Mold-blowing was an alternate glassblowing method that came after the invention of free-blowing during the first part of the second quarter of the first century A.D.
A glob of molten glass is placed on the end of the blowpipe which is then inflated into a wooden or metal carved mold. In this way, the shape and the texture of the bubble of glass is determined by the design on the interior of the mold rather than the skill of the glassworker. Two types of molds, namely single-piece mold and multi-piece mold, are frequently used to produce mold-blown vessels.
The former allows the finished glass object to be removed in one movement by pulling it upwards from the single-piece mold and is largely employed to produce tableware and utilitarian vessels for storage and transportation. Whereas the latter is made in multi-paneled mold that join together, thus permitting the development of more sophisticated surface modeling, texture and design. The Roman leaf beaker which is now on display in the J. Paul Getty Museum was blown in a three-part mold decorated with the foliage relief frieze of four vertical plants.
Meanwhile, Taylor and Hil tried to reproduce mold-blown vessels by using three-part molds made of different materials. The result suggested that metal, in particular bronze, molds are more effective in producing high-relief design on glass than plaster molds and wooden molds. In view of this, the development of the mold-blowing technique has enabled the speedy production of glass objects in large quantity, thus encouraging the mass production and widespread distribution of glass objects.
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.
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 1938. This was the beginning of the commercial blow molding process. During the 1940s 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 1939. 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 1977 to ten billion pieces in 1999. 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.
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.
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 1800s. A patent from the time shows the process being used with celluloid polymer. These early methods were not suited for mass production.
In the 1930s, 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.
One of the first steps in creating a molded plastic product is to decide on a manufacturing technique. Blow molding and injection molding are two popular processes with unique advantages and drawbacks. It’s important to develop a good understanding of both methods before you can determine which one is most suitable for your company’s needs. This blog post will discuss the difference between a blow mold and an injection mold, and the most common types of products made using each technique.
Blow Molding vs. Injection Molding
While blow molding and injection molding both involve filling molds with melted plastic, their processes and the types of objects they can create are very different. Let’s take a look at each method.
What is Blow Molding?
Blow molding creates hollow products from thermoplastic materials. Technicians create performs, or parisons, by heating and expanding plastic tubes. The preform is placed between two dies that contain the final product’s desired shape. Next, air is supplied into the tube, causing it to gradually expand and conform to the mold’s shape.
After the blowing process is complete, the product is cooled and then ejected from the mold. It is then trimmed of any excess material and prepared for secondary processes.
Blow Molding Advantages
Blow molding allows manufacturers to create high quantities of hollow plastic products in a short period of time. Some of the benefits blow molding delivers include:
Low machinery costs
Automated production
High product variety
Many production methods, such as extrusion blow molding, stretch blow molding, and others
blow molded parts
Blow Molding Products
Blow molding has become a very popular manufacturing process. Many industries use it to create containers or other products. Some of the most common applications for blow molding products are:
Automotive components
Appliance parts
Children’s toys
Industrial bulk containers
Medical supplies
Marine products
Lawn and garden items
Product packaging
Sporting goods
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.
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.
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.
Blow molding, in glass production, method of forming an article of glass by blowing molten glass into a mold. This operation is performed with the aid of a hollow metal tube that has a mouthpiece at one end. A gob of molten glass gathered onto the opposite end of the tube is enlarged by a bubble of air blown into it through the tube. This preliminary shape is then lowered into a mold and inflated by blowing until it has assumed the desired shape and pattern. The mold may be constructed of one piece, in which case it is sheared off the glass article, or it may be an open-and-shut device comprised of two parts, which allows the mold to be removed and reused.
Blow molding is a molding process used in the manufacturing industry to create hollow objects made of plastic. Like other molding processes, it involves the use of heated, liquid material that’s forced into a mold cavity under pressure. Blow molding is a special type of molding process, however, that leverages the properties of traditional glassblowing.
Overview of Blow Molding
Blow molding, also known as blow moulding in the United Kingdom, is a molding process in which heated plastic is blown into a mold cavity to create a hollow object. The defining characteristic of a blow molding is that it’s used to create hollow objects. Raw plastic is first heated, after which it’s formed into a parison. Next, the plastic parison is secured to the top of the mold. Finally, air blown down onto the plastic parison, thereby stretching it across the interior walls of the mold cavity.
Blow molding follows the same principle as glassblowing. With glassblowing, a glassblower blows air across heated glass, thereby creating a hollow glass object. With blow molding, a machine blows air across heated plastic that’s placed on top of a mold cavity. The air forces the heated plastic to expand across the interior walls of the mold cavity.
The Different Types of Blow Molding
There are several different types of blow molding, one of which is extrusion. Known as extrusion blow molding (EBM), it lives up to its namesake by extruding heated plastic into a parison. It’s a common molding process used in the manufacturing industry because of its ability to mass-produce a large volume of objects in the same size and shape.
Another common type of blow molding process is injection stretch blow molding. Using either one or two stages, injection stretch blow molding is typically used to create plastic bottles. It’s specifically effective for creating preforms of plastic bottles, which are then either sold to bottling companies or used to manufacture a bottle.
Blow Molding vs Injection Molding: What’s the Difference?
The terms “blow molding” and “injection molding” are often interchgeably when referring to molding processes. While similar, though, they aren’t necessarily the same. Both blow molding and injection molding involve the use of liquid material — typically plastic — that’s forced into a mold cavity. The difference is that blow molding is used to create hollow objects, whereas injection molding is used to create solid objects. For hollow objects, only blow molding offers a fast and effective solution for manufacturing companies.