Wetting of Comp For Pumping Stars

[OldMarine]

Is there a standard percentage of water to begin with for wetting comp to be pressed in a star plate? My charcoal comps took up to 6% to get them barely damp enough to press but I ruined some Spanish Blue by over-wetting at only 3%. I've not pressed enough to "have the feel" of the comps yet and am about to press some of Ofca's Illuminating White and don't want to screw it up since I don't have a ton of the 809 aluminum.

 

Here's the formula courtesy of rec.pyro narkive:

 

White Illuminating

BaNO3 54%
KNO3 10%
Al, Dark 20%
S 8 %
H3BO3 2%
Dex. 6%
Solvent 25% Alc./H20

[dagabu]

Is there a standard percentage of water to begin with for wetting comp to be pressed in a star plate? My charcoal comps took up to 6% to get them barely damp enough to press but I ruined some Spanish Blue by over-wetting at only 3%. I've not pressed enough to "have the feel" of the comps yet and am about to press some of Ofca's Illuminating White and don't want to screw it up since I don't have a ton of the 809 aluminum.

 

Here's the formula courtesy of rec.pyro narkive:

 

White Illuminating

 

BaNO3 54%

KNO3 10%

Al, Dark 20%

S 8 %

H3BO3 2%

Dex. 6%

Solvent 25% Alc./H20

 

No, there is not. Charcoal comets can take up to 20% water and like you found out, some can only take a couple percent. I have a small comet pump with a delrin plunger, I just add enough water to get some clumping when run through a 10 mesh screen and press one to see what it looks like. I usually hit it right on with this method.

[OldMarine]

This comp is so fluffy its got me nervous. I see it going from dust to mush very quickly. Aww well, live and learn.

[Mumbles]

I find it a little unlikely you ruined a composition by overwetting with 3% water. I've always started around 6% water, and routinely go to 12-14% for charcoal heavy compositions when pressing with an arbor press. With higher pressures, you can get by with less water, but you're into the hydraulic or pneumatic territory there.

 

I normally press compositions with high flake aluminum content with thin wheat paste actually. 10-12:1 water to instant paste instead of 6:1 or so for pasting. It makes the composition handle very nicely actually and you don't risk overwetting nearly as much. The liquid soaks in pretty well, maybe with a touch of alcohol.

[OldMarine]

Mumbles, I assume I ruined them because upon pressing I had "juice" running out of the plate and after drying they burned feebly.

I don't recall adding more than 3% water (it's not in my notes) but anything's possible.

Edited August 3, 2016 by OldMarine

[Maserface]

That's really odd, and if you didn't measure incorrectly, the only thing I can think is that you are pressing WAY too hard.

 

I pumped some green comets the other day with about 8% and they still felt quite dry.

[Merlin]

Mumbles, I assume I ruined them because upon pressing I had "juice" running out of the plate and after drying they burned feebly.

I don't recall adding more than 3% water (it's not in my notes) but anything's possible.

Are you pressing with a hydraulic press? This year I pressed crossettes with a hydraulic press and though the comp was not over wet when you get the pressure up to around 6000 psi you will get water squeezed out at the base. Still they took a couple weeks to dry at room temp and then overnight in a drying box. They would break before being dried with only hand pressure and burn poorly. Once dry they were as hard as brick and when fired they burned longer than pressed with a arbor press I assume because the comp was more densely compacted . They performed very well but they did have water pressed out at the base.

Edited August 3, 2016 by Merlin

[dagabu]

Good point, I have a notebook with my pressures on various comets and it seems that any given comet needs to be pressed at a certain pressure for a certain dwell time. Example: W39-J crosettes will take 2200 LPI, no more and not much less if water/dex bound but max out at 800 LPI with phenolic resin/alcohol.

 

Take good notes and test, test, test.

[Mumbles]

Mumbles, I assume I ruined them because upon pressing I had "juice" running out of the plate and after drying they burned feebly.

I don't recall adding more than 3% water (it's not in my notes) but anything's possible.

 

 

That's fair, and mostly why I said unlikely. It seemed off, but not impossible. I've included some hints I use. They're more directed toward glitters and streamers, but there might be some helpful info for colored stars as well. I do use an arbor press, and generally am pressing individual comets between .75" and 1.5", so you may need to adjust for a smaller star plate or different press.

 

One thing that has always helped me was "tempering" my wet composition. I mix in whatever I feel like starting with (6% for colors, about 8% for glitters, and 10% for streamers), mix it as well as I can with my hands for 5-10 min or whatever, and punch it down into the bottom of my mixing bowl into a relatively solid mass. Passing it through a 16mesh screen or so can help to get it distributed if you're having trouble. Toss a lid or a cover on and let it sit for 30min or more. Some let it sit overnight. This gives time for the water to permeate the composition, ensure everything is equally wet, and activate any binders. This is particularly helpful for high charcoal compositions. It seems like the charcoal initially soaks up the water, and then slowly releases it back out over time. This is one of the reasons that those compositions can be easy to overwet.

 

After tempering, break it back up, and screen it through a 16 mesh screen again. This helps with even loading of star plates and comet pumps. Press a tester or two. This is where the feel comes into play. They shouldn't be crumbly, but also shouldn't be soft or sticky and especially not sagging. They'll be firm but fragile. I liken it to unfired clay. The consistency is different, but it's the best analogy in my mind.

 

I do tend to low ball the water, so they rarely if ever come out too wet from the start. If they are not wet enough, I adjust with a spray bottle until just right. You can monitor the moisture content with a scale, but the exact proper moisture amount seems to change day by day. After the composition is tempered, it takes in water well and there's no real reason to repeat in my experience.

 

The last thing that helps me is keeping a clean pump. Crossettes can be a nightmare with chipping around the cavity and around the edges of the comet. I use an old toothbrush to knock off any build up, and spray occasionally with release agents. This can be silicone or teflon spray, or even cooking spray. This is likely less of an issue with drier compositions that can handle higher pressures.

[dagabu]

Me too, I usually get two good crossettes and one chipped one. Toothbrush and a dip in graphite works well for me.

[OldMarine]

Okay, I followed Mumbles and Mike Swisher's advice (which meshed almost exactly) and I must say these stars came out better than any I've pressed thus far. Kept copious notes and weighed the comp at each addition in case it was the last. It took 12% to get this comp to the brown sugar texture I was looking for. Thanks all for the help!

 

 

By the way, I do have a 6 ton hydraulic press and put 2200 on the comp which seems to be plenty.

Edited August 4, 2016 by OldMarine

[Mumbles]

I'd like to say that great minds think alike. In reality though, I've learned so much of what I know from listening and talking to Mike and other fantastic fireworkers.

[OldMarine]

A Humble Mumbles is a good thing to see amongst so many giant egos in this hobby!