What is the Key Process Parameters?
01. Raw Material Ratio
Accurate control of raw material ratios is essential for optimal foam performance and depends on refrigerator type and insulation requirements. Typically, the molar ratio of polyol to isocyanate ranges from 1:1 to 1:1.5. Blowing agent dosage is around 10%-20% of the polyol amount. Catalyst amounts are adjusted based on reaction speed and foam properties.
02. Foaming Temperature and Time
Foaming temperature is critical-too high or too low can degrade foam quality. An ideal range is 25°C–35°C. Foaming time must also be controlled to ensure complete expansion and curing. Too short a time results in insufficient strength; too long lowers productivity.
03. Mold Pressure
Pressure inside the mold affects foam density and cell distribution. Proper pressure ensures close contact with the mold, improving foam density and strength. Excessive pressure, however, may cause foam rupture or demolding issues. Typically, mold pressure is controlled between 0.1 MPa and 0.3 MPa.
04. Demolding Time
Demolding time refers to the interval from the end of foaming to the point when the refrigerator part can be removed. Shorter demolding time improves efficiency, but too early can compromise foam strength. Advanced techniques such as rapid demolding can reduce this time to 70 seconds or less without affecting quality.
What is the Performance Optimization?
01. Lowering Thermal Conductivity
Thermal conductivity can be further reduced through methods such as adding nanomaterials or using microcellular foaming technology. For example, incorporating nano-silica or nano-calcium carbonate into polyols improves thermal stability and reduces heat transfer. Microcellular technology allows smaller, more uniform foam cells, thus lowering thermal conductivity.
02. Enhancing Strength and Dimensional Stability
Selecting appropriate materials and process parameters can enhance foam strength and dimensional stability, preventing deformation or cracking due to temperature changes or mechanical vibration. Methods include increasing the polyol molecular weight, increasing isocyanate content, or using suitable cross-linking agents.
03. Improving Cell Structure
An optimized cell structure improves both insulation and mechanical performance. This can be achieved by adding surfactants, adjusting blowing agent types and amounts, etc., to control cell size, shape, and distribution, ensuring finer, more uniform, and higher closed-cell content.