DRILLING
Standard High Speed drills, ground normal angles, may be used, but the peripheral lands wear badly and care must be taken to see that the drill has not worn undersize.

SCREW CUTTING
Provided that plenty of lubricant is used, niobium may be screw-cut using a standard die-cutting head. The use of ample lubricant prevents galling on the die and consequent tearing of the thread. Roll threading is a preferred method.

SPINNING
Normal techniques of metal spinning may be applied successfully to niobium, with minor modifications. It is generally better to work the metal in stages; for example, when spinning a right-angled cup from flat sheet, several formers should be used to give steps of approximately 10°. Wooden formers may be used for rough spinning, but a brass or bronze former is essential for finishing, because the metal is soft and takes up the contour of the former. For small work, aluminum bronze or Narite tools should be used with a radius of approxi-mately 3/8 inch. If sharp angles are required, the tool must be shaped accordingly. Yellow soap, or tallow, is suitable for lubricating the material, which must be cold worked continually. The peripheral speed of the work-piece should be about 500 feet per minute. When spinning, niobium is prone to "thinning" and care must be taken to avoid this. The tool should be worked in many long sweeping strokes using a light pressure rather than a few heavy strokes.

Niobium is a highly active metal, reacting to temperatures well below its melting point with all the common gases, such as: nitrogen, oxygen, hydrogen, and carbon dioxide. At the melting point and above, niobium will react with all known fluxes, thus severely restricting the choice of welding methods. Cleanliness of the metal prior to welding is critical. An acid pickle is recommended before welding. For ambient temperature pickling, a typical solution would be 25-30% HF, 25-33% HNO2, balance H20. Coupons should be used prior to immersing the part to check the etchant rate. Removal of approximately 0.0001" is generally accepted.

FUSION WELDING
The TIG welding method is recommended for niobium. This process is commonly applied to the welding of stainless steel, aluminum, magnesium, and their alloys. It is now being used to weld reactive metals, such as titanium, zirconium and tantalum. However, some modifications in this technique are required. It is essential to completely cover the area of the molten pool and the heated zone with inert gas to avoid contamination on the weld metal. This protection must be given to the back of the weld as well as to the face. When welding butt joints without filler rod in sheet less than 0.050", the torch provides sufficient coverage to the face of the weld; the back of the weld may be protected with a stream of argon from a manifold positioned just below the weld bead. A trailing shield will afford further protection to the hot metal after the main shield has passed. Niobium can be welded satisfactorily by using standard gas-tungsten-arc (GAT), heli-arc procedures. The resulting welds are superior to those made under similar conditions with an alternating current. The argon from the torch seems to provide better protection for a smaller pool.

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INDEX  •  CORROSION RESISTANCE PROPERTIES  •  FABRICATION   
NIOBIUM PRODUCTS   •  SPECIFICATIONS of NIOBIUM   
NIOBIUM ELECTRONICS APPLICATIONS