What is the Difference Between Extrusion and Injection Blow Molding

The key difference between extrusion and injection blow molding is that extrusion blow molding involves extruding heated material, whereas injection blow material involves injecting heated material into a mold.

Blow molding is the process of forming and joining together hollow plastic parts. We can also use it for the formation of glass bottles or other hollow shapes. Generally, these manufacturing processes use three types of molding processes: extrusion blow molding, injection blow molding, and injection stretch blow molding. Generally, the first step of the blow molding process is softening plastic via heating and forming it into a parison, which is a tube-like piece of plastic with a hole in one end, allowing the compressed air to pass through. But injection or injection stretch methods form a preform.

CONTENTS

1. Overview and Key Difference
2. What is Extrusion Blow Molding
3. What is Injection Blow Molding
4. Extrusion vs Injection Blow Molding in Tabular Form
5. Summary – Extrusion vs Injection Blow Molding

What is Extrusion Blow Molding?

Extrusion blow molding can be described as a type of blow molding in which plastic is melted and extruded into a hollow tube to form a parison (a tube-like piece of plastic with a hole in one end). Thereafter, the parison is captured in a water-cooled metal mold, and the air is blown into the parison, inflating it into the shape of a hollow bottle or container. After cooling down the plastic sufficiently, we can open the mold to eject the part.

Generally, straight extrusion blow molding can be described as a way of propelling materials forward, and it is similar to injection molding at some steps. In this process, we can use the accumulator method, where an accumulator gathers melted plastic. When the previous mold has cooled and when enough plastic has been accumulated, a rod is used to push the melted plastic, and it forms the parison. There, the screw can turn continuously or intermittently. The continuous method causes the weight of the parison to drag itself, and it makes calibrating the wall thickness difficult.

What is Injection Blow Molding?

Injection blow molding is a process useful for the production of hollow glass and plastic objects in large quantities. It is also abbreviated as the IBM process. In this process, the polymer is injection molded onto a core pin that can be rotated to a blow molding station that needs to be inflated and cooled. However, injection blow molding is the last used method among the three blow molding processes. Typically, it is useful in making small medical and single-serve bottles. This process has three steps named injection, blowing, and ejection.

An injection blow molding machine has an extruder barrel and screw assembly that can melt the polymer. Thereafter, the molten polymer is fed into a hot runner manifold and is injected through nozzles into a heated cavity as well as the core pin.

What is the Difference Between Extrusion and Injection Blow Molding?

Blow molding is a process of forming and joining together hollow plastic parts. Generally, the manufacturing processes use three types of molding processes: extrusion blow molding, injection blow molding, and injection stretch blow molding. The key difference between extrusion and injection blow molding is that extrusion blow molding involves extruding a heated material, whereas injection blow material involves injecting heated material into a mold. While extrusion blow molding typically creates 2D products, injection blow molding typically creates 3D products.

The below infographic presents the differences between extrusion and injection blow molding in tabular form for side-by-side comparison.

Summary – Extrusion vs Injection Blow Molding

The key difference between extrusion and injection blow molding is that extrusion blow molding involves extruding heated material, whereas injection blow molding involves injecting heated material into a mold. In addition, extrusion blow molding typically creates 2D products, while injection blow molding typically creates 3D products.

Reference:

1. “Extrusion Blow Molding.” Find Suppliers, Processes & Material.

Image Courtesy:

1. “Blow molding process” By Basant Nayak – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Principe extrusion soufflage polymere” By Cdang, Brendan Rockey, University of Alberta Industrial Design, Christophe Poret – Own work, from http://en.wikipedia.org/wiki/File:Injection_molding.png (CC BY-SA 3.0) via Commons Wikimedia