Advice on pouring thin sections

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jscarmozza
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Advice on pouring thin sections

Post by jscarmozza » Mon Dec 26, 2016 6:23 pm

I have 2 LE Atlantics and only one set of cab castings, so I was thinking about casting another set. The panels are thin rectangular sections about 1/8" thick with a few reinforcing ribs and fastener bosses here and there, the roof panel is the largest, about 10" x 10", it's crowned and of uniformed 1/8" thickness. Patterns for these thin rectangular sections are relatively easy to duplicate, but they look like they are going to be difficult to pour in aluminum. The original pieces look to be sand cast but don't offer any clues as to how they were gated. Does anyone out there have experience pouring thin sections, and if so, can you offer any advice on gates, runners and risers? Thanks, John

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Re: Advice on pouring thin sections

Post by OddDuck » Mon Dec 26, 2016 11:20 pm

A couple of things, pour hot and vent, vent, vent. Unless there are heavy sections somewhere on the part I wouldn't worry too much about risering. An extended sprue might be helpful as well, some extra head pressure will help the metal overcome resistance from air in the cavity. If possible, try gating into an area with the reinforcing ribs to help distribute the metal.
"If you took the bones out they wouldn't be crunchy!" -Monty Python's Flying Circus

jscarmozza
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Re: Advice on pouring thin sections

Post by jscarmozza » Tue Dec 27, 2016 2:10 pm

Thanks OddDuck, I wasn't thinking vents or sprue extension, good advice. Thanks again, John

ps. Around 45 years ago, while deer hunting, I spent two days and one night somewhere south of Mt. Katahdin lost in the woods.

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Re: Advice on pouring thin sections

Post by OddDuck » Tue Dec 27, 2016 4:20 pm

Done that myself, almost. I was with a buddy, zigged instead of zagged, and took a ten mile walk in the wrong direction. Luckily we came out to the main road and got a ride back to town. The Mrs. and my mom weren't too impressed by our skillful navigation skills.
"If you took the bones out they wouldn't be crunchy!" -Monty Python's Flying Circus

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Re: Advice on pouring thin sections

Post by steamin10 » Sat Dec 31, 2016 1:13 pm

IMHO large thin sections do not pour well flat. First be aware of the pour temp, and keep it on the hot side. Second, make sure you have some silicon in the melt that allows for fluidity.

I have some wooden 2 x 4 flasks that unlock and hinge open. these I can use on their side with boards on top and bottom to contain the sand (Petrobond). The melt is poured through one of three holes between the flasks, so the metal enters by way of a sprue and forces the metal to rise rapidly in the on-edge cavity. This allows the metal to fill a small area and rise, rather than having to spread out and fill wide spread thin areas, inviting cooling and cold shuts. By keeping the hot metal on the move, you get a more secure pour. Often I will use a smaller vent opposite the pouring sprue to insure the cavity does not get air bound.

Like wise , say a car frame, could be poured on a slant to allow the complex parts to fill at the bottom and run uphill, so that an area does not chill and mis-run. By keeping the filling area smaller it helps with keeping the metal temerature up for a full run.
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Re: Advice on pouring thin sections

Post by jscarmozza » Sat Dec 31, 2016 4:34 pm

Hi Big Dave, happy new year. I'm going to have to study this method to get my head around it, it's a departure from anything I've done. Is the mold filled from the bottom similar to a horn gate? I'm going to sketch the flasks, standby for questions. John

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Re: Advice on pouring thin sections

Post by steamin10 » Sat Dec 31, 2016 9:22 pm

That is correct, a horn gate is similar. I made a set of wood flasks, just for the purpose of drilling large holes in one side to gate in beside the flat part. by clamping a turning board or plywood to the faces of the cope and drag, we can now pour on edge, making the fill at any level very rapid for thin sections. The gate is run up the side, with several inlets so the metal flow from gate to part changes up on the rise.

Any time you pour through the casting from a center port, you risk sand erosion, and inclusions, and cooling metal that can wash the sand that is overheated from a prolonged stream. Pouring through a gate quiets the metal and doesnt mix air into the melt, which has the action of expanding from the heat, and agitating the casting, with the problem of oxides getting into the meat of the casting, causing blemishes, or stringers, and weak spots.

Remember that silicon content will control fluidity, along with tramp iron content. Too much dissolved iron will make your melt pasty, and very gassy to work with. Especially with thin sections, choose scrap that is cast stock, rather than extruded. It helps eliminate the guessing game of content, due to the fact of so many compounds of aluminum. Cast stock, will be cast stock again.
Big Dave, former Millwright, Electrician, Environmental conditioning, and back yard Fixxit guy. Now retired, persuing boats, trains, and broken relics.
We have enough youth, how about a fountain of Smart. My computer beat me at chess, but not kickboxing
It is not getting caught in the rain, its learning to dance in it. People saying good morning, should have to prove it.

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Re: Advice on pouring thin sections

Post by jscarmozza » Sun Jan 01, 2017 4:03 pm

Dave, I have cash of ingots I made from discarded barbecue grills, they should contain sufficient silicon since the grills were thin sections. Should I make the sprue and ingates a little larger than usual to facilitate faster filling? The way I'm planing this, the sprue will be about 11" deep, I was going to choke it just above the ingates and fan the ingates out as they enter the mold.
John

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Re: Advice on pouring thin sections

Post by jscarmozza » Mon Jan 02, 2017 3:40 pm

Dave, I was working on the logistics of pouring the roof panel, on edge as you suggested, and was wondering if the addition of an intermediate in-gate half way up the sprue would improve filling the mold? I'm limited in the size that I can make cores since I use a toasted oven (wife won't let me bake linseed oil cores in the kitchen oven), so I'm making the core in 4 sections and can easily carve an intermediate gate through it. I read that the biggest problem with horn gates is that they push the coldest metal up the mold and tend to freeze before completely filling the mold, do you think my idea will help by allowing hotter metal to fill the last half of the mold? John

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Re: Advice on pouring thin sections

Post by Harold_V » Mon Jan 02, 2017 4:11 pm

I've been following this thread with considerable interest, as I hope to profit by the wisdom being shared.
In regards to your question about the intermediate gate----would that encourage cold shuts? I can see the possibility, but can't determine if it would or could be a reality.

Harold
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Re: Advice on pouring thin sections

Post by steamin10 » Mon Jan 02, 2017 9:13 pm

OK, you are reading the concept right. Pushing thin sections with long runs is asking for trouble, and cold metal. (cold shuts). So we must keeep the metal flowing at a good rate to keep it hotand fill larger expanses of thin sections. like a car side, or cab. It is the reason for turning the piece on edge as the volue presented is quite small.

One trick in the gating, is to provide air space for venting. That could be another gate on the edge away from our pouring cut, as it allows our now heated,(and expanding) air to vent quickly without disturbing or bubbling back through our melt. Perking the metal stream is to be avoided, as it causes oxides and such skins to be formed and included in our casting.. So we angle the inlet sprue off square, so the pour runs down the side in a stream, rather than a waterfall, keeping the pour more quiet. Generally we want a bottom ball, or sanding cavity at the bottom of our pour gate, to keep sand from flushing into our mold. once it fills with the first few onces of metal it ceases to have any effect on the cast, and traps the first bit of coool metal. If you have been paying attension, it is all about getting hot metal to the thin sections. So to help that along, we can cut runners from our pouring gate, up the side of our on edge part.. As the metal rises to that level the hot metal will now detour into the mold higher up, with enough heat to mix with what is rising from the bottom. A slow pour will allow cooling and a skin to form, and you will find a cold shut line there. So it is imperative to pour fast and hot, with purpose, until we are full. So if you can visualize the fingers of your hand along the pouring gate, that is much like what your inlet gate to the part should look like. They can be half round or similar being cut with a tube, and slightly up angled to eliminate flow problems and air bubbling into the mold.

If you are using oil sand, dont be afraid to make several molds in practice and hand gate things, remembering to smooth any loose sand and soft edges. make several molds in practice until you see what you want. Then commit the metal the next day so you are all calm and collected without haste. being in a hurry on unfamiliar ground is a recipe for disaster and popping hot metal off the floor. I speak from experience, and not all good at times. If you dont get it the first time, its ok. With the furnace hot, a remold and remelt is a snap.

I encourage you to play safe, and remember different conditions will put you on that learning curve. The difference between dreaming, and reality, is 'I want' and 'I did'.

I get a little windy at times, but I try to put my meaning clear. I am an advanced amateur, with home styled small equipment. Guys with commercial experience may differ in detail, but the essentials have not changed in several millenia.

As far as metal from the common BBQ grill, you may find it more of a die cast compound, that will have a proportion of zinc in the mix. I use this for smaller chunky parts, as it may be weak with small tabs or branches. They make good axle boxes and machine like butter. Having said that, you might find shrinkage to be a problem where window sills and tabs are made, as zinc has a terrible shrink rate, that lends itself to pressure die casting very welll. Dont overthink things, try it, adn be prepared for plan B. Sometimes we can get gooder, when we know more of the path we are on.
Big Dave, former Millwright, Electrician, Environmental conditioning, and back yard Fixxit guy. Now retired, persuing boats, trains, and broken relics.
We have enough youth, how about a fountain of Smart. My computer beat me at chess, but not kickboxing
It is not getting caught in the rain, its learning to dance in it. People saying good morning, should have to prove it.

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Re: Advice on pouring thin sections

Post by steamin10 » Mon Jan 02, 2017 10:00 pm

As a post script I ignored your mention of core mold material.

The use of hard surfacing core mold material has its own advantages, and caviats. For one, you can use a sugar and starch based mold compound to accomplish the same thing, without the paint stink in Moms oven. Using molasses is old school, and much like baking cookies. Another answer is using sodium silicate, a common paint base, formerly called water glass. Once used for coating eggs for long storage, it is available at some well stocked pharmacies, or auto parts stores as an engine block sealer. It reacts with carbon dioxide to harden off, so it can be gassed from a paint ball cylinder, or placed in a warm oven (the flame makes cardox remember).

once hardened or still plastic, amazing things can be carved and shaped into the material, and get fine detail if needed within the limits of the grain texture. Core molds are intended to get, cavities and shapes that are otherwise unmakable from simple flat forms. The Ancient Chinese evidence making brass horse bits in stacks by using a clay mold, and stacking many pieces to take a larger pour all at once, eliminating cooling problems and 'short' pouring of cooling metals. By doing such things more consistant pours yield more good parts. Jewelers use a variation of this method with their trees of parts poured at once.
Big Dave, former Millwright, Electrician, Environmental conditioning, and back yard Fixxit guy. Now retired, persuing boats, trains, and broken relics.
We have enough youth, how about a fountain of Smart. My computer beat me at chess, but not kickboxing
It is not getting caught in the rain, its learning to dance in it. People saying good morning, should have to prove it.

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