FIELD OF INVENTION
The present invention relates to development of a novel designed tightening system
aimed at overcoming ovality problem in a commutator, suitable for 630KW D.C. traction
motor used in 5000HP A.C. locomotive. Ovality is a problem which develops in
commutator of D.C. motor, by which commutator diameter gets oval with temperature
rise, leading to spark over initially and finally leading to complete breakdown of the
machine. As per IEC standard, for commutators having diameter less than 500 mm,
ovality is allowable up to 0.03 mm. But presently it has gone beyond 0.06 mm. The
present invention specifically relates to arresting the ovality problem by incorporating
necessary changes in the bolting and tightening arrangement of the commutator
assembly by replacing the complex disk spring and nut tightening system to a simpler
and stable bolted system.
BACKGROUND OF THE INVENTION
The stability of the commutator depends upon its consolidation" i.e. seasoning and proper
tightening. In existing design, stability depends on some other factors like material of
disk spring and nut and rigorous seasoning cycle of 50 hours at 3050 rpm at a
temperature of 220° C.
Accordingly core object of present invention is to provide an improved and stable design
of commutator to overcome the existing ovality problem in the DC machines.
Since development of ovality problem is closely associated with improper tightening
system of the commutator through other steel parts like disk spring and nut, another
important object of the invention is to do away with existing system and introduce an
altogether novel system of tightening the commutator with plurality of bolts.

In the prior art disk spring was used to tighten commutator assembly. Stability of
commutator depended most on springiness of disk spring material. As such the disk
spring material and hardness of the material played a crucial role in the stability of
commutator. Sometimes mild steel was also used for disk spring. Such dependence on
the quality and accuracy of single component for tightening of the commutator affected
the stability to a great extent. Presently there is no disk spring in the tightening system.
Instead of that spring washer has been used.
In the prior art a single commutator nut was used to tighten the complete bulky
assembly. Proper tightening could be achieved only when the pressure on the disk spring
is uniform and material of disk spring is as per specification. Besides that accuracy and
engagement of thread with spider is also important for proper tightening of the
commutator assembly. The present assembly does not have a single nut instead there
are 16 number. 12.9 grade special hexagonal screws used to provide more uniform and
stable tightening.
In the prior art there was 10 hrs 4 cycle seasoning at 220° C and 3050 rpm followed by
10 hrs of cooling i.e., there was a total 50 hrs seasoning for a commutator.
In the present system seasoning cycle has been reduced to 4 cycle of 5 hours each i.e.,
20 hrs cycle i.e., there is an overall reduction by 60%.
In prior art every time the assembly was required to be taken to press for tightening at
110 tones after completion of each 10 hrs cycle. This required maintaince of minimum
temperature of the job over 100° C at the tightening press machine, which could not be
ensured always due to non availability of the press, when it is needed.

In the present invention, pressuring is required to be done only at the static seasoning
cycle. During dynamic seasoning the 16 bolts will be tightened by torque wrench on
seasoning bed at 14-17 KGM torque value.
In prior art the disk spring and commutator nuts are required to be machined as it
demanded utmost dimensional accuracy. But in the present invention there are no disk
springs and nut, instead 16 number screws are used which minimizes the problem of
false tightening of the commutator and dependency of tightening on the accuracy of
single component.
SUMMARY OF THE INVENTION
In the present invention bolting or tightening arrangement of the commutator assembly
was modified from a complex disc spring and nut tightening system to a more simpler
and stable design of bolting the commutator with 16 number bolts. In the subject
invention only the commutator copper and mica segment is retained as in previous
design but the rest is changed. Mica V rings, commutator hub/spider, steel V ring and
mica bush has been completely changed to maintain the same brush gear diameter and
length. The new assembly is completely inter changeable with the earlier one.
BRIEF DESCRIPTION OF ACCOMPAYING DRAWING
Figure 1: PRESENT ART
Figure 2: PRIOR ART

DETAIL DESCRIPTION WITH ACCOMPAYING DRAWINGS
The invention will now be described in an exemplary embodiment as depicted in the
accompanying drawing. There can however be other embodiments of the same invention,
all of which are deemed covered by this description.
Commutator design developed here is an arch bound commutator complying tolerances
and hardness as per IEC 356/1971. The commutator manufacturing shall include at the
stage of assembly and consolidation of copper segments and insulating mica segments
an adequate number of static/dynamic seasoning cycles comprising cold tightening of
assembly fixture and hot tightening before machining of V groove.
The constructional elements of a commutator are as follows:
Commutator copper segment (Figure 1, 05) is cold drawn or rolled silver bearing
electrolytic copper bar having silver content .08 to 12%. Electrical conductivity at 20° C is
97%. Surface hardness and hardness at elevated temperature to be 105 HV and 103 HV
respectively.
Mica segment (Figure 1, 06) is used to separate/ insulate two adjacent commutator
copper bars. It is an alkyd vinyl bonded mica segment provides better thermal stability at
higher temperature i.e. more than 200° C. These mica segments must have
compressibility 420kg/cm2 with a stake of 12 segment having height after compression
13.296+0.2/+0 mm.

Commutator spider (hub) (Figure i, 01) used in the assembly is made up of property
class 4 (45C4) normalized carbon steel casting as per IS: 2707-1996 Gr-1. Present design
has more wide ventilation circuit and simpler tightening arrangement in place of single
nut tightening which require much pressure and accuracy during pressing and tightening.
Steel V ring (Figure 1, 08) used in the assembly is made up of property class 4 (45C8)
hardened and tempered carbon steel forging as per IS: 2004: 1991 or carbon steel
casting as per IS: 2707-1996 Gr-1. Present design is much simpler and easy to mount
than earlier one. Complexities involve in disk spring testing, mounting and tightening it
with a single nut has been removed.
There is alkyd vinyl bonded mica V rings (Figure 1, 02, 03 and 07) and bush used in the
commutator, providing it better thermal stability at higher temperature i.e. more than
200° C. The rings are consolidated electrically to have a uniform, better and stable V
profile.
Commutator assembly to be tightened using 16 Nos. property class 12.9 grade hexagonal
head screw of M 16x95 (Figure 1, 09). These 16 Nos. screw provides better stability and
uniform tightening throughout the periphery of commutator assembly.
Silicon rubber paste is used as a sealant (Figure 1, 04) for space between commutator
bar assembly and mica V rings. This is a property Class 200 based silicon to provide
sealing at higher temperature without carbonization.

WE CLAIM:
1. A commutator for overcoming ovality problem in D.C. drive based 630KW traction
motor used in 5000 HP A.C. locomotives, comprising (figure 1):
• copper segments (05),
• mica segment (06),
• commutator spider (01),
• steel V ring (08),
• mica V ring (02),
• mica bush (07),
• RTV sealant (04)
Characterized in that plurality of bolts are provided to tighten copper segments of
the said commutator.
2. A commutator as claimed in claim 1, wherein 16 numbers bolt (M16X95) (09),
figure 1 used are of property class 12.9 grade, having hexagonal head screw of
dimension of M16X95.
3. A commutator as claimed in daim 1, wherein the total consolidation of
components is done by tightening of 16 screws of property class 12.9.
4. A method for overcoming ovality problem in the said commutator as daimed in
claim 1 consisting steps of:

• tightening
• pressing
• seasoning of the commutator assembly

5. A method as claimed in claim 4, wherein tightening the commutator assembly is
done by 16 no property class 12.9 grade hexagonal bolt of dimension M 16x95.
6. A method as claimed in claim 4, wherein pressing the assembly is done by 14-17
KGM pressure with the help of M16 size torque wrench.
7. A method as claimed in claim 4, wherein electric/gas seasoning of the commutator
assembly is carried out for 4 cycle of 5 hours i.e., 20 hour cycle.

The present invention relates to a commuator which has successfully overcome the
ovality problem which develops in the commutator of D.C. motor on account of
temperature rise, leading to spark over initially and finally to complete breakdown of the
machine. The subject invention discloses method to arrest the problem by incorporating
necessary changes in the bolting and tightening arrangement of the commutator
assembly by replacing the complex disk spring and nut tightening system to a simpler
stable bolted system, simpler method of pressing the assembly by a torque wrench and
reducing the hours and cycle of seasoning by 60%.