Rubber
Compounding
Wayne Rubber supplies custom unvulcanized rubber compound across all major thermoset elastomer families through an established network of compounding partners. Whether the compound is destined for molding at our Wixom, MI facility or supplied to a downstream manufacturer for their own processing, we coordinate compound development, specification, and supply as a single point of contact.
What Rubber Compounding Is and Why It Matters
Rubber compounding is the process of combining a raw polymer base with a precisely formulated set of additives to produce an unvulcanized compound ready for molding, extrusion, or calendering. The raw polymer alone, whether natural rubber, EPDM, nitrile, or FKM, has limited useful properties. It is the compounding step that builds in the hardness, oil resistance, heat aging performance, compression set characteristics, and regulatory compliance of the final molded part.
A compounded rubber formulation typically contains five to fifteen distinct ingredients, each serving a specific function. The ratio, type, and interaction of these ingredients determines every physical property that appears on the final compound test report and, ultimately, whether the molded part performs to specification in the application.
For OEM manufacturers who receive compound as a raw material input for their own molding operations, the compound specification is as critical as the part drawing. Two compounds described identically as “70 Shore A nitrile” can have fundamentally different compression set behavior, heat aging performance, and oil swell resistance depending on their formulation. Specifying compound by ASTM D2000 line callout rather than by generic material description is the standard method for controlling compound quality across supply chain changes.
Wayne Rubber coordinates compound specification, development, and supply through our compounding partner network. Customers receive a single point of contact for compound procurement regardless of which compounding facility produces the material.
Anatomy of a Rubber Compound
| Ingredient category | Function | Examples | Effect on properties |
|---|---|---|---|
| Polymer base | The elastomeric backbone that defines the fundamental chemical and physical character of the compound | NBR, EPDM, FKM, silicone, neoprene, natural rubber, HNBR | Determines base oil resistance, temperature range, ozone resistance, and compatibility with curatives |
| Cure system | Initiates vulcanization by forming crosslinks between polymer chains during the molding cycle | Sulfur/accelerator systems, peroxide systems, bisphenol AF/onium salt (FKM), platinum catalyst (silicone) | Cure rate, crosslink density, compression set, heat aging resistance, and extractables level all depend on cure system choice |
| Reinforcing fillers | Improve mechanical properties beyond the base polymer’s capability | Carbon black (N330, N550, N660), silica, calcium silicate | Tensile strength, tear resistance, abrasion resistance, hardness. Carbon black type and loading level are the primary hardness control lever. |
| Plasticizers and process oils | Reduce compound viscosity for processing; soften the cured compound; extend lower durometer range | Naphthenic process oils, paraffinic oils, ester plasticizers (for FKM), DOA for low-temperature | Lower durometer, improved low-temperature flexibility, reduced viscosity for injection and transfer molding |
| Antidegradants | Protect the cured compound from ozone, oxygen, heat, and flex cracking during service | Antiozonants (IPPD, 6PPD), antioxidants (TMQ), waxes | Ozone cracking resistance, heat aging performance, outdoor weathering life. Critical for NBR in any outdoor or UV-exposed application. |
| Processing aids | Improve compound processability in the mixer and at the press | Stearic acid, zinc oxide, fatty acid esters, tackifiers | Mold release, surface finish, scorch safety, flow in transfer and injection molding |
| Special-purpose additives | Impart specific functional properties required by the application or regulation | Flame retardants, FDA whitelist ingredients, metal-detectable barium sulfate, conductive carbon, blowing agents for sponge | Flame resistance (UL 94), food-contact compliance (FDA 21 CFR 177.2600), X-ray detectability, electrical conductivity, closed-cell foam structure |
How Rubber Compounds Are Mixed
Rubber mixing is a high-shear mechanical dispersion process. The goal is to achieve thorough, homogeneous distribution of all compound ingredients throughout the polymer matrix, within tight temperature limits that prevent premature vulcanization (scorch) during mixing.
Intermeshing vs. Tangential Internal Mixers
The two dominant internal mixer types in rubber compounding are the tangential (Banbury-type) mixer and the intermeshing rotor mixer. Tangential mixers use counter-rotating rotors that do not mesh, generating higher rotor tip speeds and greater distributive mixing at the cost of some dispersive mixing efficiency. Intermeshing mixers use rotors that mesh as they rotate, producing higher dispersive shear and better temperature control, at the cost of lower throughput per cycle.
For most commodity compounds (NBR, EPDM, neoprene in standard grades), tangential mixing is the industry standard. For high-performance compounds where filler dispersion quality directly affects physical properties (HNBR at high carbon black loading, silica-filled compounds, specialty compounds with difficult-to-disperse fillers), intermeshing mixers produce more consistent dispersion. Wayne Rubber’s compounding partners use both mixer types, and compound specifications are matched to the most appropriate mixing process.
Available Thermoset Elastomers
Wayne Rubber supplies compounded, unvulcanized stock in all major thermoset elastomer families. Compounds are available in standard and custom durometers, specialty cure systems, regulatory-grade formulations, and application-specific variants. Each polymer family has distinct property strengths that determine its appropriate application environment.
The standard elastomer for outdoor, water, and steam service. EPDM’s fully saturated ethylene-propylene backbone resists ozone, UV, oxidation, and steam with no antidegradant requirement. Available in peroxide-cured grades for better compression set, sulfur-cured for standard applications, and FDA-grade for food and pharmaceutical use. Key compounds: 40-90 Shore A; peroxide and sulfur cure; ASTM D2000 BA/CA type; FDA 21 CFR 177.2600 grades; EPDM/PP thermoplastic vulcanizate (TPV).
EPDM Material Data →The standard oil-service elastomer. ACN content (18-50%) is the key formulation variable, with higher ACN providing better oil resistance and lower ACN extending low-temperature flexibility. Commercial-grade 70/30 NBR/SBR blends are widely available for non-critical oil service; premium 100% NBR is specified for demanding hydraulic and fuel system sealing. Key compounds: 40-90 Shore A; ASTM D2000 BG/CH type; FDA white NBR for food and meat processing; low-ACN grades for arctic temperature service.
NBR Material Data →The widest continuous service temperature range of any standard elastomer: -75°F to +450°F. Peroxide-cured for standard industrial applications; platinum-cured for lowest extractables in food, pharmaceutical, and medical applications. Available in FDA 21 CFR 177.2600, USP Class VI, AMS-qualified, metal-detectable, and LSR (liquid silicone rubber) grades. Key compounds: 20-80 Shore A; HCR and LSR; red/orange, white, blue, black, and custom colors; 3-A Sanitary Standard compliant grades.
Silicone Material Data →The highest-performance standard elastomer for combined chemical resistance and elevated temperature service. Continuous service to +400°F with resistance to petroleum oils, fuels, hydraulic fluids, acids, and most solvents. Available in Type A (diamine-cured), Type B (bisphenol-cured), and Type F (GF-type, highest fluorine content) grades, each with distinct chemical resistance profiles. Post-curing is required for all FKM compounds to complete the crosslink network. Key compounds: 60-90 Shore A; ASTM D2000 HK type; AMS-qualified grades for aerospace.
FKM Material Data →Hydrogenation saturates the butadiene double bonds in NBR’s backbone, eliminating the thermal degradation mechanism that limits standard nitrile above 250°F. HNBR maintains NBR’s oil and fuel resistance while extending service to 300°F with stable compression set and excellent ozone resistance. The correct upgrade from standard NBR for hot-oil applications in automotive powertrain, industrial hydraulics, and oil and gas equipment. Available in partially and fully hydrogenated grades with varying ACN content. Key compounds: 50-90 Shore A; ASTM D2000 CH/EE type.
HNBR Material Data →Neoprene’s chlorine-modified backbone provides an unusual combination: moderate petroleum oil resistance alongside genuine ozone and UV resistance that NBR cannot provide. Additionally, the chlorine content gives neoprene inherent self-extinguishing behavior (flame resistance) without added flame retardant. Commercial-grade CR/SBR blends for standard environmental sealing; premium 100% chloroprene for marine, refrigeration, and automotive weatherstrip applications. Key compounds: 40-80 Shore A; ASTM D2000 BC/BE/BF type; UL 94 V-2 rated grades available.
Neoprene Material Data →Natural rubber provides the highest tensile strength and tear resistance of any standard elastomer, along with outstanding resilience (elastic energy return) and low heat build-up under dynamic flexing. These properties make it the preferred compound for vibration isolation mounts, heavy-duty bridge and building bearings, conveyor belt components, and any application where mechanical toughness and fatigue resistance are primary requirements. Not suitable for outdoor UV, ozone, or oil service without protective coating or blending. Key compounds: 30-80 Shore A; sulfur-cured; SMR and TSR grades; SMR L and SMR CV for low-variability applications.
Natural Rubber Material Data →The most widely produced synthetic rubber globally, primarily used as a cost-effective replacement for natural rubber in applications where NR’s mechanical properties are not fully required. SBR has better ozone and aging resistance than natural rubber but lower tensile strength and resilience. Widely used in general-purpose industrial applications, conveyor components, flooring, and as a blend partner with NBR and CR to reduce compound cost. Key compounds: 40-80 Shore A; sulfur and peroxide cure; emulsion (E-SBR) and solution (S-SBR) polymerization grades.
SBR Material Data →The highest-performance elastomer available: continuous service to +600°F with essentially universal chemical resistance including resistance to concentrated acids, aggressive solvents, and reactive plasma environments. Used in semiconductor process equipment, pharmaceutical manufacturing, and the most demanding aerospace and chemical processing sealing applications. Significantly higher cost than FKM. Available in standard and low-temperature grades. Key compounds: 70-90 Shore A; ASTM D2000 KK type; USP Class VI and FDA grades available.
FFKM Material Data →Fluorosilicone combines silicone’s wide temperature range with resistance to fuels, oils, and solvents that standard silicone cannot resist. The trifluoropropyl side groups on the polymer backbone provide the fluid resistance while the siloxane backbone preserves the wide temperature performance from -85°F to +400°F. The standard aerospace fuel system elastomer where both temperature and fuel resistance are required simultaneously. Key compounds: 40-80 Shore A; AMS-qualified grades; MIL-R-25988 compliant formulations available.
Fluorosilicone Material Data →AEM (sold as Vamac by DuPont) was developed specifically for automotive underhood sealing applications where combined resistance to hot air, hot oil, and automotive fluids at temperatures above NBR’s service range is required. Continuous service to +175°C (347°F) with excellent resistance to oxidation and automotive lubricants. Better low-temperature flexibility than FKM at equivalent temperature rating. Standard material for automotive transmission seals, power steering seals, and hose in high-temperature underhood locations. Key compounds: 50-80 Shore A; ASTM D2000 EF type.
AEM Material Data →Polyurethane offers the highest abrasion resistance and load-bearing capacity of any rubber material, along with excellent tensile strength and resistance to many oils and fuels. Used in hydraulic cylinder rod wiper seals and piston seals where abrasion and extrusion resistance under high pressure are the dominant requirements. Not suitable for high-temperature service (above 200°F in wet environments) or hot water and steam. Cast and millable polyurethane grades available. Key compounds: 60-98 Shore A; AS568 and custom cross-sections; ASTM D2000 BG type at 70 Shore A.
Urethane Material Data →Standard, Specialty, and Regulatory-Grade Compounds
Within each polymer family, compounds are available in multiple grades differentiated by formulation objectives and compliance requirements. Wayne Rubber can specify and source the appropriate grade for the application through our compounding partner network.
General-purpose compounds for non-regulated industrial applications. Formulated to meet ASTM D2000 type/class designations at competitive cost. Available from stock or short-lead custom batch from compounder inventory.
All ingredients on FDA whitelist for repeated food-contact service. Available in EPDM, NBR, silicone, neoprene, and FKM. White and blue colorants for visual inspection programs. Platinum-cured silicone grades for lowest extractables.
Third-party biocompatibility tested per USP biological tests for plastics. Required for pharmaceutical, bioprocess, and medical device applications. Available in platinum-cured silicone and selected EPDM and FKM grades. Lot-specific test reports available.
Certified to MIL-R-6855, MIL-R-25988, and AMS aerospace material specifications. Full material traceability, first article inspection reports, and certificate of conformance documentation. Available in NBR, silicone, FKM, and fluorosilicone.
Barium sulfate-loaded compounds visible to inline X-ray and metal detection systems. Blue or custom colors for visual identification. Required by HACCP for direct food-contact gaskets and seals on lines with inline detection as a critical control point.
Peroxide-cured formulations optimized for minimum compression set in long-life static sealing applications. Specifically formulated for applications where the gasket or seal must maintain contact force over years of service without replacement. Available in most polymer families.
Industries and Applications Served
- Transmission and differential seals (HNBR, FKM)
- Engine gaskets and cover seals (NBR, HNBR)
- Underhood hose and tubing compounds (AEM, EPDM, FKM)
- Weatherstrip and body seal compounds (EPDM, neoprene)
- Fuel system O-rings and diaphragms (FKM, fluorosilicone)
- Vibration isolation mounts (natural rubber, SBR)
- Cylinder rod and piston seal compounds (NBR, HNBR, polyurethane)
- Hydraulic valve and manifold gaskets (NBR premium grade)
- Hydraulic hose inner tube compounds (NBR, EPDM)
- Pump housing gaskets and diaphragms (NBR, EPDM)
- High-pressure backup ring compounds (polyurethane, PTFE-filled EPDM)
- Hot-oil circuit seals above 250°F (HNBR, FKM)
- Tri-clamp and sanitary fitting gaskets (EPDM, platinum silicone)
- CIP/SIP-exposed gaskets (platinum-cured silicone, EPDM)
- Meat and poultry processing seals (FDA white NBR, neoprene)
- Beverage filling and valve diaphragms (EPDM, silicone)
- Metal-detectable gaskets for inline detection lines (blue EPDM, blue silicone)
- Cooking and baking equipment gaskets (platinum silicone)
- Bioreactor and fermentation vessel gaskets (USP Class VI silicone)
- Pharmaceutical process equipment diaphragms (platinum silicone)
- Autoclave door and lid seal compounds (platinum silicone)
- Drug delivery device seals and stoppers (USP Class VI EPDM)
- Cleanroom equipment enclosure gaskets (platinum silicone, FFKM)
- Analytical instrument seals (FFKM for solvent resistance)
- Fuel system seals and diaphragms (fluorosilicone, FKM)
- Environmental and avionics enclosure gaskets (silicone, neoprene)
- Aircraft hydraulic system seals (FKM, HNBR)
- Military vehicle powertrain seals (MIL-R-6855 NBR, FKM)
- Altitude-service instrument seals to -85°F (fluorosilicone)
- Structural vibration isolation mounts (natural rubber, neoprene)
- HVAC equipment gaskets and duct seals (EPDM, neoprene)
- Outdoor electrical enclosure gaskets (EPDM, silicone sponge)
- Expansion joint and curtain wall seals (neoprene, EPDM)
- Conveyor belt cover and skirt compounds (SBR, natural rubber)
- Industrial vibration isolation pads (natural rubber, SBR)
- Chemical process equipment gaskets (FKM, FFKM)
Also at Wayne Rubber
Request a Rubber Compound Quote
Provide the polymer family, ASTM D2000 designation or application requirements, durometer, required grade, and quantity. Wayne Rubber will source the compound through our partner network and quote supply for your program.