Discussion in 'Sand Mullers' started by Tobho Mott, Mar 22, 2018.
Picture of a casting? I hope to get some of this miraculous sand.
pulled straight from sand, still blazing hot.
Quick sanity check before I do something stupid...
This the right oil for my petrobond?
I thought it was 2stroke oil..
I heard that somewhere too, I think, but maybe that was for K-bond?
Just found this; I think maybe I actually am on the right track:
yes non-detergent 30 weight ... but go to a real
auto supply and order a gallon, they seldom have it on the selves, but in the back or in the warehouse, the gallon saves you a pretty penny
Seems there's a fair amount of choices out there.
Perhaps get a small sample of your sand, apply a teaspoon (few milliliters), add Isopropanol, mull well - and then see what happens?
"Hydraulic oil" is also pretty close to pure mineral oil with some anti foaming and anti-wear additives in it.
And has a usefully low viscosity as well...
Petrobond tends to want a runnier oil than thirty-weight in northern climates, and seems to benefit from it in general. (Have thought about using sewing machine oil....)
I added a capful of the 30sae non detergent oil and a couple spritzes of methyl hydrate to a couple loads from today's pour. Nothing terrible happened. I did not notice a huge differemce but it did seem maybe a little bit stickier after.
I don't think I absolutely needed to do it yet, but I have been using the sand for cast aluminum since last fall and it is now quite a bit darker red than it used to be. So I was a little worried it was losing enough oil to affect its strength, and doing it so gradually that I wasn't noticing the difference.
if you are only doing(Light) aluminum castings , you will need very very small additions of oil occasionally , cast a 12 inch billet 12 inches tall, and you will need an oil addition. lots of heat over long period of time
here is the thing, smoke is oil burning off so if your molds barely smoke or dont smoke at all, you dont need to add oil, and as mentioned repeatedly, petrobond looses green strength when it sits or if it gets cold , ignore the color change it will happen
lastly remember 11 minutes is the optimum mull time , so if you think your sand is loosing green strength, mull it longer( and no i dont mull for 11 minutes thats insane, it would take me 5 hours to mull all my sand )
When I read that, I immediately thought of this video that I watched yesterday, about 24 minutes into it his petrobond smokes like crazy and then actually catches fire.
I had that happen last summer when I cast the bronze bell. I had hauled the mold into the barn so I wouldn’t have to wrangle all that sand outside and as soon as I cracked it open it immediately filled the building with smoke and then ignited. I had waited a half hour, but between the higher than normal temp and the mass of the casting I guess it was inevitable. The extinguisher was at hand but I didn’t need it. Lesson learned.
So far no flaming molds here, but it's only been aluminum so far. But my pouring basins smoke a fair bit, as do my mold cavities if I open the molds while they're still that hot.
Now that I have added a little oil to part of the heap, I know the darkening colour of the sand doesn't tell me anything really useful anymore. But I figured that while it still has some red in it and before anything was added, I could use it as a rough indicator of how much oil I had burned out of it so far. It's seen a couple dozen or so aluminum pours since I got it, but nothing thicker than maybe a cm or so.
This was the casting I had just poured yesterday when I asked if I had the right oil, a replacement part from the comfy office chair my work sent home with me last year... Definitely not designed to survive a 14 year old boy and his video games, but if I can drill the rest of the holes in the right places and get it put back together, the boss never needs to know! If he can break this one, he's getting grounded from those damn games.
It's kinda ugly where I krazy glued the original flimsy plastic part back together, and especially on the side where I packed it full of sand for molding to thicken it so it would fill, but I didn't want to spend a lot of time turning the broken plastic part into a nicer pattern. This is a stealth part that I'm hoping nobody will ever see again once it is installed after all.
The office chair boneyard.
It fits! Springy button adjustment feature even still works (as well as the other arm's).
I should have left the recess seen on the pattern on one side where there were just 3 drilled holes in an arc through the fill thickness casting in the first pix, I had to drill and file it out so the armrest can pivot side to side. I'd gone out of my way to NOT cast that recess as you may see from the casting. But it works now!
when I worked in the foundry on USS Prairie, we used to regularly get Petrobond fires, Why, well we would put down about 4 tons of sand at a time, and pour right after lunch, we could not leave for the day until the sand was mulled, so melt and pouring would get you out to about 14:00, wait half and hour, brake out molds, and hour to mull, half hour to clean up you are on liberty at 16:00, so we often broke out brass and bronze molds, that had been on the floor cooling 20-30 minutes , sand catches fire, just shovel it up into a small pile, it goes out
p.S. terrible practice dont try at home,
I'm sure that's right, safety considerations aside, seems like a great way of ruining otherwise perfectly good sand.
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