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A few days ago, I heard an interesting little tip from an old racer while discussing the best way to put a riveted assembly together. In response to my concerns about high vibration loosening the fasteners, he said the answer was simply dipping the rivet shanks in epoxy prior to installation. While blind rivets are already a pain to remove (and this wouldn’t make life any easier), it does provide an excellent backup. No dead space means less fatigue, and the epoxy would provide secondary retention for the leftover stem.

A clever fabricator could probably combine this technique with strips of epoxy or RTV in an assembly’s seams to create a liquid-tight container without needing a welder. It’s a good way to improve reliability or sidestep the need for high-dollar equipment.

(Thanks to Flickr user Illetirres for this cool CC-licensed photo)

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9 Responses to Reader Tip: Strengthening Rivets

  1. matthew says:

    i’m skeptical of this line of thinking. i wouldn’t think there is much space left for epoxy in a properly tightened rivet. heat and vibration would probably crack any epoxy in the joint, particularly if surface prep was not perfect. my intuition says this would not make any measurable difference in a rivet application, however i don’t have any specific knowledge to back this up.

  2. Eli says:

    In the WWII aircraft factories, they would freeze the rivets prior to installation. After they were installed (or during the installation process) the rivets would warm up and expand to fill the entire hole.

    • LeeB says:

      I’ve been workin on planes starting in 1978 on DC 9 super 80′s , boing 737, Cessnas, Pipers, whatever, and I never heard that little factoid, ever. Don’t make sense to leave a important thing like filling the hole properly to cooling and heating. How exact would you have to be. Drilling rivet holes isn’t an exact science, that’s why the rivets are designed to expand and take care of that.

  3. h-bomb says:

    Epoxy is almost guaranteed to be more brittle than the surrounding metal, meaning that the epoxy is almost sure to crack while the metal rivet is still bending–well before it starts to fracture, especially if the clamping force of the rivet itself is already bearing down on the epoxy under zero-load conditions.

    Instead, I would (a) ensure that the rivet and surrounding metal have similar mechanical properties, (b) make sure the assembly is tight and hole and rivet diameters match precisely, and (c) either switch to solid rivets or the number of rivets in the assembly. If this isn’t enough, I’d try eliminating the problematic vibrations, using some sort of SOFT material or adhesive as a vibration-absorbing gasket, either between the two metal plates or as a coating for the rivet itself. Perhaps dipping the rivets in silicone (or using those fancy neoprene-coated rivets) might work better.

    It’s also no guarantee that a given adhesive will cure properly–if the rivet is on there tight enough, the polymerization reaction could be stunted by lack of oxygen. I would think an anaerobic adhesive like most threadlockers would be saver in this regard.

  4. aaron says:

    eli said it.

  5. Ken says:

    This is not intended to be critical. To correct the “Icebox rivet” comment. The rivets are called “Icebox rivets” because they are heat treated to soften them for driving. They are a higher strength alloy. After the heat treat process, oven or salt bath. They are put into the icebox to retard the hardening process. When the rivet is driven it swells up to fill the hole. Warming up and expanding has nothing to do with it. “Icebox rivets” are used today in critical aircraft structure.

  6. Paul says:

    You can buy rivets made of different materials, as I’m sure you know. You can choose a rivet of different strengths. In some situations the metal around the rivet will give way before the rivet itself and in other cases they fail at the same time, and in yet other cases the rivet fails first. This should be part of your design if you are designing a critical part. Rivets shouldn’t vibrate loose unless they are being installed without proper consideration of the conditions. I would not recommend using any glues or epoxies on rivets. Riveted parts are designed to flex some. You could weld together an aircraft and it would hold together very well, too well in fact that forces could build up and tear the metal instead of only releasing the affected area like rivets would do.

  7. Les says:

    As an aircraft structures mechanic for the last 20 years, Ken and Paul are right. Riveted joints and seams are designed for the intended strengths. They do flex, and are designed to do so. If you are really worried about the “void” between the rivet and its structure, ensure you are using the correct size of drilled hole, and don’t forget to deburr them.

    As for teh RTV method, there is a compund called PRC (protective rubber compund) that is commonly used to seal seams and joints for that purpose. Sealing only. There are many different sealing compounds for the required seal.

    For the “best way to rivet a structure together”, I prefer to use solid rivets when possible, and only used blind rivets when you cannot buck the back side. Just a thought.

  8. Andy says:

    Icebox rivets may be age hardening Al alloys – they are manufactured with a small amount of CU in the mix. This forms over a short period as CuAl2 precipitate, which creates a stronger and stiffer rivet. The rivets are driven soft, and over a period of room temperature conditions will become stronger as the CuAl2 ppte forms. To prevent the ppte from appearing too soon, the rivets are kept in the freezer. If the rivets inadvertently are left too warm and the AlCu2 ppte forms, this can be re-dissolved by heating.

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