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GB/T 13448-2019 PDF in English


GB/T 13448-2019 (GB/T13448-2019, GBT 13448-2019, GBT13448-2019)
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GB/T 13448-2019: PDF in English (GBT 13448-2019)

GB/T 13448-2019
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 77.060
H 25
Replacing GB/T 13448-2006
Test methods for prepainted steel sheet and strip
ISSUED ON: MARCH 25, 2019
IMPLEMENTED ON: FEBRUARY 01, 2020
Issued by: State Administration for Market Regulation;
Standardization Administration of the People's Republic of
China.
Table of Contents
Foreword ... 4
1 Scope ... 7
2 Normative references ... 7
3 Terms and definitions ... 7
4 Coating thickness determination ... 9
5 Specular gloss determination ... 15
6 Chromatic aberration determination ... 17
7 Bending test ... 19
8 Reverse impact test ... 22
9 Pencil hardness test ... 24
10 Organic solvent resistance test ... 26
11 Abrasion resistance test ... 29
12 Scratch resistance test ... 31
13 Cross-cut test ... 33
14 Cupping test ... 35
15 Surface resistivity test ... 37
16 Coating contact angle test ... 38
17 Water immersion test ... 40
18 Acid and alkali resistance test ... 42
19 Contamination resistance test ... 44
20 Carbon black contamination test ... 47
21 Neutral salt spray test ... 48
22 Dry heat resistance test ... 51
23 Damp heat resistance test ... 54
24 Cyclic corrosion test ... 56
25 Xenon accelerated aging test ... 59
26 UV lamp accelerated aging test ... 62
27 Atmospheric exposure test ... 65
Annex A (normative) Prepainted sheets’ coating peeling method and plating
thickness measuring method ... 69
Annex B (informative) Knoop hardness range of Zhonghua 505 coil steel
coating hardness test pencils and its corresponding relationship with Knoop
hardness of Zhonghua 101 drawing pencils ... 70
Foreword
This Standard is drafted in accordance with the rules given in GB/T 1.1-2009.
This Standard replaces GB/T 13448-2006 “Test methods for prepainted steel
sheet”. Compared with GB/T 13448-2006, main technical changes are as
follows:
- MODIFY 3 different measurement positions in the magnetic thickness
gauge method to 5 different measurement positions (see 4.5.1.2 of this
Standard, 4.5.1 of the 2006 edition);
- ADD the magnetic-eddy current thickness gauge method (see 4.5.5 of this
Standard);
- ADD the unit expression of specular gloss; ADD the provisions for the
accuracy verification of gloss meters; MODIFY the description of the
measurement angle of gloss meters (see Clause 5 of this Standard, Clause
5 of the 2006 edition);
- MODIFY the principle for determining the chromatic aberration by
colorimeter and the equipment requirements for colorimeter, and the
description of the colorimeter calibration sheet/sample; MODIFY the
chromatic aberration calculation formula (see Clause 6 of this Standard,
Clause 6 of the 2006 edition);
- In the bending test, CANCEL the provisions for the magnification factor of
magnifying glass; ADD the 90° bending test; ADD the description of
observing the cracking by magnifying glass (see Clause 7 of this Standard,
Clause 7 of the 2006 edition);
- In the reverse impact test, ADD the description of 12.7 mm punch diameter;
CANCEL the provisions for the magnification factor of magnifying glass;
ADD the description of observing the cracking by magnifying glass;
CANCEL the description of observing the cracking by copper sulfate; ADD
the content of result expression and the negotiated content in the test report
(see Clause 8, Clause 8 of the 2006 edition);
- In the clause of organic solvent resistance test, ADD the description of the
hygroscopicity of cotton cloth or cotton wool; ADD the description of the test
procedure such as “The test process shall be continuous. If the reagent
needs to be replenished, the interruption of the test process shall not
exceed 10 s”. (See Clause 10 of this Standard, Clause 10 of the 2006
edition);
Test methods for prepainted steel sheet and strip
1 Scope
This Standard specifies terms and definitions of prepainted steel sheets and
steel strips, as well as related test methods, test reports, etc.
This Standard is applicable to the determination and evaluation of the coating
properties of prepainted steel sheets and strips (hereinafter referred to as
prepainted sheets).
2 Normative references
The following referenced documents are indispensable for the application of
this document. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any
amendments) applies.
GB/T 1410 Methods of test for volume resistivity and surface resistivity of
solid electrical insulating materials
GB/T 1766 Paints and varnishes - Rating schemes of degradation of coats
GB/T 1839 Test method for gravimetric determination of the mass per unit
area of galvanized coatings on steel products
GB/T 10125 Corrosion tests in artificial atmospheres - Salt spray tests
GB/T 12754 Prepainted steel sheet
GB/T 30693 Measurement of water-contact angle of plastic films
3 Terms and definitions
For the purpose of this document, the terms and definitions defined in GB/T
12754 and the following apply.
3.1
specular gloss
Relative luminous reflectance factor of the sample in the direction of specular
When the sample holder is not full of samples, a plate of the same size as the
sample used to cover the sample holder space in order to prevent light leakage.
4 Coating thickness determination
4.1 General
4.1.1 This method is applicable to the determination of the coating thickness of
prepainted sheets.
4.1.2 The following methods can be used to determine the coating thickness of
prepainted sheets:
a) Magnetic thickness gauge method: It is applicable to the determination of
the coating thickness of the prepainted sheets with cold rolled plate and
galvanized plate as the steel substrate. This method is not applicable if
the coating thickness is less than 3 μm. This method is not applicable if
the coating is a special uneven surface effect.
b) Micrometer method: It is applicable to the determination of the coating
thickness of the prepainted sheets with various materials as the steel
substrate. This method is not applicable for coatings that are easily
deformed under the load of the micrometer measuring device. This
method is not applicable if the coating is a special uneven surface effect.
c) Metallographic microscope method: It is applicable to the determination of
the coating thickness of the prepainted sheets with various materials as
the steel substrate.
d) Drilling damage microscopic observation method: It is applicable to the
determination of the coating thickness of the prepainted sheets with
various materials as the steel substrate. When the interface of each
coating can be clearly distinguished, it can also be applied to the
determination of the thickness of each coating (primary coating, fine
coating).
e) Magnetic-eddy current thickness gauge method: It is applicable to the
determination of the coating thickness of the prepainted sheets with
various materials as the steel substrate. This method is not applicable if
the coating is a special uneven surface effect.
4.2 Principle
4.2.1 Magnetic thickness gauge method
Using the principle of electromagnetic field magnetoresistance, the coating
4.3.3.1 The measurement accuracy of the instrument shall be better than 2 μm.
4.3.3.2 Metallic sandpaper of the appropriate grade.
4.3.3.3 The material used for fixing the sample (such as resin) shall have no
damage to the coating and its color is clearly different from the coating.
4.3.4 Drilling destructive micrometer thickness gauge
4.3.4.1 The measurement accuracy of the instrument shall be better than 10 %
of the coating thickness.
4.3.4.2 Micrometer thickness gauge, which consists mainly of an automatic
drilling device and a microscopic video imaging system.
4.3.5 Magnetic-eddy current thickness gauge
4.3.5.1 The instrument’s maximum indication error is ± (1 + 3 % standard
thickness) μm.
4.3.5.2 Standard sheets of known thickness (non-magnetic films), which shall
be of similar thickness to the coating to be tested.
4.4 Sample preparation and test environment
4.4.1 The sample size is not less than 75 mm × 150 mm. The surface of the
sample shall be flat, no oil, no damage, and no burrs on the edges.
4.4.2 The test is carried out in a laboratory environment. In case of dispute, the
sample to be tested shall be placed in an environment with a temperature of
23 °C ± 2 °C and a relative humidity of 50 % ± 5 % for at least 24 h before test.
4.5 Test procedure
4.5.1 Magnetic thickness gauge method
4.5.1.1 Instrument calibration
4.5.1.1.1 USE the uncoated steel substrate of which the chemical composition
and thickness are the same as those of the sample to be tested AS the zero-
adjusting plate. ZERO the instrument at several different positions on the
surface. When the steel substrate is a galvanized plate, it shall be zeroed on
the steel substrate on which the zinc layer is removed, and the zero error shall
not be greater than 1 μm.
4.5.1.1.2 SELECT the standard sheet of which the thickness is close to that of
the measured coating to calibrate the instrument, to make it accurately indicate
the thickness of the standard sheet. REPEAT the zeroing and calibration
4.5.4.1 PLACE the sample on the drilling table; ADJUST the drilling depth
control wheel of the automatic drilling device so that the drill bit just penetrates
the steel substrate and a circular shallow angle shrinkage hole is drilled in 2
different parts of the sample.
4.5.4.2 PLACE the sample on the measuring table; ADJUST the micro video
image system so that the interface of the coating at the shrinkage hole can be
clearly imaged on the video. The thickness of each coating can be read directly
using the scale of the micro video system.
4.5.5 Magnetic-eddy current thickness gauge method
4.5.5.1 Instrument calibration and accuracy verification
4.5.5.1.1 The equipment may be calibrated by the equipment supplier using the
thickness standard sheet before leaving the factory; or it may be calibrated by
the equipment user using the thickness standard sheet according to the
specifications of equipment instructions.
4.5.5.1.2 USE a thickness standard sheet or a self-made standard sheet of
known coating thickness to verify the accuracy of the calibrated instrument. The
accuracy of the verification test and the frequency of the test can be determined
according to actual needs. When developing the accuracy requirements for
verification tests, the accuracy of the equipment and standard sheets shall be
considered. The unit of the thickness standard sheets for equipment calibration
using this method is micrometer (μm). It may use the plating thickness standard
sheets prepared by the method of Annex A, and the plating mass (g/m2) is into
thickness (μm).
4.5.5.2 Determination
4.5.5.2.1 MEASURE at least 5 different positions with a distance greater than
25 mm from the edge of the sample. In order to improve the representativeness
of the measurement results, the number of measurements can be appropriately
increased.
4.5.5.2.2 The accuracy of this method for determining the coating thickness of
prepainted sheets is affected by the following factors:
a) Bending of the sample: It shall ensure that the sample to be tested is flat
without bending.
b) Foreign particles: It shall ensure that the surface of the sample and the
surface of the probe are clean. It shall prevent foreign particles from
affecting the test results.
c) External magnetic field: The measurement result of the magnetic probe is
measured surface is the coating thickness of the sample, expressed in
micrometers (μm).
4.7 Test report
The test report shall include the following:
a) the test standard and negotiation terms adopted;
b) instrument model;
c) sample information;
d) test results;
e) test date and test personnel.
5 Specular gloss determination
5.1 General
The method is applicable to the determination of specular gloss of the coating
of prepainted sheets.
5.2 Principle
The specular gloss of the sample can be measured by determining the relative
luminous reflectance factor of the coating. The unit of measurement is GU.
5.3 Test equipment and materials
5.3.1 60° gloss meter or multi-angle gloss meter. The equipment’s
measurement indication error is not more than 1.0 GU.
5.3.2 Calibration plate: It is usually the polished glass plate or ceramic plate
that comes with the instrument for instrument calibration.
5.4 Sample preparation and test environment
5.4.1 The sample size is not less than 75 mm × 150 mm. The sample shall be
flat, no oil, no damage, and no burrs on the edges.
5.4.2 The test is carried out in a laboratory environment. In case of dispute, the
test sample shall be placed in an environment with a temperature of 23 °C ±
2 °C and a relative humidity of 50 % ± 5 % for at least 24 h before test.
5.5 Test procedure
6 Chromatic aberration determination
6.1 General
The method is applicable to the determination of chromatic aberration of
prepainted sheets.
6.2 Principle
MEASURE the spectral data of the reference sample and the sample by the
colorimeter under the International Lighting Association (CIE) standard light
source and standard observation conditions, USE the CIE color system to
calculate the tristimulus values of the reference sample and the sample, and
USE the selected chromaticity coordinates to calculate the chromatic aberration
results of the sample and the reference sample.
6.3 Test equipment and materials
6.3.1 Colorimeter
6.3.1.1 The geometry of colorimeter is usually divided into two types: directional
type and integrating sphere type. The geometry of directional type is usually
divided into 45°/0°, 0°/45° and multi-angle colorimeters. The geometry of
integrating sphere type is usually divided into d/8° and 8°/d.
6.3.1.2 The colorimeter shall be capable of measuring the spectral data of the
sample in the range of 400 nm to 700 nm under the CIE standard light source
and standard observation conditions. Due to different geometric mechanisms,
standard light sources, standard chromatic observers, color systems,
chromaticity coordinates for calculation, and detection areas of the colorimeter,
the measured chromatic aberration values are different. The geometry of the
colorimeter is related to the equipment selection. Once the geometry of the
colorimeter is selected, it cannot be changed. The test parameters such as
standard light source, standard chromatic observer, color system, and
chromaticity coordinates for calculation can be switched by the data processing
system of the colorimeter.
6.3.2 Colorimeter calibration sheet/sample
Provided by the colorimeter supplier.
6.3.3 Reference sample
A standard swatch approved by both the supply and demand parties. The
reference sample shall be stored in a dark and laboratory environment to avoid
large changes in color that may affect the determination results.
180° bending: The sample is bent 180° around itself to determine whether the
coating has peeled off or cracked, to determine the minimum thickness multiple
value of the sample that does not cause the coating to peel off or crack.
90° bending: The sample is bent 90° around itself to determine whether the
coating has peeled off or cracked.
7.3 Test equipment and materials
7.3.1 Bending test machine: It is able to bend the sample at an acute angle.
7.3.2 Flattening machine or vise: It is used to flatten the sample.
7.3.3 Scotch tape: The width is approximately 25 mm and the bond strength is
(10 ± 1) N/25 mm wide. Tapes agreed upon between the supply and demand
parties can also be used.
7.3.4 Magnifying glass: The magnification factor is determined by negotiation
between the supply and demand parties. It is generally 5 times to 10 times
magnifying glass.
7.4 Sample preparation and test environment
7.4.1 The sample size is that the width is not less than 100 mm and the length
is about twice the width. The sample shall be flat, no oil, no damage, and no
burrs on the edges.
7.4.2 The test is carried out in a laboratory environment. In case of dispute, the
sample to be tested shall be placed in an environment with a temperature of
23 °C ± 2 °C and a relative humidity of 50 % ± 5 % for at least 24 h before test.
7.5 Test procedure
7.5.1 180° bending
7.5.1.1 INSERT one end of the sample into the bending test machine for about
10 mm, PRESS the sample tightly, TURN the handle to bend the sample to an
acute angle. Then TAKE OUT the sample and INSERT it into the flattening
machine, PRESS the bent portion of the sample, that is the “0T” bent (see
Figure 1).
7.5.1.2 APPLY scotch tape along the bent surface, REMOVE the air bubbles
while flattening the tape, and then quickly PEEL OFF the tape in a 60° direction
along the bent surface, CHECK for any peeling coating on the tape. It may also
check whether the coating of the bent portion is cracked by visual inspection or
magnifying glass.
a) the test standard and negotiation terms adopted;
b) instrument model;
c) sample information;
d) description of whether it is 180° bending or 90° bending, and whether the
determination method is tape peeling or observing cracking;
e) test results;
f) test date and test personnel.
8 Reverse impact test
8.1 General
This method is applicable to the evaluation of the ability of the coating to resist
peeling off or cracking when the prepainted sheet is subjected to rapid
deformation.
8.2 Principle
ALLOW the free-falling weight to impact the sample, to deform the sample
quickly and form a convex area. CHECK whether the coating in the convex area
is peeled off or cracked, thereby evaluating the ability of the coating to resist
peeling off or cracking.
8.3 Test equipment and materials
8.3.1 Impact tester: It usually consists of a pedestal, a vertical duct, a weight
and a hemispherical punch at the end. The diameter of the punch is 12.7 mm
or 15.9 mm or other diameters. It usually uses the punch of which the dimeter
is 15.9 mm.
8.3.2 Scotch tape: The width is approximately 25 mm and the bond strength is
(10 ± 1) N/25 mm wide. Tapes agreed upon between the supply and demand
parties can also be used.
8.3.3 Magnifying glass: The magnification is determined by negotiation
between the supply and demand parties. It is generally 5 times to 10 times
magnifying glass.
8.4 Sample preparation and test environment
8.4.1 The sample size shall not be less than 75 mm × 150 mm. The sample
shall be flat, no oil, no damage, and no burrs on the edges.
expressed as whether the coating of the sample is peeled off or cracked under
the specified impact absorption energy test.
8.6.2 In the determination of the maximum impact absorption energy at which
the coating does not peel off or crack, the result shall be expressed as the
product of height and mass of the weight (J).
8.6.3 Specified impact energy absorption test or the maximum impact energy
absorption test, the test condition parameters (punch diameter, amount of
impact absorption energy, evaluation result of coating peeling or cracking).
8.7 Test report
The test report shall include the following:
a) the test standard adopted and the agreed test condition parameters;
b) instrument model, punch diameter (mm);
c) sample information;
d) test results;
e) impact absorption energy;
f) test date and test personnel.
9 Pencil hardness test
9.1 General
This method is applicable to determination of pencil hardness of the coating of
prepainted sheets.
This method specifies two test methods: manual pencil method and instrument
pencil method.
9.2 Principle
Use a set of pencils of known hardness to determine the relative hardness of
the coating surface of prepainted sheets.
9.3 Test equipment and materials
9.3.1 A set of verified wooden pencils or moving pencils, labeled 6H, 5H, 4H,
3H, 2H, H, F, HB, B, 2B, 3B, 4B, 5B, 6B, among which 6H is the hardest, 6B is
the softest, with a decreasing hardness from 6H to 6B. In general,
9.5.1.3 Starting with the hardest pencil, use each grade of pencil to draw 5
times. If the coating can be plowed twice in 5 times, use a softer pencil until it
finds a pencil that cannot plow the coating at least 4 times out of 5 times. The
hardness of the pencil is the pencil hardness of the coating to be tested.
9.5.2 Instrument pencil method
9.5.2.1 PLACE the sample horizontally on the operating table. PLACE the
mechanical trolley for pencil marking on the sample.
9.5.2.2 FIX the pencil that has been processed in accordance with the
procedure of 9.5.1.1 into the mechanical trolley so that the tip of the pencil can
be freely contacted with the surface of the sample. PUSH the mechanical trolley
so that the stroke on the sample is 6.5 mm.
9.5.2.3 CARRY OUT the mechanical trolley test with pencils of different
hardness according to the procedure of 9.5.1.3 until the hardest pencil that
cannot plow the coating at least 4 times out of 5 times is found. The hardness
of the pencil is the pencil hardness of the coating to be tested.
9.6 Expression of results
The hardest pencil hardness by which the coating cannot be plowed at least 4
times out of 5 times is taken as the pencil hardness of the coating to be tested.
9.7 Test report
The test report shall include the following:
a) the test standard and negotiation terms adopted;
b) grade and manufacturer of the test pencil;
c) sample information;
d) test results (indicate whether the manual pencil method or the instrument
pencil method is used);
e) test date and test personnel.
10 Organic solvent resistance test
10.1 General
This method is applicable to the evaluation of organic solvent resistance of the
coating of prepainted sheets.
the edge of the sample to avoid wetting the edges.
10.5.1.3 KEEP the cotton cloth moist during the test.
10.5.1.4 WIPE continuously until the coating is damaged and record the
number of wiping times or WIPE continuously to the specified number of times
to observe if the coating is damaged. The coating damage at both ends of the
wiping area is not counted. The test area in the middle with a length of 125 mm
is used as the evaluation area. The test process shall be continuous. If the
reagent needs to be replenished, the interruption of the test process shall not
exceed 10 s.
10.5.1.5 USE a new cotton cloth every time when test a new sample.
10.5.2 Instrument method
10.5.2.1 WRAP the entire contact area of the artificial finger with a certain
thickness of cotton cloth or cotton wool. Completely SOAK the cotton cloth or
cotton wool with the specified solvent by immersion or dropping. PLACE the
artificial fingertip on the surface of the sample, leaving the edge of the sample
well to avoid wetting the edges.
10.5.2.2 MOVE the fingertip by the specified number of wiping times at a speed
of one back and forth per second. The motion shall be continuous.
10.5.2.3 The absorbent cotton shall be kept moist during the test.
10.5.2.4 After the test of the specified number of wiping times, observe whether
the coating is damaged. The coating damage at both ends of the wiping area
is not counted. The test process shall be continuous. If the reagent needs to be
replenished, the interruption of the test process shall not exceed 10 s.
10.6 Expression of results
10.6.1 Manual method: It is indicated by-pass or fail under the specified number
of wiping times, or record the number of wiping times when the coating is
damaged.
10.6.2 Instrument method: It is indicated by-pass or fail under the specified
number of wiping times.
10.7 Test report
The test report shall include the following:
a) the test standard and negotiation terms adopted;
b) instrument model, solvent used;
± 5 % for at least 24 h before test.
11.5 Test procedure
11.5.1 USE the analytical balance to accurately determine the mass of each
sample, weigh to the nearest 0.1 mg.
11.5.2 PLACE the sample on the sample sheet holder with the surface to be
tested facing up; FIX it with screws. MOUNT a pair of ground abrasion wheels
on the two arms of the abrasion tester. The additional mass is such that the
total load of the arms is typically 500 g or 1000 g. PLACE the arms on the
sample; TURN ON the abrasion tester. The abrasion wheel speed is generally
60 r/min and the maximum is 100 r/min.
11.5.3 Test to the specified number of abrasion revolutions or until the steel
substrate is exposed. The vacuum cleaner shall continuously absorb the debris
from the surface of the sample during the operation of the abrasion tester.
11.5.4 REMOVE the sample, CLEAN it and USE the analytical balance to
accurately determine the mass of the sample after the abrasion resistance test.
11.5.5 After the abrasion wheel has been rotated 500 times to 1000 times or
before the new abrasion wheel is used, the abrasion wheel is ground with 25 to
50 revolutions using S-11 grinding disc sandpaper.
11.6 Expression of results
The result is expressed by the mass loss of the sample after the specified
number of abrasion revolutions (the difference in mass before and after the test),
in milligrams (mg), or by the number of abrasion revolutions after which the
steel substrate is exposed. The arithmetic mean of the test results of two
parallel samples is taken as the test result.
11.7 Test report
The test report shall include the following:
a) the test standard and negotiation terms adopted;
b) instrument model;
c) total load and abrasion revolutions;
d) sample information;
e) test results;
f) test date and test personnel.
scratches the topcoat, it indicates that the sample has failed the scratch
resistance test under the load; if the steel needle does not scratch the coating
to the steel substrate or scratch the topcoat, it indicates that the sample passed
the scratch resistance test under the load.
12.5.1.3 DETERMINE on three different parts of the sample surface; RECORD
the test results separately.
12.5.2 Test for determining the maximum load under which the coating is
scratched
12.5.2.1 According to the procedure of 12.5.1, repeat the test by gradually
reducing or increasing the mass of the weight until it finds the maximum mass
of the weight under which the coating is not scratched to the steel substrate or
the topcoat is not scratched. According to the load, the interval of reducing or
increasing the weight each time may be 100 g, 200 g or 300 g. Both the supply
and demand parties shall negotiate whether to reduce the weight or increase
the weight for test before the test.
12.5.2.2 DETERMINE on three different parts of the sample surface.
12.6 Expression of results
12.6.1 Judge whether the test is passed/failed under fixed load
If the sample passes at least two of the three tests, it is determined passing the
scratch resistance test under the fixed load.
12.6.2 Test for determining the maximum load under which the coating is
scratched
The arithmetic mean of the maximum weight of the three different measurement
positions, which is the maximum load under which the coating is scratched,
expressed in grams (g).
12.7 Test report
The test report shall include the following:
a) the test standard and negotiation terms adopted;
b) instrument model, steel needle material, load of the scratch tester;
c) sample information;
d) test results;
e) test date and test personnel.
d) test results;
e) test date and test personnel.
14 Cupping test
14.1 General
This method is applicable to the evaluation of the ability of the coating to resist
peeling off or cracking when the prepainted sheet is subjected to slow
deformation.
14.2 Principle
The punch of the cupping test machine is ejected from the back of the sample
at a constant speed to a specified height, and observe whether the coating is
cracked or peeled off from the steel substrate to evaluate the ability of the
coating to resist cracking or peeling off; or the punch is ejected from the back
of the cross-cut portion of the sample at a constant speed to a specified depth,
and peel off the scotch tape attached to the cross-cut portion, then evaluate the
cross-cut adhesion of the coating after gradual deformation by the shedding
area of the coating.
14.3 Test equipment and materials
14.3.1 Cupping test machine: It consists of a die of which the surface is
quenched and the surfac......
 
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