sherpa wrote:This is the reply from an email I sent to a mate, who is a metalurgist and has been since the 70's
Greg,
The general consensus among our welding experts is that they were probably TIG welded. It was possible that oxy was used as well.
The Chrome Moly referred to is made as tubes in AISI 4130 steel. This indicates that the steel has 0.30% carbon. Because of the thin wall section preheat is not necessary.
The steel tubes are supplied in the US to military specs for aircraft use and they are either normalised & tempered (Tensile strength about 655MPa and yield strength about 500MPa) or quenched & tempered (Tensile strength of 860-1240MPa and yield strength of 690-1140MPa).
Reynolds in UK still supply tubes for bikes (both motor and push). They quote tensile strengths of 700-900MPa (varied by the amount of cold work by drawing) and I think they also supply quenched and tempered tube. Again the material is 4130.
MIG would have caused too many lack of fusion problems back then before flux cored wire was available.
Send me a photograph of some welds.
Indeed....................personally I have never seen any Spanish frame that has been TIG or oxy fuel welded! I have been involved with trials since the late 60s, and have owned most of the Spanish bikes, so its likely I would have noticed any that had been TIG, rather than MIG welded by semi skilled workers.
4130 as such, is the designation applied to chrom-moly tube made in America and is still widely used there, the best known Reynolds tube was 531 which is manganese-moly, and was used to make some Norton featherbed production frames, which were joined using the bronze welding process. Imported 4130 tube is being used in the UK to make Rickman Mettisse frames, which are again built using bronze welding.
Tubes marketed by Reynolds today include an air hardening grade (631) which can be MIG welded, but this was certainly not available in the seventies. It seems surprising that people are happy to accept what's claimed in advertising blurb rather than taking note of how a frame is actually joined together. Another "high tensile" frame produced in the 70s, the Seeley Honda, had a sticker proclaiming "Reynolds 531", but only actually used about 75mm of this tube, which joined the rear mudguard loop, with the rest of the frame being ERW!
Back in the day, the cost of the Spanish factorys using costly imported cro-moly tubing, and the need for skilled workers to weld them together using the TIG (rather than MIG which could be carried out in a 1/4 of the time) process, would have meant production costs would have increased considerably, and I would guess it was a much better idea commercially to simply claim the cheap low carbon frames were cro-moly, as most people simply wouldnt know the difference anyway.
The very last bikes produced by Bultaco, the 6 speed white frame models, had many problems related to frames simply snapping in half under the tank, so there is a possibility that CRM tube may have been used on these, which when the basic design is poor, is far more likely to crack and fail than if cheap low carbon steel had been used.
Just to remind you this is what happened
