Glass is typically an isotropic and homogeneous material, but when subjected to stress, it becomes anisotropic and exhibits birefringence. This phenomenon occurs because the stress alters the optical properties of the glass, causing light to split into two rays with different velocities. To measure this internal stress, a polarization stress meter is used to determine the optical path difference (OPD), which is then converted into a stress value per unit thickness. This method is essential for evaluating the structural integrity of glass products, especially in pharmaceutical applications where safety and quality are critical.
Glass bottles are widely used in various industries, including food, medicine, and cosmetics. In this article, we focus on the internal stress measurement of medicinal glass containers. Internal stress arises from external factors such as mechanical forces, temperature changes, or humidity, and it can cause deformation or even failure of the glass if not properly controlled. The internal stress is defined as the force per unit area within the material that resists these external influences. If the stress level is too high, it may lead to cracks, breakage, or even contamination of the contents, posing risks to both users and the product itself.
To ensure the quality and safety of medicinal glass containers, it is crucial to measure and control their internal stress. The testing process involves specialized equipment such as the YLY-02 polarized stress meter and the CHY-B glass bottle thickness gauge. These instruments allow for precise and accurate measurements of the optical path difference, which directly relates to the stress within the glass.
The YLY-02 polarized stress meter must meet several technical specifications. For example, the brightness of the light field should be at least 120 cd/m², and the polarization efficiency must be no less than 99%. It should also include a full-wave plate at 565 nm and a quarter-wave plate, along with an analyzer that can rotate up to 1° increments for accurate readings. These features ensure reliable and repeatable results during the testing process.
When conducting the test, the sample must be free from previous stress and allowed to stabilize in the lab for at least 30 minutes. During the procedure, gloves should be worn to avoid direct contact with the glass, which could introduce additional stress or contamination. The testing method varies depending on whether the glass is colorless or colored, but the general principle remains the same: using the polarization stress meter to observe and measure the birefringence caused by internal stress.
For colorless samples, the bottom and side walls are inspected separately. A quarter-wave plate is used to create a dark field, and the analyzer is rotated to identify stress points. When the stress is low, the dark cross appears blurred, and as the analyzer rotates, distinct colors like blue-gray and brown emerge, indicating the stress intensity. For colored samples, the process is similar, but special attention is needed due to reduced visibility. In such cases, the average method can be used to determine the endpoint more accurately.
Once the angle of rotation (θ) is recorded, the stress value (δ) can be calculated using the formula: δ = T / t = θ × 3.14 / t, where T is the optical path difference, t is the thickness, and 3.14 is a constant based on the wavelength of the light source.
By applying these methods, manufacturers can effectively monitor and control the internal stress of their glass products. If excessive stress is detected, corrective actions can be taken to improve the quality and safety of the final product. We strongly encourage all relevant companies and professionals to prioritize quality and safety in their production processes.
The YLY-02 polarized stress meter and CHY-B thickness gauge, produced by Jinan Sanquan Zhongshi Experimental Instrument Co., Ltd., have been widely adopted in pharmaceutical packaging facilities. We look forward to engaging in more technical discussions and collaborations with industry peers to further enhance standards and practices.
For more information, please contact Chen Meiru at 0531-6781 3036 or 156 6677 5359. Visit http://news.chinawj.com.cn for updates and news. Editor: Hardware Business Network Information Center.
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