Processing data indicate that, under identical tooling and processing conditions, PA66 GF40 exhibits a mold wear rate 1.6–1.8 times higher than GF30, particularly in high-flow regions. Additionally, high glass fiber systems demand higher injection pressure and speed, further intensifying abrasive effects. Beyond mechanical abrasion, excessive reinforcement also accelerates thermal fatigue of molds. Reduced thermal uniformity causes larger temperature gradients per molding cycle, increasing micro-crack initiation risks, especially in standard H13 or P20 tool steels. Industrial experience shows that many failures originate not from insufficient material strength, but from over-reliance on high glass fiber content. In one connector application, increasing fiber content from GF35 to GF50 reduced mold life from an expected 800,000 cycles to less than 300,000 cycles, increasing hidden manufacturing costs by over 20%. Ultimately, glass fiber content selection is a balance between structural performance, processing stability, and manufacturing economics rather than a pursuit of maximum reinforcement.

In engineering plastic selection, glass fiber reinforced nylon is often equated with higher strength, lower deformation, and improved reliability. During early project stages, design teams frequently assume that increasing glass fiber content is a straightforward solution: if GF30 is insufficient, then GF40 or even higher grades are considered. However, real manufacturing experience increasingly shows that excessive reinforcement introduces underestimated systemic risks, particularly related to mold wear, processing instability, and long-term production cost escalation. In an automotive electronic housing project, PA66 GF30 was initially selected. Due to deformation risks under high-temperature vibration, the glass fiber content was increased to GF40. While flexural modulus improved by approximately 25% and thermal expansion was further reduced, severe mold wear appeared within six months of mass production. Gate and cavity surfaces degraded rapidly, leading to surface defects and premature mold refurbishment, ultimately delaying delivery schedules. From a material mechanics perspective, glass fiber does not provide linear benefits beyond certain thresholds. As fiber content exceeds 30–40%, fiber-to-fiber interaction increases significantly. During high-shear injection molding, insufficiently resin-coated fiber ends repeatedly contact mold steel surfaces, producing a micro-cutting wear mechanism. This wear accumulates progressively and concentrates in gates, runners, and thin-wall regions.

Moisture absorption is another factor that is frequently underestimated. Even in glass fiber reinforced or flame-retardant grades, PA66 retains a higher equilibrium moisture content than semi-aromatic polyamides. In electrical environments, absorbed moisture does more than cause dimensional change; under an electric field, it contributes to conductive path formation, accelerating the decline in volume resistivity. This explains why PA66 components may perform well in dry-state testing but approach critical limits after hydrothermal aging. PPA behaves differently due to its semi-aromatic molecular structure. The introduction of aromatic rings restricts chain mobility and stabilizes the polymer network at elevated temperatures. As a result, PPA generally exhibits more stable electrical properties during long-term thermal exposure. Its lower moisture absorption further slows performance degradation in humid conditions. Engineering test data reflects this trend. After 1000 hours of aging at 150°C, glass fiber reinforced PA66 often shows a pronounced drop in volume resistivity, sometimes exceeding one order of magnitude. Under comparable reinforcement conditions, PPA compounds typically exhibit more moderate and controllable degradation. Similar tendencies can be observed in CTI performance. This does not imply that PA66 is unsuitable for high-temperature electrical applications. The challenge lies in correctly defining its application limits. When long-term thermal exposure, electrical stress, and high reliability requirements coexist, the safety margin of PA66 becomes narrower. The advantage of PPA lies not in peak performance values, but in its stability over the entire service life.