Metal Casting Zone

Hi everybody,
This is my fist time posting a question so please bear with me.
I have built my furnace, set up my foundry and have been practicing ramming my molds. I have made several pours but I keep having the same problem.

I am trying to reproduce a cast aluminum dutch oven (the origianl mfg is 20 years out of business). It is rectangular in shape about 5 x 9 inches and has nice sloping sides which provide about 5 degrees of draft and is about 3 inches in depth. It also has legs on it that are about 1 inch high.

I am using 1/2 inch dowel rod to form my runners and gates. I have a 3/4 inch sprue and the runners are connected to the sand trap at the base of the spure.

I am trying to cast it upside down so the legs become vents. When I pour it I am getting nice smooth side walls both inside and out but I constantly have holes in the bottom. I have tried venting in the center and have even tried numerous vents but I always end up having holes between the vents . The holes have smooth rounded edges and are now about 1/2 to 3/4 inch in diameter (although not round).

I have tried longer melt time in the oven (thinking I was pouring too cold) and pouring faster incase I am just taking too long and having the metal freeze without making a complete mold. No luck so far.

Can someone give me a clue as to what I'm doing wrong?

Thanks in advance

Hi Pendragon56
Sorry you are having casting troubles ,These are the trying times when we learn. I not a experienced sand caster by any means. I cast resin and spin cast. However with what you describe here your casting is not able to fill because the metal is traping the air ,,all casts ok but traps air between the legs. Have you tryed pouring the sand mould while the mould is tilted on a slight angle,to one corner. Pour your metal into a sprue located at the lower side of the tilted mould and vent at the high corner. As the metal pours into the cavity air is pushed up to this highest corner ,if one of the legs or air vents are positioned at this location you won't lock air into your casting ,which sounds like your problem.. I make resin moulds and design them to be on a tilt when they are poured so that air is pushed out infront of the incoming resin. Same principle. If the mould is poured flat than ram up the sand mould with the item on a tilt. Did you also place vent holes in the top cope section of the mould??? Hope this helps ,,Others on this site may be more help...JOHNCAST

Hi Johncast,
Thanks for your help.
I have tried tipping the mold but only one end, I never thought of just tipping a corner.

I have what I call my sandbox or sand bed that I set my mold in so if I have run out it goes into the sand bed and is harmlessly captured. I banked this bed so the mold is tipped a little on its long axis with the sprue at the lowest end, but it is only a slight amount, say about 2 to 3 degrees. Do you recommend a greater tip angle?

All of the vents are in the cope section. Because of the way the oven was originally made there is almost nothing in the drag. I basically make a shallow drag (about 2"that becomes a flat bed. I then dust the oven, fill it with sand (petrobond)and flip it onto the bed and tap it in. This gives me a nice rounded top on the oven walls and marks what I consider to be the natural parting. I then place my runners, one directly into one of the short sides and then one on either of the long sides so the metal can enter on 3 of the four sides. I'm not sure this is the best runner / gate configuration but it has gotten me this far and I'm open for suggestions.

Here is a picture of one of my tries.


I also have pictures of another of my casting attempts in my profile so you can see what I mean and how the runners are set up.

I will probably try another pour tomorrow and I will try tipping just one corner and place more vents in that corner.

Thanks again for your help

you might also ant to try a 1/8" vent (whistler) in the middle to help get some air out. is this the same spot you keep having trouble in?

Hi aonemarine,
So far I have tried a wire size vent (about 1/16" an 1/8" vent (brass tubing) and a straw sized vent (about 1/4" in all kinds of locations. Problem is that the hole / holes never seem to be in exactly the same place twice, it's like trying to hit a moving target.

Here are the pictures from todays pour.




I had a little sand drop out of the cope that screwed up one corner but I can fix that. But as you can see I put several vents in and it still had holes. I'm beginning to think there's intelligent life in these gasses!!!

Sorry about that I'm still trying to figure out how to attach multiple pics.

Here is the second picture with the venting.

id say it is definetly fighting you a bit, time to fight back! it looks like it is having trouble with cold shuts probably because the casting is thin. try taking a nail and pushing it into the sand untill it hits the pattern, space these about every 1" apart, this will help venting. you may also need to add more and larger runners to help keep the temp and flow up. Its looks great other then the holes in it, looks like you are ramming it very hard and getting a great surface finish.
Nice project, keep us informed of the results.

nice project . put your sprue in the middle and use your legs as vents....should come out ok. the only problem is that you will have a sprue mark to polish out.

I know this may be a stupid question but since I've never heard of cold shuts before, are you using the nail to make vents or do you leave the nail in the mold during the pour?

Thanks for the help

Hi Xlchainsaw,
I thought about doing that but won't I have sand erosion and such without a basin at the bottom of the sprue? I'm ready to try anything to make it a repeatable pour. You guys have been great. It may take me a couple of days to try all the suggestions.

Thanks