When is the best time to pour after ramming up a green sand flask ? Should it be left to dry a bit or pour soon after prepared ? Thanks, John ,,,,
I think it is OK to let them sit for a day or two. I am not sure how much drying actually affects them. I do know that large unsupported hanging sections of sand may collapse if allowed to sit for a day or two. In other words I have some molds that when left open have sections that are not well suported against gravity. I have had them partially collapse ofter standing a day or two open. On the other hand, I have left them standing for four days closed without adverse effect. I usually do not leave my green sand molds exposed to drying air however. If I know they will sit for a day or more, I usually cover them with aluminum foil. Whether this is needed or not I do not know. I suspect it is not. I have tried a few times to gently torch the surface of green sand molds as I have read this is supposed to be good for them. It has not worked well for me. Denis
Thanks Denis, that's what I was wondering, if it would be good to let the moisture dry a bit or not. I'll be pouring small items with not much thickness, height, or width. Mainly concerned with the moisture at pour. I'll be venting flat and vertically. Thanks again for your hep,,, John
In the past I let some green sand mold to pour the next day. I put a cover in the sprue in case a bug thought it was a new house to live in. Most probably, unless the weather is humid, some moisture may dry out. That's a good thing as long as the clay can hold the mold in shape. If sand particles are found in the casting surface it was too dry and the sand was washed away.
Almost everything I've cast to date has sat overnight with a cover over the sprue before casting in the morning. I suspect my sand has too much bentonite and too much moisture due to issues with ramming but so far nothing has blown back out the sprue and the aluminium castings are all good (fingers crossed). My sand sets pretty hard in the heat affected areas too, so again, maybe too much bentonite.
Isn't one of the bentonites supposed to be good for dry strength? I guess molds made of sand with more of that type of bentonite should hold up better if you leave them to dry out a while. A friend of mine was saying he sometimes lets his sit for weeks even... I never let one sit longer than overnight that I can remember. Jeff
Thanks guys, I'm usually in the shop till late, 10-11 pm. I'm thinking I'll get the mold ready and let set till about 2- 3 pm next day, that way maybe a bit of the cavity surface might dry a bit. I'm using sifted adobe/sand, it sets pretty hard.
My experience has been the sand will dry out and become more brittle which can result in inclusions due to gate wash and even run out if the casting is too close to the side of the mold. I prefer to pour them asap.
we did the same in the Navy, though occasionally someone would ram up in the evening for a morning pour , so 8 hours max V/r HT1
