Reinforcing 12 Inch deep pattern for green sand?

This is my latest pattern making effort: a matchplate to cast a 30cm/12'' deep aluminium box using green sand. I plan to cast the box upside down with the top of the box being open sided, so the inside sand mould will be able to rest on the outside sand mould for support once assembled. So for such a small base to depth of the mould, the inside/core green sand mould will need some kind of steel bar reinforcement to prevent it breaking off during withdrawal from the pattern, flipping and assembly?.





The underside of the pattern:

 

You may need to come up with a procedure so that once your rammed core (drag) is rammed, flipped, and pattern withdrawn, that you don’t have to flip or turn it again. Even if you built an internal armature for it, it’s chances of remaining intact if you try to roll it outside of the pattern seem slim. Unless you use sodium silicate.
Maybe I’m missing something.

Pete

 

Sodium silicate or resin would be the smart thing to do, I'll try it with green sand first and fall back to sodium silicate if that's too weak, the thing is going to be heavy!. I had been thinking of three horizontal bars in the drag box with two rods each (six total) going vertically into the core with some support features on the ends. So something strong enough to support the weight but easy enough to ram the sand around.

Edit: You know you could have a small full depth plywood box with a bit of draft in the middle of the core to save some sand and sodium silicate: gas the core sand and withdraw the box and pattern to have a lighter weight hollow core that is still a minimum 2" or so thick in places.

 

In a somewhat similar situation I made a gagger that was a piece of 1/8" steel sheet and about 4 by6" and roughly rectangular. That plate was attached to a 2x4" piece of wood vertically and that 2x4 could be screwed to a 3/4" plywood
sheet that supported the gagger. I have subsequently learned that probably was overkill. But it sure did work. Simpler gaggers consisting of 10" or so rebar with welded-on maybe 3x3" 1/8" thick flags on each end might be enough. 2 or 3 gaggers (and maybe just one) probably would do the trick.

Silicate or epoxy would work, but would consume a lot of sand and binder. I would first play with some gaggers. Sand holds well if it is constrained from sagging. The gaggers make it all act as one cohesive block. Try it.

Denis

 

this green sand core will require Zero support, If you use the double roll, of course the problem with this is the entire mold has to me lifted and flipped, I used this technique when I make bells, and ashtrays, the greensand core is in the drag, while the exterior of your box is in the cope, ram the cope first, then flip tat to ram the drag, then flip the entire mold over and lift the cope off, I have to warn you a piece the size your doing there, the pattern has to be PERFECT, a rammer ding on the surface of the pattern, and you are not getting the mold open without damaging it ,

IF I HAD to do a piece like this that size ( I no longer cast bells) I would get a couple of endless nylon lifting slings, loop the slings over the matchplate, so you are lifting the matchplate, and the cope off the green sand core, using an engine hoist, a gantry, or a chainfall to a rafter in the Garage , an engine hoist or gantry on wheels is actually more likely to get the piece to lift straight up. this is an extremely tricky rigging evolution, remember to pretension the slings before you try and lift if they are new, they will have some stretch to get rid of

V/r HT1

P.S. large flasks often have trunnions attached to aid in this very evolution


https://www.uscargocontrol.com/prod...SZCvfV89uACeJi10uWkrHgrr4zrSczLIaAlKvEALw_wcB

 

So, Mark, do I understand you correctly that you are casting a box with the four sides and the floor all as one solid unit?

Denis

 

That sounds a lot like what I'd had in mind, I'll try Henry's methods first with this as a fall-back option.

It will be just four sides open and at the top and bottom. So the drag/interior core top touches the inside top of the cope/exterior.

Your explanation makes things clearer, I had trouble picturing the order of operations but now I can see how it would be done in green sand. I've been paying particular attention to the corners of the pattern and fairing them with thick epoxy filler as well as coating the marine plywood to harden the material a bit.

My local hardware chain has those lifting slings in stock, https://www.bunnings.com.au/gorilla-1000kg-1m-polyester-round-sling_p4211246.

 

I made moulding boxes last year and used Tim's recipe to make a very cheap core from brick layer's sand, flour, water and molasses baked in the oven,

Cheers Charlie

 

Thanks, that sounds a bit like baking linseed oil as a binder, I went to the trouble of making some sodium silicate a while back and even modifying a 5Kg CO2 cylinder and getting it filled so I'd better use that and justify all the expense .

 

I think I’d be tempted to try this method using gaggers and lifting eyes on the drag and flipping bolts/trunnions on the cope. I would first pack up the cope in the orientation as shown with the parting line as shown. Then install the drag on top of the cope and pack it up with gaggers as shown. They would have to be set so that their tops are just slightly below the level of the strike off on the drag. Then plywood board would be set on top of the drag that had holes in it so that you could bolt into the gagger‘s to secure them vertically. (Big washers would allow position errors in the holes to be compensated for) Then I would simply lift the drag straight up and allow the sand to hang there in that orientation while I removed the pattern shown in red then I would reassemble the mold and flip it so that the drag was now down and the cope up. Gates and runners would be located in the part line between the cope and drag and pouring basin would be now on the top and carved into place.

5/16” bolts would serve adequately for lift points and trunnions. This is going to weigh around a hundred pounds wild guess.

Denis

 

That's almost exactly what I'd initially imagined Denis. With 100lbs weight I think I'll ram it up at the back of the shed where I can use a hoist off the rafters and walk over with the crucible to pour in situ. I'll fabricate some flasks from 8" C section purlins with most of the width cut off with the grinder to leave a 3/4" strip internally running the length and then weld two pieces together to get 16" of height.

 

The purlin flange remnants should provide good holding power for the sand. That will be helpful in this situation and is especially important for the drag section.

A spreader bar (could be just a 2x4 timber) for the hoist will make the lift and flip easier. Good guide pins will be important.

I'll bet this will be well over 100 pounds given the steel flasks and sand weighs 100 pounds a cubic foot. You will have more sand than that, I think.

I like 1/8" galvanized steel cable with eyes made using copper crimps as lifting lines---compact and very strong, no stretch, and cheap.

Denis

 

You could pour this without even flipping the mold if you put a loose pattern for the gates and runners inside the box pattern. So, that pattern would be located down near the lower end of the gaggers in my sketch. The pouring basin and sprue would also be in the green cross-hatched sand Now what I labeled cope would the drag and v.v.

So, you’d pack the blue sand, drop in the gate and runner pattern, place the sprue pattern which would protrude slightly into the runner pattern and pack the green cross-hatched sand. Carve your pouring basin. Place the top board and bolt the gaggers. Lift the cope. The runner loose piece is pulled out as is the box pattern. Cleanup and blow out. Reassemble the mold and pour. Added: I’d have a 4” square cutout in the top board overlying the pouring basin to allow blowing it and the sprue out.

I think it would work!

Denis

 

I'd prefer to cast it upside down like your drawing shows, I can run the sprue pattern up the core and offset it as much as I can to the edge, so I can reach it with the crucible spout when pouring. So the 4" square plywood covers the basin with a hole in it for the air nozzle?.

The pattern exterior is looking good, the epoxy coating is blocked flat so the ply has a smooth finish, one more thin coat and fine sand and it'll be super smooth. The interior has thickened epoxy fillets on the corner pieces so I'll be sanding that and painting with epoxy today.

 

The 4 inch hole in the cover board is there simply so that it’s possible, while the sand is suspended, to blow out the carved pouring basin and the sprue, as well as around the runners and gates etc. that have been formed in the sand prior to reassembly of the mold. Once the mold is reassembled assuming it’s not going to be tipped, that too board can be removed entirely and then ordinary access for pouring will be available. The Hager’s wool have done their job and no longer need support from the top board.

The one area I’d be watching for shrink is the thickened area that I think provides lifting handles for the cast box.

Denis

 

That's going to be an area of concern, they aren't too crucial a feature so I can mill the finished result smooth.

 

Spent a few hours sanding the inside of the pattern with tiny custom sanding blocks with radiused edges and corners before applying the first coat of 5:1 ratio fibreglassing epoxy resin. Very pleased with it so far but ramming the sand will be the final proof of my skills. Also trimmed the purlins for the flask and cut to size, having a belt grinder with a 36 grit zirconium belt just let me straighten the cuts and deburr in minutes. I'll cut the 45 degree mitre angles and tack weld tomorrow, I'll have to grind off the zinc wherever the welds go.

A bit more sanding and a second coat of epoxy should get it close to finished:



16 inches of flask depth:



I'll be able to use the cut off strips to reinforce the joins and act as exterior handles:

 

On a different note, I can see how the end of the core will be touching the cope sand once the pattern has been removed and the mold reassembled. That change in elevation will bring your walls in pretty close together. I assume you made provision for that in your pattern’s wall thickness. (Not second guessing you, just thinking out loud.)
I’ve been reading Denis’ posts with interest but I’d like to show you a recent method I’ve used with good results. It is a “goose egg” motor cover for an old Delta Unisaw. I can’t remember the dimensions exactly but it’s about 16” across the length. I first rammed the cope, attached a piece of plywood over it, and then flipped it.


Note the hole on the top surface of the egg. There was already a 5/16 hole there for some reason so I tapped it to 3/8 to take a threaded rod. I rammed it with the rod protruding and then removed it before flipping. I also rapped the pattern a bit before proceeding.

I then rammed the drag, screwed on my bottom board, fastened the cope and drag together and then flipped the mold. After reinserting the threaded rod and adding washers to hold it in the cope, I gently lifted whilst rapping the drag flask. I then removed the pattern from the cope, cut gates, reassembled, and poured.


Pete

 

That looks pretty good Pete, there's a certain satisfaction in making unavailable parts to bring a machine back from the dead like that. The photos also give some idea of the equipment needed too. Using the plywood draft offcuts, I moved one tapered wedge 10mm relative to the other and it was less than 1mm closer, so the casting goes from 10mm to 9+mm thick. So long as I can keep the ply box lid the same thickness as the ply matchplate base, I should be good to go, with maybe a tiny thin bit of flashing to clean up afterwards.

 

So, Mark, do your box side walls stand vertically or, as I assumed, do they lean together to form a truncated pyramid?

If vertical, your draft angle is arcSin(1/300)= .16 deg. I have feeling I am missing something here. If they lean, they provide whatever the lean’s draft angle. If they don’t lean, your finish, waxing, and parting compound better be good!

Pete, your goose egg was really cool. The shape made a natural dome ceiling to support the sand in the cope. I wonder if the hole you found in the original part and the general part design may both have originated with the foundry in mind.

Denis