how to correct this casting defect???

ive seen that technique, it was very popular in britain ( with a different name, Pop off, I think??? ) , I was taught it was balderdash,

But if you follow all of Campbells and Bob Puhakka's Gating design, it might have merit. But as best as I can tell their gating systems would all but require a resin sand system , or even Die cast , and are out of the Hobbiest range

I get the suggestion, I think " fill the entire mold cavity before the runner filles and impliments the head pressure , which would cause the metal to spray ,
to me it seems that the same effect could be reached , by simply increasing the size (total cross sectional area of the gates) but in this case because of the shape of the casting that is very difficult to do, so if the gates cannot be smaller, then the runner and choke should be .

lots to think about there,

But we will know more tommorrow weather permitting

V/r HT1

 

I like the way you think, youtube seems to think I should watch some hack cast copper ingots all day,
I might have a way ( with a little financial backing) to put up at least weekly videos, of proper sand casting of real parts and plaques ,
I have e meeting soon for a little front money if it goes through I'll be dropping regular videao before the holidays

Wish me luck

V/r HT1

 

So can I assume you're thinking options 1 and 3 not, 2 and 3? Either way, I'm certain you'll far exceed the quality of most youtube casting videos.

 

There is no need to make a huge piece of silicate-bound sand. The item in question is smaller than a deck of cards. So a core box could be made just by temporarily duct taping a 4X4X1" "picture frame" to the match plate and making a silicate "core" of the pattern. That would take all of a few ounces of sand and a few grams of silicate. Then make a hollow 4X4X1 wood core print mold and remove the frame and put the core print mold onto the match plate. Ram up the plate and print mold combo. Then place (you could just pin it in place if desired like I did on the windmill box part) the core into the core print after making a gate(s) that fill from the drag into the core. Indents on the core print mold to provide location for gate ends might make life easier when cutting gates and runners. If you get into production runs, the core print mold could have provision for gate and runner patterns that would locate after ramming the cope into holes pre-drilled into the mold.

In essence I use this method on the 18" iron straight edges that I pour using a combo of green sand for the outside faces and silicate for the letters and inside faces. I poured two yesterday with very nice detail rendition and easy core sand removal post pouring. In that case I use 3.5 pounds of silicate-bound sand per core. At that rate my sand cost per mold is $1.50. I should add that the entire mold weighs about 130 pounds.

Denis

 

well Zapins wins the "no Prize" though I was trying to Give the Ingate a trim with a wood chisel, it popped off, so I installed new fillets, rammed it up and got two perfect castings, no issues with the other part, save I have a Pile of them from all the failures on the first part.

This part was one of those that really had me head scratching, I started with a rubber Pattern from Village impressions , I remember just staring at it trying to descide how to gate it , I seriously considered , a single gate through the bottom of the Trident , and then did the Math My runner would have literally been a set of chopsticks.

well alls well that ends well, loved the Lively debate Thank you Zapins

V/r HT1
P.S. K.I.S.S still holds true

 

I'm not real good with casting yet but this discussion about surge traps or spin traps is a common issue in fluid systems. we are dealing with pressures that make the metal go into the mold. One is velocity pressure the other is static pressure. they add together in a straight run. In fluid systems we use what is called an accumulator that is placed at the end of a straight run. its purpose is to absorb the velocity pressure, leaving the flow control based on static pressure or head. Static pressure is equal in all directions. so you would feed the mold through a side port off of the straight run, it typically would need to be 3 diameters toward the source from the accumulator.
The accumulator needs to be large enough with a small enough gate that the entry point on the mold has filled enough to slow down the flow into the mold chamber before the accumulator fills.
The longer the run or sprue the more velocity pressure affects the total pressure. the actual head doesn't come into play until the mold is full the static pressure = total pressure. on my projects i have been using accumulators and have accidentally eliminated the surge problems. my only fill issues have been related to insufficient chambers to provide shrinkage material. Uncontrolled velocity pressure will cause jetting, surges as well as not filling the lowest points first if the velocity is high enough to jump the low point.

I hope this makes since
Art b

 

I am a little confused by the theory and calculations that seem to come into play when discussing runners, spin traps, accumulators etc. It seems like an assumption is made and calculations are based on mold materials being impermeable. That might be somewhat true in some systems like lost wax/investment casting. But in sand casting whether it be green sand, silicate bound sand, resin bound sand or oil bound sand, permeability of the sand is quite significant. How is that accounted for in these various modeling systems? I experience this permeability quite obviously and first hand when gassing sodium silicate bound sand. And it is quite evident in green sand when I often add no (shudder) vents for formal gas escape and yet the molds fill just fine.

Denis

 

I'd love to see a few pictures of some examples

V/r HT1

 

I can stab at this a Little
the molten metal 's FLOW is not effected by the gas in the Mold unless things get extreme , now that does not mean gas is not an isue, but it normaly is not an issue in the gating system, it maybe an issue in some point in the actual mold cavity
A deep back corner perhaps, But a vent will cure that .

remember gas acts like a gas, while the molten metal acts like a liquad ( OK SO sometimes it acts more like mud , but there it is)
I dont know of any gating considerations for gas save perhaps venting the ends of Runners,

V/r HT1

 

I'd like to withdraw the question as it falls into the category of dumbass questions! Bit of a mental lapse there I think. Thanks to HT-1 for bringing me painlessly back to my senses (such as they are!).

Denis

 

Denis,
I would like to say the question you posed was valid. There's a lot going on inside the mold cavity and some of it doesn't make immediate sense. For folks new to casting (me) it's still a little like magic. I can get a good a cast but I don't really know why all the time. Seeing questions and answers like the one you asked and HT1 answered (or this whole thread!) help me visualize the flow in the mold system (gate system and mold cavity) better. Helps explain why when I tried something this way it worked and that way it didn't. That way I have a better shot making the next odd part turn out the first try. So you might feel it was a dumb question, but I was enlightened by it...so thanks for asking a "dumb" question for me!!!

 

Add choke to runner so the existing runner area is at least 1.7 to 2.7 times the area of the choke. Add vent to the end of runner...tiny little thing to just release some of the pressure and reduce the velocity. Reduce the area of the ingate that connects to the runner so the contact point to the casting is bigger than the area touching the runner. Maybe change the direction of the ingate so iron does not flow into that area on initial fill but anything that will reduce the velocity and pressure will help. Iam not a brass man and have no idea how it flows compared to cast iron but looks to me (based on my cast iron experience) that you can reduce the whole gating system to be much smaller thus taking the pressure off of it.

 

cast iron flowes faster ( less effected by friction) and it acts, very very liquad compared to all other Molten metals ,
you are probably right that I could make most of my gating systems smaller,
But because of My bad AFS gating system training that is very hard for me to do.


V/r HT1

 

I put this Post up becasue I wanted to shake the tree, just a little, and I was also hoping someone would just pull something strange out of their hat , and I could have a Gee Whiz moment ,

I knew when I gated the Pattern, that gates should never act as a choke and that one definately did , and the reason is almost silly,
to sand really small pieces like that , I glue my piece to the end of a stick sand it down, remove it from the stick,
I was in a rush and could not wait for the glue to dry, so I sanded up the smallest ingate as I could and rolled with it

I rushed,
always a bad idea

V/r HT1

 

Haha! I was in same position for a long time. I understand exactly what you mean. I get to deal with people seeing the inclusions left from sand calling it slag and I have to actually find the problem and fix it. If I kept listening to them we would be running filters and AFS gating to stop sand inclusions. Just for fun I watched them try a gating and filter test on a pattern we normally run under 10% inclusions on. I gave them minimal help in setting up the test as these were industry experts. It was an epic failure that resulted in a 90% increase in inclusions. Good times! LOL

 

HT,
Now that you figured out how to get it to work. I'm curious what the pro's thought you should do to fix it.

 

Never take advice from Someone that has something to sell. and that is my general experience with experts. they have something to sell, like John Campbell sells books, with alot of generalities , lots of jargon, and little specificity, we all Knew when I was studying to be a journeyman "1991", that AFS did not work as it was intended, they showed us 40 year old B&W xray videos of steel castings being poured , and none of them worked as we where told the AFS system works, but 90% of the time AFS does give a good casting especially large castings

but it did not scale down well at all for 1-4-4 rations with a half inch Sprue your runner would be just under 1.25 X.75 so for a small 6 inch plaque you would need WAY more metal in the gating system then in the casting or some miracle small sprue cutter , the smallest I have ever seen was 3/8

 

I think we saw most of them here save

1) Most of the experts seem fixated on venting , I got told over and over to vent different ways, Sand washing out is not a venting issue
Just a little note I have never vented my petrobond save on the castle lawn ornament , as it was quite heavy so would take some time to fill, all the plaques just get poured

2) I heard horn gate in the center, which is an absolute a$$hat suggestion , plaques (almost) always go face down, so no horn gate
if you horn gate, it is pure hell to get it off of any casting , probably the worst cleanup nightmare you can have

3) I heard foundry nail, which is a great technique to get one part out of the door, or to repair a mold , but it's not something you make repeatable "we heard that here as mig wire"

4) gate through the tridents, again clean up nightmare , i would more or less be carving the tridents out

5) I had one person advocating a single gate through the bottom of the spear, I just do not think that would get metal in fast enough

6.) lastly several people wanted to change the gates angles, so they are hitting the sides of the waves rather then flowingdirectly into the center of the mold cavity ( which would cause turbulance )


V/r HT1

P.S. note to self : if I had really thought about how I was going to gate that pattern, I couuld have made the Gating with the pattern and avoided the issue or at least been prepared , trust me when I got the pattern done, and was holding it, i Just stared at it, wonderiing where to get gates into it, it had no clean edges at all... Lesson learned