When we twist open the cap of a mineral water bottle and enjoy the cool drink, we rarely pay attention to the transparent and lightweight plastic bottle in our hands. This seemingly simple container has actually undergone a precise “transformation” from petroleum to a finished product. Its birth involves technical collaboration in multiple fields such as materials science and engineering, with the wisdom of modern industry hidden in every step.
The efficiency and quality of this process cannot be achieved without the support of professional bottle blowing equipment. Wanplas, as a manufacturer specializing in the research and production of bottle blowing machines, our equipment covers the entire process of bottle production and can provide you with the most suitable solution according to your needs.
Step 1: The “Past and Present” of Raw Materials – From Petroleum to PET Pellets
The core raw material of mineral water bottles is polyethylene terephthalate (PET), and the “past life” of this polymer material is petroleum buried deep underground. After processes such as distillation and cracking, petroleum produces basic chemical raw materials like ethylene and p-xylene. Among them, p-xylene is oxidized to produce terephthalic acid, which then undergoes esterification and polycondensation reactions with ethylene glycol, ultimately forming PET melt.
The PET melt is cut into rice grain-sized PET chips (also called PET pellets) by a pelletizer. These pellets, with a diameter of about 2-4 millimeters, are translucent or milky white and serve as the “semi-finished raw material” for mineral water bottle production. High-quality PET chips must meet strict indicators: a stable melting point between 250-260℃ and an intrinsic viscosity controlled between 0.72-0.85 dL/g. This ensures that the subsequent bottle bodies produced are both strong and have good transparency.
Our equipment can precisely match this specification of PET raw materials. Through an optimized feeding and melting system, the utilization rate of raw materials can be increased by 8%, reducing waste caused by improper raw material handling and lowering production costs.
Step 2: Pretreatment – The “Warm-up Exercise” of Drying and Melting
PET pellets have a certain hygroscopicity, and direct processing will cause defects such as bubbles and cracks in the bottle body. Therefore, pre-drying treatment must be carried out before entering the molding process. Workers send the PET pellets into a dehumidifying dryer and dry them continuously at a temperature of 160-180℃ for 4-6 hours, controlling the moisture content below 0.02%. This process is like “dehydrating and slimming” the raw materials, laying the foundation for subsequent melt molding.
The intelligent dehumidification and drying unit we integrated is equipped with heat recovery technology, which can save 15% energy compared to traditional equipment. At the same time, it is equipped with real-time moisture monitoring function to ensure that the raw materials are dried to the standard, reducing bottle defects from the source and lowering the waste rate by 12%. This process is like “dehydration and slimming” of the raw materials, laying the foundation for the subsequent melting and forming process.
The dried PET pellets are fed into the hopper of an injection molding machine and transported into the heating barrel through the rotation of a screw. The heating barrel is divided into multiple heating zones, and the temperature gradually increases from 240℃ at the feed port to 280℃ at the discharge port. During this process, the PET pellets gradually melt into a viscous melt. The molten PET melt has fluidity similar to honey and requires a certain pressure to smoothly enter the mold cavity.
Step 3: Primary Molding – The Birth of the “Embryo” (Injection Molding of Preforms)
The molding of mineral water bottles adopts a two-step method, and the first step is to inject mold preforms. The molten PET melt is quickly injected into the preform mold under the high pressure of the injection molding machine (usually 80-120 MPa). The cavity of the preform mold is test tube-shaped, with a round bottom and a reserved thread structure at the top for the bottle mouth.
Our injection molding machines are equipped with a servo drive system and use the MOOG wall thickness controller. With 100-point control, the wall thickness of the bottle blanks is ensured to be uniform. Combined with replaceable molds, the same machine can be used to produce bottles of different specifications, meeting the production needs of various product categories.
After the melt is injected into the mold, it is rapidly cooled through the cooling water channel in the mold (cooling time is about 10-15 seconds). When the temperature drops below 100℃, the PET melt solidifies and forms. Then the mold opens, and the ejection mechanism pushes out the preform. At this time, the preform is like the “embryo” of a mineral water bottle, which already has the thread of the bottle mouth and the basic prototype of the bottle body, but the bottle body part is still relatively short and thick, requiring further stretch blow molding.
Step 4: Secondary Molding – Blow Molding “Transformation” (From Preform to Finished Bottle)
The preform needs to be heated to “awaken” before blow molding. Workers put the preform into the heating machine. The infrared in the furnace uniformly heats the bottle body part of the preform, raising its temperature to 80-110℃ (this temperature range is the high elastic state of PET, which is both soft and has a certain toughness). The bottle mouth part is cooled by a special device to maintain a low-temperature hardened state to ensure that the thread structure is not damaged.
The heated preform is sent into the blow molding mold, and the cavity of the mold is the final shape of the mineral water bottle. First, a stretch rod is inserted into the preform from the bottle mouth to stretch it longitudinally by 2-3 times; then, high-pressure air (pressure is about 3-4 MPa) is quickly injected into the preform. Under the action of air pressure, the preform expands horizontally and adheres to the mold cavity wall. After 1-2 seconds of pressure holding and cooling, the mold opens, and a transparent, lightweight, and standard-compliant mineral water bottle is born.
Step 5: Quality Inspection and Packaging – Strictly Guarding the “Factory Gate”
The newly produced mineral water bottles are not directly put into use but need to undergo strict quality inspection. The inspection items include:
Appearance Inspection: Checking whether the bottle body has scratches, bubbles, or deformations, and whether the bottle mouth thread is complete through manual or machine vision;
Sealing Inspection: Filling the bottle with water, screwing on the cap, and inverting or pressurizing to test for water leakage;
Pressure Resistance Inspection: Injecting a certain pressure of air into the bottle to observe whether the bottle body breaks, ensuring that it will not be deformed due to extrusion during transportation;
Capacity Inspection: Measuring the actual capacity of the bottle to ensure it meets the marked specifications.
Qualified mineral water bottles are sent to the packaging workshop, counted, stacked, wrapped and packaged in bundles with plastic film, and then transported to the mineral water filling plant. In the filling plant, these empty bottles will be cleaned, disinfected, filled with treated mineral water, and finally capped tightly to become the finished mineral water we see in supermarkets.
After reading this article, if you are interested, please feel free to visit our official website: www.wanplas.com. We are looking forward to your joining!
