Download
chapter 30 n.
Skip this Video
Loading SlideShow in 5 Seconds..
Chapter 30 PowerPoint Presentation

Chapter 30

215 Vues Download Presentation
Télécharger la présentation

Chapter 30

- - - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

  1. Chapter 30 Processes Used to Condition Plastic Materials

  2. Objectives • Producing lightweight cellular plastics. • Annealing, to relieving stresses caused by processing. • Providing more thermal conductivity.

  3. Annealing • Annealing is used with plastics to relieve the internal stress of the material and to improve workability. • Plastic materials are annealed by subjecting them to prolonged heating at a temperature slightly above their molding temperature, then slowly cooling them under controlled conditions. • Annealing is recommended when the plastic part or product needs to have superior visual appearance, good stability, or exhibit high resistance to solvents.

  4. Ionized Radiation Processing • Electron beam acceleration is desired over the other processes. • It improves thermal, impact, wear, and chemical resistance of commodity thermoplastics. • With thermosets it improves stability, ability to withstand higher temperatures in use, resistance to chemicals and water, and abrasion resistance. • Most popular uses are cold sterilization of surgical supplies and medical disposables and cold pasteurization of food.

  5. Non ionizing Radiation Processing • Induction heating is a common non ionizing radiation process. • When used with non conducting material, a conductive metal attachment is used to transfer the heat to the work piece. • Typical RF (radio frequency) power supplies range from 1 to 5 kW (kilo watts). • The radiation can improve temperature and environmental characteristics.

  6. Conductive Plastics • Conductive plastic coatings are used in Electromagnetic Interference (EMI) shielding. • Plastics are also used as thermal insulators to dissipate heat. • Prior to the invention of thermal plastics, plastic parts exposed to heat often failed prematurely.

  7. Plastics as Electrical Conductors • Plastics are made conductive by adding metal to the plastic base material, resulting in a material referred to as synthetic material. • Metal fibers have been used as conductive elements in antistatic fibers and yarns. • Research is being conducted in using a conductive gel as a replacement for conductive solder in some industrial electronic applications.

  8. EMI/RFI Shielding • Plastic has become the dominant choice for construction of enclosures for computers, appliances, medical instrumentation, and telecommunication devices. • One important reason for the popularity is the ability to add conductive metals to the polymer as a means of controlling the EMI/RFI (electro magnetic interference/radio frequency interference). • These products can be made with standard injection molding and blow molding equipment.

  9. Electroless Plating • Electroless plating produces a coating of metal on plastic to achieve EMI shielding of plastic cases used on electronic products. • Most paints are made by adding metal flakes of nickel or silver. • The technology does not use current. Instead a chemical process is used.

  10. Plastics as Thermal Conductors • Thermal conductors are objects that transfer heat quickly. • Thermally conductive plastics weigh about 40% less than aluminum. • It is used by manufacturers of stepper motors and computer manufacturers to carry heat away from critical parts in confined spaces.

  11. Plastic Additives • Various additives may be used to provide plastics with the characteristics desired for a finished product. • Chemical preservatives are added to products such as shower curtains, boat covers, pool liners that are subject to attack by mildew, fungus, mold and bacteria.

  12. Summary • Annealing is used with plastics to relieve the internal stress of the material and to improve workability. • Electron beam acceleration is desired over the other processes. • It improves thermal, impact, wear, and chemical resistance of commodity thermoplastics. • Induction heating is a common non ionizing radiation process. • Plastics are made conductive by adding metal to the plastic base material, resulting in a material referred to as synthetic material. • Metal fibers have been used as conductive elements in antistatic fibers and yarns. • Chemical preservatives are added to products such as shower curtains, boat covers, pool liners that are subject to attack by mildew, fungus, mold and bacteria.

  13. Home Work • 1. What is a common ionized radiation process? • 2. What is a common non ionized radiation process? • 3. How are plastics made conductive?