Sequential Molding of Thermosetting Elastomers
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Solution Overview
Problem
Thermosetting elastomers face challenges in molding processes due to premature curing, which limits the ability to form articles with desired properties and configurations, as the crosslinking process prevents further molding once the elastomer is cured.
Innovation Solution
A method involving sequential molding of thermosetting elastomer portions at a first temperature where the free radical initiator has a long half-life, allowing for incremental curing without significant torque increase, followed by rapid heating to a second curing temperature to complete the curing process, enabling the formation of articles with varied properties and configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If thermosetting elastomer is molded at high temperature to accelerate curing, then productivity is improved, but premature curing (scorching) occurs preventing further molding
Solution Approach 1:
The curing process is divided into two distinct stages: a first molding stage at lower temperature where the elastomer is formed without significant curing, and a second curing stage at higher temperature to complete the crosslinking. This segmentation allows the elastomer to be molded into complex shapes first, then cured afterward, resolving the contradiction between curing speed and molding flexibility.
Solution Approach 2:
The elastomer is molded into the desired shape at a lower temperature before the curing process begins. This preliminary molding action occurs while the material remains uncured and formable, allowing complex geometries to be created. Only after the shape is established does the high-temperature curing begin, preventing scorching during the molding phase while maintaining productivity through rapid subsequent curing.
2Manufacturing precision
If thermosetting elastomer is cured completely before molding, then manufacturing precision is improved, but the ability to form complex shapes is lost
Solution Approach 1:
The process separates shape formation from curing completion by using two temperature stages. The first stage at lower temperature allows the elastomer to be molded into complex shapes without significant crosslinking. The second stage at higher temperature completes the curing process. This ensures the elastomer maintains shape formation capability during molding while achieving complete curing for manufacturing precision in the final product.
Solution Approach 2:
The temperature parameter is changed between two distinct stages: a lower temperature during molding to prevent premature curing, and a higher temperature during the curing stage to achieve complete crosslinking. This parameter change allows the material to exhibit different properties at different stages - formable during molding, then rigid and stable after curing - resolving the contradiction between shape formation capability and curing completeness.
3Reliability
If molding time is extended to prevent premature curing, then scorching is prevented, but productivity decreases
Solution Approach 1:
The curing process is segmented into two temperature stages, with the first stage at lower temperature allowing extended molding time without scorching, and the second stage at higher temperature providing rapid curing completion. This segmentation maintains reliable curing control during the extended molding phase while minimizing overall cycle time through the rapid second-stage curing.
Solution Approach 2:
The process skips the premature curing phase by molding at lower temperature where crosslinking is minimized, then rushes through the complete curing process in a rapid second stage at higher temperature. This skipping of the problematic intermediate curing state prevents scorching while maintaining productivity through the fast completion curing stage.
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 allows for the creation of articles with controlled curing, preventing scorching and enabling the combination of different elastomer compositions to achieve desired mechanical, traction, and color properties in a single molding cycle, while maintaining the ability to form complex shapes and designs.
Implementation Method 1
all free radical initiator included in the first thermosetting elastomer portion has a long enough half-life such that during the molding time the first thermosetting elastomer portion is not cured or not significantly cured
Implementation Method 2
The mold can be heated to the second, curing temperature in a rapid heating method such as induction heating, for example heating from the first temperature to the second, curing temperature in from 2 seconds to 5 seconds
Data Source
AI summary
An article is molded from first and second thermosetting elastomer compositions each comprising free-radically curable elastomer and free radical initiator but different from one another. The first thermosetting elastomer composition is molded to fill a first area of a mold cavity at a first temperature at which the first free radical initiator has a half-life≤about 10 minutes or at which the first thermosetting elastomer composition has an increase in torque less than 10% of a total increase in torque at full cure. The second thermosetting elastomer composition is then inserted into the mold cavity, and the mold is heated to fully cure the article, for example a temperature at which each free radical initiator has a half-life≤about 1 minute, with the second composition filling a second area of the mold cavity before or during heating and curing.