The fabrication methods of ceramics are classified in three categories: glass-forming, particulate forming, and cementation. In glass-forming processes, the raw materials are heated until they melt. There are five glass-forming processes: blowing, pressing, drawing, fiber-forming, and sheet-forming. The following five-minute video highlights automated glass blowing for the production of glass bottles. Again, while you are watching this video, please think back to Lesson 1 of this course and the reading in the textbook that covered different materials used for carbonated beverage containers.
Whether they're colored or clear, glass bottles and jars are green. No trees die to make this eco-friendly packaging. Glass is made of natural ingredients that are abundant. You can recycle glass endlessly, and making it uses less energy than producing metal or plastic.
The recipe for glass combines about a half a dozen natural raw materials, but the main ones are silica sand, soda ash, and limestone. Silica sand usually makes up about forty-five percent of the batch. The soda ash helps melt the silica evenly. It comprises about fifteen percent. A limestone content of about ten percent makes the finished glass more durable. They combine these ingredients with recycled glass called cullet. The factory's equipment feeds precise amounts of the materials into a furnace. Over a full day, the fiery heat two thousand seven hundred and thirty degrees Fahrenheit melts everything together producing a gooey liquid that's the consistency of honey. The molten glass pours out of the furnace. Shears cut the flow at precise intervals to produce cylindrical gobs. Each gob is the exact amount required to make one bottle or jar they dropped to a device called the scoop the scoop moves them two troughs that feed them to jar forming and bottle forming machines.
A gob of molten glass goes into a preliminary mold. In a matter of seconds, it comes out as what's called a parison a miniature version of the final bottle. Each parison and then moves into a blow mold the cavity of which is the shape of the final bottle. The equipment blows the compressed air into the parison stretching the glass outward toward the wall of the mold cavity. This process creates the final bottle shape and hollows out the inside. These are amber colored beer bottles. The color is produced by adding small amounts of iron-sulfur and carbon to the glass mix.
The factory uses a similar manufacturing process to produce other types of bottles and jars and this run the company is making 375-milliliter wine bottles out of clear glass. This run is producing 375-milliliter liquor bottles also out of clear glass, but this mold has a special feature a recessed insignia on one of the walls which produces a raised insignia on the front of the bottle.
After the bottles leave the forming machine they travel through flames. Otherwise, they would cool down too quickly and crack from thermal shock. A loader now gently pushes the bottles into what's called an annealing lehr. The bottles cool a controlled rate as they move through the lehr. This releases stress from the glass gradually. As the bottles exit the annealing lehr, a sprayer coats their exteriors with lubricant. This enables them to move smoothly through the rest of the inspection and packaging line. The bottles now line up in single file to head into the automatic inspection station. As the machine spins each bottle, cameras and probes check for imperfections such as cracks or bubbles. The inspection equipment that examines the top to check dimensions and ensure the threads for the screw cap are molded correctly. Before shipping, a worker does a final visual inspection. The proportion of cullet in glass can be as high as 90 percent. Cullet melts at a lower temperature, so for every ten percent of cullet in the mix the factory uses up to two and a half percent less energy to produce this glass. Now that's an incentive to recycle.
In the next section, we will discuss the important subject of heat treating glass to control stress.