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Sand Muller (Frankenmuller)

kevin.decelles

Active Member
Premium Member
#1
I've been sand casting since 2000, and have mixed sand by hand since I started. I always wanted a muller, and spent a long time looking over designs and watching videos etc. I started this last winter and I'm back to trying to finish it.

Disclaimer: There isn't a straight cut, good weld, circular hole on this thing. There was no plan, I just started grabbing scrap around the shop and putting it together. My only constraint was that it come apart to allow for mods/replacement parts. No layout dye, just a sharpie marker, beer, mig welder and plasma cutter.

The motor I had at the time is a 3600rpm 1hp 3phase which I am running with a VFD. To get the muller down to a good speed (20-40rpm), I geared down 6:1 with the belt drive, then 6:1 again with a chain drive. I run the motor at about 1000 rpm, but I'll eventually replace it with an 1800rpm motor which I can run faster. I went chain because of the shaft assembly, which is the front hub/rotor/drive-shaft from a 2006 ford ranger (can anyone say spare parts at pick-n-pull!). I bought a sprocket at Princess Auto that I drilled to the bolt patter on the hub, and you have an instance drive train.

The tub is an old air compressor tank I got at an auction, cut with a plasma cutter with no steady rest while squatting.......

The tub legs are from a teleport I had kicking around, and there are a few brake rotors, stair risers etc. that make up the rest of the super structure.

Inside the tub is a wheel I got from castor land. The drive shaft only comes up through the tub by about 2 inches, and I splice it to another shaft with a coupler with a couple of bolts. This makes the insert re-designable as required, and inserts a point of failure in case of too much stress.

The orange handle raises/lowers the wheel, which I've gone to after trying 'floating wheels on springs etc. in a previous design. The reality is that you can only put so much sand in the muller before it will either a) stall, or b) bind the wheel. I found that by setting the height fixed, you can identify how much pressure/compression you want and set your wheel at that level.

The muller isn't finished, I'm working on the paddles to turn the sand after it is packed. That will be a modular design as well to allow for blade replacement/placement.

Well, on with the show -- here is a video of the muller to-date:
 

kevin.decelles

Active Member
Premium Member
#3
The top cross bar (4x4x1/4 wall) was added this weekend -- The previous top member (3" channel) was flexing when I threw some welding gloves in the tub. The 'up force' is pretty impressive, which is why the bolt on the top, it keeps the shaft pushed down. The CV joint allows the shaft to rise quite a bit.
 

PeterT

Ultra Member
Premium Member
#4
Cool mechanism. I know very little about casting other than it sure is neat to watch. Is the opening chute at the bottom kind of like the grand finale to discharge 'prepared' mold sand after the mixing & wheel tamping operation?
 

kevin.decelles

Active Member
Premium Member
#5
Correct. Having it "unload" a batch with minimal effort is key. I originally designed it to have the wheel stationary and turn the drum (several of these designs on line but the challenge is how to empty the drum.

Building a muller to do 25-50 batches is a challenge outlet due to hp and torque requires. My goal is 10-12 batches one after another with a quick empty feature




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kevin.decelles

Active Member
Premium Member
#7
You can see a casting in the video / pictures. The orange knob to adjust the muller wheel was cast from an office chair

I'll post some others


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Tom O

Active Member
#9
Looks not too bad! How big your cope and drag are will be the proof and if it does stall you could use three 3/4” wide discs separated by 1/2” to plow through it .
 

kevin.decelles

Active Member
Premium Member
#10
I put sand through the muller tonight and there is still some work to do. The biggest challenge is the wheel binding due to build-up of sand in front of it. The dynamics of the sand change very quickly (especially with oil bonded). The sand goes from oily feeling to 'damn tacky' really quick. After about 5 minutes of mulling, it is bonded really well and starts to group together, sticking to anything (like dough at a bakery). This is kind of the sweet spot as you have incredible bond strength.

I raised my wheel as designed, and this allows for less compression but it requires adjustment mid batch to accommodate for the texture change.

I added a cross bar and put some plows in to break up the jambs, but it will take some fine tuning. Most designs are based on a spring loaded wheel to allow it to auto adjust. I may have to incorporate that. The other core different on my wheel is the bearing, it has a needle bearing through the center, whereas most designs are using tapered roller bearings like a headstock.

No harm no foul though as the coupler in the tub allows the center shaft to be replaced easily.

As a side note, the batch of sand I am testing was prepared by a guy from Clive AB. I went out one night about 3 years ago and picked up 100 pounds of it for 1$/pound. Talk about a cool shop....... walls made of straw and lathe/plaster. He had a very nice muller that he had made..... He had been testing different local sands and oils, and finally settled on a blend. I like it a lot. I have the red colored retro-bond sand as well, and his holds up pretty good to that.