Alloyed some brass today from scrap zinc and copper

I'd been thinking of something similar but upside down relatively speaking: ideally you'd have a spherical (least surface area) or cylindrical volume larger in diameter than the bar bar diameter up top to get the gravity assist and hydraulic the cooling metal. The three inch bar casting has a contraction void about the diameter of my little finger and two inches deep whereas as the two smaller bars obviously cooled too fast on top, yet the bottom half of the bar is a sound casting. This is where that slow burning powder Old Foundry Man sprinkles on top of the feeders or one of those combustible pouring cups would be ideal. I would have a steel disc at the bottom as a chill plate for the molten metal to hit to start the solidification and to minimize sand wash. You could easily get away with this for resin bound sand (pouring from the top) but green sand would need tight packing.

 

Why pour from the top? I was thinking bottom pour---hot metal is at the bottom. Riser at the bottom. Feeds from the bottom and freezes top down.

Denis

 

I'm lazy and don't currently have a suitably tall cope and drag so I've been using a beer keg with the top cut off. I'm also wondering if the molten brass can feed uphill against gravity, it seems all the defects are in the top half of the casting.

 

I’ve not poured any brass, but I’ve used the pour from the bottom, hot riser method described for iron hundreds of times and for aluminum a couple dozen times. And those risers feed the casting. The metal flow direction plus a heat of a generous gate and the added mass/heat of closely positioned blind riser work together to ensure the last metal in the casting to freeze is at the gate and the riser, having more mass/area ratio than the gate, freezes after it. At least that is what I think is going on.

Your defects were in the upper half because your hottest metal was there since you made an open pour. With the open pour, you can’t really alter the the bottom to top freeze and the very top cap will always freeze before an inch lower in the bar freezes. But there is no available molten metal to feed the casting—-its all casting. A burning cap might (I’m skeptical) make the very top freeze last and prevent defects. Using a top inch or two of greater diameter will push the last freeze higher and might keep it high enough so the “roof” of frozen metal might collapse to reduce or prevent vacuum defect.

It will be interesting to see what you can do to make a solid open pour.

Denis

 

I agree with your assessment of the top freezing before the area under it can solidify, I'm currently machining the second bar which is about an inch longer than the first: will it have an extra inch of good material from the bottom or will it be a fixed ratio like 45% good at the bottom and a void in the top 55%. If it's simply a matter of cutting off the top 3" of the bar and recycling it each time it may be the simplest solution. Other than all I can think of is a mould shaped a bit like a thistle on a stem: a funnel area connected to a spherical chamber and then the parallel bar (stem) below it.

 

Thistles maybe be the answer. But, it would sure be interesting to knock together a very simple plywood flask set with a 6 or 7” cope and 2” drag using the crudest of registration systems. Try the blind riser/ thick gate. I think the odds are 90+% it will work. The weight of the cope vs the top area of the casting will prevent any tendency to float.

Denis

 

there is an item( two actually) that will make the top of an open casting ( or riser) solidify last and induce directional solidification from bottom to top, exothermic riser sleeves and hot topping ( google them, i did one for yah)
https://www.foundrymag.com/issues-a...ping-techniques-for-riser-feeding-consistency

They keep the top of the riser open and feeding long enough to get a casting solid to the center,

other more hobbiest things you can do is pour the billet on a diagonal , someone recently described the technique for a plate I believe probably better the I can , the secret to this technique will make all the Campbell and Bob Puhakka followers happier then a dog licking himself , you have to pour slowly, the mold needs to fill slowly to really encourage the directional solidification ,

now all that said the best way to deal with this issue, is proper casting design, huge lumps of metal are hard to cast , put a core in it , I know I know that can be very difficult

V/r Ht1

 

Sure, those techniques have been around for a long time.

In Mark’s case, how many pieces of what size and at what cost and in what time frame? Remember, he lives in Queensland. And even with the hot topping or insulating sleeves, central piping is likely/certain. I think he wants solid round bars.

Actually, all he needs to do is today spend about 45
mins and some scrap lumber to make a very simple flask set and simply pour from the bottom with a hot riser as outlined. He’ll get his needed directional solidification and feeding at virtually no cost and no time delay. He can use the same technique for 1” or 4” bars.

Denis

 

I see perlite is used as a filler for hot topping and for ladle topping for the steel industry as it melts around 1100 degrees C http://www.schundler.com/foundry.htm it also extends the life of the ladle by forming a coating.....brass might not be hot enough to use this. Hot topping for steel and ductile iron involves aluminium thermite with an insulating filler added: https://www.foundrymag.com/melt-pou...contamination-from-feeding-aids-in-cast-steel

It might be possible to make a slower burning thermite, maybe a coarser aluminium powder or more iron oxide in the mix, copper can also be used which would be brass friendly but powdered metals are expensive so not really feasible for the home player. I'd be willing to experiment with perlite on top and a thicker fat section on the top of the casting but there'll be some optimum length to diameter ratio. Obviously there's no point casting 1/2" bar and 1" may not work either, these defects are in 2" diameter bar. The three inch bar had the deep shrink hole on top so that would indicate the two inch bar needs at least a three inch diameter feeder on top and maybe some perlite insulation on top. Denis, I'm not quite ready to make a dedicated flask if I can simply bury some steel chill plates at the bottom and have a hand carved top feeder/spout. It may well be the flask is the only way to go. Certainly casting a hollow bar is the easy solution and I know where I can get a couple of barrels full of hollow cores for those for larger diameters for free, I just need steel shot to pour in the center for weight.

I've been trying to think where I've seen a similar physics phenomenon to what I'm experiencing with the brass casting and it hit me today at work, mercury barometers. A sealed column of mercury more than 30 inches in height will pull a vacuum at the top, so if brass was a liquid all the time it would need a column 1.59 times that of mercury or about 48 inches tall. What I'm trying to say is that a smaller column of cooling brass is going to have a similar weaker vacuum effect on the cooling metal once the top solidifies with it's weight contributing to the void formation.

I screwed up the threading job on the second bar casting so I'll be cutting off 2" and starting again (this time with the compound slide locked in place ). This means I'll be sectioning the bar and also boring the middle, so I'll be soon finding the voids in it and see if the longer bar had more usable material

 

Just pour it horizontally like any other casting and feed it from a proper riser through a gate.

 

Made some more progress on the fuel needle valve body made from this brass bar. Due to the lathe compound moving on a worn nut (forgot to lock the gib) I lost the first male thread close to completion, so I machined it off and spun the bar in the lathe for the other end and cut a thread on it. The cast bar had shrink defects up the middle that were eliminated by boring up the middle so that was lucky, I would estimate 4" of the 8" long bar had shrink defects so I'll save that portion for when I need some brass tube or bushing. My current needle valve has a 45 degree cone so by using a 10-15 degree needle and the 1mm pitch thread (25.4 TPI) for adjustment I should be able to fine tune fuel flow consistently.

 

Made a final push and finished the valve, it has a 316 stainless needle and seat with a 15 degree included angle needle. The needle sits inside a brass barrel that has two O rings to seal the needle. last of all there's a half inch compression fitting one side and a nipple on the outlet for the fuel hose to the nozzles.