Nitrile Gaskets

Nitrile rubber’s oil resistance comes from its acrylonitrile (ACN) content, a polar monomer that resists swelling in nonpolar petroleum fluids. Standard gasket compounds run approximately 33% ACN, which balances oil resistance against low-temperature flexibility. Higher ACN content (40-50%) improves resistance to aromatic fuels and aggressive oils at the cost of cold flexibility; lower ACN content (18-28%) extends low-temperature service to -65°F for cold-climate hydraulic and fuel systems.

For static gasket applications, NBR’s compression set resistance is a critical property. A gasket under sustained bolt load must maintain sealing contact force over years of service. NBR’s compression set performance at 70°F is excellent; it remains acceptable at 200°F for most hydraulic and oil service. Above 250°F, NBR’s polysulfidic crosslinks begin to degrade and compression set rises steeply. For hot oil service above 250°F — high-output diesel engines, process equipment with hot hydraulic circuits, refinery flanges — HNBR is the correct specification, not a higher grade of standard NBR.

NBR gaskets resist a broad range of fluids: mineral oils, petroleum hydraulic fluids, most fuels, animal and vegetable fats, water, and dilute acids and bases. Its primary limitations are ozone and UV degradation in outdoor exposure — NBR gaskets in outdoor equipment enclosures will crack within months of direct sunlight exposure without a protective jacket — and poor resistance to polar solvents (ketones, esters, acetone), concentrated acids, and steam.

The grade question is frequently overlooked. Most gasket distributors offer “commercial grade nitrile” as their standard product. Commercial grade is a 70% NBR / 30% SBR blend — it reduces material cost but also reduces oil resistance and physical properties compared to 100% NBR premium grade. For demanding hydraulic and fuel system gaskets in industrial and automotive applications, premium 100% NBR is the correct specification. Wayne Rubber supplies both grades and can recommend the right one based on the specific fluid contact and service conditions.

Die-cutting from sheet stock is the standard method for flat gaskets of simple profile — a flat ring, a rectangular frame, or a simple flange profile. It is fast, requires no tooling for the gasket profile itself (only a cutting die or digital knife path), and is economical for low-to-medium volumes. Nearly all gasket distributors and fabricators work exclusively by die-cutting from roll stock. Die-cut nitrile gaskets are correct for most standard flange, cover, and panel gasket applications.

The limits of die-cutting: wall thickness below about 3/32″ becomes difficult to handle and install without tearing; complex profiles with internal features, multiple material zones, or three-dimensional geometry cannot be produced from flat sheet; and dimensional consistency across large production lots is limited by sheet thickness variation (typically ±10-15% on commercial sheet stock).

Compression or injection molded nitrile gaskets are required when the gasket profile cannot be produced by cutting from flat sheet. Molded gaskets with sealing beads, lips, integrated o-ring profiles, variable cross-section, or non-flat geometry require a mold cavity that defines the full three-dimensional profile of the part. Molded gaskets also offer tighter dimensional tolerances than die-cut parts — typically RMA Class A2 precision vs. ±0.015″ for die-cutting — which matters when the gasket must reliably locate within a close-tolerance housing.

For high-volume programs where consistent lot-to-lot dimensional repeatability is required, molded nitrile gaskets amortize tooling cost rapidly and provide better quality control than die-cutting from sheet whose thickness varies batch to batch. Wayne Rubber can quote both methods and recommend the most cost-effective approach for the specific profile, volume, and tolerance requirement.