Process Description

This process used at Buckhorn Rubber combines 3-D blow molding with sequential co-extrusion, and consists of extruding two different materials (e.g., a rigid polyolefin with a soft thermoplastic vulcanizate).

Using this example, the soft thermoplastic vulcanizate would be extruded, followed by the rigid polyolefin, followed again by the soft thermoplastic vulcanizate. This allows a parison with different sections of material in the extrusion direction to be produced. This process is also commonly referred to as a “hard-soft-hard” process.

An inclined clamp is moved in coordinates while the parison, that has a smaller diameter than the article diameter, is placed into the mold cavity in such a way that the remaining pinch line length is reduced to a minimum. Then the mold is closed and the parison is inflated onto the cooled walls of the mold where the plastic cools down, solidifies, and sets the part shape. Finally the mold is opened and the part removed.

Benefits of This Process

• Substantial savings (material, energy, capital, cycle times, etc.) can be attained.
• Flash is significantly reduced and easily removed.
• Parts with very complex shapes can be molded.
• Clamping forces are reduced.
• Refinishing work on outer article diameter is eliminated.
• Improved quality due to more consistent wall thickness distribution and the elimination of weak areas in pinch lines.
• Smaller extruders can be used or larger parts can be molded.
• Less energy is spent in grinding or recycling flash.
• Less degradation of sensitive materials.
• Dual material co-extrusion that offers specific physical properties.
• Parts with different flexibility/stiffness in desired sections are feasible.

View Blow Molding Presentation