Solved the sticking problem with Monocapa, but in a strange way :)

[MinamotoKobayashi]

As You remember, I had some issues to stick a prime layer around a red and green phenolic resin based stars pressed with a star plate.

The smooth and compact star walls prevent the prime to stick correctly around the stars.

Mr. NeighborJ insists to tell me that the only way to stick a prime aroud these kind of stars is make the stars cutted and squared.

And he was right, but it my modest opinion to place squared stars inside a rounded shell is the same thing to try to sit a squared ass in a

rounded toilet (excuse me for the silly comparison LOL).

I want to thanks a lot some users in this forum for some useful hints: NeighborJ, Oldmarine, Mabuse00, Baldor, Mumbles and MrB.

First of all I did the fantastic Monocapa prime. Since I do not have some chems yet, I replaced black iron oxide with red iron oxyde, and

230 mesh MgAl with 325 mesh MgAl. As charcoal I used a ballmilled airfloat charcoal that I have made from lumpwood carbon pieces

(slow burning charcoal used for willow stars).

The prime seems to works well anyway.

Then I wetted the dried Green and Red stars with a spray bottle containing 50/50 demineralized water/uncoloured denhatured alcohol.

I wetted them until the edges slightly began to crumble.

At this point I putted a lot of wetted stars inside my Lortone rock tumbler and floured them with a tea spoon full of Monocapa.

I started the rock thumbler only with one plug on and without closing with any screw, to have fast access to see what happens inside.

After 2 minutes I opened the plug, floured the stars with another tea spoon full of Monocapa and started the thumbler again.

The continue tumbling of the stars one against the other created in few minutes a rock solid prime around the stars, that in meanwhile

became rounded.

At a certain point the stars becomed dried enough and the surface becomed opaque and rough, with small but numerous protuberances.

So I slightly wetted again the stars and I started to flour them with hot meal (pine charcoal plus sulfur plus potassium nitrate plus 5% dextrin).

I followed the same procedure of the Monocapa priming and at the end I had these marvellous stars:

The process must be fine-tuned because I had stars with different sizes and most of them doubled their original size.

Besides this, I do not use high-speed stars or boosted shells, so probably the last BP prime is not necessary.

I tried to put about 50 dried stars in a tube mortar filled with some KP and granulated BP to see if the stars will ignite well, and this

was the result:

https://youtu.be/dM3tef1KEA4

Also, I tried to launch the stars against the floor to see how strong will be the prime, and the prime broken down only after the second try.

Now the final test will be made with the stars inside a 4" shell, stay tuned.

Every comment, correction, suggestion and disappointment will be appreciated!

Edited April 4, 2018 by MinamotoKobayashi

[Baldor]

Glad my comment was useful, even if wrong. :-)

 

Mumbles said in the other thread 50/50 water alcohol is not a good idea, and if mumbles says it, I believe it. Why not use only alcohol on the stars, and then let them dry? Move them around over a sieve while spraying. This should create some rugosity. if you then use a phenolic or NC binded prime as the first layer, you should have your problem solved easily. Maybe just BP with NC instead of dextrin.

[MinamotoKobayashi]

Hi Baldor.

Unluckly I have so much containers and powders that I do not want to create another one,

so I will use the classic BP meal, the powder separated from the rest of the 2FA granulated BP (-20,+8 mesh).

I'm forced to use both water and alcohol because if I wet the stars with only alcohol, the stars quickly become

soft and crumble during layering processing.

The ideator of Monocapa write this very interesting PDF:

 

http://www.pyrobin.com/files/Spanish%20Info%20.pdf

 

and at the end he suggest to use at least 63% of water in the mix, so in the next batch I will use

63% water and 27% alcohol, and black iron oxyde of course

[MadMat]

I missed you first post. Here is my suggestion for future reference; whatever you use for a binder/solvent for the star should at least have a similar solvent for the prime. The solvent for your prime should be able to "eat into" the surface of the star. This will give the best adhesion.

Edited April 5, 2018 by MadMat

[Mumbles]

For what it's worth, 2FA is -4+12. What you mention is closer to 3/4FA. 3FA is -10+16, and 4FA is -12+20.

[kaotch]

Minimota the easiest way to overcome your "non sticking" problem is to make a slurry of your prime with the binder of your choise .Dump some stars in and make shure they are totally covered with prime slurry remove the stars from the slurry and dump in "dry" mealpowder and gently shake/roll or whatever , until they are totally covered with mp. In fact this is a toro application without a starroller. Works all the time. Stars bound with phenolic resin ,pvb,dextrin and sgrs can be handled this way.

[MinamotoKobayashi]

Hello to everyone and thanks for all the suggestions!

I listened to all the members advices of this forum, and now I refined a method that seems to work very well.

I putted my cylinder shaped smooth stars inside my rock thumbler (half barrel full and without any media), and I started it for some minutes.

The stars have lost some mix, expecially around the edges, and some powder was visible inside the barrel.

At this point I sprayed a mix of 63+27 inside the barrel and actioned the device again.

Pure alcohol or acetone do not work because the stars absorb the liquid instantly and becomed soft and easily crushable.

I need to have a slightly wetted star that has enough time to grab the powder before they become completely dried.

The stars becomed slightly rounded and slightly rough.

Now, every tot minutes I opened the barrel, sprayed the mix, and putted one/two tea spoons full of Monocapa, closed the barrell

and actioned the device again.

This process vaguely remind me the step prime method: a scalar mix of some star compound and some prime

After some steps the stars created a smooth strong Monocapa layer around them.

Then I stopped to spray the liquid mix but I continued to insert the Monocapa mix: at a certain point the stars becomed dry and rough.

It is important to check often the stars state to see when they are rough enough. In fact if I insist to roll the stars, they becomed smooth again.

At this point the stars were ready to accept the hot BP meal prime as last layer: same procedure as above, and the result was this:

 

 

I am very satisfied of the result, I will try the shell asap!

Edited April 9, 2018 by MinamotoKobayashi

[CrossOut]

ned Gorski will dunk his pressed stars into 20% dextrin water solution then puts them into his prime and shakes. prime adhears nicely to the stars. alternatively you could make a 20% nc prime slurry and coat your stars with that. nc will soften the outside of your stars but will also create it's ono surface to bind to.

[bengalPyro2000]

I face big problem I used 90%bp+5% charcoal +5% Dextin mixed as a prime for

Barium nitrate and Strontium Nitrate green and red star when I dry at sun they become rock hard but after spend the night they become minor wety and lost the hardness

Plzz tell me what was the problem???

Oh I used 5%-8% 200 mesh MgAl for my prime mixture.

Plzz help

[clarkie752]

It is possible your stars absorbed some moisture from the air overnight. Barium and strontium nitrate are very hydroscopic. Try drying them and then storing them in a ziploc baggie with desiccant packets. I personally have never had this problem before but some people that live in humid climates do.

Adam

[MrB]

I'm thinking sun dried might mean hard, dry shell, soft wet core. Split a star and find out?

[Mumbles]

I've never found barium nitrate or strontium nitrate to be very hygroscopic if they were pure. I suspect that is probably the issue here.

[OldMarine]

Barium is by no means hygroscopic but strontium nitrate sucks up moisture. I dry it before making a comp and if dextrin bound dry it as long as I would a charcoal comp.