Shrinkage of Lead

[Submarine Tom]

Sam,

Tell me, what does it matter if it shrinks a bit?

Tom

[Fanie]

I have a couple of questions regarding this -

If you have a metal rod structure inside the keel, why can you not pour the lead directly into the keel, but not everything at once, pour layers instead ?

From experience I know lead stalls on the outside first where it cools of the quickest. the scrinkage is in the center. If the 'layer' you poured dies have some cavities from scrinkage it will be filled when the next layer gets poured.

This way it is much easier to handle the lead, you have iron inside for aditional strength, and you are sure that there are no air pockets or hollows in the lead, and scrinkage should play no role.

I can also imaging if you provide structure as part of the keel protruding to the inside it should make a proper bond for the lead to hold on.

As for keels falling off, I can imagine a bit of an overdesign on surface and structure where it adhere to the hull should resolve this.

[Sam III]

Originally Posted by Submarine Tom

Sam,

Tell me, what does it matter if it shrinks a bit?

Tom

I was concerned with how much larger to make the pattern for the bulb to plan for the shrinkage. My designer offered finished dimensions and I needed to hit the size, form and weight targets as the bulb was for a performance sailboat.

Sam

[TeddyDiver]

Lead tends to stick fast on a steel mould unless the mould is water cooled..
Anyway what I've found out with "tiny" 1 to 4kg pours..

[apex1]

Originally Posted by Sam III

I was concerned with how much larger to make the pattern for the bulb to plan for the shrinkage. My designer offered finished dimensions and I needed to hit the size, form and weight targets as the bulb was for a performance sailboat.

Sam

Sam
it was mentioned here long time ago, add antimony to the lead. That makes it harder and the shrinkage is almost gone. Common practice in the industry.

Regards
Richard

[mozart]

Originally Posted by alan white

It ought to be possible to remove the lead once cast and bed it in thickened epoxy.
If you coat the removed lead with several coats of epoxy and then also bed the lead into the cavity with thickened epoxy you will both eliminate any gaps and seperate the lead electrically from the stainless steel. The pre-coat will ensure the electrical barrier is thick enough where it might otherwise create a contact point between the metals when reassembled.

Thanks Alan for your kind comment. My intension is to leave the lead in the stainless steel frame which will be used as such. As we have only 0,5% salt water i do not regard the corrosion as a risk. Thgus I do not see there is a need for electric barrier. Keel bolts will be stainless as well. My only consern is how the shrinkage could be avoided, can it? or would it be possible to fill up the gap between the mould and the fabricated/welded frame later with some new lead melted in afterwords?
Mozart

[TeddyDiver]

There won't be any gap to fill. Possible shrinkage comes unevitably on the top (free) surface. Instead even if you try to take the cast out of a steel mould you need some serious hammering and end up busting the mould..

[mozart]

Originally Posted by TeddyDiver

There won't be any gap to fill. Possible shrinkage comes unevitably on the top (free) surface. Instead even if you try to take the cast out of a steel mould you need some serious hammering and end up busting the mould..

Thanks Teddy this is nice.
an other question is: what about leakage, from how small wholes would the lead leak out when pouring the melted lead into the stainless steel mould?
My welded keel is not purfect so there might be some small wholes along the weldings....

[alan white]

Originally Posted by mozart

Thanks Alan for your kind comment. My intension is to leave the lead in the stainless steel frame which will be used as such. As we have only 0,5% salt water i do not regard the corrosion as a risk. Thgus I do not see there is a need for electric barrier. Keel bolts will be stainless as well. My only consern is how the shrinkage could be avoided, can it? or would it be possible to fill up the gap between the mould and the fabricated/welded frame later with some new lead melted in afterwords?
Mozart

I am aware you want to encase the lead in a stainless shell. In any case, I would never do it because it is doubtful you'll have a perfect bond between the lead and the stainless even if no shrinkage occurs (adding antimony), since any slight grounding can loosen that poor bond.
Now you have the possability of crevice corrosion inside the thin stainless shell.
I realize you don't intend to sail in salt water. However, if it were me, I'd assume someone who bought the boat from me might sail it wherever they liked. Also, I'm not sure that corrosion couldn't happen due to other factors such as minerals or pollutants in the water.
The real issue, to me, would be whether the expensive and essentially unneeded stainless shell was worth the risks. My immediate answer would be no, based on hundreds of years of boatbuilding history where simple lead keels without anything over them have been completely practical.
I've seen few plain lead keels that didn't at one time or another had their forward end mashed in from a grounding. If that forward end has a stainless shell over it, there has to be an inner gap formed. In addition, the resultant gap will be nearly impossible to fix except by filling outside only with thiickened epoxy---- but if it had been plain lead, a half hour with a hammer would have the lead as good as new.

[Fanie]

The only way to get lead to adhere to SS is to have protrusions on the SS.

Although lead is soft, if it is in a thicker piece it becomes progressively difficult to bend. I would go the way Alan suggested. I can see the SS is not going to be the right thing to use.

If you haven't closed all the holes while pouring the lead is going to pour out of them. Lead is heavy and the pressure is much greater as a liquid than water would be. I build solder pots, the smallest hole will leak like you won't believe. No, you cannot block it with your finger

[gonzo]

We used to make molds out of wood. We whitewashed the inside to keep it from burning and as demolding agent.

[Submarine Tom]

What a project. Any pictures Sam?

Tom

[mozart]

Originally Posted by alan white

I am aware you want to encase the lead in a stainless shell. In any case, I would never do it because it is doubtful you'll have a perfect bond between the lead and the stainless even if no shrinkage occurs (adding antimony), since any slight grounding can loosen that poor bond.
Now you have the possability of crevice corrosion inside the thin stainless shell.
I realize you don't intend to sail in salt water. However, if it were me, I'd assume someone who bought the boat from me might sail it wherever they liked. Also, I'm not sure that corrosion couldn't happen due to other factors such as minerals or pollutants in the water.
The real issue, to me, would be whether the expensive and essentially unneeded stainless shell was worth the risks. My immediate answer would be no, based on hundreds of years of boatbuilding history where simple lead keels without anything over them have been completely practical.
I've seen few plain lead keels that didn't at one time or another had their forward end mashed in from a grounding. If that forward end has a stainless shell over it, there has to be an inner gap formed. In addition, the resultant gap will be nearly impossible to fix except by filling outside only with thiickened epoxy---- but if it had been plain lead, a half hour with a hammer would have the lead as good as new.

Thanks everybody for many pieces of good advice. I scrapped the stainless mold idea and went for a wooden mold made of plank with dimensions 8 by 2 inches and 6 foot long. Howard I. Cahapell tells me to paint the mold inside with waterglass. How should this be done? What will it look like? Where to get? Has anyone done it?

[gonzo]

Sodium silicate Na2SiO3 in a water solution. It is the same stuff they make muffler repair paste with

[Submarine Tom]

Sam III & mozart (two birds with one stone on this thread),

I am most interested in pictures of your projects.

How about it?

Tom