Control from the source to improve product consistency and stability
The thermal insulation performance of refrigerator doors depends largely on the density and uniformity of the foam layer. However, in the actual production process, problems such as inconsistent door foaming density, insufficient local foaming, and deformation are common, which seriously affects product quality and corporate reputation.
The reason is that the problem is often not a single one, but the result of multiple links such as foaming formula, environmental conditions, equipment status, mold design and even operating process. This article will deeply analyze the main factors causing uneven foaming density and provide targeted solutions.
1. Improper foaming formula ratio
The basic chemical reaction of polyurethane foaming comes from the ratio reaction of isocyanate (black material) and polyol (white material).
- If the proportion of isocyanate is too high , the foaming reaction will be abnormally violent, generating too much heat, causing local overheating of the door body and even bulging and deformation.
- The reasonable ratio is generally controlled within the range of 1.05 to 1.15 . Deviating from this ratio range will affect the foam structure and density distribution.
Recommendation : Calibrate the metering pump regularly to keep the raw material metering system accurate and stable.
2. Ambient temperature affects foaming reaction
PU foaming reaction is extremely sensitive to temperature.
- If the ambient temperature is too high (>30°C) , the volatilization of the foaming agent will be accelerated, resulting in rapid expansion of the foam and unstable structure.
- the temperature is too low (<5°C) , the reaction rate will be too slow and the foam will not develop well, resulting in local insufficient foaming or low density.
Recommendation : Maintain a constant temperature in the foaming workshop (recommended 18℃～25℃) to avoid large temperature differences.
3. Mold structure and precision issues
The mold is the direct container for foam molding. An unreasonable structure or insufficient precision will seriously affect the foaming effect:
- If the mold size deviation exceeds ±0.1mm , it will affect the flow path of the PU material and cause incomplete filling;
- A rough or defective mold surface may also cause foam to stick to the wall, hinder flow, and affect foaming uniformity.
Recommendation : Regularly inspect and maintain the mold to keep the inner cavity clean and smooth.
4. The pressure of foaming equipment is unstable
During the foaming process, the raw material delivery pressure determines whether its distribution in the door body is uniform:
- If the pressure fluctuation exceeds ±0.05MPa , it may lead to insufficient raw material injection in some areas or large differences in filling speed, resulting in uneven cell density and uneven structure.
Recommendation : Check the status of the booster pump, solenoid valve and mixing head to ensure stable system pressure output.
5. Improper cooling speed control
After curing, PU foam needs to be gradually cooled to room temperature to stabilize the structure.
- If the cooling speed is too fast , there will be a large temperature difference between the mold surface and the interior, resulting in internal stress concentration , which can easily cause local deformation or cracks.
- If the cooling is too slow , the cycle will be prolonged and may also cause cell collapse and structural instability.
Recommendation : Use air cooling + time control to balance efficiency and stress release.
6. Unstable quality of raw materials
Poor quality raw materials have a great impact on reaction stability:
- If the foaming agent does not meet the purity standards or contains impurities , side reactions are likely to occur during the reaction, which will seriously damage the pore structure and affect the final density.
- Large differences in raw material batches may also cause fluctuations in foam density within each batch.
Recommendation : Choose reliable suppliers and strictly implement the raw material inspection system.
7. Improper assembly process
During the assembly of the door assembly, if the foam shell is not properly positioned and the corners are not compacted, local foaming space changes will occur:
- Inconsistent cavity thickness will directly affect the distribution and expansion space of the PU material, thus forming density differences.
Suggestion : Optimize the fixture and assembly line operation process to ensure assembly consistency .
Conclusion
The uneven density of refrigerator door foaming is a systematic problem. Solving it requires simultaneous intervention from multiple dimensions, including raw materials, equipment, molds, environment, and process . Only by establishing a complete set of quality control systems can we ensure that the foaming of each refrigerator door is dense, stable, and does not deform, thereby improving the thermal insulation performance and market competitiveness of the entire machine .
If you are optimizing the door foaming process or looking for more reliable foaming equipment and raw material solutions, please feel free to contact us. We will provide you with professional support and one-stop service.