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The use of
powder metal for the creation of highly engineered and sophisticated
shapes with minimum secondary work has become very popular for both
low and high volume production. The use of Powder
Metal Technology requires a means to remove the binding material
used to hold the metal powder together and densify the metal alloy
from the powder. These requirements are fulfilled with one
or two furnaces, sometimes augmented by a solvent or catalytic
binder removal system.
Powder metal
parts typically require a thermal debind to remove some amount of “backbone”
binder in a low temperature furnace followed by sintering in a high
temperature furnace. For production
needs some part manufacturers will utilize a low temperature belt furnace for
thermal debind followed by sintering in a vacuum furnace or atmospheric
continuous furnace. In the case of
product development work, continuous furnaces are inflexible, they do not
have the ability to work with a great variety of materials, and therefore
batch vacuum furnaces are the better choice. Some vacuum furnaces have the ability to do both the thermal debind
and sinter. This is advantageous
because it minimizes handling losses and contamination issues while also
eliminating process steps.
Batch vacuum
furnaces can run a wide variety of product on any given day, making them
especially attractive to short run, small volume, or product development
work. This flexibility allows part
producers to work with a wider variety of alloys, shapes, and binders to best
develop highly technical parts.
Batch vacuum furnaces
typically come with either graphite or refractory metal linings.
Graphite linings are limited in processing
characteristics in comparison to refractory metal.
In a graphite furnace thermal debinding and
sintering can only be done under a vacuum, up to a maximum of 5 Torr of
hydrogen, or 15-30 Torr of nitrogen or argon.
Processing at higher partial pressures can be dangerous from a methane
formation standpoint as well as being very hard on the graphite itself.
Graphite also has the tendency to hold
binder material, in the form of carbon, and re-deposit this material on the
parts during the sintering process.
This makes carbon control and product uniformity difficult.
These limitations of a graphite furnace make a refractory metal furnace much more
favorable. Refractory metal furnaces
do not have any pressure limitations and can operate up to atmospheric
pressure under hydrogen, nitrogen, argon, or any combination of those gasses
as well as vacuum. This flexibility
provides the perfect tool for both research and development and production
that will vary from day to day or week to week.
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