Burning of wooden flasks seems inevitable but is also somewhat wasteful of time and resources. So, I got the (bright?) idea to try increasing the resistance of my wooden flasks by using aluminum flashing. I had made and used several times one 3-flask set for iron casting a 20 pound pour of iron. After one ot tow pours I noted a few of the most vulnerable areas and tried putting common and cheap aluminum gutter flashing on those few areas. That seemed to help, so when I made a second set, I used the first set's char marks as a guide as to where I should apply flashing tacked in place with flat-head nails. I used the flasks today and it looks like the flashing will really make a big long-term difference in flask durability. Attached are a couple pics. The right corner of the new flask might look like it is shielded, but it is really just sprayed with silver paint for purposes of providing up/down and rotational orientation markings. The charring on the left close corner of the flask is due to proximity of the crucible when pouring. I will sheild that area soon. You can see that the new shielded flasks charred minimally. Charring that occurs in the unshielded areas is due to coal-gas flames that occur for a few minutes after pouring. Denis
Blocking radiant energy is the key! I suggest galvanized flashing like I use. It stays in place by gravity and keep the flasks clean. I've been doing it since the beginning. Roof metal drip edge would work great too but I've got lots of drop laying around. Edit: Sorry I missed the point that you were shielding for the hot gas escaping between flasks. I'm only dealing with radiant energy from the crucible.
I have two snap flasks but have not found the time to make a close fitting metal jacket. Maybe it does not need to be close fitting. How much gap is appropriate? I was thinking 20 ga steel. I do like demolding out of a snap flask.
For just protecting the edge of the the flasks from the heat of the crucible I have often been using aluminum foil. As thin as foil is, it does reflect radiant heat well enough to nearly eliminate burning. But did not do it on this flask for some reason. But, I like just applying the flashing once and being done with it. I also use flashing inside the flask as as large masses of iron have enough heat to actually burn the flask from the inside out. I hammer the flashing to give it some "tooth" for the sand to hold onto.
