Thermoplastic Blow Molding Insert Protection via Bypass Pressure Equalization
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Solution Overview
Problem
Existing methods for producing hollow bodies from thermoplastic material, such as extrusion blow molding, face challenges in introducing inserts without damaging sealing elements or collapsing components due to differential pressure, which requires manual and laborious closing of inserts after production.
Innovation Solution
A method involving the use of a multipart blow molding tool to introduce and join inserts as self-contained part-volumes within the hollow body, with pressure equalization between the main volume and part-volume achieved through a bypass line, allowing for simultaneous application of pressure and preventing insert damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If differential pressure is applied during blow molding to shape the hollow body, then the hollow body achieves its desired form, but inserts such as sealing elements, valves, and bubble vessels may be destroyed or collapsed
Solution Approach 1:
The hollow body is divided into a main volume and separate part-volumes (inserts such as bubble vessels, expansion tanks, and venting lines). Each part-volume is independently formed and then joined to the main volume, allowing differential pressure to be applied separately to each segment during the molding process, thereby protecting inserts from damage while achieving precise shaping of the overall structure.
Solution Approach 2:
Inserts are pre-formed as separate part-volumes with their own sealing elements and structures intact before being introduced into the blow molding tool. The sealing elements are pre-installed and sealed on the inserts before the main blow molding process, so that when differential pressure is subsequently applied to shape the main hollow body, the inserts are already protected and cannot be damaged.
2Productivity
If inserts are introduced into the hollow body during production, then assembly efficiency is improved, but manual closing of inserts after production becomes laborious and costly
Solution Approach 1:
The forming of inserts and the closing of the hollow body are merged into a single integrated blow molding process. Inserts are formed as part-volumes within the same mold cavity as the main hollow body, and the mold closure simultaneously completes both the main body and the inserts. This eliminates the need for separate manual closing operations, reducing labor and costs while maintaining high assembly efficiency.
Solution Approach 2:
The blow molding tool itself performs the closing function for both the main hollow body and the inserts simultaneously. The mold halves close and apply pressure to both the main volume and part-volumes at the same time, making the system self-sufficient and eliminating the need for additional manual intervention or separate closing equipment.
3Device complexity
If sealing elements and valves are introduced into the hollow body during blow molding, then assembly is simplified, but the differential pressure may cause destruction of these sensitive components
Solution Approach 1:
The hollow body structure is segmented into a main volume and separate part-volumes for inserts. Each segment can be formed and pressurized independently during the blow molding process, allowing sealing elements and valves to be protected within their own sealed part-volumes while the main body is being shaped by differential pressure.
Solution Approach 2:
Sealing elements and valves are pre-installed and sealed onto the inserts before the blow molding process begins. The inserts are prepared as complete, sealed units with all sensitive components protected, then introduced into the mold. When differential pressure is applied during molding, the pre-sealed inserts are protected from pressure damage while still achieving simplified assembly.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method enables the secure and efficient introduction of inserts during the blow molding process, preventing damage and simplifying the closure process, reducing labor and costs while ensuring accurate sealing.
Implementation Method 1
a pressure equalization with the part-volume is brought about parallel to the application of pressure to the main volume
Implementation Method 2
the pressure equalization takes place by the part-volume within the closed blow molding tool being connected at least for a time to the main volume by way of at least one bypass line
Implementation Method 3
joining together the shells by closing the blow molding tool and applying pressure to the main volume enclosed by the hollow body
Data Source
AI summary
The invention relates to a method for producing hollow bodies from thermoplastic material comprising the shaping of at least one tubular preform or at least two two-dimensional, web-like preforms of plasticated thermoplastic material into a substantially closed hollow body, for example in the form of a fuel tank for motor vehicles.