Views: 0 Author: Site Editor Publish Time: 2025-05-16 Origin: Site
A well‑engineered insulating washer or gasket is crucial for maintaining electrical isolation, preventing galvanic corrosion, and ensuring long‑term mechanical integrity in a wide range of industrial, electrical, and automotive applications. This guide explores three leading materials—epoxy‑fiberglass (G‑10/G‑11/FR‑4), phenolic laminate, and polyester (PET)—detailing their composition, key performance metrics, processing methods, and optimal use cases.
Epoxy‑fiberglass laminates are manufactured by impregnating woven E‑glass fabric with high‑performance epoxy resin under heat and pressure to produce rigid, high‑strength sheets.
G‑10 (and its flame‑retardant variant FR‑4) consists of alternating layers of woven glass cloth and epoxy resin cured to form a dense composite.
Typical density is ~1.85–1.90 g/cm³, with cured sheets exhibiting minimal shrinkage (<1%) for tight thickness tolerances.
Dielectric strength: up to 450 V/mil (short‑term) and breakdown voltages >20 MV/m under standardized conditions.
Volume resistivity: ~1×10⁸ Ω·cm; surface resistivity: ~1×10⁸ Ω/sq, ensuring stable insulation in both dry and humid environments.
CTI (Comparative Tracking Index): ~175 V; arc resistance: ~120 sec, suitable for moderate‑voltage applications.
Flexural strength: up to 55 000 psi; compressive strength: ~65 000 psi, providing robust support under clamping loads.
Continuous operating temperature: up to 130–140 °C (Class B insulation), with UL94 V‑0 flame‑retardant ratings for FR‑4 grades.
Moisture absorption: <0.2%, minimizing changes in dielectric constant and preventing swelling under humid conditions.
Spacers, washers, and sleeves in electrical motors, transformers, and switchgear assemblies.
Insulating standoffs and support pads in PCB mounting and power electronics.
Flange isolation components to prevent galvanic currents between dissimilar metals.
Phenolic laminates are thermoset composites formed by bonding layers of paper, cotton fabric, or glass cloth with phenolic resin under heat and pressure.
Plain phenolic (paper‑reinforced): economical choice for low‑stress insulation.
Cotton‑fabric reinforced (Grade B‑12): higher mechanical strength and dimensional stability.
Neoprene‑faced phenolic: adds elastomeric sealing layers for fluid containment.
Dielectric strength: ~400–550 V/mil (short‑time) per ASTM D149, with oil‑immersed tests up to 500 V/mil for certain grades.
Compressive strength: ~25 000–50 000 psi depending on reinforcement; flexural strength: ~12 000–20 000 psi.
Water absorption: ~0.6–1.6% after 24 h immersion, controlled to maintain insulation resistance above 1×10⁶ MΩ.
Operating temperature: –59 °C to +149 °C for standard grades; neoprene‑faced type up to +100 °C continuous.
Resistant to oils, fuels, mild acids, and alkalis, making it suitable for automotive and pipeline environments.
Flange isolation kits for pipeline cathodic protection and electrolytic corrosion control.
Washer sets and sleeves in intake manifolds, valve covers, and fuel systems.
Bolt‑on insulating washers in power distribution and switchgear hardware.
Polyester (PET), commonly known by the trade name Mylar®, is a thermoplastic polyester film used for thin‑section washers and gaskets requiring excellent electrical characteristics and chemical stability.
Dielectric strength: 7 000 V/mil (AC) to 11 000 V/mil (DC); dielectric constant: 2.8–3.7; dissipation factor: 0.0002–0.016 depending on temperature.
Volume resistivity: >10⊃1;⁴ Ω·cm; corona resistance: one of the highest among film insulators, resisting short overvoltage surges.
Tensile strength: ~9 400 psi; flexural strength: ~11 600 psi; compressive strength: ~11 000 psi.
Operating temperature: –55 °C to +125 °C (long‑term); heat distortion ~120 °C; low moisture absorption (<0.1%) ensures dimensional stability.
Excellent abrasion resistance, UV and ozone stability for outdoor or cyclic environments.
Thin washers and gaskets in electronic assemblies, film capacitors, and coil insulation.
Sealing membranes in food, medical, and pharmaceutical equipment due to sterilizability.
Support and spacer washers in appliances, automotive sensors, and outdoor electrical enclosures.
By aligning material properties with the specific electrical, thermal, mechanical, and environmental requirements of your application, you can maximize performance, reliability, and service life of insulating washers and gaskets across industries.
