Title of Invention

"AN IMPROVED PROCESS FOR THE PRODUCTION OF SILVER BASED BRAZING ALLOY USEFUL AS FILLER MATERIAL"

Abstract An improved process for the production of silver basedl brazing alloy useful as filler material. This invention relates to an improved process for the production of silver based brazing adoy useful as filler material. In the process of the present invention copper is firet melted along w^ith silver in a resistance furnace using clay bonded graphite crucible and preheated Zn and Cd metals are added to the molten alloy. Sufficient flux is added to cover the molten surface to prevent oxidation. A cold reduction of 20% to 25% Is given to the cast ingot prior to homogenisation heat treatment for a perid of 6 to 8 has in the temperature range and then the heat-treated ingot is processed to thin sheets obtain of 5to 15 mm thickness.
Full Text This invention relates to an improved process fo-r the production of silver based brazing alloy . for use as filler (joining) material.
The silver based brasing alloy produced by the process of present, invention will be useful in brazing steel, copper, brass, gun metal, tin bronze, aluminium and manganese bronzes, silver based contact alloys, copper nickel alloy and nickel silver of all types in electrical and other industries.
The relevant existing process for the production of the conventional silver based brasing alloy (Ag-42 to 44%, Cu-15 to 17%, Zn-18 to 22 and Cd-20 to 22 ) involves melting, casting, heat treatment and processing to foils/wires with intermediate annealing.
The loss of the alloying elements in the existing process such as sine and cadmium is high (Zn-10 loss, Cd-15 loss) during melting of the alloy. Apart from these there are wide differences in melting points and densities between the alloying additions as given below, causing problems in homogeneous mixing in the melt.
Element Melting point (°C ) Density (g/cm )
Ag 961 10.50
Cu 1083 8.94
Zn 419 7.13
Cd 321 8.64
Moreover, the homogenisation heat treatment procedure of the cast slab/ ingot in the existing process is lengthy (24 hrs) causing involvement of higher electrical energy and maapower. This results in high cost of production of the said alloy in the existing process.
In our co-pending application ( 435/D/90) we have disclosed a process for making low silver brazing filler alloy having a composition range of silver-30 to 40% , silicon-2.75 to 4.25, tin-0.15 to 0.25% and balance copper wherein the melting of the alloy was done in an electric pot-type furnace using a graphite crucible and was poured in a preheated (150 to 200°C) graphite mould at about 900 to 950°C. The cast slabs were given cold reduction of 20 to 25% and then homogenised at 500 to 550°C for 4 to 8 hours. The homogenised slabs were processed to thin sheets by rolling. However, its use is restricted to electronic and vacuum tube industries only. As this alloy does not contain any volatile elements such as cadmium, sine etc. which is an important factor for use in Vacuum tube and Electronic Industries.
Therefore, further R & D work was carried out to develop an alloy for useful general purpose having a composition . range of Ag-40 to 44, Cu-15 to 17, Zn-18 to 22, Cd-20 to 22. The alloy produced by the present invention is useful for brazing steel, copper, brass, gun metal bronzes, silver based contact alloys, copper nickel alloys and nickel silver of all types and takes much shorter time through thermomechanical treatment and produces a filler material that possesses better or equivalent brazing properties to those produced by the existing processes.
In the process of present invention the aforesaid problems are overcome by adopting appropriate melting schedule like sequence of charging of alloying elements, controlling melting and pouring temperatures , using suitable flux (borax based) to minimise the the loss of Zn and Cd metals during melting and by thermomechanical treatment to reduce the heat treatment time from 24 hours to 8 hours.
The main objective of the present invention is to provide an improved process for the production of silver brazing alloy for use as filler (joining) material by overcoming the above mentioned drawbacks associated with the existing processes.
In the process of the present invention copper is first melted alongwith silver in a resistance furnace using clay bonded graphite crucible and preheated Zn and Cd metals are added to the molten alloy. Sufficient flux is added to cover the molten surface to prevent oxidation. A cold reduction of 20% is given to the cast ingot prior to homogenisation heat treatment to reduce the time period and then the heat-treated ingot is processed to thin sheets/wires for final use. The beneficial effect of initial cold reduction in improving the kinetics of homogenisation may be under stood on the basis of the reduction in the effective diffusion distances which, in turn lowers the relaxation time. The homogenised slabs are then processed into thin sheets (0.5 to 0.15 mm thickness) by cold rolling, limiting to 20 to 25% reduction prior to each cycle of reduction to avoid cracking.
Accordingly, the present invention provides, an improved process for the production of silver
based brazing alloy useful as filler material which comprises:
i) melting of Ag and Cu in the temperature range of 950 to 1000°C to get a Ag - Cu alloy in
the range of Ag-42 to 44% and Cu -15 to 17%,
ii) adding preheated Zn and Cd metals in the range of 18 to 22% and 20 to 22% respectively
to the molten Ag-Cu alloy in the temperature range of 800 to 820°C, to get a composition in
the range of Zn-18 to 22% and Cd-20 to 22%, iii) covering the surface of the melt with a flux such as borax and the like during melting, iv) pouring the melt in a preheated steel mould in the temperature range of 700 to 750°C, v) processing the cast slab for cold reduction in the range of 20 to 25%, vi) homogenising the cold reduced slab for a period of 6 to 8 hours in the temperature range of
400 to 460°C in an electric furnace followed by air cooling and
vii) cold rolling of the homogenised slab into thin sheet in the range of 0.05 to 0.15 mm thickness with intermediate annealing, limiting to 20 - 25% reduction prior to each cycle of cold reduction.
According to a feature of the invention Ag, Cu, Zn and Cd metals employed for making the alloy may be of high purity (99.99%). Melting of Ag, Cu, Zn and Cd may be done in an electric resistance furnace using clay bonded graphite crucible and casting in steel mould. Heat treatment may be done in muffle furnace and the reduction of the ingot by cold rolling. Annealing may be done after each cycle of cold reduction at a temperature range of 400 to 420 C for a period of 1 to 2 hrs.
The novelty of the process of the present invention lies in the achievement of better mechanical and physical properties compared to those produced by the existing process ( Tables I,II and III). Further the cost of production of the present invention has been reduced (30 to 40%) due to the reduction of heat treatment time from 24 hours to 8 hours and also the final yield is increased due to the reduction of oxidation of Zn and Cd metals during melting by adopting appropriate melting technique and using suitable flux.
By the process of present invention silver brasing alloy is produced having solidus and liquidus temperatures in the range of 610 to 620°C and also the loss of Zn and Cd metals has been brought down to the level of 5% and 7% respectively against 10% of Zn and 15% of Cd metals in the existing process. The wetting properties (Table III) are comparable to those produced by the existing process..

Table I Physical properties of the alloys

(Table Removed)

Table II Mechanical Properties of the alloys

(Table Removed)

Table III Wetting properties of the alloys (base metal
(Table Removed)
The following typical examples are given by way of illustration and should not be construed to limit the scope of the invention.
Example I
This experiment was carried out with 0.2kg capacity melt to get a composition of Ag-44, Cu-16 , Zn-20 and Cd-20. Melting of 18g of Ag and 33g of Cu was done in • an electric pot-type furnace using clay bonded graphite crucible at 980 C to get a Ag-Cu alloy in the range of Ag-44 and Cu-16. Additions of preheated 42g of Zn and 43g of Cd metals to the molten Ag-Cu alloy were done at 800°C to get a composition in the range of 20 Zn and 20 Cd in the alloy. Sufficient flux (borax based) was added to cover the molten surface to prevent oxidation of Zn and Cd metals. The molten bath was held for 25 minutes and then the melt was
poured in a preheated steel mould at 750°C. The cast slab was initially given a cold reduction of 20% and then homogenised at 460°C for 8 hours. The homogenised slab was rolled to thin sheet (0.125 mm thickness) with intermediate annealing treatment. The physical and mechanical properties of the alloy were determined. The results are given below.
Melting points: 610 to 620°C, Density: 9.4g/cm3, Electrical conductivity: 28% IACS, Hardness: 120VPN, YS: 28kg/mm2, UTS: 45kg/mm2, Elongation: 35 % , Contact angle'- 18°, Wetting index'• 0.29.
Example II
This experiment was carried out with 0.340kg capacity melt to get a composition of Ag-44%, Cu-15, Zn-20 and Cd-21. Melting of 150g of Ag and 52g of Cu was done in an electric pot-type furnace using clay bonded graphite crucible at 960 C to get a Ag-Cu alloy in the range of Ag-44% and Cu-15. Additions of preheated 72g of Zn and 76g of Cd metals to the molten Ag-Cu alloy were done at 820 C to get a composition in the range of 20% 2n and 21% Cd in the alloy, Sufficient flux borax was added to cover the molten surface to prevent oxidation of Zn and Cd metals. The molten bath was held for 25 minutes and then the melt was poured into a preheated steel mould at 760oC. The cast slab was then homogenised at 460°C for 24 hours. The homogenised slab was rolled to thin sheet (0.125mm thickness) with intermediate annealing* treatment. The physical and mechanical properties of the alloy were determined. The results are given below.
Melting points; 610-620°C, Density: 3.0g/cm3, Electrical conductivity. 30% IACS, Hardness: 120 VPN, Y.S.: 30kg/mm2. U.T.S.: 45 kg/mm , Elongation: 35, Contact angle: 18^ and Wetting Index: 0.30.
Example III
This experiment was carried out with 0.5kg capacity melt to get a composition of Ag-44, Cu-16, Zn-20 and Cd-20. Melting of 220g of Ag and 80g of Cu was done in an electric pot-type furnace using clay bonded graphite crucible at 950 C to get a Ag-Cu alloy in the range of Ag-44% and Cu-16. Additions of preheated 105g of Zn and 107g of Cd metals to the molten Ag-Cu alloy were done at 830°C to get a composition'in the range of 20% Zn and 20% Cd in the alloy. Sufficient flux borax was added to cover the molten surface to prevent oxidation of Zn and Cd metals. The molten bath was held for 25 minutes and then poured the melt in a preheated steel mould at ?30°C. The cast slab was initially given a cold reduction of 25% and then homogenised at 460 C for 8 hours. The homogenised slab was rolled to thin sheet (0.5 to 0.15mm thickness) with intermediate annealing treatment. The physical and mechanical properties of the alloy were determined. The results are given below.
Melting points: 608-620°C, Density: 9,30g/cm3, Electrical conductivity: 29% IACS, Hardness: 115 VPN, Y,S.: 27kg/mm2, U.T.S.: 42 kg/mm , Elongation: 35, Contact angle: 1.8° and Wetting Index: 0.30.
The main advantages of the present invention are : i) In the process of present invention, the loss of highly oxidisable metals like Zn and Cd has been reduced by adopting appropriate melting technique and using suitable flux (borax based) to the level of 5 and 7 respectively against 10% loss of Zn and 15% loss of Cd metal in the existing processes, ii) The present invention requires 8 hours of homogenisation heat treatment time against 24 hours in the existing process; this leads to savings in the cost of power, energy and manpower. less than the existing process due to the reduction of oxidation of Zn and Cd metals during melting and also saving of time during heat treatment process.



We Claim:
1. An improved process for the production of silver based brazing alloy useful as
filler material which comprises:
i) melting of Ag and Cu in the temperature range of 950 to 1000°C to get a Ag
- Cu alloy in the range of Ag-42 to 44% and Cu -15 to 17%, ii) adding preheated Zn and Cd metals in the range of 18 to 22% and 20 to 22%
respectively to the molten Ag-Cu alloy in the temperature range of 800 to
820°C, to get a composition in the range of Zn-18 to 22% and Cd-20 to 22%, iii) covering the surface of the melt with a flux such as borax and the like during
melting, iv) pouring the melt in a preheated steel mould in the temperature range of 700
to 750°C, V) processing the cast slab for cold reduction in the range of 20 to 25%, vi) homogenising the cold reduced slab for a period of 6 to 8 hours in the
temperature range of 400 to 460*'C in an electric furnace followed by air
cooling and vii) cold rolling of the homogenised slab into thin sheet in the range of 0.05 to
0.15 mm thickness with intermediate annealing, limiting to 20 - 25%
reduction prior to each cycle of cold reduction.
2. An improved process as claimed in claim (1) wherein the silver, copper, zinc and cadmium metals employed are of 99.99% purity.
3. An improved process as claimed in claims 1 and 2 wherein annealing is done after each cycle of cold reduction at a temperature range of 400 to 420°C for a period of 1 to 2 hours.
4. An improved process for the production of salved based brazing alloy useful as filler material substantially as herein described with reference to the examples.



Documents:

666-del-1996-abstract.pdf

666-del-1996-claims.pdf

666-del-1996-complete specification (granted).pdf

666-del-1996-correspondence-others.pdf

666-del-1996-correspondence-po.pdf

666-del-1996-description (complete).pdf

666-del-1996-form-1.pdf

666-del-1996-form-2.pdf

666-del-1996-form-3.pdf

666-del-1996-form-4.pdf


Patent Number 195800
Indian Patent Application Number 666/DEL/1996
PG Journal Number 31/2009
Publication Date 31-Jul-2009
Grant Date 21-Apr-2006
Date of Filing 27-Mar-1996
Name of Patentee COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH
Applicant Address RAFI MARG NEW DELHI 110001 INDIA.
Inventors:
# Inventor's Name Inventor's Address
1 SAILENDRA CHANDRA DEV NATIONAL METALLURGICAL LABORATORY JAMSHEDPUR BIHAR INDIA.
2 CHITTUR SUBRAMANIAN SIVARAMAKRISHNAN NATIONAL METALLURGICAL LABORATORY JAMSHEDPUR BIHAR INDIA.
PCT International Classification Number C22C 5/06
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA