[python] Re: brazing vs. welding


Mmm ... I enjoy reading posts based on thorough insight and experience

olaf



On 14 dec 2005, at 10.23, Ralf Weigel wrote:

Hi Arthur,


I bought a similiar set from Rothenberger a couple of years ago (just with the one-way oxygen bottle), to use it in my goldsmith workshop. This is also exactly the scale of work it's suited for.

I still use the torch, because I never found such a lightweight and handy one for a reasonable price elsewhere. But I have relpaced oxygen and gas bottles (originals too small and expensive) , their respective rubber hoses (originals too short) and made myself a more powerful nozzle. It is my main tool for brazing (and melting silver for castings), tough I posess an industrial size oxygen- propane torch for brazing and cutting purposes as well.

Something in your mail strikes me a bit odd. If you already know about brazing, than please skip the next lines.

Silver filler normally melts far below 900°C. If there is one with this melting point (I'm too lazy to look it up yet), then the silver content would be minuscule and the mechanical advantages to classical brass filler very small.
When brazing frames with butt joints (that is, without sleeves [Muffen] or overlaps), you have to prepare the pieces with considerable precision. The maximum gap should be below 0.2 mm. With filler high in silver (30-40%), even smaller gaps are required.
Your torch has to deliver enough heating power, as even a low melting silver filler needs a temperature considerably higher than its melting point to join well with the steel surface. Also you steer the filler around the joint with the torch, it follows the highest temperature. I made tests propane torch vs. oxygen-propane torch with LAg35 filler. Both torches made reasonable-looking joints. But the propane torch joint brakes off at much less load than the other one, showing a steel surface with few filler remains, while the oxy-propane torch joint showed a break in the filler, leaving both steel surfaces covered with filler remains. The same might happen if your oxy-propane torch is not powerful enough and you do not reach the desired temperature. If you like, I could try it and tell you the result, the original nozzle must be still somewhere.

I finally settled for WIG (or TIG) welding for frame parts, which required an investement of about 500 Euro. With ebay, it might be less. But there where additional reasons to get the kit, not only bicycle-building. Small parts like cable holders or fixtures I braze to the frame.

Make yourself a happy christmas....

Ralf

Arthur K. schrieb:
Grüss Gott Jürgen,
Hello to Jukka and All !
thank you for the answers of my questions.
Well, i allready hold the hardware-store-steel in my hand and after a long time of thinking i decided to braze my first frame, because a MAG-Welder dosen't worth it for me right now.
My suggestion is to buy a Rothenberger Braze-Kit like this one :
http://www.ivvt.de/Rothenberger/roxy400.jpg
Cost around 200€ new on Ebay
( maximum material thickles for weling : up to 2,5mm, for brazing up to 5mm) with silver Filler (silver-based alloys) with melting temperature around 900°C.
How about this idea ? Do you think i will get enough stability with a brazed frame, when i choose the same material (rectangular steel) ?
Does anyone got experience with brazing of frames ?
By the way , i want to build a Tricycle like the Trixstar
(http://www.trixstar.co.uk)
It's the perfect geomerty in my eyes !
Greetings from cold Munich
Arthur
Am 13 Dec 2005 um 16:06 hat Jürgen Mages geschrieben:
>> My questions: What kind of material (size) did you use for the frame ?

Mild steel (Baustahl) rectangular tubing with 1.5 mm wall thickness.


>> Did you braze (what kind of filler) or weld (electro or autogenous)
> Weld, MIG welder(or how it say?)

 I used MAG (with CO2) for all my frames.


 >> Which way is the the best to bulid a homemade frame ?
 > I build only way I can...

 Jukka is right. It depends on your skills, equipment and
 preferences. If you want to build the ultimate light and
 stiff frame, it's carbon fiber (CF)...

 Pfüadi,
 Jürgen.

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