Carbon Brush Grade Functions
Carbon brushes are key components
for mechanical devices to conduct electricity between the movable and
stationary parts. It is important to understand the functionality of the
brushes to use them appropriately. Carbon brushes are categorized into
different grades based on the manufacturing process and the types of carbon and
other elements used.
The four basic brush grade
families include:
·
Carbon Graphite
·
Electrographites
·
Graphite
·
Metal Graphite
Carbon Graphite
Pioneers of this industry, this
grade Carbon brushes are made of
very strong materials with outstanding cleaning action. Carbon graphite brushes
have low current densities 45 amps/in² (7 amps/cm2); hence these brushes are
used on old and slow speed machines with maximum surface speeds around 4000
feet/minute (20.3 m/Sec). As these brushes output high friction, it does not
fit in the recent day commutators, but are helpful as good contacts and base
for metal-infused grades.
Electrographite
Electrographite brushes when
baked over 2400°C is transformed into a graphite structure. For an excellent
commutating capability and long life, the density, strength, hardness, and
resistance are regulated with a specific mix of raw material composition and
processing. High temperature removes pollutants, which makes the electrographite
brushes abrasive-free. These brushes are normally porous enabling treatment using
organic resins or inorganic materials. This makes the brush strong and lubricating
increasing its life at high operating temperatures and low humidity.
This kind of treatment enables electrographite
brushes to function in contaminated surroundings. Friction in electrographite brushes
are introduced by a specific mix of raw material prior to graphitization and by
treating the product with resins. These brushes can operate at 80 amps/in²
(12.4 amps/cm2) continuously and surface speed of 7000 feet/minute (35.6
m/sec). There might be much bigger values amidst their functioning, which apply
extensively to the industrial, transportation, mining and aerospace industries
on both AC and DC machinery.
Graphite Brushes
Graphite made of natural or
artificial graphite combined with resin or pitch to form a layered brush. These
brushes comprise of ash, which makes them abrasive. Artificial graphite is not made
of ash or does not comprise of the flaky structure as in the natural graphite.
The slip rings in the graphite Einhell carbon brushes comprise of filming
and excellent riding qualities on both commutators, when they are at densities
45 to 65 amps/in² (7 to 10 amps/cm2). These brushes are not resistant, but high
surface speeds are its best characteristics. When the brushes operate at
contaminated environment, the commutator or slip ring is protected by the fast
filming properties. Commutator threading occurs in contaminated atmosphere,
which can be reduced due to low porosity and high density.
Metal Graphite Brushes
Metal graphite brushes are made of
natural graphite and fine metal powders. The most common metal is copper followed
by silver, tin, lead and other metals. Any such materials can be used. These
brushes have low resistance and are ideal solutions for numerous applications. Metal
graphite comes in handy for commutators such as generator plating when low and
high-density collide with each other. These brushes are also used in induction
motors with high brush current densities and for grounding brushes due to low
contact drop.
