Free ionsalso free ion current
  Charged air molecules from a corona electrode that never attach to powder but still land on the part.
• Groundalso grounding, earth
  The electrical path from the part through hooks, racks and conveyor to earth that lets charged powder stick.
• Hot flockingalso hot flock, preheat spraying
  Spraying powder onto a part that is already hot, so the powder melts on contact and builds a thick film. Shop talk
• kValso kilovolts, voltage
  Kilovolts, the voltage setting on a corona gun that governs how hard it charges the powder.
• Reciprocatoralso recip, gun mover
  The machine that moves automatic guns up and down so they sweep the full height of parts passing on the line.
• Shootalso spray, shot
  To spray powder, as in shooting a part or shooting a color. Shop talk
• Spittingalso spits
  Powder bursting out of the gun in clumps, leaving lumps and heavy spots on the part. Shop talk
• Transfer efficiencyalso TE, first-pass transfer efficiency
  The share of sprayed powder that ends up on the part rather than in the booth.
• Tribo gunalso tribo, triboelectric gun
  A powder gun that charges particles by rubbing them against a plastic tube, with no high-voltage electrode.
• Wrapalso wraparound, electrostatic wrap
  Charged powder curling around edges onto the back of a part that the gun never pointed at.

Ovens, cure schedules, temperature profiling and what too much or too little heat does to a film.

• Cookalso bake, cooked
  Line slang for curing parts in the oven, and in the past tense, for parts that got too much heat. Shop talk
• Cure schedulealso cure, bake schedule
  The time at temperature a powder needs to cure fully, measured at the part's metal, not the oven air.
• Flowalso flow and leveling, flow-out
  How far and how smoothly melted powder spreads out before it gels, which sets surface smoothness.
• Gel timealso hot plate gel time, stroke cure
  How many seconds a powder takes at a set temperature to go from melted to a rubbery gel that no longer flows.
• IR curealso infrared cure, IR oven
  Curing powder with infrared emitters that heat the film and part surface directly by radiation.
• Oven profilealso profile run, oven curve
  A temperature recording from thermocouples on real parts as they travel through the cure oven.
• Overbakealso overcure, overbaked
  Cure that went too hot or too long, causing yellowing, gloss loss and brittle film.
• PMTalso part metal temperature, metal temp
  Part metal temperature, the temperature of the substrate itself, which is what actually drives the cure.
• Pre-bakealso outgas bake, degas bake
  Heating a casting or galvanized part before coating to drive out trapped gas that would blow holes in the film.
• Rampalso ramp-up, come-up time
  The heat-up time a part needs in the oven before it reaches cure temperature and the cure clock starts. Shop talk
• Undercurealso undercured, underbake
  A film that did not get enough time at temperature to crosslink fully, so it looks fine but performs poorly.

Thickness, gloss, color, hardness, adhesion, corrosion and weathering tests used to accept or reject work.

• AAMA 2604also 2604
  The mid-tier North American architectural coating spec, requiring five years of Florida exposure with limited fade.
• Chalkingalso chalk
  A powdery residue on a weathered finish where sunlight has broken down the resin at the surface.
• Cross-hatch adhesionalso crosshatch, tape test
  An adhesion test that cuts a grid through the film, pulls tape over it and rates how much coating comes off.
• Delta Ealso dE, color difference
  A single number for how far a color is from its standard, read by a spectrophotometer.
• Film buildalso DFT, dry film thickness
  The thickness of the cured coating, usually given in mils or microns.
• Fingernail testalso thumbnail test, nail test
  The rough floor check of cure: dig a thumbnail into a cooled part and see if it marks. Shop talk
• Glossalso gloss level, 60-degree gloss
  How mirror-like a finish is, read with a gloss meter at a fixed angle, usually 60 degrees.
• Impact testalso reverse impact, direct impact
  A test that drops a weighted punch onto a coated panel and checks whether the film cracks or lifts.
• MEK rub testalso MEK rub, solvent rub
  A cure check that rubs the film with a cloth soaked in methyl ethyl ketone and rates how much softens or rubs off.
• Milalso thou, mils
  One thousandth of an inch, exactly 25.4 microns, the everyday unit for coating thickness in North America.
• Pencil hardnessalso pencil test
  A scratch test that rates film hardness by the hardest pencil lead that will not gouge it.
• Salt sprayalso salt fog, B117
  An accelerated corrosion test that holds scribed coated panels in a warm salt fog for hundreds of hours.

What goes wrong on the finished part, from orange peel and craters to outgassing and specks.

• Bloomalso blooming, haze
  A hazy, greasy film that forms on cured powder, often wiping off with a cloth.
• Crateralso fisheye, cratering
  A round dimple in the cured film where something with low surface tension pushed the melted powder away.
• Cross-contaminationalso cross contamination, specking
  Specks of a different color or chemistry carried into a powder run from equipment, air or reclaim.
• Gassy
  Describing a casting, galvanized part or batch of metal known to outgas and ruin the finish. Shop talk
• Holidayalso holiday void, skip
  A skip, void or pinhole in the coating where bare metal is exposed.
• Orange peelalso peel, OP
  A dimpled surface texture like the skin of an orange, the most common appearance complaint on powder.
• Outgassingalso gassing, out-gassing
  Gas escaping from a porous substrate during cure and blowing pinholes, bubbles or craters through the film.
• Picture framingalso framing, edge build
  A visible border of heavier or darker coating around the edges of a flat panel. Shop talk
• Pinholealso pinholing, pin holes
  A tiny hole running through the cured film, often down to bare metal.
• Seedsalso gel particles, lumps
  Small hard lumps in the cured film from gelled or fused bits of powder rather than outside dirt. Shop talk
• Trashalso dirt, dirt in film
  Floor word for dirt, lint, fibers and debris cured into the finish as bumps. Shop talk
• Yellowingalso gas yellowing, overbake yellowing
  A yellow shift in whites and light colors caused by overbake or by fumes in gas-fired ovens.

Racking, hanging, masking, conveyor speed and the day-to-day running of a coating line.

• Hangalso load, hang parts
  To load parts onto hooks or racks at the start of the line. Shop talk
• Hooksalso hangers, S-hooks
  The wire hangers that hold parts on the conveyor and carry the ground connection. Shop talk
• Line speedalso conveyor speed, fpm
  How fast the conveyor moves, in feet per minute, which sets washer time, spray time and oven time all at once.
• Maskingalso mask
  Protecting threads, holes and contact surfaces from powder with heat-resistant tape, caps and plugs.
• Plugsalso caps and plugs, silicone plugs
  Silicone stoppers pushed into holes and threads so powder stays out, often reused many times. Shop talk
• Rackingalso rack, fixturing
  The racks, hooks and fixtures that carry parts through the line, and the job of arranging parts on them.
• Recoatalso second coat, re-spray
  A second coat of powder over a cured first coat, used to fix rejects or build a multi-coat system.
• Two-coatalso 2-coat, two-coat system
  Describing a finish built from a base coat and a top coat, each sprayed separately. Shop talk

Frequently asked questions

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