Blow Molding Explained

Written by Wall Street News on January 17, 2018. Posted in Commercial plastic jugs, Hdpe bottles, Plastic containers

Blow mold design

Plastic products are very important for a number of industries around the United States and across the globe. Domestically, the plastics industry is responsible employing about one million people. It is the third largest manufacturing industry in the country. It puts about $375 billion into the American economy. Making plastic bottles is an important part of that business. The process most often used in making plastic bottles is called “blow molding.” There are three different types of blow molding that can be used in the manufacture of plastic bottles and other containers. Here they are:

  • Stretch Blow Molding: In this kind of blow molding, the manufacturer uses a molecular alignment that has two axes, this is also called “biaxial.” When this process is used, the preform is stretched or elongated by mechanical means in the mold. The blowing process is then implemented to get the plastic to the shape and size that is desired. In this kind of blow molding, the temperatures that are used are lower than those needed for other types of blow molding. The temperature range is also smaller. As a consequence, the process can be a lot harder to manage and control. On the flip side, when you are dealing with making plastic bottles this way, they tend to be stronger and harder to break than when other methods are used. It is also less material intensive than other methods. PET bottles are often made through this method of blow molding.
  • Extrusion Blow Molding: When a large quantity of plastic bottles or other containers need to be made, the go-to way to produce them is often extrusion blow molding. There are also a lot of times when this process will combine making plastic bottles with the process to fill them in the same assembly line type set up. The way this is done is that the plastic is melted and then put into a tool called a “parison.” This is often little more than a tube of plastic that is hollow. The manufacturer takes the parison and puts it into a metal mold that is much cooler. Air is then introduced to the plastic parison to cause it to expand to the size of the mold. This makes it conform to the mold and becomes the desired shape and size. After it has been made to conform to the proper size and shape, the plastic is cooled and removed from the mold.
  • Injection Blow Molding: This is a kind of blow molding process that requires two steps. Plastic is first melted and then placed in a heated mold. This mold is set up to surround a hollow core rod, also known as a blow tube. The process is very similar to plain old injection molding. After the plastic has been added to the mold, the assembly is placed in a larger mold where the air is inserted and the mold is finished. Once complete, the new plastic product is removed from the blow tube. This is the least widely used blow molding process in use today. It is most often used for single-serving plastic bottles or for smaller plastic bottles such as those that are used in medical devices and for medical purposes.

To get an idea of how important making plastic bottles is to the economy, it is important to note that every hour, Americans use about 2.5 million plastic bottles. The world uses and produces nearly 600 billion pounds of the material every year. Every year, this goes up by about 5%.

While the plastics industry has been under fire over the past few years, making plastic bottles for a number of purposes is often the most environmentally friendly way to go. In today’s world, two pounds of the material can transport 1,300 ounces of liquid. It takes at least three pounds of aluminum, eight pounds of steel or 40 pounds of glass to move the same amount of liquid. When that fact is considered along with the availability of recycling facilities, it is clear that with plastic, people can do more with less and that is always a good thing for the environment.

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