Annealing process of glass bottles

The heating stage serves as the beginning of the process. Its core is to steadily raise the initial temperature of the glass bottle, which is lower than the annealing temperature, to the stable annealing temperature, laying the foundation for stress relief. The heating rate needs to be adjusted in accordance with the product characteristics: the rate for ordinary glass bottles is usually 20℃/min-30℃/min, while for glass bottles with thick walls and special shapes, the rate should be slowed down. Heating too quickly will cause a sudden increase in the temperature difference between the inside and outside of the bottle, generating new stress. If it is too slow, it will prolong the production cycle and reduce efficiency. Balancing the rate is the key at this stage.

The holding stage is the core guarantee for the annealing effect, aiming to ensure uniform temperature in all parts of the glass bottle and fully release stress. The insulation temperature should be 20℃ to 30℃ lower than the glass transition temperature, which can not only ensure stress relief but also prevent the bottle body from softening and deforming. The holding time is calculated based on the wall thickness, with each millimeter corresponding to 1 to 2 minutes. For instance, a glass bottle with a wall thickness of 6 millimeters needs to be held for 6 to 12 minutes. At the same time, it is necessary to monitor the temperature of the annealing furnace with the help of equipment to prevent incomplete stress relief caused by local temperature differences.

During the slow cooling stage, the glass bottle should be slowly cooled from the holding temperature to a lower annealing temperature to avoid generating new stress due to rapid cooling. The cooling rate is strictly controlled within the range of 5℃/min to 10℃/min. Uniform cooling can be achieved by adjusting the ventilation volume of the annealing furnace and the flow rate of the cooling medium. If the cooling is uneven, the weak parts of the bottle body are prone to deformation and cracking due to uneven force, which directly affects the product qualification rate. Therefore, uniform cooling is the key point at this stage.

The rapid cooling stage is the final stage of the process, aiming to rapidly cool the glass bottles from a lower annealing temperature to room temperature to enhance production efficiency. The rapid cooling rate needs to be adjusted according to the product conditions: thin-walled and simple-shaped glass bottles can be cooled quickly. Thick-walled and complex-shaped glass bottles need to slow down the rate to prevent breakage. During the process, the condition of the bottle body needs to be observed in real time. If any abnormality is found, parameters should be adjusted promptly to ensure that efficiency is improved while maintaining the bottom line of product quality.