Glass Bottle Manufacturing Process
The main types of glass:
Type I - borosilicate glass
Type II - Processed soda lime glass
Type III - soda lime glass
Materials used to make glass include about 70% sand and specific blends of soda ash, limestone and other natural materials - depending on the properties needed in the batch.
When producing soda lime glass, crushed, recycled glass or cullet is another key ingredient. The amount of broken glass used in this batch of glass is different. The cullet melts at a lower temperature, which reduces energy consumption and requires less raw material.
Borosilicate glass can not be recycled because it is heat-resistant glass. Due to its heat resistance, borosilicate glass will not melt at the same temperature as soda-lime glass and will change the viscosity of the fluid in the furnace during the remelting phase.
All the raw materials used to make glass, including cullet, are stored in bulk houses. They are then gravity fed into the weighing and mixing zone and finally to the batch hopper that supplies the glass furnace.
Methods for Producing Glass Containers:
Blown Glass is also known as molded glass. In creating blown glass, gobs of heated glass from the furnace are directed to a molding machine and into the cavities where air is forced in to produce the neck and general container shape. Once they are shaped, they are then known as a Parison.
There are two distinct forming processes to create the final container:
Blow & Blow Process - used for narrow containers where the parison is formed by compressed air. Compressed air is used to form the gob into a parison, which establishes the neck finish and gives the gob a uniform shape. The parison is then flipped to the other side of the machine, and air is used to blow it into its desired shape.
Press & Blow Process- used for large diameter finish containers in which the parison is shaped by pressing the glass against the blank mold with the metal plunger.
A plunger is inserted first, air then follows to form the gob into a parison.
At one point this process was typically used for wide mouth containers, but with the addition of a Vacuum Assist Process, it can now be utilized for narrow mouth applications as well.
Strength and distribution is at its best in this method of glass formation and has allowed manufacturers to “lightweight” common items such as beer bottles to conserve energy.
Conditioning - no matter the process, once the blown glass containers are formed, the containers are loaded into an Annealing Lehr, where their temperature is brought back up to approximately 1500° F, then reduced gradually to below 900° F.
This reheating and slow cooling eliminates the stress in the containers. Without this step, the glass would easily shatter.