I have a question for folks who do aluminum casting more often than I do. I have always tried to do my casting when the relative humidity is 50% or less. In the summer months in Virginia that is pretty hard to do. I got some casting done this past Monday on a cool. dry morning. Things came out alright. Had some small issue with porosity in the parts due to moisture. I did not do any degassing. But I do have commercial degassing tablets I could use. Is there any reason I should not ram my sand molds, using PetroBond a day or two before I cast them? I have enough sand and copes and drags that I could get all my molds ready and wait for a good weather morning. I have some sand cores I have to make for some of these and that takes time that I could be heating and pouring! Please offer constructive advise, suggestions. Jgaertner
You can save those molds for weeks if you so desire. Petro molds do not dry out appreciably in that time period. I have put them aside for a week or two with no bad effects. If you wanted to be extra "cautious," just cover them with foil. I almost always hold green sand molds for 24 to 48 hours prior to casitng them. I usually do put foil over the drag to prevent mice getting in. But I notice no degraded performance (there is theoretical reason to think it might be better) when allowed to dry for a couple days. Ammen talks about baking green sand cores to fully dry them. One caution is that they might become crumbly for handling if that is necessary. Here are images of a green sand casting that I held 24 hours and cast this morning. It is 18" long and 3" high. Weighs a total of 19 pounds with each casting in the pair being a shade over 12#. Some may not recognize the 2" square portion of the sprue as containing a ceramic filter. These were cast with a matchplate. The fin is .050 thick. Denis
Thanks for the feed back. I am encouraged to try this. We are supposed to have lower humidity on Monday, so I could ram all my moulds Sunday and cover them up, as you suggest. I have never had mice but I have had bees go into my rammed moulds before pouring! I will report back on this thread as to how it goes for me? Jgaertner
I did not say so until I edited my post above that this was a green sand casting made from a mold held 24 hours. If my green sand can handle 24 to 72 hours (the longest I've tried so far) storage, your petrobond can go much much longer without concern. Pack one today and then do one Sunday. Pour them side -by-side on Monday. I will be amazed if you can detect any difference. Denis
I've let PB moulds sit for 3 weeks before. I have to put plywood on top to keep the neighbors cat from walking on them. Most often, I ram the night before so I can pour early morning.
