Igniter Pyrogen Mold Making

[GregGleason]

As one who likes to makes his own igniters, I like to have a uniform diameter for the diameter. One way to do this is via straws, where the straw is packed with pyrogen and left to cure. Once cured, the straw is slit open with a knife and you are on your way.

An alternate method is using mold making techniques to create a form in which the pyrogen can cure. Once cured, you distort the flexible mold and work the pyrogen out.

My first mold ended in disaster, I think that was because the Alumilite (which was a few years old and had not been stored well) didn't cure properly. The next mold that I made worked ok, but it was the harder Alumilite material, which doesn't flex much.

This third attempt, will use Alumilite 3.

In addition to the Alumilite, I'll need something else. Legos.

Greg

 

[GregGleason]

Yesterday, I had one of my children hunt down the Legos that I would need for this small project.



In addition, to the Legos, I would need some clay. So as part of planning for the project, I made a trip to Hobby Lobby. As a bonus, I think this was on sale.



Greg

 

[jpummil]

Subscribed...

op:

 

[fyrwrxz]

I, myself, have always enjoyed dissolving Legos in acetone. Kinda revenge for stepping on them in bare feet when my kids were young!
(I'm sure someone has an EX formulae using filtered Lego juice...)

 

[GregGleason]

I had another child help with the mashing of the clay into the mold base. I then used a length of nichrome wire to level the clay with the Legos.



I then added the plugs that would form the igniter pyrogen voids. I got the small aluminum tubing from Ace Hardware, and it has a diameter of 5/32". I used some 5 minute epoxy to form a rounded cap of sorts. No reason to do that, more of an aesthetics choice.

I cut the tubing with a hobby saw to lengths of about 1.25". The plugs sit approximately 0.75" above the clay base.



Greg

 

[GregGleason]

Now it was a case of building up the Lego walls.



And now with the completed Lego walls.



Greg

 

[GregGleason]

I had to calculate the volume of the Lego walls, so I could mix up an appropriate amount of Alumilite. The volume was an easy Width x Length x Depth calculation.



The small cup I used is, geometrically speaking, a frustum. I had a frustum volume function already in Excel, so I plugged in the values to arrive at the volume of the cup. I then used the "Mark I" eyeball to do the rest and marked the cup with a Sharpie.

I then set out the Alumilite 3 for pouring the mold, so finally I was getting down to business. The Alumilite 3 comes with 2 containers. The mix ratio is 10 parts base to 1 part catalyst.



Greg

 

[thobin]

Humm very interesting indeed.

TA

 

[GregGleason]

I weighed out the base portion, watching the volume of the base. The base weighed out at about 62 grams, so the catalyst was weighed to 6.2 grams. Then I mixed it thoroughly with a craft stick for a few minutes.



I then poured the mold mix into the Lego walls. I did a "high pour" where the stream goes thin as it goes into the Lego walls. This is supposed to minimize air bubbles. After pouring, it is set aside to cure for 18 hours.



Greg

 

[marcusSRG]

Cool. Nice use of your kids. I have pondered the idea of using a spare RMS nozzle as a form--sit an inverted nozzle on top if a vial of pyrogen, instert your leads through the top of the nozzle and into the pyrogen and slowly draw it back out. I just might need to pull out my igniter stuff and a nozzle and try that out...

 

[GregGleason]

The estimate for Alumilite came out pretty well, as I only had a little left. This little bit can be used as a gauge for the level of curing that has takes place.




Here is a picture after the initial cure, about 2 hours after the pour. As you can see, it has settled a little bit below the initial level of the pour. Also, you can see a few bubbles that migrated to the surface. There may be a few air bubbles near the forms, but as long as they are not large it shouldn't be a problem.



Soon we will see how things turned out. Tomorrow.

Greg

 

[GregGleason]

Here is the final product!

It came out pretty well.



I'll post a video on removing the Legos and showing the mold, if there is any interest.

Greg

 

[Onebadhawk]

If there's any interest????????????????????

If you don't post that video
We'd all like your home address
so all 3000 of us can come over and see how
it came out and you can describe the process too us............

I, for one would like coffee and cake..............

Teddy

 

[Target]

This rates among one of the best DIY projects I have seen here. Thank you for posting.

 

[Onebadhawk]

This to rate among one of the best DIY projects I have seen here. Thank you for posting.

+1.

 

[GregGleason]

Thanks for the kind comments! I do appreciate them.

Here is a link to the video where the Legos are broken down:

https://www.flickr.com/photos/9960539@N07/9388942488/

Here is a comparison video, showing an older mode as compared with the new one.

https://www.flickr.com/photos/9960539@N07/9387620404/

Greg

 

[Handeman]

Ok, so why the flexible mold? Won't the pyrogen break and come apart when you flex the mold to get it to come loose? I have my own receipt for pyrogen, but I know it wouldn't work in a mold like that. If I try to take it out before it fully hardened, and still had some flex, it would break apart and some would stay in the mold. If I left it harden, it would break or crack when flexing the mold.

It sounds like a good idea, but I don't know how it's supposed to work. I'm thinking that a 2 piece mold you can put some mold release in would work as well and allow you to open it up and get the igniter out without damaging the pyrogen.

With all that said, I've never made any molds like you are making so I'll be following this. I hope it works well. I would like to use this technique, especially with small igniters for 29mm and 24mm Hobbyline reloads.

 

[GregGleason]

Ok, so why the flexible mold? Won't the pyrogen break and come apart when you flex the mold to get it to come loose? I have my own receipt for pyrogen, but I know it wouldn't work in a mold like that. If I try to take it out before it fully hardened, and still had some flex, it would break apart and some would stay in the mold. If I left it harden, it would break or crack when flexing the mold.

It sounds like a good idea, but I don't know how it's supposed to work. I'm thinking that a 2 piece mold you can put some mold release in would work as well and allow you to open it up and get the igniter out without damaging the pyrogen.

With all that said, I've never made any molds like you are making so I'll be following this. I hope it works well. I would like to use this technique, especially with small igniters for 29mm and 24mm Hobbyline reloads.

That's a great question. Since my igniters use an epoxy laminate based binder, it has a bit more structural integrity, than say an NC lacquer based binder. The epoxy based igniters should work well with this. I'll test that theory in another thread.

For igniters that wouldn't work with a highly flexible mold, the more rigid one would likely work better. And as you say, a two-part mold would work better. In that case the first mold pouring would be at the longitudinal midline of the plugs. Followed by a second pouring to complete the other side.

Most of what I fly is for the Hobby Line RMS. I will make another mold set with a smaller diameter igniter (probably a 0.125", and maybe another set 1/32" smaller), since I ruined a Blue Thunder grain on a reload trying to force it into the C-slot.

Greg

 

[GregGleason]

For those of you who would like to know the particulars of the mold mix that I used, here it is.



If you get it at Hobby Lobby like I did, it helps to use their 40% coupon.

https://alumilite.com/ProdDetail.cfm?Category=Silicone Rubber&Name=Alumilite's High Strength 3

Greg

 

[blackjack2564]

If you check out restaurant supply or even Staples, etc. you can buy 1000 bar straws/coffee stirrers for 4.85 .

Cut in half that's 2000 molds for small igniters. Cut in 1/3's that's 3000!
They will fit as small as F-24/F-39 size nozzles and easily fit G's

Check around the bars in restaurant's you eat at, the coffee pot at work, etc for small sizes..... I found the absolute smallest at the free coffee bar at my bank [of all places]. And brought them a box of stirrers for one of theirs! Ya need 24 ga. shooter wire to use them. Now I have a lifetime supply.

It just seems easier to me to push the straws into the pyrogen, several times to fill, rather than try to fill a mold with it.....guess time will tell.

 

[cavecentral]

If you check out restaurant supply or even Staples, etc. you can buy 1000 bar straws/coffee stirrers for 4.85 .

Cut in half that's 2000 molds for small igniters. Cut in 1/3's that's 3000!
They will fit as small as F-24/F-39 size nozzles and easily fit G's

Check around the bars in restaurant's you eat at, the coffee pot at work, etc for small sizes..... I found the absolute smallest at the free coffee bar at my bank [of all places]. And brought them a box of stirrers for one of theirs! Ya need 24 ga. shooter wire to use them. Now I have a lifetime supply.

It just seems easier to me to push the straws into the pyrogen, several times to fill, rather than try to fill a mold with it.....guess time will tell.

I had no luck filling straws until I started injecting the pryogen via syringe. Fill straw, add wire. Make um pretty fast that way.

 

[qquake2k]

I never thought about molding pyrogen. I've always just dipped.

 

[cavecentral]

I never thought about molding pyrogen. I've always just dipped.

Mold epoxy based. Dip NC based.

 

[GregGleason]

You can "dip" epoxy based igniters, they just ... do not look all that great.

But they still work and here is an example:

https://www.flickr.com/photos/9960539@N07/8919958104/

Greg

 

[qquake2k]

I've never heard of epoxy based pyrogen, just NC. My last igniters I didn't use NC, I used a different substance that I read about online. Easier than NC and seemed to work fine.

 

[cavecentral]

You can "dip" epoxy based igniters, they just ... do not look all that great.

But they still work and here is an example:

https://www.flickr.com/photos/9960539@N07/8919958104/

Greg

Ok. Well I would not recommend the converse unless it is really thick. Lots of shinkage / air pockets from evaporation.

 

[GregGleason]

In my first post, I made the comment that I like to have a uniform diameter for the igniters, but I really didn't explain the "why" for the preference. The reason is that I like the igniter to fit snuggly in the C-slot, not too tight or not too loose, so that I can have a fair expection that the igniter will not move after it has been set in place. I have had moments of doubt with past igniters on whether on not the placement has changed, from the time the igniter was placed until the time the leads were hooked up. This is one method of mitigating the risk and giving me one less to worry about when I launch. That is why I wanted to have a range of diameters available to me, so I could use the best fitting igniter for whichever motor I was using. Hopefully that helps to explain CJ's post, too (thanks for chiming in CJ!).

Have I mentioned that I am a just a tad on the OCD side? :wink:

Greg

 

[Target]

Thanks for the kind comments! I do appreciate them.

Here is a link to the video where the Legos are broken down:

https://www.flickr.com/photos/9960539@N07/9388942488/

Here is a comparison video, showing an older mode as compared with the new one.

https://www.flickr.com/photos/9960539@N07/9387620404/

Greg

Greg if time allows please post a vid of the igniters being dipped. This really is a nice technique you came up with

 

[BobH48]

Have I mentioned that I am a just a tad on the OCD side? :wink:

Greg

Wow, I never would have guessed!

 

[GregGleason]

Greg if time allows please post a vid of the igniters being dipped. This really is a nice technique you came up with

I plan to do that in the near future. I need to make up some bridge wires first and then I should be ready.

Greg