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Mokume laminate issues


#1

Hey there all hoping someone may be able to shed some light on an
issue that has come up with my latest attempt at a mokume laminate.
The billet consisted of 7 layers of sterling silver, 2 layers of
gilding metal and 4 layers of copper. The thickness of each layer was
about 1.5mm (with a base layer of silver at 3mm) making the total
thickness around 20mm, and they where 70mm x 90mm.



The stack was heated at 740 c for about 25mins under 610 psi of
pressure. No shielding atmosphere was used but the metal was fluxed
and under that much pressure that it should not be an issue.

After heating the billet was forged around the edges until cool and
seemed to have bonded fine. This was proven when i trimmed the edges
and all layers where shown to be bonded.

Now is where the problems showed up on the third pass through the
rolling mill, not working it very hard for fear of it falling apart,
the middle layer of copper seems to have failed. The bond seems okay
as there is still copper on the silver either side but the copper
itself seems to have fallen apart.

Just hoping someone out here may have some idea as to what went
wrong. I’m suspecting that perhaps the temp was a bit to high and
held for too long and the grain structure has grown to much,
something that could possibly be solved by forging more rather than
rolling. Or the other thing that occurred to me is that I didn’t
anneal before rolling after forging but being the middle layer that
has failed and having not been reduced that much in the forging
process i’m not so sure about this.

Anyway i’ve attached some images of the billet cooking, the billet
prior to rolling and the resulting failure. Any advice would be
greatly appreciated as this is rather frustrating with the
quantities of silver i’m experimenting with.

Ben Pearce


#2

Hello Ben the way it looks in the picture it seems as if you might
have rolled it without annealing in between in opposing directions,


#3

I wouldnt blame your production technique, id be very suspicious of
the copper you used. All copper sheet is NOT the same!!.

To give you an example, Car/truck radiators made from copper up to
around the 1950’s/60’s used electrolytic grade copper.

These radiators do not corrode away like later made ones.

the reason the latter rot is that the grade of copper is made from
recycled scrap with other metals included.

This causes external electrolytic rot and these rads last about 7/8
yrs.

So Id suspect the copper you used was not of the highest grade, ie
ASTM B.152-ETP called electrolytic tough pitch.

the best electrical grade you can get.

This is produced under special conditions that exclude oxygen.

Ive had another experience, electrical lightning conductor is made
from crap copper. Hot forge it and it cracks and crumbles away. The
best as above is never a problem.

Id get back to your copper supplier and ask for a refund, but check
what grade you asked for or specified.

Could have come from China.!!

Also, getting back to technique in making your laminate, I was under
the impression that between each layer you sprinkled silver brazing
particles to aid adhession along with a minute amount of flux to
exclude oxide formation. but ive never made this laminate so cant
really advise.

Have you made this before and got the results you expected? In
discussions with the technicaldept of Johnson Mattey many yrs ago
over the production of a double’ l needed for an enamelling
project…

This was 10% fine gold and 90% fine silver with a finished thickness
of 10/1000 in.

They always solder the 2 metals together to ensure a proper
molecular bond before rolling down to size.


#4

Is the zinc rich gilding metal touching the layers that are
delaminating? I didn’t know you could use gilding metal to bond to
other metals in mokume gane. I can’t imagine the zinc fumes from
soaking the billet at high temperatures not creating all kinds of
problems with lamination.

If you need a third metal other than copper or silver perhaps try a
different metal?

Rick Powell


#5

Ben -

How are you bonding the layers? If you are diffusion bonding, have
you considered that 25 minutes is not enough time for diffusion to
occur in the center of the stack? As everything looks pretty clean to
me, this may be the issue.

Debby


#6
Is the zinc rich gilding metal touching the layers that are
delaminating?

The gilding metal is only in contact with the silver and if anything
i’ve found gilding metal and sterling bond together better than
other combinations perhaps due to the zinc content.

I'd like to see more of your setup, the induction heater sounds
very cool. 

If I can get my head around uploading images i’ll post a picture of
the setup.

Ben


#7

Hi there id like to put this image in my topic about Mokume laminate
issues. It is a picture of my bonding set up that has been
requested.

Thanks, Ben


#8
The stack was heated at 740 c for about 25mins under 610 psi of
pressure. No shielding atmosphere was used but the metal was
fluxed and under that much pressure that it should not be an issue. 

Some things to think about

Flux is a no-no you are not melting it you are trying to diffuse it.
You want absolutely nothing between the sheets of metal.

You must use a protective atmosphere whether it is from charcoal or
a gas bottle. O2 will travel easily between the layers bonding to
the exposed metal greatly limiting the diffusion process.

I use more like 6000 psi, 610 will not insure intimate contact
between layers.

Forging is your friend, rolling too early will ruin a perfectly good
billet. The force from rolling is not evenly distributed across the
section of the billet. This is in part due to the small size rolling
mills used by studio metalsmith larger industrial mills can apply a
greater amount of force and get greater penetration of that force.
The outer faces experience the most force and show the most
deformation the middle is the least affected and is mostly pulled
along by the movement of the outer layers. You can see this in the
way the leading and trailing edges become convex as you roll. So the
middle layers will not get the same amount of cold work.

I too would like to see your induction heating setup.

James Binnion
James Binnion Metal Arts


#9

Nice hot press. I do think you are going to need to figure out how to
provide an inert or reducing atmosphere to get consistent good
bonding.

James Binnion
James Binnion Metal Arts


#10

Nice set up! Now that is some good compression force!

Of course, it’s also the biggest heat sink Imaginable but I have
seen this method work with excellent results.

Rick Powell


#11
Nice set up! Now that is some good compression force! Thanks :) Of
course, it's also the biggest heat sink Imaginable but I have seen
this method work with excellent results. 

The laminate is actually insulated from the metal of the press by
some heavy duty refractory material, which it has to be in order for
the inductionheating system to work, the metal billet is the only
part of the set up that actually heats up. A piece 150mm x 100mmm x
15mm thick reaches about 700c in 10mins but smaller pieces actually
take a bit longer. You wouldn’t want to go near it with a pace maker
or credit cards as the magnetic field it generates is quite strong
i’ve had my watch vibrate when within about 30cm (1ft) of it. It’s
definitely fun to play with and working in the preciousmetal
industry gives me quite a bit of freedom to stuff up with decent
amounts of material that would otherwise cost me hundreds of $$ I
just keep track of the quantities and throw it in the scrap bucket
for refining. Ben


#12

I used to know Mr Wilkinson who had the last commercial workshop
producing Sheffield plate which is silver diffusion bonded to copper.
His last work was producing sheet to make lighthouse reflectors and
those for oil lamps onthe railways and electrical contacts. I think
the factory building still stands in Coleshill NR Birmingham. The
fused plate was superior to electroplate in these applications. Mr
Wilkinson went through the process with me which I then used to
produce very successful multi layer laminates. His methods were born
of the 18th century, the factory had a coke fired furnace which gave
a reducing atmosphere. He firstly prepared the mating faces to be
laminated by scraping with sharp scrapers. No emery paper or sand
paper or files for fear of contamination. The face could not be
touched and had to be perfectly clinically clean. The were brought
together and hammered on hisanvil with a huge planishing hammer. This
not only closed the gaps but a metallurgist friend of mine suggested,
may have started the process of migration. Iron plates were wired on
either side of the billet, so holding everything tightly and closely
together. He then mixed up a thick mixture ofborax to seal the gap
between the copper and silver, thick so as not to flow between the
layers. He put the billet in the furnace and watched, through a peep
hole, occasionally moving them to hotter or colder parts of the
furnace. He was looking out for a flash like quick silver, as he
called it, at the joint between the metals, when this occurred he
quickly moved the billet to a cooler part of the furnace before it
all melted. I think somewhere I should have pictures and his written
description of his procedures, he he retired only in the late 1960’s.
I was still in touch with him in the 1980’s he is dead now. His fused
metal had to be perfectly bonded to stand up to processes of spinning
and pressing.

Hope this is of interest
Hamish


#13

Hamish,

I’d love to see whatever images you have.

I rather like Sheffield and its past. Sheffield plate being no
different.

Ric Furrer

[Edit]

How can I share files and pictures with the list?
http://www.ganoksin.com/gnkurl/ftp

Or… send the files to the attention of service@ganoksin.com and
we will upload them for you…

[/Edit]


#14

Hi Ric

I am going to have a look for my papers, trouble is it was so long
ago. I put some of my own “Sheffield Plate” examples in Ganoksin
vessel on line exhibition if you want to see what I did under Mr
Wilkinsons instructions.

Regards
Hamish