As you all probably know liquid flux is a game changer but being based in NZ liquid flux is pretty much non-existent here. Comweld vapaflux used to be my go to but my supply has since dried up and to get some from Australia is over $1700 for a 19L drum which is the smallest they sell; as for NGP who stock Gasflux type W they won’t ship to NZ since it’s considered dangerous goods.
Anyway, my solution to this is to make my own copycat type w flux with the same concentrations and materials listed on the type w safety sheet. Gasflux type w is listed as 55% trimethyl borate, 25% acetone, and 20% methanol.
Now acetone and methanol are easy to find but trimethyl borate is quite restricted in NZ so I have to make my own. What is trimethyl borate? Trimethyl borate is made by dissolving boric acid into methanol which is refluxed and then distilled to separate the trimethyl borate from the excess methanol, instead of distilling to pure trimethyl borate I calculated to correct quantities to end up with the right concentrations. Here’s what I’ve done to yield a bit under 1.5 gal of homebrew liquid flux.
We’ll start off with what quantities of material I purchased in NZD.
2000g of boric acid - $25.50
1347mL of acetone - $19.99 (2L)
4041mL of methanol - $98.00 (5L)
I started by mixing the 2000g of boric acid into the 4041mL of methanol in a heat-proof container (for me it was a clean stainless steel pot) and then refluxing for 1hr at 60°c until all the boric acid was dissolved, once it had cooled back down I measured the volume to check the loss (my reflux wasn’t completely sealed so refluxing evaporated a tiny bit of methanol) and topped the solution back up so I have the same volume before I refluxed. Now all you need to do is add in your 1347mL of acetone and you have homebrew gasflux type w to add into your inline fluxer and then store in a sealed container which for me was my gas fluxer
Now I will note that I did this mad scientist project by math calculations and haven’t tested the results with titration methods so I’m not sure if I ended up with 55% trimethyl borate and 20% methanol, having consulted some family members who studied chemistry they mentioned that my methanol concentration will probably be around 15-20% depending on my loss rate but I fixed that by topping up the methanol.
Now the end product in my opinion is liquid flux, the flame is a deep green and the joint brazes like a torch with liquid flux so I’m happy with the results.
I’ve just been looking into this too as I needed to refresh my supply. I ended up paying £120 for 5 litres from the UK company Plasmatech. £40 of that was a hazardous shipping cost.
I can buy Trimethyl Borate here in the UK but the cheapest I could find in smallish quantities is over £80 a litre. I guess I’m paying the labour for the distillation process.
Anyway, I gave up as it really did seem cheaper buying the Plasmatech product.
I’m also buying from Plasmatech in the UK at the mo. As far as I can tell it’s the best option for us here? Though I am now very tempted to make some myself.
I called Weldability about their liquid flux and the operative didn’t even know what I was talking about! IIRC they wouldn’t ship and collection was the only option (Nottingham-London).
Adam this is a lot of Kiwi ingenuity going on here, well done! I am also in CHCH and looked into the supply a few years ago but gave up due to cost and availability of the gasfluxer and the liquid flux. Let us know if you are ever breaking bad again and willing to share, if there is a local supply I would be keen to change my set up.
Wow that’s super cheap! To get some delivered to NZ it was $400nzd just for postage! It totalled to a little over $700 to get a 1 gallon tin landed which is bonkers…
Yo Simon! I’ll flick you the recipe and you can make some yourself! I also had trouble finding an inline fluxer unit but there’s actually quite a few floating around chch but people here like to hoard as you know, I got lucky through a friend of a friend and was given a jet fluxer unit for free! Will dm you my recipe over FB keep an eye out.
I don’t really understand the chemistry involved in how it all works but I do know I get frustrated when I need to switch back to paste flux when silver brazing. Anyone find any solutions to that? As I said I don’t understand the chemistry but I assume the flux in the gas just isn’t active until it hits a certain temp?
With the liquid flux I made it works for silver, I wasn’t actually sure if it’d work so I silver soldered a couple of joints and cut them open and they were perfect. Liquid flux works by having acetylene bubble through a tank of liquid flux where the flux is absorbed into the acetylene which then goes out the torch, I’m probably not the best to explain it so I’ll point you to the Gasflux video on inline gas fluxers…
Also in my experience an inline fluxer almost acts like a shielding gas… Paste flux when it’s fresh in the joint is good but when it dries up and you don’t have as much on the joint or rod the molten bronze skins over and looks solid when it’s liquid, it also doesn’t move around and follow the heat as nicely; with an inline fluxer it gets rid of the skin the forms and follows the torch tip, I’ve cut open a couple inline fluxed joints and there are far less inclusions and the joint is a lot cleaner. Through trial and error, I found that liquid flux runs hotter so I went down a tip size and it helps to keep the filler rod and joint in the cooler part of the flame when you want everything to solidify to allow to to cool in the “shielding gas”… Hope this helps.
Super interesting stuff here! Chemistry is a bit of a dark art to me, more like alchemy
Just out of curiosity, as a question to someone who has taken an inline fluxer apart before: Do you think one could entirely DIY such a thing? What do the components look like? Are the valves all off-the-shelf-items? Does it require any fancy seal materials because the liquid flux is corrosive or something like that?
From the outside, it looks doable to me but I guess I’m missing something…
I won’t lie I’m a bit spoilt having two sisters with masters degrees in chemistry to help me not blow myself up!
My inline fluxer in a Jet-flux MK4, mine is super simple and only had 1 moving part so it was very easy to rebuild… I stripped it apart and cleaned it with hot water to dissolve all the old crusty flux and replaced all the sealed, I used fuel safe o-rings I got from an auto parts store and lubed them with silicone grease; I did replace all the brass fittings and taped them up with telfon tape to be safe. It hasn’t leaked yet and I’ve been testing it with soapy water fairly often to check. Do keep in mind that you’re bubbling low pressure acetylene through the gas fluxer so it’s not super dangerous, just make sure you have a good quality flashback arrestor so you don’t blow yourself up!
The flux I made isn’t corrosive but it is probably the most flammable thing out there second to petrol vapours; The type w liquid flux that I copied is hygroscopic so you need to keep it sealed off as to not absord water, I’d be more worried about water in my gas lines and inline fluxer than the seals going.
Here’s a link to a really simple design that is easy to copy, I was originally going to copy it before I was given my jet-fluxer unit.
Thanks @Fingerprint I knew the mechanics of how the system works but not really the chemistry as to why it works. I’m not sure why it never occurred to me to try silver brazing with it. I think that in the early days when I was going to make my own gasfluxer, I’d read about making sure there were valves to allow a pass-through for silver brazing. And from there I just never considered it.
Anyway, in light of your reply, I just tried out some test pieces. It definitely works. But from an initial play around, I can’t quite get it to do what I want. My first take is that it’s definitely harder to get an idea of metal temps. When using paste flux, I rely on the change that happens with that, I don’t really expect much colour change in the metal for silver brazing temps. Or at least the paste flux tends to mask it anyway. It feels like the optimum temperature window is narrower but again, that might just be that there’s no paste flux to mask what’s going on. In the first couple of attempts, it felt like I couldn’t get the silver to flow as much as I wanted, and getting it much hotter felt like stuff was starting to burn. I did clean everything down with acetone but again I wonder if the paste flux cleaning action is way better than I can manage manually and what I’m seeing blackened is actually just dirt/grease/residue.
As I said, the fillets round bottle bosses for example are bigger than I would like. I suspect I just need to practice more. I have probably silver brazed about 10,000 bottle bosses over the years and I suppose I have too much muscle memory to easily change what I’m doing.
I’ve attached some pics of parts that I cut apart. You can see there’s definitely penetration and I have no doubt that in practice it would be fine. My concern right now is more of a cosmetic one.
I do also wonder what it would be like to do something like a lug or sleeve? Without the flux being inside the joint to start with, I’d be really interested to see how much penetration I could get without using paste.
This has turned into a bit of a ramble. Thanks for starting the conversation though, I’m definitely going to experiment some more.
To be fair I thought you couldn’t use a fluxer with silver too and used to turn my fluxer off to do silver work; one day I saw Brodie using his gas fluxer with silver so I thought I’d give it a try and see if it worked and it did!
On the topic of paste flux I still use a little bit brushed on to act as a temperature indicator for silver and bronze, I always use lots of paste flux in lugs and inside fillet joints to ensure I get good penetration because I doubt the bronze would melt fully into the lug without flux inside to help draw it in.
Interesting about the silver fillets being bigger, I quite like large fillets so those nice big fillets are ideal in my opinion. Potentially try a small torch tip, I found smaller torch tips turned up allowed me to get smaller fillets.
