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The Composition of a Glass Bottle Production Mold
A glass bottle production mold is not a single unit but a highly precise and complex system of components. Its design is critical for determining the final bottle’s shape, dimensions, and quality. The process is a two-step forming operation, requiring two main mold systems.
1. The Blank Mold (or Parison Mold)
The Blank Mold is the first station. Its job is to receive a gob of molten glass and form an initial, preliminary shape called a parison, which looks like a rough version of the final bottle.
Key Components:
Mold Body: The main housing with a cavity that defines the parison’s initial shape.
Neck Ring Mold: This is one of the most critical and precise parts. It forms the finish of the bottle—the threads, lip, and sealing surface. Because the finish is essential for closure, the neck ring mold must be manufactured to extremely high tolerances.
Plunger: A metal rod that moves vertically inside the mold. Its functions are:
To push upwards into the glass gob, creating a hollow space inside the parison (this is called the “counter-blow” process).
To retract, allowing air to be blown in.
Funnel: Guides the glass gob accurately into the blank mold.
Process: Glass gob enters → Plunger rises, creating a hollow space → Compressed air is blown from above (“counter-blow”), forcing the glass to take the shape of the blank mold, forming the parison.
2. The Blow Mold (or Finish Mold)
After the parison is formed, the blank mold opens. The parison is then transferred (often by an invert mechanism) into the Blow Mold. At this stage, the parison is hot and soft. The Blow Mold’s job is to give the bottle its final shape through high-pressure air.
Key Components:
Mold Body: Typically consists of two halves (left and right) that open and close. The internal cavity is an exact replica of the bottle’s final external shape.
Bottom Plate: A part that moves upwards from below to form the base of the bottle. It seals tightly with the mold body to create the complete molding cavity.
Process: The parison is transferred into the blow mold → The mold closes → High-pressure air is blown from the top (“final blow”), inflating the soft parison to match the internal contours of the blow mold.
Supporting Systems & Critical Parts
Beyond the core molds, a complete system includes:
Cooling System: A network of internal channels in the mold walls circulates cooling air or water. This is vital for:
Solidifying the glass quickly.
Preventing the glass from sticking to the mold.
Maintaining a stable production temperature for consistent quality and high output.
Venting System: Very fine grooves or pores on the mold cavity surface. These allow trapped air to escape when the glass is blown, ensuring the glass fills every detail of the mold and preventing defects in the bottle.
Types of Blow Molds
Depending on the bottle design, blow molds come in different configurations:
Two-Piece Mold: The most common type for round bottles. Comprises left and right halves and a bottom plate.
Three-Piece Mold: Used for non-round bottles (e.g., square, oval). It has three main sections (e.g., left, right, and shoulder sections) plus the bottom plate.
Molds with Inserts: For bottles with complex handles or undercuts, movable inserts are used to allow the finished bottle to be released.
Summary & Analogy
You can think of it like this:
The Blank Mold is like a sculptor creating a rough preliminary shape (the parison).
The Blow Mold is like a finishing craftsman who takes that shape and perfects it into the final, detailed product.
The Neck Ring Mold and Plunger work together to form the bottle’s “mouth,” ensuring it can be sealed perfectly.
The Cooling and Venting Systems are the essential “life-support” that make the entire process efficient and reliable.
The entire mold system is made from special, high-quality iron or steel alloys, precision-machined and heat-treated to withstand the extreme heat (over 1000°C) and continuous operation. Its design and quality directly determine the final bottle’s accuracy, appearance, and production efficiency.
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