Different Epoxy for Different purpose??

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NewtonsLaws
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Different Epoxy for Different purpose??

Postby NewtonsLaws » Sat Mar 18, 2017 5:15 pm

Hi New to HPR.
Aiming for L1 cert next rocket in April.

Was told to use JB Weld for attaching motor retainer to motor mount tube for temperature.
But not to use JB Weld for fillets as too brittle.

Ok got that.

BUT should I use JB Weld for
centring rings to motor mount tube?
centring rings to body tube?
shock cord to motor tube?

Or stick with fillet epoxy?

and is 5 min epoxy ok or do I need to use 15min epoxy?
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Re: Different Epoxy for Different purpose??

Postby SpaceManMat » Sat Mar 18, 2017 6:27 pm

Really only the retainer needs JB, even then for a 38mm motor any decent expoxy would probably do.

Some people do use JB for fin fillets, but only normally when they have a black fibreglass rocket that they don't want to paint.

Either 5 or 15 minute expoxy is fine it more about what you are comfortable using.
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OverTheTop
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Re: Different Epoxy for Different purpose??

Postby OverTheTop » Sat Mar 18, 2017 6:43 pm

Hmm. Glue threads are always contentious. Many opinions.

Data sheet is king. Know the specs and what you want to achieve.

Having said that, there are rules of thumb.

Personally I would use JB for anything in contact with the motor casing. Its higher temperature rating helps it keep its specifications under the increased temperature there.

I use West Systems 105/206 (slow set) for everything else. It is what I have so it is what I use. Never let me down along the way to L3 or Mach 1.8 yet. There are some other epoxies that are slightly stronger but harder to source, so I stick with WS (no pun intended). It is a bit slow sometimes, but working the joint in hot weather with faster hardeners can be stressful.

Generally the quicker the set the less strength the joint has. It is a bit of a generalisation, but generally right. As I said earlier, the data sheet is king in this area. Remember you need to mix them correctly to achieve the specifications. I mix by weight exclusively.

This is only one opinion :)
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Re: Different Epoxy for Different purpose??

Postby Kryten » Sun Mar 19, 2017 10:58 am

I concur with the comments by OTT.
5 minute epoxy will work, but generally speaking, epoxies with longer set times are usually better - primarily due to the different hardener (the part "B") and the resulting structure of the cross-linked polymer.
I believe 5 minute Araldite becomes more brittle over time, so I would avoid it (although I did use it in one of my mid-power rockets for convenience)
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OverTheTop
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Re: Different Epoxy for Different purpose??

Postby OverTheTop » Sun Mar 19, 2017 11:46 am

5 minute Araldite


Avoid it like the plague...
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Re: Different Epoxy for Different purpose??

Postby NewtonsLaws » Mon Mar 20, 2017 5:37 pm

Thanks everyone!

I was looking at Loctite epoxy spec sheet.
it seems to have a higher termparater rating (150 deg C) and strength than Selleys araldite.

Any thoughts?

And where does one get this other magic stuff?
It does not seem to be in the common bunnings etc.
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OverTheTop
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Re: Different Epoxy for Different purpose??

Postby OverTheTop » Mon Mar 20, 2017 8:44 pm

I usually buy West Systems at Carbatec (http://www.carbatec.com.au) but they don't have a large range of hardeners or sizes. They do suit what I buy though. Probably worth a look.

You local boat-building place can probably help too, although if you mention the word "marine" the price will likely go up :) . Make sure you go through the data before purchasing.

Just Google and you should be able to find it.

JB can be purchased at Australian Rocketry and many other places.

Forgot to mention. You might be able to get some epoxy donated from some HPR flier(s) that have some to spare, if you don't need much.
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Re: Different Epoxy for Different purpose??

Postby Lamp » Fri Mar 31, 2017 8:52 am

For an L1 rocket (unless you are doing a glass tip to tip or rolling your own tube) all you really need is "hobby" epoxy like BSI. Blake sells this in the Aus rocketry shop. I tend to use either the 15 min or 30 min stuff to make sure I have enough working time.

For higher strength requirements I also use West Systems but typically with 205 fast hardener (about 30min working time), generally with chopped CF (injected internal fillets) or Wests micro fibre filler (for external fin fillets).

JB weld is great for anything attached to the motor mount tube (retainer, CR) but to be honest, you could get away with not using it. A small HPR motor will not get hot enough for long enough for you to really need it...but having said that, I always use it for these applications :wink:
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