I. Incomplete Gas Removal (Core Cause): The high viscosity of the foaming mixture makes it prone to trapping air during agitation. Excessive mixing speeds or inadequate vacuum degassing prevent air bubbles from escaping in time. Rapid surface curing creates a smooth "skin" that traps internal air, resulting in a dense network of hidden internal voids upon final curing.
II. Imbalanced Formulation Ratios: Incorrect ratios of blowing agents to catalysts are common triggers. An excess of blowing agent causes continuous internal micro-foaming, leading to secondary expansion after the surface has set. Excessive catalyst accelerates surface curing-creating a hard exterior and a loose interior-which prevents bubbles from escaping and causes them to accumulate as dense voids.
III. Abnormal Temperature Rise During Curing: Large foam blocks have significant thickness and slow internal heat dissipation, leading to a stark temperature difference between the core and the surface during curing. Rapid internal temperature rise and heat concentration trigger localized, continuous foaming; since the surface has already set and cannot relieve pressure, dense, closed-cell voids form internally.
To resolve these internal void defects and ensure uniform foam texture, production processes should be optimized by refining agitation techniques, ensuring effective vacuum degassing, precisely adjusting the blowing agent-to-catalyst ratio, slowing the initial curing rate, and balancing curing temperatures to allow internal bubbles to escape properly.
