Created on 01.12
Zoned IR Control for Complex Shapes: Improving Coating Uniformity
Complex parts rarely heat evenly. Edges, corners, ribs, and thin sections can reach higher surface temperatures faster, while shadowed areas and thick sections lag behind. If you compensate by increasing overall power, you often trade one problem for another—edge overheating, solvent pop, or uneven gloss.
Zoned IR control solves this by letting you shape heat where it’s needed. Instead of one “global” setting, you create a controlled temperature ramp across the geometry and across the conveyor width.
What “zoning” means in practice
A “zone” is an independently controlled heating section (or group of emitters) that can be adjusted without changing the rest of the dryer. Zoning helps you:
- reduce edge overheating without slowing the whole line
- lift cold areas without scorching hot areas
- keep flash-off stable before higher-temperature curing
- improve repeatability when parts or coatings change
Why complex shapes create uneven drying
1) Geometry changes radiant exposure
Edges and protrusions can “see” more radiant energy, while pockets and recesses may be partially shielded.
2) Mixed thickness changes heat-up rate
Thin sections heat quickly; thick sections act like thermal buffers. This affects both evaporation and film setting.
3) Wet film thickness is never perfectly uniform
Small thickness differences can amplify drying differences—especially at higher line speeds—making some areas prone to defects while others remain under-dried.
Typical defect patterns zoning can fix
Pattern A: “Edges dry first, center stays wet”
- Likely cause: edge flux too high or center flux too low
- Zoning move: reduce edge zone output, increase center zones, verify alignment and distance across width
Pattern B: “One side looks different”
- Likely cause: heater alignment, distance variation, airflow bias, or zone imbalance
- Zoning move: rebalance left/right zones and confirm mechanical centering
Pattern C: “Gloss variation around ribs/corners”
- Likely cause: local hotspots cause the film to set early
- Zoning move: soften early-zone power near hotspots; shift energy to mid-zone for controlled evaporation
Pattern D: “Solvent pop appears on raised features”
- Likely cause: early surface skinning on hotspots
- Zoning move: reduce early-zone intensity on those areas, extend stabilization before higher heat
How to design zones (a practical planning method)
Step 1: Map your part into “thermal risk areas”
Mark where you expect:
- hotspots: edges, corners, thin walls, raised bosses
- cold spots: recessed areas, shadowed regions, thick sections
Step 2: Choose zoning direction(s)
Most lines need one or both:
- Across-width zoning: left / center / right (or more segments)
- Along-line zoning: early / mid / late (staged heating)
Step 3: Keep early zones gentler
For coating stability, the first zone should rarely be the “strongest” zone. A staged profile is usually safer:
- early: gentle pre-warm
- mid: effective evaporation
- late: stabilization / equalization
Tuning workflow: distance → staged power → speed
- Lock distance for safety and repeatability
Keep enough clearance to tolerate part height variation without accidental flux spikes.
- Build a staged ramp with zones
Start with conservative early-zone power and distribute energy into mid zones.
- Increase speed last (in small steps)
For each speed increase, adjust zone power thoughtfully—avoid solving speed issues by only pushing early zones.
Commissioning checklist (fast, repeatable)
- Verify mechanical alignment and consistent distance across width
- Start with conservative early-zone settings
- Tune edges and corners first (reduce hotspots)
- Bring up cold spots using mid/late zones, not early spikes
- Validate with stable measurement points:
- one hotspot location (edge/corner/rib)
- one cold spot location (recess/shadow)
- one “typical” flat area
- Document recipes: zone outputs + distance + line speed + coating/substrate
Measurement note: thickness and process verification
Film thickness variation strongly affects drying response and appearance stability. If thickness measurement is part of your quality workflow, follow recognized practices and document the measurement method and locations.
FAQ
1) How many zones do I actually need?
Start simple. Many lines improve significantly with 3 zones across width and 3 along the line. Add zones only when the defect pattern clearly demands it.
2) Why not just increase overall power until everything dries?
Because hotspots will get worse first—leading to early skinning, solvent pop, gloss variation, or surface damage.
3) What’s the safest way to tune zones on a live line?
Change one zone at a time and watch where the defect pattern moves. Lock distance first, then tune staged power, then adjust speed.
4) Do zoning strategies change between coatings?
Yes. Different coatings respond differently to ramp rate and solvent release. That’s why recipe documentation per coating family matters.
5) How do I define “drying/curing stage” in a standardized way?
For standardized language and test concepts around drying/curing/film formation, you can reference recognized test methods.
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