Glass Product Production Process and Technology

The production of glass bottles is a complex and sophisticated industrial process, primarily involving steps such as raw material preparation, melting, molding, annealing, inspection, and packaging. Below is a detailed explanation of the production process for typical glass bottles (soda-lime glass)：

Core Raw Materials

1、Silica Sand: The main component (about 70%), providing silicon dioxide to form the glass network skeleton.

2、Soda Ash: Reduces the melting temperature.

3、Limestone/Dolomite: Provides calcium oxide and magnesium oxide, enhancing chemical stability and hardness.

4、Broken Glass: Recycled and reused glass fragments, referred to as "cullet." It can significantly reduce energy and raw material consumption (the proportion can reach 60-90%).

5、Auxiliary Raw Materials:

●Clarifier: (e.g., sulfate) helps remove bubbles in molten glass.

●Colorant: (e.g., iron oxide, chromium oxide, cobalt oxide) imparts color to the bottle.

●Decolorizer: Eliminates the green tint caused by iron impurities in the raw materials.

●Flux: Further reduces the melting point.

Main Production Process

1、Raw Material Weighing and Mixing:

Various raw materials (silica sand, soda ash, limestone, broken glass, etc.) are automatically weighed according to the precise formula ratio.

The weighed raw materials are fed into a large mixer (e.g., a drum mixer) for thorough mixing. The uniformity of mixing is critical to glass quality and melting efficiency.

2、Melting:

The blended raw materials (batch) are continuously fed into the glass melting furnace via a feeder.

The melting furnace is a large high-temperature furnace with a refractory brick-lined melting pool, typically heated by fuels such as natural gas or heavy oil.

The temperature reaches approximately 1500-1600°C, melting the solid raw materials into a viscous, uniform, bubble-free glass liquid.

The melting process consists of stages:

●Melt Zone: Raw materials are rapidly melted into primary molten glass at high temperatures.

●Clarifying/Refining Zone: The temperature is slightly increased or maintained to reduce the viscosity of the glass liquid. Bubbles rise and are expelled, and the glass liquid becomes clear and homogeneous with the action of the clarifier.

●Homogenization Zone: The temperature is slightly lowered to ensure uniformity in glass liquid composition and temperature.

●Cooling/Adjustment Zone: The glass liquid temperature is evenly reduced to the optimal viscosity range for molding (approximately 1000-1200°C).

3、Molding:

This is the key step to shape the molten glass liquid into a bottle. The two most common molding processes are:

●Blowing Method: Primarily used for narrow-mouth bottles (e.g., beer bottles, beverage bottles).

●Feeding: The regulated glass liquid flows from the melting furnace into the feeding channel. The feeder (usually a rotating bowl and scissor mechanism) cuts the glass liquid into droplets of specific weight and shape.

●Prototype Making: The droplets fall into the prototype mold. Compressed air is blown in from below ("counter-blowing") to inflate the glass, forming the bottle mouth and body prototype (called a "parison").

●Flipping: The prototype mold opens, and the parison is transferred to the blow mold via a flipping mechanism.

●Final Forming: Compressed air is blown into the blow mold from above, inflating the parison against the inner wall of the mold to form the final bottle shape.

Press-Blow Method: Primarily used for wide-mouth bottles (e.g., jars, sauce bottles).

●Feeding: Same as above.

●Prototype Making: The glass droplet falls into the gathering mold. A punch presses down from above, hydraulically pressing the glass into the mold cavity to form the bottle mouth and a solid glass block with the bottle body prototype (called a "blank").

●Transfer: The gathering mold opens, and the blank is transferred to the blow mold.

●Final Forming: Compressed air is blown in from above to inflate the blank into the final bottle shape.

Molds need to be precisely manufactured (typically cast iron) and equipped with an effective cooling system. The inner wall shape of the mold directly determines the final shape and surface texture of the bottle.

4、Hot End Coating (Optional but Common):

The newly formed bottle is very hot (approximately 400-500°C). Before entering the annealing furnace, a very thin layer of tin or titanium compound vapor is often sprayed onto the hot end.

Function: Forms a protective film on the bottle surface, significantly enhancing the bottle's strength (improving scratch resistance and lubricity, reducing friction damage during subsequent transportation) and chemical stability.

5、Annealing:

During the cooling process of the newly formed bottle, residual stress can develop due to varying thicknesses and uneven cooling rates. This stress makes the bottle fragile and prone to breakage.

The annealing furnace is a long, slow-moving tunnel furnace with precisely controlled temperatures.

The bottle is uniformly heated to a temperature near the glass's annealing point (approximately 540-570°C) and held for a period to relax internal stress. It is then slowly cooled at a strictly controlled rate (especially through the strain point) until it reaches near room temperature. Effective annealing eliminates harmful stresses, ensuring the bottle's mechanical strength and thermal stability.

6、Cold End Coating:

After the bottle cools to near room temperature (usually at the exit end of the annealing furnace), cold end spraying is performed.

A very thin layer of liquid lubricant (e.g., oil-based or water-based stearates, polyethylene wax, silicone, etc.) is sprayed onto the outer surface of the bottle.

Function:

●Increase Lubricity: Reduces scratches caused by friction between bottles on conveyor lines and filling lines, preserving appearance.

●Improve Strength: Fine scratches are stress concentration points, and the coating reduces their occurrence.

●Prevent Surface Adsorption: Reduces dust adhesion.

7、Quality Inspection:

The automated production line is equipped with various online inspection devices:

●Mouth Inspection: Ensures the bottle mouth's dimensions, roundness, and sealing surface flatness meet requirements.

●Wall Thickness Inspection: (e.g., laser scanning) Ensures uniform bottle thickness and compliance with standards.

●Dimension Inspection: (e.g., optical inspection) Checks bottle height, diameter, and verticality.

●Appearance Inspection: (high-speed camera + image processing) Detects defects such as cracks, stones, bubbles, stains, and deformation.

●Pressure Testing: (spot-checking) Tests the bottle's internal pressure resistance (especially for carbonated beverage bottles).

Non-conforming products are automatically rejected.

8、Packaging:

Bottles that pass inspection are packaged according to customer requirements.

Common methods include stacking on pallets and securing with stretch film or packaging in plastic turnover boxes/cartons.

The packaged finished products are stored or directly shipped to customers (filling plants).

Key Characteristics

Continuity: Modern glass bottle factories feature highly automated continuous production processes, operating 24/7 from raw material input to finished product output. Once the melting furnace is ignited, it typically runs continuously for several years before shutdown for maintenance.

High Temperature: Extremely high temperatures are involved in the melting and forming stages.

Precision Control: Raw material ratios, melting temperatures and atmospheres, droplet weight and shape, forming parameters (pressure, time, mold temperature), annealing curves, etc., all require extremely precise control to ensure stable product quality.

High Energy Consumption: The melting process consumes significant energy, which is one of the main costs and environmental concerns in the modern glass industry.

Recyclability: Broken glass is an important raw material, and glass bottles can be 100% infinitely recycled.

Ths process describes the production of generic soda-lime glass bottles. While the raw material formula, melting temperature, and process details of special glasses (e.g., high borosilicate glass heat-resistant bottles) may differ, the core steps (mixing, melting, forming, annealing, inspection) are similar.