Aluminium braizing

[Ben Wilson]

Bear in mind that there will always be some HAZ which doesn't have weld on it and even the slightest undercut will make the stress concentrations a lot worse.

I had a huge argument with the welding teachers at tech about weld profiles and the resultant stress raisers..

[SL666]

a good weld shouldn't have any undercut anyway

[airfireman1]

look up on the net a company by the name of HENROB. I think thats the name, they make a very small welding torch and claim it suitable for small jobs icluding braising aluminium.They are an australian company

[Ben Wilson]

I've got one - You can weld aluminium with it, but it still sucks.

[TA22 GT]

Why? - I can't remember my metallurgy too well, but if you heat the base metal until the granular structure expands, then add a filler material with a lower melting point which capillaries between the grains of the base material. Once it cools the granular structure locks over the filler material creating a strong bond.

Theoretically it should work most metals - chrome molly doesn't like it as its granular structure expands too much and it cracks.

Theoretically you're right. However aluminium needs a fair amount of heat and using a TIG gives good localised heat which results in a very neat job if you know how to do it.

If you get scientific and test oxy to TIG it maybe the same strength if both are done well. BUT, my point is that TIG is the way to go and gives the best finish. If you're happy for it to look like crap then oxy will do fine.

Cheers,
Simon

[Toda+TRD=Hybrid GE]

your best chance for alloy is a TIG its stronger better finish once you learn how to the possibilities are much better then brazing.
Plus if u can braze you can tig its basically the same

[clubagreenie]

You can braze cr molly, most good bike (bicycle) frames are steel cromo and are still brazed.

As for ally if you can get to the back of the sheet have someone heating it from behind as well, keeping the heat in the material.

I've seen more people using (gassed) MIG for ally than TIG, having the machine dedicated to it rather than swapping to/from steel setups.

[Toda+TRD=Hybrid GE]

[QUOTE=clubagreenie].

I've seen more people using (gassed) MIG for ally than TIG

i'm not saying it's not possible but in my experience the finish with the TIG is more presentable then when using a MIG. I suppose it depends on the application of the job wether it's seen or not.

[Ben Wilson]

You can braze cr molly, most good bike (bicycle) frames are steel cromo and are still brazed.

Are you sure - I'll double check my welding book tonight, but I'm sure it said that the structure of cr molly opened up too much, letting too much braze metal in which then caused internal stresses and cracking...

[clubagreenie]

Ths is a longish paste but from the oldest producer of frames from reynolds tubing, details techniques that can be used with different grades depending on their original manufacture method. Some can be brazed, some tiged or brazed.

MATERIALS



As mentioned above, all Jackson frames are built using Reynolds or Columbus steel tubes. Reynolds TI is the oldest manufacturer of tubes specifically designed for bicycle frame building. Reynolds currently offers 5 different qualities of tubing, 525, 631, 725, 753, and 853. Of these 5 varieties many different configurations can be realized. Bob Jackson Cycles builds main frame tubes with the top 4 qualities only. In addition Jackson will build using various grades of Columbus tubing.



The tubes used in Jackson frames and a brief description of these follows, but first a brief description of “Chromoly” that is so often used to describe bicycle frame tubes. Chrome moly which in its generic state should carry a SAE/AISI number 4130 will in the best case scenario have a tensile strength of 80,000 psi., before welding. These values are for 4130 produced by a reputable steel manufacturer. Generic “Chromoly” supplied by an unnamed source or imported oriental steel should be looked upon with a great bit of skepticism.



Hi tensile steel should best be reserved for plumbing pipes and should not even be considered for a bicycle frame. Jackson will not build with either of these materials.
REYNOLDS 525 / 525 OS info

Reynolds 525 non heat treated chrome moly has been in Reynolds inventory of bicycle tubes for many years. Since 1998 it has been reconfigured and up graded to a strength level very similar to that of Reynolds legendary 531 tubing. The primary reason for it existence is its ability to be tig welded, thus producing lower cost and lower quality frames. It has no advantage over 531 except for this singular feature. Jackson does not use this tubing for the 3 main tubes as there is no added benefit to the cyclist.

REYNOLDS 531C / 531ST / 531OS

No longer produced by Reynolds, due to its inability to be tig welded.

REYNOLDS 631 / 631OS info



Reynolds 631 Air Hardened tubing is a tubeset based on their 853 Air Hardened technology. This tubeset has replaced 531 as the basic material used to construct Jackson frames. The primary difference between 853 and 631 is the lack of heat treating applied to the an 853 tubeset, thus producing 631 tubing. At the present time 631 will only be available as main tubes and must be combined with either 525 or 725 stays to complete the frame. Jackson will be using 725 oval stays with these main tubes in their oversized configurations. This designation will be replacing Reynolds 653 & 731OS tubes. Tig welding is possible, however to bring 631 to its optimal strength level, brazing and the much larger heated area produced will greatly increase the finished joints ultimate strength.


REYNOLDS 653 / 653 RECORD / 731OS

No longer produced by Reynolds, due to its inability to be tig welded.

REYNOLDS 725 / 725 OS info

Reynolds 725 Chrome moly tubing can be used to build a complete frame or can be used as seat and chainstays to produce either 631 or 853 frames. The 725 is an up grade over 525 when used as a stay material. It offers increased strength without an increase in weight.

REYNOLDS 753 / 753 OS



No longer produced by Reynolds, due to its inability to be tig welded.



This was the benchmark by which all high performance bicycle frames have been judged for the last 20 years. Possessing a 195,000 psi tensile is among the strongest tubes currently available for the manufacture of high performance, light weight, ultra responsive road frames. This tubing uniquely combines terrific power transmission ability, lively ride, responsiveness and a high degree of comfort, while producing some of the lightest frames available.



BICYCLE GUIDE tested a sub 20 pound Bib Jackson 753 in their June 1995 issue and used such terms as "The four pound Jackson floated up longish canyon climbs", and "your back just doesn't get sore on this bike".



Unfortunately 753 frames will never be seen in great numbers. Frame builders having access to this material is closely controlled. Builders must be certified as to their proficiency in low temperature silver brazing 753 by Reynolds. Only after having passed a structural test on their work will they be certified and sold these tubesets. Another drawback is the cost of silver brazing material as compared to that of brass, approximately $150.00 per pound compared to $9.00. Having to keep the area to be joined at a maximum of 1200 degrees, tig welders are immediately ruled out, along with their ability to mass produce 753 frames. It is primarily for these reasons that 753 frames are not offered by the bicycle giants. Highly skilled labor and time consuming hand work are not the direction large companies wish to move in.

753 OS This is an oversize version of 753 featuring even better power transmission abilities than normal sized 753. A special 753 Anniversary tubeset has been created for Bob Jackson Cycles to commemorate the sixtieth anniversary of Bob Jackson Cycles and the introduction of 531 tubing. It features specially drawn short butts, reduced wall thickness, oversize seat stays and oval chainstays. Only 60 of these set have been manufactured by Reynolds, once they are gone no more will be produced. Unfortunately all of these have been used.



REYNOLDS 853 / 853OS info



Reynolds 853 is a high strength, 210,00 psi, heat treated, air hardened steel alloy. Careful control of the alloying elements combine to give these tubes enhanced mechanical properties surpassing other materials currently available.



The main advantage of Reynolds 853 is its ability to air harden after joining, a characteristic not shown by other chrome molybdenum / manganese molybdenum materials presently on the market. When building frames using either TIG welding or high temperature brazing, above 1600 degrees, the joints increase in strength as the frame cools to room temperature.



LUG CONSTRUCTION IS THE PREFERRED METHOD OF JOINING 853. It allows a much larger area to be heated than tig welding which concentrates the heat to a very small area at the weld. This completely goes against the “AIR HARDENING” building philosophy of the material and adds nothing to the strength of the joint. It is however a much cheaper joining method, requiring less time and skill to perform.



Due to the superior mechanical properties of 853 tubing, there are several benefits which will translate directly to the cyclist. The wall thickness of 853 has been reduced to 0.4 mm, a full 0.1 mm thinner than Reynolds other top of the line 753 tubing. This translates into a frame weight of under 3 pounds 5 ounces for a 56 cm frame (less fork). Because of the added hardness of this alloy the chances of denting the tubing are no greater than that of present materials being employed. The final significant advantage is the increased stiffness of the frame and its ability to transmit all of the cyclist power into forward motion. The oversized 853 tube set, with its oval chainstays represents the ultimate in power transmission. Aside from the 853 OS tubeset, conventional diameter sets are available which will allow for a more comfortable ride, while still retaining most of the benefits associated with 853 oversize.



853 is currently produced in 8 tube tubesets. There are no fork blades drawn from this alloy. Bob Jackson will supply 853 frames with your choice of fork material., and configuration.

[ed]

reynolds is proprietry cromo though

not sure if its behaves the same as the garden variety 4130 regular bicycle stuff

[Ben Wilson]

Forgot to check my book, it relates mainly to aircraft spec stuff. Interesting stuff though.