Here Is Everything You Need to Know About Blow Molding

Blow molding can be found around you and you don&#;t even know it. That soda that your drinking has a plastic bottle, which was blow-molded.

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In the United States, The plastics industry is the 3rd largest manufacturing industry. Plastics make our lives easier and help us produce things more cost-effectively.

But what exactly is it? And how does it work? Read on to find out!

What is it?

This process can be used to manufacture plastic products. The process involves heating a plastic tube (known as a preform or parison) to its melting point and then putting that into the cavity of a mold.

They then use compressed air to inflate the molten plastic like a balloon so that it takes the shape of the mold but is hollow inside. The amount of plastic used and the air pressure determines how thick the final product is.

The History

Blow molding has its roots in glass blowing, where a craftsman would heat the glass to its melting point and then blow through a tube to inflate the glass. This process has been around since as far back as the s. A patent from the time shows the process being used with celluloid polymer. These early methods were not suited for mass production.

In the s, they developed commercial machines to manufacture blow-molded bottles and made mass production possible. The materials available were too brittle and took too long to produce to effectively utilize the process to make large quantities.

Blow molding exploded into industrial prevalence with the creation of low and high-density polyethylene. This revolutionized many industries including the soft drink bottling industry and the automotive industry.

What Can You Make?

You can make just about any hollow plastic container with blow molding, but the process isn&#;t limited solely to bottles. Here are some commonly blow-molded products:

• Construction Barrels and Barriers
• Stadium Seating
• Coolers
• Fan Housing
• Toys and Sporting Goods
• Watering Cans

Blow molding is also widely used in the automotive industry and makes the design and mass production of auto parts simple and cost-effective. Here are some commonly blow-molded automotive parts:

• Automotive Ductwork
• Liquid Reservoirs
• Mud Guards
• Consoles
• Seating
• Storage Systems
• Electrical Covers
• Fenders
• Paneling

To sum up, blow molding has a wide variety of uses and is a great way to produce a large number of parts inexpensively.

The Process

There are a few different types of blow molding. Their differences lie mostly in how they form the parison, the size of the parison, and how the parison moves between the molds. The main types of blow molding are:

• Extrusion Blow Molding (EBM)
• Injection Blow Systems (IBS)
• Injection Stretch Blow Molding (ISBM)

Modern blow molding is a largely automated process, allowing for the production of thousands of parts in a short time period. The process includes the following steps:

• Plastic pellets are fed into the machine via a hopper or screw depending on the machine.
• Plastic melts and then gets shaped into a parison, which looks like a tube with a hole at one end.
• Clamped in place inside the mold.
• Compressed air inflates the parison.
• The heated plastic balloons to fill the space of the mold.
• After the plastic cools, the machine opens the mold and removes the part, sending it on to any applicable finishing, if any.

Furthermore, with IBS and ISBM, a preform replaces the parison. Tubes with a single hole made ahead of time, know as a preform, are manufactured through injection molding. A single perform design might be used for several different designs of blow-molded products and is another way to streamline production in some cases.

Blow Molding Materials

Plastics that are suited for this process include:

• PVC
• PET
• Nylon
• ABS
• EVA
• TPE
• Low and High-Density Polyethylene
• Polypropylene
• Co-polyester
• COP and COC
• Polystyrene

The wide variety of materials available for use in blow molding means that you can use the process to develop parts to fit your exact needs.

Advantages

There are many advantages to the blow molding process over other forms of plastic product manufacturing. Blow molding is a cost-effective alternative to injection molding, with both production and machinery being cheaper typically.

Blow molding works well for products that are one single piece. It can produce objects that do not require assembly or the connecting of halves. Therefore, particularly effective for containers that require exterior threading.

Blow molding also reduces flash. Flash is the little burs or plastic bleed around seems of products. This excess plastic from the production process requires extra finishing work to sand off or remove it before a part can be shipped. Blow molding techniques create a little-to-no flash, resulting in quicker turn around times for blow-molded products.

Your Product&#;s About to Blow Up!

Choosing blow molding to bring your product to life is a great solution for mass-producing simple, effective designs without spending too much money. We have a talented team of trained professionals who can take your product from idea to reality. In short, we&#;ll work with you throughout the design and production processes to ensure that the end result is a product you can be proud of.

So, contact us today so we can assist you in getting your product out of your head and out into the world!

Blow Molding

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Introduction

This article gives comprehensive information about the blow molding process and its raw materials. Read further to learn more.

• Overview of blow molding
• History of blow molding
• The blow molding process
• And much more&#;

Chapter One &#; What is an overview of blow molding?

Blow molding is a manufacturing process used to produce hollow plastic items from thermoplastic materials. It involves heating a plastic tube, called a parison or preform, and inflating it within a mold. The parison is placed between two mold halves, which define the shape of the final product. Air is then introduced to expand the tube, causing the plastic to thin out and take the shape of the mold. After the molding process is complete, the product is cooled, removed from the mold, trimmed, and readied for any additional processing.

Bottling and packaging are the primary applications for blow molding, accounting for approximately 49% of the global market share. Other significant applications include the building and construction, consumer products, and transportation sectors. The global blow molding market was valued at around $78 billion in and is projected to grow at an annual rate of 2.8% from to . Common raw materials used in blow molding include polyethylene (PE), polyethylene terephthalate (PET), and polypropylene (PP).

Chapter Two &#; What is the history of blow molding?

The origins of plastic blow molding can be traced back to the ancient practice of glass blowing. Both molten glass and plastic can be shaped by introducing air into the material. The earliest method of molding glass, known as free-blowing, dates back to the 1st century BC. Glass mold-blowing, an alternative technique, was developed around the 1st century AD.

The earliest blow molding material after glass was natural rubber, with the process patented by Samuel Armstrong in the s. A significant advancement occurred in the s when Plax Corporation developed the first blow molding machine using cellulose acetate as the raw material. In , Imperial Chemical Industries introduced low-density polyethylene (LDPE) from England, which proved to be more suitable for blow molding and spurred further developments in the process. By the s, blow molding had been commercialized, leading to rapid growth in the industry.

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Chapter Three &#; What is the blow molding process?

This chapter covers the basic blow molding process, which is relatively simple and involves several key steps: melting, homogenizing, extruding, molding (blowing), cooling, and ejection. Depending on the design and intended use of the final product, manufacturing plants may incorporate additional processes, such as extra cooling or heating cycles, as well as the use of additives and colorants. These extra steps are tailored to meet specific requirements for the final product.

• Plastic Resin Feeding or Charging:

  The first step in the blow molding process is plastic feeding. This is done by conveying the plastic pellets into the extruder hopper. Vacuum pumps draw pellets from big bags or bulk containers and transfer them into the raw material silos or hoppers. A rotary feeder at the bottom of the silo controls the rate of feeding into the plastifier or extruder. Compressed air is then used to convey the stored pellets to the extruder hopper. In other systems, plastic pellets from big bags or bins can be vacuum conveyed directly to the extruder hopper without the need for a separate conveying air system.

  
  
• Plasticizing or Melting:

  As the plastic resin enters and goes through the extrusion machine, it is melted by continuous kneading and heating. Electric heating elements or heating bands are wrapped around the extruder barrel to provide heat for melting the polymer. The extruder screw has different sections that serve a specific purpose. These are feeding, compressing, and metering. The extruder screw is designed to provide sufficient shearing and compression to homogenize and extrude the plastic.

• Parison Extrusion or Preform Injection:

  This process is the preparation of the parison or preform to be inflated. This is done by extruding the plastic through free extrusion or injection into a preform mold. The different processes in producing the preform are discussed in detail in Chapter 3.

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• Sealing or Clamping: Sealing or clamping involves a split die that captures the preform. The ends of the parison (extrusion blow molding) are sealed except for one hole, typically the container opening, where the compressed air will be injected.
• Inflation or Blow Molding:

  This step is where the plastic takes its form. Compressed air is introduced inside the preform. This inflates the preform until it is molded according to the profile of the die.

  
  
• Cooling and Ejecting:

  The next step is the cooling process. Typically, as the plastic touches the die, it cools at a predefined rate which stabilizes the dimensions of the product. After cooling, the mold opens and ejects the product.

• Trimming:

  Flashing is generally evident in extrusion blow molding. Most blow molding machines have auto deflashing features as the dies clamp the preform. But in some instances, flash is present at the top and bottom parts of the product, especially at the opening where compressed air is injected. This excess material is trimmed by a rotating knife. To minimize wastage, some systems collect the excess materials, grind them, and feed them back to the extrusion machine.

• Leak Test:

  This is the typical quality control method used in manufacturing bottles or packaging materials. In this step, either vacuum or compression is generated inside the container. The machine will then check if air enters or escapes the container by monitoring the pressure. If a leak is sensed from the container, it is rejected and fed back into the system.

  
  
• Other Secondary Processes and Packaging:

  Secondary processes include labeling, marking, and printing. After completing the secondary processes, the products are packed and distributed to manufacturers or end consumers.

  
  

Chapter Four - What are some of the leading blow molding machines?

Numerous machines are designed to optimize the blow molding process. Below are five brands that manufacture blow molding machines used in the United States and Canada, including specific models and their distinctive features:

Brand: Graham Engineering Corporation

Model: Graham Rotary Wheel Blow Molding Systems

Description: Graham Engineering Corporation provides Rotary Wheel Blow Molding Systems, renowned for their high-speed production capabilities. These systems feature multiple molds mounted on a rotating wheel, allowing for continuous production and high output rates. Graham's machines are celebrated for their efficiency, accuracy, and versatility in manufacturing a broad array of blow-molded products.

Brand: Bekum America Corporation

Model: Bekum H Series Blow Molding Machines

Description: Bekum America Corporation specializes in blow molding machines, notably their H Series models. These machines are equipped with advanced features, including servo-driven extrusion units, precise parison control, and adaptable mold clamping systems. Bekum's H Series is recognized for its energy efficiency, rapid cycle times, and versatility in producing a wide range of blow-molded products.

Brand: Kautex Machines, Inc.

Model: Kautex KBB Series Blow Molding Machines

Description: Kautex Machines, Inc. produces the KBB Series Blow Molding Machines, which are widely recognized in the industry. These machines feature multi-layer extrusion capability, accurate parison control, and high-speed performance. Kautex's machines are noted for their dependability, high productivity, and ability to manufacture intricate blow-molded products.

Brand: Wilmington Machinery

Model: Wilmington Blow Molding Systems

Description: Wilmington Machinery offers Blow Molding Systems tailored for diverse applications. Their machines are characterized by a compact design, energy efficiency, and precise control. Wilmington's systems are known for their durability, flexibility, and capability to deliver high-quality blow-molded products across various sectors.

Brand: Milacron LLC

Model: Milacron Extrusion Blow Molding Machines

Description: Milacron LLC's Extrusion Blow Molding Machines are celebrated for their efficiency and precision. These machines come equipped with features such as closed-loop parison control, high-speed operation, and adaptability to a wide range of materials. Milacron's machines are renowned for their robustness, accuracy, and consistent production of high-quality blow-molded items.

Keep in mind that the availability and specifications of individual models can change over time. For the latest and most accurate details regarding the blow molding machines offered by these manufacturers in the United States or Canada, it is advisable to reach out to the manufacturers directly or consult their most recent product catalogs and technical documentation.

Chapter Five &#; What are the different types of blow molding?

There are two main types of blow molding: extrusion and injection blow molding. They differ according to the method of producing the preform or parison. Preform is the more general term used to describe the heated plastic tube while parison is commonly associated with extrusion blow molding. A third type, stretch blow molding, is basically a modification of the two main types that are used for creating biaxially oriented plastics. These processes have their pros and cons that aim to serve a particular application.

• Extrusion Blow Molding: Extrusion blow molding involves the extrusion of a parison with a predetermined length which is held by a split die on its ends. The parison is sealed in one end while the other end is fitted to an air supply. Compressed air is introduced which inflates the parison. The dies are typically cold which cools the inflated molten plastic as it meets the die surface. When the dimensions of the product are stable, the mold is opened to eject the product.

  There are two main types of extrusion blow molding categorized by the method of extruding the plastic to create the parison. These are continuous and intermittent blow molding.

  
  

  • Continuous Extrusion Blow Molding: In this method, the parison is continuously extruded from the extrusion machine. Polymer homogenizing is performed continuously. Once the parison is extruded, it is then cut to length by the closing mold halves. These mold halves can be configured into different types according to the mounting and movement of the mold. One configuration is the shuttle press type which can hold single or multiple parisons positioned horizontally next to each other. Shuttle press is cheaper than the other configurations but has a lower throughput.

    
    

    Another type is the rotating wheel which can be horizontal or vertical. In this type, several molds are located at the periphery of a rotating wheel. Different sections of the rotating wheel correspond to the blow molding processes of parison clamping, cutting, inflating, cooling, and ejecting. The molds are continuously used as they revolve around the wheel axis. The rotating wheel type is suitable for high volume production.

    
    

    Continuous blow molding is suitable for producing small to medium-sized plastic parts requiring lesser investment and less complex operation. However, to produce larger products, plastic with the right viscosity and good melt strength must be used. This is to prevent any sagging which can affect the quality of the product. Continuous blow molding is also used for blow molding heat-sensitive plastics such as PVC. This is due to the shorter cycle times that limit the degradation or unwanted curing of the polymer.

    
    

  • Intermittent Extrusion Blow Molding: In intermittent blow molding, the extrusion process starts when there is enough melt mass inside the extruder head or accumulator. Homogenizing and homogenizing is done intermittently inside the extrusion barrel. At the end of the barrel, the batch is held until sufficient volume is gathered and the previous batch is finished. Different types of machines are available for extruding the parison. The most popular are the reciprocating screw and accumulator head machines. The reciprocating screw type operates by retracting the screw as the melt collects in the extruder head. Once the batch is prepared, the screw moves longitudinally that compresses and extrudes the melt mass creating a parison. The accumulator head type, on the other hand, works by collecting the melt mass inside an accumulator head. Once the batch and mold are prepared, a ram pushes the melt to form the parison.

    
    

    Intermittent blow molding is used for producing large products. The main advantage comes from the independent rates of accumulation and extrusion. This allows faster extrusion of large parisons. Faster extrusion means shorter suspension time and little sagging. Thus, products made from large parisons can be achieved even with plastics having low melt strength.

    Extrusion blow molding can create a more sophisticated product with multiple layers by employing the coextrusion technology. Coextrusion blow molding involves the independent extrusion of plastics with different properties. The multilayered plastic melt is collected and prepared in a coextrusion head similar to an accumulator type. Multiple rams press on the coextrusion head forcing the melt through a die with several die cores. Once the multilayered parison is formed, the usual process of blow molding continues. Coextrusion is used in applications that require good barrier properties while at the same time provide structural rigidity and low cost. Examples of these are bottles for carbonated drinks and oils, chemical containers, and fuel tanks.

    
    

• Injection Blow Molding: This process combines injection molding in forming the preform with blow molding. The injection blow molding process starts by melting and homogenizing the plastic. This is done in a plastifier and screw extruder which is typically a reciprocating screw. This operates with similar principles to that of the intermittent extrusion process. Its main difference is the use of a preform mold with a metal rod enclosed in the center. The typical mounting of these metal rods is a rotating table with three sections, each corresponds to a phase of the blow molding cycle.

  The first phase is the melt injection. When the batch is complete, it is injected into a preform mold containing the metal rod. The preform mold consists of two dies; one is stationary while the other is movable. After injection, the temperature of the plastic is lowered until sufficient viscosity is attained to hold its shape. The second phase involves transferring the preform into another set of molds that contain the profile of the final product. The preforms are then blown to shape. After achieving the dimensions of the mold, the plastic is then cooled for ejection. The last phase is the ejection phase where the die is opened to release the product.

  
  

  Some injection molding machines can have extra phases. The additional phases are used for additional heating or cooling cycles, preform conditioning, coating, and other secondary processes.

• Stretch Blow Molding: Stretch blow molding, also known as injection stretch blow molding, is basically a modification of the injection blow molding process. This process also includes the three main phases with an additional step in the blow molding phase. In stretch blow molding, the preform is created by injecting the plastic melt into a die with a metal road at the center. The developed preform is then transferred to the product mold in preparation for the blow molding phase. Before inflating the preform, it is first stretched to a specific length by a stretch rod. After stretching, the plastic melt is then inflated to the shape of the final product. After molding, the product is then cooled and ejected.

  
  

  Stretch blow molding is not limited to plastic injection. Stretching can also be achieved in an extrusion blow molding machine. This is done by partially extruding the parison and stretching it with a pull rod. It is then enclosed by a die and is inflated to shape.

  
  

  The main objective of stretch blow molding is to create a product with a biaxially oriented plastic. Biaxial orientation is the process in which the plastic is stretched in two directions. In the longitudinal direction, the plastic is stretched by the stretch rod while in the lateral direction, the plastic is stretched by inflation. A biaxially oriented plastic has many desirable qualities including high impact, tensile, and tear strength, improved barrier properties, and excellent transparency. With the increased mechanical properties, bottles and packaging materials can be made with thinner walls. Note that not all plastics can be biaxially oriented. Moreover, the plastic resin must have the right properties and quality for it to stretch without tearing or producing specks or other defects. Plastics used in this application are PET, PP, and PVC. PET is a common biaxially oriented plastic that is used to produce clear plastic bottles.

Chapter Six &#; What is Raw Materials?

There is a wide array of raw materials that can be used for blow molding. Blow molding materials are commonly thermoplastics that do not easily degrade upon heating. Blow molding is extensively used in the manufacture of plastic bottles which is why most raw materials have properties suitable for such application. Currently, blow molding is gaining momentum in the transportation, construction, and consumer goods industries. This makes engineering plastics such as polyamides and polycarbonates viable to be blown molded as well.

• Polyethylene (PE): Polyethylene is the most widely used blow molding material. Polyethylene has many desirable characteristics such as easy processability, toughness, and flexibility which are retained even at low temperatures, odor and toxin free, excellent clarity, good water barrier properties, good electrical insulation properties, and low cost. It has two main types: high-density polyethylene (HDPE), and low-density polyethylene (LDPE).

  
  
  • High-density Polyethylene (HDPE): Among the types of polyethylene, HDPE is the more dominant raw material in terms of market share. Its molecular structure is linear with little branching resulting in higher intermolecular forces. This gives HDPE its high specific strength.
  • Low-density Polyethylene (LDPE): LDPE has a branched polymer chain that has weak intermolecular forces. This results in lower tensile strength and barrier properties. Nevertheless, it has better impact strength and resilience than HDPE.

• Polyethylene Terephthalate (PET): PET, specifically biaxially oriented PET, is known for its low permeability to carbon dioxide. This makes the material desirable for producing bottles for carbonated beverages. The downside of using PET, however, is its affinity with water. It tends to absorb water which makes processing difficult as the resin needs to be dried before extrusion.

  
  
• Polypropylene (PP): Polypropylene is a polymer that can have a wide range of properties that depends on its molecular weight, morphology, crystalline structure, additives, and copolymerization. It can be made into polymers with a high degree of crystallinity; thus, higher tensile strength and hardness which is comparable to HDPE. Moreover, they can withstand higher temperatures without loss of strength or degradation. The disadvantages of using PP are its susceptibility to UV degradation and oxidation.
• Polyvinyl Chloride (PVC): Polyvinyl Chloride is another versatile material that can be formulated with different stabilizers, plasticizers, impact modifiers, processing aids, and other additives. It can be made into rigid or flexible plastics by modifying the amount of plasticizers. Moreover, they offer better clarity than other versatile plastics such as PP. However, PVCs can release harmful pollutants, acids, and toxins during processing or degradation. Its compounding ingredients are now being regulated by FDA, EPA, and other organizations.

• Nylon or Polyamide (PA): Polyamide is considered as an engineering plastic characterized by its high toughness, high impact strength, resistance to solvents, good abrasion resistance, and can be modified to have high heat resistance. PA production mostly goes into the manufacture of fibers. Only about 10% of PA production volume is used in plastic forming processes. The common applications of blow-molded PA are automotive parts and fuel tanks.

  
  
• Polycarbonate (PC): Polycarbonate is easily processed by different molding methods, with injection molding and sheet extrusion being the most common. In blow molding, its usual application is bottle production. Polycarbonates are known for their high impact strength, heat resistance, good electrical insulation, transparency, good water barrier properties, and inherent flame retarding properties.
• Copolyester: Copolyesters are described as having very high thermal oxidation stability, inherent flame resistance, chemical inertness, excellent clarity, and good mechanical properties. It can be molded into thin-walled containers at high speeds. Moreover, it has intrinsic lubricity and non-stick properties making it viable for molding.

• Cyclic Olefin Copolymer (COC): COC is a family of fully amorphous polymer resins that are desired because of its comparable properties with PVC without the negative effects. It is best suited for food packaging, medicine bottles, and vials production because of its low water vapor permeability. The properties of COC can be altered by developing specific blends of polyolefins. Some of the properties that can be modified are its elasticity, transparency, vapor transmission rate, and coefficient of friction.

  
  
• Acrylonitrile Butadiene Styrene (ABS): ABS is a common plastic that is characterized by having good hardness and rigidity while having some degree of toughness. When blow molded, they can have a very good surface finish making them suitable for the manufacture of consumer goods. Protective coatings are usually applied due to their poor resistance to UV and only adequate resistance to most acids and alkalis.

Conclusion

• Blow molding is a type of plastic forming process for creating hollow plastic products made from thermoplastic materials. The process involves heating and inflating a plastic tube known as a parison or preform.
• Plastic blow molding originated from the ancient process of glass blowing. Both glass and plastic in their molten state can be formed easily by introducing small amounts of air inside the molten material.
• Blow molding is a fairly straightforward process that includes melting, homogenizing, extruding, molding (blowing), cooling, and ejection.
• There are two main types of blow molding: extrusion and injection blow molding. They differ according to the method of producing the preform or parison.

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