Shrinkage of Lead

Discussion in 'Fiberglass and Composite Boat Building' started by Sam III, Dec 2, 2008.

  1. Sam III
    Joined: Sep 2007
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    Sam III Junior Member

    I'm tooling up for a lead bulb for the keel on our production boat.

    Does anyone know the 'shrinkage' per Inch for lead? I need to oversize the mold to allow for shrinkage when the lead cools.

    Any input for a souce of lead for keel bulb casting?

    Thanks in advance.

    Sam
     
  2. Guest62110524

    Guest62110524 Previous Member

    from my exp it does not shrink, for instance when poured into a mold, if it shrank it would pull away from the mold, or shell keel, and it does not, it stays clued to the box, or shell , steel or alloy
     
  3. waikikin
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    waikikin Senior Member

  4. PAR
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    PAR Yacht Designer/Builder

    Actually lead shrinks quite a bit. Most molds for ballast castings take this into account and are made slightly over size. This procedure has a second benefit, which permits some trimming up to fair things out.

    The size of the pour and the general dimensions of the casting also can have a substantial effect on the amount of shrinkage. If you post the general dimensions of your appendage, I can tell you how much shrinkage to expect.

    The avarage rule for lead casting is about 1/64th in length, which is about an inch across 10'.
     
  5. Sam III
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    Sam III Junior Member

    The bulb is 1350 mm long and 212 mm at it's widest.

    That would make for 2.6 % (5/16/12) or 1.5 % (3/16/12) or .1 % (1/64/12) depending on which chart you use.

    I can do that automatically with the software I use just a lot of discrepency between 1/64th and 5/16th's.

    The number I got for the keel fin (cast iron) was .8 %.

    Hmmmm.

    Sam
     
  6. PAR
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    PAR Yacht Designer/Builder

    ~21 mm shrinkage along it's length, 3 mm (or less) across it's width.
     
  7. Jimbo1490
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    Jimbo1490 Senior Member

    If you use lead recycled from lead/acid batteries you get basically zero shrinkage. That lead is alloyed with antimony, which is one of only two metals that expands when it cools. When carefully alloyed with lead (to which it is similar in physical characteristics), the shrinkage and expansion are in perfect balance. I don't know if it's going to be practical or even of value to do this, just a thought. :)

    Jimbo
     
  8. Stumble
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    Stumble Senior Member

    Sam,

    unless you have a lot of experience working in lead I would recomend you outsource the keel fabrication to a specialty shop for two reasons.

    The first is that since you are in the US you will have to deal with all of the OSHA requirements for working with a toxic substance. I don't know what they are for lead off hand, but the cost just for the equipment could be pretty expensive. Certainly in the range of the extra cost of haveing a reputable company that specializes in keels make them.

    Secondly there are a number of liability issues that could arrise from doing the work yourself. First of course is the long term health effects from workers being exposed to toxic substances. In the event someone does have long term health effects from working for you, the potential exposure could be huge, and while workers comp would likely cover it, you may also be caught under the Jones act or Longshoreman's Act either of which could drastically increase the liability of this type of problem

    The second legal issue is that the most common major problem for new boats is keels falling off due to faulty construction or poor enginearing. By outsourcing the manufacturing you have a chance that should something go wrong you can make a claim against them for any incurred damage. Particularly if there is a chance they screwed up the keel in the manufacturing process.


    Of course if you are really ready to pour your own keels, good luck. But as an attorney these are a few of the things that would concern me.
     
  9. PAR
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    PAR Yacht Designer/Builder

    I've poured lead several times and didn't have OSHA show up once. Stand up wind and work with care. Insure the mold is dry (really dry) as any moisture will produce an explosion of molten lead, which you honestly don't want raining down on you. My last few pours were done in a cast iron bath tub.

    In a production environment, you will have liability issues and OSHA will have to be consulted/conformed to.

    Many production facilities do job out their keels for this reason. If you want to control production quality, then an in-house pour, will offer the best oversight.

    The keels that are falling off boats are typically racers, where the engineering margin of safety is fairly low, in an effort to increase ballast/displacement ratio, which makes them go faster. On most production boats, this isn't a big issue, with literal hundreds of thousands of keels still hanging onto the bottoms of their mother craft, decades after construction.
     
  10. Stumble
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    Stumble Senior Member

    Par,

    I only mentioned OSCA since he said this was for a boat about to go into production. Which I assumed meant he was the builder of (indicating a commercial operation).

    And true keels don't exacally have a habit of falling off. But from a liability standpoint the potential cost of even one doing so is huge. One case I know quite well, the asked for damages were in the tens of millions since one of the crew was lost as sea. And happen to be makeing $500,000+ as a doctor.
     
  11. Sam III
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    Sam III Junior Member

    I have a very small shop and will not expect employee's / contractor's to do the casting. I actually enjoy it.

    I have a 'boutique' shop and expect to only build 10 or so boats a year.

    As for liability, I agree, that there are all kinds of exposures in the boat building business that's why I have liability insurance.

    I am having the keel fin cast by a foundry, much higher tempuratures and health risks. Not ready to invest in a full blown foundry....

    But based upon the quotes for the bulb which is realitively low temperature casting, only 700 degrees F, seems to be pretty high. This premium is more than I think it's worth for the job and I can take the savings and spend 1/2 of them for more liability insurance if I want.... Though I am a bit insurance poor at the moment. ;-)

    As for the safety issure, work in an open area, wear protective clothing (cotton fibers, they burn through, but don't ignite and melt on you), organic resperator, face shield, welders gloves and welders apron. Don't let anyone stand around to observe unless they are dressed up to work as well.

    I've done this before but didn't need to maintain the accuracy needed for a production boat.

    Thanks for the input all.

    Sam
     
  12. Guest62110524

    Guest62110524 Previous Member

    yes well since your post Par, I found a 12 foot length does shrink 8 mm, or 5 sixteenth inch
    so seeing as my pours were 14 inch, wide in compartments I noticed bugger all shrinkage
    strange really ,exp rates, lead melts at lo temps, you would think exp would be low, but its actually higher than most
     
  13. TeddyDiver
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    TeddyDiver Gollywobbler

  14. mozart
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    mozart Junior Member

    stainless steel keel profile to be filled with lead

    I have planned to fill a fabricated stainless steel ballast keel consruction with lead.
    Size of keel construction is 3 feet long, 2 inches wide, 6 inches high.
    The stainless steel material is approx 1/8 " think. What will haoppen when filled with lead? Will it shrink so that there is a risk of having air insted of lead in both ends of the completed casted ballast keel?
    What can be done to aviod it?

    Thanks in advance.
    Mozart
     

  15. alan white
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    alan white Senior Member

    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.
     
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