Vertical Process Foaming Technology

The vertical process for the continuous production of PU flexible foam is a patented technology developed by Hymon International Ltd. in the UK during the 1980s. Its rapid adoption and development within the polyurethane industry are attributed to its notable advantages:

Features of the Vertical Process:

①　Reduced Space Requirements: The required area is significantly reduced to 600 m².

②　Lower Material Flow Rates: Total material flow is reduced to 20–40 kg/min.

③　Versatile Foam Production: The same equipment can produce both cylindrical and rectangular foam blocks by simply replacing specific components.

④　Efficient Material Usage: Foam blocks have consistent dimensions, and trimming waste is reduced to 4%–6%.

⑤　Uniform Physical Properties: The physical properties are evenly distributed across the same cross-section of the foam block.

⑥　Minimized Start/Stop Losses: Defective foam lengths are limited to around 1 m.

⑦　Suitable for Medium-Scale Production: Ideal for factories with annual production capacities of 500–4,000 tons, with low investment costs and reduced labor requirements.

Process Overview:

The vertical process comprises the following steps: raw material storage, measurement, mixing, input, foaming, curing, foam lifting, cutting, and foam transport.

Detailed Operation:

• Material Preparation and Foaming:

Various raw materials are measured using metering pumps and mixed in a mixing head before being delivered to the foaming tray to begin the foaming process. Foaming occurs inside a polyethylene bag, expanding horizontally as the cross-sectional area increases. The foam cells’ long axes align horizontally.

Within the foaming chamber, density decreases from bottom to top, creating a gradient due to gravity. The gravitational effect prevents intermixing between material layers, ensuring uniform physical properties across the same cross-section.

• Curing:

The foam enters the curing section, equipped with a heating cylinder surrounded by insulation. Pre-heating the cylinder to approximately 65°C accelerates foam curing. During continuous operation, the heat from the foaming process maintains this temperature.

• Foam Lifting:

A slat conveyor with small pins (approximately 1.5 cm long) pierces the foam's outer surface and elevates it continuously in a circular path formed by ten conveyor slats.

• Cutting and Transport:

Foam blocks are cut to predetermined lengths using a saw and then transported to the curing area.

Key Process Control Factors:

Maintaining the balance and stability of the formulation during the foaming process is crucial. Operators should closely monitor raw material temperature, curing temperature, environmental temperature, material flow rates, pressure, mixing factors (e.g., stirring speed, mixing head pressure, air injection volume), and catalyst dosage. Timely adjustments ensure high-quality foam production.

Common Operational Issues and Solutions:

①　Foam Tightening or Shrinkage:

• Cause: Excess tin catalyst, fast gelation, or excessive foam stabilizer leading to closed cells.
• Solution: Reduce tin catalyst or foam stabilizer dosage.

②  Foam Rupture:

• Cause: Incorrect formulation or metering pump errors; inadequate tin catalyst or foam stabilizer.
• Solution: Adjust formulation, check pump calibration, and inspect for contaminants or mechanical issues.

③  Foam Slipping:

• Cause: Conveyor pin failure, extended rise time, or insufficient curing.
• Solution: Adjust curing temperature, foam rise timing, or conveyor speed.

④  Compression Lines:

• Cause: Conveyor speed mismatch or uneven foam output.
• Solution: Adjust conveyor speed or foam flow rate to eliminate lines.

Common Foam Defects, Causes, and Remedies:

By systematically addressing chemical and mechanical factors, manufacturers can optimize vertical process operations and ensure consistent foam quality.