How are Glass Bottles Made?

How are glass bottles made? Although traditional glass blowing and blow molding glass methods are still used by artists and custom applications, most glass bottle manufacturing is an automated process. 

The development of glass bottle processing peaked with the advent of feed and flow machines, which allowed manufacturers to generate larger production volumes than ever before. Glass production is divided into two main categories: container production and sheet production. Bottle processing is part of glass container production. In this guide, we'll break down the steps on how to make a glass bottle

The glass bottle manufacturing process takes place in multiple steps in a glass container factory. First, the glass is formed into bottles through a hot-end process, which involves melting and blowing, and then new bottles may be treated in-house. From there the bottle can be annealed. Finally, they are inspected and packaged in the cold end process.

The first stage of the glass bottle production process begins with the hot-end process, which typically uses a lot of heat to produce and shape glass containers. 

The furnace is first used to mold molten glass, which is fed into the furnace as glass raw material. Soda-lime glass raw material accounts for the majority (about 90%) of the glass product type and is usually composed mainly of silica, with calcium oxide and lime each accounting for about 10%. 

Small amounts of aluminum oxide, iron oxide, barium oxide, sulfur trioxide, and magnesium oxide also account for about 5% of soda-lime glass. Before melting, a cullet (recycled glass) is added to the raw material, making up between 15% and 50% of the final glass composition.

Other elements are added to color the glass before it is melted. Amber glass bottles get their color from nickel, sulfur, and carbon, although natural impurities in the sand can also cause this color. Other colors can be achieved by adding various materials:

Black: Iron, although it can also include magnesium oxide, copper, and carbon.

Purple and red: manganese or nickel oxide.

Blue: copper and cobalt oxide.

Aquamarine (can vary between blue and green): naturally occurring iron or added iron. You can also get teal by mixing cobalt and chrome.

Green: iron, chromium, and copper. A yellow-green color can be obtained with chromium oxide.

Opaque white glass: tin, zinc oxide, calcium, fluoride, or phosphate.

Once the raw material is fed into the furnace, the internal temperature can be as high as 1675 degrees Fahrenheit. The molten glass is then fed into a refiner, allowing the bubbles to escape the liquid. Next, one of two molding methods is applied: pressure blowing or blow blowing.

Compression blow molding is performed in a single section (IS) machine and is the more common method in glass container production. IS machines have 5 to 20 sections, all identical, each of which can complete the glass container forming process at the same time. A result is a machine that can produce 5 to 20 containers simultaneously.

When molten glass reaches between 1050 and 1200 degrees Celsius, it is said to be in its plastic stage, and it is at this stage that pressing and blowing begin. Shear blades are used to cut glass into cylindrical shapes called gobs. 

The cut gob falls and rolls under the force of gravity through the appropriate channels to the die. The metal plunger presses the block into the blank mold, where it takes on the shape of the mold, which is then called a parison. Next, the parison is moved into the final mold, where it is blown into the mold to take on its final dimensions. This process is typically used for wide-mouth glass containers, but can also be used to make ampoules.

Like pressure blow molding, blow-blow molding takes place in an IS machine, where the gob is released at the plastic stage and moved into the mold. In blow-blow molding, however, compressed air is used to push the gob into the blank mold to push the gob into place. 

The gob, now the parison, is then inserted into the corresponding final mold and blown again to form the inside of the glass container. Glass bottles with different neck thicknesses can be manufactured using blow-blow molding.

After molding, the bottle is usually treated internally, a process that makes the inside of the bottle more resistant to chemical attack, an important factor if the bottle is used to hold alcohol or other degrading substances. Internal treatment can be performed during or directly after molding and typically involves treating the bottle with a gas mixture of fluorocarbons. Glass containers can also be externally treated to strengthen the surface or reduce surface friction.

Once formed, some bottles may experience stress due to uneven cooling rates. The annealing furnace can be used to reheat and cool glass containers to correct stress and make the bottle stronger.

During this stage of glass production, bottles or glass containers are inspected and packaged. Inspections are usually done in combination with automated and mechanical inspections to ensure the integrity of the final product. 

Common failures include inspections (glass cracks) and stones (fragments of the furnace, which are subsequently processed into the final container), which are important because they can damage components. Packaging methods vary from factory to factory, depending on the specific type of bottle and scale of production.

Glass is chemically inert and less permeable than plastic, making it better able to withstand processes like pasteurization while containing more corrosive substances. Glass bottles are especially important in the food and beverage industry because they don't affect flavor and don't lose flavor and carbonation as quickly as plastic.

While many people are familiar with the glass bottles used to hold beer and wine, there are also glass feeding bottles, baby bottles, soda bottles, and water bottles. In addition to beverages, glass bottles are used for food ingredients, sauces, and jams. In addition, glass is used to package products such as pharmaceuticals, cosmetics, and essential oils; it can also be used in labs or spray bottles.

Amber glass bottles are ideal for holding medicines, beer, and other light-sensitive items. The amber color of the bottle filters out UV and blue light, thereby preventing these products from breaking down, called photo-oxidation. Without this filtering of high-energy light waves, beer can break down and destroy its flavor over time, while essential oils can change the smell.

Now that we've covered glass bottle manufacturing, including hot-end and cold-end processes and their applications, we hope this information will better assist you in your sourcing. If you would like more information on other technical topics or would like to purchase glass bottles, please contact us.

Das Packaging is a custom glass container manufacturer with 25 years of experience. We can turn your creative ideas into real products, personalized and branded. Our goal is to provide one-stop world-class packaging solutions and services second to none that exceed your expectations.