Having recovered fully from my Freudian slip ,and with aplogies to the late Andre Reiss, for applying an incorrect Christian name, I would like to thank, again, all those List members who have sent contris both on and off the List in response to my original contribution.
Not for the first time when attempting to discuss matters with a highly technical focus..in this case "fusion welding" it is interesting how definitions vary between the States and the UK...although to be honest I think we are taking about the same process.
Over here the characteristic of a "fusion" weld is that the parent metal being joined is actually melted and the union or joint is produced on subsequent cooling and solidification.Generally speaking the two main heat sources used are gas welding (more often than not,,but not always, by means of oxy-acetylene) and electric arc. In the case of gas welding the fused joint can be produced using the parent metal only, or together with a filler rod of a similar, but usually not identical metal. With electric arc, an electrode/filler rod is used.
I have gas-fusion welded many many articles together, including tubes of quite fine gauges, using very fine nozzles, but the point that I was attempting to make is that it would take superb skill, which I doubt that I have, to join a chrome-moly or chrome-manganese tubing with a wall thickness of 0.5, 0.6 and 0.7 such as the Reynolds tubes used by Reiss on his Reyhand frames to the much thicker walled head-tube and to the much thicker still mild steel bottom bracket sleeve. I reckon I could achieve a weld not unlike TIG in its appearance but Reiss went further he produced large fillets.
At every joint in the main triangle of a cycle frame there is a joint in which an open-ended tube has to be jointed to a fully cylindrical one. Whenever a torch flame is applied to such a joint the heat always tends to migrate to the "free" metal ie the open tube, which because it has less mass heats up more quickly giving rise to the risk of seriously melting the end of the tube, even before the mass of the fully circular tube gets any where near becoming molten.
When bronze welding/fillet brazing such joints it is comparatively easy to play the torch flame on to the bigger mass ie the circular tube whilst gently bringing the "free" tube end up to the melting point of the brazing materal, which is much lower than the meltingpoint needed in a steel-to-steel fusion joint. Again when bronze welding a joint and achieving a large weld fillet it is a simple case of either making multiple passes with a small dia. rod and very small flame or one pass with a larger dia. rod and a slightly larger flame. In both cases the filler rod can be moved about under the tip of the flame when in a relatively "pasty" consistency to produce a bead but in neither case is the the parent metal of the tubing actually melted.
The process that I am trying to identify is how Reiss managed so successfully to fusion weld the thick tube-thin tube/ open end-closed tube joints, and to build up beads/fillets of weld that so closely resemble bronze-welded ones. If he used multiple passes with a small filler rod, he stood the risk of over heating the joint, while if he used the fat rod-one pass system the heat required to melt the filler rod and fuse the parent metal at the same time would have been, of necessity, quite substantial. The liquidus range of bronze-welding material is far wider than that of the low carbon steel filler rods used in fusion welding and permits a wide margin of safety to the welder.
I must be missing a trick here...the theory is one thing,, but putting it in to practice is much more difficult..and would need real skill to produce work of the calibre of Andre Reiss'.
Norris Lockley..feeling the need to get back to the torch...Settle UK