Recycling scrap aluminum

Discussion in 'Lost foam casting' started by garyhlucas, Jul 8, 2019.

  1. garyhlucas

    garyhlucas Silver

    I have a whole bunch of scrap 6061 and quite a few pieces have stainless bolts broke off in them. I am thinking just tossing them in a crucible and the stainless will sink to the bottom allowing me to pour a part and then drain off the extra aluminum and dump the stainless junk at the bottom. Any problem doing this? I’d like to clean and cast in one go to reduce how much propane I burn.

    Getting ready to pour the same pump housing I did before without adding the silicon to see how it compares.
  2. Petee716

    Petee716 Silver Banner Member

    It's probably not a deal killer, but it would be better if you could minimize it. Lots of people pour with steel crucibles and although not recommended it suits their needs just fine. I dont know much about metallurgy or iron pickup but I understand that stainless doesn't hold out against liquid aluminum any better than other steel. One method of minimizing how much steel goes in is to load your crucible with clean material and while its heating up place an end or area containing a bolt over the exhaust hole. Once the metal is hotshort you can pull or knock the bolt out with pliers or a rap on the ground or what have you. Then place it into the crucible and on to the next. A little prep of the material with a bandsaw and bimetal blade might be helpful as well. It's more goofing around but I'd rather prevent it than have to deal with it in the bottom of the crucible.
    Just my 2 cents.

  3. Rasper

    Rasper Copper

    For what it's worth, stainless alloys with molten bronze like sugar dissolving in hot coffee. Steel is far slower. I made some stainless skimmers back in my early days. They didn't last one melt. Steel skimmers last for years.

  4. oldironfarmer

    oldironfarmer Silver Banner Member

    If you don't overheat it I think it will work just fine. I try to grab bolts with my tongs and hang onto them and let the aluminum melt around them but with aluminum they will stay in the bottom unless you grossly overheat it. You may affect the metallurgy but I doubt you'll notice it.
  5. DavidF

    DavidF Administrator Staff Member Banner Member

    Ive been using a stainless steel skimmer for years and still haven't totally worn it out. I also melted down something that had some needle bearings in it. Those buggers went partially into suspension (my assumption) and wound up in my casting, I didnt find them until I machined the casting. For what its worth I would try to get the metal as clean as possible before melting it down, breaking it down while hot short is a good idea, or maybe use a filter during your cast.
  6. garyhlucas

    garyhlucas Silver

    So on the recycling front I did 3 castings last night two using straight scrap, a mix of 6105 and 6061 just because that is what was in the bucket. The other one used some of the excess from the previous pour where I added silicon. All three came out quite nice which surprised me. One was a little short of complete fill, I just stopped too soon. All had some defects that were due to things other than pouring them. Biggest issue was I was too aggressive mixing the drywall mud and en-trained air bubbles. Another was failing to tip the part and getting drywall mud everywhere. I thinned the drywall mud a lot and I think I need to thin it even more.

    I made some pouring cones from the aluminum tape as shown in Kelly's video. Too much work for me. So I tried something else. I made an offset pouring cup with a sprue on it and put packaging tape on top before dipping it in Sodium Silicate furnace cement slurry to a depth of about 2". I did a couple and let them dry. Then I simply glued them onto the part and dipped the part in drywall mud up past the furnace cement. I then removed the packaging tape and just poured right into the foam. The drywall over the furnace cement means no sand gets in. Lots of smoke and flame but the pours worked fine. I think the next time I will use a soldering gun with a shaped wire to simply remove most of the foam from inside the cup area. If it works out I am going to cut hot wire template for cutting these out quickly and then I can dip up a dozen at a time so they are ready to glue onto a part.

    Tired right now I will have to post some pictures later
  7. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    If you are dipping, it needs to be much thinner. Thicker slurries will entrain air bubbles. Also, put a little dawn dishwashing soap in your slurry, and wipe or spritz your pattern with soapy water. It will act as a surfactant and the slurry will lay down nicely on the pattern.

    Pictures please!

    I've never had any luck hollowing out foam. Counterproductive in fact, but I do like to get the foam out of the pouring cup so you can quickly develop some head pressure over the sprue and feed system. Without doing so you tend to get a lot of turbulence in the pouring well and defects.

    Pictures....or it didn't happen.

    Sometimes, the simplest approach can be the best. Try just putting a small cone on top your sprue, fill your flask to the top of the cone and place a kush cup over it, fill to top of cup (to prevent run-outs) as shown. Some use a soup can but I use a piece of smooth muffler tube, 2 1/2" in diameter by 4" long. The aluminum slug in the cup will shrink enough you can pull the cup off and reuse it. After a few uses it gets a nice oxide layer and slides off easier.

    Pouring Cup.jpg

    I would suggest square sprue and square cone (pyramid). The reason being it will be less prone to aspirate air with a round pouring well. For the angle on the pyramid, search angle of repose. It's the angle the sand will naturally form if you pour it into a pile. If you make the pyramid that angle the sand will remain stable from the hydrostatic pressure of the pour.

    .....remember, some lost foam casters do nothing more than pour onto a square sprue slightly protruding from the sand and get decent results, but your getting advice from a guy that has used foils sprues, offset pouring wells, contact pouring ladles....etc:rolleyes::rolleyes:

    Your results may vary.

    Tobho Mott likes this.
  8. garyhlucas

    garyhlucas Silver

    So here are few pictures. One is of the fuzzy sticks I made for sanding using velcro tape and a 3M cubital sand paper with velcro backing. I am learning quickly that carefully preparing the foam pattern is really important for best results. radiusing all the corners inside and out helps a lot with coating uniformly. Another picture shows the different pouring cups I made. I showed the bottom of the wide one with the offset after I broke it off. The furnace cement seemed to work very well. You can see the coating of drywall mud is too thick, cracks in the corners, need to thin it even more.

    We have a dehumidifier running because the air conditioning vent sweat in our house. Hung two of the patterns over the air vent on top of it. Man does that dry them quickly! You can easily coat in the morning and pour the same afternoon.

    Had to wait for my grandson to come home to pour because of the two man crucible tongs. I just cut all the parts for a one man set. Hope to weld it up this coming weekend and really want to show what I did.

    The one part I cast is the bracket to hold the router on a CNC router I am making parts for. My grandson is on the FIRST robotics team in high school and we need a router. Here is a screen shot of what it will look like. We had special requirements. It has to portable and pass through a standard 36" door so it can't be more that 34-1/2" wide (trim). We have to be able to put it in a closet when not in use. We want to cut metal so it has a coolant pan under the table and vertical slide doors to contain the chips. One door is clear all the rest are being built with sound proofing. It is a bridge design using about $3500 worth of donated aluminum and has full 24" x 48" cutting area. With the doors raised slightly a 4x8 sheet of plywood or other material can slide right through the side and be cut. My plan is to perfect the casting by the end of the summer and supply a kit of machined parts to the team. Then I actually want to cast some parts that will go into next years robot.

    Attached Files:

    Tobho Mott likes this.
  9. garyhlucas

    garyhlucas Silver

    Another thing I have learned. You burn quite a bit of fuel just getting the furnace and crucible hot. The first pour took about 30 minutes to heat up. Dropping the crucible right back in the furnace and recharging only took about 15 minutes ready to pour.
    I also realized that there is a lot energy in that exhaust coming out of the box on the side of the furnace. A simple open rack would allow me to preheat metal before charging the furnace each time.

    Metal buckets and sand are cheap and the buckets I use had chain in them. They have gasketed clamp cover lids too. So setting up for multiple pours also saves fuel. I have 3 buckets now, I think 4 would be even better.
  10. garyhlucas

    garyhlucas Silver

    I cleaned up all the parts I cast and cut off the sprues. In doing that I can see lots of porosity in the metal. Also the I can see now that there are defects from the way the metal filled. So for the next casting I am again going to add some silicon.

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