Rivnut Fastener

General Composites Discussions Composites Talk
#1

Does anyone use rivnuts? I have been using bonded fasteners for everything, but I’m trying to design a spoiler mold that I can process faster. In order to do that, I’m going to use an internal silicone bladder and make the spoiler as one piece. The problem, is that the part requires use of fasteners on the underside. If I make the part as one piece, I won’t be able to go in and bond a fastener to the underside of the spoiler, like I have been doing previously when making the part in 2 pieces (top and bottom, that are then bonded together.

My fear with rivnuts, is that the little “notch” that keeps the nut from spinning freely after installation, would easily strip and be totally useless if it was ever over-tightened.

I’m interested in everyone else’s experiences with this…or if you have a suggestion for a better “blind” fastener, I’m all ears…

#2

I often used them in my last job. We worked with steel and I always hated working with them. When they worked they worked great. When they didnt, it was a disaster. Hard to drill back out without chipping paint or damaging the metal. In your case. I think I would shy away from them. They would often compress unevenly and the bolt would then bind halfway through and yes the little notches would slip. You may be able to try and retighten the rivnut and get it to work but chances are no.

Take into account this was going into metal. They may go into carbon easier and work easier. I was just giving you my experience with them

#3

Rivet nuts work great, use them very often. You can always do a loading test prior to applying them in production parts to validate their strength and effectiveness.

#4

I was thinking about possibly inserting a thin sheet of perforated tin, steel, or aluminum, into the prepreg layup so that it’ll be bonded into the part. Then I’d feel safer about the nut not stripping and spinning freely, but I’m still nervous about a rivnut holding. These would be the only things holding an automotive spoiler on…

#5

I’ve used them for fastening spill plates to wings, but not for mounting point of wings. Typically this is done with a recess in the wing which a metal or composite bracket is glued and fixed in secondary. Once again, whatever you decide to do, make sure to validate it first. A simple homemade load fixture could help you do this. Good luck!

#6

As you’ve mentioned, encapsulating metal within the lay-up plies will give a better form of “grab” for the rivnut. it will also give you more confidence in the fixture.

#7

i have used perforated nuts in the past and secured them between layers during the layup. they work really well and spread the load out. just put some wax in or tape over them before curing.

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