hashashan Posted December 12, 2006 Share Posted December 12, 2006 Hi, Anyone tried to pump stars with THF/PVC or NC laquer? i just cant get them pumped, the mixture is so sticky that the air cant get through and they dont get pressed anyone managed to do it? Link to comment Share on other sites More sharing options...
Mumbles Posted December 12, 2006 Share Posted December 12, 2006 I know people have pumped NC bound dragon eggs before. With pumping the key really is to use as little wetting agent as possible. For comets 6% is generally the standard. Some require more, and some less. I've heard of pressing very large comets with 4% moisture and being able to fire them day of pressing. I'm sure you could use both of the agents you described for pressing. THF/PVC would be easier. Add all your PVC and add 6% THF, kneed together and press. Link to comment Share on other sites More sharing options...
ltf Posted December 12, 2006 Share Posted December 12, 2006 Should try close to home first don't you think? hmmm used NC liquer with PVC (the PVC was in the stars composition obviosly, there was a low precentage of NC in the liquer in order that more PVC will dissolve) they wern't rock hard but still suitble for working easily. *posted just with Mumbles, sorry, my post is not necessary anymore. Link to comment Share on other sites More sharing options...
Mumbles Posted December 12, 2006 Share Posted December 12, 2006 Don't wory about it. The info you provide is still good and useful. It's always good to get a first hand experience report. Link to comment Share on other sites More sharing options...
hashashan Posted December 13, 2006 Author Share Posted December 13, 2006 the problem is that i cant get a homogenus mix with THF unless i get it too liquid and then i can press. as soon as i add the THF the PVC disolves in it and creates lumps Link to comment Share on other sites More sharing options...
Mumbles Posted December 13, 2006 Share Posted December 13, 2006 Perhaps try spraying the THF onto the comp and kneeding it. More than likely you're pouring it in and dissolving some PVC and just creating a lump of comp that is dificult to break up. You must also kneed it. This may take a while depending on the solvent-binder system. Link to comment Share on other sites More sharing options...
hashashan Posted December 13, 2006 Author Share Posted December 13, 2006 thats the problem with THF, it will disolve pravcticaly anything .. therrefore i cant spray it Link to comment Share on other sites More sharing options...
FrankRizzo Posted December 14, 2006 Share Posted December 14, 2006 The best plan would be to place the mix in a polyethylene container like a Ziploc freezer bag and then add the solvent. Leave it sit for a few minutes so the solvent can permeate through and then kneed it through the bag to achieve homogeneity. I frequently use this technique to make glitter and whistle mix. Link to comment Share on other sites More sharing options...
Mumbles Posted December 14, 2006 Share Posted December 14, 2006 The problem with that is that polyethylene of all sorts is not resistant to THF. My best advice is to to make some dextrin and save the THF for more fun projects. Link to comment Share on other sites More sharing options...
hashashan Posted December 14, 2006 Author Share Posted December 14, 2006 The mix contains magnesium and i dont want to coat it. but what if the mixture contains stuff that will react with water even nastier then magnesium, and besides dextrin will ruin a bit the color making it paler Link to comment Share on other sites More sharing options...
DeAdFX Posted December 14, 2006 Share Posted December 14, 2006 Use different solvent like methylene chloride or methyl ethyl ketone{MEK}. Both should be fairly easy to find.... You shouldn't have to much trouble finding MEK Link to comment Share on other sites More sharing options...
hashashan Posted December 14, 2006 Author Share Posted December 14, 2006 They are not hard to find at all but they also dont dissolve PVC. THF is the only solvent that really dissolves PVC Link to comment Share on other sites More sharing options...
rocket Posted December 14, 2006 Share Posted December 14, 2006 MEK dissolves PVC that’s why it used as a primer before for gluing. Acetone should as well. Mind you I may be wrong as I have never used pure PVC. Link to comment Share on other sites More sharing options...
hashashan Posted December 14, 2006 Author Share Posted December 14, 2006 MEK and acetone dissolve PVC very poorly, it slightly liquify it, however if the PVC is dissolved in THF it makes a fine paste and the stars then are rock hard just like PVC pipes. and yes .. THF is considered the only thing that dissolve PVC good-enough Link to comment Share on other sites More sharing options...
FrankRizzo Posted December 14, 2006 Share Posted December 14, 2006 The problem with that is that polyethylene of all sorts is not resistant to THF. My best advice is to to make some dextrin and save the THF for more fun projects. According to my ASTM guide, THF has fair compatibility with LDPE at temperatures up to 120F. Continuous contact (days) will cause softening. Of course, ziploc bags are only a mil or two in thickness so they may soften at a faster rate. Link to comment Share on other sites More sharing options...
Mumbles Posted December 15, 2006 Share Posted December 15, 2006 The reference I looked at gave the same resistance at 20C and 60C. It said it could cause swelling, softening, and stretching. It was specified for PE tubing, so maybe the additives are what cause it. My university references wern't working the other night so I couldn't check any proper resources. Link to comment Share on other sites More sharing options...
Pyroman2 Posted December 16, 2006 Share Posted December 16, 2006 I know what you are talking about, Hashman... I did some stars with PVC and I use THF as the solvent.The mix - green stars (barium nitrate, Mg, PVC) after THF is added, and the comp. for stars gets gooey. I can't imagine, how you could pump this stars :|It is very hard to press this composition, so I just cut the stars.Maybe if you first dissolved PVC in THF and then add this solution to the mix, it would help you. You have right, acetone isn't good solvent, I try used NC lacquer.. and pumped stars weren't too hard. sorry for my english, Regards Pyroman2 Link to comment Share on other sites More sharing options...
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