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  1. #21
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    I have my black flux.....

    I have been thinking about the comments to use an additional heat source as mentioned several times and will look into this. I admit I was hoping for a simple solution for what I was hoping was a simple project, but as I read the comments I now see that this isn't quite so simple!

    I can successfully Silver Braze thinner materials; this is the first time I have tried Silver Brazing anything with this much mass. ...off to make some practice samples and figure out how to set up some auxiliary heating!

    Thanks again.

    -Jim

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    Quote Originally Posted by sabre1fv View Post
    I have my black flux.....

    I have been thinking about the comments to use an additional heat source as mentioned several times and will look into this. I admit I was hoping for a simple solution for what I was hoping was a simple project, but as I read the comments I now see that this isn't quite so simple!

    I can successfully Silver Braze thinner materials; this is the first time I have tried Silver Brazing anything with this much mass. ...off to make some practice samples and figure out how to set up some auxiliary heating!

    Thanks again.

    -Jim
    Try this - get a lump of steel about the same size and shape - ish and see how quickly you can heat it up until it's ready for the silver braze,...……...if you want it quicker - try using muffs as well as altering flames.

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    You can also set-up a makeshift hearth with stacked Kiln brick or Fire brick, it really helps throw some radiant heat back onto the parts. 80 grit production cloth, followed by an acetone wash. Always remember to scratch in the same direction you want the silver to flow, as the capillary action helps out as well. Don’t forget to scotch brite and acetone wash your filler rod as well, silver needs to be clean clean clean. Braze ASAP, don’t fiddle around. Good luck!

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    Possibly not relevant here,but a lot of abrasive paper and cloth has a stearate coating to shed swarf,and this stearate coats the metal being ground,and has a definite effect on further processes.............hard to remove .too.

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    Quote Originally Posted by john.k View Post
    Possibly not relevant here,but a lot of abrasive paper and cloth has a stearate coating to shed swarf,and this stearate coats the metal being ground,and has a definite effect on further processes.............hard to remove .too.
    That was why I was taught to use carpenters glass paper, ……...but IME sand blasting (with windscreen etching grit - whatever that is) takes a lot of beating.

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    +1 on the practice part.

    I often do batches of brazed up vacuum fittings. The best results are always found after I've
    run a few that are so-so to start. Then I get in the groove.

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    I have been silver brazing or soldering since 1975 or so and recently commented on another thread on this forum regarding silver brazing. I typically use oxy acetylene but have also used straight acetylene from a presto lite torch, propane from a bernzo matic type torch and propane oxy. They all work well and oil is not really an issue as no oil exists at the soldering temps and any remaining carbon from the oil that gets burned off is easily handled by the flux. To prepare metal surfaces I use a 3 corner scraper or abrasive paper and never had an issue with either. Overheating can be a problem so concentrating your heat on the larger part is necessary. Also, it may be better to cut small pieces of solder or even wrap the rod with a coil of solder. If I understand your assembly correctly, a bored out rectilinear cube placed over a rod, I would wrap a coil of solder over the shaft at one end and then concentrate heat on the shaft at the opposite end of the solder coil. You will need to heat the other end of the shaft as well and some on the block too. When you get to temperature, the solder should melt and flow into the space between the parts and continue towards the hot side - solder always flows to the heat. More solder can be added to the same end as the coil and when the solder appears at the heated or opposite end, you know you have done it right. The challenge with your parts is the thin wall of the block as if you play the torch on it to much, it will overheat and oxidize and then all is for naught. Also, the flux can be dissolved in hot water, much easier than grinding or scrapping it off. You may also want to pickle the parts when your done but only after a satisfactory soldering job.

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    Initial results are promising!

    I practiced with the black flux on scraps to get an idea of the right color red of the metal to add the Silver Braze and also when 'too red' ruined the flux. It did seem that my standard rosebud tip should work. I made up sample parts yesterday and brazed them together this morning - came out better than I expected. But how to know how good? So I machined off the sleeve to see the braze material pattern - there were small pockets where there was no braze material, but the base mat'l (5/8" solid steel stock) looked to have a yellowish appearance as if the flux had wetted the surface but I didn't add enough material to fill the entire cavity...

    The working time of the black flux was quite long, perhaps minutes because I used a soft flame and kept moving it over the pieces as best as I could - or did I get lucky......

    Previous comments about using a BBQ/furnace are quite good and would have been my next attempt if the rosebud tip didn't work well enough. The comment about setting up a rotisserie was excellent! I will set up something that will allow the assembly to rotate, though it will turned by my assistant... I may even try to incorporate the additional heating source several posters have suggested since I am doing so much fixturing.

    My prep for the parts is to sand the steel to bright metal, clean with Lacquer Thinner and completely cover the faying surfaces with the flux, plus the outside of the sleeve to hopefully protect the finished surfaces.

    I will add, that in retrospect, if I ever do this again I will make the 5/8 bar longer to extend through the sleeves to allow me to apply heat to that end to better pull the braze mat'l through the joint then cut off the extra, AND it will take advantage of Gazz's suggestion to make rings of braze mat'l.

    Thank you again to everyone for sharing their 'pearls of wisdom' - a lot of good tips and information that pushed me in directions I wouldn't have thought of

    -Jim

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    Quote Originally Posted by Limy Sami View Post
    That was why I was taught to use carpenters glass paper, ÖÖ...but IME sand blasting (with windscreen etching grit - whatever that is) takes a lot of beating.
    Windscreen etching grit, what is it and grit size?
    We all have favorite blasting media and mixes for cleaning before solder/braze.
    Do you dip in the ultrasonic after blasting to get rid of those microscope sized particles?
    How long from blast to braze, has that exposure to air ever been a problem leading to very small voids or pinholes?
    Bob

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    Don’t use lacquer thinner to clean, it leaves surface film which will a) inhibit the directional flow and b) prevent joining between layers.

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    What is the best solvent/cleaner for wiping off parts and filler metal prior to assembly? I have used Lacquer Thinner for all my TIG welding projects since it 'seemed' better than Acetone. I purchase both Acetone and Lacquer Thinner in 1 gallon containers at a 'big box' store, so neither is reagent grade. Someone did suggest Acetone.... Opinions or suggestions?

    Thanks.

    -Jim

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    Default Flame condition is important here .

    Quote Originally Posted by sabre1fv View Post
    I need to Silver braze some mild steel blocks (like a sleeve) to a 5/8" diameter mild steel shaft; the blocks are not much bigger than the 5/8 shaft and do not have much mass; radial clearance is .001 to .002". The blocks are 1.5" long and I have added a 1/4" hole through two sides to aid in the braze flow and provide an area for adding the braze material in the middle of the block. First attempt failed because I overheated the flux (turned black) - I was using a #4 tip on a oxy/acet welding torch with a slight carburizing flame. I thought about using the rosebud tip, but thought that would be overkill. To me, the big problem seems to be heating up the 5/8 bar without overheating the flux. I did start with clean, well fluxed metal on both parts.

    I have machined off the first block (did get some flow of the braze material) and now have about .003 to .004" radial gap, and sanded off the burnt flux. The flux I have is Harris Stay-Silv and I am using Silvaloy A45 brazing alloy. I need maximum surface area adhesion between the bar and blocks so TIG welding or TIG brazing won't work for strength reasons.

    I did check several pages of posts under Silver brazing and didn't see any other similar posts.

    Thank you in advance for any tips or suggestions you can provide.

    -Jim
    The flame you are using will introduce impurities into the process, the carburising flame is normally reserved for a hard facing process.
    For silver soldering a neutral flame is adequate, equal amounts of gas, no impurities.
    For brazing and bronze welding we use the oxidising flame, to wrap the zinc in an oxide layer to prevent volatilisation of the zinc from the alloy.
    Have fun .

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    See if you can source some of the proper, " old style " flux and wire containing cadmium.

    I talked to some producers at the last Essen welding show about problems such as you describe and they confirmed that cadmium containing products are still made, at least in eurostan, but only supposed to be used in aerospace applications............

    This says it all.

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    Most of the jibber-jabber about impurities from the flame or type of gas is just that, at least in the case of one-off or low numbers silver brazing.

    At industrial scale, aerospace or high volume, tens of thousands to millions of parts, yea sure, go to town, spend weeks researching.

    For the rest of it, just heat the dam thing up.

    The routine use of solvents for pre cleaning for GTAW and brazing is usually a bad idea. Most of the time you are just smearing the oils around, and leaving a nice coat behind when the solvent evaporates, after all isnít that what you do when you lacquer or paint?

    Only use lacquer thinner to thin lacquer, itís bad stuff. Itís just better to avoid it if you can.

    Water based alternatives exist for most applications, and allow you to actually flush the surface clean. Safer, better, cheaper more pleasant. Why wouldnít you go that route? ďItís a nasty powerful chemical it MUST be better!Ē .. I used to by into that silly nonsense myself

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    I had the same thoughts. Even some fire bricks just set up to form an enclosure would probably work.

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    Default We invented it.

    Quote Originally Posted by cyanidekid View Post
    Most of the jibber-jabber about impurities from the flame or type of gas is just that, at least in the case of one-off or low numbers silver brazing.

    At industrial scale, aerospace or high volume, tens of thousands to millions of parts, yea sure, go to town, spend weeks researching.

    For the rest of it, just heat the dam thing up.

    The routine use of solvents for pre cleaning for GTAW and brazing is usually a bad idea. Most of the time you are just smearing the oils around, and leaving a nice coat behind when the solvent evaporates, after all isnít that what you do when you lacquer or paint?

    Only use lacquer thinner to thin lacquer, itís bad stuff. Itís just better to avoid it if you can.

    Water based alternatives exist for most applications, and allow you to actually flush the surface clean. Safer, better, cheaper more pleasant. Why wouldnít you go that route? ďItís a nasty powerful chemical it MUST be better!Ē .. I used to by into that silly nonsense myself
    Brain dead reply, itís common knowledge that the flame is a major factor between success and failure, even for the home workshop, back to basics, and stay focused, itís information thatís readily available to anybody, and normally the suppliers of the flux and the wires will give you a welding procedure to get your results free of charge, or you could mix a cyanide pill with water and wash it down with a tin of bud, to clear your head like.

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    hello Bob, missed your post or I'd have got back sooner.

    The grit - Aluminium oxide this brand Clarke 7.5kg 80-120 Grit Aluminium Oxide Powder - Machine Mart - Machine Mart

    no ultra sound just a blast with clean air

    Blast to braze ? …..usually as long as it takes to get the flux on and joint assembled, ….never knowingly had pinhole problems.

    FWIW An old stager told me that during WWII when he had women silver soldering parts their hand cream could be a problem, so with the oil & crap in my skin I use disposable nitrile gloves when handling parts to be silver soldered, …………...passed that tip on to several guys all of whom liked it.

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    I use black flux a lot, but white flux will stay active for a very long time if you don't overheat it. With proper heat control, it should still be active after you are done brazing the joint. Pink is usually the color I go for with 45% or 56%. I feel like the main problem here is heat control, not contamination. Flux will take care of a lot of minor contaminants. The key to heat control is patience. You have to move the flame around, and flick the flame off the part if it starts heating too much.

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    Quote Originally Posted by Limy Sami View Post

    FWIW An old stager told me that during WWII when he had women silver soldering parts their hand cream could be a problem, so with the oil & crap in my skin I use disposable nitrile gloves when handling parts to be silver soldered, …………...passed that tip on to several guys all of whom liked it.
    That is a very good tip. We do the same and it does makes a difference.
    You add flux which is supposed to make all things good. Who would think you or your employees fingers are the problem on a shorted braze?
    Bob

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    I agree with Bob that using the gloves is a very good idea. Years ago we found fingerprints etched into some steel parts due to the salt in the food people were eating. These gloves didn't exist back then...

    -Jim


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