Recycling zinc anodes

Discussion in 'Metal Boat Building' started by wildman, Apr 23, 2010.

  1. wildman
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    wildman Junior Member

    Now this may be an absolutely stupid idea but I'd like some opinions based in fact/experience.

    Since I have been replacing anodes on my 42ft hull at 50% consumption for several years I have a modest supply of half used zincs in my garage. I had a go at making a mold and experimenting with recasting them with straps embedded.

    This was successful but dare I trust them to protect my steel hull?

    I have reasoned that by using a clean steel mold that the zinc purity will be the same as the original anodes and therefore just as effective.
     
  2. mark775

    mark775 Guest

    You are going to have some slag to skim but these are far and away better than any store-bought ones available. Be careful.
     
  3. wildman
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    wildman Junior Member

    Well I did skim some slag off.

    Why would they be better than store bought ones?

    And what would you suggest I be careful of? All I can think of is safety issues re molten metal splashing and the risk of introducing impurities into the orginal metal.

    Have you done this before?
     
  4. MikeJohns
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    MikeJohns Senior Member

    They will be fit for purpose, the alloying will not change re-casting them.

    If you have any queries about anodes your'e welcome to email me directly, I'm in Margate.
     
  5. Frosty

    Frosty Previous Member

    This is interesting --whats wrong with keeping the discussion public?
     
  6. marshmat
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    marshmat Senior Member

    I've come across a few articles on re-casting old zincs. I don't see any reason to suspect it wouldn't work. The alloy doesn't change, and the dross and slag are apparently fairly easy to skim off the top of the melt.

    Zinc melts at about 420 C (787 F), achievable with amateur equipment (propane works). Of course, the usual safety precautions for working with molten metal will apply, especially proper cleaning and pre-heating of the moulds and straps.
     
  7. TollyWally
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    TollyWally Senior Member

    That makes sense. I know about the dangers of water. I've been to several keel pourings but quite frankly it was all blind leading the blind type of affairs.
     
  8. wildman
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    wildman Junior Member

    Here's what I did. CAVEAT: I am inexperienced in this and DO NOT recommend anyone trying it. I only list this in hope that someone tells me what I have done wrong.

    Melted partly consumed anodes in a stainless steel pot. These were melted over a propane torch and cast into the concave base of some Aluminium soft drink cans. In the process dross/slag was removed. The can bases were heated to burn off any paint or residue that may have been there. I found that starting with small pieces first helped to get it melting efficiently and maintained a good layer of molten metal in the bottom of the pot to ensure that new pieces were well "wetted".

    I made a simple mold from some mild steel angle welded in a rectangle and bolted to a steel base plate. To facilitate reasonably easily release I made sure that the welds were smooth. The base was bolted on so that I could remove it and belt out any stuck castings with a hammer.

    I found that the best way to get consistent heating was to build a small furnace from bricks with the mold on top and the business end of the propane torch right up under the mold.

    Turned the gas on and got the mold nice and hot then carefully, with tongs, I placed each of my slugs into the melt one by one. DO NOT DROP them in.

    When the mold was filled with molten metal, with tongs again, I placed the original strap into the melt then allowed to cool naturally. The strap was cleaned first.

    I used welding gloves and safety glasses when handling the melt.

    The process required melting the metal twice. It just seemed easier and safer to handle the metal that way at the time rather than trying to purify it and cast at the same time. That pot of molten metal got quite dicey to handle when there were 4-5kgs in it. And I found that if I didn't have quite enough clean metal for a continuous pour (or spilt some dross into the mold) then I'd have to start over with trying to remelt a large lump of metal - which is harder than the small slugs.

    See photos attached.
     

    Attached Files:

  9. wildman
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    wildman Junior Member

    Matt

    Where would I look for such articles?
     
  10. marshmat
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    marshmat Senior Member

    Wildman,

    There was a good article in Practical Boat Owner (UK) quite a few years ago, issue 398 I think. But it sounds like you already have it all figured out; your process makes sense and appears to address most of the potential pitfalls I can think of.
     
  11. wildman
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    wildman Junior Member

    To help Google help you ->

    Found two articles listed here http://marinedirectory.ybw.com/reprints/results1.jsp

    Melting down and reusing zinc anodes, John Smith
    Practical Boat Owner
    March 2003 p62

    Anodes - reuse old ones, Vic Croft
    Practical Boat Owner
    June 2000 p139
     
  12. CDK
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    CDK retired engineer

    Wildman, you know by now that your recycled anodes can safely be used to protect your boat.

    I do hope you carried out your experiments outside and didn't stand on the downwind side of your melting pot: melting old zinc produces some very unhealthy gases.
     
  13. wildman
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    wildman Junior Member

    Thanks CDK. That is a good point! I did read about such a thing in my prepartory research and consequently keep my big doors open and face well away from the melt. Arms length is the rule - hence my difficulties in handling that 4-5kg pot!
     
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  14. mark775

    mark775 Guest

    Good job, Wildman! I hate seeing bits and pieces go into the landfill! I have about 400 lbs. of 'em and also like saving thousands of dollars (over a lifetime) on zincs. Aluminum melts at 660°C - be careful as it happens fast.
     

  15. wildman
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    wildman Junior Member

    Update. A couple of things happened on my way on to the slip today. The first was that as I prepared to leave my berth my neighbour (who has a 60ft steel hull) informs me he is using Aluminium and that the tugs boats in our same small bay are also using them. Why? Cost! They are marginally cheaper kg for kg. But, 1kg of Al has more protective capacity than 1kg of Zn - so in theory you should need less and hence it will cost less. How much less is a guess I can't make.

    The second thing was that on haul out I found most of my anodes corroded more or less equally except for two both on the stbd side. Two mounted in a similar location but on the port side were in need of replacing. These two were the same make/size as the stbd side two. The port side lies along side an unpowered dock while the stbd is some 6 metres from the next dock. The dock is held up by rusting steel pylons - am I protecting the landlord's (docklord's??) pylons?
     
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