Materials Science Applied to Household Appliances

Transcription

1 Abstract Materials Science Applied to Household Appliances Adapted from PNNL Teachers Handbook* This exercise gives students experience with materials used in products that they are around every day. It provides an opportunity for them to explore, discover, and handle the inner makings of common household items. Students will use simple tools to disassemble household appliances, such as a toaster or curling iron, and categorize the engineering materials that were used to manufacture the appliance. Module objectives: Students will study basic safety procedures, and will gain confidence and experience using simple tools, as they disassemble common household appliances and other manufactured items. Students may gain valuable insight into manufacturing methods and practices, and the reasoning that goes into the choice of an engineering material for a particular application. Student learning objectives: At the end of this activity, students will be able to: Plan and carry out an investigation related to consider how materials are used in real applications, by dismantling an appliance and categorizing the use of each material. Use appropriate tools in their intended way to assist in dismantling the appliance. Develop a model to describe how and why materials are used as they are used. Communicate the information obtained to the class group. Core competencies for Engineers and Technicians 0.A Demonstrate Good Communication Skills 0.B Prepare tests and analyze data 7.A illustrate the General Nature of Metals 7.K Compare Thermal, Physical and Other Properties of Materials Unit data: Key words: fibers, composite materials, metals, ceramics, polymers,

2 Type: Lab Target grade levels: All Time required: One 50-minute class period Suggested prerequisite: Module on Classification of Materials Equipment and supplies needed: Old appliances (such as toasters, irons, hair driers, wind-up toys, clocks, curling irons, cameras, mechanical or electrical toys). These types of appliances are generally available at area thrift stores. Screwdrivers, Phillips and straight edge (Most screws can be undone with miniscrewdrivers, but you will want to have some large-handled screwdrivers to loosen hard turning screws Pliers and Wire cutters Containers (plastic or paper bags) Permanent marker pens Ohm meter or continuity device Safety glasses Instructor background information: Applications of materials in products depends on materials properties and the ability to manufacture the material in the needed form. Metals are the basis of applications in many household products, but their use has been superceded in recent years by other classes of materials which may have similar or better properties and often cost less. Because of their broad range of properties, both synthetic and natural polymers play an essential and ubiquitous role in everyday life. Polymers already have a range of applications that far exceeds that of any other class of material available to man. Current applications extend from adhesives, coatings, foams, and packaging materials to textile and industrial fibers, composites, electronic devices, biomedical devices, and optical devices. Ceramics offer many advantages compared to other materials. They are harder and stiffer than steel; more heat and corrosion resistant than metals or polymers; less dense than most metals and their alloys; and their raw materials are both plentiful and inexpensive. Until the 1950s, the most important ceramic materials were (1) pottery, bricks and tiles, (2) cements and (3) glass. Modern technical ceramics now include a wide range of materials and products such as high temperature superconductors,, ferroelectric capacitors, blades for kitchen knives, infrared optical windows, magnets, porcelain, oxygen sensors, gas burner nozzels, biomedical implants, mechanical bearings, fuel cells, and many types of electrical and thermal insulators.

3 The earliest man-made composite materials were straw and mud combined to form bricks for building construction. More recently, researchers have also begun to actively include sensing, actuation, computation and communication into composites, which are known as Robotic Materials. There are many composite materials and while we may be aware of some, such as fiberglass and carbon epoxy, there are many others ranging from the mundane, reinforced concrete (a mixture of steel rod and concrete), pneumatic tires (steel wires in vulcanized rubber), many cheap plastic moldings (polyurethane resin filled with ceramic particles such as chalk and talc) to the exotic metal matrix composites used in the space program (metallic titanium alloys reinforced with SiC ceramic fibers), and your automobile, such as engine pistons (aluminum alloys filled with fibrous alumina) and brake discs (aluminum alloys loaded with wear-resistant SiC particles). Caution: Everyone in the proximity of the work area as well as workers with materials or tools must wear safety glasses at all times during this activity. Module procedure: 1. Dismantle the appliance using the tools needed to remove the appliance s casing and inner parts. 2. Place disassembled parts into containers labeled metals, ceramics, polymers, and composites. 3. Develop a model that describes the different uses of the materials encountered. Name some reasons certain materials are more commonly used than others. Could there be a better material to use than what is found in your appliance? Why do you think the manufacturer decided to use the material currently used in the appliance? 4. Record observations about the disassembled appliances in the laboratory record book. Is there a particular part or mechanism that could be drawn to show special details of this appliance? Record your observations in your journal. Details could include the following a. Drawings of appliances or specific parts b. Type of appliances worked on c. Types of material the major parts of the appliance are made from (What parts are made of metals, ceramics, polymers, composites?) d. Reasons why materials were chosen for specific purposes of the appliance e. Possible reasons the inventor or manufacturer used some unusual materials to make some parts of the appliance. 5. Extend the class discussion from module to include these new data on real appliances. In the real appliance, in addition to material properties, are there any other reasons why one material might be chosen in place of another? Does cost of a specific material play a part?

4 Caution: Safety glasses need to be worn at all times. Reference: *Materials Science and Technology Teachers Handbook, Pacific Northwest National Laboratory, Richland, WA 1994, Available under Classification of Materials at emonstrations-%20introductory.pdf Evaluation packet for module Student evaluation questions (discussion or quiz): 1. Make a list of the testing methods that can be used to separate or classify the three major types of materials. 2. Make a Table that shows corresponding properties (such as ductility or thermal conductivity) for ceramics, polymers, and metals. 3. Explain your rationale for classifying a material as a composite based on the Table that you made for Question 2. Instructor evaluation questions: 1. At what grade level was this module used? 2. Was the level and rigor of the module what you expected? If not, how can it be improved? 3. Did the activity work as presented? Did they add to student learning? Please note any problems or suggestions. 4. Was the background material sufficient for your discussion with the students? Comments? 5. Did the activity generate interest among the students? Explain

5 6. Please provide your input on how this module can be improved, including comments or suggestions concerning the approach, focus and effectiveness of this activity in your context. Course evaluation questions (for the students) 1. Was the activity clear and understandable? 2. Was the instructor s explanation comprehensive and thorough? 3. Was the instructor interested in your questions? 4. Was the instructor able to answer your questions? 5. What was the most interesting thing that you learned? This work is part of a larger project funded by the Advanced Technological Education Program of the National Science Foundation, DUE #