Flexibility can be an asset — but not for a substrate used in the manufacture of an extremely sensitive electromechanical (EM) device.
Typically used in industrial machinery, medical devices, and consumer products, EM devices include mechanical and electrical components. Due to the critical nature of these devices, they usually require a high degree of structural rigidity for optimal performance.
Consider a rubber garden hose being stiff on a cold morning but pliable after warming in the sun. Now think of how an EM device would fare on a rubbery, flexible substrate compared to a rigid, inflexible surface. Not good, right?
So, when a client noticed a significant degree of movement in the substrates used to manufacture their sensitive electromechanical device, they contacted Innovatech Labs to help evaluate the problem.
The Problem
The customer was designing a product using a carbon epoxy composite. Renowned for exceptional mechanical properties, this substrate has extensive use in aircraft, automotive, and high-quality consumer products.
However, the customer’s device was not performing to expected standards; they observed a high degree of movement in the substrates. Which led to the question: Had the epoxy been cured correctly per the supplier’s specifications?
The Solution
When the client reviewed their production line, they uncovered possible issues in how the temperature of the cure was measured and with the ovens used to cure the epoxy.
Based on these concerns, the client cured four samples for testing. Samples 1 and 3 were cured in new ovens, and samples 2 and 4 were cured in old ovens. Thermocouples were placed on the composite substrates in all four ovens to get an accurate temperature measurement.
The client sent the four samples to Innovatech Labs for Differential Scanning Calorimetry (DSC) analysis — a test that measures the amount of energy absorbed or released by a sample when it is heated or cooled. DSC can observe even the most subtle phase transitions, making it an ideal choice to evaluate the degree of polymer curing in a material.
Above: Results of DSC scan. Click for larger view
The Results
The temperature at which an epoxy is cured has a direct impact on the glass transition temperature (Tg) of the finished epoxy. The Tg is the temperature range where a solid goes from a rigid or glassy state to a more pliant or rubbery state. The Tg is typically denoted by the midpoint of this temperature range for simplicity.
The data showed the Tg of the epoxy substrates cured in the old ovens were around 95°C. In contrast, the Tg of the substrates cured in the new ovens were around 120°C.
The client’s EM device routinely experienced temperatures above 95°C. When subjected to high temperatures, the substrates cured in the older ovens would exhibit micromovement, causing failures to occur. When Tg of the cured epoxy was near 120°C, there were no failures.
Based on this Differential Scanning Calorimetry analysis from Innovatech Labs, the client moved all production to the new ovens to ensure a suitable Tg of the carbon epoxy composite substrate. Not only did this change solve the problem, but it also provided a baseline for optimal substrate behavior.
Are Your Substrates a Moving Target? We Can Help You Understand Why.
Since 1990, Innovatech Labs has supported a wide range of industries with personalized lab testing services, rapid turnaround times and innovative approaches to materials analyses.
Email us to learn more about using Differential Scanning Calorimetry Services for quality control. Or, contacts us by phone at 888-740-5227.
Sources of Inspiration:
- Source material: https://docs.google.com/document/d/1tgYmknrxP1bKK5pCp76FwZegdee-GzJ2DeXqhOLN4lA/edit
- Case Study Layout: https://www.innovatechlabs.com/app-analysis-nitinol/
- Another example of failure analysis case study: https://www.innovatechlabs.com/app-plasticparts/
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