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Detection principle and application method of quantitative polarization stress meter

  • Source: Unknown
  • Date: October 27, 2020
  • Number of views: two hundred and eighty-four
Glass stress control is an extremely important link in glass production process. The method of applying appropriate heat treatment to control stress has been well known by glass technicians. However, how to accurately measure the glass stress is still one of the difficult problems for most glass manufacturers and technicians. The traditional empirical estimation has become increasingly inadequate to meet the requirements of today's society for the quality of glass products. Today, Dongyi Seiko introduces the commonly used stress measurement methods in detail, hoping to help and inspire everyone.
 
1、 Theoretical basis of stress detection
 
1.1 Polarized light
 
As we all know, light is an electromagnetic wave, its vibration direction is perpendicular to the direction of travel, and it vibrates on all vibration surfaces perpendicular to the direction of travel. If a polarizing filter is introduced into the optical path, which only allows light in a certain vibration direction to pass through, polarized light can be obtained, referred to as polarized light. The optical equipment made according to the optical characteristics is a polarizer (polarization stress detection instrument).
 
1.2 Birefringence
 
Glass is an isotropic body with the same refractive index in all directions. If there is stress in the glass, the isotropic property will be destroyed, causing the change of refractive index. The refractive index of the two principal stress directions is no longer the same, which leads to birefringence.
 
1.3 Optical path difference
 
When polarized light passes through a stressed glass with thickness t, the light vector will split into two components that vibrate in the x and y stress directions respectively. If vx and vy are the speeds of the two vector components respectively, the time required to penetrate the glass is t/vx and t/vy respectively. If the two components are no longer synchronized, there is an optical path difference δ
 
 
2、 Main technical data
1. Measurement accuracy ± 4nm
2. Diameter of polarizer φ 150mm
3. Workbench rotation angle 0-360 °
4. Wavelength of full wave plate: 565nm
5. Check the polarizer scale 2 °
6. Instrument weight 23Kg
7. The overall dimension of the instrument is 450mm long * 470mm wide * 700mm high
 
 
3、 Detection principle
（1） Qualitative measurement principle: the working principle of this instrument is polarized light interferometry. Since it is equipped with a full wave plate, this instrument can not only measure the internal stress value of glass qualitatively or semi quantitatively according to the interference color sequence in the polarization field. The relationship between interference color and optical path difference is shown in Table (I)
（2） Principle of quantitative measurement
The sodium light emitted by the light source will become linearly polarized light after passing through the polarizer. When the linearly polarized light passes through the tested sample and 1/4 wave plate with birefringence optical path difference, its vibration direction will rotate by an angle. The value of angle Q (in degrees) is the birefringence optical path difference of the tested sample δ Is proportional to its relationship λ Take sodium light as 589.3 δ 589.3Q/180=3.27Q, when Q=1 °, δ= 3.27nm (each degree is equivalent to 3.27nm)
 
 
4、 Usage
（1） Qualitative measurement
(1) Turn on the power and push the toggle switch to the qualitative measurement gear (structure diagram 5)
(2) Rotate the polarizer hand wheel (structural drawing 1) to the zero scale
(3) Push up and down the pull rod, push up and pull out the pull rod (structure figure 4), push down the pull rod (structure figure 5) to put the full wave plate into the light path, and the color of the field of view is purplish red,
(4) Put the test piece into the field of view of the interference field, observe the surface of the tested piece through the polarizer, and qualitatively judge the annealing quality (the quality of the test piece) according to the interference color. If the color of the field of view is basically unchanged after the test piece is put into the optical path and rotated, it is still purplish red or only slightly changed (from dark red to purplish red), indicating that the quality of the rejection is good. If some parts of the test piece are rotated, The interference color changes greatly (such as green
Or yellow) indicates poor annealing quality.
（2） Quantitative measurement
(1) Connect the power supply, push the toggle switch to the quantitative measurement gear (structural drawing 9),
(2) Rotate the galvanometer hand wheel (structural drawing 1) to the zero scale.
(3) Push the pull rod up and down, push the pull rod up (structural drawing 4), push the pull rod down and pull out (structural drawing 5), so that the 1/4 wave plate is placed in the optical path, and the field of view is dark
(4) Put the tested sample on the workbench and rotate the test piece. If the tested piece rotates more than 45 ° and is still in the dark field, it is stress free. If a shiny part appears on the rotating test piece, it means that the tested piece has stress. The bright part of zui means that the stress zui is large. The tested part in the rotating field of view (namely the bright part of zui) becomes a dark field of view. Then rotate the stage 45 ° and rotate the hand wheel of the polarizer (structure drawing 1) to make the tested part (bright part) of the test piece in the field of view The value of the polarization dial of the darkening field readout detector is degrees and then multiplied by 3.27, which is the stress of the measured piece. The unit of stress angle is nm (nanometer). Each degree is equivalent to the optical path difference of 3.27nm. The path difference per unit thickness can be calculated by measuring the thickness of the measured piece.
 
 
The above is the report of Shenzhen Dongyi Precision Equipment Co., Ltd. on "quantitative polarization" Stress meter Test principle and usage ". Glass stress detection is very important in glass quality detection. Shenzhen Dongyi Seiko Equipment Co., Ltd. specializes in the supply of stress testers, glass stress testers, Japanese original stress testers, fsm-6000le surface stress testers and other stress detection equipment, and provides professional laboratory solutions and equipment support services. Consulting hotline: 400-992-8117

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