Unlocking the Molding Diagram: How Extrusion Blow Molding Actually Works

Introduction: More Than Just Lines on a Paper

I talk to factory managers and business owners every day. Some have been in the industry for thirty years, running massive operations. Others are just starting their first bottling line and looking for a partner who understands their vision. But there is one thing that always comes up.

It is understanding exactly what happens inside the machine.

When you look at a technical molding diagram, it can look like a chaotic mess of arrows, circles, and vectors. But it is actually a map to your profit. I am Slany Cheuang from LEKAmachine. I want to break down the Moldagem por extrusão e sopro (EBM) diagram into plain English. No complicated engineering talk. Just the facts.

What is Extrusion Blow Molding Anyway?

Let’s start with the basics. Moldagem por extrusão e sopro is the fundamental process we use to make hollow plastic parts. If you see a frasco de xampu, a chemical drum, or a plastic tool case, it was likely made this way.

The “diagram” is just a fancy way of showing the journey of the thermoplastic. It goes from a hard pellet to a finished recipiente. At LEKAmachine, we specialize in this technology. We build the machines that make this diagram come to life, handling the full supply chain including order management and qualidade controle.

Step 1: The Hopper and the Extruder

The journey starts at the very top of the diagram. This is where you pour in your raw materials. Usually, this is PEAD, PP, or PVC plastic pellets.

The diagram shows these pellets dropping into a long heated barrel. Inside, there is a screw that turns and pushes the plastic forward. This is the “Extrusion” part of the name. As the screw rotates, it creates friction and shear heat, achieving plasticization—turning the pellets into a molten state.

Our FORMA and AERO series use specific screw designs to make sure the plastic melts evenly. We focus on the qualidade of these components because if this part of the diagram goes wrong, your bottle looks lumpy or suffers from poor structural integrity.

Step 2: Creating the Parison (The Hot Tube)

This is the most important part of the diagram. The melted plastic comes out of the cabeça da matriz as a hollow tube. We call this tube a parison.

It looks like a long, hot, plastic sock hanging down. In the molding diagram, this is usually a vertical line dropping down between two metal plates. Controlling the thickness of this tube is critical.

• If it is too thin, the bottle breaks during drop tests.
• If it is too thick, you are wasting expensive plastic resin.

Growth-stage brands often worry about profit margins, so minimizing waste here is vital.

Step 3: The Mold Closes (The Clamping Unit)

Now we move to the “Molding” phase. The two metal plates I mentioned? That is your mold. In the diagram, you will see arrows pointing inward.

O mold closes around the hot plastic tube. It cuts off the bottom and holds the top tight. Our TITAN series is famous for this because it has massive clamping force designed for big industrial drums. It is synonymous with strength and stability. It needs to hold tight so the plastic doesn’t leak out under the immense internal pressure.

The Process in Action

It is easier to understand if you see it moving. Watch this short clip to see the mold closing and the bottle forming.

Step 4: Blowing it Up

This is the magic moment. A blow pin inserts into the mold (usually from the top or bottom). Air is blown inside the hot tube.

The diagram usually shows this as blue arrows expanding outward. The air pushes the soft, viscoelastic plastic against the cold metal walls of the mold. It takes the shape of your bottle immediately.

You need precise pneumatic pressure here. Standard blow pressure is around 0.6 Mpa for most of our machines. This pressure ensures the plastic reaches every corner of the mold cavity for a perfect finish.

Step 5: Cooling and Ejection

The plastic cannot stay hot forever. The mold is chilled with water, typically running at a pressure of 0.2-0.3 Mpa. This cools the plastic down instantly so it becomes hard.

In the diagram, this is often the “pause” before the mold opens. Once it is cool, the mold opens up. The finished bottle drops out or is taken out by a robot hand. Then the cycle starts all over again.

On our high-speed AERO series, this happens incredibly fast. This series is engineered for high-volume, continuous production to maximize your output.

Why You Should Care About the “Deflashing” Station

Most diagrams leave this part out, but I won’t. When the mold closes on the tube, it pinches off extra plastic at the top and bottom. We call this “flash.”

It looks like a little tail on the bottle. A good extrusion blow molding machine knocks this off automatically. This scrap plastic isn’t wasted. You can grind it up and put it back in the hopper.

Sustainability is a big deal for our clients, particularly those in Europe who are pushing for the use of recycled materials like rHDPE. Being able to reuse your flash immediately helps with those sustainability goals.

Matching the Diagram to the Machine

Not every diagram looks the same because not every machine is the same.

• For heavy industry: If you need to make big chemical drums or floaters, the diagram is bigger. You need a machine like our TITAN series, which is built for large-capacity, high-strength industrial containers.
• For high speed: If you are making small medicine bottles very fast, the diagram moves quicker. You would look at our AERO series, the wind-fast solução for automated lines.
• For flexibility: And if you need to switch between different bottle shapes often? Then the FORMA series is your versatile friend, born for diversity and flexibility.

Understanding your product size helps you read the diagram correctly.

Troubleshooting Using the Diagram

Why do I teach customers to read these diagrams? Because it helps you solve problems.

• If your bottles have thin corners, look at the “Parison” step in the diagram.
• If the surface looks rough, look at the “Extruder” heating step.

Knowing the flow helps you talk to my serviço team when you need support. We provide full supply chain service, but knowing the basics helps you run smoother.

Conclusion: Let’s Build Your Line

The molding diagram is just a map. You need the right vehicle to drive the route. Whether you are in the USA, Russia, Indonesia, or Canada, the process is the same.

You melt, you extrude, you clamp, you blow, you cool.

If you are ready to turn this diagram into a real production line, let’s talk. I can help you compare and choose the best factory or machine for your specific project.