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I get blisters on my billet  when it gets to about 1/4 inch thin or less.

Is there pockets of air or flux traped?

it seems to happen after folding.

 

I hammer them down and run them through my press and it seems to eliminate them but I am not 100% sure................

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It would be hard to tell without a picture to see what we are dealing with here.  Trapped flux could be a possibly.  I doubt that they could be caused by air.

 

Doug

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A trick from the late Larry Harley:

 

If you see a blister, it's trapped flux or something preventing a weld in that spot.  Take a sharpened rod and hot-punch a hole into the blister at welding heat, then immediately re-weld without reheating. One fast sequence of action. It should go away, and the poked hole won't affect the pattern that much.  If it turns into a an edge delamination, try to clean out the pocket and pack it with brown sugar, re-weld.  The sugar is basically pure carbon once it burns, lowering the welding temperature at the weld location and acting as a sort of anti-scale goo. 

 

I've saved a few billets that way.

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OK

I will try the hole poke next time it happens.

I have ground these blisters in the past when the billet was cold but lost a lot of material & it takes too much time.

 

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You can even use a slitting chisel if you have one.  And while the technique isn't guaranteed to work every time, it's better than not trying to save it at all.  

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Could be simply because it would be easier to pack in brown sugar and have it stay in place without falling out.  Just a guess though.

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It was probably what Larry had on hand, knowing him. :lol: last time I did this trick I used a pcket of turbinado, and it worked fine.  Honestly, salt might work too.  I think it's more of a magic thing, something to make you think you're doing something special.  Sometimes forge welding needs that. ;)

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We can always assume the sugar is important since it will provide a reducing atmosphere and coat the surfaces with carbon, both things that will help with a forge weld.  

 

I worked at a foundry once that would though a handful of sugar packets on top of the poured investment molds before putting a 55 gallon drum over it.  The reducing atmosphere prevented pin-hole defects.  I asked "why sugar packets?" and was told that they were cheap, easy, and readily available.  

 

Totally not related story, but it cracks me up every time I think about it.  When I was fresh out of college I got hired on at a foundry.  The following December they sent me to the annual Technical and Operating Conference for the Steel Founders Society of America.  Great program where lots of innovation is presented in an effort to improve the industry as a whole.  I have since presented a few times myself, and I'm sure I will again, probably in 2022.  Anyway, I'm still very new to the foundry industry and I'm trying to soak up as much as I can.  One presentation just blew my mind.  A foundry down in Mexico (POK, great folks) were making essentially giant gears to crush sugar cane (this is where it becomes vaguely related to the discussion at hand).  We're talking 8-12' diameter gears (I can't remember exactly, but pretty dang big).  The way the teeth of these gears are formed is with cores (little sections of mold that are made separately and added into the bigger mold to create finer geometry).  These cores would need to be made such that they collapse a little after pouring, otherwise the gears will get hot tears at the base of the teeth.  They tried everything they could think of to get these cores to collapse properly.  Hollowing them out completely, drilling a bunch of holes, adding "filler" material that wasn't so rigid like vermiculite, etc.  They were explaining all these problems and their attempted solutions to their customer, the sugar mill folks.  Their customer then said "have you tried adding brown sugar?"; they had not (obviously; who would think to try that?).  At this point in the presentation the whole audience chuckles a bit.  The presenter says they were pretty desperate and didn't have much to lose, so why not humor the customer and try one with brown sugar?  It worked.  I start looking around the audience to see if anyone is going to call BS, but all I see is a few people nodding as if to say "yes, yes, I can see how that would work out well".  It was, and in my mind still is, wild.  As far as I know, it is still the process they use today.  Next time I talk to one of them I will have to ask.  In conclusion: brown sugar is metalworking magic fairy dust.  

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So that's why I've seen a core recipe that was basically brown sugar greensand!  Well, dry loam bound with molasses and baked.    :lol:

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