Understanding Polymer Manufacturing: Blow Molding

AxisNorth is back wiBlow Molded Plastic Bottleth another installment of “Understanding Polymer Manufacturing”. In this article, we will explore the ins and outs of blow molding, and how AxisNorth can help you find the perfect supplier for all your plastic manufacturing needs.

What is Blow Molding?

Prior to really diving into blow molding, we first must have a surface-level understanding of what this plastic process is and how it works.

Blow molding is the process of using a plastic tube often called a parison or preform. Then blowing a pressurized stream of air into the parison until it takes the shape of the mold. Typically this process is used to create hollow plastic parts typically used in the bottling and packaging industries.

Often closely associated with injection molding. Although the processes are similar they differ in the products manufactured. Think of the two in simple terms such as this, injection molding creates solid objects, blow molding creates hollow objects.

Blow Molding Process

You now have a basic understanding of blow molding, but how does the process work? What goes into each part? Let’s look at each step in the blow molding process.

  • Materials: As mentioned previously blow molded products are made from a parison or preform. These components start as raw materials or plastic pellets. Most common materials used in blow molding are like any other plastic process such as polyethylene (PE), polyethylene terephthalate (PET), and polypropylene (PP).


  • Crafting the Parison: Plastic pellets are fed into a hopper which then goes through an extrusion machine, pellets are melted down and either injected or extruded into the parison. Whether you extrude or inject the parison is dependent on the finished product


  • Sealing and Clamping the Parison: Sealing and clamping the mold is the next step. The parison is forced into a fixture that seals one portion and the other end is left open. The reason behind leaving one end of the parison open is this is where the compressed air will be fed into the product in its final molding stage.


  • Inflation and Forming: This stage is when you can see the product take shape. Two dies clamp down around the parison and the air tube. The dies contain the mold of the final product such as a water bottle. Air is rapidly introduced into the parison causing it to stretch to the constraints of the mold. The plastic then cools and is ejected, a new parison then takes its place.


  • Finishing and Trimming: Finishing and trimming is a constant through every plastic process so you can count on talking about it to everyone. After the component is ejected it then is pulled for any secondary processes, such as final assembly or trimming excess material.


Types of Blow Molding

There are three main types of blow molding. Each of these different processes offers advantages that are unique to that process.

  • Injection: In this process, a parison is injected to fit around a core rod. The core rod then transfers to a mold where it blows air into the parison which takes the shape of the mold. Lastly, the rod transfers the finished product out of the mold.


  • Extrusion: Extrusion can be continuous or intermittent. In continuous, parisons are constantly fed into the mold, and the components are removed by a blade chopping off the completed part. In intermittent, after the component is molded and cooled the dies open and drop the component out.


  • Injection Stretch: The injection process combines processes from both injection and traditional blow molding. First plastic is injected into a mold, typically a threaded cap, then is cooled and transferred to be blow molded. The plastic is reheated in the blow molding machine and air is forced in to create the finished product.


Blow Molding at AxisNorth

Ready to get started on your next project? AxisNorth is here to assist you with every step in the process. We have a wide network of trusted vendors who have been thoroughly vetted and have proved time and time again to be the best in the business. No matter the product, no matter the process let AxisNorth assist you!