Tungsten wire forms and properties

Dimensions and Tolerances for Wires

*standardized tolerance, other tolerance ranges on request
Mentioned tolerances refer to finished sizes. Tolerances for redrawing wires: ±4% (in mm).

Convertion of wire weight g [mg/200 mm] in wire diameter d [μm] (based on r = 19,35 g/cm³):
d = 18,1383 g ½ [μm]

Convertion of wire diameter d [μm] in wire weight g [mg/200mm] :
g = (d/18,1383)² [mg/200 mm]

(1) For Diameter =< 0,450 mm (= 615,5 mg/200mm) see „Table of Standard Sizes for Tungsten < 615,5 mg/200 mm“

other requirements on request

Crack Levels

Cracks and splits are detected by eddy current checkers (measuring sensitivity d/50).
Measuring categories d/5 and d/10

d: wire diameter
S: length of all splits and cracks in relation to total length of the wire [%]

other requirements on request

Wire:

Drawn

Drawn wire has an oxide surface layer with graphite cover. These wires are generally suitable for redrawing and several other applications where said graphite oxyde cover is not disturbing or is removed during further working. For a number of applications a product in the condition as drawn is not suitable. To meet those requirements OSRAM offers specially aftertreated wires, e. g. cleaned, annealed, polished and grinded.

Cleaned

For applications where the oxyde graphite cover is disturbing we recommend the clean condition. This includes electropolishing of the wire surface or annealing of oxyde and graphite. Depending on the cleaning method tungsten shows different grades of surface roughness that become evident in different grades of gloss (dull grey to high gloss) but which do not relate to the surface purity of the wire.

Suitable in halogen applications

Wires suitable for halogen technology meet high requirements in respect of cracks (crack level 1B). Furthermore, the level of crystallization is controlled and evaluated following a recrystallization annealing.

Straight wire

A wire is considered as straight wire if:
- the height of the arch h of a wire section hanging free through two points at a distance of 100 mm is smaller than 10 mm; diameter of wire > 25mg/200 mm
- the spiral diameter is bigger than the diameter of the spool core; diameter of wire < 25 mg/200 mm.

Wire diameter

The wire diameter at the beginning and/or the end of a delivery unit (rod, collar, reel) is checked.
Wire ends with smaller diameters cut down to a length of 200 mm are weighed on precision scales and given in mg according to the table below.

In addition to diameter checks as described above we offer you to subject the wires to a 100 % check along the total length of the wire as requested by you.

Cracks

Cracks are defined as longitudinal defects of different lengths and depths. These are of no importance in some uncritical applications. For applications where cracks may have a disturbing effect on the rod or wire working process or on the end product a variety of qualities (crack levels) have been defined. A distinction is made between crack depths > d/5 and > d/10 as well as for (special applications) >d/50 (d = wire diameter). The crack levels are the summed up lengths of all cracks having a certain depth in relation to the total rod/wire length (in %). The cracks are detected by means of eddy current checkers (sensitivity d/50).

Tensile strength Rm, range of total elongation A

Tensile strength Rm is an important property which may determine the function and later use of a tungsten wire. Tensile strength is defined as the max. tensile force (in N) in relation to the base diameter (in mg/200) of the wire. Tensile strength and elongation are determined by means of tensile testing machines according to DIN. This includes tearing of a 100 mm long wire sample with a constant speed of 60 mm/min. The tensile strength and the range of total elongation is illustrated in a typical example as shown below:

The tensile strength and the range of total elongation resulting during the production process is given under "Technological Properties of Tungsten" in relation to the respective diameter of delivery.

See Table of Standard Sizes of Tungsten < 615,5 mg/200mm  (PDF 69kB)