Extrusion blow mold concept

Extrusion-blow molds are fundamental tools used in the manufacturing process of hollow plastic parts using the extrusion technique followed by blowing. This process combines the extrusion of a molten plastic tube, called a parison, with its subsequent inflation within the mold to obtain specific three-dimensional shapes and desired internal cavities. The molds allow the produced parts to be shaped and finished, ensuring precise dimensions and characteristics.

These molds are designed to withstand the thermal, mechanical and pressure conditions typical of the extrusion-blow molding process, which is widely used in the plastics industry for the manufacture of containers, tanks, toys, and other hollow components. The correct conception and manufacturing of these molds is key to guaranteeing quality, repeatability and production efficiency.

Process Overview

The extrusion-blowing process begins with the feeding of thermoplastic resin into an extruder where it is melted and homogenized. Subsequently, the molten material is extruded forming a continuous tube called a parison, which is captured within the closed mold. The mold is closed around the parison and pressurized air is introduced inside, inflating the parison against the inner walls of the mold to acquire the desired shape.

Once the plastic cools and solidifies, the mold is opened and the molded part is ejected. This cycle is continually repeated to obtain large volumes of products with hollow shapes and uniform walls. Synchronization between the extruder, the mold and the blowing system is essential to optimize quality and production.

Specific stages of the process

In the first stage, extrusion, the plastic resin is heated and transformed into a viscous flow that is expelled through a circular nozzle to form the parison. The second stage, blowing, consists of introducing compressed air that expands the parison against the walls of the mold. Finally, in the third stage, the molded part is cooled so that it retains its shape and the finished product is ejected.