How to Select Carbon Brushes for Motors and ... - Morgan AM&T

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COMMUTATOR SURFACE CONDITIONS 14 Satisfactory Conditions Satisfactory Conditions Slot Bar Filming - repeating light and dark Slot fi Bar lming Filming patterns - related repeating to the light number and of dark armature fi lming patterns coils per related slot. This to the pattern number is dependent of armature on coils the per machine slot. This design pattern and is usually dependent not a on function the machine of the brush design grade. and usually not a function of the brush grade. Blotchy Film - this nonuniform filming Blotchy condition is Film the most - this common nonuniform appearance. filming The condition accumulated is the most tolerances common in appearance. the machine such The accumulated as commutator tolerances roundness, in brush the machine contact pressure, such as commutator unequal roundness, magnetic brush fields contact and chemical pressure, vapors unequal all contribute magnetic to fields this type and of fi chemical lm development. vapors all contribute to this type of fi lm development. Dark Film - if uniform over the entire commutator Dark Film surface - if uniform is acceptable. over the entire This condition commutator can surface be the is acceptable. result of a high This filming condition brush can be grade, the result higher of current a high densities filming or brush the presence grade, of higher chemical current vapor contamination. densities or the presence of chemical vapor contamination. Light Film - over the entire commutator surface Light Film is one - of over the many the entire normal commutator conditions often surface seen is one on of a the well many functioning normal conditions machine. Film often tone seen is on dependent a well functioning on the brush machine. grade and Film current tone is density. dependent on the brush grade and current density. Concerned Conditions Unsatisfactory Conditions Concerned Conditions Unsatisfactory Conditions Slot Bar Burning - results in commutator erosion Slot Bar of Burning every second, - results third, in commutator or fourth bar erosion depending of every on second, the winding third, design or fourth of the bar armature. depending on Improper the winding brush design material, of brush the armature. design or Improper electrical brush adjustment material, of the brush machine design can or cause electrical this condition. adjustment This of condition the machine severely can cause damages this condition. the commutator This and condition reduces severely brush damages life. the commutator and reduces brush life. Bar Burning - is the erosion of the trailing edge Bar Burning of the commutator - is the erosion bar. Failed of the machine trailing components, edge of the commutator maladjusted bar. electrical Failed symmetry machine of components, the machine maladjusted or a poor commutating electrical symmetry brush can of the result machine in bar or burning. a poor commutating If not corrected, brush this can condition result in bar can burning. cause severe If not commutator corrected, damage this condition or a can fl ashover. cause severe commutator damage or a fl ashover. Bright Spots - a freckled appearance of the Bright fi lm usually Spots caused - a freckled by machines appearance that are of subjected the fi lm usually to frequent caused overload by machines cycles. that If are the bright subjected spots to disturb frequent only overload the fi lm, cycles. a machine If the can bright operate spots disturb for long only periods the fi of lm, time a machine with this condition. can operate If severe for long metal periods transfer of time begins, with this the bright condition. spots If could severe progress metal transfer to dangerous begins, bar the burning bright spots or fi could lm stripping. progress to dangerous bar burning or fi lm stripping. Streaking - of only the fi lm is not detrimental to Streaking the commutator. - of only the Brush fi lm and is not commutator detrimental to life the are commutator. not at risk in Brush this condition. and commutator If metal transfer life are not develops, at risk this in this condition condition. will progress If metal into transfer threading. develops, this This condition type of will fi lming progress can be into dependent threading. on This current type density of fi lming or brush can grade. be dependent on current density or brush grade. Unsatisfactory Conditions Unsatisfactory Conditions
ush design or electrical adjustment of the machine can cause this condition. This condition severely damages the commutator and reduces brush life. can result in bar burning. If not corrected, this condition can cause severe commutator damage or a fl ashover. can operate for long periods of time with this condition. If severe metal transfer begins, the bright spots could progress to dangerous bar burning or fi lm stripping. into threading. This type of fi lming can be dependent on current density or brush grade. Unsatisfactory Conditions Copper Drag - occurs when high energy transfers copper in a molten state. These particles become coated by contaminants from the surrounding environment or the brush treatment and do not oxidize properly to form the fi lm on the commutator surface. These particles accumulate at the edge of the bar, eventually shorting across the insulating mica. This condition needs to be addressed immediately when discovered or serious damage may occur. Chamfering the commutator bar edges is necessary to stop the progression of this condition. Grooving - is the uniform circumferential wear, the width of the brush, that is exhibited on the commutator. Excessive abrasive dust in the atmosphere or an abrasive brush can cause this condition. Extreme light spring pressure (below 1.5 psi) can also cause this condition. Proper brush applications and fi ltering the air on force ventilated motors can reduce the commutator wear. Some people call this “Ridging” because of the resulting ridges on each side of the groove. Pitch Bar Burning - results in commutator bars being eroded in a pattern related to 1/2 the number of brush arms, progressing into a pattern equal to the number of brush arms. This condition is caused by a cyclic mechanical or electrical disturbance such as an unbalanced armature, misaligned shafts, bent shaft, bad bearings, weak foundation, failed equalizers or a poor riser connection. If not corrected this condition will result in a fl ashover. Threading - is machining of the commutator by copper particles in the brush face. The excessive copper transfer occurrs due to low spring pressure, light loading or contamination. These particles are trapped in the porous carbon brush and work harden, creating a tool that machines or gauls the commutator surface. The machine can operate for long periods of time with this condition, but reduced commutator and brush life will be experienced. Call our Application Engineering Dept. if you would like help improving your NAT SCP 4/08 INDEXX Commutator Condition or Brush Performance. 864-458-7777 or 1-800-543-6322
Page 1 and 2: 1 How to Select Carbon Brushes for
Page 3 and 4: Grade Characteristic Definitions Gr
Page 5 and 6: St = 3 x P x L / ( 2 x W x T²) St
Page 7 and 8: Electrographitic Brush Grade AY B34
Page 9 and 10: Electrographitic (continued) Brush
Page 11 and 12: 1 2 3 251 Forrester Dr. Greenville,
Page 13: T508 T550 T563 T566 T573 T583 T606

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