ADDITIVES | REINFORCEMENT
Envalior, General Motors and Schaeffler, received the 2025 SPE Innova- tion Award in the Powertrain category for a thin-wall actuator gear design made from Stanyl PA46
mm gear wall, reduced weight by 30% and space and cost by 20%. The design used 50 or 60% glass fibre reinforcement, followed by post-mould heat treatment. The fibre orientation is governed by the injec- tion moulding process, including the gate design, flow path, and mould geometry, explained Willian Barreto, Application Development Engineer at Envalior. “At 50–60 wt% glass fibre, viscosity is significantly increased, so a high-flow material such as Stanyl PA46 is required to achieve proper filling of thin-wall sections while still enabling a con- trolled and beneficial orientation profile,” said Barreto. He said that fibre orientation is primarily affected by flow-induced hydrodynamics and fibre–fibre interactions.
Sizing and heat He added that fibre sizing strengthens adhesion between the glass fibre and the polymer matrix, which enables load transfer and improves mechan- ical performance. The post-mould heat treatment (ie, annealing) adds further dimensional stability and performance by acting primarily on the polymer matrix, with indirect effects on the reinforced system.
“In semi-crystalline polymers such as PA46, heat
Right: Bearings for hydraulic cylinders require precise dimensional stability, says Hallite
treatment can further develop the crystalline structure and densify the amorphous phase, improving stiffness, thermal resistance, and wear performance,” said Barreto. “Injection moulding – especially in thin-wall, highly filled parts – intro- duces internal stresses due to orientation and differential shrink- age. Annealing helps relax these stresses, improving dimensional stabil-
16 COMPOUNDING WORLD | June 2026
ity. For precision components such as actuator gears, annealing can be used to stabilize geometry prior to use. This is particularly relevant when tight tolerances are required and dimensional changes during service must be minimized. The glass fibres themselves are not affected by the heat treatment. However, they influence how the polymer re- sponds, for example by acting as nucleation sites for crystallization and by reducing overall shrink- age. At high glass fibre contents, dimensional changes during annealing are typically lower than in unfilled materials.” Barreto added that similar benefits can often be achieved with higher mould surface temperatures to promote a “resin-rich surface” that better encapsulates fibres.
GF in bearings Hallite Seals, part of Michelin’s Advanced Sealing Technologies (AST), designs its own compounds for its seals and other components for the fluid power industry. The company has used its knowledge of reinforced thermoplastics to manufacture Type 565 precision bearings for hydraulic cylinders using an injection moulding process and a novel tool design that manages the material flow and the cooling profile to minimize dimensional instability, said Andrew Iddeson, Technology Director for AST. The bearing application requires precise dimensional stability, because the bearings provide alignment within the cylinder to reduce the potential for leaks. Compressive strength is also crucial. “These parts carry the load in the cylinder,
preventing metal-to-metal contact in cylinder parts, which leads to damage and consequently leakage,” said Iddeson. “Tensile properties are important to provide a small degree of flexibility, to allow assembly without brittle fracture.” The company identified material formulations and optimized the processing parameters and physical design of the tool to create precision parts. In polyamide and acetal-based compounds for bearings, short-glass fibre reinforcement helps improve dimensional stability, strength properties, and tribological properties, particularly wear-resist-
IMAGE: HALLITE
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IMAGE: SPE
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