514_6-brushes-for-electrical-machines-en.pdf

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BRUSHES FOR ELECTRICAL MACHINES
Technical guide
ISO 9001: 2000
I
ISO 14001
CONTENTS
Pages
I
The grade groups
I
Principal characteristics of brush grades
I
Rationalization of brush grades
I
Applications
I
Important remarks
I
Shapes and main dimensions of brushes
I
Fittings and mounting methods
I
Fittings for divided brushes
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The brush on the machine
I
Recommendations for fitting brushes on machines
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Other available services
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On ordering brushes
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Data herein contained are provided for general information purpose only and are not binding. CARBONE LORRAINE shall have no liability whatsoever with respect to information contained herein. Duplication, reproduction or translation of any
information contained herein, in whole or in part, is strictly prohibited without prior written consent of CARBONE LORRAINE.
3
THE GRADE GROUPS
There are five principal groups each corresponding to a particular mode of manufacture.
To cer tain principal groups it is convenient to adjoin one subgroup concerning impregnated grades.
The Note STA BE 16-22 treats this subject and indicates the particular properties of these special materials.
We give below a summary on the method of manufacture of each group, the main characteristics of each
group (given under the conventional headings on pages 6 and 7), the principal applications and the limits of
application for the majority of grades in the group.
A
CARBOGRAPHITIC BRUSHES
These are made from mixtures composed of amorphous carbon powders, natural and artificial graphites
ground, selected and agglomerated with a binder.
The powders thus moistened and dryed are compressed and the plates thus obtained are cooked in order to
coke the binder.
Main character
Brushes having a good commutating ability, with a good polishing action and a medium value contact drop.
They resist high temperatures and variable loads.
Principal applications
Old slow machines with or without interpoles and generally at low voltage. Modern machines working with
permanent magnets, servomotors, universal motors.
Limit of application
Current density 8 to 16 A/cm
2
(maximum), depending on cases.
Admissible peripheral speed: up to 25 m/s.
Note
There is a range of carbographitic grades for universal motors of fractional power and up to several kW.
These products are not stated in this technical guide. Please, ask for the specific literature.
EG
ELECTROGRAPHITIC BRUSHES
Prepared from carbon powders and coke they are then subjected to other thermal treatments particularly at
high temperature (above 2,500°C) in order to transform the basic amorphous carbon into artificial graphite.
Main character
These brushes have medium contact drop and low or medium friction, they have reduced losses and are
particularly adapted to high speed applications.
Principal applications
For all industrial modern machines whether stationary or for traction, high speeds, low, medium and high
voltage and constant or variable loads.
Brush current densities:
8 to 12 A/cm
2
(maximum) under steady conditions,
20 to 25 A/cm
2
(maximum) for short duration peaks.
Admissible peripheral speed: up to 50 m/sec.
LFC
SOFT GRAPHITE BRUSHES
The base constituent is purified natural graphite or previously ground artificial graphite, then mixed with other
constituents in well defined quantities, agglomerated with appropriate binders and fired in order to coke the
binder.
Main character
Soft, plastic brushes having very good resistance to shock and mechanical vibration. Generally they have
good cleaning properties.
4
Principal applications
Steel and stainless steel rings for high speed synchronous machines.
Limit of application
Brush current density:10 to 13 A/cm
2
(maximum).
Admissible peripheral speed: 65 to 90 m/s (even to 100 m/s).
CG-MC
METAL GRAPHITE BRUSHES (CG - MC - CA)
These brushes are made by mixing in suitable proportions purified natural graphite and copper in powder form
with the addition of powders of other metals. The mixed powders are then compressed and baked in an
atmosphere and at a temperature chosen to give the degree of solidity and cohesion desired.
Equally a part of the metal graphite group are those brushes (EG and A) which are impregnated under
pressure with pure molten copper or a mixture of molten copper, silver or salts (of metal impregnated
page 7).
Main character
Dense or very dense brushes with low friction and very low contact drop therefore leading to very low losses
and high currents.
Principal applications
DC machines of slow speed and low or very low voltage. Bronze rings of slow speed asynchronous motors,
heavily loaded, with or without brush lifting gear. Rings of synchronous motors of low or medium speed.
High current collection on rotating collectors, special machines, slip-ring assemblies.
Limit of application
Brush current density;
12 to 30 A/cm
2
(maximum) continuously,
about 100 A/cm
2
instantaneous transient peaks according to metal content.
Admissible peripheral speed: up to 35 m/s, according to metal content.
Note
There is a range of copper graphite and metal graphite grades which permit the unitary moulding of mass
produced brushes for small low voltage machines. These products are not stated in this technical guide.
Please, contact us.
BG
BAKELITE-GRAPHITE BRUSHES
Natural or artificial graphite is ground and agglomerated with a thermo-hardening resin of the bakelite type.
The mixture is compressed and polymerized at a suitable temperature.
Main character
Brushes are of high mechanical and electrical resistance, good commutating properties, cleaning properties
with high contact drop and therefore high losses. Can work at very low current densities.
Principal applications
AC commutator motors of the Schrage or Schorch type. Many DC machines, either traction or stationary, of
medium speed and load.
Limit of application
Brush current density: vary with grades (better on low load motors).
Admissible peripheral speed: up to 40 m/s.
Note
There is a range of resin agglomerated grades which permits the unitary moulding of mass produced brushes
for modern motors of fractional power and several kW. Please, contact us.
5
PRINCIPAL CHARACTERISTICS OF BRUSH
Resistivity
Maximum
current
density
Flexural
strength
Contact
drop
Shore
Hardness
Apparent
density
GRADE
GROUP
GRADE
Friction
Metal
content
%
Upper
speed
limit
15
(
(
49)
µΩ.cm
µΩ.inch
2 250
(886)
MPa
PSI
26
21
20
16
16
10
12
25
19
19
21
27
21
21
21
31
24
33
22
26
26
15
34
28
36
31
36
48
35
34
35
27
33
∆U
en V
M
H
H
M
H
M
M
M
M
M
M
M
M
M
M
M
M
M
M
H
H
M
M
M
M
M
M
M
M
H
H
M
M
A/cm
2
m/sec.
A/inch
2
ft/sec.
12 to 20
(75 to 125)
A 121
A 122
1,75
1,67
1,60
1,57
1,57
1,46
1,26
1,60
1,49
1,52
1,60
1,62
1,66
1,53
1,52
1,60
1,57
1,60
1,55
1,46
1,46
1,62
1,72
1,61
1,69
1,77
1,67
1,82
1,68
1,57
1,57
1,70
1,70
30
27
40
30
27
10
12
40
29
27
35
57
50
52
52
60
58
64
60
52
52
40
40
33
77
77
77
90
80
74
75
71
68
L
L
L
L
L
L
L
M
M
M
M
M
L
M
M
M
L/M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
45 000
(17 716)
10 to 12
(65 to 75)
15
49)
Carbo-
graphitic
A 176
A 210
A 252
52 500
(20 670)
8 to 10
(50 to 65)
30
(98)
25 000
(9 840)
8 to 10
(50 to 65)
(
(
25
82)
45 000
(17 716)
10 to 12
(65 to 75)
25
82)
Soft
graphitic
LFC 501
LFC 554
EG 34D
EG 389P
EG 396
EG 362
EG 40P
EG 313
EG 367
1 900
(748)
6 to 10
(40 to 65)
75
(246)
2 000
(748)
11 to 13
(71 to 84)
100
(328)
1 100
(433)
12
(75)
50
(164)
1 600
(630)
12
( 75)
50
(164)
1 600
(630)
12
(75)
50
(164)
2 500
(984)
12
(75)
50
(164)
3 200
(1 260)
12
(75)
50
(164)
5 000
(1 968)
12
(75)
50
(164)
4 100
(1 614)
12
(75)
50
(164)
Electro-
graphitic
EG 332
EG 387
EG 300
EG 98
EG 369
EG 319P
EG 321
EG 365
EG 7099
EG 9599
EG 9117
EG 8019
4 200
(1 653)
12
(75)
50
(164)
3 500
(1 378)
12
(75)
50
(164)
4 200
(1 653)
12
(75)
50
(164)
3 400
(1 338)
12
(75)
50
(164)
5 500
(2 165)
12
(75)
50
(164)
7 200
(2 834)
12
(75)
50
(164)
7 200
(2 834)
12
(75)
50
(164)
5 300
(2 080)
12
(75)
50
(164)
1 100
(433)
12
(75)
45
(148)
1 600
(630)
12
(75)
45
(148)
3 300
(1 300)
12
(75)
50
(164)
4 700
(1 850)
12
(75)
45
(148)
Impregnated
electro-
graphitic
EG 8067
EG 8220
EG 7097
EG 341
EG 6489
EG 8285
EG 7655
3 900
(1 535)
12
(75)
45
(148)
5 000
(1 968)
12
(75)
50
(164)
4 000
(1 575)
12
(75)
50
(164)
7 200
(2 834)
12
(75)
50
(164)
7 200
(2 834)
12
(75)
50
(164)
5 400
(2 126)
12
(75)
50
(164)
5 600
(2 200)
12
(75)
50
(164)
CONTACT DROP
Contact drop
in volts
Sum of both polarities
Symbol
Indication
High
Medium
Low
Very low
Very very low
Friction
H > 0.20
0.12 < M < 0.20
L < 0.12
The value of contact drop
and friction is given by the use
of symbols having
the following significance
H
M
L
VL
VVL
H>3
2.3 < M < 3
1.4 < L < 2.3
0.5 < VL < 1.4
VVL < 0.5
6

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