PetroBond Sand Molding & Casting...
And a bit on Pyrometers
This is the view out behind the foundry...
It is also the first day in weeks that the mercury went as high as -12C, warm enough to run the furnace, but with snow and wind.
This little wood stove, is able to throw off quite a bit of heat (after an hour or so...)
The stove is locate just on the other side of the wall (from the molding room), but enough heat comes through the open doorway that it's semi-comfortable to work.
This is my first attempt at ramming-up a mold ever.
Inititially I tried to use the vibratory action of the sawz-all, but it was too noisy and wasn't much better than by doing it manually.
The angle iron is to strike-off back of the mold.
At this point, I've rammed-up 3 (three) different molds, and broke them up, to get a feel for how much to compact the sand, before the flask can't be rolled and to determine where sprues should be placed and other misc details that have been unknown to me to this point.
You can read about this all you want in a book, but until actually doing it, rolling the flasks, having the sand fallout etc... it's all just theory.
The molds are heavier than I thought, and the need to have adequate draft, or taper on the patterns is greater than I'd made allowances for.
The "Art of Rapping", or gently moving the pattern in the sand to ease it's removal is also unappreciated, until tried. Though speaking rhyme in sync to urban noise, I believe is over-rated...
After 4 (four) test or mock molds, this is one that I'd like to cast, and have opted to make it as simple as possible, avoiding the wood gate patterns and sprue skimmers...
It took 2 tries to get to this point on the third attempt. Since this is a 12" by 16" flask, the trick to separating it is to have the cope & Drag on their side, with molding boards on the top & bottom, and then easing the drag back down with a molding brd.
I have limited access to a commercial foundry thermometer, as well as the opportunity to have an identical unit, provided I can fix it.
After much comparison, and measuring points for voltage levels between the two, I found a cold solder joint located under the LCD Display.
The unit did work for a few minutes but started to have issues with the display after that.
Rather than loose a lot of time on an item that I have been without up until now, I opted to just see if it would be of use, and stuck with the working unit on casting day.
Right off I learned a lot about my furnace, and why I should invest more time into fixing the other unit.
My furnace to date has been running WAY TOO HOT... upwards of 2100F before I started to cycle the burner on & off for 2 to 3 minute periods to keep the temp in the 1500 to 1700F range.
Also I found that I've likely been pouring my metal too hot as well...
It took over 5 minutes with the cover open, after skimming the dross before the pot was down to 1350F... which is the upper limit for Aluminum to be poured at.
This is a reasonable shot of the pot being degassed with a charge of the chlorine solution.
I opted to use this image, as it showed the Hydrogen Chloride vapour, as opposed to another image that showed the slag bubbling up.
Compared to the typical pyrotechnics that accompanies an LFMC pour, this was rather anti-climatic.
No need to hold your breath and pound the metal blindly to the mold through billows of black toxic smoke.
Just pour into the sprue steady, and watch it come up out of the riser.
This image clearly shows the effect of the heat on the sand as a 1/4" of black penetrates into the petrobond.
The plaque has no inclusions or sand stuck to the surface. Almost ever LFMC casting needed to be wire-brushed heavily to get down to the metal.
This may have been due to finally pouring at a reasonable temperature, or perhaps from the sand or both.
The black sand that is shown on the cast plaque simply fell away once the casting was removed from the sand.
The Foam pattern has stood-up very well and shows no sign of deformation or wear from being molded in the sand. The plaque has 2 minor flaws that make it unsuitable for release, but for once I still have the pattern available and could recast it on the same day if time allowed.
This is more of an experimental casting than the flat 2D patterns I've been making to date.
It is a 3D contoured image of a Large Mouth Bass.
With a metal version I will be trying to restore more of it's original image detail with an air brush, but that is another project...
This pattern had significant draft on it and was easy to withdraw from the sand. Like the plaque shown above if could be used many more times to render a pattern if need be. Since this is just a proof of concept type casting (I think it will need a few more incarnations before I have what I want), I may just cast it off a la LFMC to compare the 2 castings.
These small spikes are the vents that were poked into the cope.
Like all aspects of these two castings, I'm more than impressed.
This last image is the Plaque ID system that I will be implementing to keep track of multiple casting releases (pending the development of patterns)...
So, in conclusion, I have no regrets on the financial expense of the commercial sand, or the labour and materials required to start into cope & drag casting.
And now have a much greater appreciation for the value of a pyrometer for improved quality and fuel savings.
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