Foam dosing calibration sandwich panel line work means proving that the A-side and B-side pumps deliver the right chemical ratio and total output at the real line speed. If your PU/PIR panels show voids, soft edges, foam overflow, or early skin separation, check dosing before blaming the steel sheet, adhesive film, or operator.
Foam Dosing Calibration Basics
A foam dosing calibration sandwich panel line check sets the real A-side and B-side flow, confirms the chemical ratio by weight, and matches total foam output to panel volume per minute. On a PU/PIR sandwich panel line, you verify pump output with weighed shots, then prove the result with core density, adhesion, and cut-surface checks.
This guide assumes a continuous metal-faced PU/PIR line with a high-pressure foaming machine, moving double-belt laminator, side blocks, and adjustable line speed. It doesn’t apply cleanly to discontinuous mold presses, hand-pour repair work, or low-pressure pourers with long open-time recipes.
A-side is normally polymeric MDI, such as Wanhua PM-200, BASF Lupranat M20S, or Covestro Desmodur 44V20L. B-side is the polyol blend: polyol, catalyst, surfactant, flame retardant, blowing system, and additives. The ratio comes from the chemical supplier’s formula sheet, not from last month’s HMI habit.
| Check point | Normal target | Shop-floor tool | Stop sign |
|---|---|---|---|
| A/B ratio by weight | Formula tolerance, often +/-1% after calibration | Digital scale and timed shot | One side drifts every repeat |
| Total foam output | Calculated kg/min +/-2% before trial panels | Weighed output test | HMI flow and real weight disagree |
| Material temperature | Supplier recipe value, often 20-25 C | Tank sensor and handheld probe | Viscosity changes during the shift |
| Mix pressure | Stable within machine setting range | Foamer pressure display | Pulsing, split pressure, streaked foam |
At first this looks like a chemistry issue. On a moving panel, timing is just as guilty: a 2-second delay at 6 m/min moves the foam start point by 200 mm. That can leave the leading edge starved even when the ratio is perfect.
Output Math
Start with panel volume, then add a practical loss factor. The target output is:
foam output kg/min = line speed m/min x panel width m x core thickness m x target core density kg/m3 x loss factor
Example: a 50 mm panel, 1.0 m effective width, 6 m/min line speed, 42 kg/m3 target core density, and 1.05 loss factor needs:
6 x 1.0 x 0.05 x 42 x 1.05 = 13.23 kg/min
If the recipe calls A:B = 100:110 by weight, split the 13.23 kg/min into 6.30 kg/min A-side and 6.93 kg/min B-side. Don’t round this casually. On an 8-hour shift, a 0.3 kg/min error becomes 144 kg of chemical, and it usually appears as either wasted foam at the side blocks or low-density areas near the edges.
Core density should be checked by cutting a known-size foam sample and weighing it. ISO 845:2006 defines apparent density testing for cellular plastics and rubbers, and it is a useful reference when your buyer asks how density was measured during acceptance testing.
For PIR, be more careful with heat. PIR formulas usually run a higher isocyanate index than standard PU formulas, so copying a PU ratio into a PIR batch can make the foam brittle, hot, and unforgiving. That mistake shows up fast when the panel leaves the double belt and the cut edge looks glassy instead of evenly closed.
Pump Calibration Procedure
Run calibration when the raw materials are at production temperature. Cold MDI and warm polyol don’t meter the same way, even if both tanks look full and the HMI says “ready.” Viscosity changes the pump load, and pump load changes real output.
- Circulate A-side and B-side until tank temperature, return temperature, and hose temperature are stable.
- Zero the scale with a clean, dry collection bucket.
- Run separate timed shots for A-side and B-side, usually 30 or 60 seconds.
- Weigh each shot immediately and convert it to kg/min.
- Repeat at low, normal, and high production pump speeds.
- Adjust the pump coefficient, encoder pulse value, or inverter setting according to the foamer manual.
- Run a mixed shot and check cream time, gel time, tack-free time, and cell structure.
- Produce short trial panels, then cut samples after cure for density and adhesion checks.
On a custom PU sandwich panel production line, we prefer weighed calibration over trusting the flowmeter alone during commissioning. Flowmeters are useful for trend watching. A scale tells you what the pump actually delivered.
Keep the calibration bucket clean. A small amount of cured foam stuck inside the bucket can add 50-100 g, which looks small until the operator uses that number to correct the whole pump curve. Also, don’t calibrate during foamer purging. Wait until recirculation is steady and the pressure trace has stopped jumping.
For plants that switch between foam core and mineral wool products, a PU and rockwool panel production line needs recipe separation in the HMI. Mixing a rockwool belt speed setup with a PU foaming recipe is a simple way to create a very expensive trial run.
Dosing Drift Defects
A bad panel tells you where to look, but don’t read one defect as one cause. Low density can come from under-output, late pour start, poor side sealing, or raw material temperature drift. Cut the panel first. Guess later.
| Panel symptom | Likely dosing issue | First check | Fast correction |
|---|---|---|---|
| Edge voids | Total output too low or pour width too narrow | Density near both side blocks | Raise output or adjust traverse |
| Foam overflow | Output too high for line speed | Side leakage and belt pressure | Reduce kg/min or raise line speed |
| Brittle core | Isocyanate side too high | A/B weighed shot | Restore recipe ratio |
| Soft core | Polyol side too high or low reaction heat | Gel time and density | Check B-side flow and temperature |
| Skin separation | Low foam contact pressure or bad timing | Cut peel area | Check output, sheet preheat, belt gap |
Delamination deserves special attention because it often looks like an adhesive problem. If the foam doesn’t rise into full contact with the steel skin before the panel enters the pressure zone, the skin may release later during cutting, stacking, or transport. The same process checks used for PU sandwich panel delamination apply here: inspect the cut face, check skin temperature, verify belt gap, and confirm the foam fill pattern.
A practical field test: cut a 300 mm section from the panel start, middle, and end. If the start section has voids and the middle is good, the issue is usually pour timing or acceleration. If all three sections are light, recalculate output. If density is fine but adhesion is poor, look at sheet surface, preheating, and contamination.
Records, Safety, And Timing
Keep one calibration sheet per recipe. It should show raw material batch numbers, tank temperatures, A/B ratio, pump speed, actual kg/min, line speed, panel thickness, density result, and operator name. Simple paper records work. A blurred phone photo of the HMI doesn’t.
A good schedule for most PU/PIR plants:
- Daily: one quick weighed output check before stable production.
- Weekly: full low-normal-high pump curve check.
- After maintenance: recalibrate after pump seal, filter, hose, flowmeter, or mixing head work.
- After material change: recalibrate when changing MDI supplier, polyol batch, blowing agent system, or PIR/PU recipe.
- Seasonal shift: verify when workshop temperature changes by more than about 5 C.
Safety belongs in the calibration routine, not in a poster near the door. MDI exposure can irritate eyes and the respiratory system; the NIOSH Pocket Guide for methylene bisphenyl isocyanate lists exposure routes, symptoms, and protection data for MDI. Use closed handling where possible, keep ventilation running, and don’t let operators lean over open shot buckets.
One more plant-floor rule: never “fix” a calibration problem by secretly changing the recipe ratio to make today’s panels look acceptable. That hides the fault from the next shift. Correct the pump output, record the change, and run a short panel before returning to saleable production.
FAQ
How often should dosing be calibrated?
Check dosing daily with a quick weighed shot, then run a full pump curve weekly. Recalibrate immediately after pump maintenance, raw material changes, recipe changes, or clear temperature shifts in the workshop.
What causes PIR density drift?
PIR density drift usually comes from temperature change, pump wear, wrong line speed, blocked filters, or unstable blowing agent content. Start with weighed A/B output before adjusting chemistry.
Can dosing cause panel delamination?
Yes. Low output, late pour timing, or wrong A/B ratio can reduce foam contact pressure against the steel skin, which can lead to panel delamination after cutting, stacking, or installation.
Which tests confirm foam calibration?
Use weighed A/B shots, total kg/min calculation, core density samples, cut-face inspection, and adhesion checks. For export orders, record the method, sample size, operator, date, and raw material batch.
If your PU/PIR panel line needs commissioning support, recipe change checks, or dosing fault diagnosis, YZ Welding can help review the foaming machine settings, double-belt timing, output calculation, and acceptance test process before small dosing errors turn into rejected panels.
