Stretch Blow Moulding Mandrel for Uniform Preform Deformation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The existing two-stage injection stretch blow molding process faces challenges in producing small capacity plastic containers with improved CO2 barrier properties and uniform stretching, as preforms with small internal diameters are prone to local cooling and uneven deformation when using traditional stretching mandrels, leading to issues like bursting or uneven wall thickness.
Innovation Solution
A stretch blow molding process where the preform is heated to at least 70°C and a stretching mandrel with a body and tip is inserted to uniformly contact the inside wall of the preform, allowing for uniform temperature change and increased stretching without mandrel instability, enabling greater strain hardening and improved barrier properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a traditional stretching mandrel is used in two-stage injection stretch blow molding, then the preform can be stretched, but local cooling and uneven deformation occur leading to bursting or uneven wall thickness
Solution Approach 1:
The stretching mandrel is designed with varying diameters along its length, creating different contact characteristics at different locations. The larger diameter sections provide stable contact and stretching control, while the smaller diameter sections prevent excessive contact pressure and local cooling. This local variation in mandrel geometry resolves the contradiction between achieving uniform wall thickness and maintaining stretching reliability.
2Volume of moving object
If the preform internal diameter is small, then container capacity is reduced, but mandrel stability decreases leading to stretching issues
Solution Approach 1:
The stretching mandrel features a non-uniform diameter profile with larger diameter sections positioned strategically within the small-diameter preform. This allows the mandrel to maintain adequate contact and stability even in small preforms, while the varying geometry prevents excessive contact pressure that would cause local cooling and deformation issues.
Solution Approach 2:
The stretching process uses a dynamic approach where the mandrel is inserted to a controlled depth and the stretching force is applied progressively. The mandrel's varying diameter profile dynamically adapts to the preform geometry, providing stable contact where needed while allowing flexibility in other areas, thus maintaining mandrel stability in small capacity containers.
3Strength
If the stretching mandrel contacts the preform wall, then stretching is achieved, but local cooling occurs causing uneven deformation
Solution Approach 1:
The stretching mandrel is designed with varying diameters that create optimized contact zones. The smaller diameter sections reduce contact pressure and minimize heat transfer to the mandrel, preventing local cooling. The larger diameter sections provide stable stretching control. This local differentiation resolves the contradiction between achieving sufficient stretching for strength and maintaining temperature uniformity.
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 process results in plastic containers with enhanced strain hardening, reduced susceptibility to stress cracking, and increased strength, allowing for lighter designs with improved CO2 barrier properties and uniform material density, particularly suitable for small volume containers.
Implementation Method 1
the preform body is heated to at least 70° Celsius
Implementation Method 2
the preform body and the preform base are stretched into the cavity, the preform body and the preform base are deformed according to the cavity
Implementation Method 3
by introducing a fluid into the preform under pressure
Implementation Method 4
is stretched by a gas blown into the preform according to the mold cavity of the blow mold inflated
Data Source
Figure 1~3b
Figure 4
AI summary
The invention relates to a stretch blow moulding process for producing a plastic container from a preform (11), having an elongated, tubular preform body (21), extending along a centre axis (12) of the preform (11), with a first end (23) and a second end (25), which is substantially opposite from the first end (23), wherein the first end (23) is closed by a preform bottom and the second end (25) is adjoined by a neck part (31) with a pouring opening (35), and with a wall (13), bounding an interior space (19) of the preform (11), with an inner side (17) and an outer side (15). In the process, the preform body (21) is heated to at least 70° Celsius and introduced into a cavity of a blow mould. A stretching mandrel with a stretching mandrel body and a stretching mandrel tip is made to enter the preform (11), until the stretching mandrel tip reaches the preform bottom (23). Then, the preform body (21) and the preform bottom (23) are stretched into the cavity by the stretching mandrel, and then the preform body (21) and the preform bottom (23) are deformed according to the cavity by introducing a fluid into the preform (11) under pressure. While it is entering the preform (11), until it reaches the preform bottom (23), the stretching mandrel thereby makes contact with the inner side (17) of the wall (13) in the region of the preform body (21) at at least one predetermined partial region.