Why Good Carbide Is Important
Using good carbide
is like using thin kerf saw blades. The
differences are not dramatic but they are
important. Good carbide will reduce breakage and
give better quality cuts overall.
Choosing The
Correct Grade Can Make A Huge Difference In
Performance.
In our fourteen most
common grades the hardness (Rockwell A) ranges from
84.5 to 92.3, density (g/cc) runs from 13.5 to 15.05
and Transverse Rupture Strength (psi.) goes from
270,000 to 400,000 - Obviously the differences in
wear and impact resistance from the top to the
bottom are huge.
Creating Various
Shapes
Tungsten carbide is
a powdered metal material. Parts are shaped four
ways. The first ways is molding, molds are built
and the tungsten carbide is pressed to shape. The
second way is ‘green state’ machining. Tungsten
carbide manufacture is a multi step process. After
one of the steps you have a shape that is softer
than sidewalk chalk and that can be shaped easily.
After this ‘green state’ shaping the part is ‘finish
sintered’ and shrinks about 40% with consequent
dimension and edge changes. The third way is to
take a finished shape and grind the desired
configuration. The fourth way is to take two or
more parts and join them typically by brazing.
1. Molding - lowest
part cost but figure at least $3,000 - $5,000 for
the mold. Good shape and edge definition.
2. Green state
machining – high labor cost. Shape and edge
definition depend on design. If shape and edge
definition are critical this is usually followed by
grinding after the final sintering.
3. Grinding –
diamond is necessary. The speeds can be very good
and shape and edge definition can be excellent.
4. Brazing carbide
to carbide - uncommon as the whole, purpose is to
use as little expensive carbide as possible and to
braze it to steel or similar.
In general (This is for standard tungsten carbide
- see the advanced materials section for ways to get
around these limitations.)
More cobalt means it
is harder to break but does not wear as well.
Smaller grains mean
more wear resistance.
More wear resistance
means less toughness, which is the ability to
withstand fracture.
Toughness increases
with an increase in cobalt and with an increase in
grain size.
Hardness increases
with a decrease in cobalt content and a decrease in
grain size.
Transverse rupture
strength (T.R.S.) increases with an increase in
cobalt content.
