title: A new method to predict optimum cure time of rubber compound using dynamic mechanical analysis

authors: Shuib, Raa Khimi

subjects: rubber

abstract: The degree of vulcanization of a rubber compound has a big influence on the properties of the final product. Therefore, precisely defining the curing process including optimum cure time is important to ensure the production of final products having high performance. Typically, vulcanization is represented using vulcanization curves. The main types of equipment used for producing vulcanization curves are the oscillating disc rheometer (ODR) and the moving die rheometer (MDR). These can be used to plot graphs of torque versus time at a constant temperature to show how cure is proceeding. Based on the results obtained, optimum cure time (t₉₀) is calculated as the time required for the torque to reach 90% of the maximum achievable torque. In this study, the use of Dynamic Mechanical Analysis (DMA) for assessment of t₉₀ was assessed. DMA was carried out using shear mode isothermal tests to measure the changes in material properties caused by vulcanization. The results revealed that the shear storage modulus (G′), shear loss modulus (G′′), and tan δ all reflect the vulcanization process, however, tan δ gave the best representation of level of vulcanization. Indeed, the curve of tan δ was able to be used to derive the t₉₀ for rubber compounds and showed good agreement with the results from an MDR.

text: A new method to predict optimum cure time of rubber compound using dynamic mechanical analysis The degree of vulcanization of a rubber compound has a big influence on the properties of the final product. Therefore, precisely defining the curing process including optimum cure time is important to ensure the production of final products having high performance. Typically, vulcanization is represented using vulcanization curves. The main types of equipment used for producing vulcanization curves are the oscillating disc rheometer (ODR) and the moving die rheometer (MDR). These can be used to plot graphs of torque versus time at a constant temperature to show how cure is proceeding. Based on the results obtained, optimum cure time (t₉₀) is calculated as the time required for the torque to reach 90% of the maximum achievable torque. In this study, the use of Dynamic Mechanical Analysis (DMA) for assessment of t₉₀ was assessed. DMA was carried out using shear mode isothermal tests to measure the changes in material properties caused by vulcanization. The results revealed that the shear storage modulus (G′), shear loss modulus (G′′), and tan δ all reflect the vulcanization process, however, tan δ gave the best representation of level of vulcanization. Indeed, the curve of tan δ was able to be used to derive the t₉₀ for rubber compounds and showed good agreement with the results from an MDR.

year: 2013

title: Tensile properties of Ti-6Al-4V discs produced by open die powder compact forging of pre-alloyed HDH powders

authors: Raynova, Stiliana (Stella) Rousseva

subjects: Forging

abstract: Open die powder compact forging was employed for consolidation of Ti-6Al-4V(wt.%) powders which were produced by a hydride-dehydride (HDH) process. The powders were initially warm-compacted into cylindrical shapes. Induction heating was used for preheating the compacts prior to forging into plates. The effect of the forging parameters such as temperature and pre-sintering time on the microstructure and tensile properties of the forged plates were studied. Porosity and the alpha-beta phase distribution were investigated to enable a better understanding of their effect on the fracture behaviour of the tensile tested specimens. The fracture surfaces of the broken tensile specimens were analysed using Scanning Electron Microscopy (SEM) to find the correlation between microstructure, residual porosity and fracture behaviour. A combination of high ultimate tensile strength of over 1200MPa and a good ductility reflected by an elongation to fracture of around 10% was achieved in some of the forged discs.

text: Tensile properties of Ti-6Al-4V discs produced by open die powder compact forging of pre-alloyed HDH powders Open die powder compact forging was employed for consolidation of Ti-6Al-4V(wt.%) powders which were produced by a hydride-dehydride (HDH) process. The powders were initially warm-compacted into cylindrical shapes. Induction heating was used for preheating the compacts prior to forging into plates. The effect of the forging parameters such as temperature and pre-sintering time on the microstructure and tensile properties of the forged plates were studied. Porosity and the alpha-beta phase distribution were investigated to enable a better understanding of their effect on the fracture behaviour of the tensile tested specimens. The fracture surfaces of the broken tensile specimens were analysed using Scanning Electron Microscopy (SEM) to find the correlation between microstructure, residual porosity and fracture behaviour. A combination of high ultimate tensile strength of over 1200MPa and a good ductility reflected by an elongation to fracture of around 10% was achieved in some of the forged discs.

year: 2012

title: Māori, Tongan and Chinese households: Medications and elder care

authors: Nikora, Linda Waimarie

subjects: medications

abstract: Research reveals that medicines are frequently not taken as intended, stockpiled for future use, discontinued when symptoms fade or passed to others. Medications are material objects with therapeutic uses that enter into and take on meaning within people’s lives. In this way they are culturally embedded phenomena that carry meanings and shape social relationships and practices. The symbolic meanings given to medications and cultural relations are important for understanding variations in medication practices. Households with elders often contain more medications and have more complex age-related medical conditions. In households where members are engaged in the reciprocation of care among two or three generations, medications within and between these relationships take on a range of dynamic meanings. In this paper, we explore how interactions between household members affect medicines-taking practices of elders and their families from three cultural groups: Māori, Tongan and Chinese. This research was funded by the Health Research Council of New Zealand and the Marsden Fund of the Royal Society of New Zealand.

text: Māori, Tongan and Chinese households: Medications and elder care Research reveals that medicines are frequently not taken as intended, stockpiled for future use, discontinued when symptoms fade or passed to others. Medications are material objects with therapeutic uses that enter into and take on meaning within people’s lives. In this way they are culturally embedded phenomena that carry meanings and shape social relationships and practices. The symbolic meanings given to medications and cultural relations are important for understanding variations in medication practices. Households with elders often contain more medications and have more complex age-related medical conditions. In households where members are engaged in the reciprocation of care among two or three generations, medications within and between these relationships take on a range of dynamic meanings. In this paper, we explore how interactions between household members affect medicines-taking practices of elders and their families from three cultural groups: Māori, Tongan and Chinese. This research was funded by the Health Research Council of New Zealand and the Marsden Fund of the Royal Society of New Zealand.

year: 2010