If the manufactured PU cushion has quality problems such as uneven surface and bubbles, it may be caused by the following reasons:
1. Material problem
PU material dehydration is not thorough: If the PU material is not thoroughly dehydrated during the manufacturing process, it may contain residual water, which will form bubbles during the foaming process, resulting in an uneven surface of the cushion.
Formula design problem: During formula design, if the isocyanate is too free, or if no catalyst is added and the isocyanate is too free, it may also cause bubbles.
2. Process problem
Water is mixed during stirring: When preparing PU material, if water is accidentally stirred into the stirring process, the water will also form bubbles during the foaming process.
Unreasonable mold design: If the smoothness of the mold and the mold texture are unreasonable, bubbles and material pinholes may be caused. Generally, the vertical depth of the mold pattern should not exceed 1mm to avoid the generation of bubbles.
Insufficient filling rate: The filling rate refers to the ratio of the finished product density to the free foaming density. If the filling rate is insufficient, pinholes and bubbles may also be generated. The optimal filling rate should be greater than 200%.
Too fast reaction rate: During the PU foaming process, if the reaction rate is too fast, the gas may not be discharged in time, thus forming bubbles.
Too high mold temperature: Too high mold temperature may cause the PU material to solidify prematurely during the foaming process, making it impossible for the gas to escape, thus forming bubbles.