Glass jars are widely used in the canning industry. The advantages are that they are stable in nature and do not undergo chemical changes with food. Moreover, the contact surface between glass canned food and metal is small, and it is not easy to react; the glass is transparent, and the contents of the jar can be seen. Buy; empty cans can be reused, economical and convenient. The disadvantage is that it is heavy, brittle and easy to break, and it is inconvenient to transport and carry; the content is easy to fade or change color; the heat transfer is poor, and the temperature change is required to be uniform and moderate, and it cannot withstand the changes of sudden cooling and sudden heating. At present, glass jars are developing towards thin-walled and high-strength, and new bottle types are constantly coming out. The health departments of industrialized countries have officially stipulated that only glass jars can be used for infant food.
The glass jar is made of quartz sand, soda ash and limestone in a certain proportion, melted at a high temperature of 1500 ℃, and then slowly cooled and formed. Glass jars of different volumes and shapes can be made by using different molds during cooling and forming. The raw material composition affects the properties and color of the glass. In order to improve the thermal stability of glass jars and meet the needs of can production, it is generally necessary to go through a heating and annealing procedure. The production process of glass jars is: raw material grinding, sieving, batching, mixing, heating and melting, forming, annealing, and inspection.
Glass jars of good quality should be transparent, colorless or slightly cyan, with good chemical and thermal stability, usually not broken under heating and pressure sterilization conditions, the body of the jar should be straight and smooth, uniform in thickness, and the jar should be smooth. The mouth is round and flat, the bottom is flat, and the tank body must not have serious defects such as air bubbles, cracks, stone chips and streaks.
There are many forms of glass jars, but now the most used is the four-spin jar, followed by the roll-sealed victory jar. The key to the glass jar is the sealing part, including the metal jar lid and the glass jar mouth. The Victory Can is composed of a can lid, a rubber ring and a glass can body made of tinplate or painted iron. It has good sealing performance and can withstand heat and pressure sterilization, but it is inconvenient to open and the shape needs to be improved. Its volume is 500mL. The four-spin can is composed of a can lid made of tinplate, a rubber or plastic gasket, and a glass jar with a thread on the neck of the can. When the can lid is tightened, the claws on the inside of the can lid match the threads to compress the washer. That is to achieve the purpose of sealing.
