Views: 5 Author: Site Editor Publish Time: 2020-06-11 Origin: Site
Tungsten lamp filaments, which operate at temperatures in the range of 2400° C, are successfully mounted on molybdenum wire; the wire acting both as a heat sink and a support while lowering the temperature at the support junction. Likewise, molybdenum sees wide use in the construction of power tube grids and support structures that also require high temperature strength, low vapor pressure and low thermal expansion. High temperature vacuum and hydrogen atmosphere furnaces also rely on the use of molybdenum rod and molybdenum wire to form resistance-heating elements.
Dimensions and Tolerances
Wire diameters are generally expressed in terms of inches or mils (thousandths of an inch). For thin wires from 0.001 inches up to 0.020 inches, the size of the wire is measured by weight per unit length. That is, the weight expressed in mg of a 200mm length of wire.
The standard diameter tolerance is ± 3% of the weight measurement. For mandrel applications, the tolerance is normally ± 1%.
To calculate diameter, the equation is:
D (in mils) = 0.98648 x square root(mg weight / 200mm length)
For thicker wires from 0.020 inches up to 0.250 inches in diameter, the inch or mil measurements are used. The tolerances are expressed as a percentage of the diameter. Standard tolerance is ± 1.5%.
Other Useful Equations:
meters/kilogram = 194628 / (diameter in mils)2
mg/200mm = 1.0276 x (diameter in mils)2
Note: Formulae for MB are different, and available upon request.
Tensile strength for molybdenum wire is usually expressed in grams per milligram weight of a 200 millimeter length (or) g/mg/200mm. The normal range of values is 40 to 60 grams. In general, as tensile strength increases, wire straightness decreases.
The measure of the straightness of a metal wire is obtained by cutting a ten inch long piece of wire and allowing it to lie on a flat clean surface. The maximum deviation from a straight line along its length is the quantitative measure of its straightness. In general, as the degree of the straightness increases, tensile strength decreases.
Out of Roundness
Out of roundness of wire does not exceed 4% of the wire diameter. It is measured as follows:
Out of Roundness = (Max Diameter – Min Diameter) / Max Diameter x 100
Quality and Finish
Wire is free of scratches, kinks and distortions insofar as they are harmful to the intended use of the product. Surface finish is supplied in the black, as drawn condition, where drawing lubricants and oxides are retained on the surface, or in the cleaned condition by firing in hydrogen or electrochemical etching.
Wire is spooled on clean, defect free spools. For very large diameters, wire is self coiled. Spools are level filled without piling near flanges. The outer end of the wire is properly marked and attached securely to the spool or self coil.