Inverted Conical Preform Bottom for Stretch Blow Molding
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Solution Overview
Problem
The existing stretch blow molding process results in a thicker bottom surface section of bottles due to insufficient stretching caused by internal temperature differences and delayed stretching, leading to increased weight and non-uniform thickness, while attempts to reduce thickness are hindered by the undercut problem in mold design.
Innovation Solution
A preform with an inverted truncated conical bottom section, where the thickness of the bottom surface-forming portion is increased by a gently curved convex surface, allowing for more efficient stretching and preventing undercut issues, enabling the reduction of the bottom surface section's weight without excessive resin retention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the bottom section thickness is increased to facilitate stretching, then stretching is improved, but the preform cannot be released from the mold due to undercut
Solution Approach 1:
The patent inverts the conventional approach by making the bottom section thickness greater than the barrel section thickness, rather than making it smaller. This inversion allows the bottom section to stretch earlier and more effectively, eliminating resin excess while avoiding undercut issues through the inverted truncated conical geometry with draft angle
Solution Approach 2:
The patent employs asymmetric thickness distribution where the bottom section has greater thickness than the barrel section. This asymmetric design is achieved through the inverted truncated conical shape with draft angle, allowing different regions to stretch at different rates and achieve uniform final thickness without mold release problems
2Weight of moving object
If the bottom section thickness is reduced to reduce weight, then weight is reduced, but stretching is insufficient causing resin excess
Solution Approach 1:
The patent applies preliminary action by designing the bottom section with greater initial thickness before stretching. This preliminary thickness increase ensures that the bottom section stretches earlier and more effectively during the blow molding process, preventing resin excess and achieving uniform thickness without requiring post-stretching weight reduction
3Manufacturing precision
If injection pressure is increased to reduce bottom section thickness, then thickness is reduced, but whitening occurs due to flow orientation
Solution Approach 1:
The patent changes the geometric parameters of the bottom section by using an inverted truncated conical shape with draft angle, creating a thickness distribution that is greater than the barrel section. This parameter change allows the bottom section to stretch earlier and more effectively, achieving uniform thickness without requiring excessive injection pressure that would cause whitening
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
The preform design facilitates uniform stretching, reducing the weight of the bottle's bottom surface section while maintaining sufficient thickness for durability, and prevents the undercut problem, allowing for efficient mold release and reduced resin excess.
Implementation Method 1
the amount of internal heat contained in each part of the preform is proportional to its thickness
Implementation Method 2
the temperature in the stretched portion is reduced, and the stretched portion resists stretching
Implementation Method 3
a closed-end preform that is formed by injection molding of a plastic material, used to form a bottle by stretch blow molding
Implementation Method 4
the greater the thickness is, the larger the amount of internal heat is contained and the easier the stretching can be carried out
Data Source
AI summary
A preform having an inverted truncated conical bottom section is used. The inclined inner surface of a bottle bottom surface-forming portion of the bottom section is formed into a gently curved convex surface that extends from the lower portion of a bottle bottom edge-forming portion of the bottom section to a curved portion in the lower portion of the bottom section so that the thickness of the bottle bottom surface-forming portion is greater than the thickness of the barrel section of the preform and the thickness of the bottle bottom edge-forming portion. The increase in thickness of the bottom section improves the efficiency of stretching the bottom section, and the circumferential wall of the bottom section can thereby be efficiently stretched. This allows a reduction in weight (thickness) of the bottom surface section of a stretch blow molded bottle, and a reduction in weight of the bottle is thereby achieved.