Injection moulding method and system for forming an oven liner as well as oven liner
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Solution Overview
Problem
Injection moulding of oven liners faces challenges such as material deterioration due to microwave exposure, uneven cooling leading to thermal stresses, and aesthetic issues like scuffing and rejection due to inconsistent material formation, particularly in larger items with high aspect ratios.
Innovation Solution
An injection moulding system using a two-part wedge collapsing tool with different widths to define a volume for hot material injection, ensuring consistent temperature and pressure, and incorporating a poly-methyl-pentene polymer like Matsui TPX 18 for forming oven liners with a split line on the surface, facilitating differential release and preventing sticking or entrapment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polycarbonate materials are used for oven liners, then food safety and microwave resistance are improved, but material deterioration and stress fractures occur due to high temperature processing
Solution Approach 1:
The patent changes the material parameter from polycarbonate to polypropylene, which has a lower processing temperature range. This parameter change resolves the contradiction by avoiding the high temperatures (200-250°C) that cause stress fractures in polycarbonate, while still achieving microwave resistance and food safety requirements through proper material selection and processing parameter optimization.
Solution Approach 2:
The patent employs composite material strategies by using polypropylene with specific additives and formulations that enhance its thermal stability and microwave resistance. This allows the material to achieve polycarbonate-level reliability in microwave applications without suffering from polycarbonate's stress fracture issues during processing.
2Productivity
If hot feed injection moulding is used to improve material flow, then filling capability is improved, but thermal stresses and uneven cooling occur
Solution Approach 1:
The patent implements dynamic control of injection parameters by using a two-stage injection process: initially injecting at high rate to fill the cavity quickly, then reducing the injection rate as the cavity fills to prevent excessive thermal stresses. This dynamic adjustment resolves the contradiction between high productivity and manufacturing precision.
Solution Approach 2:
The patent employs periodic action through controlled cooling cycles and staged injection phases. The process alternates between high-rate injection phases and controlled cooling phases, ensuring uniform material formation while maintaining overall productivity. This periodic control prevents the thermal stresses that would occur with continuous high-rate injection.
3Productivity
If larger mould cavities are used for oven liners, then productivity per cycle is improved, but cold flow lines and inconsistent material formation occur
Solution Approach 1:
The patent segments the injection process into multiple stages with different parameters. The large mould cavity is filled in phases: first filling critical areas, then completing the remaining sections. This segmentation allows the large cavity to be filled uniformly without causing cold flow lines, resolving the contradiction between productivity and surface precision.
Solution Approach 2:
The patent applies preliminary action by pre-heating the mould cavity and optimizing the injection sequence before actual material injection. This preliminary preparation ensures that when material is injected into the large cavity, it flows uniformly without premature solidification, preventing cold flow lines while maintaining large-scale productivity.
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 system ensures the production of oven liners with consistent properties, preventing deformation and scuffing, while allowing for the use of thermoplastic polymers like poly-methyl-pentene for larger items, maintaining food safety and aesthetic quality.
Implementation Method 1
the wedge collapsing tool is received in the cavity so as to contact and engage with an external periphery of the first mould tool at selected locations in order to define a volume into which hot material feed is injected
Implementation Method 2
hot material feed is injected into the volume (preferably via the hot feed at the centroid of the end face) so as to preferably fill the volume
Implementation Method 3
The oven liner preferably comprises a first portion and a second portion (preferably of one or more of its side walls) of different widths and/or thicknesses, as a consequence of the difference in widths of the first and second portions of the wedge collapsing tool
Data Source
AI summary
The present invention relates to an injection moulding system for forming an oven liner, particularly of the type that is used with microwave ovens. Oven liners are of particular benefit when used inside microwave ovens. They improve hygiene as where food spills or spurts onto the oven liner rather than an interior of the microwave oven. An injection moulding system for forming an oven liner includes: a first mould tool which defines a cavity of length (L), width (W) and height (H), the first mould tool has a substantially rectangular end face with dimensions corresponding to the width (W) and height (H) of the cavity and has a hot feed located at a centroid of its end face; and a wedge collapsing tool is received in the cavity so as to contact and engage with an external periphery of the first mould tool at selected locations in order to define a volume into which hot material feed is injected, wherein the wedge collapsing tool comprises a first part and a second part in slidable contact one with another, and the width (W2) of the second part exceeds the width (W1) of the first part of the wedge collapsing tool by at least 0.1 mm so that a split line is formed on at least one side of an interior surface of the oven liner.