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Team Modus™ on 03/09/2022

Aerospace Material Specification Materials

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    In the early days of aviation, the concerns about materials used in aircraft rested heavily on weight and durability. Since the days of biplanes and open cockpits, aircraft have gotten quite a bit more complicated. And so have the materials used to build them. 

    In aerospace, there’s no room for error. Errors can lead to malfunctions that put lives at risk. That’s why the materials used in aircraft are so strictly regulated. More specifically, the materials used for aircraft are governed by the Aerospace Material Specification (AMS). 

    In this post, the Modus Advanced team walks you through AMS basics, subcategories of AMS materials and examples of silicones that fall under each. Read on to learn more.

    Modus has served as a manufacturing partner to companies in aerospace and defense for years. Why do they keep coming back to us? Because we get it right — from selecting the ideal AMS materials to producing the final product. Want to work with us? Reach out.

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    About AMS Materials

    The AMS is governed by the Society of Automotive Engineers (SAE). The SAE maintains a large database of all of the specifications that fall under AMS, and it continuously updates them. Collectively, this database of specifications governs equipment, procedures and processes related to material use in aircraft.

    AMS Categories

    Because silicone rubber is one of the most common materials we work with to create parts like gaskets for aerospace applications, we will take a closer look at some of the AMS subcategories that govern silicone rubber used in aircraft.

    AMS 3301

    This part of the AMS specifications mandates required properties for silicone rubber used in aircraft that comes in the form of molded shapes, extrusions, tubing, strips or sheets. 

    Specialty Silicone Products (SSP), one of the highest-quality materials producers in the silicone industry, offers a silicone material that is fully compliant with AMS 3301. It’s called SSP-1331-T. Available as sheet stock or pre-molded compound, SSP-1331-T has a durometer of 40 and resists temperatures between - 85 degrees Fahrenheit and 400 degrees F, as well as petroleum-based oils commonly found in aircraft.

    AMS 3302

    AMS 3302 also governs sheets, strips, tubes, extrusions and molded shapes of silicone rubber to be used in aircraft, but it imposes slightly different specifications in terms of durometer, temperature resistance, shelf life and more.

    An SSP product that exemplifies this AMS material is SSP-1773. Also available as pre-molded stock or sheet stock, this silicone is somewhat harder than the AMS 3301 spec calls for at a durometer of 50, but it isn’t resistant to extreme temperatures.

    AMS 3345

    AMS 3345 materials are meant to resist weathering and the oil used in aircraft engine pistons. They do remain flexible within reasonable temperatures but may not be resistant under all extreme conditions.

    SSP-1778 is a material that satisfies the requirements of AMS 3345. This silicone comes as a pre-molded compound that is heat-cured. It has a durometer of 50.

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    AMS 3356E

    Primarily meant for parts used in sealing or operation under temperatures that range from -67 degrees F to 446 degrees F, AMS 3356E materials are often found in parts of aircraft in which they may be exposed to aircraft piston engine oil because they are resistant to this harsh substance.

    One SSP silicone that meets the criteria established by AMS 3356E is SSP-1808. This brick red silicone has a durometer of 60 and is resistant to high aniline point petroleum-based oils. However, if this material comes into contact with low aniline point petroleum-base fluids or gasoline, it may swell, making it unsuitable for applications that may present such an environment.

    AMS 3325

    This AMS specification applies to fluorosilicone rubber sheets, tubes, strips, extrusions and shapes. While materials within this category can be used in a wide variety of applications, they are particularly handy in situations that may present exposure to lubricating oils or jet fuels.

    SSP-2496 is a good example of an AMS 3325 material. It is a 60-durometer silicone that comes in sheet or pre-molded form. In lab testing, this material demonstrates resistance to oils and fuels.

    AMS 3305J

    AMS 3305J materials are resistant to temperatures that range from -85 degrees F to 401 degrees F, as well as corrosive substances like petroleum-based lubricating oils. They are typically unsuitable for contact with gasoline, as exposure to gasoline can cause them to swell.

    At a durometer of 80 and rated for the exact right temperature resistance, ​​SSP-2554 is a great example of an AMS 3305J material.

    AMS 3303

    AMS 3303 materials are meant for general purpose use in aircraft applications. They can come in the form of sheets, tubes, strips, molded shapes and extrusions. 

    At a durometer of 60, SSP-352 is an SSP material that meets the specifications of AMS 3303, as well as the specifications of MIL SPEC AA 59588 Class 2A and 2B, Grade 60. 

    AMS 3304

    AMS 304 materials are relatively hard, with durometers between 65 and 75, and they are meant for general purpose aerospace use

    SSP-389 falls squarely in the required durometer range of AMS 3304 at 70. It also meets the requirements of the MIL SPEC AA 59588, Class 2A and 2B, Grade 70, specifications.

    Choosing the Right Aerospace Manufacturing Partner

    If you are designing a part for use in an aerospace setting, it will need to incorporate materials that comply with AMS standards. That much may be obvious at this point, but what may not be so obvious is how to choose the right manufacturing partner to help you make that happen.

    Most converters like to say they can do the job, but they aren’t all the best or even ideal for your particular design. Here are a few ways to make your choice:

    • Ask the manufacturer to demonstrate specific experience with AMS materials.
    • Look for indications that the manufacturer has in place a robust quality system.
    • Consider whether the manufacturer offers engineering support to help you choose the right materials and make sure your design is manufacturable and cost-effective.
    • Check for AS9100 certification (the gold standard quality certification for manufacturers in the aerospace industry).

    The answers to those questions will rule out the majority of manufacturing partners. And we suspect one of the very few left on your list at the end will be Modus Advanced.

    Manufacture It Right with Modus

    With good reason, aerospace manufacturing is one of the most stringent and difficult industries in which to operate. But the Modus team has thrived in this space for two key reasons: 

    1. We respect the specs (AMS in this case).
    2. We put quality first, always.

    That’s how we provide real partnership to companies in the aerospace industry, and it’s how we’ll treat your design, too. We offer not only access to AMS silicones and other compliant materials, but guidance on when and how to use them, as well as how to make your design more cost-effective and manufacturable.

    Ready to get started? Contact us online or give us a call at 925-960-8700.


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