MadModder
Gallery, Projects and General => How do I?? => Topic started by: DavidA on January 19, 2016, 12:38:44 PM
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Just a quick one.
Which flux do you recommend for brazing carbide tips onto steel tools ?
Dave.
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Err??? Silver solder foil and borax.
As Mr Punch said That's the way to do it
Regards
Norman
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Iff you ear using bronze brazing rods then siff flux , for silver solder easy flow or tenacity .
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Hi DavidA,
I can second what Fergus OMore & chipenter have said, using silver solder and a borax/borate-based flux.
More specifically, we at Johnson Matthey usually recommend to our customers to take a size-based approach. That is, if you are brazing pieces of tungsten carbide which are less that 10mm (in the largest dimension), then you are good to use normal silver solder (e.g. our 55% silver "Silver-flo 55 (http://www.jm-metaljoining.com/pdfs-products/Silver-flo%2055.pdf)") and a normal "white" brazing flux (e.g. our Easy-flo Flux Powder (http://www.jm-metaljoining.com/pdfs-products/Easy-flo%20Flux%20Powder.pdf)).
If the carbide pieces' largest dimension is larger than 10mm, but less than 20mm, then we would recommend using a specialist brazing alloy for carbide (e.g. our Argo-braze 502 (http://www.jm-metaljoining.com/pdfs-products/Argo-braze%20502.pdf) or 49H (http://www.jm-metaljoining.com/pdfs-products/Argo-braze%2049H.pdf)) These alloys are less free-flowing than the standard silver solders and so produce a thicker joint. This helps eliminate cracking of the joint or carbide during cooling, which can result because of the different expansion and contraction of steel and carbide.
For 10 - 20mm pieces flux-wise, whilst it is possible to use a white flux such as Easy-flo, we might be looking towards the superior oxide-reducing capability of a boron-modified (brown/black) flux, such as our Tenacity No. 6 (http://www.jm-metaljoining.com/pdfs-products/Tenacity%20No.%206%20Flux%20Powder.pdf).
If the carbide parts are bigger than 20mm, then we would recommend a tri-metal product. These products are basically two pieces of brazing alloy foil bonded either side of a copper core. This copper core will not melt during brazing (Tm 1083°C) but will only act to artificially thicken the joint, again limiting cracking during cooling. An example of this from ourselves would be Argo-braze 49LM Tri-foil (http://www.jm-metaljoining.com/pdfs-products/Argo-braze%2049LMT.pdf). This would want to be used with a brown flux.
A brown flux should always be used if the carbide contains titanium and/or tantalum carbides.
If you want to find our more general information about carbide brazing, then we have a bookelet dedicated to the process and the typical products used on our website:
Tungsten Carbide and PCD Brochure (http://www.jm-metaljoining.com/pdfs-downloads/Argo-braze%20-%20Tungsten%20Carbide%20and%20PCD.pdf)
I hope this is of some help, please feel free to message me if you have any more questions.
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Thanks for the replies.
I've not tried this before, but fortunately I have plenty of old carbide tips to practice on.
Dave.
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Good to hear DavidA, the main thing to focus on (if you are using a compatible flux and alloy, which most "common" ones will be) is to accommodate the cooling stresses. This gets more important the larger your carbide pieces are.
Some things we tell our customers would be to not place the still-hot, just-joined parts onto a large (cold) steel slab to cool and definitely never to quench in water which carbide is involved. Minimum should be air cooling, if you can put them into something which will further slow the cooling rate down, such as vermiculite, a hot oven etc., then this will further help prevent cracking.
Good luck.
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brilliant advice- I always wondered about the copper foil- I was told it was to cushion the carbide in use - which always struck me as odd! :med: