Knowledge of internal stress in pharmaceutical glass bottles

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Knowledge of internal stress in pharmaceutical glass bottles

Knowledge of internal stress in pharmaceutical glass bottles


Pharmaceutical glass material is one of the earliest materials used in pharmaceutical packaging in China, which is characterized by brightness, transparency, easy disinfection, corrosion resistance , high temperature resistance and good sealing performance . Currently, it is still the preferred packaging material for common infusion , antibiotic powder , freeze-drying preparation , vaccine , blood and biological preparation . The main products are controlled white and brown bottles and molded brown medical glass bottles, with capacities ranging from small 1ml bottles to large 500ml bottles .


During the production and processing of medicinal glass bottles, residual stress inevitably exists.  Internal stress is a very important physical property that affects the quality of glass. Its existence will reduce the mechanical strength and thermal stability of glass,  so when the internal stress of medicinal glass bottle is large or exceeds the allowable value, it may break in the process of transportation , high temperature sterilization, medicine filling and storage .


The internal stress in the bottle is mainly determined by the annealing process in production. When the annealing process is incorrect and unstable, the annealing quality cannot be guaranteed. After annealing treatment, more or less will also exist. If the internal stress is controlled within a certain range, so that it is not concentrated in one place, then we think it is safe.


Annealing treatment is an essential stage in the production of pharmaceutical glass bottles. It is a heat treatment process to eliminate or reduce the residual stress in glass to the allowable value, so as to ensure the probability of self-explosion of glass products during production, transportation and storage, so as to play a good role in protecting drugs and liquid medicines. Due to the characteristics of glass itself determines its poor thermal conductivity, resulting in the glass in the process of annealing because of the temperature difference there must be stress. The residual stress is reduced or homogenized to a minimum by annealing to enhance the mechanical strength and thermal stability of the glass. This annealing is a heat treatment process in which the thermal stress present in the glass is eliminated or reduced to the allowable value as much as possible.


The annealing process includes four stages: heating, heat preservation, slow cooling and fast cooling. The holding time should be controlled accurately according to the thickness of the wall. In the slow cooling phase, the cooling rate should be strictly controlled to avoid new stresses.


In the production line, we usually use a simple qualitative stress meter to detect the stress in the glass bottle. However, this method can only be used to roughly test whether internal stress exists in the glass container, or the approximate range of stress. Can't test accurately. It is generally stipulated that the internal stress should be less than 40nm/mm in the national standards for pharmaceutical packaging materials. In order to detect the specific data, it is necessary to use a precise polarization stress meter to make accurate quantitative measurement. However, it is not enough to only use the polarized light stress meter, because the stress meter can only measure the light path difference, we must know the wall thickness at the stress to finally calculate the internal stress value. Therefore, the use of polarized light stress meter and wall thickness meter can accurately test whether the stress value of medicinal glass bottle is within the specified range.



Taian Youlyy Industrial Co., LTD., is a company specializing in the production of medicinal glass bottle, medical bottle cap production enterprises, the company has advanced a full range of inspection, laboratory instruments, for high temperature steam sterilization, grain in surface water, water resistant, heavy metal precipitation, vertical axis deviation, internal stress and freezing resistance, good thermal endurance testing project.