Lead Bulb

[matalag]

Dear Friends,
I am constructing a sail boat of 40' with lead bulb fin keel.I coul not find any professional casting guy in my city.There are some but no experince.So I need some info and drawins help casting the bulb(1.7 ton)in one piece.

[dimitarp]

Hi,
First you need to make or cast a steel shell and then to fill hollow with lead. If you do not use the steel shell then you need to cast the bulb with lead-antimony alloy.

[Raggi_Thor]

We made a wooden template by revolving a naca 0018 profile.
Then we made a sand form (mold) and cast the bulb in two halfs.
I think it's possible to make concrete mold also.

[matalag]

Thank you very much for your quick reply
Regards

[gonzo]

You can make a form with wood. Paint the inside with whitewash (lime) so it doesn't burn the wood. The main difficulty is in melting enough lead to pour in one operation.

[SeaSpark]

Concrete can crack or even explode when heated suddenly.

[dougfrolich]

We have made a plaster cast over a foam plug. Split the cast in two longways, Set the cast in sand as one piece with several vents along the top, and a filling port. Metled the lead over a Propane burner in a s.steel pot that had a gate valve off the bottom side. It took about 1 hr to melt 1,000lbs of lead. The largest pieces were about 50lbs. before we put them in the pot, smallest were about 2lbs. we added little by little until it was all melted cleaned off the slag as we went along. Then opened the gate valve and filled up the cast all at once. It bubbled popped and steamed. But since it was all buried in sand and vented well it result was a very nice 1,000lb bulb.

[Danimal]

dougfrolich - can you explain a little more about the process - not entirely sure - is the plaster sacrificial?

could be stupid question but haven;t looked into this at all