Electrical-static discharge in single point diamond turning machining of contact lens polymers
- Authors: Kadermani, Mohamed Munir
- Date: 2015
- Subjects: Electric discharges , Electrostatics , Contact lenses , Polymers
- Language: English
- Type: Thesis , Masters , MEngineering (Mechatronics)
- Identifier: http://hdl.handle.net/10948/4055 , vital:20508
- Description: Single Point Diamond Turning (SPDT) is a technology widely applied for the fabrication of contact lenses. One of the limiting factors in polymer machining is wear of the diamond tool due to electrostatic discharge resulting in poor surface quality of the machined products. The research work presented in this dissertation highlights the electrostatic properties of contact lenses during machining operations and the effects these properties have on the surface quality of the work piece materials. Two contact lens samples were experimented on, Definitive 74 (Silicone Hydrogel) and Tyro 97 (Rigid Gas Permeable). The electrostatic surface potentials (ESPs) were measured during turning operations using an electrostatic voltmeter and the surface roughness measurements were taken using a surface profilometer. Response Surface Methodology (RSM) techniques were employed to create predictive models for both surface roughness and ESPs with respect to the cutting speed, feed rate and depth of cut. Predictive surface roughness models were successfully generated for both materials and the cutting speed and feed rate were identified as the parameters with most effect on surface roughness. In addition, an electrostatic model was successfully generated for the Definitive 74 contact lens material which cited the cutting speed and feed rate as the most effective parameters on the material’s electrostatic behaviour. However, no relationship was evident between the machining parameters and electrostatic behaviour of Tyro 97.
- Full Text:
- Date Issued: 2015
- Authors: Kadermani, Mohamed Munir
- Date: 2015
- Subjects: Electric discharges , Electrostatics , Contact lenses , Polymers
- Language: English
- Type: Thesis , Masters , MEngineering (Mechatronics)
- Identifier: http://hdl.handle.net/10948/4055 , vital:20508
- Description: Single Point Diamond Turning (SPDT) is a technology widely applied for the fabrication of contact lenses. One of the limiting factors in polymer machining is wear of the diamond tool due to electrostatic discharge resulting in poor surface quality of the machined products. The research work presented in this dissertation highlights the electrostatic properties of contact lenses during machining operations and the effects these properties have on the surface quality of the work piece materials. Two contact lens samples were experimented on, Definitive 74 (Silicone Hydrogel) and Tyro 97 (Rigid Gas Permeable). The electrostatic surface potentials (ESPs) were measured during turning operations using an electrostatic voltmeter and the surface roughness measurements were taken using a surface profilometer. Response Surface Methodology (RSM) techniques were employed to create predictive models for both surface roughness and ESPs with respect to the cutting speed, feed rate and depth of cut. Predictive surface roughness models were successfully generated for both materials and the cutting speed and feed rate were identified as the parameters with most effect on surface roughness. In addition, an electrostatic model was successfully generated for the Definitive 74 contact lens material which cited the cutting speed and feed rate as the most effective parameters on the material’s electrostatic behaviour. However, no relationship was evident between the machining parameters and electrostatic behaviour of Tyro 97.
- Full Text:
- Date Issued: 2015
Teaching and learning electrostatics using everyday knowledge, indigenous knowledge and scientific argumentation
- Authors: Loggenberg, Ernest Wilfred
- Date: 2012
- Subjects: Electrostatics , Ethnoscience
- Language: English
- Type: Thesis , Masters , MEd
- Identifier: vital:9505 , http://hdl.handle.net/10948/d1008412 , Electrostatics , Ethnoscience
- Description: South African School Curriculum, calls for the integration of IKS within school science (Department of Education, 2006, Department of Basic Education, 2011). Lightning is an area of high interest in the Eastern Cape and is used as the topic in this study which focuses on the integration of indigenous knowledge systems in science education. The study investigated the impact of an intervention strategy framed around the use of scientific argumentation and the integration of everyday knowledge and indigenous knowledge systems (IKS) into the teaching of electrostatics at Grade Ten level. The impact focused on the teachers’ ability to implement the strategy, the electrostatics knowledge gained by learners, the learners’ argumentation ability, and the motivational and confidence levels of both teachers and learners. The sample comprised eight schools (the science teachers and their Grade Ten Physical Science learners) in the Uitenhage District of Education of the Eastern Cape Province of South Africa. Qualitative data were generated via interviews, classroom observations, pre- and post test questionnaires with open-ended questions to evoke meaningful responses that could not be anticipated by the research, and argumentation writing frames for both teachers and learners. Limited quantitative data were generated via the argumentation writing frames and the more close-ended questionnaire questions. The findings of the teacher and learner argumentation frames and the teacher checklists which revealed that the intervention impacted positively on the teachers’ ability to integrate IKS into their teaching practice. The use indigenous knowledge as the context for argumentation appears to have been a more effective way of introducing the concept than doing so within a scientific context (which the learners found difficult). The intervention facilitated an enhanced level of understanding on lightning, and assisted with the creation of the “third space” and border crossing between IKS and western science. The individual interviews disclosed the teachers’ improved ability to integrate IKS, IKS improving the facilitation of the argumentation strategy, and their improved motivation and confidence.
- Full Text:
- Date Issued: 2012
- Authors: Loggenberg, Ernest Wilfred
- Date: 2012
- Subjects: Electrostatics , Ethnoscience
- Language: English
- Type: Thesis , Masters , MEd
- Identifier: vital:9505 , http://hdl.handle.net/10948/d1008412 , Electrostatics , Ethnoscience
- Description: South African School Curriculum, calls for the integration of IKS within school science (Department of Education, 2006, Department of Basic Education, 2011). Lightning is an area of high interest in the Eastern Cape and is used as the topic in this study which focuses on the integration of indigenous knowledge systems in science education. The study investigated the impact of an intervention strategy framed around the use of scientific argumentation and the integration of everyday knowledge and indigenous knowledge systems (IKS) into the teaching of electrostatics at Grade Ten level. The impact focused on the teachers’ ability to implement the strategy, the electrostatics knowledge gained by learners, the learners’ argumentation ability, and the motivational and confidence levels of both teachers and learners. The sample comprised eight schools (the science teachers and their Grade Ten Physical Science learners) in the Uitenhage District of Education of the Eastern Cape Province of South Africa. Qualitative data were generated via interviews, classroom observations, pre- and post test questionnaires with open-ended questions to evoke meaningful responses that could not be anticipated by the research, and argumentation writing frames for both teachers and learners. Limited quantitative data were generated via the argumentation writing frames and the more close-ended questionnaire questions. The findings of the teacher and learner argumentation frames and the teacher checklists which revealed that the intervention impacted positively on the teachers’ ability to integrate IKS into their teaching practice. The use indigenous knowledge as the context for argumentation appears to have been a more effective way of introducing the concept than doing so within a scientific context (which the learners found difficult). The intervention facilitated an enhanced level of understanding on lightning, and assisted with the creation of the “third space” and border crossing between IKS and western science. The individual interviews disclosed the teachers’ improved ability to integrate IKS, IKS improving the facilitation of the argumentation strategy, and their improved motivation and confidence.
- Full Text:
- Date Issued: 2012
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