GB/T 30020-2023 PDF English (GB/T 30020-2013: Older version)
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Test method for determining defects of glass - Photo elastic scanning method
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GB/T 30020-2023: PDF in English (GBT 30020-2023) GB/T 30020-2023
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 81.040.10
CCS Q 30
Replacing GB/T 30020-2013
Test Method for Determining Defects of Glass - Photoelastic
Scanning Method
ISSUED ON: MARCH 17, 2023
IMPLEMENTED ON: OCTOBER 1, 2023
Issued by: State Administration for Market Regulation;
Standardization Administration of the People’s Republic of China.
Table of Contents
Foreword ... 3
1 Scope ... 5
2 Normative References ... 5
3 Terms and Definitions ... 5
4 Testing Principle ... 6
5 Testing Devices ... 6
6 Testing Steps ... 8
7 Testing Records ... 9
8 Testing Report ... 9
Appendix A (informative) Self-explosion Risk Assessment of Tempered Glass ... 11
Bibliography ... 13
Test Method for Determining Defects of Glass - Photoelastic
Scanning Method
1 Scope
This document describes the testing principle, devices, steps, records and reports of determining
glass defects through the photoelastic scanning method.
This document is applicable to the testing of defects that cause stress concentration in
transparent glass and its products, and provides a reference for assessing the possible self-
explosion risk of tempered glass in service.
2 Normative References
This document does not have normative references.
3 Terms and Definitions
The following terms and definitions are applicable to this document.
3.1 photoelastic scanning method
Photoelastic scanning method is a method of scanning the glass under test with polarized light
and determining the location of glass defects through the stress concentration spots.
3.2 tensile stress zone of tempered glass
Tensile stress zone of tempered glass refers to a zone distributed within the range of 0.2 h ~ 0.5
h from the upper and lower glass surfaces, and the tempering stress is the tensile stress in the
thickness direction of the tempered glass.
NOTE: h is the thickness of tempered glass.
3.3 compressive stress zone of tempered glass
Compressive stress zone of tempered glass refers to a zone distributed within the range of 0.2
h from the upper and lower glass surfaces, and the tempering stress is the compressive stress in
the thickness direction of the tempered glass.
5.4 Image Analysis System
It consists of a computer, buzzer and analysis software, and shall be able to automatically
identify the image with a sudden change of stress concentration light spot caused by defects
and send out an alarm.
5.5 Digital Magnifying Glass
The magnification shall be higher than 60 times, and the depth of field shall be larger than 12
mm. It shall be able to read and identify the color and size of defects on the glass surface and
inside the glass, and the depth from the glass surface and take pictures.
6 Testing Steps
6.1 Transmission-type Testing
The transmission-type testing is a testing method, in which, the polarized light vertically passes
through the glass from one side of the glass and reaches the analyzer on the other side. It is
applicable to the testing of single-piece and multi-layer composite glass and shall be carried out
in accordance with the following procedures:
a) Determine the cleanliness of the glass surface. If stains and dust on the glass surface
obviously affect the light transmission and transparency of the glass, the glass surface
shall be cleaned first, so as not to affect the test results;
b) Respectively place the polarizer and the analyzer of the transmission-type
photoelastic meter on the two sides of the glass under test and align them with each
other; turn on the plane light source, and the polarized light reaches the analyzer
through the glass;
c) Scan the glass under test. The mode of scanning movement can be hand-held or
mechanically carried equipment. The direction of scanning movement can be
horizontal or vertical. The speed of scanning movement is not higher than 50 mm/s;
d) The information image of the glass stress birefringence field during the scanning
process is collected by the industrial camera, and transmitted to the image analysis
system for automatic analysis and identification;
e) If the image analysis system does not issue an alarm, then, synchronously move the
polarizer and the analyzer to the next adjacent position for the next testing, until an
alarm signal appears;
f) Use the digital magnifying glass to further analyze the sudden change point of stress
concentration light spot corresponding to the alarm signal, so as to determine the color,
distribution depth (tensile stress zone of tempered glass or compressive stress zone of
tempered glass), type and size of the defect;
g) In accordance with the above-mentioned procedures, complete the scanning of the
entire area of the glass under test, and record the location of the glass containing
defects and the defect information;
h) When the on-site testing does not use or unconditionally uses the industrial camera to
collect the information image of the glass stress birefringence field during the
scanning process, conduct the identification with the naked eye.
6.2 Reflective Testing
The reflective testing is a testing method, in which, the polarized light is incident at an angle of
45 to the glass surface from one side, then, reflected by the glass surface to the analyzer on the
same side. It shall be carried out in accordance with the following procedures:
a) In accordance with the requirements of 6.1, clean the glass surface;
b) Place the reflective photoelastic meter on one side of the glass. If it is coated glass,
then, the reflective photoelastic meter shall be placed on the non-coated surface. If
there is interference light on the other side that affects the testing effect, a dark shading
cloth or shading plate shall be used to cover the other side; the testing can also be
performed at night, so as to avoid the impact of sunlight;
c) The scanning mode, image acquisition, analysis and identification, and defect
information recording of reflective testing shall comply with the requirements of 6.1.
7 Testing Records
In accordance with the testing results, provide the defect classification and location in the
scanned image, and count the number of point defects in the glass under test. In accordance
with the following method, classify and record the defects:
a) Heterogeneous particles: they can appear in different shapes. Record the shape, color,
depth from the surface (judge whether it is tensile stress zone of tempered glass or
compressive stress zone of tempered glass) and maximum size of the heterogeneous
particles. The colors can be divided into light color and dark color. In addition,
relevant information (sample name, specification, size and type) of the glass under
test also needs to be recorded.
b) Bubbles: they generally appear as a circle or ellipse. Record the maximum size of the
bubbles;
c) Other types of defects (such as: glass surface scratches, burns and bruises, etc.).
8 Testing Report
The testing report shall include:
Appendix A
(informative)
Self-explosion Risk Assessment of Tempered Glass
JG/T 455 specifies: strictly speaking, only the spontaneous explosion of tempered glass under
no load is called self-explosion of tempered glass. There are many factors that lead to the self-
explosion of tempered glass. The stress concentration caused by defects, such as: the phase
transformation expansion of nickel sulfide particles, bubbles and heterogeneous particles in the
glass are the main factors causing the self-explosion of tempered glass. The surface damages
(scratches, burns and bruises), poor processing on the edges, excessive tempering, uneven
tempering stress and excessively large sizes of tempered glass will increase the risk of self-
explosion. The inside and surface of tempered glass in engineering applications will inevitably
contain tiny defects. Since tempered glass is a product with internal stress, when the
superposition of the concentrated stress caused by internal defects and the tempering stress
exceeds the local strength of the glass, the self-explosion of the tempered glass can be triggered.
Through the photoelastic scanning method, detect the defects containing stress concentration
inside the tempered glass, and replace the tempered glass that is more prone to the self-
explosion risk or adopt other safety protection measures, which can reduce the probability of
safety accidents caused by the self-explosion of tempered glass.
The factors influencing the degree of self-explosion risk of tempered glass are related to the
type, size and distribution location of defects. In accordance with actual engineering statistics,
defects, such as: bubbles, light-colored heterogeneous particles and heterogeneous particles
distributed in the compressive stress zone of tempered glass cause less risk of self-explosion of
the tempered glass, while dark-colored heterogeneous particles distributed in the tensile stress
zone of tempered glass have a greater risk of self-explosion. In the actual testing process, it is
advisable to classify the self-explosion risk levels in terms of the defected defects in accordance
with the above-mentioned influencing factors and the following stipulations.
---Level au: not prone to self-explosion risk. For tempered glass that has no foreign
particles or bubbles inside the glass, and no scratches, burns and bruises on the surface,
the risk of self-explosion is extremely low.
---Level bu: the risk of self-explosion is relatively low. For tempered glass with bubbles
inside the glass, heterogeneous particles distributed in the compressive stress zone, and
scratches, burns and bruises on the surface, the risk of self-explosion is relatively low.
---Level cu: there is a certain risk of self-explosion. For single or multiple light-colored
heterogeneous particles distributed in the tensile stress zone inside the glass, there is a
certain risk of self-explosion.
---Level du: prone to self-explosion. For single or multiple dark-colored heterogeneous
particles distributed in the tensile stress zone inside the glass, there is a relatively high
......
Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.
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