geem
Well-known member
Anybody had their anchor chain sheradised? It is supposed to give a harder zinc finish than hot dipped galvanising. A friend had his done and speaks highly of it
Sheradising
- Thread starter geem
- Start date
greeny
Well-known member
Hmmm.......................Interesting. For those who don't know what it is.
"Sherardizing is a solid diffusion process in which goods are heated in the presence of zinc dust and inert material as sand. The process is normally carried out in a slow rotating closed container at temperatures ranging from 320 ºC to 500 ºC. The zinc / iron alloyed coating is subsequently zinc phosphated resulting in clean passivated surface. The coating closely follows the contours of the basis material, and uniform coatings are produced on articles, including those of irregular shape. Process follows international standard EN 13811 “Sherardizing. Zinc diffusion coating on ferrous products. Specification”
Sherardize coatings have a mat grey surface and may show scratches resulting from normal contact with other fasteners. Due to the hardness of the coating, such scratches are superficial and not detrimental to its corrosion resistance.
Due to the diffusion on zinc in the base material surface, coating adhesion is better than hot dip galvanized and mechanical galvanized coatings.
Sherardizing coatings show a harder, smoother surface finishing compared to hot dip galvanizing, as well as a better control of coating thickness. These facts allow a better control of friction between cone shape of wedge bolt and their expansion clips, making they convenient for expansion anchors. On the opposite, hot dip galvanizing items may not provide sufficient control of friction sensitive parts, and its operation can be adversely affected. While achievable coating thickness of sherardize are similar to HDG ones, control thickness is superior."
Sourced from Google.
"Sherardizing is a solid diffusion process in which goods are heated in the presence of zinc dust and inert material as sand. The process is normally carried out in a slow rotating closed container at temperatures ranging from 320 ºC to 500 ºC. The zinc / iron alloyed coating is subsequently zinc phosphated resulting in clean passivated surface. The coating closely follows the contours of the basis material, and uniform coatings are produced on articles, including those of irregular shape. Process follows international standard EN 13811 “Sherardizing. Zinc diffusion coating on ferrous products. Specification”
Sherardize coatings have a mat grey surface and may show scratches resulting from normal contact with other fasteners. Due to the hardness of the coating, such scratches are superficial and not detrimental to its corrosion resistance.
Due to the diffusion on zinc in the base material surface, coating adhesion is better than hot dip galvanized and mechanical galvanized coatings.
Sherardizing coatings show a harder, smoother surface finishing compared to hot dip galvanizing, as well as a better control of coating thickness. These facts allow a better control of friction between cone shape of wedge bolt and their expansion clips, making they convenient for expansion anchors. On the opposite, hot dip galvanizing items may not provide sufficient control of friction sensitive parts, and its operation can be adversely affected. While achievable coating thickness of sherardize are similar to HDG ones, control thickness is superior."
Sourced from Google.
Metalicmike
Active member
We never stop learning
geem
Well-known member
I am going to have my chain done. I don't find HDG effective when full-time liveaboard with chain deployed 99% of the time. My 2 year old chain is already showing signs of corrosion. I may well do the anchor as well for similar reasons
Bouba
Well-known member
How did you find a sherardizer ?
geem
Well-known member
A friend had his done by Sherradising UK in Wigan. Phone number 01942230178
Neeves
Well-known member
Sharadizing has now been overtaken by 'better' technogy. The process is now known as Thermal Diffusion Galvanising.
Sheradizing, is still practised in many countries round the world. The original process depends on the rotating oven being filled with the products being coated, silica (quartz sand) and the zinc being used to coat the articles. The process is conducted at lower temperatures than HDG and is more conducive to coating HT steels. The popularity of Sheradising was hit with fears of silicosis - hot silica does not sound too pleasant.
There are now newer processes that dispense with the hot sand.
TDG is now conducted in rotating ovens (a bit like a ball mill, without the balls).
The surface area of the charge is calculated, or known (there are crib sheets for chain and many of the items commonly processed) the coating characteristics of the zinc are known and it is a simple calculation to define what coating thickness will be provided. Common HDG coating thicknesses are 'about' 70 micron, can vary from 50 microns to 100 microns. The US Navy and Marines specify 80 microns min (and I specify 100 microns, see below). Compared to HDG the process takes more time. TDG is the specified process for the studs holding up wind turbines, and studs to reinforce mines, clips for railway lines and nails for nail guns are common items processed. The US Navy use the process for tie down chains and for small; craft anchor chains.
Because TDG is 'better' than HDG there has been a tendency to reduce coating thickness with TDG - as many items that are galvanised commonly are not subject to abrasion. The TDG and HDG coating seems to have similar characteristics in a chemical, acid, environment.
The resultant coating is harder than HDG - and hardness is directly related to abrasion resistance.
The life of anchor chain is effectively defined by abrasion resistance and the US Navy/Marines and my tests underline the superior coating abrasion resistance of TDG. The Navy was persuaded simply because of the financial savings (and the ability to coat HT chain).
There now a number of competitive TDG coating technologies, largely as briefly described above, and one difference is that the zinc addition is not just zinc powder but includes a cocktail of additives. One process is known as Armorgalv another is Greencote (or Green Coat).
I worked with Armorgalv in Australia and specifically the then General Manager trialing different chain under different conditions. I had my chain, a G80 6mm replacing 8mm G30 processed and the 6mm chain has slightly better strength than the 8mm it replaced. I conducted abrasion testing as well as tensile testing. Since then I increased the chain specification to G100 and have 'managed' coating of almost 10 rodes, 6mm and 8mm, since - the objective has always been replacing a larger chain with a smaller one - saves weight. I also had all the components coated at the same time, large end links and chain hooks.
Jonathan
Sheradizing, is still practised in many countries round the world. The original process depends on the rotating oven being filled with the products being coated, silica (quartz sand) and the zinc being used to coat the articles. The process is conducted at lower temperatures than HDG and is more conducive to coating HT steels. The popularity of Sheradising was hit with fears of silicosis - hot silica does not sound too pleasant.
There are now newer processes that dispense with the hot sand.
TDG is now conducted in rotating ovens (a bit like a ball mill, without the balls).
The surface area of the charge is calculated, or known (there are crib sheets for chain and many of the items commonly processed) the coating characteristics of the zinc are known and it is a simple calculation to define what coating thickness will be provided. Common HDG coating thicknesses are 'about' 70 micron, can vary from 50 microns to 100 microns. The US Navy and Marines specify 80 microns min (and I specify 100 microns, see below). Compared to HDG the process takes more time. TDG is the specified process for the studs holding up wind turbines, and studs to reinforce mines, clips for railway lines and nails for nail guns are common items processed. The US Navy use the process for tie down chains and for small; craft anchor chains.
Because TDG is 'better' than HDG there has been a tendency to reduce coating thickness with TDG - as many items that are galvanised commonly are not subject to abrasion. The TDG and HDG coating seems to have similar characteristics in a chemical, acid, environment.
The resultant coating is harder than HDG - and hardness is directly related to abrasion resistance.
The life of anchor chain is effectively defined by abrasion resistance and the US Navy/Marines and my tests underline the superior coating abrasion resistance of TDG. The Navy was persuaded simply because of the financial savings (and the ability to coat HT chain).
There now a number of competitive TDG coating technologies, largely as briefly described above, and one difference is that the zinc addition is not just zinc powder but includes a cocktail of additives. One process is known as Armorgalv another is Greencote (or Green Coat).
I worked with Armorgalv in Australia and specifically the then General Manager trialing different chain under different conditions. I had my chain, a G80 6mm replacing 8mm G30 processed and the 6mm chain has slightly better strength than the 8mm it replaced. I conducted abrasion testing as well as tensile testing. Since then I increased the chain specification to G100 and have 'managed' coating of almost 10 rodes, 6mm and 8mm, since - the objective has always been replacing a larger chain with a smaller one - saves weight. I also had all the components coated at the same time, large end links and chain hooks.
Jonathan
Neeves
Well-known member
There have been some disasters.
Galvanised anchor chain used in an acidic environment - the coating, any coating does not last. Do not use any galvanised product in a slow moving, nutrient rich environment (muddy, smelly water).
Most items galvanised do not suffer abrasion, steel girders (even those used for Iron Bru) - abrasion rates are better with TDG but it is cost effective to insist on an even thicker coating.
Some clown from Tasmania seems to have copied what I did but ignored the need for a good coating - the chain did not last - he made no specification for coating thickness. A chain maker in Oz believed the hype and they too did not check coating thicknesses - rejection levels were expensive. Specify and check.
In my Post No7 I omitted to mention that TDG uses no acid, a source of hydrogen embrittlement, HE (in HT steels). The cooling process TDG almost has exactly the same profile as the ASTM recommended process to remove HE in pickled steels.
Jonathan
Galvanised anchor chain used in an acidic environment - the coating, any coating does not last. Do not use any galvanised product in a slow moving, nutrient rich environment (muddy, smelly water).
Most items galvanised do not suffer abrasion, steel girders (even those used for Iron Bru) - abrasion rates are better with TDG but it is cost effective to insist on an even thicker coating.
Some clown from Tasmania seems to have copied what I did but ignored the need for a good coating - the chain did not last - he made no specification for coating thickness. A chain maker in Oz believed the hype and they too did not check coating thicknesses - rejection levels were expensive. Specify and check.
In my Post No7 I omitted to mention that TDG uses no acid, a source of hydrogen embrittlement, HE (in HT steels). The cooling process TDG almost has exactly the same profile as the ASTM recommended process to remove HE in pickled steels.
Jonathan
Last edited:
howardclark
Active member
Yes had it done on my last boat - a Westerly- was very happy with the results
geem
Well-known member
Considering my G40 chain is only 2 years old and starting to rust, it may give a longer life than HDG so worth a try. I doubt it can be any worse
RunAgroundHard
Well-known member
What is the cost differential between HDG and Sheradising?
Neeves
Well-known member
The decks of landing craft are abrasive, to make them non slip, conventional tie down galvanised chain is heavy. TDG offered opportunity to use High Tensile chain allowing use of small, so lighter, chain but not sacrificing strength. The US Navy/Marines found the TDG coating gave a longer life, saving significant replacement costs.
If you anchor in tidal rivers extensively and for prolonged periods with high nutrient levels the acid environment will destroy any galvanising (and the chain). This is TDG coated 6mm G100 chain.
Anecdotally the Gulf of Thailand has similar issues
Jonathan
If you anchor in tidal rivers extensively and for prolonged periods with high nutrient levels the acid environment will destroy any galvanising (and the chain). This is TDG coated 6mm G100 chain.
Anecdotally the Gulf of Thailand has similar issues
Jonathan
geem
Well-known member
We had similar issues at Portobello in Panama. Anchored in a bay with a couple of rivers discharging into it and deep silty mud. It stripped our galvanising in a week or two.
We don't make a habit of anchoring in such places. We are more concerned with the warm waters of the Caribbean and achieving more life out of our chain than HDG seems to deliver. Whilst we are back in the UK, it's an opportunity to get the chain treated as it's impossible when we are back in the Caribbean. I need to melt the lead out of the anchor and decide whether to HDG or Sherardize it. We don't have an option for any other treatment close enough to make it worthwhile
Neeves
Well-known member
For preparing an anchor for galvanising, specifically a Spade.
Removing lead and galvanising a Spade anchor
Its not a difficult process to remove the lead. You 'simply' need to restrain the anchor, arrange the anchor so the lead flows out freely, heat the lead, blow torch, in the ballast chamber, direct heat on the lead and on the exterior of the chamber. The toe of the anchor I was working on was small but had holes in the toe (which I guess were introduced to allow the anchor to be suspended for dipping in the zinc bath). But when I had the whole lot hot and molten pressure had built up in the toe and molten lead exited the toe in a fountain - it would be distressingly painful - I had no idea this would happen and I was working from the opening in the ballast chamber.
I had weighed before and after and made up for some losses (of lead) from lead fishing weights. I had roofing lead as well but the weights were cleaner.
I simply filled the chamber with 'frozen' lead and progressively melted and added to the molten bath. When I had finished I added about 10ml thickness or resin to seal the chamber.
You don't need any interruptions, keep children, dogs and telephones out of sight and earshot. If you are interrupted - you will lose some or all of the heat
The finished anchor, when TDG coated, is a matt dark grey colour - very different from hot dipped galvanising. I have never seen a genuine Sharardised coated item.
As an aside
If you decide to add connectors, a chain hook or bridle plate - you can buy connectors and chain hooks from a distributor of lifting equipment (including chain). The components come painted or powder coated. I simply used paint stripper and a wire brush (+ heavy duty rubber gloves). I needed multiple coating of paint stripper on some items.
I have a pdf on our chain - if anyone wants a copy send an email by PM and I'll send a copy.
Jonathan
Removing lead and galvanising a Spade anchor
Its not a difficult process to remove the lead. You 'simply' need to restrain the anchor, arrange the anchor so the lead flows out freely, heat the lead, blow torch, in the ballast chamber, direct heat on the lead and on the exterior of the chamber. The toe of the anchor I was working on was small but had holes in the toe (which I guess were introduced to allow the anchor to be suspended for dipping in the zinc bath). But when I had the whole lot hot and molten pressure had built up in the toe and molten lead exited the toe in a fountain - it would be distressingly painful - I had no idea this would happen and I was working from the opening in the ballast chamber.
I had weighed before and after and made up for some losses (of lead) from lead fishing weights. I had roofing lead as well but the weights were cleaner.
I simply filled the chamber with 'frozen' lead and progressively melted and added to the molten bath. When I had finished I added about 10ml thickness or resin to seal the chamber.
You don't need any interruptions, keep children, dogs and telephones out of sight and earshot. If you are interrupted - you will lose some or all of the heat
The finished anchor, when TDG coated, is a matt dark grey colour - very different from hot dipped galvanising. I have never seen a genuine Sharardised coated item.
As an aside
If you decide to add connectors, a chain hook or bridle plate - you can buy connectors and chain hooks from a distributor of lifting equipment (including chain). The components come painted or powder coated. I simply used paint stripper and a wire brush (+ heavy duty rubber gloves). I needed multiple coating of paint stripper on some items.
I have a pdf on our chain - if anyone wants a copy send an email by PM and I'll send a copy.
Jonathan
Neeves
Well-known member
I stand to be corrected but the standard for gal thickness for HDG is 70 microns. I've measure chain and the average might be 70 microns but it can vary, even on the same length of chain. Most galvanised product does not suffer abrasion.
For HDG you will almost certainly need to follow the galvanisers practice - aiming for 70 microns. Asking for a thicker coating is not recommended as the resultant coating can flake.
With Thermal Diffusion Galvanising the US with a 80 micron spec and myself, may 750m of chain in total, 100 microns has had no downside except
You need to persuade the operator to add the extra zinc, he needs to cost the extra time for the process and you, the customer needs to pay. I don't think that zinc dust is prohibitevely expensive but the extra energy need to run the oven and 'lost' production are a cost. To me the extra 30% is, approx, another year at anchor (plus or minus) and if the operator is not being ridiculous - its worth paying for. Its worth reiterating - the operator thinks he knows best - but he does not use anchor chain 365 - he is an expert on galvanising and will not realise the short life chain might have. You may need to be persuasive. It helps if you can do this face to face.
The Armorgalv process includes grit blasting prior - this removes any superficial ruse and paint - Sheradizing may be different. If you have the facility - driving on a damp beach removes rust and paint from chain, simply tow the chain. I suspect doing something similar might work on a road. The chains I use are supplied grit blasted and oil (diesel) in 'sealed' drums but as still grit blasted (belt and braces).
My coating thickness meter really only works on flat surfaces, more sophisticated meters can measure curved surfaces. I took single links and sliced them in half (thin blade on an angle grinder), lengthwise, and then joined the half links every 10m along the rode. I could then measure the thickness and give some of the links to the owner of the new chain (they could have them checked (if they so wished) against the 100 micron spec).
Because I was coating Quench and Tempered chain the process re-tempers the chain and some strength is lost. I had the chains tested prior and subsequent to the TDG process. If one knew the Q&T process of the original chain it might be possible to alter the heating and cooling schedule of the TDG process to better match the original Q&T process. Q&T details appear to be closely guarded secrets
Jonathan
For HDG you will almost certainly need to follow the galvanisers practice - aiming for 70 microns. Asking for a thicker coating is not recommended as the resultant coating can flake.
With Thermal Diffusion Galvanising the US with a 80 micron spec and myself, may 750m of chain in total, 100 microns has had no downside except
You need to persuade the operator to add the extra zinc, he needs to cost the extra time for the process and you, the customer needs to pay. I don't think that zinc dust is prohibitevely expensive but the extra energy need to run the oven and 'lost' production are a cost. To me the extra 30% is, approx, another year at anchor (plus or minus) and if the operator is not being ridiculous - its worth paying for. Its worth reiterating - the operator thinks he knows best - but he does not use anchor chain 365 - he is an expert on galvanising and will not realise the short life chain might have. You may need to be persuasive. It helps if you can do this face to face.
The Armorgalv process includes grit blasting prior - this removes any superficial ruse and paint - Sheradizing may be different. If you have the facility - driving on a damp beach removes rust and paint from chain, simply tow the chain. I suspect doing something similar might work on a road. The chains I use are supplied grit blasted and oil (diesel) in 'sealed' drums but as still grit blasted (belt and braces).
My coating thickness meter really only works on flat surfaces, more sophisticated meters can measure curved surfaces. I took single links and sliced them in half (thin blade on an angle grinder), lengthwise, and then joined the half links every 10m along the rode. I could then measure the thickness and give some of the links to the owner of the new chain (they could have them checked (if they so wished) against the 100 micron spec).
Because I was coating Quench and Tempered chain the process re-tempers the chain and some strength is lost. I had the chains tested prior and subsequent to the TDG process. If one knew the Q&T process of the original chain it might be possible to alter the heating and cooling schedule of the TDG process to better match the original Q&T process. Q&T details appear to be closely guarded secrets
Jonathan
