Bad casting! Beginner problems

[jpfalt]

The problem with pouring into the back is that the metal flow will wash out the detail on the front of the plate.

Using a runner all around the part with gates spaced around the edge of the part would help, particularly if the center of the back of the part is heavily vented. Increasing the cope thickness to increase the metal pressure in the runner will also help.

[Fender]

If it's any consolation, I have some locomotive builder plate castings that are 2/3 filled, just like yours. I think you're on the right track. If you do all the things suggested and still don't have success, then put a 1/16" backer on the plate before molding.

[oldgoaly]

use some double sided tape to add a 1/4" thick plywood to the back of your plate, also try a riser on the opposite side this gives the air in mold a way out. More runners to the plate. The metal is cooling / solidifying before it flows thru the plate. Thin castings are a pain, here is some of my castings that didn't flow right, they would probably work in cast iron. I haven't tried heating the molds, but that maybe an option. http://www.mediafire.com/?afkkpqwzki1rz
tt

[Fender]

I guess the no vents needed with Petrobond may be not quite accurate, huh?

OK, this is a terminology thing. "Venting" a mold is done by making a series of holes, usually with a stick or wire. When a mold is vented, the molder jabs the stick or wire into the sand multiple times in the cope (top half) and in the drag (bottom half) from the outside, but not quite penetrating into the cavity formed by the pattern. The idea is to allow the steam from the sand to escape, but not allow the molten metal to run out.
A "riser" is a hole in the cope which connects the mold cavity to the outside, allowing the metal to come up the riser when the mold has been filled with metal. Petrobond doesn't have any water in it, so you don't need to vent it. But you may well need a riser, either to let the air in the mold escape quicker (such as for your casting), or to feed the casting as it cools (in the case of a casting with a heavier cross-section).

[jpfalt]

To clarify,

Venting is done with a wire, anywhere from 1/16 dia up to 1/4 inch. It isn't intended to actually penetrate to the mold cavity, but to improve ability of gasses to go through the sand.

A riser is connected to the mold cavity with a large gate and is intended to feed metal into thick casting sections as the metal solidifies and shrinks as it cools.

A pop-off is also connected to the cavity in the mold, either by coming off the upper surface of the cavity or from an edge of the cavity through an exit gate that lets gasses and metal exit the mold cavity. An other reason this is done so that any loose bits of sand can carry out of the mold and not make a surface defect in the casting. When you pour into a mold with a pop-off, you actually want to see some indication that the metal has come back up the pop-off.

[Fender]

Hmmm, another term to add to my vocabulary: pop-off. Hadn't hear that one.

[oldgoaly]

Venting I've seen more in green sand to combat the water/steam given off by sand, oil sand makes smoke tend not to create pressure like steam can. tt

[Harold_V]

Hmmm, another term to add to my vocabulary: pop-off. Hadn't hear that one.

It would be nice if Jim explained that one for us. I have a keen intereset in foundry work, but no practical experience. There's much I have to learn.

Harold

[drillpoint]

First off thanks for all the input. At this point I am getting well into the learning curve and I am keeping records as Steamin 10 suggested. Venting or rather lack of it, does not seem to be the main or even a major problem. And feeding from above, in this case, does not appear to be a problem with washout of detail. I have tried to keep the changes to somewhat of a minimum in the hopes of isolating the main causes of failure. I have several more pictures here showing 3 more pours. Large venting was used in all 3. A taller stack on the sprue did not appear to have any noticeable positive effect. Adding 1/4" to the plate did result in a complete plate as I suspected it would so then I tried about 1/8th " plate added above. This was the last attempt and it had huge vents at the outer corners which were of no help at all. The detail in this one is about as good as I am hoping for but the backing plate needs to cover the entire area. I will try some huge runners and gates on the next try without adding thickness. I still haven't tried the alcohol and heating the mold yet. This bronze has a great color, even better than silicon bronze I think and it doesn't create any slag, dross or whatever. Now if I can only get it flow at 1/32" .... Doug

[drillpoint]

This is the last attempt

[Harold_V]

Can success be far behind?

Harold

[oldgoaly]

Getting better! Good luck!