Compressed-Air Mold Locking for Blow Molding Parting Lines
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Solution Overview
Problem
Conventional blow molding processes often result in parting lines due to unfavorable volume ratios between the locking mold and the container, leading to defective containers, as the development of force in the locking mold lags behind the rapidly expanding container bubble, causing material to press into open mold gaps before complete closure.
Innovation Solution
A method using a compressed air-operated mold locking device, where control compressed air is introduced early to secure the blow mold segments before blowing pressure is applied, utilizing a controllable relief valve to manage pressure and prevent mold opening during high blowing pressures, allowing sequential application of control and blowing air to maintain a robust closure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If blowing pressure is applied to the locking mold parallel to the pre-blowing and final blowing, then the mold locking device is actuated to hold the blow mold closed, but the force development in the locking mold lags behind the rapidly developing container bubble, causing material to press into mold gaps and create parting lines
Solution Approach 1:
The patent applies preliminary action by introducing control compressed air into the mold locking device before the main blowing pressure is applied to the preform. This early pressurization ensures the mold segments are already firmly closed and the locking force is fully developed before the container bubble expands, preventing material from pressing into mold gaps and eliminating parting lines.
Solution Approach 2:
The patent implements preliminary anti-action by using control compressed air to create a counter-pressure in the mold locking device that opposes any potential opening forces on the mold segments. This preliminary counter-action ensures the mold remains firmly closed during the critical initial phase of blowing when parting lines are most likely to form.
2Force
If the volume of the locking mold is large relative to the container volume, then the locking mold can provide sufficient holding force, but the feed line cross-section for introducing blowing air into the preform is significantly larger than that for the mold locking device, leading to different volume flows and rates of filling
Solution Approach 1:
The patent uses control compressed air as an intermediary medium to actuate the mold locking device. This separate control air line with its own regulator allows independent control of the locking device's pressurization rate, decoupling it from the main blowing air flow. This enables precise synchronization of mold closure with the blowing process regardless of the different feed line cross-sections.
Solution Approach 2:
The patent applies parameter changes by using a regulator on the control compressed air line to adjust and control the pressure and flow rate of air entering the mold locking device. This allows optimization of the pressurization speed to match the blowing process, ensuring the mold segments close firmly at the correct moment regardless of the volume ratio between locking mold and container.
3Ease of operation
If a separate electromagnetically controlled valve is provided for independent control of mold locking pressurization, then the duration and force of guard locking can be controlled independently, but the system complexity increases
Solution Approach 1:
The patent employs pneumatic control by using a regulator and control compressed air line to manage the pressurization of the mold locking device. This pneumatic approach provides smooth, continuous control of the locking force and duration without the need for complex electromagnetic valves, maintaining simplicity while achieving independent control capability.
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 approach ensures reliable form locking and prevents parting lines by exerting a consistent holding force, maintaining the blow mold in a closed state and avoiding high pressure-induced gaps between mold segments, thus improving the quality of blow-molded containers.
Implementation Method 1
the mold locking device being pressurized with compressed air for the purpose and for the duration of generating the holding force
Implementation Method 2
utilizing a controllable relief valve to manage pressure and prevent mold opening during high blowing pressures
Implementation Method 3
control compressed air from a control compressed air line has a controllable relief valve, the form locking device being acted upon at least at times with control compressed air from the control compressed air line
Data Source
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AI summary
The invention relates to a method for holding together a multi-part blow mold of a blow molding station for blow molding containers from preforms made of a thermoplastic material in their closed state, using a compressed air-operated mold clamp (14) exerting a holding force, wherein the mold clamp (14) is supplied with compressed air for the purpose and duration of generating the holding force, wherein the blow molding station has a relief valve controllable by means of control compressed air from a control compressed air line, and wherein the mold clamp is supplied with control compressed air from the control compressed air line at least temporarily. The invention further relates to a blow molding station and a blow molding machine.