Questions about Making Metal Flasks

I am about to make a metal flask from hot rolled flat bar. Before dropping 120 bucks for the material and investing a few hours in fabrication I thought I should bounce the idea off folks here. I have a pattern for 50 pounds of cast iron that requires a cope and drag each 4 inches deep, 14 inches wide and 40 inches long. I hope to cast this pattern 20 times in the next year or so and figure I could use it for other smaller patterns by installing temporary "partitions" to reduce its length as needed. I have been using wood patterns with fair success but I think I would be better off using hot rolled and bent steel.

What I think would work would be to have 3/16" by 5 1/4" flat bar bent into a wide shallow "u" shape so that I would end up with 4" vertical sides and 5/8" flanges. I would cut it with 45 deg miters and point the flanges to the inside of the flask to act as keys to retain the sand. The ends would have studs welded on to facilitate lifting and turning as well as clamping of cope to drag. I would also weld on a couple of tabs oriented to the outside of the flask and placed along the mating surfaces to allow clamping of cope to flask. The usual guide pins would be included as well.

What do you folks think of the the proposed thickness of flat bar, flange dimensions and general concept. Am I on the right track? Are there better alternatives?

 

Well, don't everyone speak at once. In the absence of any guidance I did get some plate sheared to 5 1/4" width and got a 5/8" flange bent into them and have welded up one flask. Will finish number two tomorrow. Had something of a hassle getting the steel shop to get the bends done with reasonable (by no means perfect) accuracy. By paying close attention and using bar clamps to tweak it one way and another it has gone together square and without visible winding. So, that is encouraging. Pics and more tomorrow. The dimensions are 42" by 14" by 4".

 

sorry man.. it's your sandbox. I play with playdoh and hot wax.

 

42" by 14" by 4" you will need a helper!!! and you will have to use some supports to keep the center of the mold from sagging or even dropping out... 4 inch is awful small (insulation wise) for cast iron, I hope your pattern is very close to flat or you will have issues... speaking of issues, a flat piece of cast iron is very prone to twisting while cooling in the mold... very interested to see what you come up with...
V/r HT1

 

Even with the 5/8 flange I'm thinking about the steel flexing over that 40 inches as the sand is rammed in. There may need to be some strategically placed cross members in 2 or 3 locations down the length of the flask halves to keep them from spreading while they're being rammed or manipulated.
The added features would also help with the above mentioned dropout. That may not even be enough to prevent dropout. Since your using it for a lot of the same casting it would be worth some fabrication time to make some internal structure specific to the pattern you're using.

Pete

 

Thanks, all, for the input.

I use a chain fall and spreader-bar for lifting and turning the flasks/molds. Way too much for me to lift precisely when splitting the mold and repositioning it.

I have been thinking I will need to weld in some stiffeners (angle iron) longitudinally and maybe vertically inside the flasks and you guys' thoughts are confirming that.

Pics late today.

Mold Failure tomorrow?

 

You'll be OK. Good support for the drag during the rollover and bars may be needed with the cope. Weight the cope directly on the sand in addition to clamping the flask to prevent any uplift.
HT 1's point about the thickness might call for a non combustible bottom board. I have charred them with much smaller pours. Fifty pounds of 2500 degree iron will transfer a lot of heat.

 

Well I got the flasks 90% fabricated today. Here are a few pics.
I think they MAY have been rigid enough without reinforcing the long sides of the flasks. But, I hated to think of another flask failure (used wood ones on this part previously). So I went ahead and tacked in angle iron 1 1/4 x 1/8 " as you can see. With the angle tacked in the flasks are very very rigid deflecting almost not at all when I stand on the long sides. I will be adding some tabs to allow clamping them together in addition to the straps that bolt onto the ends and also serve as pivots for lifting and turning.

I hope to fire up my furnace tomorrow and will add some photos of my bench and muller as well as lifting setup if that works out.

 

Looks beautiful. Fingers crossed.
Robert

 

Nice work. I'm looking forward to seeing your rig!

Pete

 

Thanks for the above comments,guys.

I will be using a bottom board for insurance and to help protect the sand while I move the molds from the bench to a spot where I can pour them. A few more sips of morning coffee and I am back to welding on tabs for clamping, locating pins,and attaching a bottom board can just screw onto the flask flange, I think.

A couple of notes for anyone who might also try making bent-plate flasks:
1) Bending the flanges causes internal stresses in the steel which will tend to make the resulting channel shape bow toward the flanges. In my case I pressed this out and got rid of the last traces of it by intentionally reversing that bow(clamping the sides bowed away from the flange) about 1/4" over 42" and tacking in the angle while so positioned. That was just a guess on how much to compensate that worked out pretty close.
2) Talk with your steel bender to see how small a flange he can bend. My 5/8" flange is pushing the small end of that press-brake limit. 3/4 would have been easier, might have resulted in less bow (don't know that for sure) and would have been fine from a functional point of view. As it was, when I came to pick up my steel, the worker made excuses about a couple of the bends only being 75 deg or so due to the small flange size. It took some talking to get him to go back to the brake and pay a little closer attention. Off-the-shelf channel could be used, of course, but would be very heavy and expensive. I did a fair bit of searching to try to find a commonly used "U" shape of steel similar to what I used, but could not find one. If anyone knows of such, please speak up.

 

Locating pins and side clamping tabs are in place. Clamping via 1/4-20 SHCS with captured nut. Next bottom board and top board for flipping cope.

 

is the barn door track trolley with chain fall and spreader bar attached to the flasks on my molding bench. The bar’s down arms are long enough to allow the cope and drag to be lifted and inverted.the trolley rolls to the left and right so that a completed mold can be placed on the floor. From there it slides on waxed boards to a gravel apron for pouring.



I had partial success with prior pours in a wood flask but made classic newbie error like pouring short or leaking flask.
Here is a casting (uncleaned) that I came within a pound of pouring completely. The casting is 36” long and weighs 55 pounds with runner, risers, and gate.

 

Wow! Thats an impressive casting. What's it for??

Lovely flasks you've made. If I could offer some advice - make the pins longer so they clear the total height of your pattern, so the draw is guided until it's completely clear
I really dig the trunnion setup - clever!

 

I think you very correct about the pins needing to be longer. I did have longer pins on a prior flask set, but they caused some binding on the draw. That may have been because the pins slid inside a tube and not just a thin ring. If the draw was not perfectly straight the pin bound inside the tube (actually a longish hole in a solid block) so I think I was down on long pins when I made these. But that’s no reason to give up on them without a modified approach. Anyway, steel bits just tack welded on come off pretty easily with a cutting wheel on an angle persuader.

The casting is for a camelback straight edge used in checking and scraping precision ways on lathes, mills, and the like. This an original design that makes up into a straight edge about half as heavy as most of similar length and width. That why I call it a “Foster Featherweight” if you can call anything CI “featherweight.” ;-). Once the runner and gates are cut off and the sole is milled it weighs around 20 to 22 pounds depending on how thin you want the sole.

 

Excellent - I've seen those used before. 55lbs of castiron, whoa.

On my flasks I have an "X" end/pin - the precision, reference end. All references are from this side. The opposing side has a pin that must align with the long axis, but it's distance from X can vary a bit - and the hole on this side is a machined slot. The X pin registers everything on the X side in two axis, and the other side in only one axis.
This permits the flasks to rock just a bit, preventing hard binding like you're describing. I can take some pictures tomorrow if that would be easier to convey the design

If what you have there works - stick with it!

 

Yes, I let will let the casting cool overnight in the sand as a Navy study done years ago shows that alone reduces retained stress significantly. http://www.dtic.mil/dtic/tr/fulltext/u2/620556.pdf. Aging cast iron, while long endorsed and practiced, has little if any actual scientifically demonstrable beneficial effect on cast iron castings as shown in the 1948 Navy study. Formal stress relief with heating to around 1100F, holding, and then down ramping over 12 hrs relieves almost all retained stress.

Then, prior to milling it flat to within a couple thousandths (actually can get a bit closer than that) it does get a formal stress relief by heating to about 1100f and then is held for a couple hours with a 12 hr down ramp. A theoretical argument for stress relief after milling could be made. Stress relief after milling has not proved necessary. Half a dozen previously commercially cast and stress relieved straight edge castings made from this pattern have proven very stable post precision scraping over the last couple years.