Aerospace and defense applications place demanding requirements on rubber and elastomeric components. Temperature changes, vibration, environmental exposure, weight considerations, tight dimensional requirements, and long service expectations can all influence the performance of a seal, gasket, tubing, or custom profile.
For these applications, selecting the right elastomer and designing the extrusion around its operating environment are critical.
Custom rubber and silicone extrusions can be manufactured in a wide range of profiles to provide sealing, cushioning, isolation, protection, and other functions within aerospace and defense equipment.
Northwest Rubber Extruders (NWRE) manufactures custom rubber extrusions and custom silicone extrusions for demanding OEM and industrial applications.
This guide explores several factors engineers and purchasing teams should consider when specifying custom extruded components for aerospace and defense applications.
Why Aerospace Applications Require Specialized Elastomers
Rubber components used in conventional industrial equipment may operate within relatively predictable conditions.
Aerospace applications can be very different.
Depending on where the component is installed, it may encounter:
- High temperatures
- Extremely low temperatures
- Rapid temperature changes
- Ozone
- UV exposure
- Moisture
- Vibration
- Repeated compression
- Fuels or oils
- Chemicals
- Pressure changes
- Long service requirements
A rubber material that performs well in one part of an aircraft or aerospace system may be completely inappropriate somewhere else.
Material selection should therefore begin with the actual operating environment.
Common Uses for Rubber Extrusions in Aerospace
Extruded elastomer profiles can perform many functions within aerospace equipment and supporting systems.
Potential applications include:
- Door seals
- Hatch seals
- Window seals
- Equipment enclosure seals
- Protective edging
- Tubing
- Channels
- Gaskets
- Vibration isolation
- Environmental seals
- Electrical enclosure seals
- Equipment compartment seals
- Protective profiles
- Custom sealing components
The profile can be designed around the geometry of the assembly rather than requiring engineers to adapt their design around an existing standard rubber shape.
Silicone Extrusions for Aerospace Applications
Silicone is frequently considered for aerospace applications because of its ability to perform across demanding temperature conditions.
Depending on the specific compound and requirements, silicone can provide:
- Excellent high-temperature performance
- Excellent low-temperature flexibility
- Excellent ozone resistance
- Excellent UV resistance
- Good environmental aging characteristics
- Flexibility across a broad range of conditions
These properties make custom silicone extrusions worth considering when temperature extremes are an important part of the operating environment.
Silicone can be extruded into profiles such as:
- Tubing
- Bulb seals
- D-shaped seals
- Channels
- Solid strips
- Hollow profiles
- Custom geometries
The specific silicone formulation should be selected according to the application and any applicable performance requirements.
EPDM Extrusions for Aerospace and Ground Equipment
EPDM is another elastomer that may be considered for certain aerospace-related applications, particularly when weather and environmental exposure are important.
EPDM provides excellent resistance to:
- Ozone
- UV exposure
- Weather
- Water
- Environmental aging
These characteristics can make EPDM useful for exterior seals, ground-support equipment, enclosures, transportation systems, and other applications exposed to outdoor conditions.
However, EPDM generally isn’t the preferred material for regular exposure to petroleum-based oils and fuels.
If fuel or oil exposure is expected, another elastomer may need to be considered.
Material Selection Starts With the Environment
One of the biggest mistakes when specifying a custom rubber extrusion is selecting a material based on a single property.
For example, choosing a material because it has excellent temperature resistance isn’t enough if the same component will also encounter a chemical with which the material is incompatible.
Engineers should evaluate the entire operating environment.
Important questions include:
What Is the Temperature Range?
Identify both minimum and maximum operating temperatures.
Also determine whether exposure is continuous or intermittent.
Will the Component Encounter Fuel or Oil?
This can eliminate certain elastomers from consideration.
Is the Component Exposed to UV or Ozone?
Exterior components may require strong resistance to environmental aging.
Will the Component Be Continuously Compressed?
Compression-set characteristics may become important.
Will the Extrusion Experience Vibration?
The profile and material need to perform under repeated mechanical movement.
Are There Specific Material Requirements?
Aerospace and defense programs may require materials that meet particular customer, industry, or application-specific specifications.
NWRE’s Material & Engineering resources provide additional information related to elastomer selection.
High-Temperature Rubber Extrusions
Temperature is often a major consideration in aerospace component design.
Some rubber materials begin to lose desirable physical properties when exposed to elevated temperatures.
Depending on the compound, silicone can offer strong performance at higher temperatures and may be considered for applications near:
- Engines
- Electrical systems
- Lighting systems
- Heating equipment
- High-temperature machinery
- Aerospace support systems
However, engineers should avoid specifying a material based only on a general temperature rating.
Actual performance can depend on:
- Duration of exposure
- Mechanical load
- Compression
- Chemical exposure
- Pressure
- Compound formulation
The complete application should be reviewed.
Low-Temperature Flexibility
Low-temperature performance can be equally important.
Certain elastomers become harder and less flexible as temperatures fall.
If a rubber seal needs to continue compressing or flexing in a cold environment, low-temperature performance becomes critical.
Silicone is frequently considered for applications requiring flexibility across a wide temperature range.
The exact compound should still be evaluated against the application’s minimum operating temperature and other environmental conditions.
Vibration and Shock
Aircraft, vehicles, machinery, and defense equipment can experience substantial vibration.
Rubber components can be used to help:
- Cushion contact points
- Reduce vibration transfer
- Protect adjacent components
- Create flexible interfaces
- Maintain seals between moving surfaces
Profile geometry can significantly influence performance.
A solid rubber bumper behaves differently from a hollow extrusion.
Likewise, a soft bulb seal behaves differently from a dense rectangular profile.
The design should reflect the type and magnitude of movement the component is expected to experience.
Custom Sealing Profiles
Many aerospace sealing challenges cannot be solved effectively with an off-the-shelf rubber profile.
A custom extrusion allows the cross-sectional geometry to be designed around the assembly.
Possible designs include:
D-Shaped Seals
A D-profile can provide a flat mounting surface with a compressible rounded section.
P-Shaped Seals
P-profiles combine a sealing bulb with an extended mounting section.
Bulb Seals
Hollow bulb seals can provide substantial compression using relatively low force.
U-Channels
Channels may provide protection or fit around an edge.
Tubing
Tubular profiles can be manufactured in different outside diameters, inside diameters, and wall thicknesses.
Custom Hollow Profiles
Internal cavities can be engineered to influence compression characteristics.
Complex Custom Profiles
Multiple functional features may sometimes be incorporated into a single continuous extrusion.
Solid vs. Hollow Aerospace Profiles
Whether an extrusion should be solid or hollow depends on its function.
Solid Profiles
Solid rubber profiles may be useful when the component requires:
- Greater resistance to deformation
- Protection
- Impact absorption
- Spacing
- Edge protection
- Physical support
Hollow Profiles
Hollow extrusions are commonly used when easy compression is important.
Potential applications include:
- Door seals
- Hatches
- Access panels
- Equipment enclosures
The internal cavity allows the extrusion to deform more easily when pressure is applied.
This can help create a seal without requiring excessive closing force.
Durometer and Aerospace Rubber Components
Durometer measures the hardness of rubber.
A lower-durometer material is generally softer and easier to compress.
A higher-durometer material generally provides greater resistance to deformation.
However, engineers shouldn’t select durometer without considering profile geometry.
A hollow profile manufactured from a relatively firm compound may compress more easily than a solid profile manufactured from softer rubber.
Important factors include:
- Required sealing pressure
- Compression
- Mechanical load
- Installation
- Flexibility
- Profile geometry
- Operating temperature
The material, hardness, and profile should work together as a system.
Compression Set and Long-Term Sealing
Some aerospace seals remain compressed for extended periods.
For example, a seal around an access panel may remain compressed whenever the panel is closed.
Over time, certain elastomers can develop permanent deformation.
This is known as compression set.
If a seal doesn’t recover sufficiently after compression, its ability to maintain contact with the mating surfaces can decrease.
Compression-set performance can be influenced by:
- Elastomer
- Compound formulation
- Temperature
- Compression percentage
- Duration
- Profile geometry
Applications involving long-term compression should consider these factors during material selection and profile design.
Tolerances for Custom Aerospace Extrusions
Dimensional requirements can be particularly important in aerospace manufacturing.
However, rubber behaves differently from machined metal.
Elastomers are flexible and can change dimension during:
- Extrusion
- Curing
- Cooling
- Cutting
- Handling
Complex profile geometry can also influence dimensional control.
Engineers should identify dimensions that are genuinely critical to:
- Fit
- Compression
- Sealing
- Installation
- Alignment
Applying unnecessarily tight tolerances to every dimension can make manufacturing more difficult without necessarily improving component performance.
Critical dimensions should be discussed early in the project.
Aerospace Quality Requirements
Quality systems are particularly important when manufacturing components for aerospace customers.
NWRE maintains a dedicated Quality Control program and information regarding its quality certifications and processes.
Depending on the project, customers may have specific requirements involving:
- Material documentation
- Dimensional inspection
- Lot traceability
- Manufacturing records
- Customer specifications
- Quality documentation
These requirements should be communicated during the quoting process rather than after production begins.
Providing documentation requirements early allows the manufacturer to evaluate them as part of the overall project.
Prototype and Production Considerations
Before moving into production, engineers should consider whether samples or initial production pieces will need to be evaluated.
Testing may help verify:
- Fit
- Compression
- Installation
- Material behavior
- Dimensional requirements
- Interaction with mating components
This can be particularly valuable when replacing an existing component or developing a new custom profile.
Changes are generally easier to address before full production requirements are established.
Rubber Extrusion vs. Rubber Molding
Not every aerospace rubber component should be extruded.
Extrusion is best suited for parts that maintain a consistent cross-sectional profile.
Examples include:
- Seals
- Tubing
- Channels
- Strips
- Continuous profiles
If a component has complex three-dimensional geometry that changes throughout the part, custom rubber molding may be more appropriate.
Molded components can incorporate features such as:
- Mounting holes
- Variable thickness
- Complex surfaces
- Inserts
- Rubber-to-metal bonding
Some aerospace assemblies may use both extruded and molded rubber components.
Questions to Answer Before Requesting a Quote
Providing detailed information early can make the quoting and manufacturing process more efficient.
Whenever possible, provide:
Drawing: Include cross-sectional dimensions and identify critical tolerances.
Material: Specify the elastomer or applicable material specification.
Durometer: Provide required hardness when known.
Temperature: Identify minimum and maximum operating temperatures.
Environmental exposure: Include UV, ozone, moisture, oils, fuels, and chemicals.
Quantity: Provide estimated order quantities and annual usage.
Length: Specify continuous lengths, coils, or cut pieces.
Application: Explain what the component needs to accomplish.
Quality requirements: Identify documentation, inspection, or traceability requirements.
Secondary operations: Include cutting, joining, adhesive, or other fabrication requirements.
The more application information available at the beginning of a project, the easier it is to evaluate the manufacturing requirements.
Choosing a Custom Rubber Extrusion Manufacturer for Aerospace Applications
When evaluating a manufacturer, engineers and purchasing teams should look beyond whether the supplier can simply produce the shape.
Consider capabilities related to:
- Material selection
- Custom tooling
- Dimensional control
- Quality systems
- Secondary operations
- Documentation
- Production consistency
- Technical support
A manufacturer that understands both material performance and extrusion design can help identify potential manufacturing considerations before production begins.
Custom Aerospace Rubber and Silicone Extrusions from NWRE
Northwest Rubber Extruders manufactures custom rubber and silicone profiles for customers with demanding industrial and OEM requirements.
From simple tubing and strips to hollow seals and complex custom profiles, components can be manufactured according to customer drawings, material specifications, and application requirements.
Explore our Rubber Extrusions, Silicone Extrusions, Material & Engineering, Quality Control, and Industries Served capabilities.
Have an aerospace or defense extrusion drawing or specification you’d like reviewed? Request a Quote from Northwest Rubber Extruders.