What happened here?

[Rasper]

I had some defects in the recent pour of "The New Girl". I have some ideas about what happened. What do you think?



Her other side has little of that "rash".



I accidentally broke the brushed on investment off of her knee so the knee had the poured investment only. The difference is obvious; the surface texture is rough due to the coarser poured investment, and there were air bubbles which you can see, but there is none of the black rash.



My two primary ideas are that either I poured too hot, or that I didn't quite burn out all of the wax residue. I tend towards the insufficient burn out theory, and that the brushed on investment of plaster and silica flour held the wax residue longer than the poured investment since it is less permeable to air.

Richard

[F.C.]

I see a variety of things, i.e., metal may have poured too hot, unburnt wax residue reaction to metal contact, inclusions, air bubbles, cold shuts/or inadequate venting, and in my opinion the pour may have been too turbulant during the fill within the mold void which caused what appears to be developed dross to occur due the turbulant action that caused flaring of some of the metal's alloys due the metal temp being too hot at initiation of the pour. Without seeing how the product was gated it's difficult to determine a more precise theory as to what caused all the defects. Some are relatively obvious but... there are more things that may have caused similar reactions in the mold aside from just possible inadequate gating and/or reaction to unburnt residue. One thing you must always lean toward is complete burnout of all combustibles within the mold, AND... pour your mold while it is still virtually too hot to handle by bare hands.

[F.C.]

Very nice work, by the way... how big of a casting is this?

[Rasper]

She is 16 inches long. She is cast in Everdur. I heated the metal to 2300 F. and of course lost some of that in getting the crucible to the shank and the pouring. The investment mold was probably about 1000 F. when I poured it.

I poured her feet down, bottom fed. I always use bottom feed to avoid turbulence. There were gates to the soles of each foot—two gates to the lower foot. I also had a gate half way up. You can see the stub of it under her butt. It is attached to her crotch and goes on up and attaches to the inside of her abdomen There was a good sized riser at the top attached to her armpit.

There was some brown residue visible when looking down the main sprue before pouring.

[F.C.]

Sounds like the temp was ok. Your explanation of the knee area sounds logical. Appears your gating (by theory) was a sound choice, odd that it didn't fill entirely at the collar bone area. Was there more to this piece or did you intend to have it without head and arms? My guess about the black rash is due to unburnt residue having a reaction to the metal. Might burnish off with a good wire brushing and some light sanding. Evedure is a good metal choice!! Question, did you "gag" the pouring cup or merely pour into it till you felt the piece had become full? Gagging a cup is important to avoid air bubbles, odd slag that wasn't removed during skimming, etc. It also eliminates unnecessary turbulance during the pour.

You have a nice eye for anatomy... well done!! I do think, though, your work is salvagable without too much trouble.

[Rasper]

It filled the entire mold. That's where she ends. Once you see the base I have made you will get the picture.

I am leaning 95% towards using this as a door stop and pouring her again. To sand off that rash would remove a lot of detail. I had considered applying a liver and a cupric nitrate patina, and then filling the rash in with dark green Bondo, but I want her to be better than that.

Gagging? I carve a slight narrow place in the main pouring sprue maybe six inches below the top of the pouring cup, and I pour as fast as I can without dumping metal all over the place. Is that what you mean by gagging?

Given the lack of black rash on the knee area, I am moving forward with the hypothesis that the brush on silica flour investment coats hold wax residue longer than does the plaster/brick dust investment, and that I must burn these things out longer.

Richard

[F.C.]

Gagging the cup entails this: When you begin the pour, keep the pour spout of the crucible as close as you can to the lip of the pour cup and dump in the melt as quick as possible causing the pour cup to fill entirely to a point where it almost overspills and actually rounds over on the top of the cup and connects with the spout of your crucible and the flow of metal going in, then maintain that capacity till you see one of your risers come up to level with the top of your mold. This takes practice, often (till you master the technique) you will lose metal over the top and cause waste, but eventually you will get a feel for it and it'll become second nature. In doing so, the flow going into the mold will be consistant without any inclusion of air bubbles or dross as the dross will accumulate on the surface of the pour cup and not be drug into the mold with the metal flowing in. That's about as simple as I can explain it. Untill you experience it you may not fully understand. It takes considerable practice, that I assure you. But it's important with all casts you do, regardless the configurationn of the interior cavity. I sincerely wish we lived close enough to where I could show you firsthand. Seeing it happen seems too simple of a method to affect any change but once you see the end result it'll click in your mind why it is necessary. All foundrymen will tell you its importance regardless what it is you're casting, or what metal you're pouring. Never pour from an elevated position where the metal "falls" into the pour cup... this causes considerable turbulance and drags in with it whatever flux is left on top of the melt including whatever dross didn't get skimmed off, plus pulls in air inclusions that can have difficulty floating out the opposite end before the melt freezes.

[mite5255]

Hi Frank. How about we all rock up at your shed and you play teacher

Mike

[mite5255]

We students of cause would supply all after class refreshments

[Rasper]

She's a doorstop. I poured a new wax today.

R