SECTION 1 -INTRODUCTION TO BRUSHES AND CARBON GRADES
Question 1:9 Are There Any General Principles For Grade Selection?
For practical purposes the answer is restricted so Sliprings, DC Machines, Schrage type machines and Universal motors. The manufacture of the machine will generally select a grade appropriate for the design of the machine assuming it will operate at full load. However this is often not correct for the actual load.
In the absence of other information the brush supplier should be contacted with all relevant name plate and application information.
For general applications the following groupings may be assumed until the actual selection can be confirmed by the brush supplier our until selection is proven satisfactory in service.
:1 Slipings
Use low resistance electrographite carbon for current density less than 10amps/cm2 and generous ring dimensions and cooling. Use copper graphite with 50%-75% copper for current density up to 15A/cm2. Low speed very high current welding jigs etc. require copper graphite up to 95% copper.
:2 Low Voltage DC Motor (Up to 48V)
For low voltage machines such as battery powered vehicles, winches, starter motors etc. use copper graphite brushes with a percentage of 25%-75% copper. Generally the higher the voltage, the less copper percentage is required depending on the brush configuration.
:3.General Industrial DC Motors
Voltages 350-500V will require electrographite brushes of medium to high resistance. Lower load can permit the use of higher resistance brushes. As a general rule use the brush with the lowest resistance that will achieve minimum arcing but still generate enough heat to permit good film forming.
:4 AC/DC Universal Series Motors
These motors, used in power tools and appliances, operate at high speed and normally do not have interpoles. For this reason they tend to require good commutating brushes or relatively high resistance.
Hard carbon brushes, high resistance electrographite or resin bonded brushes are normally required for these motors.
Question 1:10 Are There Any Standards For Brushes?
The information has been drawn from experience of Morganite Taiwan Limited Application Specialists combined with a wide range of published information from major carbon supplier and motor manufacture. However, the material can not be downloaded, copied or used without written permission.
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