Tobho's HT1-Inspired Cement Mixer Muller Build

Yeah thanks Peedee, I saw your post over there, it does sometimes get complicated duplicating threads between the 2 forums, but I know people who are on one but not the other and I don't want anyone left out... Well anyhow, thanks for that idea!

Heard from HT1. He rcommended switching to 50/50 southern/western Bentonite and adjusting clay from 4.5 down to 4% and adding 1% dextrin. Or maybe trying just the dextrin first, which is what I'm leaning towards since I haven't found the southern (calcium) bentonite locally... yet.

I found out there are several types of dextein, but it looks like the yellow aka canary type is what I need here for my molding sand.

Also, he alsuggeated to dust the molds with graphite, especially for heavier sectioned stuff like the greensand ingot molds I use. I can get spray on graphite here and the spray can has iso alcohol and a trace of propane in it too. I wonder is I could do the 'spray it on and light it on fire' trick and get the same beneficial effect as just dusting on dry graphite powder...? Powdered graphite is around too I'm sure, but the spray on type is much easier to get to from where I am...

Rocco's post on the other site was nice too, suggesting I try pouring Everdur into my Smelko sand to see if that stuff sticks too...

I will get back and reply over there soon.

Jeff

 

Gotcha HT1, and thanks again!

Jeff

 

Another copy/paste post from AA, mostly:

I can confirm the new sand sticks to the bronze way more than the Smelko sand I used to face the patterns with does; must be some additives in play, presumably the "carbonaceous additives" Tim Smelko told me about.

Already got a kilo of cornstarch to bake to make the dextrin I'll add on HT1's recommendation (technically he suggested buying some on ebay, not making my own, but you guys know me... my bad not his if that goes wrong somehow); internet says that will work to make yellow dextrin, which internet also says is the kind of dextrin that is used as a foundry sand additive...

Before I heard from HT1 I had already reached out to a local blacksmith I just found out about, about buying a couple pounds of bituminous coal dust, which I thought might possibly be an OK substitute for sea coal. I think sea coal is more used for a ferrous casting sand additive, but I popped over after work and bought the smallest bag of coal he ever sold and that I will probably never need for $5 anyhow. Money well spent, since I got to shoot the $#!& with him for a while and look around his smithy, and now I have something to put in the kids' stocking next XMas. Nice little shop in his back yard, he has 4 coal forges (all strictly old school, no propane or power hammers to be seen) for teaching small classes, a few of anvils (one ENORMOUS one) and hammers and tongs and all the other stuff you'd expect to see, plus plenty of space to move around.. Also does a very small amount of sand casting, but I did not get into his other shed to squeeze a handful of his kitty litter greensand and see how it feels (told me it's mixed 5:1 (no muller), wow that sounds like a lot of clay...).

He said he may get in touch about maybe casting some bronze crossguards for his knife classes, which sounds like a lot of fun to me... No promises were made or anything, but keeping my fingers crossed!

Josh Van Noy from https://www.vansblacksmithing.ca/ is the guy I went to visit. Really nice guy. Mostly teaching classes and selling smithing supplies and coal these days, but says he's been putting hammer to hot metal for 20 years.

Jeff

 

Well, I made the adjustments to my new sand that HT1 recommended: adjust clay content from all sodium bentonite to a 50/50 mix of sodium and calcium bentonite and add 1% dextrin.

Since I had already picked up the "sea coal" I added 1/2% of that too.

The dextrin made a HUGE improvement to my sand's stickiness and green strength!

Poured a test mold in aluminum, and this was the first mold made with my homemade sand that actually filled. Coping down to mold the antler opener was a joy, no crumbly sand to worry about like when I tried to mold a similar pattern before tweaking the sand.

I also mulled it in a different order based on some references HT1 had sent me: added the water BEFORE the additives. Worked great!

Thanks again HT1.



Sand just fell off the castings, but left a layer of blackened sand sort of like how petrobond does. Smelko's recipe doesn't do that FWIW. I haven't tried again with bronze yet to see if the coal dust will prevent the sand sticking to the bronze as I'm hoping it will. That and trying a smoother pattern than those cheap Chinese iron castings I copied here, to see how smooth a finish it'll give compared to my sand from Smelko which I believe has finer grains.

Anyone wanna guess what's written on the other side of the other opener?

Jeff

 

Drink beer!! LOL Love it!

 

Yup. Or should I say yap...

Jeff

 

Remulling the dextrin sand after it gets blackened, it seems to lose some of its stickiness. I'm not sure how much to add back in, I would guess it depends on the casting's surface area. I found after pouring and remulling the bottle opener mold, just mixing the now darker sand back into the pile helped a lot, so I'm waiting until the whole heap starts to change colours, then I'll add some back in.

Poured another test mold yesterday.

No more stuck on sand! Great green strength. Zero flashing... Other than one massive runout.

I waited a couple seconds and resumed pouring once the runout froze off and blocked the gap. Since the part was all in the drag, this worked great. Got lucky that time!





Thanks again for the great advice HT1!

Jeff

 

This is out of chronogical order. Video of some test molds and test castings, from before I added the dextrin and coal dust to my sand. It's just the original sodium bentonite and silica mix.

(Ok, I swear, the next time, "bentonite," gets autocorrupted to read, "Bento items," I'm'a scream.)

Shows how the sand wasn't as strong as I'd like, and how the sand was sticking to the bronze. The castings were all failures as well, I guess that's what I get for trying a new alloy and some new sand all at once.

I was reading Pat's 8 attempts at casting his steam engine base, and as I was admiring his persistence, I realized I'd forgotten to post this here...

I hope you guys get a laugh out of all my molding bloopers, some of the failures were just me forgetting how I have molded the one part before, included mainly just for laughs. Though maybe you will be able to see how the sand was still a little crumbly at that point as well. There's a part 2 in the works that will show how I tried again using my old sand for facing to see if it would stick to the bronze like the new sand (much less so), up through the aluminum.inum bottle openers and the success full bronze skull casting. But now that you've seen the results of the fixed up sand, here's how it went with the messed up sand:



Close-up of the stuck-on-sand version of the skull casting:



Jeff

 

Heh, the sand in the scoop mold did look good... Until the greensand core broke off.

Maybe that was my fault, I might have bumped the side of it opening the mold... But I don't think so, the sand just didn't have the strength I'm used to.

Jeff

 

Great tip, many thanks (again)!

In retrospect I probably also should have just left it closed the first time instead of trying the Olfoundryman style test close...

Jeff

 

Sounds like it could work. To be honest the trouble I was expecting was getting that thin casting to fill, not being able to mold it!

If it broke off from just hanging and not from bumping the side(s) of the drag (still not 100% sure which it was), I really believe the updated and improved sand I've got now would have held up.

Jeff