Title of Invention	SINTERING PROCESS FOR THE MANUFACTURE OF VACUUM INTERRUPTER CONTACTS HAVING GOOD ELECTRICAL AND MECHANICAL PROPERTIES AND MORPHOLOGY
Abstract	This invention relates to a sintering process for the manufacture of vacuum interrupter contacts. The process comprises blending 75% by weight of copper powder and 25% by weight of chromium powder. The chromium powder contains impurities less than 0.7% and oxygen content of 500 ppm - 7000 ppm. The blend is compacted at 600-900 MPa. The compacted mass is sintered at eutectic temperature of 1070 -1080°C followed by machining the cooled sintered mass into contacts.

Title of Invention

SINTERING PROCESS FOR THE MANUFACTURE OF VACUUM INTERRUPTER CONTACTS HAVING GOOD ELECTRICAL AND MECHANICAL PROPERTIES AND MORPHOLOGY

Abstract

This invention relates to a sintering process for the manufacture of vacuum interrupter contacts. The process comprises blending 75% by weight of copper powder and 25% by weight of chromium powder. The chromium powder contains impurities less than 0.7% and oxygen content of 500 ppm - 7000 ppm. The blend is compacted at 600-900 MPa. The compacted mass is sintered at eutectic temperature of 1070 -1080°C followed by machining the cooled sintered mass into contacts.

Full Text	FORM 2 THE PATENTS ACT, 1970 (39 of 1970) As amended by the Patents (Amendment) Act, 2005 & The Patents Rules, 2003 As amended by the Patents (Amendment) Rules, 2006 COMPLETE SPECIFICATION (See section 10 and rule 13) TITLE OF INVENTION A sintering process for the manufacture of vacuum interrupter contacts INVENTOR Name : Tandel Keyur Nationality : Indian national Address : Advance Materials and processes Centre, CG Global R&D Centre Crompton Greaves Ltd, Kanjur (East), Mumbai 400 042 APPLICANTS Name : CROMPTON GREAVES LIMITED Nationality: Indian Company Address : CG House, Dr Annie Besant Road, Worli, Mumbai 400 025, Maharashtra, India PREAMBLE TO THE DESCRIPTION The following specification particularly describes the nature of this invention and the manner in which it is to be performed: FIELD OF INVENTION This invention relates to a sintering process for the manufacture of vacuum interrupter contacts. This invention also relates to vacuum interrupter contacts manufactured by the process of the invention. BACKGROUND OF INVENTION Vacuum interrupters are used in power distribution systems to isolate sections of the power distribution systems under fault conditions. Vacuum interrupters comprise fixed contacts and moving contacts brazed or otherwise fixed to the respective electrodes and located in vacuum sealed ceramic chambers or envelopes. The contacts are normally made of copper (Cu) and chromium (Cr). When the contacts are in the closed position, large currents pass through the contacts and when the contacts open intense arcing takes place due to breaking of heavy currents. In order to allow heavy currents to flow with least resistance and to withstand intense arcing, the contacts should have good mechanical and electrical properties and good morphology ie the chromium in the contacts should be rounded and should not have sharp edges as sharp edges reduce the current carrying capacity of the contacts. A process for the manufacture of vacuum interrupter contacts comprises liquid phase sintering, in which copper and chromium powders are blended together in 75% by weight and 25% by weight, respectively. Ideally the Chromium powder should have less than 0.7% impurities. The 2 blended powder is compacted at pressures of 50-100MPa and sintered at temperatures above the melting point of copper ie around 1120-1220° C for about 8-12 hours. During sintering, the compacted mixture is held in a mild steel vessel comprising a thick lining of alumina or graphite which is required as liquid Cu formed during sintering has a tendency easily to form bonds with mild steel. The sintered mass is cooled and subjected to isostatic pressing at about 75000-87000 pounds per square inch. The pressed mass is sintered again at about 1120-1220° C for about 8-12 hours and is cooled down to ambient temperature followed by machining into contacts. As sintering is carried out twice at high temperatures, the energy consumption of the process is very high and the process is expensive. The process time is increased reducing productivity of the contacts. Handling of the liquid Cu during sintering is difficult and inconvenient. It also requires the mild steel vessel with alumina or graphite lining. The contacts formed by the above process have well rounded chromium and hence good morphology as the sharp edges of the chromium tend to dissolve in the liquid copper at the sintering temperature. Another process for the manufacture of vacuum interrupter contacts is solid phase sintering which is similar to liquid phase sintering except for the difference that the sintering is carried out below the melting point of copper ie around 1020-1050°C for about 8-12 hours. The solid phase sintering process has the same disadvantages associated with liquid phase sintering process except that the energy consumption in solid phase sintering is not as high as in liquid phase sintering as the sintering is carried out at lower temperatures. Additionally in solid phase sintering the sharp edges of the chromium are not rounded and therefore the morphology of the contacts formed by the solid phase sintering is not as good as that of the contacts obtained by liquid phase sintering. 3 Besides, both the liquid phase sintering and solid phase sintering require chromium containing less than 1000ppm of oxygen as during sintering only a small portion of the oxygen content in the chromium is removed . If the oxygen content in the contacts formed by the sintering processes is not less than 1000ppm, the oxygen in the contacts will gasify during operation of the vacuum interrupters and the released oxygen will disturb the vacuum level maintained in the vacuum interrupters thereby reducing the performance efficiency of the vacuum interrupters. Use of chromium powder containing less than 1000ppm of oxygen content further adds to the cost of the above processes. OBJECTS OF INVENTION An object of the invention is to provide a sintering process for the manufacture of vacuum interrupter contacts, which process reduces the manufacturing time thereby increasing productivity of the contacts. Another object of the invention is to provide a sintering process for the manufacture of vacuum interrupter contacts, which process reduces energy consumption and is economical. Another object of the invention is to provide a sintering process for the manufacture of vacuum interrupter contacts, which process produces contacts with good electrical and mechanical properties and morphology. 4 Another object of the invention is to provide a sintering process for the manufacture of vacuum interrupter contacts, which process removes increased oxygen content in the chromium during sintering. DETAILED DESCRIPTION OF INVENTION According to the invention there is provided a sintering process for the manufacture of vacuum interrupter contacts, the process comprising the following steps: (a) blending 75% by weight of copper powder and 25% by weight of chromium powder; the chromium powder containing impurities less than 0.7% and oxygen content of 500 ppm -7000 ppm; (b) compacting the blend at 600-900 MPa; (c) sintering the compacted mass at eutectic temperature of 1070 -1080°C; and (d) machining the cooled sintered mass into contacts. The following experimental examples are illustrative of the invention but not limitative of the scope thereof. The percentages in the examples are by weight. 5 Example 1 (Liquid Phase Sintering) 25% chromium powder containing 0.7% impurities and 1000 ppm of oxygen content and 75% copper powder were blended in a blender. The blended mix was compacted in a hydraulic press at 600 MPa. The compacted mass was held in a mild steel vessel with alumina lining and sintered in a vacuum furnace at 1220 °C for 8 hours. The sintered mass was cooled down and subjected to isostatic pressing in a hydraulic press at 87000 pounds per square inch. The pressed mass was sintered again as stated above. The sintered mass was cooled down to room temperature and machined into a contact. Example 2 (Solid Phase Sintering) 25%o chromium powder containing 0.7% impurities and 1000 ppm of oxygen content and 75% copper powder were blended in a blender. The blended mix was compacted in a hydraulic press at 50 MPa. The compacted mass was held in a mild steel vessel with alumina lining and sintered in a vacuum furnace at 1050°C for 8 hours. The sintered mass was cooled down and subjected to isostatic pressing in a hydraulic press at 87000 pounds per square inch. The pressed mass was sintered again as stated above. The sintered mass was cooled down to room temperature and then machined into a contact. Example 3 (Process of the invention at eutectic temperature) 25%) chromium powder containing 0.7% impurities and 1000 ppm of oxygen content and 75% copper powder were blended in a blender. The blended mix was compacted in a hydraulic press at 600 MPa. The compacted mass was held in a mild steel vessel with alumina lining and 6 sintered in a vacuum furnace at 1075 °C for 8 hours. The sintered mass was cooled down to room temperature and machined into a contact. Example 4 (Process of the invention at eutectic temperature) 25% chromium powder containing 0.7% impurities and 7000 ppm of oxygen content and 75% copper powder were blended in a blender. The blended mix was compacted in a hydraulic press at 600 MPa; The compacted mass was held in a mild steel vessel with alumina lining and sintered in a vacuum furnace at 1075 °C for 8 hours. The sintered mass was cooled down to room temperature and machined into a contact. The electrical and mechanical properties and morphology of the contacts obtained by Examples 1 to 4 are tabulated in the table below: Table 7 The experimental results clearly show that the density, conductivity and morphology of the contacts manufactured by the process of the invention namely Examples 3 and 4 were as good as those of the liquid phase sintering of Example 1. The micro hardness was improved in the contacts of Examples 3 and 4. The experimental results also show that a considerable portion of the oxygen content in the chromium powder is released and reduced during sintering at the eutectic temperature of Examples 3 and 4. Therefore, it is not necessary to use chromium powder comprising less than 1000ppm of oxygen content in the process of the invention. Instead chromium powder containing oxygen content of up to 7000 ppm can be used in the process of the invention. Energy consumption is reduced as sintering is carried out only once and the process steps are reduced as compared to liquid and solid phase sintering. Therefore, the process time is considerably reduced and productivity is increased and the process is economical. A possible explanation for the improved morphology of the contacts of Examples 3 and 4 is that the sharp edges of the chromium dissolve in the Copper partly in liquid state at the eutectic temperature sintering. 8 We Claim 1. A sintering process for the manufacture of vacuum interrupter contacts, the process comprising the following steps: (a) blending 75% by weight of copper powder and 25% by weight of chromium powder; the chromium powder containing impurities less than 0.7% and oxygen content of 500 ppm - 7000 ppm; (b) compacting the blend at 600-900 MPa; (c) sintering the compacted mass at eutectic temperature of 1070- 1080°C; and (d) machining the cooled sintered mass into contacts. 2. A process as claimed in claim 1, wherein the chromium powder comprises oxygen content of 7000 ppm. 3. A process as claimed in claim 1 or 2 , wherein the chromium powder comprises oxygen content of 1000 ppm. 4. A process as claimed in anyone of claims 1 to 3, wherein during sintering of the compacted mass at the eutectic temperature a part of the copper and chromium forms into liquid so as to improve the morphology of the contacts. 9 5. A process as claimed in claim 1 or 2, wherein during sintering of the compacted mass at the eutectic temperature of copper, substantial portion of the oxygen content in the chromium powder is gasified and reduced. 6. Vacuum interrupter contacts obtained by the process as claimed in anyone of claims 1 to 5 Dated this 27th day of March 2007 10 ABSTRACT A sintering process for the manufacture of vacuum interrupter contacts. The process comprises blending 75% by weight of copper powder and 25% by weight of chromium powder. The chromium powder contains impurities less than 0.7% and oxygen content of 500 ppm - 7000 ppm. The blend is compacted at 600-900 MPa. The compacted mass is sintered at eutectic temperature of 1070 -1080°C followed by machining the cooled sintered mass into contacts.

Full Text

FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2006
COMPLETE SPECIFICATION (See section 10 and rule 13)
TITLE OF INVENTION
A sintering process for the manufacture of vacuum interrupter contacts
INVENTOR
Name : Tandel Keyur
Nationality : Indian national
Address : Advance Materials and processes Centre, CG Global R&D Centre
Crompton Greaves Ltd, Kanjur (East), Mumbai 400 042 APPLICANTS
Name : CROMPTON GREAVES LIMITED
Nationality: Indian Company
Address : CG House, Dr Annie Besant Road, Worli, Mumbai 400 025, Maharashtra, India
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the nature of this invention and the manner in which it is to be performed:

FIELD OF INVENTION
This invention relates to a sintering process for the manufacture of vacuum interrupter contacts.
This invention also relates to vacuum interrupter contacts manufactured by the process of the invention.
BACKGROUND OF INVENTION
Vacuum interrupters are used in power distribution systems to isolate sections of the power distribution systems under fault conditions. Vacuum interrupters comprise fixed contacts and moving contacts brazed or otherwise fixed to the respective electrodes and located in vacuum sealed ceramic chambers or envelopes. The contacts are normally made of copper (Cu) and chromium (Cr). When the contacts are in the closed position, large currents pass through the contacts and when the contacts open intense arcing takes place due to breaking of heavy currents. In order to allow heavy currents to flow with least resistance and to withstand intense arcing, the contacts should have good mechanical and electrical properties and good morphology ie the chromium in the contacts should be rounded and should not have sharp edges as sharp edges reduce the current carrying capacity of the contacts. A process for the manufacture of vacuum interrupter contacts comprises liquid phase sintering, in which copper and chromium powders are blended together in 75% by weight and 25% by weight, respectively. Ideally the Chromium powder should have less than 0.7% impurities. The
2

blended powder is compacted at pressures of 50-100MPa and sintered at temperatures above the melting point of copper ie around 1120-1220° C for about 8-12 hours. During sintering, the compacted mixture is held in a mild steel vessel comprising a thick lining of alumina or graphite which is required as liquid Cu formed during sintering has a tendency easily to form bonds with mild steel. The sintered mass is cooled and subjected to isostatic pressing at about 75000-87000 pounds per square inch. The pressed mass is sintered again at about 1120-1220° C for about 8-12 hours and is cooled down to ambient temperature followed by machining into contacts. As sintering is carried out twice at high temperatures, the energy consumption of the process is very high and the process is expensive. The process time is increased reducing productivity of the contacts. Handling of the liquid Cu during sintering is difficult and inconvenient. It also requires the mild steel vessel with alumina or graphite lining. The contacts formed by the above process have well rounded chromium and hence good morphology as the sharp edges of the chromium tend to dissolve in the liquid copper at the sintering temperature. Another process for the manufacture of vacuum interrupter contacts is solid phase sintering which is similar to liquid phase sintering except for the difference that the sintering is carried out below the melting point of copper ie around 1020-1050°C for about 8-12 hours. The solid phase sintering process has the same disadvantages associated with liquid phase sintering process except that the energy consumption in solid phase sintering is not as high as in liquid phase sintering as the sintering is carried out at lower temperatures. Additionally in solid phase sintering the sharp edges of the chromium are not rounded and therefore the morphology of the contacts formed by the solid phase sintering is not as good as that of the contacts obtained by liquid phase sintering.
3

Besides, both the liquid phase sintering and solid phase sintering require chromium containing less than 1000ppm of oxygen as during sintering only a small portion of the oxygen content in the chromium is removed . If the oxygen content in the contacts formed by the sintering processes is not less than 1000ppm, the oxygen in the contacts will gasify during operation of the vacuum interrupters and the released oxygen will disturb the vacuum level maintained in the vacuum interrupters thereby reducing the performance efficiency of the vacuum interrupters. Use of chromium powder containing less than 1000ppm of oxygen content further adds to the cost of the above processes.
OBJECTS OF INVENTION
An object of the invention is to provide a sintering process for the manufacture of vacuum interrupter contacts, which process reduces the manufacturing time thereby increasing productivity of the contacts.
Another object of the invention is to provide a sintering process for the manufacture of vacuum interrupter contacts, which process reduces energy consumption and is economical.
Another object of the invention is to provide a sintering process for the manufacture of vacuum interrupter contacts, which process produces contacts with good electrical and mechanical properties and morphology.
4

Another object of the invention is to provide a sintering process for the manufacture of vacuum interrupter contacts, which process removes increased oxygen content in the chromium during sintering.
DETAILED DESCRIPTION OF INVENTION
According to the invention there is provided a sintering process for the
manufacture of vacuum interrupter contacts, the process comprising the following steps:
(a) blending 75% by weight of copper powder and 25% by weight of chromium powder; the chromium powder containing impurities less than 0.7% and oxygen content of 500 ppm -7000 ppm;
(b) compacting the blend at 600-900 MPa;
(c) sintering the compacted mass at eutectic temperature of 1070 -1080°C; and
(d) machining the cooled sintered mass into contacts.
The following experimental examples are illustrative of the invention but not limitative of the scope thereof. The percentages in the examples are by weight.
5

Example 1 (Liquid Phase Sintering)
25% chromium powder containing 0.7% impurities and 1000 ppm of oxygen content and 75% copper powder were blended in a blender. The blended mix was compacted in a hydraulic press at 600 MPa. The compacted mass was held in a mild steel vessel with alumina lining and sintered in a vacuum furnace at 1220 °C for 8 hours. The sintered mass was cooled down and subjected to isostatic pressing in a hydraulic press at 87000 pounds per square inch. The pressed mass was sintered again as stated above. The sintered mass was cooled down to room temperature and machined into a contact.
Example 2 (Solid Phase Sintering)
25%o chromium powder containing 0.7% impurities and 1000 ppm of oxygen content and 75% copper powder were blended in a blender. The blended mix was compacted in a hydraulic press at 50 MPa. The compacted mass was held in a mild steel vessel with alumina lining and sintered in a vacuum furnace at 1050°C for 8 hours. The sintered mass was cooled down and subjected to isostatic pressing in a hydraulic press at 87000 pounds per square inch. The pressed mass was sintered again as stated above. The sintered mass was cooled down to room temperature and then machined into a contact.
Example 3 (Process of the invention at eutectic temperature) 25%) chromium powder containing 0.7% impurities and 1000 ppm of oxygen content and 75% copper powder were blended in a blender. The blended mix was compacted in a hydraulic press at 600 MPa. The compacted mass was held in a mild steel vessel with alumina lining and
6

sintered in a vacuum furnace at 1075 °C for 8 hours. The sintered mass was cooled down to room temperature and machined into a contact.
Example 4 (Process of the invention at eutectic temperature) 25% chromium powder containing 0.7% impurities and 7000 ppm of oxygen content and 75% copper powder were blended in a blender. The blended mix was compacted in a hydraulic press at 600 MPa; The compacted mass was held in a mild steel vessel with alumina lining and sintered in a vacuum furnace at 1075 °C for 8 hours. The sintered mass was cooled down to room temperature and machined into a contact.
The electrical and mechanical properties and morphology of the contacts obtained by Examples 1 to 4 are tabulated in the table below:
Table

7

The experimental results clearly show that the density, conductivity and morphology of the contacts manufactured by the process of the invention namely Examples 3 and 4 were as good as those of the liquid phase sintering of Example 1. The micro hardness was improved in the contacts of Examples 3 and 4. The experimental results also show that a considerable portion of the oxygen content in the chromium powder is released and reduced during sintering at the eutectic temperature of Examples 3 and 4. Therefore, it is not necessary to use chromium powder comprising less than 1000ppm of oxygen content in the process of the invention. Instead chromium powder containing oxygen content of up to 7000 ppm can be used in the process of the invention. Energy consumption is reduced as sintering is carried out only once and the process steps are reduced as compared to liquid and solid phase sintering. Therefore, the process time is considerably reduced and productivity is increased and the process is economical. A possible explanation for the improved morphology of the contacts of Examples 3 and 4 is that the sharp edges of the chromium dissolve in the Copper partly in liquid state at the eutectic temperature sintering.
8

We Claim
1. A sintering process for the manufacture of vacuum interrupter
contacts, the process comprising the following steps:
(a) blending 75% by weight of copper powder and 25% by weight of chromium powder; the chromium powder containing impurities less than 0.7% and oxygen content of 500 ppm - 7000 ppm;
(b) compacting the blend at 600-900 MPa;
(c) sintering the compacted mass at eutectic temperature of 1070- 1080°C; and
(d) machining the cooled sintered mass into contacts.

2. A process as claimed in claim 1, wherein the chromium powder comprises oxygen content of 7000 ppm.
3. A process as claimed in claim 1 or 2 , wherein the chromium powder comprises oxygen content of 1000 ppm.
4. A process as claimed in anyone of claims 1 to 3, wherein during sintering of the compacted mass at the eutectic temperature a part of the copper and chromium forms into liquid so as to improve the morphology of the contacts.
9

5. A process as claimed in claim 1 or 2, wherein during sintering of the compacted mass at the eutectic temperature of copper, substantial portion of the oxygen content in the chromium powder is gasified and reduced.
6. Vacuum interrupter contacts obtained by the process as claimed in anyone of claims 1 to 5
Dated this 27th day of March 2007
10

ABSTRACT
A sintering process for the manufacture of vacuum interrupter contacts. The process comprises blending 75% by weight of copper powder and 25% by weight of chromium powder. The chromium powder contains impurities less than 0.7% and oxygen content of 500 ppm - 7000 ppm. The blend is compacted at 600-900 MPa. The compacted mass is sintered at eutectic temperature of 1070 -1080°C followed by machining the cooled sintered mass into contacts.

Documents:

578-MUM-2007-ABSTRACT(18-4-2011).pdf

578-MUM-2007-ABSTRACT(28-12-2011).pdf

578-mum-2007-abstract(28-3-2007).pdf

578-mum-2007-abstract.doc

578-mum-2007-abstract.pdf

578-mum-2007-claims(28-3-2007).pdf

578-MUM-2007-CLAIMS(AMENDED)-(18-4-2011).pdf

578-MUM-2007-CLAIMS(AMENDED)-(28-12-2011).pdf

578-mum-2007-claims.doc

578-mum-2007-claims.pdf

578-mum-2007-correspondence(10-4-2007).pdf

578-MUM-2007-CORRESPONDENCE(16-11-2011).pdf

578-MUM-2007-CORRESPONDENCE(20-12-2011).pdf

578-MUM-2007-CORRESPONDENCE(3-12-2008).pdf

578-mum-2007-correspondence-received.pdf

578-mum-2007-description (complete).pdf

578-mum-2007-description(complete)-(28-3-2007).pdf

578-mum-2007-form 1(10-4-2007).pdf

578-MUM-2007-FORM 1(18-4-2011).pdf

578-mum-2007-form 13(18-4-2011).pdf

578-MUM-2007-FORM 18(3-12-2008).pdf

578-mum-2007-form 2(28-3-2007).pdf

578-MUM-2007-FORM 2(TITLE PAGE)-(18-4-2011).pdf

578-MUM-2007-FORM 2(TITLE PAGE)-(28-12-2011).pdf

578-mum-2007-form 2(title page)-(28-3-2007).pdf

578-MUM-2007-FORM 26(18-4-2011).pdf

578-mum-2007-form-1.pdf

578-mum-2007-form-2.doc

578-mum-2007-form-2.pdf

578-mum-2007-form-26.pdf

578-mum-2007-form-3.pdf

578-MUM-2007-MARKED COPY(18-4-2011).pdf

578-MUM-2007-MARKED COPY(28-12-2011).pdf

578-MUM-2007-PUBLICATION REPORT(3-12-2008).pdf

578-MUM-2007-REPLY TO EXAMINATION REPORT(18-4-2011).pdf

578-MUM-2007-REPLY TO HEARING(28-12-2011).pdf

578-MUM-2007-SPECIFICATION(AMENDED)-(18-4-2011).pdf

578-MUM-2007-SPECIFICATION(AMENDED)-(28-12-2011).pdf

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Patent Number

250750

Indian Patent Application Number

578/MUM/2007

PG Journal Number

04/2012

Publication Date

27-Jan-2012

Grant Date

24-Jan-2012

Date of Filing

28-Mar-2007

Name of Patentee

CROMPTON GREAVES LTD

Applicant Address

DR.ANNIE BESANT ROAD, WORLI, MUMBAI.

Inventors:

#	Inventor's Name	Inventor's Address
1	TANDEL KEYUR	ADVANCE MATERIALS AND PROCESSES CENTRE CG GLOBAL R&D CENTER, CROMPTON GREAVES LTD., KANJUR (E), MUMBAI-400042.

PCT International Classification Number

H01H33/66

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA