Infrared Curing of Glass Fiber Composite Tube : Optimization of the curing cycle

Sammanfattning: This thesis has investigated the possibility of optimizing curing time by changing the energy source from a conventional oven to infrared radiation (IR) and if it is possible to achieve similar results as the company's current production of glass fiber composite tubes.   Many different parameters (time, temperature, heating rate, and rotation speed) might influence a cured composite tube's properties. Reduced factorial experiments were conducted to test all these parameters cost-efficient where each parameter was tested at a high and low level. However, every possible combination was not investigated.   Temperature measurements during the curing cycles, energy calculations, three-point bending, and differential scanning calorimetry analysis were conducted to compare the two different curing methods, hot air and IR curing. The current production flexural strength and glass transition temperature (Tg) have acted as benchmark values that the tubes cured with IR would have to reach to be considered a reliable manufacturing method. Differential scanning calorimetry (DSC) analyses were conducted to measure the Tg and three-point bending to determine the flexural strength. Due to that no standard exist for three-point bending of composite tubes, an in-house method was created and verified with a finite element simulation in Abaqus, to measure the flexural strength. The simulated reaction force was circa 76.9% of the measured force at the same displacement during the three-point bending test of the tubes. The simulation found that the stress concentration did occur at the same locations as the fracture occurred in the three-point bending test.     The temperature difference between the top of the laminate and the core was close to zero degrees for the current production by hot air in a thermal oven. A more significant temperature difference between the core and top of the laminate was found during curing with IR. However, a higher rotation speed was found to create a more evenly temperature distribution in the composite.    No clear correlation between the Tg and the flexural strength was found, as the literature suggests while comparing each test cured with IR. Nevertheless, by comparing every test cured with IR with the current production of the tube, it was determined that a lower Tg could cause a lower flexural strength. However, the lower flexural strength for the tubes cured by IR could also be explained by the temperature difference found between the core temperature and the top of the laminate during the curing process.       The reduced factorial experiments showed that it was possible to reach similar properties by curing with IR and reducing the curing time by 69.3%. Time and the combination of time and temperature were found to affect the result when it comes to the glass transition temperature. Regarding flexural strength, no parameters were found to impact the outcome. By investigating the time and temperature further, the curing time could be reduced to 71.3% compared with the current production and still achieve similar properties. Nevertheless, the energy use for curing with IR was found to require 8.3 times more than the current production.