This standard specifies the technical requirements, test methods, inspection rules, marking, packaging and storage of silver graphite electrical contacts containing 3%, 5% and 10% graphite. This standard applies to silver graphite electrical contacts produced by powder pressing, sintering and extrusion, or sintering and re-pressing processes. This series of products are mainly used as closing, opening contacts and sliding contacts of low-voltage switchgear. GB 12940-1991 Technical conditions for silver graphite electrical contacts GB12940-1991 Standard download and decompression password: www.bzxz.net

National Standard of the People's Republic of China
Technical specification for silver-graphite electrical contacts
Technical specification for silver-graphite electrical contacts
1 Subject content and scope of application
GB12940—91|| tt||This standard specifies the technical requirements, test methods, inspection rules, marking, packaging and storage of silver graphite electrical contacts containing 3%, 5% and 10% graphite.
This standard applies to silver graphite electrical contacts produced by powder pressing, sintering and extrusion, or sintering and re-pressing processes. This series of products are mainly used as closing, opening contacts and sliding contacts of low-voltage switchgear. 2 Reference standards
GB2828
Batch-by-batch inspection and counting sampling procedures and sampling tables (applicable to inspection of continuous batches) GB5163 Determination of density of permeable sintered metal materials GB5586 Basic performance test method for electrical contact materials GB5587. Basic shapes, dimensions, symbols and markings of silver-based electrical contacts 3 symbols, codes and marking methods
3.1: Symbols and codes
a.
Q
bP
Ｒ
c.
dY
represents the fiber type silver graphite electrical contact produced by sintering extrusion method: represents the ordinary type produced by sintering composite pressing method Silver graphite electrical contact; represents the P-type soft silver graphite electrical contact that has been annealed and heat treated after re-pressing, - represents the P-type hard silver graphite electrical contact that has been re-pressed. 3.2 Labeling method
C
3.3 Labeling examples
See Table 1.
Ag
c
(A)
State Bureau of Technical Supervision approved A
Process method
Graphite group on 1991-06-06 Percent content of cents
Graphite (carbon element symbol)
Silver (element symbol)
The first pinyin of touch, which represents electrical contacts
1992-03- 01Implementation
Standard
Note
Indicate
CAgC(3)Q
CAgC(5)Q
CAg C(10) Q
CAgC(3)P
CAgC(5)P
Technical requirements
4
Example
GB12940—91|| tt||Table 1
containing
meaning
Q-type AgC electrical contacts containing 3% graphite
Q-type AgC electrical contacts containing 5% graphite
Q-type AgC electrical contacts containing 10% graphite
P-type AgC electrical contacts containing 3% graphite
P-type AgC electrical contacts containing 5% graphite|| The chemical composition, mechanical and physical properties of tt||silver graphite electrical contact products (referring to the silver graphite electrical contacts 4.1
products whose welding surface is not decarburized and not covered with silver layer) are as specified in Table 2.
Product name
Silver graphite (3) Q
Silver graphite (5) Q
Silver graphite (10) Q
Silver graphite (3) P
Generation
Table 2
No.
CAgC(3) Q
CA8C(5)Q
CAgC(10) Q
CAgC(3)P
Silver graphite (5)PAgC(5)P
Chemical composition, mechanical and physical properties of silver graphite electrical contacts Chemical composition, wt%||tt ||Graphite
Content
3
5
10
3
5
Limit
Deviation
±0.5
± 0.8
±1.0
±0.5
±0.8
Impurities
Not greater than| |tt||0.5
Silver
Content
Remainder
Dense
Mechanical, physical properties
Degree
g /cm
not less than
9.1
8.6
7.4
9.1
8.6
hardness HB||tt| |MPa
not less than
343
343
294
R：245
Y：392
R： 245
Y: 392
Note: The conductivity IACS% is calculated based on the international standard soft copper resistance of 1.7241uQ.cm as 100% conductivity. 4.2 Colloidal graphite powder should be used to manufacture silver graphite electrical contacts. See Appendix A for the requirements for colloidal graphite powder. Resistivity
uQ.cm
is not less than
2.2
2.5
3.0
2.4
3.2||tt ||Conductivity
IACS%
not less than
78
69
57bzxZ.net
72
54|| tt||The dimensional tolerance, surface roughness, etc. of 4.3 silver graphite electrical contact products should comply with GB5587 regulations. Special requirements shall be agreed upon by both parties.
Chemical composition analysis, when the process is stable and the raw materials remain unchanged, only the carbon content or silver content is analyzed. 4.4
The surface of 4.5 silver graphite electrical contacts shall not have defects such as cracks, bubbles, scars, falling edges, missing corners, dirt and delamination. The edge burr height should not be greater than 0.1mm.
The metallographic structure of 4.6 silver graphite electrical contact products should be evenly distributed, as shown in Appendix D Figure D1 to Figure D5. The metallographic structure of silver graphite electrical contact products should not have cracks, squeeze fishtails, or 100μm4.7
GB12940-91
length on the entire observation surface of the grinding specimen (arithmetic mean of length and width) inclusions or aggregation of graphite particles, or silver-rich areas and obvious silver bands, the defect metallographic diagrams are shown in Appendix E, Figure E1 to Figure E10.
There are two supply methods for 4.8 silver graphite electrical contacts: Q-type silver graphite electrical contact products are available in decarburized and non-decarburized versions, and P-type silver graphite electrical contact products are available without silver layer. and silver-coated two types. The thickness of the decarburized layer and silver-coated layer, as well as the density and hardness after decarburization, are determined by both parties. 4.9 For silver-graphite electrical contact products with decarburization or silver-coating layers, the decarburization layer or silver-coating layer should not have continuous graphite lines, and there should be no cracks at the bonding interface between the decarburization layer or silver-coating layer and silver graphite. and 100 μm long inclusions or aggregates of graphite particles. 5 Test methods
5.1 The thickness and burr height of silver graphite electrical contact products should be checked with an outer diameter dry scale with a graduation value of 0.01mm. The other dimensions should be checked with a vernier caliper with a reading value of 0.02mm or other applicable Instruments and tools are inspected. 5.2 The apparent quality shall be inspected visually or with the help of a 10x magnifying glass, tool microscope or projector. 5.3 Density, hardness and resistivity shall be measured in accordance with GB5586. If the sample is found to absorb water when measuring density, it shall be carried out according to the method specified in GB5163. The hardness shall be measured on the working surface of the product. , 5.4 The chemical composition analysis of silver graphite electrical contacts shall be carried out in accordance with the provisions of Appendix F. 5.5 For metallographic structure inspection, the Q-type silver graphite electrical contact should be taken on two cross-sections perpendicular to and parallel to the fiber direction, and the P-type silver graphite electrical contact should be taken on a cross-section perpendicular to the working surface. For silver-graphite electrical contact products with a decarburized layer or a silver-coated layer, the metallographic structure inspection should include the joint surface part. See Appendix C for the metallographic structure inspection method. 6 Inspection Rules
6.1 Quality inspection of electrical contact products shall be carried out in batches by the technical inspection department of the production unit. Each batch should be produced with the same batch of ingredients and the same process.
6.2 Silver Graphite Electric Contact Product Quality Inspection, Sampling Methods and Judgment Rules. 6.2.1 Appearance inspection 100%.
6.2.2 Dimensional inspection is carried out according to the secondary normal inspection sampling plan of GB2828 (see Appendix B) Level II general inspection level. The qualified quality level (AQL value) is 2.5 for thickness and 4.0 for other dimensions. 6.2 .3 Density, hardness, resistivity, chemical composition, and metallographic structure inspection shall be carried out according to the secondary normal sampling plan of GB2828, in which density and hardness shall be sampled according to the S-2 special inspection level. Its qualified quality level (AQL value) is 4.0; resistivity, chemical composition and metallographic structure are sampled according to S-1 special inspection level. Its qualified quality level (AQL value) is 10. See Appendix D. 6.2.4 Chemical composition analysis, if the unit weight of the contact is less than 0.5g should be double sampled. Density, hardness, and metallographic structure inspection can be performed on the same sample.
6.3·For chemical composition analysis and density determination of silver graphite electrical contact products, the decarburization layer and silver coating layer must be removed. 6.4Q type silver graphite resistivity measurement can be carried out by cutting a 50mm long sample from the extruded strip before slicing. For special-shaped extruded strips, they must be processed into regular resistivity samples for measurement. For the measurement of P-type silver graphite resistivity, standard samples must be made according to the same process as the product. The standard sample size is 50mm × 10mm × 4mm. 6.5 When the user accepts the product, if it finds that it does not meet this standard, it must report it to the manufacturing unit within two months after receiving the product. 7 Marking, packaging, transportation and storage
7.1 Each batch of products should be accompanied by a product certificate and inspection form. 7.2 The product certificate should indicate:
8 Contact product name (or code) specifications and batch number (or number); b. Contact weight or number of particles
c. Manufacturing date; ||tt ||d. Name of manufacturing unit
e: Seal of inspector and inspection department.
7.3 Product inspection sheet content:
GB12940-91
&. Product name or code, specifications and batch number (or serial number); b. Contact weight or number of particles;
C. Product mechanical, physical properties, chemical composition and metallographic photos; d. Inspection date;
e. Name of manufacturing unit
f. Seal of the inspector and inspection department.
7.4 silver graphite electrical contacts should be packaged according to the same composition and specifications. 7.5 products should be packaged in plastic bags after being wrapped in paper. The weight of each bag of contacts shall not exceed 1kg. Packed in plastic bags and cardboard boxes, the net weight of each box shall not exceed 4kg. Each box should be marked with the contact name, specifications, weight or number of particles, production batch number or serial number, and name of the manufacturing unit. 7.6 When electrical contact products are shipped, they should be packed in packaging boxes and filled with soft materials. 7.7 The packaging box should be accompanied by a packing list, which should indicate: a. Total number of bags (boxes)
b. Number of bags (boxes) of electrical contacts of various types or sizes; c. Net weight of electrical contacts;
d． Packaging date;
e. The packager prints the signature.
7.8 The packaging box should be marked:
8. Name of manufacturing unit;
b. Gross weight and net weight;
c. If the inspection sheet is attached, please add:
d. Moisture-proof and shock-proof signs.
7.9 silver graphite electrical contact products should be moisture-proof and shock-proof during transportation. 7.10 Silver graphite electrical contact products should be stored in a warehouse with a non-corrosive atmosphere and protected from moisture. GB12940—91
Appendix A
Colloidal graphite powder
(Supplement)
A1 Colloidal graphite powder should be used to manufacture silver graphite electrical contacts, and its graphite purity should not be less than 99%, the ash content in graphite is not more than 1%. Determination of A2 graphite purity and ash content:
A2.1 Instruments and equipment: Use general laboratory instruments. A2.2 Measurement procedure:
Take 2g of stone powder that has been dried at 105~110℃ for 2h (use a 1/10000th balance) and transfer it to the porcelain that has been burned to constant weight and place it at 800~850℃ In a Maofu furnace, burn to constant weight and weigh. A2.3 Results and calculations
The percentage of ash content and graphite purity in colloidal graphite powder is calculated according to formulas (A1) and (A2): (m,-m2)×100
Ash content (% ) 三
2
Graphite purity (%) =2-(\,=mz)×100.2
Where: m, the mass of porcelain crucible and ash, g||tt ||m2
The weight of a porcelain crucible burned to constant weight, g. Appendix B
Product Inspection Sampling Form
(Supplement)
(A1)
(A2)
B1 The data quoted in this appendix are partly extracted from GB2828 Check the counting sampling procedures and sampling tables batch by batch for reference when using this standard. B2 secondary normal inspection sampling table is shown in Table B1. Symbols in the table:
Gold
Use the first sampling plan under the arrow. When the product quantity is greater than or equal to the batch size, the judgment array of the sampling plan remains unchanged;
Use the arrow First sampling plan above; *—use the applicable sampling plan below
Ac—acceptance number;
R. ——Number of unqualified judgments.
Batch range
pieces
1~8
9~15
16~25
26~50
51~90
91~150
151280
281~500
501~1200
1201~3200
3201~10000| |tt||10001~3500 0
35001~150000
150001~
500000
Sampling number yellow code
Special inspection level||tt ||S-1
A
A
A
A
B
B
B||tt ||c
c
c
c
o
D
-2
S||tt| |A
A
B
B
B
C
c
c
D
D
D
E
S-3
A
A
B
B
C
0
D
D
E
E
F
F|| tt||G
G
GB12940—91
Table B1 Sampling Table
General Inspection
Inspection Level
B||tt ||0
D
E
F
G
H
L
M
N
P
Number of samples
Quantity code
B
c
D
E||tt| |F
G
H
K
L
M
N
sampling times
number
first
second
first
second
th
th
th||tt ||Second
First
Second
Second
Second
Second|| tt||Second
Second
Second
th
Second
th
th|| tt||No.
Second,
No.
Second normal inspection sampling plan table
Accepted quality level (AQL)||tt ||Number of samples
2
2
3
3
5
5
80||tt| |8
13
13
20
20
32
32
50
50
80
80
125
125
200
200
315
315|| tt||500
500
Cumulative drawing
Quantity of samples
2
4
3
6|| tt||5
10
8
16
13
26
20
40||tt| |32
64
50
10G
80
160
125
250
200
400
315
630
500
1000
2.5
Ae
R.
pieces
v
0
1
0
3
4
2|| tt||6
5
2
3
5
5
7
10||tt| |12
11
18
19
16
11
2627

4.0
A
0
0
3
6
R
!
pieces
2
2
3
5
6
7
9|| tt||12
18
11
26
10
13
11
19||tt| |16
27
10
A.
2
6
R.
2
9
10
5
9
1213
7
11|| tt||1819
1116
2627
Batch range
pieces
more than 500001
sampling quantity code
Special inspection level
s-1
D
S-2
E
s-3
H
GB12940-91
Continued Table B1
General inspection
Inspection level
0
Number of samples
Quantity code||tt| |Q
Sampling times
Number
First
Second
Appendix C
Secondary normal inspection sampling plan table|| tt||Accepted Quality Level (AQL)
Sampling number
Quantity
800
800
Metallographic inspection method for silver graphite electrical contacts| |tt|| (reference part)
C1 This appendix is ??the reference method for metallographic inspection of silver graphite electrical contacts. C2 metallographic sampling
Cumulative sampling
Quantity of samples
800
1600
C2.1P type silver graphite electrical contact product is taken perpendicular to the contact The cross section of the working surface is the metallographic observation surface. 2.5 | | tt | | Ae Re | C3 Metallographic Sample Preparation
4.0
A. Re
pieces
C3.1 Fix the intercepted sample with the mounting method, and then polish it step by step from coarse to fine with water sandpaper or metallographic sandpaper. C3.2 After polishing, polish the sample on a polishing machine until the surface is bright and has no scratches. C3.3 After washing the polished sample with water, dry it immediately with filter paper. 10
AcRe

C4 samples do not need to be etched. Place them under a metallographic microscope to check the metallographic structure and defects of the product. Use 200× for metallographic structure inspection and defects. Check with 100×.
The measurement of C5 aggregates, inclusions and silver-rich areas is carried out with the eyepiece micrometer of the microscope. The measurement value is the arithmetic mean of its length and width.
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