Brazing metals for boilers

[taff]

Hello Folks,
Just a few words about brazing metals for our copper boilers for our model locomotives. Some years ago I was heavily criticized in the model Engineering press for recommending "Sifbronze" for some of the joints in our boilers. Its some years since I last built a copper boiler but I am now about to be confronted with this job once again and I am interested in current opinion about joining metals. At the time, and since, I have never really got to the bottom of the reasoning against "Sifbronze" and I have no reason to doubt its quality's for boiler construction. Many years ago when I was in the industry "Sifbronze" was used throughout the shipyards for joining copper pipes an attaching bronze flanges to copper pipes etc., most of which carried high temperature water or steam and no one ever mentioned any problems with it. So I'm asking what is the current thinking and recommendations among you experienced boiler builders. I am very interested to know.
Taff.

[jasonb]

I think its the sulphur in teh smoke thats the problem not steam/water and I'm sure the Australian code does not allow its use someone more learned can confirm.

J

[jma1009]

ive got a large quantity of the sifbronze rod for BRAZING with,
(as opposed to MIG/TIG welding modern stuff which is quite different and requires de-oxidised copper and completely different techniques).

alec farmer used sifbronze extensively on sub assemblies on his boilers, and refers to it in his book/bible on model boilermaking.

LBSC also extensively used sifbronze on boilers, though he was fortunate (and rare) at the time to have oxy-acetelyne. in LBSC's later designs he made it quite clear that references to 'brazing rod' were to sifbronze, and he had all the up to date technical specs issued by the makers.

i am wondering of there is some confusion with the much older practice of using brass rod for brazing with, which of course is quite unsuitable for boiler work.

i would also be interested to know why sifbronze has gone out of favour and the technical reasons behind this... or is it simply that 'sifco' no longer make the old sifbronze brazing rod ? (have a look at their website)

i have recently completed a replacement boiler for one of my locos using silver solder throughout, but the original boiler was professionally built by the late tom goodhand of rochester/gillingham kent with sifbronzed joints and lasted for over 50 years!

[cupalloys]

Sifbronze is basically a brass with a little tin added to improve the flow characteristics. In certain circumstances the water can remove the zinc (dezincification) and cause porous/weak joints. For example British Standards for your domestic hot water cylinder specifically excludes brass type brazing materials in their construction because of this potential problem.

The problem is exagerated in cylinders because of the continuous thermal cycling and the fact that the joints are always in contact with the water 24/7. These two conditions do not apply to steam locomotive boilers.

Hot water cylinders are brazed with cheaper CuP (copper phosphorus) alloys that contain no zinc or silver. However these joints, when subjected to an atmosphere containing sulphur (like in coal fired steam boilers), fall apart. Hence the model engineer does not use these alloys.

Sifbronze is relatively cheap - no silver - and will undoubtedly produce strong leaktight joints.

But it has its disadvantages compared to a silver solder.
Being brass it can't be used to join brass components eg bushes.

It melts at about 900 degrees C.
It is difficult to attain even heating at this temperature to promote capillary flow - the most important characteristic of brazing/silver soldering. . This can induce the model engineer to use a welding technique ie heating the rod not the joint. The rod may not fully penetrate the joint. This can lead to a superficially sound joint which in effect has a crack built into it where the alloy has not penetrated. This is a "skill thing"

The high temperature causes greater expansion and distortion.

You are forced to use oxy-acetylene.

The workshop gets considerably hotter!

These are the reasons that silver solders are used in the first place. You pays your money and you takes your choice.


keith

PS the cynics should be aware that we also sell brass alloys but not anything like as much.
Why?
There is a lot of experience out there regarding copper boilers and their construction. The vast majority want silver solder.

[Shawki Shlemon]

The OZ code does not allow use of brazing materials with 15% or less silver or containing phosphorus in boiler construction .

[steam4ian]

G'day Shawki

I can't lay my hands on my copy of the Code.

I thought that brazing alloys could be used vs silver solder provided they were bronze (not brass) and did not contain phosphorus. The diagrams in the code show where brazing can be used and the differences in the joints; brazed joints need less/no overlap.

For all that I can't see why phos bronze can't be used outside the firebox or smoke box but I suppose it's considered safer to rule it out altogether.

Regards
Ian

[jma1009]

far be it from me to question keith's very detailed advice, but he does have a certain vested interest, and i would query his suggestion that sifbronze rod is a brass alloy as opposed to a bronze alloy.

yes sifbronze has a high melting point, but it is no higher than when annealing copper to flange up boiler plates. i have always used sifbronze by applying a ring or strip of sifbronze and heating the other side of the work till it flushes round, using sif-flux (dark red powder mixed up to a stiff paste). clearances must be generous and the joints well chamfered. the only exception to the above is when sifbronz-ing the ends of superheater elements where heating the whole job other than from the other side of the joint cant be avoided...but ive never had a problem.

sifbronze is also very useful for cast iron, and steel.

i have never had a problem sifbronzing parts with a propane torch, so long as plenty of suitable firebricks are used to create a furnace type surround. the same applies when annealing copper plates for flanging.

i am sure that if an expert such as the late alec farmer thought there was a risk of de-zincification with sifbronze he would not have used it in the construction of his boilers.

cheers,
julian

[ettingtonliam]

What is sifbronze made of? Instinct suggests its a bronze, otherwise would't it be called sifbrass? Does it have any tin in it? My understanding is that if the major components are copper and tin its a bronze, if its primarily copper and zinc its a brass, so what is it?

Regards
richard

[abby]

There is more than one "sifbronze" alloy , I have used a nickel alloy , sifbronze no.4 , which is silver coloured and a fair match for steel.

[cupalloys]

Yes , we at CuP Alloys have a vested interest - that interest is ensuring that our customers braze and continue to braze and we care not what materials the model engineer uses as long as it produces the lowest cost high quality joint and meets the customers specification. We supply brazing alloys of all descriptions.

Sifbronze No 1 conformed to BS 1845 CZ6.
Composition 57 -61% Copper 0.25 - 1.0% Tin balance Zinc

Sifbronze No2 conformed to BS 1845 CZ8
Composition 46 - 50% Copper 9-11% Nickel balance zinc

In my book an alloy containing so much copper and zinc and so little tin is a brass. Bronze is a copper tin alloy.

Why are they called sifbronze? Ask SIF!

regards

keith

[taff]

Hello Folks,
Many thanks to you all for the excellent and considered reply's you have given to my initial thread. From what you have all said I can see that there is no need for me to worry about the use of "Sifbronze" in our model boiler construction and I will continue to use it and recommend its use. The Australan Miniature Boiler Safety Coimmittee's Code of practice has been mentioned and I have a copy of this in front of me as I write. Regarding Brazing Alloys "Sifbronze" is not mentioned anywhere in it, however a material known as "Tobin Bronze" is mentioned as being suitable. Many years ago I contacted Dave Merrifield, the Hon Sec of the AMBSC about this and Dave informed me that he had knowledge of both and in his opinion "Tobin bronze" was virtually the same as "Sifbronze". Perhaps Shawki could clarify a point in his reply whereby he states "fillers shall not contain phosphorus OR less than 15% silver shall not be used". I see that in section 2.3.2.1 it states filler metals containing phosphorus AND less than 15% silver shall not be used ( the capitals are mine). When considering both statements it will be seen that there is a difference and I rather think that Shawki's contribution is correct but it would be nice if we could have that confirmed.
Taff

[jasonb]

How did you reach that conclusing the other posters seem to think because it has Bronze in its name it will contain copper/tin and have said that they would not use a brass type rod.

Mr CuP has shown that it is really a zinc/copper allow eg brass.

Why not just ask your boiler inspector as at teh end of teh day he's the one who will give it a cert or not.

J

[ettingtonliam]

[quote author=shawki board=general thread=6479 post=63145 time=1311673334]The OZ code does not allow use of brazing materials with 15% or less silver or containing phosphorus in boiler construction .[/quote][/i]

Theres a world of difference between this statement and 'filler metals containing phosphorous and less than 15% silver shall not be used.' In Shawki's version, sifbronze No. 1 is out, because although it doesn't contain phosphorous, it doesn't contain 15% silver. In the second version, sifbronze no 1 is OK because it doesn't contain phosphorous, and therefore has no need to contain at least 15% silver.

How is the Australian code generally interpretted in this respect?

I've been trying to find out what the composition of Tobin Bronze is, but without success. My old text books refer to it as an alternative for sifbronze, and refer to them both as fillers for bronze welding, even though, on the face of it, sifbronze No. 1 is a brass, because I don't think 1% tin is enough to regard it as a true bronze.
I'm confused.

Richard

[jasonb]

Found this which suggests it more brass than bronze

"Naval rolled brass (Tobin bronze) contains about 60% copper, 39% zinc, and 0.75% tin. This brass is highly corrosion-resistant and is practically impurity free."

J

[davet]

Hi All

I have dug up my copy of the Oz boiler code, aMbSC Code Part 1 - issue 7 - 2001 - copper boilers.

This might not be the latest version but I'm sure the contents for soldering/brazing materials would not have changed.

*****************************************************
Section 2.3.1 - Bronze Brazing

AS 1167.1 - 1993 Welding and brazing - Filler materials

Alloy RCuZnA Tobin Bronze

Section 2.3.2 - Silver Brazing

AS 1167.1 - 1993 Welding and brazing - Filler materials

alloy A2
alloy A3
alloy A4
alloy A6
alloy A7
alloy A410

2.3.2.1 Silver brazing filter metals containing phosphorus and less than 15% silver shall not be used.

2.3.2.2 Copper phosphorus brazing alloys shall not be used.

***************************************************

In another section the code states that the Silver brazing method is preferred and if bronze brazing is employed then it shall be carried out by persons experienced in the process and care to be taken not to overheat and prolonged heating during the bronze brazing.

Therefore, if you want to bronze braze then as long as the filler material meets the stated specification it should be ok, with a recognition to the issues with the actual brazing process.

I have googled the RCuZnA material and there are not very many hits. Maybe CupAlloy could expand on this bronze brazing material, there must be alternatives. On the other hand maybe the producers of the Oz boiler code could expand on the bronze brazing alloys suitable for our application.

Hope this helps to stimulate some more discussion on this issue, with the price of silver solder getting higher and higher maybe it is time to review so that the overall cost of our hobby can be kept to a reasonable level, with of course the first and foremost eye on the safety aspects of making a pressure vessel.

Regards

DaveT
Kuala Lumpur

PS - Allan

If by quoting from the Oz code is deemed to be an infringement copyright etc, please delete this reply.

[Tel]

I don't think the AMBSC is going to get too upset Dave!

But the topic has highlighted something that I've noticed for a long time - many people still confuse the processes of brazing and silver soldering (not 'silver brazing') they are two entirely different processes and, until folks can grasp that concept they will continue to wallow.

[davet]

Hi Tel

I totally agree that there is a confusion of terms when it comes top silver soldering/silver brazing and that is what I like about the Oz code, as it provides a central focus point for the manufacture of pressure vessels for our purposes.

Still nice and cool west of the Blue Mountains ? Hope the workshop is heated so at least you can continue work in comfort.

Now back to the issue of Tobin Bronze.

I have now gone looking for info on the Tobin Bronze and found this :

www.gentronics.com.au/userfiles/file/comweld%20tobin%20bronze%20rod.pdf

This pdf file provides the best info on the Tobin Bronze material that I have seen in my hunt on the net and also provides an alternate standard (AWS/ASME-SFA A5.8/A5.27: RB Cu Zn-A). Please remember that the standard quoted in te Oz boiler code is an Australian Standard, it is interesting if you google for "tobin bronze brazing" the first page of results are mainly Oz based companies, I think this shows that the "Tobin Bronze" is a very Oz based product and more difficult to source outside of Oz.

I have attached the pdf file as well so that it is available for future reference as well to users of this forum.

They also have a different way of expressing ("RCuZnA" as stated in the Oz code) which is "R CuZn-A" so this will make it harder to search for on the net.

From the pdf file the typical rod composition is :

Zn: 37.5% (Zinc)
Si: 0.30% (Silicon)
Sn: 0.50% (Tin)
Cu: Balance (Copper)

so Tobin Bronze is a Copper and Zinc material with two trace elements (Silicon and Tin) from this composition it should be easy to find a compatible rod elsewhere in the world.

The comparable CIG product is "Comcoat T flux coated Tobin Bronze
AS1167.1 & 2: R Cu Zn-A", again note the "R CuZn-A"format.

I do not have access to the Australian Standard AS1167 but there would be a direct correlation to a British Standard or other international standard and it would be nice to identify these standards to reduce (and hopefully) eliminate this confusion on the options for construction of our boilers.

Regards


DaveT
Kuala Lumpur

Attachments:

[davet]

Hi All

Now I have tracked down the SIF sifbronze products on the www.weldability-sif.com page.

Sifbronze No1 is the closest product to Tobin Bronze in their product range, with its chemical composition being :

Zn: Balance (Zinc)
Si: 0.30% (Silicon)
Sn: 0.30% (Tin)
Cu: 60% (Copper)

So for Sifbronze No.1 compared to Tobin Bronze, the Zinc content is slightly higher, the copper and tin contents are slightly lower and silicon content is the same, to my eyes a very similar product to Tobin Bronze.

I think before I would use the Sifbronze on a boiler I would get input and comment from the owners/producers of the Oz boiler code or another suitably qualified person to ensure that the small differences in the chemical composition are not going to affect the strength of the joints.

I think the main issue with using Tobin Bronze or Sifbronze No.1 in our application is the high melting point compared to the silver brazing materials, about 900C for Tobin Bronze and about 700C for the silver brazing and the use and availability of oxy acetylene to provide the heat source.

More info to chat about !!!!

Regards


DaveT
Kuala Lumpur


PS From the Weldabilty site :

1kg of 55% silver solder No.43, cadmium free - 1.5mm dia = £1,359.12 (inc. vat)

1kg of Sifbronze No.1 - 1.6mm dia = £42.48 (inc. vat)

Attachments:

[alanstepney]

My personal view is that a boiler takes so much work, and is such an essential part of a model, that I only want to do it once and then I hope / expect it to last at least as long as the rest of the loco.

Hence I will use the best materials for the job, irrespective of price. (I just cry when I look at my bank balance!)
For me, Easyflo 1 and / or 2, (or the Cupalloys equiv) are the only option.
At least I KNOW that it will do the job and outlast me.

I really REALLY dont want to build a boiler and then find it fail in a short time, and have to do it all over again.

[Shawki Shlemon]

While Tobin ( bronze brazing ) is allowed in the code but it is not recommended because of high temperature involved in the process . Also test pieces may be required by the boiler inspector . I personally stick to the code requirements and it is in the interest of the builder to do so rather than trying to find some alternatives that are close just to save a few dollars . Most builders in the hobby are not professionals and therefore silver solder is the easiest method , it may cost more , that is if he/she does not overheat the boiler or joint using cheaper bronze method, if the joint is overheated and damaged it may end up costing much more .I don't want to go into the composition of the materials used , professional people have done that and recommended specifications in the code , they are good enough for me , they have been proven satisfactory and options are provided with conditions and that is what I like with our code .I have seen overheated joints even with silver solder using oxy . I am sure a professional welder can braze a boiler together or copper welded satisfactorily and that is allowed in the code but it is not a common procedure among the majority of the people , we have over 50 members in our club and more than 100 boilers and non is brazed or welded , a few are steel boilers and that is another issue .Sometimes is even cheaper to buy a boiler than make it so the cost is a factor at the end when the boiler is complete .