Brazing torch

A D, I wouldn't want to be trying to brass braze with a flux designed for silver solder personally; the likely lower temperature tolerance of the silver solder flux may render it useless by the time your brass solder is ready to flow.

Also, do you have a compelling reason to want to brass braze here rather than silver braze?

It's hard to tell if your torch is too small. The job doesn't sound a particularly big one.The standard burner with the 404 is, I believe, 4.76 kW, which is a relative tiddler in the propane torch world. Reassuringly, you do say the steel is getting red hot easily. But do you know that to successfully brass braze, the steel has to get considerably hotter and redder than when silver brazing with typical silver solders?

Even if you do know this, we come back to your present flux and its probable inadequacy for brass brazing.

Hi AD,

The Bullfinch should handle that work with no problems, provided the work is clean, you use the right flux (?) and you can 'contain' the heat (I use a simple hearth inside).

This is a similar sized part (3mm laser cut steel - base being about 35mm square) and the only problem I had (at first) was not allowing any gap for the Sifbronze to flow into. Second attempt worked fine - just a problem of my technique, not the torch.

Here is the finished part - not perfect perhaps but very strong. If you look in my 'Brazing' photo folder, you will see some larger items I brazed with the Bullfinch. Only when trying to join the very large plate to its base (it's about 180 x 120 x 100mm) did it struggle with the Sifbronze - and I had to use silver solder to complete it. These days, I would have just added some more heat from one of my other (disposable) propane.butane mix torches (as the metal radiant area was quite large) - and shielded it better.

.

The Bullfinch 404 is not a replacement for Oxy/A but works very well for small ferrous fabrications. There are many users of Sievert torches here (I have a similar (non-Sievert) torch myself) and they are certainly good where I want large volumes of heat (e.g. for boiler work). However, the Bullfinch is very good for the work I use it for - and Sifbronze is at least an order of magnitude cheaper than silver solder (which I still use of course for non-ferrous brazing).

So I'd suggest you practice with Sifbronze and the right flux - making sure that the work is correctly shielded and the filler can flow into a slight gap in the parts (similar to silver soldering really).

Have a look here - I use the 1.6mm rod by the way (£26.85 for 1kg ! ). They also do the correct Sifbronze Flux - 500gm for £13.75 (inc VAT) which will last you some time.

Sifbronze No 1

Regards,

IanT

Hi Bill,

I was thinking the flux might be causing problems.

As for brass brazing- no I have no objection to using silver solder-which I might end up doing yet.

I was mainly making long drill bits with silver steel and for that purpose bought some brass rods believing them to be stronger and cheaper than silver, and it worked on those. So I suppose my reason for brass brazing on this occasion is really because that's what I've got at the minute. And since it failed I want to know whether the torch is at/past its limit with this size of steel.

Hi IanT

Looking at what you have brazed there I think the torch should definitely be able for what I was doing.

When you say the work should be properly shielded - what would you suggest using? I'm using fire bricks to insulate for now but I'm not sure how effective these are.

I will try again once I get the correct flux.

Thanks both for your advice!

I have had a Bullfinch torch for close to 50 years now, only once have I had a fault the auto ignition failed and the company fixed it and charged only return postage ! As far as the job in hand is concerned it should handle it comfortably but as already said you will need to make up a hearth, however beware some "fire bricks" are designed to absorb heat not reflect it, e.g. the ones from storage heaters, so make sure you have the correct bricks or other material.

Almost all my work is silver solder but for brazing you can use Borax, old fashioned yes but it was used pretty exclusively until better fluxes were developed.

The Bullfinch torch can generate the high temperatures required to brass braze but it really helps if you can prevent that heat being leached away - so work needs to be held (or supported) in such a way that it's not conducted away - and anything you can also do to prevent it being simply absorbed by it's surroundings (rather than reflected back on to the work) also helps. You want all the heat focused on the work, not wasted elsewhere. Same as silver brazing - just more so, because of the higher temperature required.

I use ceramic blanket and also the ceramic (?) bricks that CuP sell for most work - and you can make simple supports out of tin or wire that will hold work but conduct very little heat away. It's not hard to do once you start thinking how best to keep the heat in...

Here's the work piece that I showed in my earlier post, before I started heating it (I turned it over) and as you can see, I'm using ceramic blanket and the work is sat on a simple tin support (cut from a can). It will glow white hot (but won't melt) and is wide enough to be fairly stable (you don't want to blow things over). So start with small items and work upwards in size as you get the hang of things would be good advice I think.

Regards,

IanT

Edited By IanT on 15/04/2020 23:15:59

Be careful with ceramic fibre once heated over 600 deg.C.

**LINK**

OK - that's good to know.

Thank you

IanT

Hi.

I am confused!

The link seems to tell me that the potential problem occurs at temperatures in excess of 1000 deg C not 600 deg C. At 1000 deg C, most of the components being assembled by the model engineer will have melted or are on the point of melting! Such a temperature does not relate to using a silver brazing alloy although it might at a push relate to overheating a copper-zinc brazing alloy. Beware of boiling off the zinc.

The link also seems to tell me that the potential problem stems from prolonged heating in kilns and furnaces (years). Most brazed joints are completed in minutes.

But the link also seems to tell me that there are no special precautions relating to the transportation and storage of the blanket. My experience of stockist warehouses bears that out.

But although the model engineer may use it but he doesn't handle it. Any irritation is negated by common sense and adopting good brazing practice. Wear gloves - marigolds (other makes available!) That statement lies alongside recommending that you don't pick up the brazing rod by the hot end.

But more seriously. Steel takes longer to heat up and if the alloy doesn't flow consider changing the flux to one with a longer life. Alternatively consider reducing the brazing temperature and time by using a silver brazing alloy. Your choice.

A Sievert torch has a very wide range of heating capability. It's ideal for the amateur model engineer. I've got one myself! It will give you what you need.

As ever, if you want any information regarding the brazing process, materials or equipment then give my colleagues at CuP Alloys a call.

Keith

I would really have liked to have Oxy/A available in my workshop but there are rental costs and safety concerns involved that prevent it's use in my Shed. For larger work I do the occasional spot of MMA welding but to call my efforts 'agricultural' would be an insult to the farming industry. I'd like to have TIG but again I don't think I'd use it sufficiently often in my modelling to be a good investment.

I certainly use silver solder for my non-ferrous fabrications and sometimes also for (ferrous) work that I cannot heat sufficiently with the Bullfinch (which clearly is not a complete replacement for Oxy/A). However, there are quite a few small jobs where SIFbronze is perfectly useable with the Bullfinch and very economic. Yesterday, I bent a couple of small brackets up that needed fixing via a tapped hole - so I brazed some thickening bits on the ends which will be drilled and tapped as captive nuts. Nothing fancy and I could have silver soldered them - but the Bullfinch brazed them very easily and I have plenty of SIFbronze to hand - so I don't worry about using it

I could have used silver solder of course - but I try to reserve stocks for my non-ferrous work because it's not cheap.

418 (18%) silver solder currently costs £13.60 for 2.5m (melting at 776-815C) - although I generally use a 430-type (30%) silver solder (melting at 655-75C) at £18.56 for 2.5m. I'm quoting 1.5mm solder btw - I also use 455 'wire' for very fine work (cannot recall what I paid for it).

So it would be very nice to use silver solder for everything - but SIFbronze (875-895C) currently costs £26.85 for 60 metres (x 1.6mm) and the Bullfinch lets me use it where appropriate. As I don't expect silver solder to get any cheaper going forward, I think SIFbronze makes good economic sense for some uses - although I certainly agree it might not suit other peoples needs. We all do different work.

With regard ceramic blanket (purchased from CuP btw) - I have used it as work support material in a 'mini-forge' (a baked bean tin with the top and part-side removed) and have certainly managed to 'fuse' it - it became very brittle and seemed to almost melt in some parts. I'm not going to worry too much about this but will be sure to wear gloves when handling the ceramic and will now take more care with wrapping, sealing & disposing of it after such use - so thank you Bootlegger for your note.

Regards,

IanT

Oxy-propane any better for you? No rental costs.

You can also cut down on safety concerns if you use an oxygen concentrator, which can provide more than enough oxygen for most work except cutting and large-capacity heating.

It could be Bill - although I'd probably go the £65 deposit 'bottle' route - I have a torch that would work with a new tip - but I'd also need hoses, gauges and blow-backs too - so maybe best to just buy a complete kit.

I looked at the Smiths Little torch - which for my work (with the larger nozzles) might be handy. The Cooksons Oxygen Concentrator to go with it is £500 though - so about £700 altogether...

Steeping back a bit - as a Hobbyist, I started way back with a butane torch that came with a variety of nozzles and used 2kg 'blue' Camping Gas bottles. It was mostly used for soft soldering (sweating) where my electric iron wasn't up to it. When I started using silver solder more, I purchased a B&Q style screw-on nozzle with disposable cans, which worked but were fairly expensive and sometimes inconvenient (running out half way through jobs).

I'd signed up for a six-week evening welding class but just about everyone else was a vintage car restorer and it was hard to get near the MIG & TIG setups (one of each) but no one else seemed interested in the Oxy/A - with half a dozen work stations free. So I started to bring small work in and braze it - which worked very well.

When I looked for an alternative to the DIY Cans - I first looked at the Bullfinch Auto Torch but realised for a few pounds extra I could have the Auto Brazing Torch (404) - so got that instead.

The Bullfinch is very well made, needs no setting and is push-button ignition. I use it for both silver and brass (SIF) brazing and it is very economical with the propane. It is my go-to torch for just about everything I do in the workshop - apart from boiler work. Others will have different needs no doubt.

As an aside - I was looking at some 1/4" steel plate about 16"x18" yesterday that I need a foot square of - and it would be nice to just flame cut it. I see YouTubes of folk grinding their way through similar stuff but I'm a bit chicken where angle grinders are concerned and it's not right for my power saw. I'll probably stick it on the big horizontal - slow but I won't have a heart attack in the process.

Regards,

IanT

Ian, most oxy-con users I know bought their machine as a reconditioned one [with 12 month guarantee] from this source.

I've got the Smith's Little Torch, and also the heavy duty oxy-propane torch sold by The Welders Warehouse [and available elsewhere in different guises].

Hi Bill,

The vast majority of brazed joints between two steel components are made using a brass filler metal. The reasons are clear. The joints are strong and the filler metal is cheap. Why use anything else?

In all cases, you would change to a silver solder only to satisfy a technical issue eg colour match, dissimilar component materials, to reduce distortion by making the joints at a lower temperature. Another possibility is that your heat source won't deliver enough heat.

In the last case, the first option is to fit a bigger burner. Such a burner does not have a higher flame temperature but does burn more gas and as such develops more heat. Bullfinch will tell you the heat rating of your existing burner.

The higher flame temperature of oxy-gas flames does not always generate more heat.

The flame profile often pushes the user to adopt a welding technique that will lead to a lack of penetration of the filler into the gap and a weak joint.

So, in a nutshell, the cheapest option would appear to be, stick with the brass rod and simply fit a bigger propane burner. (What? - this guy sells silver solders!)

No good? Either buy a new/different torch generating more heat (not forgetting to amend your heating technique it's easy enough but needs to be done)

Alternatively buy some silver solder but only use it where necessary. As before make sure you use an appropriate flux.

You pay your money and take your pick!

Keith

PS The cheapest joints are not made using the cheapest silver solder. (But I would say that wouldn't I?) But that's another topic!

Edited By CuP Alloys 1 on 22/04/2020 08:30:16

Useful links Bill, thank you.

Again, I found myself looking at an old camping trailer chassis that's been sat around unused for many years and which is now immobile. I used to drag a small exhibition track around in it but don't do that these days. Need to cut it up but I can't really justify that big torch (and all the associated stuff) for one or two jobs I'm afraid.

I do have of an Aldi bandsaw and of course an angle grinder - but I much prefer to use these things in stands with everything well bolted down. I'm not so keen on free-handling them where something might suddenly snap or move unexpectedly as might be the case here. Would not have thought twice about it 20 years ago - but I'm a bit more cautious these days.

Thanks again for the links - I've booked marked them (just in case)

Regards,

IanT

Ian, cutting does require a lot of oxygen - more than a 5 litre oxy-con like mine can deliver, so it's likely you would have to have an oxygen cylinder as well as or instead of an oxy-con if you wanted to cut that chassis. As you say, hard to justify economically unless you're cutting regularly.

If my soldering/brazing activities had started out in an engineering/model-making field rather than a jewellery-making one, it's unlikely I'd have spent on oxy-propane set-ups in addition to the several propane-only torches and assorted burners I've got.

It's really for purposes like the following [see the soldering task starting at 3.56] that I bought the Smith's torch; it allows you to give very localised heat [so reducing the risk of desoldering previously soldered joints nearby] but also heat that is intense enough to quickly overcome the effects of unavoidable heat sinks such as the special collet-to-shank-holding tweezers the demonstrator is using in the video.

Expanding on what Keith says, my perception is that many users of brazing torches don't initially appreciate that a relatively low flame temperature [e.g. with propane only] isn't the primary limiting factor in the kind of brazing work they can do; volume of heat is likely to be the more important factor, and this can easily be solved with a Sievert or Bullfinch system if you have a choice of burners on hand. I know I failed to fully appreciate the importance of volume [as opposed to temperature] myself initially when I moved up from jewellery soldering to bigger work.