Glass bottles are an indispensable type of container in our daily lives. As packaging materials, glass bottles are primarily used for a wide range of products such as food, oil, wine, beverages, condiments, cosmetics, and liquid chemical products. The production process of glass bottles by manufacturers involves a variety of techniques. This article aims to answer questions and provide insights into the manufacturing process of glass bottles. It will guide you through the production techniques of different types of glass bottles.
1.Raw materials of glass bottles
The raw materials for glass production consist mainly of sand, soda ash, limestone, and feldspar, which together make up over 98% of the glass raw materials. Other materials include clarifying agents, colorants, and decolorants. Additionally, to promote glass recycling and reduce energy consumption, crushed glass is utilized as a significant raw material, typically ranging from 1% to 10%, and sometimes even up to 100%. This is why glass is considered an environmentally friendly material capable of recycling.
We can clearly see the function of each raw material from the table below:
|-About 70% of the glass comes from this, a pure natural raw material. -Glass network forming body
-SiO2 melting point 1750°C
-Processing (washing, crushing, screening…)
-Key points: iron content, humidity, particle size step by step)
-Purity: 99% (pure sand) to 80% (feldspathic sand)
-Source: sea, wind erosion, river, crushing
|-12% of glass comes from this
-Accounts for 30 to 50% of raw material costs
-Natural or synthetic raw materials
-Reduce melting temperature
-Reduce glass viscosity
|-12% of glass comes from this
-Key point: iron content
-Improve glass forming properties
-Increased risk of crystallization
|Feldspar, Nepheline, Ringstone
|-Introduction of Alumina (+Sodium, Potassium, Silicon)
-0-3% of glass comes from this
-Natural raw materials
-Key point: iron content
-Improve glass properties
-Reduce the risk of crystallization
-Iron oxide, pyrite
-Reduce energy consumption
Depending on the different raw materials used, glass bottles are generally categorized into Class I, Class II, and Class III, each distinguished by the adoption of different glass composition systems. Class I glass is borosilicate glass, while Class II and Class III are soda-lime silicate glass. Class II is primarily derived from Class III and undergoes dealkalization treatment on the inner surface using SO3 or NH4SO4 powder. (Note: The purpose of dealkalization treatment is mainly to improve the water resistance of glass bottles, making them suitable for packaging neutral to weakly alkaline injectables.) For common cosmetic glass packaging, Class III glass is predominantly used, considering its resistance to corrosion from the contents of cosmetics.
2. Mixing Material Preparation
2.1 Mixing Material Feeding
This is a process of uniformly mixing all the raw materials in the appropriate proportions and continuously feeding them into the kiln for heating and melting through a feeding machine. Before entering the kiln, the raw materials are weighed by electronic scales under their respective silos, batched and proportioned. Typically, each raw material is weighed per batch, and batch accuracy is crucial. The sensitivity of the scales is monitored daily, with calibration performed weekly to ensure accuracy. Once weighed, the raw materials are conveyed to the mixer. In some factories, crushed glass is added after the mixing process to minimize wear on the mixer. The mixed batch is then transported to the kiln via a horizontal belt or a monorail tram.
To reduce dust, layering, and fly materials during transportation, proper moisture is often added before mixing. This creates a wet mixture that enhances batch control in the kiln, which is advantageous for efficient melting.
Melting refers to the process in the kiln where raw materials are heated to high temperatures. The kiln temperature is typically around 2300°F (1260°C). The melting process can be divided into five stages:
- Up to ~100°C: Drying of the mixed batch to eliminate excess moisture (humidity reduced to approximately 4%).
- Up to ~700°C: Solid-phase reactions between carbonates.
- From 800°C onward: Elimination of carbonates and reaction with silica (constituting about 16% of the weight).
- From 850°C onward: Reduction reactions of carbon with sulfates and iron oxides.
- From 1200°C onward: Clarification accompanied by the expansion of silica.
In the soda-lime-silicate glass container industry, there are mainly two types of kilns: horseshoe flame kilns and cross-fired flame kilns.
The diagram below illustrates the structure of a horseshoe flame regenerative chamber kiln.
This type of kiln features two small furnaces side by side at the back wall of the kiln, with the regenerative chamber located behind them. Each small furnace is equipped with 2-4 heating burners, which can use different fuels such as heavy oil or natural gas depending on the kiln size. The flame exits from one side of the small furnace, makes a 180° turn, and exits from the other small furnace. The route taken by the flame and exhaust gasses resembles a horizontal 'U.' This design ensures a relatively long residence time for the combustion gasses in the kiln, thereby saving energy.
3. Conveying and Shearing
In general, for the shaping of container glass, the glass exiting the kiln is at a high temperature. Therefore, the molten glass first flows into a refractory material channel, also known as the feeder channel (see the diagram below). The feeder channel cools the glass to the working temperature while ensuring uniform temperature distribution in the cooled glass.
One of the design styles for the feeder channel
Within the feeder channel, the evenly heated glass is cut into droplets by the shear system. These droplets are then conveyed through the channel to the forming machine and molds.
4. Forming Process
Common methods for shaping glass bottles and glass jars can be categorized into two main types: manual forming and mechanical forming. The predominant production method nowadays is the use of mechanical forming processes.
4.1 Handmade Glass Bottle Production
Manual glass blowing, due to high labor costs, complexity, and low production efficiency, is generally only used in the production of small batches of special, extra-large glass bottles or high-value artistic glass products. The process involves approximately 10 steps, each of which requires manual intervention.
- Gathering: The process begins with gathering molten glass from the furnace using a blowpipe. The glass is collected by dipping the end of the blowpipe into the molten glass, allowing it to adhere to the pipe.
- Marvering：The process begins with gathering molten glass from the furnace using a blowpipe. The glass is collected by dipping the end of the blowpipe into the molten glass, allowing it to adhere to the pipe.
- Initial Shaping:The glassblower shapes the glass by blowing air into the pipe or using tools to manipulate the material. This stage sets the basic form of the glass object.
- Adding Color or Design(Optional)：If desired, the artisan may add color or create intricate designs by incorporating colored glass rods or other decorative elements. This step adds a personalized touch to the final product.
- Reheating: To keep the glass malleable, it is periodically reheated in the furnace. This allows the glassblower to continue shaping and refining the piece.
- Blowing and Shaping: The glassblower continues to blow air into the pipe, expanding the glass bubble. Various tools are used to shape and refine the object to achieve the desired size and form.
- Transfer (Optional):In some cases, the glass object may need to be transferred from the blowpipe to another rod called a punty. This allows the artisan to work on the open end of the piece.
- Final Shaping:The glassblower performs additional shaping and refining to perfect the form and details of the object. This stage requires precision and skill.
- Cooling:Once the desired shape is achieved, the glass object is carefully placed in an annealing oven. The slow cooling process relieves internal stresses and ensures the glass cools uniformly, reducing the risk of breakage.
- Cutting and Finishing (Optional):After the glass has cooled, the artisan may cut, polish, or engrave the piece to add finishing touches or create specific textures.
4.2 Mechanical Forming
In mechanical forming, the high-temperature molten glass, after being sheared, takes on a preliminary shape through the coordination of the forming machine and molds. Subsequently, it undergoes processes such as hot finishing or cold cutting at the mouth.
There are two mainstream practices in production:
A: Blow-and-blow method for narrow and small bottle necks.
B: Press-and-blow method for larger-mouthed bottles and jars.
A: Blow-and-Blow Method
Once the sheared droplets fall, in the blow-and-blow shaping process, the droplets are compressed into the initial mold using compressed air, creating a 'parison.' The parison is then transferred to the final mold, where it is again blown to shape the interior of the glass bottle. The blow-and-blow method allows for the production of glass bottles with different neck thicknesses (for narrow containers).
Diagram of the Blow-and-Blow Method
B: Press-and-Blow Method
The sheared droplets fall and are pressed into the initial mold with a metal plunger, where they take on the shape of the mold and become a 'parison.' In the press-and-blow process, the formation of the parison is achieved not by compressed air but by extruding the glass within a sealed space using a longer core in the initial mold cavity. The parison is then transferred to the final mold, followed by the same steps of inversion and final shaping as in the blow-and-blow method. This process is commonly used for wide-mouth glass bottles.
Diagram of the Press-and-Blow Method
Finally, the bottles and jars produced by these two methods are gripped and extracted from the forming molds, then placed on a bottle cooling plate with bottom-up cooling air, awaiting transfer to the conveyor of the annealing process.
we can know the process details from the three image:
The cut embryo(droplets) reaches each flow tube through the material diversion trough, where the control is entirely mechanical.
The flow tube sends the droplets to the individual molds
After the embryo has entered the initial mold, a hollow glass vial has formed
The initial mold after forming is clamped into the mold, and the sealing and blowing begins at this time. Of course, the mold will be configured with cooling holes and cooling devices according to various factors such as the shape and thickness of the glass bottle during the production, so as to make qualified products.
The extruded glass is passed through a large and long iron box, where the temperature is gradually lowered to remove stress from the glass
As glass cools, it contracts and solidifies. Uneven cooling or rapid cooling can introduce stress into the glass, making it brittle, prone to breakage, or even causing it to explode. The annealing furnace heats the glass bottles and jars to approximately 580°C and then slowly cools them, eliminating the stress generated during glass shaping to ensure the safety of glass containers. The duration of the annealing process depends on the glass thickness and typically takes 20 to 60 minutes.
6. Glass Bottle Inspection
Before inspection, the bottles undergo a cold-end coating treatment, lowering the temperature of the glass containers to around 100°C to prevent scratching.
After leaving the annealing furnace at the cold end, to ensure product quality, we employ technologies such as LED beam inspection, camera inspection, and comprehensive inspection to detect faults not visible to the naked eye.
These include, but are not limited to, seal surface inspection, size analysis, wall thickness detection, damage detection, bottom edge scanning, and surface scanning.
Any bottles not meeting the standards are automatically rejected, and these rejected bottles are recycled by melting and reused as raw materials. Automated inspection ensures a stable quality for our customers.
7. Glass Bottle Packaging
The packaging method for glass bottles depends on customer requirements. For large quantities of goods without the need for individual packaging, and to ensure the safety of glass products during subsequent transportation, we typically use the following two packaging methods: Bulk Pack and Standard Pallet Packaging.