GOST 25947-83
GOST 25947−83 (ST SEV 3914−82) sintered hard Alloys. Method of determination of specific electrical resistance (Change No. 1)
GOST 25947−83
(ST CMEA 3914−82)
Group B59
STATE STANDARD OF THE USSR
SINTERED HARD ALLOYS
Method of determination of electrical resistivity
Sintered hard metals. Method of determination of electric resistance
AXTU 1909
Valid from 01.01.85
to 01.01.90*
_______________________________
* Expiration removed
Protocol N 4−93 inter-state Council
for standardization, Metrology and certification
(IUS N 4, 1994). — Note the manufacturer’s database.
DEVELOPED by the Ministry of nonferrous metallurgy of the USSR
PERFORMERS
N.Kudrya, V. I. Tumanov, A. A. Zaluzhny
INTRODUCED by the Ministry of nonferrous metallurgy of the USSR
Member Of The Board V. P. Snurnikov
APPROVED AND put INTO EFFECT by Decision of the USSR State Committee for standards 27 Oct 1983 N 5166
The Change N 1, approved and put into effect by the Decree of the USSR State Committee for standards from
Change No. 1 made by the manufacturer of the database in the text IUS N 6, 1989
This standard specifies a method for determining the electrical resistivity of sintered hard alloys.
The method consists in passing through the sample constant electric current and determining the voltage drop at a certain part of its length.
The standard fully complies ST SEV 3914−82.
(Changed edition, Rev. N 1).
1. SAMPLING METHOD
1.1. (Deleted, Rev. N 1).
1.2. For testing produce three samples.
1.3. (Deleted, Rev. N 1).
1.4. Samples for testing must have a minimum length of 60 mm. is allowed to use the samples with circular or rectangular cross-section. A sample with a circular cross section shall have a diameter of (6±0,2) mm, with rectangular — section dimensions (6x8) mm, with a maximum deviation of ±0.2 mm.
1.5. The surface layer of the sample should be removed to a depth of not less than 0.1 mm. the surface Roughness should be not more than 1.5 µm. On the surface of the specimen before the test should not be cracking or visible defects of the structure.
2. EQUIPMENT
To determine the specific electrical resistance is used the installation diagram is shown in the drawing.
1 — set of sample resistances of class 0.01 (reference); 2 — investigated resistance; 3 — galvanometer sensitivity about 1·10A/div.; 4 — the normal Weston element; 5 — a constant current source; 6 — rheostat; 7 — potentiometer DC or bridge Thomson; 8 — rheostat; 9 — DC source; 10 — a DC ammeter of class 0.5.
Fixture design for sample mounting and attachment of current supply contacts and strain relief shall provide:
sharp knife contacts the surface to relieve stress;
close contact between the sample and contacts for current supply and relieve tension;
minimum transitional electrical resistance between the terminals to relieve stress and the sample;
measure the distance between the contacts to ease tension, which should be at least 15 mm;
in the measurement of electrical resistivity of tungsten carbide are recommended contacts for stress relief carbide 92% WC +8% co, while the measurement of electrical resistivity of titanium-tungsten alloy contact alloy 5% TiC +10% Co +85% WC.
Device type]-1 to measure the diameter and cross sectional area of the sample according to GOST 24703−81 or other device to ensure the specified accuracy.
Caliper according to GOST 427−75 or other device to ensure the specified accuracy.
(Changed edition, Rev. N 1).
3. PREPARING FOR THE TEST
3.1. Measure the distance between the contacts to remove the voltage error of less than 0.1 mm.
3.2. Measure the diameter or cross section of the specimen. This should be done at least three measurements on different parts of the estimated length of the specimen to obtain the average value of the diameter or cross-section.
4. TESTING
4.1. The test is performed at a temperature of (293±5) K (20±5) °C.
4.2. The sample is installed in the fixture and pressed against him contacts for current supply and relieve tension. Through the sample electric current of a certain strength, and a potentiometer measured the voltage drop on a reference resistance to determine the exact value of the current flowing through the sample. Then measure the voltage drop between the contacts. To eliminate the parasitic electromotive forces change the direction of current through the sample on the opposite and again measure the voltage drop between the contacts. For each sample spend not less than six measurements (three in one direction, three the opposite). Measurements should be made at a value of the current to avoid heating of the sample. The recommended amount of surge current 1 A.
5. PROCESSING OF THE RESULTS
5.1. Electrical resistivity ,
Ohm·cm is calculated according to the formula
where — the voltage drop between the contacts;
the amount of current flowing through the sample And;
the cross — sectional area of the specimen, mm
;
— the distance between the contacts, mm.
5.2. For the value of the resistivity taking the arithmetic average of the six measurements, rounded to the nearest 0.1 Ohm·cm (1
Ω·m).
