30" Precision Square Iron Casting completed. 55 Pounds.

Very nice! Please post one after machining.
Robert

 

Wow. Thanks for posting. That is quite a casting.
Mark

 

Thank you both. I will not be machining it. It goes to a manufacturer of CNC equipment in the SW. He has milling and grinding equipment and will be buying one or two for his shop. He thinks there may be other folks interested. We'll see. Molding and casting that baby is at the outer limits of my molding capability and foundry capacity.

Denis

 

Well I poured it again.
After having the cope sand separate from the drag sand on the prior attempt a week or so ago, I had better luck with plywood board holding down the sand and a large vent cut into the cope to the pouring cavity at the far end of the mold.

I also modified my cope flask to eliminate the dropout problem I was having with the cope when I rotated it after removal of the pattern. The sand along the upper edge of the cope was not well supported and half the time would drop out---very frustrating as this was the very last step in a 2 to 2.5 hour molding session. So I drove a set of nails to support the sand in both the upper and lower edges of the cope and that seems to have completely prevented the problem. I have no idea if I have twice as many nails or just enough nails, but it is working well.

This image is of the fallout and the arrows indicate the defect. This is the side that rotates up and over as the mold is inverted for reassembly after drawing the pattern.


Here are the nails

Here is the video:

A couple things to notice:

The mold is intentionally raised a few inches on the far end--away from the pouring end which should be good for filling but also adds hydrostatic pressure.

I added a large pouring basin to the top of the mold. It is about 4.5" high and made of molding sand enclosed by a wood frame and molded on top of the drag. It has about a 6.5" square funnel-like opening to provide a large "target" for the poured metal. The crucible is very full making the first portion of the pour hard to accurately aim. Usually, for less full crucibles, I can pour into a 4" square or reasonably accurately. But this crucible was full to within 1" of the top. It worked very well. I could have done a little better at keeping the basin full. I find it a big advantage to have video to review after the poure as in the heat of battle it's hard to remember the details.

The pieces of plywood screwed to the top of the flasks (wood frame) prevent the sand from bulging upward due to hydrostatic pressure and gas pressure. My previous pour failed (in the interval since my first pour) as the cope sand got pushed apart by those forces----no bueno.

The resulting casting with blind risers and vent:


I weighed it as it is at 63 pounds. It is nice and square and free of twist. As you can see, there was scant metal to spare---one of the reasons I used the auxiliary pouring basin so as not to lose any.

Denis

 

Nice work Denis!

I had similar problems with drop-out on the aluminium moulding box pattern. After several different methods failed, I pinned a strip of timber about 1/4" x 1/2" around the inside bottom of the cope and on the intermediate dividers; problem solved.

To stop it falling out of the top of the cope when removing the pattern, I screwed a sheet of MDF onto the cope and similarly I placed a piece of MDF under the drag before moving it far,

Cheers Charlie

 

Yah, I keep the sand trapped between plywood or steel all the time on this pattern when moving and turning it. BUT, there comes a time when I have to remove the plywood and the pattern and flip the cope to place it on the drag. That is the "moment of truth" or, too often, frustration. In this case the long "bar" of sand was rolling downward and shearing off its base at least half the time. Intuition suggested the heads of the nails would restrain the sand from rolling forward and the shafts would prevent it sagging. Correct intuition or not, it works reliably.

I remember reading that in WWII days when aircraft engines were molded in huge quantities with amazingly intricate detail in the fins etc, pins were used to help support the sand.

Denis

 

It would be cool if your customer will close the loop by sending a couple of photos of the finish machined parts for your to post here. Thanks for sharing.
Mark

 

My customer has promised pics and maybe video. He received the casting today and is pleased.

Denis