Complete Specification
of
Formulation of Chemistry and Manufacturing of Interpole Part through Powder Metallurgy for use in Starter- Generator of DC
Motor used in Aircraft Application
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S.No. Content Sheet No
1 Title of the invention
2 Field of invention
3 Use of invention
4 Prior art
5 Draw backs of prior art
6 Comparison between prior art and present invention
7 Aim of the invention
8 Summary of the present invention
9 Brief description of drawings
10 Statement of invention
11 Detailed description of invention
12 Drawings & worked examples

1) Title of the invention
Formulation of Chemistry and Manufacturing of Interpole Part through Powder Metallurgy for use in Starter- Generator of DC Motor used in Aircraft Application
2) Field of invention
The present invention is about qse of sponge iron powder to produce the interpole part for use as Stator-Generator in DC motor to neutralize reactance voltage and cross magnetizing effect to improve commutation in PC motor.
3) Use of invention
The sponge iron powder is used in interpole composition to make a single part to achieve the desired density of 7.1(+/-0.2) g/cc and magnetic induction of 150 (+/-10) gauss at 530amp current.
4) Prior art
The interpole part was made of two sections of structured steel which were joined by Copper brazing.
5) Draw backs of prior art
In the earlier method, interpole part was made of two sections of structured steel which were joined by Copper brazing. This resulted in non-uniform magnetic property and density in the Interpole part leading to high reactance voltage and high cross magnetizing effect.
6) Comparison between prior art and present invention
The magnetic property & density is achieved as per the design requirement due to single structure of the powder metallurgy part as compared to Copper brazed structural steel part.
Table 1: Comparison of properties.
Desired Parameters ' Structural steel part Powder metallurgy
Interpole part
. ■ . i
Magnetic field (Gauss) " *~" 100 ' 150
Density (gms/cc) ^ ' *~ "' 6.5 to 6.8 7.1 to 7.25
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7) Aim of the invention
Aim of the invention is to develop a new Interpole part using powder metallurgy method which gives desired magnetic property & resulting in less arcing in the brushes of the DC motor.
8) Summary of the present invention
The.present invention is formulation of the interpole part used in DC Motor using powder metallurgy. The formulated part finds application i n aircraft DC M otor s ystems. For the said application, the part needs to have excellent magnetic & neutralize reactance voltage and cross . magnetizing effect to improve commutation in DC motor. These properties are achieved in the present invention by formulating part with Iron powder through powder metallurgy route.
9) Brief description of drawings

Figure 1: Sectional view of Starter-Generator showing Interpole
10) Statement of invention
Formulation of Interpole part through powder metallurgy route using sintered iron for the application in the aircraft DC motor to neutralize reactance voltage and cross magnetizing effect to improve commutation in DC motor.

11) Detailed description of invention
The present invention is best suited for DC motor of 9 kW starter. The interpoles are located between main poles in neutral zone of stator of starter generator The winding over interpole carries the same current as armature and creates magnetic line of forces in neutral zone. These line forces are out by armature conductors generating a voltage in them. This voltage is.in opposite polarity of unwanted voltage (that is produced by distorted line of force due to armature reaction) and cancels it. The result is less arcing in the brushes leading to an improved commutation.
The interpoles are supposed to be made of soft magnetic material. We have manufactured the interpole part using sponge iron powder by powder metallurgy method to get the sintered iron which requires less machining. In the sintered part, adequately high permeability and saturation, low. residual induction and coercive force is achieved by higher sintered density and temperature. A sintered part is manufactured at sintering temperature of 1020°C and sintering load of 2 tons. The sintered part is tested for hardness, chemical, micro analysis, density and magnetic property. All these parameters are achieved as per the requirement. The magnetic induction is controlled by sintering-density and sintering temperature of the powder using the small size particles in the mixing and compaction process of manufacturing.

Annexure-II
TITLE: Formulation of Chemistry and Manufacturing of Interpole Part through Powder Metallurgy for use in Starter-Generator of DC Motor used in Aircraft Application
Claims "We claim"
1 Interpole part manufactured through powder metallurgy process is designed to use in
9kw Stator-Generator of DC motor, the details of which is hitherto not available in open
literature.
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2 The formulation of the part has been developed by Foundry and Forge Division of HAL, Bangalore and the parameters are optimized to use the part in aircraft DC motor of capacity 7.5 to9,0Kw.
3 The powder metallurgy process used in the part is a new concept to achieve desired soft magnetic material to use in Stator-Generator of DC motor.
4 The composition is tested in 7.5KW and 9.0KW DC motor stator-Generator .The results of the test is satisfactory& Repetable.