BERT T
Well-Known Member
Crosby C Links are available from http://www.tecni-lift.co.uk/Crosby-10mm-G335-Chain-Missing-Link-1250-kgs-WLL-221-013-156
10mm £8.37 + vat if anyone is interested.
10mm £8.37 + vat if anyone is interested.
Chain-link concerns: valid?
- Thread starter dom
- Start date
Neeves
Well-Known Member
There is a lot of misinformation on G70. It is made to exactly the same 'brittleness' spec as G30 and G43. All 3 should have a minimum elongation at break of 15% - so if G70 is brittle - then G40 is also brittle! G80, G100 and G120 is meant to be made to an extension to break of a minimum of 20% - so HT chains are less brittle than 'our' chains. However these are voluntary specifications and some chain fall outside these 'recommendations'. But G100 and G120 are made to be used in polar environments as low as -40 degrees - and if the they were brittle this, low temperature, would exacerbate the issue.
Most responsible chain makers will supply a test certificate for the batch, from which you are buying your chain. The certificate will define strength at break usually in Newtons, the % extension to break and the Proof Load to which the chain was imposed. Any chain from a reputable supplier (except China) will be marked with the grade, 3, or 40 or 10 and some mark indicating who made it, 'P' for Peerless, A for Maggi's Aqua 7 - the marks are all a bit crude - but it seems to work.
The numbers, 3 or 40 etc refer to the strength of the wire from which the chain is made - so 3 (or 30) means 300MPa, 40 means 400 MPa except for imperial chain which will be 430 MPa. The 70 refers to 700 MPa - which is the strength of the wire - heat treatment degrades that strength so galvanising can reduce the 700 MPa to something lower.
I'm generalising but using G70 has nothing to do with 'cost' or spending unnecessary money - a G70 chain, say 8mm with the same (or similar) strength to a 10mm G40 chain might have a similar cost (because the G70 is 'smaller') - but the costs and strengths vary depending on who you buy from and where, in the world, you buy. Buying G70 then allows you to carry a smaller chain - which might have nothing to do with 'saving' weight - it might allow you to carry more chain for the same weight (which might be advantageous if you have a small, or shallow, chain locker.
Galvanised G70 has been used for decades, admittedly by a very small minority - but usage is growing. There has been not one report of chain failing through hydrogen embrittlement. G30, from a reputable supplier is highly reliable, reports of failure are noticeable by their absence - that has not stopped a slow trend toward G40 or G43. There is no logic behind some usage - or nothing that is not very subjective.
However G70 is currently one use only, once the gal has gone you have worthless scrap - so long term its not a good buy (if you think chain should last for ever). Also if you change to G70, from a larger less strong chain - then you need a new gypsy - and they are not cheap.
Jonathan
Most responsible chain makers will supply a test certificate for the batch, from which you are buying your chain. The certificate will define strength at break usually in Newtons, the % extension to break and the Proof Load to which the chain was imposed. Any chain from a reputable supplier (except China) will be marked with the grade, 3, or 40 or 10 and some mark indicating who made it, 'P' for Peerless, A for Maggi's Aqua 7 - the marks are all a bit crude - but it seems to work.
The numbers, 3 or 40 etc refer to the strength of the wire from which the chain is made - so 3 (or 30) means 300MPa, 40 means 400 MPa except for imperial chain which will be 430 MPa. The 70 refers to 700 MPa - which is the strength of the wire - heat treatment degrades that strength so galvanising can reduce the 700 MPa to something lower.
I'm generalising but using G70 has nothing to do with 'cost' or spending unnecessary money - a G70 chain, say 8mm with the same (or similar) strength to a 10mm G40 chain might have a similar cost (because the G70 is 'smaller') - but the costs and strengths vary depending on who you buy from and where, in the world, you buy. Buying G70 then allows you to carry a smaller chain - which might have nothing to do with 'saving' weight - it might allow you to carry more chain for the same weight (which might be advantageous if you have a small, or shallow, chain locker.
Galvanised G70 has been used for decades, admittedly by a very small minority - but usage is growing. There has been not one report of chain failing through hydrogen embrittlement. G30, from a reputable supplier is highly reliable, reports of failure are noticeable by their absence - that has not stopped a slow trend toward G40 or G43. There is no logic behind some usage - or nothing that is not very subjective.
However G70 is currently one use only, once the gal has gone you have worthless scrap - so long term its not a good buy (if you think chain should last for ever). Also if you change to G70, from a larger less strong chain - then you need a new gypsy - and they are not cheap.
Jonathan
Neeves
Well-Known Member
Jimmy Green sell grade 70 with an oversize link on one end.
Oversize is the key word, they are huge and have an oversized price to match. Stg70 is a lot to pay for a large shackle for 8mm chain! Maybe Maggi want to discourage usage?
Are there any other options.
Jonathan
RobbieW
Well-Known Member
Curiosity question then: are the G30/40 chains also not regalvanisable ? If not whats the materials difference that makes this so ... TiA
Its not that I think chain should last for ever, though the Wedge website does use an example of a user that has had 4 or 5 regalv cycles, but the quality of a regalv seems to mean that the protection gives, anecdotally, up to 10 years against about 3 from the manufacturers galv process
vyv_cox
Well-Known Member
Grade 70 has the same composition as Grade 40, the difference being that it is heat treated - hardened and tempered. It is then galvanised. In the regalvanising process the chain is first dipped in hydrochloric acid to remove any zinc from the previous galvanising. The theory is that because this chain is harder there is a risk of hydrogen embrittlement, a rather poorly understood process in which hydrogen atoms diffuse into the metal where they can nucleate cracks. My own recollection from college and subsequent enquiries suggest that G70 is nowhere near hard enough for hydrogen embrittlement to occur but the chain industry insists it is so.
I have had two nominal Grade 30, perhaps 40, chains regalvanised. The difference in surface appearance is chalk and cheese, with clearly a lot more zinc on the regalv ones. There are photos on the website. My original one is in Greece. After buying it in Corsica, I believe made by Maggi, it was end-for-ended after two seasons but one year later clearly needed to be regalvanised. It was done by BE Wedge in 2009 or 2010, has been used extensively since and still has no trace of rust.