What is the polyurethane molding foaming process like?

Process flow:

1.Raw material inspection: Check hydroxyl value, moisture content, solid content, NCO content, and other material properties.

2.Ingredient preparation: Mix polyether polyol blends according to the formula.

3.Pouring: Feed materials into the mold following a set trajectory, flow rate, and pouring time. Control the temperature of raw materials and mold, as well as the pouring pressure.

4.Molding: The two raw materials react at a certain temperature to form foam (curing).

5.Demolding: Greatly affected by the release agent.

6.Cell opening: After demolding, the foam needs to be punctured to break the foam cells; otherwise, shrinkage may occur.

7.Post-curing: The foam is not fully reacted upon demolding and must undergo post-curing, which takes around 6 hours.

Process flow diagram (from formulation to pouring)

Process control:

 -Pressure:

The purpose of pressure cycling is to balance the system.

High-pressure cycle pressure = pouring pressure (Europe); high-pressure cycle pressure ≥ pouring pressure (current).

Unbalanced pressure can lead to: pouring weight fluctuations, overshoot, poor mixing, incorrect POL/ISO ratio, inconsistent mixing, and material crossover.

 -Raw material temperature:

Among all process parameters, stable temperature is the top priority. Fluctuations cause variations in other system parameters.

For example: temperature changes lead to changes in material viscosity, causing poor mixing and product defects.

Target material temperatures:

      --POL: 25 °C, with ±1 °C fluctuation

      --ISO: ±5 °C fluctuation

 -Foaming density:

Too high increases cost; too low leads to poor appearance and inadequate physical properties.

 -Pouring trajectory:

Mainly affects product appearance and can influence hardness in some cases.

 -Precise metering:

Ensures uniform formulation ratios and consistent product firmness.

 -Effective mixing:

Affects foam appearance and performance (e.g., dark cells).

 -Formulations:

Currently, the main systems used are TDI/MDI systems.

      --MDI system: density range 52–60 g/cm³

      --TDI system: density range 35–45 g/cm³