Understanding Extrusion Blow Molding (EBM)
Have you ever seen a person at the fair or at the mall during the holidays, blowing glass to create beautiful, artistic designs? It’s mesmerizing how a random piece of colored glass can be manipulated by precisely placed hot air and become such a masterpiece. This art form actually inspired the current method of manipulating plastics to form many of the items we use every day, from water bottles to toys and so many things in between. This artful method is called Extrusion Blow Molding and it’s a common and inventive way of mass producing hollow, lightweight products that are also durable and waterproof.
Using hot air to form glass was originally introduced in 1938, when the first blow molding machine was invented. Of course over time, the method has improved upon and has been adapted for other uses in several industries, including bottles and machine parts.
Though plastic bottles are commonplace and can be found everywhere in homes, cars and offices, it might surprise you to learn that machine parts are also made in the same way from high quality plastic material.
These parts can be found performing in some of the most hardworking and depended upon pieces of machinery used every day. Additionally, things like interior and exterior car parts and medical supplies rely on the items manufactured from this method.
The Main Players In the Extrusion Blow Molding Process
So how does one go about creating something from plastic that is as durable as bottles, which are able to withstand varying temperatures, survive being tossed into a cooler or endure tumbling around in the back of the car?
While there are many important parts to this incredible method, there are a few often referred to components that make up the basics of the extrusion blow molding process:
- Material, in this case a high quality plastic, often polyethylene terephthalate (PET or PETE)
- Extruder, the die that shapes the plastic into a parison
- Parison, the shape of the plastic before it enters the mold
- Mold, the metal form where the parison is placed to receive the hot air and become its desired shape
- Flash, residual material cut from created piece for a finished product
The Roles of the Individual Parts
As with anything else, it all starts with a good foundation. In this method, that would be the material. While there are other forms of material used, like the glass mentioned above, here the focus is on plastic. There are several different types of plastics that are used with this method, depending on the desired outcome and purpose of the item being produced.
The most common plastic, Polyethylene terephthalate (PET or PETE), is the one employed in many of the products you use every day. Because this material withstands water and is durable even although it’s very light, it is ideal for many of the products you come into contact with constantly. You will find it produced to hold beverages, soaps and even cosmetics.
This plastic is then placed into what is called an extruder (where we get the method name, Extrusion Blow Molding). This part plays a very important role in the process, because it prepares the plastic for the mold. Here, the material is melted and fashioned into a tube for the next phase of the process. This piece is what is known in the industry as a parison.
The parison resembles a tube. One end is solid, while the other end has a hole in it. Once the parison is formed, it is pushed down into the detailed confines of a cooled metal mold. This is an encasement that will form the soft plastic into the desired hollow shape. This process will determine the strength and thickness of the walls of the item.
After the parison has been trapped by the mold, it is then injected with compressed hot air, expanding and forcing it pneumatically to the full limits of the mold. Once the parison has been completely filled with air so that it is pushing against the sides of the mold, the plastic is cooled and then hardens into the shape of the mold. Once the new plastic piece has completely cooled down and solidified, it is removed from the mold.
The flash is any fragment of residual plastic that is attached to the finished product, but isn’t part of the mold appearance and is considered undesirable. Any flash that remains is removed and the product is finished.
The Different Methods of Molding
In Extrusion Blow Molding, there are two types of methods: Continuous and Intermittent.
The continuous method is used for materials that are hollow and small in size.
The intermittent method is used for more intricate items.
The Key Advantages of Extrusion Blow Molding
Now that you have a basic understanding of Extrusion Blow Molding, it would help to understand the advantages. Products manufactured with this method can be produced more economically due to the cost of the machinery and the molds involved.
This method has a fast production rate, because items can be continuously produced. The ability to manufacture intricate parts and the fact that what is produced is recyclable, add to the benefits of this system.
The Necessary Equipment Needed for the Production
Because of the different products produced by this molding process, there are several varieties of extrusion blow molding machines to go with each of these product needs. Each one must be calibrated and designed to handle the different materials as well as produce all of the various standards of density, strength and reliability of the products they are outputting.
Additionally, there must be qualified technicians trained to handle these complex and delicate machines.
And what happens if these machines break down with all of the hardworking parts constantly put to the test, mass producing quality items? Fortunately, there are manufacturing companies that specialize in parts for these high maintenance machines. Ironically, they use some of their own specialized molding machines to produce these parts.
Understanding the process, players and types of Extrusion Blow Molding might make you look at water bottles a little differently. After all, they are just another form of useful art like the glass vase on the counter.
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