For several years I have been casting a 36" Camelback Straight Edge in cast iron. I have always filled the mold from the center with 2 gates and two hot blind risers that are necessary to prevent shrink defects. 3 out of 4 times or so this resulted in a good casting. But every so often I would get a casting with almost adequate filling, but lacking just a few ounces of a full fill with the defect always being located at one end or the other of the mold. Having failures was very annoying and it took me quite a while to come to the conclusion that ambiguity of metal flow direction during filling might be the root cause of the problem. A failure on Friday last week got me to rethinking the problem and I came to the conclusion that the fact that the mold was leveled and the gates was central would allow for the metal to flow left or right in a somewhat disorganized and variable fashion could allow temporary stagnation of flow at one end or the other. This stagnation would cause cooling and thickening of the metal and could result in inadequate filling. So, I decided with some trepidation to radically change the gating by placing it on one end of the casting and raising the ungated end 1" relative to the gated end so that the mold would fill steadily from the gate toward the other end. I poured the mold that way today and it worked nicely. I hope it will work well each and every time in the future. My suspicion is that it will be reliable. A few pics: This is the filling defect I had had sometimes in the past but not today. Classic gating The new gating with a generous hot blind riser and gate on the left end of the mold. The casting including pouring basin and generous blind riser weighs 44 pounds. I poured it in 11 seconds. This makes sense. The prior filling defect is similar in cause to that often seen when a flat plaque-like casting is poured level rather than slightly inclined. Here is a vid. I added ferrosilicon and stirred it after skimming just before pouring. Denis
Follow up: It looks like the new method described above is going to consistently yield good results. I’ve now cast the pattern this way three times with uniformly good results. I sure am happy to have efforts pay off with a good casting. I cast one this morning and it is in my heat treat oven now. Denis
I have poured three more times since posting above and will go for the seventh end-pour tomorrow. One thing I have learned is that it needs to be poured fast. I video the pours as that is a convenient means of observing the fill time of the mold. On two occasions when the pour took about 18 to 20 secs, I found hints of a cold shut at the to last rib on the bow. I interpreted that to mean that the iron had had enough time to cool and get sluggish at the far end of the mold. Since then I have made sure that I have a big runner and large gate that encompasses nearly the entire end of the mold. Doing so results in a 11 to 12 second pour, no sand washing and no cold shuts. Happily the shut was very tiny and superficial. For the end use of the casting there was no harm. But, you can be sure the runner and gate are as large as practical on today’s mold. Denis PS. I’ll be relining my furnace soon. It will be Blu-Ram segmental and wool.
I did pour it again today. I suppose everyone is tired of this pattern by now. But, it seems to keep teaching me various lessons as I continue to pour it. Today's fill time hit the target of 12 secs. And once again there was no cold shut seen. The vents filled well and I made a new observation from the video about the gas/smoke coming out of the vent while the pour was in progress and the change in smoke/gas once the vent filled. I am going to put that in a separate thread rather than bury it here. I thought I would point out the finish change as corresponding to decreasing iron temperature seen in these photos and I detailed the gating I used. Overview of casting. Note the progressively shinier finish as the metal proceeded from the gate to the right side of the mold. Here is the blind riser with one vent spike broken off. Another view with spikes intact and showing how gate is cut to include nearly all of the end of the mold cavity. The spikes are equal in height to the head height of the pouring basin. (I make the pouring basin quite large with tumblehome so I can pour fast using my trolley without slopping metal.) This I did to be sure there would be no vacuum defect in the casting as I felt that moved the last point to freeze well into the riser. Seen from the rear. Filter is seen in foreground. It is not well demonstrated visually here but the center of the riser is depressed indicating it did feed the casting. The pattern for the riser is convex on top. The right-sided vent spikes. I will edit this post later tonight once I have made the other thread with the video showing the vents during the pour. Later: Here is the link http://forums.thehomefoundry.org/in...rvation-of-green-sand-vents-passing-gas.2180/ Denis
