commutator manufacturing -...

Commutator Manufacturing

Commutator Engineering (Pty) Ltd

MICHAEL TERREBLANCHE


August 20, 2015

Table of Contents

List of Figures ................................................................................................................................................. 3

1. Introduction ........................................................................................................................................... 4

2. V-Ring Commutator components.......................................................................................................... 4

3. Building a new Commutator, step by step ............................................................................................ 5

3.1. Machining the inner ring ............................................................................................................... 5

3.2. Machining the clamping rings ....................................................................................................... 5

3.3. Machining the copper bars and adding the Risers ........................................................................ 6

3.4. Clamping copper bars for machining ............................................................................................ 8

3.5. Machining the copper bars ......................................................................................................... 10

3.6. Undercut and bevel ..................................................................................................................... 11

3.7. Clamping the Commutator bars .................................................................................................. 12

3.8. Baking .......................................................................................................................................... 14

3.9. Testing ......................................................................................................................................... 15

4. Advantage of V-ring Commutators ..................................................................................................... 15

5. Additional photos of Commutator Engineering .................................................................................. 17

6. Conclusion ........................................................................................................................................... 19

7. References ........................................................................................................................................... 19


August 20, 2015

List of Figures

Figure 1: Commutator components .............................................................................................................. 4

Figure 2: Commutator inner steel ring………………………………………………………………………………………………………5

Figure 3: Two inner ring ribs.......................................................................................................................... 5

Figure 4: Commutator clamping rings ........................................................................................................... 6

Figure 5: Riser bar connections ..................................................................................................................... 7

Figure 6: Machined copper bars .................................................................................................................... 7

Figure 7: Copper bars with isolation ............................................................................................................. 8

Figure 8: outer clamping ring ........................................................................................................................ 8

Figure 10: Large outer clamping ring ............................................................................................................ 9

Figure 9: Pressing outer ring onto copper bars ............................................................................................. 9

Figure 11: Clamped copper bars and already started with machining ....................................................... 10

Figure 12: V-cut machined into Copper bars .............................................................................................. 11

Figure 13: Undercut and Bevel of Commutator .......................................................................................... 12

Figure 14: Inside of clamping ring ............................................................................................................... 12

Figure 16: Hot molding mica sheet ready to form ...................................................................................... 13

Figure 15: Commutator clamping illustration ............................................................................................. 13

Figure 17: Mica after being formed ............................................................................................................ 14

Figure 18: Clamped Commutator ready for baking ..................................................................................... 14

Figure 19: Rotation test for looseness ........................................................................................................ 15

Figure 20: Commutator being disassembled .............................................................................................. 16

Figure 21: Commutator Engineering workshop building ............................................................................ 17

Figure 22: Lathes used ................................................................................................................................. 17

Figure 23: Isolation molds and milling machines in the background .......................................................... 18

Figure 24: outer holding rings ..................................................................................................................... 18


August 20, 2015

1. Introduction

On 19 August 2015 M. Kollmitz, F. Shuda and M. Terreblanche were given a plant tour at Commutator

Engineering (Pty) Ltd, Randfontein. The director, S. Engelbrecht, explained and showed the process of

making and assembling a Commutator for a DC motor. The business employs 15 permanent employees

and does all the relevant work required on site.

The business was subcontracted by Delba to construct a new Commutator for a DC motor used by

Columbus at ZM1, coiler motor. This was due to the conventional molded construction of the motor’s

Commutator, and thus it cannot be disassembled without damaging the entire Commutator.

2. V-Ring Commutator components

Figure 1 shows a V-ring Commutator with a cutout to illustrate the different components discussed in

this report.

Figure 1: Commutator components

Raiser

Shaft

Outer clamping ring

Clamping bolts

Inner clamping ring

Armature windings Copper bars

Inner ring


August 20, 2015

3. Building a new Commutator, step by step

3.1. Machining the inner ring

The inner ring (Figure 2) is machined out of steel and will connect the shaft to the rest of the

Commutator components. The inner ring is connected to the motor shaft by four ribs. Figure 3 shows

two ribs in place to illustrate the concept.

The ribs are added to leave an air space in between the majority of the shaft and the inner ring of the

Commutator to improve Commutator cooling.

Figure 2: Commutator inner steel ring Figure 3: Two inner ring ribs

3.2. Machining the clamping rings

The clamping rings are machined from steel. They will hold all the copper bars and the insulation

between these bars (or the Commutator conductive part).

Figure 4 shows the two clamping rings (outside shown) and Figure 14 shows the inside of the clamping

ring with its V-cut that will fit into the machined copper bar V-cut.


August 20, 2015

Figure 4: Commutator clamping rings

3.3. Machining the copper bars and adding the Risers

The copper bars are machined from copper bus bars cut to the required length. Each bar is machined

with a taper to form a V. This is to give the circular shape once all the copper bars are pressed together.

A slot is also machined on the one end where the copper Risers are Silver soldered to the bars, as seen in

Figure 6. Silver solder is used because of the reliable and electrical conductive bond it creates, compared

to other braising techniques.

The purpose of the riser bar is to connect the copper bars of the Commutator to the field coils of the

Armature as illustrated in Figure 5.


August 20, 2015

Figure 5: Riser bar connections

Each riser has a half round bend in it to help absorb vibration and allow for thermal expansion. This can

clearly be seen in Figure 6.

Figure 6: Machined copper bars

Machined copper bar

Slot for Riser

Silver soldered Riser

Machined copper bar

Riser

Armature windings

Armature steel core


August 20, 2015

3.4. Clamping copper bars for machining

The required amount of copper bars are put together, with isolation material in between each copper

bar, within a clamping ring (Figure 9). Figure 7 shows the isolation material between two copper bars.

The tapered cut can also be seen in Figure 7.

Figure 7: Copper bars with isolation

The clamping ring is a Tool used in the manufacturing process of the Commutator and consists of two

main parts, the outer ring and the inner rings (split into three pieces), as seen in Figure 8. The three

pieces of the inner ring slides on a taper cut on the outer ring, as illustrated in Figure 9. Thus the more

the inner ring moves down the smaller the inner ring radius becomes.

Figure 8: outer clamping ring

Outer clamping ring

Inner clamping ring


August 20, 2015

The assembled inner ring gets pushed down by a hydraulic press, with a force of 40 tons, to give a ‘solid’

copper ring that can be machined on a lath. Figure 9 illustrates this concept in a section cut drawing.

Figure 10: Large outer clamping ring

Outer clamping ring

Inner clamping ring

Copper bars Pressed down, 40t

Figure 9: Pressing outer ring onto copper bars

Fixed on press

Copper bars

Risers

Clamping ring


August 20, 2015

Figure 11: Clamped copper bars and already started with machining

Figure 11 shows a ring clamping the combination of copper bars that has already been machined.

One can clearly see the amount that the clamping ring inner moved down on the taper to securely clamp

the copper bars and isolation together for machining. Each copper bar is tested to ensure proper

electrical isolation between all the bars.

3.5. Machining the copper bars

The copper bars are machined to give the final form for the combination of copper bars, or Commutator

conductive part, while still in the Clamping ring (tool).

This requires the ends to be machined smooth and the V to be cut on both sides to accommodate the

clamping rings as seen in Figure 12. The machining is different for each Commutator, depending on the

specific design requirement.

Outer clamping ring

Inner clamping ring

Copper bars


August 20, 2015

Figure 12: V-cut machined into Copper bars

3.6. Undercut and bevel

The depth of the recess or groove, in between each copper bar, in the Commutator must not be

excessive, otherwise insulation failure may result from the collection of dirt in the groove. The depth

should be approximately equal to the distance between adjacent segments [1], as illustrated by X in

Figure 13.

It is most important that all insulation should be removed from the sides of the groove and no traces left

which will can subsequently project and disturb the brush contact [1] preventing good commutation.

This process is to undercut the Commutator.

After recessing the segment edges should be beveled, illustrated by Ø in Figure 13, off to ensure that

there are no outward projecting burs and also no trace of insulation left flush with the Commutator [1].

Figure 17 illustrates a Commutator that has been machined, undercut and beveled.

V-cut in Commutator


August 20, 2015

Figure 13: Undercut and Bevel of Commutator

3.7. Clamping the Commutator bars

The inner and outer end clamping rings are put on the machined V of the Commutator and then they are

then pulled together by bolts. Figure 14 illustrates the clamping of the copper bars, insulation and

clamping rings.

The bolts are torqued to the required load to clamp the Commutator conductive parts to such an extent

that the outer ring tool, that held it in position for machining, loosens and can then be removed after the

bolts were tightened to the required initial torque.

Figure 14: Inside of clamping ring

Copper bars

Mica

Bevel angle


August 20, 2015

Mica (Micanite) is used as isolation material between the steel inner ring and copper bars.

Hot molding Mica is build up from splinters or flakes of mica bonded together and impregnated under

pressure with a resin bond. This eliminates veins of impurity and more uniform thickness and dielectric

strength can be obtained [1].

Prepared Hot molding Mica sheets (Figure 16) are used and formed to the required V-shape to isolate

the clamping rings from the copper bars (illustrated in Figure 15). The cuts seen in Figure 16 allow for

easier shaping of the mica when molding (reduces material and aids overlapping of material). These cuts

can also be seen in Figure 17 after being shaped. Electrical isolation is tested between all the conductive

parts throughout this process of assembly.

Figure 16 shows the molded Mica (hot molding Mica) that fits in the V slot in-between the clamping rings

and copper bars. The hot molding Mica is formed under high temperature in a 20 ton pressing process.

Figure 16: Hot molding mica sheet ready to form

Copper bars

Clamping direction

Clamping rings

Clamping bolts Center point

Figure 15: Commutator clamping illustration

Molded Mica

Reduction in Commutator radius while clamping

process


August 20, 2015

Figure 17: Mica after being formed

3.8. Baking

The assembled Commutator is put in an oven for 6 hours at 200 degrees Celsius. This is to remove any

moisture and to cure the copper bars after machining. All the clamping bolts are torqued again after the

baking process to tighten the copper bars to their final required torque.

Figure 18 shows an assembled Commutator before backing.

Figure 18: Clamped Commutator ready for baking

Brush run surface

Raisers (Machined type)

Clamping bolts

Clamping ring


August 20, 2015

3.9. Testing

The final test is to spin the Commutator above its rated speed (150% of rated speed) to check for any

looseness and the correct balance. A final electrical resistance test is also done to confirm that all the

copper bars and risers are properly isolated from each other and from the rest of the Commutator.

Figure 16 is the turn wheel assembly that is used to run every Commutator build to its required testing

speed.

Figure 19: Rotation test for looseness

4. Advantage of V-ring Commutators

The main advantage of the V-ring Commutator is that it can easily be disassembled, with only the

damaged part then being replaced. This will save a lot of money and time in the event of future

damage/refurbishment of the Commutator.

It will take about a month to make the V-ring Comutator for the ZM1 coiler DC motor and at a very high

cost but any work done from then on will save numerous hours at a fraction of the cost.


August 20, 2015

Figure 20: Commutator being disassembled

Figure 17 shows a V-Ring Commutator being disassembled for refurbishment at Commutator

Engineering.


August 20, 2015

5. Additional photos of Commutator Engineering

Figure 21: Commutator Engineering workshop building

Figure 22: Lathes used


August 20, 2015

Figure 23: Isolation molds and milling machines in the background

Figure 24: outer holding rings


August 20, 2015

6. Conclusion

This document was made possible by going to Commutator engineering and meeting with the director, S.

Engelbrecht. There are numerous learning experiences outside of Columbus and not all of them costly.

These experiences are then again shared by the individuals who learnt it to the advantage of Columbus

Stainless and its other employees.

7. References

[1] Morganite Carbon brushes and electrical machines, intersegment insulation for commutators (p. 176)

1988 reprint

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