How is Flexible Polyurethane Foam Produced?

Chemical Mechanism

The mechanism of polyurethane two-component liquid reaction molding can be represented by the following equations:

NCO + OH → NH-CO-O-  (Gelation, exothermic)  

NCO + H₂O → NH₂ + CO₂ (Foaming, endothermic)  

Tank Capacity and Motor/Pump Specifications

Foaming Process & Characteristics
Soft foam processes generally adopt a one-step method. First, polyol, water, catalyst, foam stabilizer, external foaming agent, etc. are premixed and enter the mixing chamber through one channel, while TDI enters through another channel. The component ratios are controlled by metering pump and flow measurement systems. The mixing head is a high-speed agitator; once the two components are mixed, the reaction begins immediately.

Foaming Stages

Cream time (5–10 sec): Operable period with fluidity.

Rise time (40–80 sec): Liquid solidifies into foam. Curing takes 3–6H at room temp (2H at 100°C).

Prepare materials according to production needs. PPG, POP, and TDI are stirred and temperature-controlled at 22 to 25°C. Powder, catalyst, and color paste are strictly prepared according to formula ratios and stirred appropriately before foaming (small materials stirred at 80 RPM for 1.5 hours). Stirring stops during foaming to avoid bubbles affecting foam quality.

Regularly test flow rate standards and adjust if necessary.

TDI, MC, water, air flow scales.

Adjust conveyor belt width (about 2.5 inches wider than standard).

Adjust base plate: first plate tilt 3 to 9 degrees; higher density requires larger tilt and lower plate; lower density requires smaller tilt and higher plate.

Edge raising adjustment: tilt and height.

Prepare edge film, raised edge film, release paper.

Fix the swinging head filter screen and adjust its width and frequency (16 times/min); large agitator speed 3000-4000 RPM, higher density means faster speed; small agitator 6000 RPM, lower density means lower speed.

Input standard frequencies, adjust TDI, MC, water display scales, and air flow scales to standard values.

Foaming process

Turn on component switches to circulate components back about 10 minutes.

Turn on automatic mode.

Turn on lighting, exhaust, heating system, swinging head.

Turn on silicone oil stirring for about 30 seconds until normal input.

Turn on mixing head stirring until stable at 4000-6000 RPM.

Open all valves to allow simultaneous component flow into the mixer for mixing.

Turn on foaming switch and conveyor belt.

Foaming begins; monitor TDI, MC, water, and air flow rates for normal operation.

Observe base plate status and adjust conveyor speed to avoid feeding issues and stabilize milky white stage.

Monitor foaming stages: milky white, initial foam, foaming, gelation, and adjust catalyst amount accordingly.

Turn off automatic mode, swinging head, large agitator, small agitator, and all material switches.

Turn on MC to clean mixing head and pipes.

Close TDI feeding valve, flush TDI pipeline with MC, retain MC inside the pipeline.

Power off.

Low-Density Foam Formulations (Reference)

Raw material usage calculation references:

PPG: affects density and softness = density * (water + MC/9) * 1.15 - powder amount

POP: affects density, rigidity, resilience, porosity (below 60%)

TDI: affects hardness = (8.68 + moisture * 9.67) * TDI index

Powder: affects density, tear strength ≤ 30% PPG

Water: affects density and hardness = PPG / density / 1.15 - MC / 9

MC: affects density, softness, size, and quantity of foam cells

Amine: mainly affects TDI and water reaction, 0.1-0.2% of PPG

Tin: mainly affects PPG (POP) and TDI reaction, 0.15-0.5% of PPG

Silicone oil: affects foam cell uniformity 1-2%

Usage = 1-2% PPG + 40% (moisture - 3.5) + MC * 0.06 + 1% powder

Air: affects foam cell nucleation (100-150 L/H)

Material Impact Summary

TDI: High index → cracking; low index → weak foam.

Water: Excess → stiffness; deficit → reduced catalysts.

Amine/Tin: Imbalance causes cracks or shrinkage.

Silicone: Affects cell uniformity (1–2% optimal).

Air: Nucleation control (100–150L/H).