Pretreatment tunnel sizing calculator
Choose the metal, the duty of the coated part and spray or dip. The tool proposes the stage sequence, from a three-stage combined degrease and phosphate to the seven stages of a QUALICOAT-class aluminium line, gives the length of each stage at your line speed, the tank volumes, the dryer, and draws the process flow as a diagram you can download.
Method
The stage sequence follows the process the coating needs: degrease and rinse as a minimum; a conversion coat and its rinses for adhesion and corrosion class; alkaline and acid etch stages and a conversion stage for architectural aluminium. The chemical supplier's process sheet governs the chemistry and the contact times; the tool takes the times as inputs with typical defaults.
In a spray tunnel the stage length equals line speed times contact time, plus a drain zone between stages that keeps one chemistry out of the next. In a dip line the contact time is the immersion time and the tank length follows the longest part; the tool gives the immersion schedule and tank sizes instead of a tunnel length.
Tank volume follows the pump flow and the turnover: the tank holds the flow of a few minutes so that the chemistry stays stable. The dryer after the last rinse runs at the same line speed for the dwell the part needs to leave dry and warm.
Assumptions and defaults
- Spray contact times default to 90 s degrease, 30 s rinse, 60 s conversion, 60 s etch; immersion times to 180 s degrease, 60 s rinse, 150 s conversion, 120 s etch. These are typical published values; your chemistry's process sheet replaces them.
- Drain zone between spray stages defaults to 1.0 m, tank turnover to 3 minutes, pump flow to 30 m³/h per stage.
- The example line used for the check: two spray stages followed by a 10 m dryer and a 20 m curing tunnel.
What the result does not tell you
The tool sizes stages and tanks. Tunnel material, nozzle layout, heating of the stages, water treatment and effluent, and the conductivity targets of the final rinse are fixed with the chemical supplier on the proposal.
Questions this tool answers
Short answers; the tool gives the numbers for your case.
How many pretreatment stages does a powder coating line need?
Three for indoor steel parts with a combined degrease and iron phosphate; five when a separate conversion coat and a deionised rinse are needed for outdoor duty, galvanised steel or aluminium; seven for architectural aluminium to a QUALICOAT-class specification, with alkaline and acid etch stages before an aluminium conversion coat.
Should the pretreatment be spray or dip?
Spray suits open parts at conveyor speed and gives short contact times by impingement. Dip reaches cavities, tubes and dense racks that spray cannot, at longer immersion times. Long parts and profiles are often dipped; sheet-metal parts on a conveyor are usually sprayed.
How long is a pretreatment tunnel?
Each stage is the line speed times the contact time plus a drain zone. A five-stage spray tunnel at 1.5 m/min with typical contact times is in the order of 15 to 20 m before the dryer; the tool gives the exact figure for your times and speed.
Have the result checked against your parts
Send the result with a photograph of the parts and the hall sketch. We reply with a sized proposal.