Injection Molded Preform Base Tapering for Concentricity
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Solution Overview
Problem
Conventional injection moulding processes for producing preforms with high flow-length-to-wall thickness ratios face challenges such as high fill pressures leading to non-concentricity, increased material costs, and longer cycle times, which are exacerbated by the crystallization of thermoplastic materials at high pressures and temperatures, causing blockages and restricting resin flow.
Innovation Solution
The design of an injection moulded thermoplastic preform with a central part featuring a downwardly and radially inwardly tapering portion that reduces fluid pressure near the gate, combined with a second upwardly and radially outwardly tapering portion to accelerate resin flow and minimize crystallization, allowing for higher flow rates and reduced filling times while maintaining concentricity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high injection pressure is used to fill the mould cavity, then the mould cavity can be filled with molten plastics material, but non-concentric preforms are produced due to core flexing
Solution Approach 1:
The patent changes the physical parameters of the base portion by creating a dual-density structure with a high-density central region and a lower-density peripheral region. This structural parameter change allows the base to withstand high injection pressures without excessive flexing, maintaining preform concentricity while enabling cavity filling at high pressures
Solution Approach 2:
The base portion is segmented into distinct density zones - a central high-density region and a peripheral lower-density region. This segmentation allows different parts of the base to perform different functions: the central region provides structural support to prevent core flexing, while the peripheral region allows controlled deformation for concentric preform formation
2Productivity
If faster injection rate and higher melt temperature are used, then mould filling is enabled, but fill pressure remains high
Solution Approach 1:
The patent changes the rheological parameters of the molten plastics material by raising the melt temperature, which reduces melt viscosity. This allows faster injection rates to be achieved while managing fill pressure through the combined effect of reduced viscosity and the base portion's pressure distribution characteristics
3Stress or pressure
If base thickness is increased to reduce fill pressure, then material flow restriction is reduced, but material costs and thermal energy consumption increase
Solution Approach 1:
The patent applies local quality by creating regions of different densities within the base portion. The central high-density region provides the necessary structural support to manage fill pressure, while the peripheral lower-density region reduces overall material consumption. This local differentiation allows pressure management without proportionally increasing total base material quantity
Solution Approach 2:
The base portion is segmented into functional zones with different material densities, allowing the central region to bear the mechanical load of pressure resistance while the peripheral region uses less material, thereby reducing total material consumption while maintaining pressure management capability
4Productivity
If high fill pressure is used, then resin flow rate can be increased, but crystallization causes blockages and restricts resin flow
Solution Approach 1:
The patent changes the thermal parameters by maintaining higher melt temperatures and using the base portion's thermal mass to prevent rapid cooling. This parameter control prevents crystallization during injection, ensuring resin flow continuity at high flow rates without blockages
5Strength
If preform weight is increased, then material strength is improved, but material costs and thermal energy consumption increase
Solution Approach 1:
The patent applies local quality by concentrating higher density material in the central region of the base portion where structural strength is most needed, while using lower density material in the peripheral regions. This localized strengthening provides necessary preform strength while minimizing total material consumption
Solution Approach 2:
The preform base is segmented into high-strength central regions and lower-material-consumption peripheral regions, allowing strength to be optimized where required while reducing overall material quantity and associated costs and energy consumption
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 enables a significant increase in resin flow rate up to 200 grams per second, reduces filling time to less than 2 seconds, and achieves higher concentricity, leading to material cost savings and reduced thermal energy consumption by allowing for thinner preform bases and longer lengths with reduced wall thickness, while minimizing crystallinity-induced blockages.
Implementation Method 1
a first, downwardly and radially inwardly tapering portion (15) therebetween which increases in thickness from a radially outer end (17) of the first tapering portion (15) adjacent to the hollow transition portion (8) to a radially inner end (19) of the first tapering portion (15) adjacent to the gate part (20) and the middle part (11) opposite the gate part (20), wherein the first tapering portion (15) allows the injected resin to be urged back through the gate part (20) at the end of the injection moulding cycle at a lower fluid pressure in the vicinity of the gate part (20)
Implementation Method 2
a second, upwardly and radially outwardly tapering portion (24) extending away from the central part (14) to connect to the hollow body portion (6), wherein the second tapering portion (24) increases in thickness from the central part (14) to the hollow body portion (6)
Data Source
Figure 1~2
Figure 3
AI summary
An injection moulded thermoplastic preform (2) for blow moulding to form a container, the preform (2) comprising a lower closed base portion (4), a hollow body portion (6), a hollow transition portion (8) between the lower closed base portion (4) and the hollow body portion (6), and an upper open end portion (10) adjacent to an upper part of the hollow body portion (6), wherein the closed base portion (4) comprises a central part which extends over at least 50% of an internal radius of a lower end (16, 25) of the hollow body portion (6), the central part having an external surface (109, 29, 36, 5) which comprises an outwardly raised gate (64, 68) part surrounding a central longitudinal axis of the preform (2) and a first peripheral part surrounding the gate (64, 68) part, the first peripheral part being convex and an internal surface (18, 9) which is concave and comprises a middle part opposite the gate (64, 68) part and a second peripheral part surrounding the middle part, wherein the first and second peripheral parts define a first, downwardly and radially inwardly tapering portion (15) therebetween which increases in thickness from a radially outer end (117, 17) of the first tapering portion (15, 24) adjacent to the hollow transition portion (8) to a radially inner end (119, 19) of the first tapering portion (15, 24) adjacent to the gate (64, 68) part and the middle part opposite the gate (64, 68) part, and the transition portion (8) comprises a second, upwardly and radially outwardly tapering portion (24) extending away from the central part to connect to the hollow body portion (6), the second tapering portion (15, 24) increasing in thickness from the central part to the hollow body portion (6).