New Casting Pattern Evolving --- Angle Plate. Metrology version and Fixturing Version

I did cast the mold yesterday and most things worked out as planned. However, I did not pin or otherwise fasten in place the core.. I thought it would be held in place by pressure from the inflowing iron and by being sandwiched by the cope and drag. And the core shifted into the mold cavity. It was prevented from migrating outward as its print shape restricted outward movement, but not inward. It is possible the gases got behind the core as molten iron contacted the core. Or, perhaps, it shifted as I transported the mold and core out to the pouring area.

There are several ways I could prevent future shifting. Simplest would be to simply drill a couple holes in the core at right angles to the flat sides of the core and then use aluminum or steel pins (wood might off-gas enough to cause problems) to pin it in place. The one shortcoming of that approach is that it provides no mechanical fail-safe to prevent me absentmindedly placing the core oriented bottom-up rather than correctly. I know for sure that I’ll make that error sometime unless I do something to make accidental inversion mechanically impossible.

So, I intend to modify my core box so that two stubby nubs protrude from one side of the core side of the core. And then I’ll add corresponding nubs protruding from the pattern for the core print. That way there will always be a visual clue to ensure proper core orientation. I do believe that one could skip making the formal impression in the core print and simply press the core with nubs into the cope or drag especially if the nubs were located 3/4” back away from the edge of the mold cavity. So located, they would just press into the sand and lock in the core but probably would not crack the sand near the mold cavity. But I know me, and I’ll go the extra step to reduce the chance of making one more dumbass mistake.

Even though the print was a “failure,” I consider the exercise to be part of the high cost of learning. I was pleased to see the guessed-at location of the riser worked out well and the riser piped just fine, and the registration between cope and drag was spot-on, there were no shrink defects or cold shuts or sort pours. So, ya, 90% great. ;-). It’s that other 10% that’ll get ya!

I’ll put up pics when it gets light out and I can take good photos,

Denis
You can see the core "tried" to emboss my lettering.

That little nubin on the left upper corner corresponds to the most distant lower surface of the drag. In the last few months i have been making a little depression in such a location to collect any bits of sand that sometimes wash out of the mold. That allows for extra metal to snip away after casting and prevents having a raggedy corner should there have been a sand defect. In this case as in most it was not needed. But it is cheap insurance. The sprit on the top side opposite is the vent hole filled partially with iron.


Here is a view of the riser that piped fairly deeply---not a surprise given the faily chunky nature of the casting base and upright. I figured this should have been the last area to freeze and that seems borne out by the lack of shrink defects anywhere else.


I hope to have another go at this on Wed.

Denis

 

At long last:

 

HOORAY! Nice casting. Should work great for you, once the millwork is done.

Roger

 

Thanks, Roger. First, I will stress relieve in my kiln. Then I’ll mill it. 1150F for an hour should do it.

Denis

 

After the successful casting I decided to place the pemporary riser and sprue patterns on my match plate.

Here are a few pics of the process of milling pockets for the pattern piece bases which are 1/8" thick. The 3/8 radius of the plates matches the recess made by the 3/4" end mill.

A pocket just cut

Setting the riser pattern in place

Sprue and riser pressed into place




Here I placed the drag pattern for the runner on the cope pieces to be sure I had the orientation corrrect prior to cutting the pocket.


None of the pattern pieces are glued into place. The milled fits are tight enough to just try them again snapped into their recesses. Then I will glue them after one more casting.

Denis

 

Nice job Denis!

 

Here are a couple more pics:
Cope view of runner system


End view showing the sprue lining up with the "splash basin"


Will try it when there is the next break in the rain.

Denis

 

I did mold the plate today. The inset patterns worked perfectly. And they stayed in place without glue or screws. I will next be attaching them to the board with glue assuming this mold fills nicely and results in a good casting.

I did detail a somewhat unconventional draw method in another thread. http://forums.thehomefoundry.org/in...ely-deep-match-plate-without-guide-pins.2466/

I made the core using sodium silicate tonight for use tomorrow.

Denis

 

I used a pinned-in-place sodium silicate core on this mornging's pour.

Sorry, this image is "soft" but does give an overview of core location. In the foreground is the drag runner and base of the sprue and riser.


Core pinned in place with 1/8" aluminum welding filler rod. The pins are about 3" long and seem more than adequate.


Denis

 

More matchplate work this time for a 48" camelback straight edge.

Tue left image shows one side already glued up and the right shows the clamping method used.
I used West System epoxy thickened to about the consistency of sour cream to adhere the pattern half to the sign-board plywood backing. The glue squeezed out nicely filling all gaps between the backer and the pattern. I carefully scraped away excess and did final cleanup with IPA. I will finish the join between the pattern and board with unthickened epoxy which should provide a nice micro fillet. Drywall screws provided clamping.



You can see the shiny "seam" of thickened epoxy especially in the right foregraound.


BTW, if this pattern looks "dirty," it is! It has been well used with multiple applications of wax and graphite. I do not plan to repaint it as it has functioned well as is as a split pattern.

Denis

 

I am curious about the shrinkage you might see with the thicker casting section and where the proper riser location would be. It would be interesting to see it on a simulation.

 

Yes a sim would be fun.

You might be able to see the black riser 2.3 dia by 2.3” high on the one image. I pour from that end hot and fast. This arrangement may not be ideal, but it does work. Pouring twin-gated near the center with hot risers on each gate was unreliable—-sometimes ok and 1/3 the time not. End pouring has been better. I am switching to the matchplate for easier (hoped) molding. One molding problem with the split pattern has been a tendency for the cope pattern to drop out when splitting the mold. Various strategies to prevent the pattern dropout have been futsy and slow. Time to change methods.

I’ll post more details about the riser/sprue/runner/gate later today.

Denis

 

Without going into too much detail, I played around with it a little bit. Could not see the entire gating system so played by ear on some of the feeders and connections. In one pic ( 4 view bottom left pic)you will see small shrink (red spots) close to riser. I saw that same spot in every sim except the one without riser so feel as though riser is contributing to it. In the pic with no riser (top pic) there seems to be much more shrinkage but it is all in line with the ingate/feeder. So if I did it the same way you did you may be impeding on your core and may have caused the core to move. If you move the riser closer to the sprue towards the center of the casting it would move it closer to the shrink area that I saw and would not be impeding on the core. You could possibly have internal shrink in that spot but lots of variable go into play. Mainly pouring temp and chemistry. That being said... if you have been successful like it is you may not want to change anything. It was fun to do something a little different and gave me a chance to use some of the features I normally do not get to use too often, but I also was just doing it for fun and would have had to be a little more precise and take a lot more effort if it were a high volume job.

 

Billy,

Thanks for you carefull look at this. I am sorry and surprised I did not give followup obn the pinned-in-place core. That system worked just fine. The previous arrangement with nothing to hold the core in place allowed the core to float and be displaced by the strong current of flowing metal. No surprise that thte core displaced in that case. But, just pinnning it held in right where it needed to be.

By gating right at the junction of the two legs of the plate and by having a good sized hot riser right there and in close proximity to the gate, I was able to move the last solidifying area into the riser. So, the riser piped well and there were no evident shrinks. I have been tendinig to use good-sized risers that are about 5/8" from the edge of the casting and are not simple cylinders but rather have a tapering bulge near the gate, That style of gate has worked well as I think it maintains a mass of hot metal that is slower to cool than the casting itself and maintains a hot gate that solidifies after the rest of the casting has gelled.

Here is a drawing of one riser that would be used at the end of the camelback casting shown above. It works reliably.


Here is an unfinished print of a riser that would be used in the center of aprism casting. It also works well. Both have central depressions on top to promote collapse/piping and both have genreous connections to the casting with the bulge near the gate.


Each riser is about 2" tall and about 2" diameter. Both have thicker sections than the adjoining areas of the casting. So, I think the last area to cool in in that part that tapers into the main body of the riser.

Denis

 

I like the pre shrink dimple in the top of the riser as well...keep that area as hot as you can. The sims showed it to shrink quite well. I was looking at casting something similar in size so curiosity made me look at shrinkage on this part for future reference. We dont have a lot of shrink around here since we closed all of the hand molding lines and hunter lines. I have not used the simulation shrinkage tools a lot and am trying to become more familiar with them.