How Glass Bottles and Jars are Made
When lightning strikes sand, nature makes glass. For more than 100 years, O-I Glass has recreated Mother Nature’s magic by combining natural materials and heat to make glass bottles and jars. Our passion for making glass lies in its endless benefits, from the health of the planet to the health of families. We love glass.
Glass Container Manufacturing Process
Glass packaging is made of three natural ingredients: silica sand, soda ash and limestone. The materials are mixed with recycled glass, called “cullet.” Cullet is the main ingredient in O-I’s glass bottles and containers. Globally, our glass containers contain an average of 38% recycled glass; we’ve manufactured glass bottles with as much as 90% recycled glass in Europe. Together, these four ingredients—sand, soda ash, limestone, and recycled glass–make up the batch mixture.
The batch mixture heads to the furnace. The furnace is heated by gas and electricity to about 1550 degrees Celsius to create molten glass. The furnace runs 24 hours a day, seven days a week, and can process several hundred tonnes of glass each day. Many O-I plants have multiple furnaces to support glass making.
When the molten glass mixture comes out of the furnace, it flows into a refiner, which is essentially a holding basin covered by a big crown to contain the heat. Here, the molten glass cools to about 1250 degrees Celsius and air bubbles trapped inside make their escape.
The molten glass then goes to the forehearth, which brings the glass’s temperature to a uniform level before entering the feeder. At the end of the feeder, shears cut the molten glass is cut into “gobs,” and each gob will become a glass container.
The end product starts to take shape inside the forming machine as each gob is dropped into a series of moulds. Compressed air is used to shape and expand the gob into a glass container. The glass continues cooling at this point in the manufacturing process, dropping to roughly 700 degrees Celsius.
After the forming machine, each glass bottle or jar goes through an annealing step. Annealing is needed because the outside of the container cools quicker than the inside. The annealing process reheats the container and is then gradually cooled to release stress and strengthen the glass. Glass containers are heated to about 565 degrees Celsius and then cooled slowly to 150 degrees Celsius. Then the glass bottles and jars head to the cold end coater for a final outside coating.
Inspecting Glass Bottles and Jars
Each glass bottle and jar is put through a series of inspections to ensure it meets O-I’s highest standards. Multiple high-resolution cameras inside machines scan as many as 800 glass bottles each minute. The cameras sit at different angles and can catch miniscule defects. Another part of the inspection processes includes machines exerting pressure on the glass containers to test wall thickness, strength and if the container seals correctly. O-I’s experts also manually and visually inspect random samples to ensure quality.
If a glass bottle or glass jar doesn’t pass inspection, it goes back into the glass manufacturing process as cullet. Containers that pass inspection are prepared for transportation to food and beverage manufacturers, who fill them and then distribute to grocery stores, restaurants, hotels and other retail locations for shoppers and customers to enjoy.
Glass is endlessly recyclable, and a recycled glass container can go from the recycle bin to store shelf in as little as 30 days. So once consumers and restaurants recycle their glass bottles and jars, the glass manufacturing loop starts again.