Why not Nomex for LPR shock cords?

[SolarYellow]

I was thinking about getting even lighter Kevlar string for shock cords in little BT-20 and below rockets. There's some discussion of how Kevlar isn't really all that flame resistant. It occurred to me, why not use heavy-ish Nomex thread?

This link doesn't have anything above Tex 90, and I'm not sure how robust that is. https://www.ebay.com/itm/194186823903?var=495278032678

This one has some Tex 200: https://www.ebay.com/itm/115794536998

I'm talking about 13mm powered stuff here, mostly BT-5 and BT-20, possibly a BT-50 if I'm trying to keep it really light. Not anything bigger. At least the thread is cheap. It might hold knots better than Kevlar and/or have its strength reduced less by having knots tied in it. For <$10, I might just get some to try it.

Any experts on its characteristics and use?

 

[Steve Shannon]

Compare their material properties:
https://osnf.com/kevlar-vs-nomex-aramid-comparison/#:~:text=Both%20Kevlar®%20and%20Nomex,of%20the%20para%2Daramid%20variety.

You’ll see very little difference in heat resistance for operating temperatures - only 25°. Kevlar actually has a higher decomposition temperature.

Try it and let us know, please.

 

[kjhambrick]

I was thinking about getting even lighter Kevlar string for shock cords in little BT-20 and below rockets. There's some discussion of how Kevlar isn't really all that flame resistant. It occurred to me, why not use heavy-ish Nomex thread?

This link doesn't have anything above Tex 90, and I'm not sure how robust that is. https://www.ebay.com/itm/194186823903?var=495278032678

This one has some Tex 200: https://www.ebay.com/itm/115794536998

I'm talking about 13mm powered stuff here, mostly BT-5 and BT-20, possibly a BT-50 if I'm trying to keep it really light. Not anything bigger. At least the thread is cheap. It might hold knots better than Kevlar and/or have its strength reduced less by having knots tied in it. For <$10, I might just get some to try it.

Any experts on its characteristics and use?

@SolarYellow --

Do you understand the Tex System of measurement ?

I don't ...

I wonder what Tex 90 or Tex 200 Nomex yarn translates to as a diameter ?

From what I see online, it is a measure of weight per unit length ...

It seems that 1-Tex equates to 1-gram per Kilometer ?

For example: Service Thread: Yarn Conversion Calculator

EDIT: Maybe @Steve Shannon's link giving the density of Nomex as 1.38 g/cm^3 could be applied ?

Thanks !

-- kjh

 

[SolarYellow]

Yes, it's grams/1000m.

 

[SolarYellow]

Bought the roll of Tex 200 in red. Nearly a mile and a half of the stuff for $20, so I'll probably be happy to share some around with my friends. And will think up new and creative uses for it. Will update as I work with it, test strength, etc.

 

[kjhambrick]

Bought the roll of Tex 200 in red. Nearly a mile and a half of the stuff for $20, so I'll probably be happy to share some around with my friends. And will think up new and creative uses for it. Will update as I work with it, test strength, etc.

@SolarYellow --

Have you received the Tex 200 Nomex Thread ?

How does it look ?

-- kjh

 

[SolarYellow]

Yes, and it looks good. The spool is big. Can easily see it being the mile and a half, a few lifetimes' supply in any case. I imagine any LPR chutes I make will have red shrouds. Maybe I'll bring it to an AARG launch and share.

Don't have time to mess with it much in the near future. Was waiting to post something until I'd actually done something. Thinking the first use will be shock cords in some little 13mm powered rockets.

 

[kjhambrick]

Woo Hoo, another local AARG flier @SolarYellow ?

I look forward to meeting you !

I guess you'll be the guy with the red Nomex Shroud Lines on his chutes

-- kjh

 

[SolarYellow]

I'm mostly Tripoli Houston, but have been to a few ROC launches at Lucerne. I might go fly with those NAR squares at JSC once in awhile. And I want to get up to AARG and meet some of the maestros up there.

 

[86mustang408w]

Nomex will melt too, I've just stuck with kevlar.

 

[jimzcatz]

I have nomex shock cords.

 

[86mustang408w]

I have nomex shock cords.

Nomex or Kevlar?...

 

[cwbullet]

Kevlar in my book.

 

[86mustang408w]

Nomex is weak and will break. Kevlar is what you want, Nomex is for chute protectors...

 

[86mustang408w]

Kevlar in my book.

Every chapter.

 

[SolarYellow]

Nomex has much lower strength than Kevlar, but it also has approximately proportionally greater elasticity, so the shock of the impulse when it gets stretched out to the end should be reduced. They may have something like a similar ability to handle a given scenario, if the peak loads due to shock at the end of extension are the thing that breaks them.

Also, I'm looking at using thick thread on tiny rockets, so if it does break, I'll watch both pieces fall.