Pouring Shank For The A8 Crucible

When considering fabricating a pouring shank for my A8 crucible, I thought that a 1" slice of of 6"x 1/4" OD round tube would do the job.  However, the quasi-parabolic shape of the crucible meant that it would be resting on the thin upper knife-edge of the steel pipe - not exactly the best situation.  What to do?

Then I hit on the idea!  Cut the slice in half and "rotate" each slice up and into the parabolic shape!  Some persuasion on the slices with the hydraulic press and I had the two halves of the slice nestling nicely against the parabolic shape of the crucible.

To join the 2 pieces together, I tack-welded 2 pieces of 1"x 1 1'2"x 1/4" rectangular bar stock between the slices and did a test-fit.  A few whacks here and there (remove the crucible first!) made a nice fit for holding the crucible.  After which, a applied the welding to both sides.  The end-result looked like this. 

A bit of "persuasion" here-and-there with the angle grinder and we had a "ring" that fit the parabolic shape of the crucible.

With the "slices" nicely fitted, the next step was to add the shank.  A piece of 5-foot long 3/4" square tube cut at a rough 22 1/2 degree angle nicely did the job.

The next step was to add a handle to the 5-foot shank.  A 1" slice of of 2"x 4" square tube fit the job.

Which after all of this testing, fitting, welding, and grinding, we had a the outline of a pouring shank that looked like the one two-photos above.

A loose crucible loaded with molten metal without a locking mechanism to keep the crucible in the pouring shank isn't exactly a good idea. I was looking for something that would come down on the top of the crucible and hold it in place so that it wouldn't fall out when I tipped the crucible over for pouring.

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"Angular" Sand Cores

Roger H asked if I had any tips and tricks on making "angular" sand cores.  Not every sand core is going to be in a straight parallel plane.  Some sand cores are going to go around corners, widen out where we don't want them to, and take off in all directions.  It would be nice if we could simply mold the sand in the shape that we wanted and zap it with CO2 and.......  voila!....... instant sand core!  Unfortunately, life just ain't like that.  These types of sand cores require a bit of imagination and thinking in trying to make the core box. 

One of the best principles I can think of is screwing the sides of the core box together with screws, rather than gluing and doweling them.  This allows us to take the core box apart to release the sand core very easily.  Here's an example of one of my first core boxes where I did that.   At first I tried to dowel and glue the box together in two halves - but that didn't work.  Scrap that idea.  And then I came up with the idea of screwing the sides together.  Here's the end result. 

The next challenge I had was a bit more complex.  This was a corner bracket for an oil lantern that was perched on the back of a train. 

On this one, I had to modify an existing core box as I wasn't able to get the solid sand core out of the core box.  That required a hammer and chisel.  Through trial and error and at least 24 rejected sand cores, I was able to come up with a core box that worked.  In our railway restoration work, it helps if we have an original that we can use as our pattern.  In this case, the original (black) was modified by adding some core prints (yellow). 

Now how do we make the core box?  It took quite a bit of imagination but this is where having a circle of friends comes into play.  The pattern and core box was done by my Jedi Master friend, Ross, who gave it to the foundry for casting.  They procrastinated for over 18 months before I went up to the foundry and retrieved the core box to make the sand cores myself.  However, there was a problem.  The sand core wouldn't release from the core box. 

So through trial and error, we disassembled the core box with the band saw, cut a few pieces of plywood to replace the pieces we had removed, sanded and filed the grooves to get rid of the undercuts, until we had a workable core box.  We then went to town producing a dozen sand cores for our castings. 

And here's what the final core box looks like.  Four pieces made up of bits-and-pieces of wood glued together, backed by two pieces of plywood front-and-back.

 And here's another shot viewed from the end where we stuffed the sand mix.   

 The above photo gives you an idea of all of the bits-and-pieces of wood that were glued together to make the body of the core box.  Lots of angles and different planes on that one, eh!?

Another trick that I've seen (but I haven't used) is to make a hydrocal (plaster of Paris) core box.  This comes in handy when you have a model of the sand core but you don't have the core box.  This can be a bit tricky as it requires a lot of grease so that the sand core will release from the hydrocal.  Sculptors use this technique when casting their work in bronze or plastic resin.  Take a look at some YouTube videos and you will see what I mean. 

And here's a photo of a core box that I used in casting this bronze injector handle.  I needed to make sure the centre of the handle wasn't solid bronze as the handle is connected to steam heat.  From the photo, I can't tell which handle is the original and which one is the replica.  

As we get more ideas, we'll add then to this post. 

The Foundry Cart Frame - We Get A Start

Over the Christmas holidays of 2011, I picked up some 3/4" square tubing at Superior Metals and cut it up into bits and pieces to make a cart for my foundry.  In about 2 hours, the frame was all welded together.  In another two hours, I had the welds nicely ground.

Here's some views of the frame for the cart.

However, when I re-examined the frame and compared it to the foundry, it was obvious that 3/4" square-tube steel was too light.  So, it all had to go into the scrap bin.  Oh well, chalk it up to a learning experience.  (We managed to give it to someone who could use it for something else.)

A couple of weeks later, I visited Superior Metal Centre and picked up some 1" square tube.  This had a 1/8" cross section which resulted in a much more rigid frame.  Here's a photo of the frame complete with cast-iron casters and the foundry lid-lifting mechanism bolted on.

The Foundry Cart With Lid-Lifting Mechanism

Needless to say I gained a lot more experience with MIG welding in fabricating this second cart.  

I had previously acquired a 20" diameter gas pipeline steel pipe that I prepped for the body of the foundry.  This involved trimming the ends of the pipe so that they were square with the body of the pipe.  

Next, I had to cut two circular disks from a piece of 3/16" steel plate with the plasma cutter - one for the bottom of the foundry and one for the lid.  I next cut 8" circular holes in both of the steel discs.  The hole in the bottom piece served as a "drain" in case I spilled some molten metal inside the foundry.  The hole in the lid piece would allow me to "charge" (fill) the crucible with metal, and to let the hot gases escape.  

Inside the Foundry Body Steel Disc Welded To The Bottom

With the foundry body completed, I next turned to the lid.  I had a piece of 3/16"x 6" piece of steel rolled so that when I stitched it up with some weld, I had a 20" diameter ring that would fit on top of the foundry body.  

I then took that second 20" diameter steel disc and spot-welded it to the steel ring.  I now had the "lid" for my foundry.  

Inside The Lid

I wanted to have an "infrared reflector" sitting on top of the lid so as to reflect the heat back into the body of the foundry.  The reflector had to be 6" off the top of the lid.  In order to do this, I drilled a series of 3/8" holes around the lid opening.  I next welded some 5/16" extension nuts onto the underside of the lid.  Because the heat from the welding warped the thread of the extension nuts, I had to re-thread the nuts.  With the nuts rethreaded, I next installed some 6" bolts into the top of the foundry lid.

Inside The Lid With The Extension Nuts

On Top Of The Lid With The 6" Bolts Added

When the lid was lifted off of the body of the foundry and set back in place again, I wanted to make sure that everything would align properly.  The last thing I needed was to mess around trying to align the lid with the foundry body with red hot molten metal.  

To do this, I added some weld to the outside edges of the lid.  These welds would serve as "registration marks".  Using my copper plates to build up the weld, I added weld to the edges of the lid so that, when the lid was lowered onto the body of the foundry, the lid would settle exactly on top of the foundry.  

With this work done, it was time to see if the lid would fit on top of the foundry body.

The Lid Fitted To The Foundry Body

Next was to attach the foundry body to the foundry cart.  I drilled 3 holes through the bottom of the foundry body and into the cross-pieces of the welding cart.  I made sure all 3 holes lined up.  I next welded extension nuts on the inside of the foundry so that I could screw 5/16" bolts through the bottom of the foundry cart and into the foundry body.  This would securely attach the foundry to the cart.  While this was quite the exercise, I did manage to succeed without making the air too blue with my swearing.

With this part completed, I next turned to the lid-lifting mechanism.  This required a bit of thought.  I came up with the idea of a trailer jack bolted to a 3/16" steel plate welded to the foundry cart.  This served as a base to attach the trailer jack.  I drilled some holes in the base of the jack which aligned with the holes I drilled into the 3/16" steel plate.  A bit of a learning exercise but I managed to succeed.

Foundry Body Bolted To Cart.  Lid-Lifting Mechanism In Place

But would it work!?  Time to try it out. 

Does The Lid-Lifting Mechanism Work?

Eureka!!  It works!!  I turned the crank around several times and saw that the lid was lifting off the body of the foundry!  With the lid separated from the body, I could then swing the lid out of the way.  This would allow me to lift the crucible of molten metal out of the foundry.  

With the foundry body and the cart completed, I next have to cut a hole for the burner, install the burner holder, and start adding refractory to the foundry body.

While I'd like to say this all took place within a short period of time ... it didn't.  With a lot of off-and-on again and on-again-off-again, I managed to get this far in about 18 months.  In the meantime, I had lots of fun doing it.  I managed to greatly improve my welding skills.  I also had to do a bit of thinking about how I was going to assemble all of the bits-and-pieces of steel. 

A very good exercise in thinking things through to the end before starting to cut up the bits-and-pieces of steel.  

The Backyard Foundry - Some Concept Plans

Been thinking about how I would go about building my backyard foundry.  Starting with Dave Gingery's book on "Building A Gas-Fired Crucible Furnace" (aka "How To Build Big Bertha!"), I modified things a bit to come up with this concept.

So this is the start.  We'll start building the dolly-frame next week.  Would have started today except that Superior Metals Centre was closed.

Screw The Core Boxes, Eh!!

One of the tricks-of-the-trade I learned with the Sodium Silicate/ CO2 experience was a better way to make core boxes.  My first attempts resulted in a core box built in two pieces with wooden pegs to join the together - the same way you join the two halves of a split-pattern.

That was a complete failure - for two reasons.  Firstly, trying to pull apart two halves of a 3-sided core box (one end, half of one side and half of another side) didn't work.  The sand core got stuck in the core box and had to be broken out.  Secondly, without realizing it, one of the core boxes had an extremely large "undercut" (remember this was my first experience making sand cores!).  I ended up with a solid chunk of sand stuck in this angled core box.  The only way to get the sand core out was to dig it out with a screwdriver.  So much for that idea!

Then I hit upon the idea of joining the sides of the core box together with screws.  When the sand core had solidified, it was a simply matter of undoing the screws.

The solidified sand core easily released from the sides of the core box as each pair of screws was undone.  I could then give the sand core an extra couple of shots of CO2 with all 6 sides of the sand core exposed. 

All in all, a great first-time experience.  No muss, no fuss, no cleaning up my wife's oven, eh!?

So let's get down to building our backyard foundry!

Sand Cores Using Sodium Silicate and Carbon Dioxide (CO2)

Sand, when mixed with the correct ratio of sodium silicate, rammed into a core box, and then exposed to carbon dioxide (CO2), will result in a very hard and durable sand core.  Never having used sodium silicate (and never having made sand cores before!), this was an excellent lesson in learning what works and what doesn't. 

PQ Corporation is the largest manufacturer of sodium silicates, one of the most widely used chemicals in the world.  Their brochure on sodium silicate has this table which describes the various strengths of sodium silicate available. 

N-Grade Sodium Silicate
The key measure of sodium silicate is the weight ratio of its two major components - Silica DiOxide (SiO2)to Sodium Oxide (Na2O) (the column titled "Wt. Ratio SIO2 / NA2O").  The most commonly available sodium silicate has a weight ratio of 3.22 parts of Silica DiOxide to 1 part of Sodium Oxide with a solids content (active ingredients) of 37.6% (8.90+28.7=37.6 from Table 2 above).  The rest (62.4%) is water.  This is sold as "N" grade sodium silicate and is NOT the best choice for making sand cores as it doesn't provide very good strength to the sand core.  The sand core will slowly disintegrate when handled.  This type of sodium silicate has the viscosity of a cheap liquid dishwashing soap. Table 2 above describes it as a syrupy liquid. 

I made the mistake of using the 3.22 N-grade sodium silicate (it may even have been a weaker solution) with very poor results.  Even after 24 hours and constant exposure to CO2, the sand cores wouldn't hold together. For those that did stick together, I would end up with loose sand grains in my hand whenever I handled them. 

RU-Grade Sodium Silicate
The best type of sodium silicate for making sand cores has a weight ratio of 2.40 parts of Silica DiOxide to 1 part of Sodium Oxide with a solids content (active ingredients) of 47.05% (13.85+33.2=47.05 from Table 2 above) - a 25% increase in active ingredients over the N-Grade stuff!!  This is typically sold as "RU" grade sodium silicate and has the viscosity of concentrated liquid laundry detergent - it pours very slowly.  Table 2 describes it as a heavy syrup. 

I got some 2.4 RU-grade sodium silicate from CM and today mixed up a batch of sand to make some sand cores.

Mixing The Sand And Sodium Silicate
I first got all of my supplies, cups, bags, and stir sticks together and laid them all out on a sheet of plastic to make the cleanup easier.  (The McDonald's cup is my supply of sand - easier to pour from a small cup than from a 25 kg bag, eh!?)  I then put a smaller sheet of plastic down on top of the larger sheet so that I could easily recover any spilled sand.

To make the sand cores, I first filled the core box with dry 90m silica sand and poured it into a Ziploc bag.  I added about 10% more dry sand as it will compact more when the sodium silicate is added to the mix.

Using my Canadian Tire "Star-Frit" scale, I weighed the baggie at 376 grams.

I put an empty plastic cup (clean and dry!) on the scale and zeroed it out.

I next decanted 38 grams (10%) of 2.4 RU-grade sodium silicate from my large supply bottle into the cup.

I poured the liquid into the bag of sand and rolled the sand, sodium silicate, and bag between my hands until the sand and sodium silicate were well and uniformly mixed.  The mixture felt only slightly damp but would clump together when squeezed. 

Stuffing The Core Box
To make sure the CO2 would penetrate the sand core, I placed 1/4" steel rods into the middle of the core box so that I would have holes through the middle of the sand core.  I spooned a small amount of sand mix into the core box and rammed the sand mix around the sides of the box and the steel rod.

More sand mix, more ramming until the core box was filled to the top.  I struck the sand mix level with the top of the core box and lightly patted the sand mix so that it was firmly compacted across the top.  With a twist, I removed the steel rods from the middle of the sand core leaving nice 1/4" holes through the middle of the sand core.

Using The CO2 Gas
I wouldn't have believed it if I hadn't seen it in person but....  it only takes a few seconds of CO2 gas to turn the loose sand into a hard sand block!!  The secret is in how the CO2 is applied to the sodium-silicate-sand mix.

On the right-side of the photo above, you can see a block of wood with a couple of holes in it.  And, in the photo below, you can see a plastic container with a hole in the top.  Using my blow gun attached to the CO2 cylinder, and pressing down on the top of the plastic container, I slowly gave a 2-second shot of CO2 into the container.  This immediately hardened the surface of the sand core.

Removing the plastic container, I then placed the wooden block on the top of the core box, aligning the hole in the wooden block with the hole(s) in the sand core.  I slowly gave each hole a 2-second shot of CO2.

I then undid the screws of the core box.  Voila, the sand core easily separated from the sides of the wooden core box.  In less than 20 seconds from the time of applying the CO2 to starting to undo the screws, I had a solid sand core!  Whoodathunkit, eh!!??

I then repeated the CO2 process for my second sand core.  The solidified sand core easily slid from the core box.

Ratio of Sodium Silicate To Sand (By Weight!!) Is Very Important!!
The whole secret in using sodium silicate is in the sand mix and the application of the CO2.

In my first try at using sodium silicate, I was short about 3 tablespoons of sand mix.  I hastily mixed up a small batch that had about 30% sodium silicate.  Bad news!!  It wouldn't hold its strength even when repeatedly exposed to the CO2.  The sand core was still as soft as when I had rammed it into the core box.  I presume the extra liquid prevented the CO2 from penetrating the sand core.  So, whether you use a 6% ratio or a 10% ratio, the relative ratio (by weight) of sodium silicate to sand is very important.  It doesn't take a lot of sodium silicate. 

How You Apply The CO2 Is Very Important!!
While CO2 is heavier than air, my first attempts at using sodium silicate weren't that good.  I placed the wet sand cores into a plastic bag and applied the CO2.  On my trip to Alumaloy Castings, I saw how they applied the CO2 to the sand - a small cup-like device attached to their CO2 hose, and a piece of wood with a hole in it held on top of the sand core and aligned with the holes in the sand core.  A couple of 2-3 second shots of CO2 and the sand core was as solid as a rock.

It was obvious I needed to apply the CO2 in a more "aggressive" fashion.  So I modified my process using a 1-litre plastic container with a hole drilled in the top.  I was then able to drive the CO2 right into the exposed surfaces of the sand cores.

To get the CO2 into the holes created by the 1/4" steel rods, I simply drilled a couple of holes into a piece of 1/4" plywood so that I could drive the CO2 right through the middle of the sand cores.

Bigger sand cores?  Simply use a bigger plastic container.  These sand cores were almost instantly as hard as a brick with very smooth surfaces and sharp edges. 

In any event, I'm very pleased with the results.  Now we go into full-scale production with the sand cores using sodium silicate and CO2. 

Next up:   An easier way to make the core boxes.

Mold Making 101 - Colours For Patterns

Patterns are usually made of wood and finished with smooth painted surfaces.  In addition to providing a smooth finished surface that allows the pattern to be removed from the mold, the paint is used to identify the different part of the pattern (pattern, core prints, surfaces to be milled).  The American Foundryman's Society has adopted the following colour codes for painting patterns. 

Nonferrous
Pattern - yellow
Coreprint - black
Machined areas - red
Loose piece mating areas - yellow with red strips
Gating for mounted patterns - yellow

Ferrous
Pattern - black
Coreprint - yellow
Machined areas - red
Loose piece mating areas - yellow
Gating for mounted patterns - yellow

There are other colours for other types of metals.   

Next up:  Making sand cores using Sodium Silicate and Carbon Dioxide (CO2)