Ovalizing Insert for Uniform Blow Moulding Parison Thickness
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Solution Overview
Problem
In blow moulding of hollow bodies, achieving uniform radial distribution of polymer thickness is challenging, especially when the final piece lacks cylindrical symmetry, leading to excessive material waste due to uneven wall thickness.
Innovation Solution
An extrusion head with a cylindrical chamber, a force plug, and an ovalizing insert that adjusts the radial distribution of the internal surface of the polymer, allowing for controlled thickness adjustment through a plunger mechanism, ensuring even thickness distribution in the parison.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a tubular parison with constant thickness is blown in the mold, then the blow moulding process is simple, but the polymer distributes non-uniformly resulting in excessive material waste
Solution Approach 1:
The patent applies preliminary action by deforming the parison within the extrusion head before blow moulding occurs. The mandrel with its deformable outer skirt pre-shapes the parison wall thickness distribution, so that when blowing occurs, the material distributes uniformly in the mold. This pre-deformation eliminates the need for complex adjustments during the blow moulding process itself.
Solution Approach 2:
The patent implements local quality by creating non-uniform wall thickness in specific regions of the parison through the deformable mandrel. The outer skirt of the mandrel can be locally deformed to reduce wall thickness in areas where material will be redistributed during blowing, ensuring uniform final wall thickness while using less total material.
2Manufacturing precision
If the mandrel outer skirt is deformed by purposely provided plates to achieve even wall thickness distribution, then uniform thickness is obtained, but the device complexity increases
Solution Approach 1:
The patent applies dynamics by making the mandrel's outer skirt deformable rather than rigid. The outer skirt can dynamically adjust its shape during parison formation to optimize wall thickness distribution. This dynamic capability replaces the need for multiple fixed deformation plates, simplifying the overall device structure while maintaining manufacturing precision.
3Manufacturing precision
If structural changes are made in the extrusion head to achieve uniform thickness distribution, then even wall thickness is obtained, but the adaptability for different production types decreases
Solution Approach 1:
The dynamic deformability of the mandrel's outer skirt allows it to be reconfigured for different production requirements without permanent structural changes. The same extrusion head can adapt its mandrel shape to produce different parison geometries and wall thickness distributions, maintaining versatility across different product types while achieving uniform wall thickness in each specific application.
Data Source
AI summary
An extrusion head (1) for blow moulding of hollow bodies comprises: a body (2) and a force plug (3) set within the body so as to define a cylindrical gap (4), through which the molten plastic material fed by an extruder can flow; a die opening (6) set at the bottom end of the body (2); a bottom part (30) of the force plug (3), set within the die opening (6) so as to define an annular gap (10) communicating with the cylindrical gap (4) for exit of the tubular parison; and a plunger (20) supporting at the bottom an ovalizing insert (40), slidably mounted within a chamber (32) formed in the bottom part (30) of the force plug. The plunger can pass from a retracted, resting, position, in which the bottom edge (48) of the ovalizing insert is located within the chamber (32), to an extracted, working, position, in which the bottom edge (48) of the ovalizing insert projects at the bottom with respect to the bottom edge (38) of the bottom part of the force plug.