denul
04-30-2012, 10:13 PM
With the recent nearly simultaneous arrival of 2 Mihec four cavity HP molds,in 41 and 45 caliber, I was ready for a long weekend of casting. Friday afternoon was extremely frustrating, because my thirty one-year-old RCBS Pro melt started having problems with freezing at the spout. I do not have a lead thermometer, and I had the temperature control set on the highest (900) setting. I started running a probe up into the spout, which would temporarily allow enough flow to cast perhaps three or four times, with inevitable narrowing and then stoppage of the flow. Using a propane torch on the spout would allow for a few minutes of casting as well, but both the probe and the torch represent an unacceptable interruption of any attempt to get a good casting rhythm going.
I drained out my pot for the first time in probably twenty five years, and found that my early years of foolishly melting wheelweights directly in the pot had allowed the accumulation of quite a bit of baked on clay, probably from road dirt, on the inside of the pot, but nothing like that was visualized in the valve mechanism. After I cleaned and scrubbed all that out, I refilled the pot with cleaned wheelwight ingots, which I have gone to using for the past ten years or so. These are prepared and fluxed separately in a bottom poor modified cast iron skillet with ingot molds. The problem persisted, and I was fairly sure that my alloy was plenty hot, because when it was flowing, the freezing time in the mold was substantial enough to require a several second delay before opening the sprue plate to prevent smearing.
After reviewing a number of threads here relating to similar problems with this and other casting furnaces, it was looking more and more like I needed to call RCBS to return the thing. I did not see any easy way to get inside to try to work on it and would not have known what to do if I did. Saturday I tried again, with the same results,until my brother, who is not into casting (but enjoys watching me mess things up) came by, and told me that it looked like my furnace was only half full. He was right! For some reason I had been running it half full since the very beginning of this casting session, and I had almost never done that in the past.
Several of the posts on his site have indicated that the addition of sprues back into the pot interfere with the flow, because of chilling the lead excessively. I have always been one to put sprues back in, and I realize that many people do not do that. Nevertheless, after filling the pot to within an inch of the top, and then flexing heavily with sawdust, leaving a layer of sawdust residue on the top, the spout freezing problem was completely eliminated. I was able to get both molds into an excellent rhythm, and produced about twenty five pounds of very fine looking hollowpoints.
For now, this technique is workable for me, and may represent a solution for others having problems with the freezing spout. I believe that the increased thermal mass of the full pot solves a lot of problems because it allows continuous introduction one pound ingots, spues, and defective bullets without freezing the spout. This really does help production. Again, I recognize that this technique will be rejected by many who do not believe in returning anything to the furnace during a casting session.
With my alloy, in my furnace, under my conditions, the consistency of the bullets seems unaffected by this technique, probably because my ingots are all from a larger consistent batch. The greater then one half inch layer of sawdust residue also minimizes any splatter when returning sprues to the melt. Just thought I would mention all this, and I apologize for the length of this post, but it really did seem to help in my limited experience. Others having similar problems might want to give it a try.
I drained out my pot for the first time in probably twenty five years, and found that my early years of foolishly melting wheelweights directly in the pot had allowed the accumulation of quite a bit of baked on clay, probably from road dirt, on the inside of the pot, but nothing like that was visualized in the valve mechanism. After I cleaned and scrubbed all that out, I refilled the pot with cleaned wheelwight ingots, which I have gone to using for the past ten years or so. These are prepared and fluxed separately in a bottom poor modified cast iron skillet with ingot molds. The problem persisted, and I was fairly sure that my alloy was plenty hot, because when it was flowing, the freezing time in the mold was substantial enough to require a several second delay before opening the sprue plate to prevent smearing.
After reviewing a number of threads here relating to similar problems with this and other casting furnaces, it was looking more and more like I needed to call RCBS to return the thing. I did not see any easy way to get inside to try to work on it and would not have known what to do if I did. Saturday I tried again, with the same results,until my brother, who is not into casting (but enjoys watching me mess things up) came by, and told me that it looked like my furnace was only half full. He was right! For some reason I had been running it half full since the very beginning of this casting session, and I had almost never done that in the past.
Several of the posts on his site have indicated that the addition of sprues back into the pot interfere with the flow, because of chilling the lead excessively. I have always been one to put sprues back in, and I realize that many people do not do that. Nevertheless, after filling the pot to within an inch of the top, and then flexing heavily with sawdust, leaving a layer of sawdust residue on the top, the spout freezing problem was completely eliminated. I was able to get both molds into an excellent rhythm, and produced about twenty five pounds of very fine looking hollowpoints.
For now, this technique is workable for me, and may represent a solution for others having problems with the freezing spout. I believe that the increased thermal mass of the full pot solves a lot of problems because it allows continuous introduction one pound ingots, spues, and defective bullets without freezing the spout. This really does help production. Again, I recognize that this technique will be rejected by many who do not believe in returning anything to the furnace during a casting session.
With my alloy, in my furnace, under my conditions, the consistency of the bullets seems unaffected by this technique, probably because my ingots are all from a larger consistent batch. The greater then one half inch layer of sawdust residue also minimizes any splatter when returning sprues to the melt. Just thought I would mention all this, and I apologize for the length of this post, but it really did seem to help in my limited experience. Others having similar problems might want to give it a try.