Introduction
H. Cross Co. is the leading specialty metal rolling manufacturer of precision
ribbons, sheets, foils and strips of molybdenum and molybdenum-base alloys. It
also supplies wire, rod and a comprehensive line of custom and lamp industry
products. These include elliptically etched foil, platinum clad wire and ribbon.
Our "Lamp Seal Products" section covers
these products.
History
C.W. Scheele discovered molybdenum in 1778 in a substance that he called
molybdic acid. P.H. Hjelm isolated it as an element in 1790. Between two-thirds
and three-fourths of the world supply of molybdenum comes from mines where its
recovery is the primary objective of the operation. The remainder is recovered
as a by-product of certain copper mining operations, largely in the United
States and Chile.
Fabrication and Applications
Molybdenum has a high melting temperature and it is impractical to transform it
into ingot forms by conventional furnace melting techniques. Its manufacture by
powder metallurgy consists of three distinct phases: the decomposition of the
ore and its reduction to pure metal powder, the pressing of this powder into
bars and the sintering of these bars into solid ingots and the swaging, rolling
or drawing of these ingots into desired forms and sizes. Some products are
fabricated from arc-cast ingots. Prefabricated or continuously compacted and
sintered electrodes made from metal powder are arc-melted in a water-cooled
copper mold. The process is usually carried out in a vacuum, although in some
instances inert-atmosphere melting is employed.
Finishes
After drawing or rolling operations have been completed, the material may
be cleaned by exposure to elevated temperatures in a reducing atmosphere.
Treating the surface chemically or electrolytically could also clean
molybdenum.
The material may be further reduced after processing by electrolytic
etching. The cleaned material can be electroplated with such elements as
gold, silver, nickel and copper, for use primarily in electronic tubes.
Platinum-clad wires are also available.
Packaging
Each H. Cross Company product is delivered in packaging specifically
designed for the product's application. As an example, wire is furnished
on returnable plastic reels, each containing a single length of wire
measuring 50 meters (197 feet) minimum. If required, H. Cross Company can
adapt standard packaging methods or develop new ones for your special
needs.
In addition to pure molybdenum H Cross Company also
produces materials from 50/50 Molybdenum Rhenium Alloy and TZM Molybdenum Alloy:
50/50 Moly Rhenium
This alloy offers the strength of molybdenum with the ductility and
weldability of rhenium. It is a more expensive alloy and it is available in a
limited size ranges. It offers significant advantages in thin foil applications
for high temperature delicate parts, especially those that must be welded. Note
that, although this alloy is nominally 48% rhenium, it is customarily referred
to 50/50 moly/rhenium. In addition to foil this material can also be made in
wire and rod form from .005" to .250".
TZM Alloy (titanium, zirconium, molybdenum)
Molybdenum's prime alloy is TZM. This alloy contains 99% Mo, 0.5% Ti and
0.08% Zr. TZM offers twice the strength of pure molybdenum at temperatures over
1300°C. The recrystallization temperature of TZM is approximately 250°C higher
than molybdenum and it offers better weldability than pure molybdenum.
TZM's finer grain structure and the formation of TiC and ZrC in the grain
boundaries inhibit grain growth and the related failure of the base metal as a
result of fracturing along grain boundaries. This characteristic also gives it
better properties for welding. TZM generally costs around 25% more than pure
molybdenum but in high heat and strength applications it can be well worth the
cost differential.
TZM is generally available in sheet and foil in the same size ranges as pure
moly with the exception of very thin foil. Call or
email for more specific.
|
