Importance of baking time and temps.

[Fernet]

I used to be very dissapointed with the toughness the powder paint got after baking when following the suggested time and temp(ca 15min, 200 C). Perhaps the temp on the oven was off some. I don't have a termometer to check how warm it actually is in there. The jihheads only got marginally tougher than without baking.

So I tried to turn the nob down to 150 C(way below recommended time) and left the jigheads in there for one to two hours and damit. The stuff got hard. I can now hit it with a hammer and the shape of the jig gets deformed but the paint stays intact. I bend shatterblades 70-ish degrees without a crack. It was miles better than I could have ever imagined it could be.

Now, should I even bother with the recommendations or will that make things noticably tougher?

Thanks

[triplextackle]

temp at 200 is to low

should be 350 for 15-20 min

[psv]

triplextackle

150 C = 302F

200C = 392F

I usually bake at 350 for 20 minutes and never have any problems.

[Ogajiga]

"Fernet", a customer reports good results baking at 250*F for half an hour with 7-1 bismuth-tin alloy heads. I think even 300*F might be do-able with Bi90 Sn10.

[triplextackle]

WOOPS I SHOULD READ MORE CAREFULLY, BEFORE I REPLY . DIDN'T CATCH THE C

[Fernet]

I see now that I used too much heat before, hence the poor results.

Hawn, I actually do bake the 90-10 at ca 300F. Very tiny "sweatdrops" appears on about half off them but they are no problem to remove with the thumbnail. They sit on the surface of the paint, making no scars after removal. Just one or two per jig so not much hassle.

Hawnjigs, I'll throw in a huge thanks for leading me in and helping me out with the BiSn business. Here goes:

Thanks mate.

[Ogajiga]

"Fernet" thanks for the info on "sweating" at 300*F. Given the 520*F melting point of bismuth I don't understand why a portion of a high bismuth alloy can apparently melt at the 58-42 eutectic temp of 281*F, perhaps "sagacious" can help?

[sagacious]

"Fernet" thanks for the info on "sweating" at 300*F. Given the 520*F melting point of bismuth I don't understand why a portion of a high bismuth alloy can apparently melt at the 58-42 eutectic temp of 281*F, perhaps "sagacious" can help?

Hawnjigs, you've pretty much nailed the answer. The tin/bismuth eutectic component of the alloy is the sticky wicket. That component won't form what's called a "solid solution" with room-temp bismuth. So, at lower temps, only some of the Sn/Bi eutectic will melt-- but not the rest of the bismuth. As the eutectic melts it expands and some of it 'sweats' out of the alloy forming small silvery beads on the surface. In some high-tin alloys this common, and in this case 10% tin is plenty to cause this phenomenon. It can also often be seen upon melting tin/lead alloys that contain more than a few percent tin, especially simple binary Sn/Pb alloys.

Usually, if you reduce the heat the silvery beads will cool, contract, and collapse back into the base metal matrix. In the case of a jighead painted with powderpaint, the eutectic sweat bead(s) form and extrude through the softened powdercoat. As the powdercoat cures, it seals and cuts off the 'escape route' of the liquid metal bead, leaving it stranded on the surface of the painted jig.

Your metallurgy 101 quiz is over, students. Time's up, pencils's down!

[Ogajiga]

Thanks, "sagacious", for clarifying the thermal instability of Sn alloys. I've experienced that Pb90Sn10 is somehow the optimal alloy in one (& only) of my tuff pour molds. Guess I'd better heads up on the 361*F eutectic border of that one too.