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TABLE 21: CIRCULAR SAWING OF NIOBIUM
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STOCK DIAMETER
OR THICKNESS
in
(mm)
|
TOOL
MATERIAL
AISI
(ISO)
|
PITCH
in/tooth
(mm/tooth)
|
SPEED
fpm
(m/min)
|
FEED
in/tooth
(mm/tooth)
|
|
_ - 3 |
M2, M7 |
0.20 — 0.75
|
70 |
0.005 |
|
3 — 6 |
M2, M7 |
0.50 — 1.10
|
55 |
0.005 |
|
6 — 9 |
M2, M7 |
0.75 — 1.30
|
45 |
0.007 |
|
9 — 15 |
M2, M7 |
0.90 — 1.75
|
35 |
0.007 |
|
(6 — 80)
|
(S2, S4) |
(5 — 20)
|
(21) |
(0.13) |
|
(80 — 160)
|
(S2, S4) |
(12 — 30)
|
(17) |
(0.13) |
|
(160 — 250)
|
(S2, S4) |
(20 — 35)
|
(14) |
(0.18) |
|
(250 — 400)
|
(S2, S4) |
(25 — 45)
|
(11) |
(0.18) |
FORMING OPERATIONS
The forming characteristics of niobium
and niobium alloys are similar to mild steels. Niobium is
well suited to deep drawing, and the metal may be cupped and
drawn to tube, although care must be taken with lubrication.
Niobium sheet metal can be formed easily without special working
techniques. These operations are facilitated by niobiumÕs
low rate of work hardening.
There are two unusual features that
must be considered when working with niobium and its alloys.
First, no appreciable softening occurs below 400¡C, because
of its high melting point. Also, sheathing protection is not
practical, since the sheathing material is likely to be softer
than the niobium. NiobiumÕs cold working properties are excellent.
Annealing is necessary after the surface has been worked 90%,
with heat treatment at 1200¡C for one hour causing complete
recrystallization of material cold worked over 50%. The annealing
must be performed in an inert gas, or preferably, in a high
vacuum. Guidelines for a few select forming operations are
given below:
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-handed 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 approximately 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.
Ten of Eleven 1
2 3
4 5
6 7
8 9
10 11
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