Introduction
Hot press molding of sponge materials is widely used in automotive interiors, furniture, packaging, and sports equipment. However, two frequent production issues—edge cracking and surface burning—often compromise product quality, reduce yield, and increase costs. This article analyzes the root causes of these problems and presents practical, professional solutions to help manufacturers improve both quality and efficiency.
1. Edge Cracking: Identify and Relieve Stress Points
1.1 Root Causes
Edge cracking commonly occurs during demolding or cooling. Main causes include:
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Poor material ductility: Certain fabrics or composites become brittle after heating, especially at corners or stress points.
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Uneven pressure distribution: Mold misalignment or unbalanced pressing leads to localized stress concentrations.
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Improper timing of forming and cutting: Premature cutting before full shaping can cause the sponge to tear.
1.2 Optimization Solutions
✅ Material Optimization
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Use more ductile fabrics or add plasticizers such as TPU to increase flexibility;
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Adjust the foam formulation to reduce cross-linking density and brittleness.
✅ Process Adjustment
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Ensure the sponge is fully formed before activating the cutting function;
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Use a “low-high-low” pressure curve to avoid edge stress concentration.
✅ Mold Design Improvements
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Increase mold edge radii (recommended ≥ R1mm) to reduce sharp stress zones;
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Check mold parallelism to ensure even pressure distribution across the surface.
2. Color Change & Burning: The Importance of Thermal Control
2.1 Root Causes
Yellowing, blackening, or burning during hot pressing usually results from:
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Excessive temperature: Materials like PU sponge degrade above ~180°C;
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Overly long pressing time: Extended exposure to high heat causes oxidation or carbonization;
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Local overheating: Uneven heating plates or poor mold conductivity create hot spots.
2.2 Optimization Solutions
✅ Accurate Temperature Control
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Use a PID temperature control system to maintain plate temperature within ±3°C;
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Set safe temperature ranges per material type (e.g., PU: 150–180°C, EVA: 130–160°C);
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Shorten the heating time by optimizing curing parameters.
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✅ Material and Mold Enhancements
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Choose materials with higher thermal stability;
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Use molds with better thermal conductivity, such as aluminum or chrome-plated steel;
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Ensure heating plates are flat to avoid localized overheating.
Conclusion
Edge cracking and surface burning are common yet solvable challenges in sponge hot pressing. By optimizing materials, mold structure, and processing parameters, manufacturers can greatly improve product quality and consistency. With the development of intelligent temperature control and heat-resistant materials, the sponge hot forming process is moving toward higher precision and smarter production