How are water bottles molded?

Manufacturing process for forming and joining together hollow plastic parts

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Blow molding (or moulding) is a manufacturing process for forming hollow plastic parts. It is also used for forming glass bottles or other hollow shapes.

In general, there are three main types of blow molding: extrusion blow molding, injection blow molding, and injection stretch blow molding.

The blow molding process begins with softening plastic by heating a preform or parison. The parison is a tube-like piece of plastic with a hole in one end through which compressed air can enter.

The plastic workpiece is then clamped into a mold and air is blown into it. The air pressure inflates the plastic which conforms to the mold. Once the plastic has cooled and hardened the mold opens and the part is ejected. Water channels within the mold assist cooling.

History

The process principle comes from the idea of glassblowing. Enoch Ferngren and William Kopitke produced a blow molding machine and sold it to Hartford Empire Company in . This was the beginning of the commercial blow molding process. During the s the variety and number of products were still very limited and therefore blow molding did not take off until later. Once the variety and production rates went up the number of products created soon followed.

The technical mechanisms needed to produce hollow-bodied workpieces using the blowing technique were established very early on. Because glass is very breakable, after the introduction of plastic, plastic was used to replace glass in some cases. The first mass production of plastic bottles was done in America in . Germany started using this technology a little bit later but is currently one of the leading manufacturers of blow molding machines.

In the United States soft drink industry, the number of plastic containers went from zero in to ten billion pieces in . Today, an even greater number of products are blown and it is expected to keep increasing.

For amorphous metals, also known as bulk metallic glasses, blow molding has been recently demonstrated under pressures and temperatures comparable to plastic blow molding.[1]

Typologies

Extrusion blow molding

In extrusion blow molding, plastic is melted and extruded into a hollow tube forming a tube like piece of plastic with a hole in one end for compressed gas - known as a parison. The parison is captured by closing it into a cooled metal mold. Air is blown into the parison, inflating it into the shape of the hollow bottle, container, or part. After the plastic has cooled, the mold is opened and the part is ejected.[2]

"Straight extrusion blow molding is a way of propelling material forward similar to injection molding whereby an Archimedean screw turns, feeding plastic material down a heated tube. Once the plastic is melted the screw stops rotating and linearly moves to push the melt out. With the accumulator method, an accumulator gathers melted plastic and after the previous mold has cooled and enough plastic has accumulated, a rod pushes the melted plastic and forms the parison. In this case the screw may turn continuously or intermittently.[3] With continuous extrusion the weight of the parison drags the parison and makes calibrating the wall thickness difficult. The accumulator head or reciprocating screw methods use hydraulic systems to push the parison out quickly reducing the effect of the weight and allowing precise control over the wall thickness by adjusting the die gap with a parison programming device.

Continuous extrusion equipment includes rotary wheel blow molding systems and shuttle machinery, while intermittent extrusion machinery includes reciprocating screw machinery and accumulator head machinery.

Spin trimming

Containers such as jars often have an excess of material due to the molding process. This is trimmed off by spinning a cutting blade around the container which separates the material. The excess plastic is then recycled to create new moldings. Spin Trimmers are used on a number of materials, such as PVC, HDPE and PE+LDPE. Different types of the materials have their own physical characteristics affecting trimming. For example, moldings produced from amorphous materials are much more difficult to trim than crystalline materials. Titanium nitride-coated blades are often used rather than standard steel to increase life by a factor of 30 times.

Injection blow molding

The process of injection blow molding (IBM) is used for the production of hollow glass and plastic objects in large quantities. In the IBM process, the polymer is injection molded onto a core pin; then the core pin is rotated to a blow molding station to be inflated and cooled. This is the least-used of the three blow molding processes, and is typically used to make small medical and single serve bottles. The process is divided into three steps: injection, blowing and ejection.

The injection blow molding machine is based on an extruder barrel and screw assembly which melts the polymer. The molten polymer is fed into a hot runner manifold where it is injected through nozzles into a heated cavity and core pin. The cavity mold forms the external shape and is clamped around a core rod which forms the internal shape of the preform. The preform consists of a fully formed bottle/jar neck with a thick tube of polymer attached, which will form the body. similar in appearance to a test tube with a threaded neck.

The preform mold opens and the core rod is rotated and clamped into the hollow, chilled blow mold. The end of the core rod opens and allows compressed air into the preform, which inflates it to the finished article shape.

After a cooling period the blow mold opens and the core rod is rotated to the ejection position. The finished article is stripped off the core rod and as an option can be leak-tested prior to packing. The preform and blow mold can have many cavities, typically three to sixteen depending on the article size and the required output. There are three sets of core rods, which allow concurrent preform injection, blow molding and ejection.

Injection stretch blow molding

Injection Stretch Blow Molding has two main different methods, namely Single-stage and Double-stage process. The Single-stage process is then again broken down into 3-station and 4-station machines.

In the single-stage process, both preform manufacture and bottle blowing is performed in the same machine. The older 4-station method of injection, reheat, stretch blow and ejection is more costly than the 3-station machine which eliminates the reheat stage and uses latent heat in the preform, thus saving costs of energy to reheat and 25% reduction in tooling. The process explained: Imagine the molecules are small round balls, when together they have large air gaps and small surface contact, by first stretching the molecules vertically then blowing to stretch horizontally the biaxial stretching makes the molecules a cross shape. These "crosses" fit together leaving little space as more surface area is contacted thus making the material less porous and increasing barrier strength against permeation. This process also increases the strength to be ideal for filling with carbonated drinks.

In the two-stage injection stretch blow molding process, the plastic is first molded into a "preform" using the injection molding process. These preforms are produced with the necks of the bottles, including threads (the "finish") on one end. These preforms are packaged, and fed later (after cooling) into a reheat stretch blow molding machine. In the ISBM process, the preforms are heated (typically using infrared heaters) above their glass transition temperature, then blown using high-pressure air into bottles using metal blow molds. The preform is always stretched with a core rod as part of the process.

See also

References

Bibliography

Are you curious how raw plastic is turned into bottles? Wondering how many types of water bottles are there? Not sure what an extrusion blow machine is but do you want to learn more? Curious how your ketchup bottles are different from single-use plastic bottles? This article will answer all these questions and more. 

Although there has been a push to slowly reduce the presence of plastic in our lives, plastic bottles still form the backbone of many industries worldwide, and in this article, we&#;ll take you through the entire process. 

What are Plastic Bottles Made Of?

To understand how a plastic bottle is made, we must go over all the different types of plastic bottles are made from. Contrary to misconception, there are various, very different kinds of plastics, and they all require different approaches. By learning more about these materials, their advantages, and their disadvantages, you&#;ll get a more broader look into how plastic bottles are made, and that&#;s precisely why we&#;ll go over the most common plastics bottles are made of below! 

#1 Polyethylene Terephthalate (PET)

PET bottles are one of the most common types of plastic bottles. They&#;re used for beverages such as water, soft drinks, juices, and milk bottles. PET is a clear, strong, and lightweight plastic that is easily molded, making it an ideal choice for use in the production of plastic bottles.

Advantages:

1. Lightweight: PET bottles are lighter than glass bottles making them easier and cheaper to transport, reducing both costs and carbon footprint. 
2. Transparency: PET bottles are clear, allowing consumers to see the contents of the bottle. Transparent bottles can be particularly important for products such as mineral water or fruit juices, where the color of the liquid might impact the prospective customer&#;s purchasing decision. 
3. Durability: PET plastic bottles are strong and durable, making them less likely to break or crack during shipping or handling.
4. Cost-effectiveness: PET is a relatively inexpensive material, making it a cost-effective option for packaging products.

Drawbacks:

1. Permeability: PET bottles are slightly permeable, which means that oxygen and carbon dioxide can pass through the walls of a bottle and affect the taste and quality of the liquid inside.

#2 High-Density Polyethylene (HDPE)

HDPE bottles are another common type of plastic bottle used for packaging a wide range of products, including milk, juice, cleaning agents, and personal care products. And although they are interchangeable in use with PET bottles in a lot of cases, they also have unique qualities that make them uniquely suitable for specific applications. 

Advantages:

1. Strength and Durability: HDPE bottles are strong and durable, resistant to impact and chemicals, which makes them an excellent choice for packaging harsh chemicals, such as cleaning agents.
2. Recyclability: HDPE is a highly recyclable material, and recycled HDPE can be used to create new bottles or other products. This can help to reduce waste and conserve natural resources.
3. Versatility: HDPE bottles come in a range of sizes and shapes, making them suitable for a wide range of packaging applications.

Drawbacks:

1. Low Heat Tolerance: HDPE has a low heat tolerance, which means that it may not be suitable for packaging products that require high-temperature sterilization.

#3 Polyvinyl Chloride (PVC)

PVC bottles are less common than PET or HDPE bottles and are primarily used for packaging products such as detergents, cleaners, and chemicals. 

Advantages:

1. Resistance to Temperature: PVC bottles can withstand a wide range of temperatures, making them suitable for packaging products that require high temperatures during packaging or shipping. 
2. Transparency: PVC bottles are clear, allowing consumers to see the contents of the bottle before purchasing. And although it is more important for PET bottles&#; use cases, PVC bottles still benefit from the visual appeal. 

Drawbacks:

1. Chemical Leaching: PVC bottles can leach chemicals, including phthalates and bisphenol A (BPA), which have been linked to health concerns.
2. Low UV Resistance: PVC bottles are not resistant to ultraviolet (UV) radiation, which can cause them to degrade and discolor over time.

#4 Low-Density Polyethylene (LDPE)

LDPE bottles are a popular type of plastic bottle used for packaging products such as shampoo, lotion, and other personal care items. LDPE is an ideal choice for packaging applications that require flexibility and durability.

Advantages:

1. Flexibility: LDPE bottles are flexible and can be easily squeezed, making them ideal for packaging products such as lotions and shampoos.
2. Lightweight: LDPE bottles are lightweight, which not only makes them cheaper to transport but also makes products that use these bottles easier to hold and more comfortable. 

Drawbacks:

1. Limited Heat Resistance: LDPE has a relatively low heat tolerance, making it unsuitable for various applications that require high heating during various stages of production. 
2. Limited Strength: LDPE bottles are not as strong or durable as other types of plastic bottles such as PET or HDPE, which makes them less suitable for packaging applications that require tough materials. 

The Ways a Bottle is Made

There&#;s no &#;one way&#; you can make bottles. Various types of molding processes are used to make plastic bottles. Understanding these molding processes is essential to learning how a plastic bottle is made. 

#1 Injection Blow Molding

Injection blow molding is a widely used manufacturing process for producing hollow plastic bottles in large quantities. This process is typically used for producing bottles with tight tolerances and high-quality finishes. Injection molding involves two main stages: the injection molding of a preform and the blow molding of the preform into the final shape of the bottle.

Advantages

• Injection molding can produce bottles with consistent thickness and a highly detailed finish. This makes it an ideal choice for producing bottles for the pharmaceutical and cosmetic industries, where precision and aesthetics are critical. I
• This manufacturing technique can be almost entirely automated, which means you can produce large quantities of bottles in a relatively short period. This helps reduce production costs and increase efficiency. 

Disadvantages

• The initial tooling costs for injection blow molding are higher than other manufacturing methods, making it more suitable for high-volume production runs rather than small batches.

#2 Extrusion Blow Molding

Another widely used manufacturing process for producing hollow plastic bottles, extrusion molding is typically used for producing bottles with thin walls and large capacities. This process involves three main stages: the extrusion of a parison, the inflation of the parison into a preform, and the blow molding of the preform into the final shape of the bottle.

Advantages

• This plastic bottle manufacturing process can produce large quantities of bottles with minimal material waste. The process is highly automated, which helps to reduce labor costs and increase efficiency. 
• Extrusion molding offers the ability to produce bottles with complex shapes and intricate designs. However, the process can be limited by the size and shape of the mold, which can affect the final design of the bottle. An extrusion blow molding station deals with larger molds better. 

Disadvantages

• The quality of the manufactured bottle can be affected by factors such as mold temperature, cooling rate, and blow pressure, which can require careful monitoring and adjustment. There&#;s more room for error with extrusion molding.

#3 Stretch Blow Molding

Widely used for producing plastic bottles for carbonated drinks, water, and other beverages, the stretch molding process involves stretching a preform of molten plastic into the final shape of the bottle using a combination of heat and pressure. This is typically done in two main stages: putting a preform into an injection molding machine and the stretch molding of the preform into the final shape of the bottle.

Advantages

•  Stretch molding also allows for the production of lightweight bottles with excellent barrier properties, which helps protect the contents from oxygen and moisture making it an ideal choice for the food and beverage industry where product aesthetics are critical.

Disadvantages

• the initial tooling costs for stretch molding can be high, making it more suitable for high-volume production runs. The process also requires careful monitoring and control of the temperature, pressure, and stretching forces to ensure the quality of the final product is up to certain standards. This is the most expensive and most intricate plastic bottle manufacturing process on our list. The results, which are high-end reusable bottles, might certainly be worth it. 

Step-by-Step Guide on How to Make a Bottle 

Now that you have a broad understanding of how melted plastic gets turned into a plastic bottle, it is time to go over a step-by-step guide. Although as you probably understand by now, the process can differ somewhat depending on the materials and manufacturing method you use. 

1. Prepare the raw materials: The main raw material for plastic bottles is petrochemicals, which are refined into ethylene or propylene. These chemicals are then processed into plastic pellets, which serve as the raw material for making bottles.
2. Melt the plastic: the plastic pellets are melted and extruded into long tubes using a machine called an extruder. The tubes are then cooled and cut into shorter lengths. These lengths are known as preforms, which are smaller versions of the final bottle.
3. Injection molding: In the preform injection molding stage, the preforms are heated again and placed into a mold that shapes them into the desired bottle shape. The mold is then cooled, and the preform is ejected from the mold.

• Blow molding: Once the preform has been molded into the desired shape, it is transferred to a bottle blow molding machine. The preform is clamped into the machine, and compressed air is used to inflate the preform, taking the shape of the final bottle. The pressure from the compressed air also ensures that the bottle&#;s walls are even and uniform in thickness.
• Inspection and quality assurance: After the bottle has been formed, excess material is trimmed off, and the bottles are inspected for any defects or imperfections. This is an important step to ensure that the bottles meet the required standards for quality and safety.
• labeling: Once the bottles have been inspected, they are labeled with product information, such as brand name, product name, and ingredients. They are then packaged for distribution to customers.

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