Brazing rods/flux

[GraemeVW]

I need to try my hand at brazing cast iron.
I think I know just enough to have a go, but am a little confused about rods.
I see flux coated, flux cored, general brass brazing, silicon bronze, and probably others.

Do you still need flux with flux core, or flux coated?

Hoping to get this done with mapp gas, but the items I want to braze are quite small so I should be ok getting them hot enough.
I'm aware of the need to pre heat and slow cool.
Thanks.

 

[GraemeVW]

Sif is now crap, india/chinese crap, avoid.

CASTOLIN

Or plain Low Fuming Bronze and make your own flux

Make my own flux?

I'll look for the rods but I suspect I'll be limited to what i can order, in small quantities, from eBay.

Edit, I had seen sif, so thanks for the warning, I'll stay away.

 

[Kram]

Hoping to get this done with mapp gas, but the items I want to braze are quite small so I should be ok getting them hot enough.

If its a good fit with little gap, silverflo 55 needs a lot less heat. Needs easyflo flux.

Silicon bronze is higher temp than brass based brazing.To do it with mapp the parts need to be tiny.


Flux temperature needs tosuit the melting temp of the filler. Borax is good for brasses or 800-900c temp range, if I remember correctly.

 

[GraemeVW]

If its a good fit with little gap, silverflo 55 needs a lot less heat. Needs easyflo flux.

Silicon bronze is higher temp than brass based brazing.To do it with mapp the parts need to be tiny.


Flux temperature needs tosuit the melting temp of the filler. Borax is good for brasses or 800-900c temp range, if I remember correctly.

I'm going to be building up a missing tooth on a gear.
Silicone bonze may be out then.
I guess I'm looking for normal general brazing rods then. They are about 400° ish right?
If I get flux coated, do I need more flux?

 

[GraemeVW]

Looking at rods, in not sure why the internet told be it was 400°. All the ones I've found are 8-900.
I have melted brass with my mapp torch before, but getting this hot enough may be tricky.
I'll practice, if I can't, I'll take it to a friend's and use his oxy/acetylene. Will just be more awkward to cool slowly over there.

 

[GraemeVW]

Just realised I already have borax flux for silver soldering.

 

[GraemeVW]

900 degrees is more accurate. 400°C is soldering

I think there are some low melting point 'brazing' rods, which is what Google was telling me about. Having found them in eBay, I'm going to guess they aren't proper brazing rods, but more soldering as you say.

I may try silver soldering it then. That's about 700° ish, depending on what types I still have.

 

[GraemeVW]

Borax and touch of jewellers rouge for cast

Excellent, I have both.

 

[GraemeVW]

Silver soldering is for joining two materials together you can't build up with ht

Yes. I was deciding if I build it up with braze, or insert a new piece and silver solder.
Might be easier for me, with whatbi have and without having to learn something new, to go with the second option.

 

[GraemeVW]

Silver soldering is for joining two materials together you can't build up with ht

Although, I'm probably could build up. Just not very much.
I should have 3 temp ranges of silver solder. I have 1 tooth with a small chip. Working down through from hard to easy, I may be able to build it up enough. Won't be easy though.

The missing teeth, no chance!

 

[GraemeVW]

No chance. That's just not how silver solder works.

I've done lots of gear teeth, both with Bronze and with Flame Spray Nickel.

Bronze is great, easy to cut.

Flame spray is the best.

Why no chance?
I can build a 0.5mm layer with silver solder I reckon.
I should have one that melts around 650, one that melts around 700, and one that melts around 750.
I've done a fair bit of silver soldering over the years, I think I have a reasonable chance of building up maybe 1.5mm.

I've never tried building it up on purpose, but I've certainly had to file bits down where I got it on too thick. Might take some experimenting but I bet it's doable.

 

[GraemeVW]

Silver solder is designed for joining components, filling gaps via capillary action.

Do the job properly or not at all i say.

All you need is oxygen and propane

I trained in silver smithing for a while and spent 10 years of my hobby life making fine jewellery. I'm comfortable with silver solder. Proper silver solder. It's 75% silver. Not the silver solder with like 5% in it.
I know it's capillary action, every time I've used it I've been trying to use as little as possible with no surface build up. Use too much, get it wrong, and it can build up though. I'd just have to do what i always used to do, but learn to do it badly.

To clarify, I wouldn't be trying to build up a whole tooth. If I use silver solder, I'll cut out the broken tooth with a fair bit of root and shape some steel to a tight fit and solder it in.

The building up, I'm only taking about a chipped tooth. It has a U shaped chip out the middle. I could cut it out and replace, like the others, but I think it wouldn't be impossible to build it up.

 

[GraemeVW]

Just mulling over options at the moment. First off I'll see if I can get it hot enough to braze. I have a load of sheet 25mm vermiculite board so I can build a close enclosure to keep heat in.