Wife left me, lost my job, dog died.....J/K!!! Not that kind of depression. But it does sound like the start of a country song, eh? Anyway... This is about casting. I have done some casting in brass for my handles and guards and I just got in some Petrobond. ( was using a sand clay mix to start) Things have improved greatly with the petrobond but I am experiencing a depression or crater of sorts in the middle of my piece on the topside of the finished cast while cooling. The brass is filling up the void totally and from the outside, looking at the pour and exit holes, all is good when I stop pouring. But....it settles in the middle of bigger pieces during the cool down. Is there a way to stop this or am I doing something wrong? https://photos.app.goo.gl/whPG35p5jmo23DZM6
Since no one else has chimed in, shrinkage is normal as metal in its liquid state takes up more space than solid state. Are you pouring until the brass comes up the sprue and vent holes? Found this old-school article: https://nvlpubs.nist.gov/nistpubs/jres/8/jresv8n1p37_A2b.pdf
Thanks again Dan, I looked at the link...wow...I got some reading to do. I have a exit hole and a pour hole and I stop pouring when there is a pool of liquid forming around the exit hole. My pour hole is pretty much full and burning with a nice light blue fame at top for a bit. I pour 1 to 2 inches from one end of cast and the exit hole is at the opposite end of the cast as far away from the pour hole as I can get it without going past the cast. Both my exit and pour tunnels are solid when I cut them off. Perhaps I will try either moving the exit hole more to the middle, or add a second exit hole. It's a heck of a thing to just blindly experiment with but.... Thx again for the info.
The pour and exit spout need to hold enough material to help with shrinkage. Mold mass will slow cooling and allow material flow back from pour spout and overflow, preheating of mold will help as well. A longer preheat may be needed which is a easy fix. forgot to add if there is shrinkage between spouts then add in another overflow centered on the shrinkage
Thank you John, I will try increasing the size of my exit hole and put it in the middle or add a second, or both.
