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The keel is 8,600 pounds of lead alloyed with 4% antimony for hardness cast in two pieces, a fin and a beaver tail bulb.
Mars Metals wanted over $10,000 to cast it so I decided to cast it myself. I have done some sand casting in the past and this is just a little bigger. But pure lead ingots run about $.50/ pound and enough antimony to bring it to 4% would cost over $1,200.
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 I didn't know about the antimony when I bought 8,000 pounds of old X-ray shielding for 14
cents/pound. Fortunately, I was able to resell it at a small profit. (not counting my labor having to load it twice.)
With a little research I found that tire weights are 3% antimony and sell for 8 to 12 cents/pound. So for the past year I have been making a regular run of tire stores picking up about
1,000 pounds each trip and leaving behind some bewildered store managers. "You need lead to build a what!?"
When I get the weights back to the shop they are melted down to remove the clips and cast into 20 pound ingots. I
can melt about 200 pounds each cycle in my casting furnace. For more detail on using wheel weights as a source of lead ballast, see Wheel Weight Economics.
I accumulated a bit over 8,000 pounds and went to Troy, AL to buy 1,000 pounds of 12% antimony lead from a
battery recycler. I will have about $1,000 in the lead and about the same in casting cost and the stainless keel bolts.
I have to say that all of the distributors and suppliers that I have worked with on the keel have been enthusiastically
supportive. The folks at Sanders lead analyzed my lead for free and calculated how much high antimony lead I
needed. Ashland Chemical researched my requirements, recommended the proper binder and introduced me to a
distributor that would sell small quantities. Georgia Sand broke a pallet of foundry sand to give me the quantity I
needed and several of the tire companies have posted pictures of the boat over their balancing station as a reminder to keep the used weights.
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 The patterns were built up in two halves from particle board section
profiles braced with scrap 2x4s and filled with spray foam. The foam was shaped with a Sureform and covered with Bondo. Then it was faired with the old faithful long board. The dimensions were oversized
about 3/16" in the thicker areas and 1/16 in the thinner areas to allow for shrinkage as the lead cooled. |
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The only split that provided a straight parting line with draft to remove the pattern from the
 mold was along the vertical
centerline. This made placing the sprue (the hole for pouring the lead in) a bit complicated. if the mold were poured in the usual way with the cope over the drag. I decided to cast the
mold on its side and place the sprue and vents as the ramming proceeded.
The sand was American Foundrymens Society 70 sieve silica. The bulb took 2,600 pounds. Ashland Chemical recommended their LinoCure AA binder and Velvalite Zircon
slurry for a wash. I rented a paddle type mortar mixer to use as a mull. The instructions called for 1.5% binder by weight which worked out to about a pint and a half per 100
pounds of sand. I was a bit concerned as the resulting mix was loose and produced weak clumps. Not at all what I was used to with regular green cans casting. I was tempted to
boost the ratio. Thank goodness I didn't.
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My son, Trey, ramming the drag with a 4x4.
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Once the drag (bottom half of the mold) was rammed, it was sealed with plywood and 2x4s and rolled over. Weight of the drag, pattern and sand was about 1,500 pounds so the gantry and a pair of chain
falls was handy for the roll over.
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The mold board was removed and the top half of the pattern was laid over it. The Cope was placed and bolted in place.
As the top half was rammed, some 4" PVC pipe was placed to form the sprue and vent.
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The bottom half ready to set the top pattern. The black stuff is powdered graphite parting powder.
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The mold was allowed to cure for about a day rolled on its side and then split open. The pattern was removed.and the mold cured another day. Then I washed it down with the zerconia/alcohal slurry
and lit it off to burn off the alcohol and set the zirconium. This gave the mold a hard fairly smooth finish.
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 The "crucible" was an old cast iron bath tub mounded on concrete block and
supported with fire brick. The block was lined with a fireclay/cement stucco to shield it from the heat.
After much discussion on rec.crafts. metalwork I designed a drain plug that consisted of a 4x3 pipe reducer. The inside was turned to a 15 deg taper
and a matching steel plug was turned, drilled and tapped for a lifting rod. The rod runs through a lever so the flow can be controlled from the side out of danger.
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 A 4" black iron pipe served as the pouring spout. I added an ell to
the end and should have added an extra short length below that to control the lead. As it was, the lead spewed out in every direction but down the sprue.
That's my brother Bill in the background and supervising the pour. He always shows up for the fun parts.
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Site last modified:04/12/04
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