Swimming Goggles Material Selection
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Introduction Initially when we were given this project my topic was oven trays. By my own admission I am no expert in the kitchen so the idea of doing a detailed project on one of its common utensils did not enthral me. I also felt that they would be quite simple to design because they are so simple in shape. I wanted something more interesting and challenging. That is why I asked ot change to swimming goggles. Swimming is something that I am both interested in and partake in and I felt that the numerous different shapes and plastics in its design would make for an interesting project. Throughout the project I have attempted to be as clear and concise as possible. It begins by outlining what the requirements of goggles are and then goes on to talk briefly about each separate part. One part is then looked at in detail, both its material selection and its production process. Some general design issues are then discussed and costs are also dealt with. It is important to note that there are many different designs of goggles on today's market. These range from small top of the range racing goggles to large bulky deep sea diving goggles. In this project I have decided to discuss a typical pair of swimming goggles that anyone might use when they go swimming in the gym or on holidays. In general I have attempted to use photos, diagrams, charts and tables to help emphasise the point I am trying to get across as well as to make the project more visually tedious. All references are listed at the back of the report and numbers in square brackets are used to identify them. I hope that the project gives sufficient details into the design process of a pair of swimming goggles. General Polymer Information Polymers are molecules which consist of a long, repeating chain of smaller units called monomers.
Polystyrene already contributes to much of the worlds pollution and it is for this reason that it is becoming less and less popular as a manufacturing material. The Final Choice While all of the materials described above have many benefits in terms of being used in swimming goggle lenses they are rarely seen. This is because there is a more popular and more suitable choice which is used in almost every design throughout the industry-Polycarbonate. The following section will now take a detailed look at polycarbonate and explain why it is used ahead of the other materials Polycarbonate (PC) Polycarbonate is a tough, dimensionally stable, transparent thermoplastic that has many applications which demand high performance properties. This includes being used in not only swimming goggles but many different types of lenses. From eyeglasses to high performance skiing goggles many make use of polycarbonate. Polycarbonate can be synthesized from bisphenol A and phosgene (carbonyl dichloride, COCl2). The following diagrams and explanations show how this occurs. The first step in the synthesis of polycarbonate from bisphenol A is treatment of bisphenol A with sodium hydroxide. This deprotonates the hydroxyl groups of the bisphenol A molecule. The deprotonated oxygen reacts with phosgene through carbonyl addition to create a tetrahedral intermediate (not shown here), after which the negatively charged oxygen kicks off a chloride ion (Cl-) to form a chloroformate. The chloroformate is then attacked by another deprotonated bisphenol A, eliminating the remaining chloride ion and forming a dimer of bisphenol A with a carbonate linkage in between. Repetition of this process yields a polycarbonate with alternating carbonate groups and groups from bisphenol A.  So now that we know how it is formed the next thing to look at is why it is suitable to be used in the lens industry. The following list shows some of the relevant properties of PC: Figure 7: Table Showing Properties of PC  Mechanical properties Elongation at break 100 - 150 % Elongation at yield 6 - 8 % Flexibility
The final environmental issue is in the area of the production process used to make the lenses. This should be done in a way to minimise any harmful side effects to the environment. This means that things should be done to reduce the power required and to ensure that no harmful bye-products are produced. The process described in the manufacturing section above is a relatively "clean" process and shouldn't harm the environment. Commercial Exploitation This term appears to have a number of vastly different definitions. I will now briefly look at the main three understandings of the term. In some cases it refers to exploiting the work force that is producing the good or excessive damage to the environment arising from the production process. However this later point is more environmental exploitation. The exploitation of the work force relates to a number of things ranging from child labour to sexism in the work place. The second understanding of the term refers to exploiting, or making the most of the market in which the good finds itself. Things like patenting designs and setting up monopolies are examples of this type of exploitation. In effect it means producing a good and at the same time preventing others from producing the same, or a similar, design. The final way in which the term can be interpreted is in relation to the consumer or user of the product. In this case it is a question of how the consumer is encouraged to buy the product and how this number can be maximised. This understanding of the term is more of a marketing related one as opposed to an engineering one. In the case of swimming goggles none of these factors play a huge role. So long as a fair and just production process is used and the product is marketed as well as possible there is not a lot more that we as design engineers can do. ?? ?? ?? ?? 1
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