Galvansing Chain?

RufusM

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Well I wouldn't bother, because:

1. New length will be shiny
2. New chain will be unstressed (unlike old chain)
3. Hard to galvanize between links
4. If you have had a few years from it - it's had it's life
5. How easy do you sleep at anchor?


Go on treat yourself - Jimmy Green did me a cracking deal and beautifully spliced to a length of rode.

No relationship with Jimmy Green - honest. SWMBO is watching!! /forums/images/graemlins/laugh.gif /forums/images/graemlins/laugh.gif
 

jimbaerselman

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Interesting. You imply that chain loses strength with age, or after being stressed with use. What's the mechanism? Fatigue? or work hardening?

I have to admit to re-galvanising twice, and owning a nice shiny chain after each event, without any apparent difficulty with galvanising between links. It's now 20 years old . . . is this dangerous practice?

Does hot dip galvanising modify the strength through heat treatment at all?
 

hylass

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Before galvanization, you should confirm that the link diameter has not diminished excessively from wear or oxidation. A 10% loss of thickness is the maximum acceptable.

Check with your galvanizing company to verify two important points:

• Make sure the company uses an acid bath powerful enough to remove any length markers painted on the chain. If this is not the case, you must burn the paint off with a gas torch before you bring it in, otherwise these links will not receive proper treatment.

• Make sure the company uses a vibrating drum during the cooling process, which inhibits the chain links from sticking together.

Otherwise, each link fuses with the next, rendering the chain unusable. You don’t want to have to meticulously free each link one by one with a hammer; this is boring work without any guarantee of success, and it only damages the recent galvanization and requires an immediate repetition of the whole scenario.

Extract from the book :THE COMPLETE ANCHORING HANDBOOK
 

Bajansailor

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Most commercial vessels have no galvanising at all on their chain cables, and they seem to last for a reasonable time.

As Hylas says, the only important aspect to consider would be if any of the links are excessively worn. I am sure that a cable which just looks a bit tired still has a lot of life left in it! Especially if you can get it re-galvanised.
 

MoodySabre

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I didn't bother - a very rusty chain on the boat when I bought - age unknown. Local chandler at Dauntless, Benfleet has 8mm calibrated at £1.90 a metre and octoplat about the same. A very satisfying 45 mins doing the fancy splice. Loverly chubly and much cheaper than Jimmy Green.
 

Roach1948

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Re: Galvanising Chain?

Thanks for the tips. I have oversized chain for my yacht and it is not rusty yet - just looks a bit manky - so maybe I should continue to use as I am sure it has quite a lot of life left.
 

Mudplugger

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Re: Galvanising Chain?

If you really want to, then have a chat with the mob at Witham (having a Wogan moment & can't remember the name) but they are in the Tele. Book. Otherwise go and have a chat with I.Y.E @ Levington. They seem to be the Eastern region chain specialists and supply everyone else! So, very competitive. HTH
 

Birdseye

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[ QUOTE ]


Does hot dip galvanising modify the strength through heat treatment at all?

[/ QUOTE ]

Not significantly - the temperature isnt high enough.

Had my chain re galved in the plant I had, and all the operatives did was to whack it with an iron bar as it came out of the zinc bath, and this freed up the individual links.

If you want new chain, forget the chandlers and instead go to your local lifting tackle place (yellow pages, big city) as they will operate at half chandlery prices. And yes, they can get in calibrated chain, though you may well have to explain to them exactly what it is when you order .
 

Birdseye

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[ QUOTE ]
[ QUOTE ]
Does hot dip galvanising modify the strength through heat treatment at all?

[/ QUOTE ]
I understand it does if it's high tensile chain.

[/ QUOTE ]

Anchor chain should not be high tensile ie hardened and tempered alloy steel.
 

Searush

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Any one know first-hand of any small boat situation where an anchor CHAIN has snapped? Shackles break & come undone, cleats fail, ropes chafe, but "Chains breaking?" - I doubt it!!!!!

Not hearsay reports please - eyewitness, official reports or first-hand only!
 

hylass

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yes..
I was present at, at least two problems.. one with a swivel and another one with a broken chain..

More, on my own boat: a breaking of the axis of the anchor connector..

DSCN0135-copie.jpg
 

GMac

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Re-galvanising does effect the strength especially if a high tensile alloy chain (which I agree you should not be using anyway). Anyone who thinks getting a G7 or G8 chain and galvanising it for their boat is stupid stupid stupid and not that bright as well. Galvanising those chains can decrease the load by 50% if not more if done by a bunny. Just don't go there.

If the guy on the bath is a bunny you can suffer 25% lose of strength, I've seen it happen. Generally a good guy is OK but only do it once or get it proof loaded after if you do it more times. Probably will be OK but better safe than sorry.

No good manufacturer makes un-calibrated short link chain.

I've seen 6 broken anchor chains 1st hand and have been told of many more, about 1/2 of those I believe to be true. It is not common but does happen and is increasing. The increase is purely due to the increased amounts coming out of the east. Generally their calibration is poor to no-existant and the proof loads, if applied at all, are a lot lower than what we have been used to, in some cases 40% lower. This obviously means the WLL is 40% less as well.

So re-galvanising is not a bad thing but something to be done baring in mind the possible downsides.
 

cliff

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[ QUOTE ]
[ QUOTE ]
[ QUOTE ]
Does hot dip galvanising modify the strength through heat treatment at all?

[/ QUOTE ]
I understand it does if it's high tensile chain.

[/ QUOTE ]

Anchor chain should not be high tensile ie hardened and tempered alloy steel.

[/ QUOTE ]O.K. here we go......
Though the hot dip galvanising process may vary slightly from plant to plant, the fundamental steps in the galvanizing process are:
Soil & grease removal - A hot alkaline solution removes dirt, oil, grease, shop oil, and soluble markings. Pickling - Dilute solutions of either hydrochloric or sulfuric acid remove surface rust and mill scale to provide a chemically clean metallic surface.
Fluxing - Steel is immersed in liquid flux (usually a zinc ammonium chloride solution) to remove oxides and to prevent oxidation prior to dipping into the molten zinc bath. In the dry galvanising process, the item is separately dipped in a liquid flux bath, removed, allowed to dry, and then galvanised. In the wet galvanising process, the flux floats atop the molten zinc and the item passes through the flux immediately prior to galvanising.

Galvanising - The article is immersed in a bath of molten zinc at between 435-455° C. During galvanising, the zinc metallurgically bonds to the steel, creating a series of highly abrasion-resistant zinc-iron alloy layers, commonly topped by a layer of impact-resistant pure zinc.

Finishing - After the steel is withdrawn from the galvanising bath, excess zinc is removed by draining, vibrating, blowing with superheated steam or - for small items - centrifuging. The galvanised item is then air-cooled or quenched in liquid.

As far as I am aware the type of chain normally used for small boat anchor chain is made from normalized bar stock, by normalizing I mean the bar stock has undergone a heat treatment process that has the object of relieving internal stresses, refining the grain size and improving the mechanical properties. The steel is heated to 800-900° C according to analysis, held at temperature to allow a full soak and cooled in still air.

Alloy chain (becoming more popular) will subsequently be quenched and tempered however the tempering temperature should be in excess of 450°C in order to form Sorbite which has greater ductility and toughness than Troostite which is formed at lower tempering temperatures. For anchor chains the greater ductility and toughness is an advantage rather than the lower toughness and ductility and higher tensile strength if tempered at a lower temperature.

As hot dip galvanising is carried out at 435-455°C the properties of standard low carbon grade (mild steel) will not be adversely affected – think about it – the chain has already been galvanised so could be considered to have already been “tempered” at 455°C.

Now we come to tempering, however, technically tempering is a process done subsequent to quench hardening, so if the chain is “normal mild steel and has been normalized during manufacture and not quenched it cannot be "tempered".

Quench-hardened high Carbon or allow parts are often too brittle. This brittleness is caused by a predominance of Martensite. This brittleness is removed by tempering. Tempering results in a desired combination of hardness, ductility, toughness, strength, and structural stability.

Tempering is not to be confused with tempers on rolled stock - these tempers are an indication of the degree of cold work performed.

The mechanism of tempering depends on the steel and the tempering temperature. The prevalent Martensite is a somewhat unstable structure. When heated, the Carbon atoms diffuse from Martensite to form a carbide precipitate and the concurrent formation of Ferrite and Cementite, which is the stable form.

Tool steels for example, lose about 2 to 4 points of hardness on the Rockwell C scale. Even though a little strength is sacrificed, toughness (as measured by impact strength) is increased substantially. Springs and such parts need to be much tougher — these are tempered to a much lower hardness. (At a higher Tempering temperature).

Tempering is done immediately after quench hardening. When the steel cools to about 40 ºC after quenching, it is ready to be tempered. The part is reheated to a temperature of 150 to 400 ºC . In this region a softer and tougher structure Troostite is formed. Alternatively, the steel can be heated to a temperature of 400 to 700 ºC that results in a softer structure known as Sorbite. This has less strength than Troostite but more ductility and toughness.

The heating for tempering is best done by immersing the parts in oil, for tempering upto 350 ºC and then heating the oil with the parts to the appropriate temperature. Heating in a bath also ensures that the entire part has the same temperature and will undergo the same tempering. For temperatures above 350 ºC it is best to use a bath of nitrate salts. The salt baths can be heated upto 625 ºC. Regardless of the bath, gradual heating is important to avoid cracking the steel.

After reaching the desired temperature, the parts are held at that temperature for a time dependant on thickness, then removed from the bath and cooled in still air.

Quenched and Tempered chain would then go on for galvanizing.

There are mechanisims that could result in embrittlement of the chain or to be more precise embrittlement of the heat affected zone (resulting from the flash weld) however under controlled conditions this embrittlement should not occur.

From a metallurgical point of view I would have no hesitation in having chain regalvanised however the cost of regalvanising and proof testing old chain against the cost of new chain would be the deciding factor for me.

To give the chain to the "man down the road" would not be advisable IMHO. If you want to regalvanise the chain try to find a specialist Company that does (re)galvanising of chain as part of their normal operations.
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cliff

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Brilliant. I do love it when somebody knowledgable talks dirty.

[/ QUOTE ]And I didn't even mention primary or secondary Widmanstätten /forums/images/graemlins/laugh.gif
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Bajansailor

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I had a text book at college 25 years ago called 'Engineering Materials and their Applications' by the indomitable duo Flinn & Trojan.
Still have the book.
Baffled me back then, and still baffles me now.
But your explanation above was much easier to understand than their ramblings, thanks for taking the trouble.
I reckon you should write your own book......
 
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