New problem

[Cherokee]

OK, here are some pic's from this morning's attempt. Still have the little pocket but there appears to be an irregularity on the hinge side of the 6th cavity. Several pics:

#1 Cast that cavity only, note odd shape on hinge side near the parting line

#2 Can see the irregularity

#3 The offending depression

#4 Trying to show the irregularity on the hinge side

No petroleum solvent, soap & water with tooth brush for cleaning. Casting in heated indoors, about 69*, the same as summer with the AC going. Preheated on hot plate with the blocks closed.
That cavity is the last one poured, and it does look like it is not casting a good body like the other 5 cavities. Now that it's cooled down, I'm going to examine it again.

 

[Dusty Bannister]

Sure looks to me like whatever you use to lube the sprue plate has migrated into the cavity. When the mold is dry, wash well with brake cleaner or acetone which leaves NO oil residue. Not sure what you are using for lube on the sprue plate hinge, but use less and apply more often. With all those surface bubbles on the casting, it sure looks like you have oil residue off gassing. Fix that while you are at it and maybe leave the blocks open when heating so that stuff will be driven off. Are the blocks coming fully together, or did you lightly stone a little off where the mold blocks come together under the sprue plate to aid venting. If the blocks do not open easily when heated, but not filled, you have something binding and that needs to be addressed too.

Take a good look at the bottom of the sprue plate and see what is built up that will interfere with the cavity as well. I think that is most likely your source of trouble.

 

[Cherokee]

Good thoughts Dusty, I scrubbed the cavity again with soap & water for another test. Mold is heating again right now. The lube is Bullplate and I use very little, its just built up some over the many casting sessions, I cleaned all that off as well. The sprue plate bottom is smooth and free of specks. Blocks open freely cold or hot, will verify that again in a few minutes. I can see no daylight between the blocks or the blocks and the sprue plate so I believe the blocks are mating properly. I'll be doing another test in a few minutes.

 

[fiver]

Cherokee:
try pressure pouring a couple.

you might want to pull the sprue plate and clean up around the hinge bolt too.
the nose does kind of look like your pouring into a non stick bake pan and the stuff is gassing off.

 

[Cherokee]

No joy in Mudville...same results. Blocks open fine and bullets from the other 5 cavities looked fine like always, but the depression is still there from the 6th cavity. I did pull it all apart and cleaned everything, including around the hinge bolt, before this last test. One more thing, I'm going to try Dusty's suggestion of acetone on that cavity. Thank you gentlemen for your comments.

 

[KeithB]

Is the dent on the side nearest the hinge bolt, or all the way across the cavity from the hinge bolt? If it is near the hinge bolt, I'd just have to believe that some type of oil/lube is crawling from the hinge, between the top of the mold and the sprue plate, and down into the cavity where it outgasses. There is a lot of area under the sprue plate around the hinge that is never exposed for cleaning unless the plate is removed.

If the dent is on the other side then I have nothing to offer.

 

[Cherokee]

Good observation Keith, however, I took the sprue plate off and everything was cleaned with acetone along with the offending cavity as Dusty suggested. The depression is on the hinge side. I also replaced the wave washer on the hinge, it had lost its "wave".

I just finished my last test...no change in the results. I tried pressure casting as well as my normal method...same results: Depression at the same spot but rest of bullet smooth as it should be. I guess I can live with the mold as 5 cavity and be done with it. I do have a second 6 cavity for the same bullet if this one get any more flaky. Thanks for all your input.

 

[Creeker]

No answers here but that just ain't right.

 

[Ian]

I'm with Creeker. That's the strangest mould issue I've ever seen.

 

[Cherokee]

There has got to be a reason and I'll continue to work on it but I'm done for now.

 

[Ian]

I don't blame you. Call it a five-shot mould for now and let us know if you get it sorted out in the future.

 

[fiver]

I talked to dusty [Duane] about this in some PM's and we are both kind of baffled also.
Initially I sort of thought it was sucking air back into the cavity somehow but the square void is the weird part.

I'm now wondering if maybe the mold itself could have a void in it right in that area and the air cavity in the aluminum might be the culprit.

I would just plug the sprue with some jb weld and run it as a 5 cavity, but I like a good mystery when it's solved.

 

[Dusty Bannister]

And giving it some more thought, I got to wondering if perhaps the Bull Plate is still present and off gassing a bit. Having never seen the bottom of the sprue plate, I would not know if it is concave as originally made, or perhaps lapped flat for a better fit (reduced venting) and with a snug hold down/hinge bolt, any off gassing would go the path of the least resistant, which would be toward the cavity, and that would/could form the air bubble from the off gassing source. The last comment about preheating the mold was with the blocks closed. Open might be better since you are trying to encourage any oil residue to dissipate.

I suggested it is break time, and give it another shot later on. But after an aggressive cleaning with Dawn Detergent and very hot water followed by acetone on a Q-tip moderately wrapped with 0000 steel wool. Twist the q-tip by hand and flush often with the acetone and dry completely before casting again. It might even be a good idea to boil the blocks and plate to help with oil removal. And do the same harsh scrubbing on the bottom of the sprue plate and perhaps on the top of the mold block. Anyone have a clue what the hold down bolt looks like? Maybe there is oil in the bolt hole that feeds the issue. Just soap and water and an acetone rinse apparently is not moving the offending source of the oil.

I have a mold block with the same cavity configuration and have never lapped the sprue plate, but have lapped the top of the mold blocks. Plate tension has never been addressed. I have never had this problem but did get oil bubbles in the casting when I got on too much beeswax. We know it will work out. Probably would be helpful if someone was looking over the shoulder to see exactly what was going on though.

 

[RBHarter]

Have you poured a bullet with out the sprue plate ?
That would rule out vents if it is good .

 

[Cherokee]

I identified the problem this afternoon. There was a small glob of metal stuck to the edge of the cavity right in the curvature just before the end of the left half of the cavity (opposite the hinge). I did not see that until under strong light and high magnification. There was also some traces of metal stuck to the lube groove and near the nose. These were causing the dent in the drive band, the void in the lube groove and bubble effect on the nose. However, the problem still is not fixed satisfactorily.

I attempted to scrape the metal out with a hard stick, did not work. Fired up the torch and put some heat on the metal, thinking it would melt, it did not. Kept the heat on and used the hard stick again and got some of the metal to flake off, never did melt. Eventually I could not see any metal in the cavity so I tried casting some. Bullets come out better, no depression, but you can still see imperfections. I'll give it another heat and scrape treatment later.

It may still end up a 5 cavity but at least I know what the problem was. BTW, my alloy is 3/3/94 for this bullet. I have heard of brass molds tinning and I know alloy will stick to molds, but it always come off under heat. My question is: If this was metal, and it seemed to be so, why would it have stuck so firmly to aluminum blocks ? Why did it not melt when the hot metal (725*) was poured into the cavity or when I torched it ?

 

[Brad]

I wonder if it was a burr that got shoved into the cavity and ground into the mould. That would explain it not melting.
Have you considered a light polish with fine grit and a spinning bullet?

 

[KeithB]

I wonder if there was a pit or void in the raw material used to make the mold. That would explain having oil trapped in it and outgassing when heated. It would also make any metal/metal oxide/dirt trapped in there difficult to remove.

 

[Cherokee]

Since I have cast many thousands of bullets with the mold, I don't think there was a burr, and the location of other "scum" or oxide near the nose and on the lube groove as well. Could be a block defect that just showed up. Anyway, I'm going to try lapping the cavity.

 

[Ian]

The FOD being metal oxide scum stuck there would explain why it wouldn't melt.

 

[Cherokee]

OK, I learned something Ian, oxide will not melt...didn't think about that.

Dusty suggested I lap the cavity with 0000 steel wool on a dowel to remove the rest of the oxide and clean it good, this worked. Bullets now look fairly normal...it's back to a 6 cavity mold.

Thanks everyone for the help. I learned a few things along the way and the mold is back to its old self.