The last few pours I have done have lifted the boxes ....same castings as I have poured before My castings have always bin sandy as I cannot get sea coal .but I have only had one box lift on me before and that was because I didn't way it down. One all the iron was in the cope .... Two where full and then lifted ....skin coat of the mold was full .that's how I know . My pouring temperatures is by eye ....can you get cast iron to hot . Thanks Todd
Did you use a slightly taller cope or have more gating? Same weighting on top? A taller cope will create more metal pressure so could float the cope where a shallower cope will not. More gating area can add to the lifting force. But, I think the most likely cause is the parting surface not being tight. If the flash is still molten that becomes extra surface area and floating force and once it moves a little, it moves a lot. Best, Kelly
So the big gear is what I poured first...horn gate other side....might have washed up some sand The small gear was next it turned out like I thought .....lost some parts of the teeth removing it The cover plate was last is 3 in in diameter And 1/4 thick poured no problem and nice gray iron .....put 2 Lb in the to much iron pail By the burnt in sand on the first casting ...thinking to hot ....and to far a drop in the horn gate
The iron would be more fluid and stay liquid longer but I dont think the heat would cause more lift on the cope. Something beside temp has changed since the successful parts were made. I agree with Kelly that it is most likely a change in head pressure created by more height...cope thicker..pouring from higher distance above mold...or a pressure change in gating...bigger sprue or smaller ingates or both.
You've made some great observations about the potential factors that could be affecting your results. It could be a combination of changes in temperature, mold thickness, pouring distance, or gating pressure.
Just use clamps, since I have been using clamps there has never been a mold lift on me. Weights can always be under estimated and leak but a clamp cannot let a mold rise and leak.
