A Guide to Rubber Molding for Aerospace Applications

Synthetic rubber materials are versatile and durable, withstanding extreme operating conditions in many applications. Aerospace rubber molded parts are used in mission-critical applications to seal, insulate, and secure components. Here, we will look at how rubber materials are used in aerospace and defense applications, typical molding processes, rubber material options, and their properties.

Rubber Products in the Aerospace & Defense Industry

Aircraft, spacecraft, and satellites all depend on aerospace-grade rubber materials and other elastomers built to provide high performance in the most demanding applications. They can be used in very high and low temperatures and are resistant to corrosion and damage from lubricants, fuel, hydraulic fluids, and propellants.

Precision-engineered aerospace rubber parts are designed into engines, hydraulic actuators, power supplies, and other assemblies where a tight seal or insulation enable critical functionality. Several examples include:

O-Rings
Seals
Gaskets
Grommets
Over molded poppets and valves

Rubber Molding Processes for Aerospace

MIL-SPEC and aerospace standards include specifications and tight tolerances for design and manufacturing in order to maintain reliable function in harsh conditions. Several rubber molding processes are used for custom aerospace components, including these four common operations:

Rubber Compression Molding: A rubber preform piece is placed between the upper and lower portions of a mold. The mold closes and is clamped together, compressing the preform into the desired shape. Excess is trimmed and the part is removed and cured.
Rubber Injection Molding: Screw extruders pressurize and heat rubber material and feed it into a mold. The material fills the cavities for a precise shape.
Rubber to Metal Bonding: Bonding adhesive or a mechanical bonding process adheres rubber to a metal or plastic part which is the substrate. The rubber is over molded over the substrate into the desired form or profile.
Liquid Injection Molding (LIM): is an injection molding process that combines a high viscosity liquid in two parts that is mixed with a platinum catalyst to enable a much faster cure rate compared to the injection molding of high consistency (HCR) rubber. The faster cure rate makes it ideally suited for high-volume manufacturing.

Aerospace Rubber Product Applications

High-performance rubber is used in a variety of aerospace and aviation applications, including:

Rockets and missiles
Hydraulic actuators
Gas turbine engine seals
Auxiliary power devices
Valves and fittings
O-rings for pumps, valves, oil reservoirs, and connectors
Rubber and fabric composites
Engine wiring clips
Rubber cap stoppers
Manifold gaskets
Radial lip seals

Aerospace Rubber Properties

To maintain a robust seal or cushion between components, aerospace rubber must have low levels of compression set in order to retain its shape.

These properties make synthetic and silicone rubbers suitable for use in aerospace applications:

Extreme high and low-temperature tolerance
High corrosion and abrasion resistance
Blocks or absorbs sound and mechanical vibration
Long service life
High tensile strength

Rubber Materials for Aerospace Applications

Aerospace rubber components can be made from several synthetic and silicone rubber materials. Common choices for top performance are:

Viton™: One of several fluoroelastomers (also referred to as FKM), this material has high tensile strength, excellent mold release, increased mold flow, and improved extrusion performance. It has outstanding heat and chemical resistance and superior sealing capabilities for liquid-tight applications.
Ethylene Propylene Diene Monomer (EPDM): EPDM offers exceptional resistance to hot water, steam, cold weather, ultraviolet and sunlight, ketones, dilute acids, and alkalis. It is a common choice for seals and gaskets. It is not recommended for uses that expose it to aromatic hydrocarbons (e.g., benzene, toluene, xylene) or solvents.
Nitrile: A type of Buna rubber, nitrile is resistant to oils, alcohols, greases, silicones, water, fuels, and hydraulic fluids. It is strong and stretchy. Gaskets, seals, and diaphragms are common applications, though it should be used at temperatures below 250°F. It also provides high compression set, abrasion resistance, and tensile strength.
Butyl: Also called IIR (isobutylene isoprene rubber), butyl rubber is a copolymer of isoprene and isobutylene. Excellent for sealing applications, it offers excellent resistance to chemicals, ozone, heat, abrasion, heat aging, and tearing. This material should not be used at temperatures above 250°F or in contact with fuels, mineral oils, and some solvents.
FKM: A group of fluoroelastomers (including Viton™) that resist exposure to heat, UV radiation, and chemicals. These materials provide low levels of compression set, long service life, and excellent sealing properties.

Advanced Aerospace Rubber Products From RD Rubber Technology Corporation

RD Rubber Technology Corporation is a leader in custom-molded rubber parts and components. Our commitment to quality and customer service has set us apart since our founding in 1986. We offer custom molding, machining, cryogenic deflashing, and support services including design, prototyping, curing, ultrasonic cleaning, and Class 8 cleanroom molding and inspection. We are ITAR registered and hold AS 9100:2016 and NIST 800-171 certifications.