Custom Rubber
Formulation
Standard catalog compounds solve most sealing and molding applications. Custom formulation is what Wayne Rubber brings to the programs where a standard compound does not meet the performance requirement, the regulatory specification, or the processing constraint. We work with engineers to translate application conditions into a compound specification, then source and qualify that formulation through our compounding partner network.
When a Catalog Compound Is Not Enough
Most rubber parts can be made from standard compounds available from any compounder’s catalog: a 70 Shore A NBR for a hydraulic gasket, a 60 Shore A EPDM for a water system seal, a 70 Shore A platinum-cured silicone for a food processing application. Catalog compounds are optimized for the most common applications and are available at short lead times in production quantities.
Custom formulation becomes necessary when the application falls outside the envelope a catalog compound was designed for. This happens more often than engineers expect because catalog compounds represent the center of each polymer family’s performance range. Applications at the edges of that range, or applications that require two properties to be simultaneously optimized that are typically in tension with each other, require a compound built specifically for the purpose.
The most common triggers for custom formulation work are: a temperature requirement at the edge of the polymer family’s rated range; a fluid compatibility requirement not covered by standard reference oils; a regulatory compliance requirement that standard grades do not satisfy; a compression set requirement tighter than standard peroxide-cured grades achieve; a processing requirement (viscosity, scorch safety, flow characteristics) that a standard compound cannot meet in the available tooling; or a failure investigation where the root cause is a formulation deficiency rather than a geometry or process issue.
Wayne Rubber approaches custom formulation as an application engineering conversation first. The goal is to characterize the service environment completely before specifying the compound, because incomplete service condition characterization is the most common reason a custom compound fails to solve the original problem.
Common Application Challenges That Drive Custom Formulation
Applications where the service temperature is above the standard compound’s rated range, or where the low-temperature flexibility requirement pushes below standard glass transition temperature. Examples: Continuous oil service at 280°F where standard NBR degrades but HNBR cost is a concern. Outdoor seals in northern climates requiring flexibility to -65°F where standard EPDM is marginal. High-temperature steam sealing above standard peroxide EPDM’s rated limit. The formulation response is polymer selection, cure system optimization, and plasticizer choice targeting the specific temperature constraint.
Service fluids outside the standard petroleum, water, and reference oil categories tested in catalog compound data sheets. Examples: Biodiesel and alternative fuel blends that attack standard NBR through ester-phase attack. Peracetic acid and hydrogen peroxide sanitizers at elevated concentration in food processing CIP systems. Specific pharmaceutical solvents or active pharmaceutical ingredients (APIs) requiring extractables validation. Specialty hydraulic fluids (phosphate ester, water glycol, synthetic esters) not covered by standard D471 reference oil testing.
Static sealing applications where the seal must maintain contact force over an extended service life that standard compounds cannot meet. Examples: Subsea equipment designed for 25-year service life without replacement. Buried infrastructure gaskets where resealing is not practical. High-cycling flanged joints in process equipment where retorquing is operationally impractical. Formulation response is peroxide cure system selection, crosslink density optimization, and antidegradant package design targeting the specific temperature and time requirements of the compression set specification.
Applications where standard compound certification is insufficient for the regulatory environment. Examples: Pharmaceutical applications requiring USP Class VI certification with lot-specific biocompatibility test reports. Defense programs requiring MIL-R-6855 or AMS qualification with full material traceability. Food processing applications requiring combined FDA 21 CFR 177.2600 compliance, 3-A Sanitary Standard certification, and metal-detectable additive in a single compound. REACH and RoHS compliance requirements for European market rubber components.
Applications requiring two properties simultaneously that standard formulations treat as trade-offs. Examples: High abrasion resistance with low durometer for a sealing surface that must both resist wear and conform to an irregular mating surface. Low compression set with high elongation for a diaphragm that must recover fully from large deflections over many cycles. Excellent oil resistance with low-temperature flexibility extending below -40°F for an arctic hydraulic system. Each of these requires formulation work to find the compound design space where both requirements are satisfied.
Applications where the compound must be reformulated to process correctly in the available tooling or production equipment. Examples: A compound with correct cured properties but viscosity too high to fill a complex transfer or injection mold without short shots. A compound with correct durometer and chemistry but scorch safety too low to survive the preheat cycle in a large compression mold without premature cure. A compound with correct properties but processing aids that cause mold fouling, requiring formulation adjustment to maintain production efficiency.
From Application Requirements to Qualified Compound
Custom rubber formulation follows a defined development sequence from application characterization through production qualification. The rigor of each step scales with the criticality of the application and the regulatory requirements that govern it.
Key Tests in the Formulation Qualification Sequence
| Test | Standard | What it validates | When it is critical |
|---|---|---|---|
| Compression set | ASTM D395 Method B | Permanent deformation after sustained compression at service temperature. Primary indicator of long-term sealing contact force retention. | All static sealing applications. Extended service life programs. High-temperature service where crosslink stability is the design constraint. |
| Heat aging resistance | ASTM D573 / D865 | Change in tensile, elongation, and hardness after oven aging at service temperature. Determines the compound’s temperature rating and long-term stability. | All applications above 200°F. Any application where the ASTM D2000 Type designation governs the specification. |
| Fluid immersion resistance | ASTM D471 | Volume swell, hardness change, and tensile change after immersion in service fluid or reference oil. Confirms compound compatibility with the specific fluid contact. | All oil, fuel, chemical, and solvent-contact applications. Especially important for non-standard fluids not covered by reference oil data. |
| Low-temperature brittleness | ASTM D746 | Pass/fail brittleness test at specified low temperature. Confirms the compound retains flexibility at the lowest service temperature. | Outdoor applications in cold climates. Arctic service. Any application where cold-start or low-ambient sealing is required. |
| Tensile and elongation | ASTM D412 | Tensile strength at break, elongation at break, and modulus at specified elongation. Baseline mechanical property validation for the formulation. | All applications. The fundamental compound mechanical property test that confirms the formulation is correctly vulcanized and properly dispersed. |
| Ozone resistance | ASTM D1149 | Cracking resistance after ozone chamber exposure. Critical for polymers susceptible to ozone attack in outdoor or industrial ozone-present environments. | Outdoor service with NBR, SBR, or natural rubber. Industrial environments with elevated ozone from electrical equipment. Automotive weatherstrip applications. |
| Extractables and leachables | FDA 21 CFR 177.2600 / USP methods | Migration of compound ingredients into contact fluids. Confirms regulatory compliance for food, pharmaceutical, and medical applications. | All food-contact, pharmaceutical, and medical device applications. Required for FDA, USP Class VI, and 3-A certification. |
Custom Formulation Specialties
Wayne Rubber’s compounding partner network covers the full range of thermoset elastomer formulation work. The following formulation territories represent the most frequently requested custom compound programs.
Peroxide-cured formulations optimized for minimum compression set in static sealing applications with extended service life requirements. Cure system selection, crosslink density, and antidegradant package are all tuned to the specific temperature and duration of the compression set requirement.
Compounds for sustained oil service above 250°F where standard NBR crosslinks degrade. HNBR formulations with optimized hydrogenation degree and ACN content for the specific temperature ceiling and oil type. FKM compounds where the temperature exceeds HNBR’s range or where aggressive fuel contact is also present.
Platinum-cured silicone and EPDM formulations meeting FDA 21 CFR 177.2600, USP Class VI, NSF-51, and 3-A Sanitary Standards. CIP and SIP chemistry compatibility is validated alongside food-contact compliance. Metal-detectable grades with barium sulfate loading available in any compliant polymer family.
Formulations maintaining elasticity at temperatures below standard compound glass transition points. Plasticizer selection and polymer grade selection (low-ACN NBR, specialty EPDM, fluorosilicone) are the primary levers. Critical for arctic hydraulics, outdoor northern-climate seals, and altitude-service aerospace applications.
Formulations meeting UL 94 V-0 or V-2 flammability ratings for electrical enclosure gaskets, transit vehicle interior components, and applications governed by fire safety codes. Neoprene’s inherent flame resistance is formulated and certified; halogen-free flame retardant additive packages are developed for EPDM and other polymers where neoprene’s properties are otherwise unsuitable.
MIL-R-6855 Class 1 and Class 3 certified NBR and FKM compounds. AMS 7259, 7276, 7277, and related AMS specification compounds for fluorosilicone and FKM. Full material traceability, first article inspection reports, and lot-specific test data for program qualification. Material certificates referencing specific AMS or MIL designation by lot number.
FKM and FFKM formulations for contact with aggressive chemicals, concentrated acids, solvents, and reactive compounds outside the resistance envelope of standard elastomers. FKM Type GF (highest fluorine content) for resistance to polar solvents and methanol-blend fuels. FFKM for universal chemical resistance where standard FKM is attacked.
Natural rubber and SBR formulations optimized for resilience, dynamic fatigue resistance, and low heat build-up in vibration isolation mounts, flexible couplings, and high-cycle dynamic seals. Compound optimization targets minimum tangent delta (damping factor) at service frequency and temperature for the specific vibration isolation application.
Conductive carbon black-loaded compounds achieving specific surface or volume resistivity targets for ESD protection, EMI shielding, and static-dissipative gasket applications. Available in EPDM, silicone, and NBR base polymers. Resistivity is specified and tested per ASTM D991 or ASTM D257 as part of the qualification protocol.
What to Provide When Requesting Custom Formulation
Custom formulation programs begin with a technical discussion, not a purchase order. The information below guides the initial conversation. Providing as much detail as possible up front shortens the development timeline significantly because it eliminates the back-and-forth that is otherwise needed to characterize the application before formulation work begins.
- Service temperature range: Minimum and maximum continuous service temperature at the compound interface. Note separately if the cleaning cycle, post-cure, or sterilization temperature exceeds the process temperature.
- Fluid contact: All fluids the compound contacts, including the primary process fluid, any secondary exposure (lubricants, coolants, cleaning agents), and the cleaning chemistry if CIP or SIP is used. For petroleum fluids, specify the aromatic content or fluid designation if known.
- Physical property requirements: Target durometer, minimum tensile strength, maximum compression set at service temperature, and any other properties governed by the application drawing or specification.
- Regulatory requirements: FDA 21 CFR 177.2600, USP Class VI, NSF-51, 3-A, MIL-spec, AMS designation, or other applicable compliance requirement. State whether lot-specific test reports or third-party certification is required.
- Failure mode of current compound (if applicable): Whether the current compound fails by hardening and cracking, swelling, compression set loss, delamination, or another mechanism. This is often the single most useful piece of information for guiding formulation target-setting.
- Processing method and tooling: Whether the compound will be compression molded, transfer molded, injection molded, or extruded. Any known processing constraints such as mold temperature limits, press cycle time, or scorch safety requirements from the existing cure cycle.
- Volume and timeline: Annual production volume and the development timeline, including whether a prototype quantity is needed before production qualification and when production release is required.
Also at Wayne Rubber
Discuss a Custom Formulation Program
Describe the application, the failure mode of the current compound, and the performance target. Wayne Rubber’s engineering team will assess the formulation territory, recommend the polymer and cure system direction, and outline the development and qualification process for your program.