The arithmetic that changes a quote
Run the defaults and the shape of the problem appears immediately. A batch of 180 parts, each with four plugs, two caps, one disc and 26 inches of tape, needs 720 plugs and 360 caps fitted. At 50 percent recovery that is 360 new plugs and 180 new caps bought for this run. The tape comes to 390 feet, which is seven 60 foot rolls with 30 feet left on the last one. The parts hang two to a hook, so 90 hooks are in use, filling five bars at 20 hooks each, and at six trips before stripping that is 15 hooks dealt with this run.
The number that dominates all of it is the last one: at a minute and a half a part for masking and unmasking together, 180 parts is four and a half hours. On most jobs that is more time than spraying takes, and it is time that scales with feature count rather than with area. A quote built on square feet has no way of seeing it.
Recovery is a measurement, not a policy
Reusable plugs and caps are only reusable if they come back. In practice they get dropped, they get thrown out with the packaging, they harden after enough oven cycles, and they tear on removal. A shop that assumes 90 percent recovery and actually achieves 50 is buying twice the plugs it planned for, and the difference is invisible because plugs are bought in bags of hundreds and nobody counts them.
The way to get a real figure is to count a batch out and count it back in once. It takes ten minutes and it is usually a surprise. The same measurement tells you something about oven temperature and dwell, because a recovery rate that falls over time is often the plugs hardening rather than the operators losing them.
Why hooks fail as a coverage problem
Electrostatic application needs the part earthed through its hook. Each pass through the oven leaves cured film at the contact point, and cured film is an insulator. The resistance rises gradually, so nothing fails on a particular day. What happens is that coverage in recesses gets slightly worse, powder sits less well on edges, and rejects creep up in a way that gets blamed on the gun, the powder, the humidity and the operator, in roughly that order.
Treating hooks as a consumable with a life in oven trips is the fix, and it makes the cost visible. At 90 hooks in service and six trips of life, this run consumes 15 hooks. Whether those are stripped and returned to service or replaced is an ordinary cost comparison, and either way it belongs in the price of the run rather than in the overhead where it usually hides.
Where this sits
The coating material for the same batch is on the powder usage calculator, which needs the coatable area of a part rather than its feature count. That area is what the fabricated steel surface area calculator builds from a bill of materials. If the parts are being plated rather than coated, the racking question is the same shape but the loading is set by current: the electroplating time and current calculator covers it. For surface preparation before any of this, the abrasive blast media calculator costs the abrasive.
Questions people ask
Should masking time really be counted separately from spraying?
Yes, because the two scale on different things and mixing them hides the expensive one. Spraying scales with area. Masking scales with the number of features that have to stay bare, which has almost nothing to do with area: a small bracket with eight tapped holes takes far longer to mask than a large flat panel with none. Quoting a job by the square foot and then discovering that every part needs six plugs is one of the more reliable ways to lose money on a coating run, and it happens because the two costs were never separated in the first place.
How do I work out my own recovery rate for plugs?
Count a batch out and count what comes back once. Draw a known quantity, keep it in a separate tub for that run only, and count what returns to the tub after unmasking. The gap is your recovery rate for that part and that oven cycle. Do it a second time a few months later, because recovery usually falls as the stock of plugs ages and hardens. If the number turns out much lower than you assumed, the useful follow-up question is whether the loss is at removal, in the bin or in the oven, because those have different fixes.
Why does the tape figure ask for inches per part rather than rolls?
Because inches per part is measurable and rolls per run is not. Mask one representative part, then take the tape off and lay it against a rule. That gives you a number that stays true when the batch size changes, whereas an estimate in rolls has to be redone every time. Note that the figure wants total run length rather than the number of pieces, since two short pieces and one long one of the same total length come off the same roll at the same rate.
What if my parts hang more than one to a hook?
Put the number in the parts per hook field and everything downstream follows, including the hook count, the rack count and the hooks consumed. Be careful that the figure reflects reality rather than intent: parts that theoretically hang three to a hook often go on two at a time because the third one swings into its neighbour in the oven or shadows it during spraying. Hanging density also has a direct effect on transfer efficiency, since parts that shield each other are parts that overspray each other.
Does this include the cost of the coating?
No. This page is consumables and masking labour only, deliberately, because those are the costs that get left out. Coating material is a function of area, film thickness and the density of the material, which is a different calculation entirely and lives on the powder usage calculator for powder and on the coating spread rate calculator for liquids. Oven time, handling, inspection and packing are also not here. Adding this page total to a material total gets you close to a run cost, but the oven and the handling are still missing.