plastic moulding and glass cutting operations.pptx

plastic moulding and glass cutting operations

1. Plastic and Glass Processing

2. Plastics processing

3. Plastics History

4. General properties : more durable, harder, tough, light. Typical uses : automobile parts, construction materials. Plastic types: Thermosets Examples : Unsaturated Polyesters : lacquers, varnishes, boat hulls, furniture Epoxies and Resins :glues , coating of electrical circuits, composites: fiberglass in helicopter blades, boats, …

5. Plastic types: Elastomers General properties : these are thermosets, and have rubber-like properties. Typical uses : medical masks, gloves, rubber-substitutes Ex a mpl e s : Polyurethanes : mattress, cushion, insulation, toys Silicones : surgical gloves, oxygen masks in medical applications joint seals

6. General properties : low melting point, softer, flexible. Typical uses : bottles, food wrappers, toys, … Examples : Polyethylene: packaging, electrical insulation, milk and water bottles, packaging film Polypropylene: carpet fibers, automotive bumpers, microwave containers, prosthetics Polyvinyl chloride (PVC ): electrical cables cover, credit cards, car instrument panels Polystyrene: disposable spoons, forks, Styrofoam™ Acrylics (PMMA : polymethyl methacrylate): paints, fake fur, plexiglass Polyamide (nylon): textiles and fabrics, gears, bushing and washers, bearings PET ( polyethylene terephthalate): bottles for acidic foods like juices, food trays PTFE (polytetrafluoroethylene): non-stick coating, Gore-Tex™ (raincoats), dental floss Plastic types: Thermoplastics

7. Plastics Processing: Extrusion

8. Plastics Processing: Blow molding (a) The hollow piece of heated glass (parison) is first created by a blow mold (see text-book Fig 17.25) 3-piece mold heated glass (b) The mold is put together (c) Plunger and hot air push the glass up (d) Hot air blows the glass out towards the mold surface (e) Mold comes apart, bottle is removed - similar to glass blow-molding -

9. Plastics Processing: Thermoforming Sheet of plastic  Heated (soft)  Molded using a shaped die

10. Plastics Processing: Compression and Transfer Molding used mostly for thermosetting polymers mold is heated and closed using pressure plastic flows to fills the cavity flash must be trimmed by finishing dishes, handles for cooking pots skis, housing for high-voltage switches some rubber parts like shoe soles and even composites such as fiber-reinforced parts

11. Plastics Processing: Compression and Transfer Molding compression molding transfer molding (more complex shapes)

12. Plastics Processing: Injection Molding - Probably the most common, most important, most economical process

13. Plastics Processing: Injection Molding Cycle of operation for injection molding

14. Ceramics

15. Glasses Clay pro d u c ts Refractories Abrasives Cemen t s -optical - comp o s i te reinforce - co n ta i ners/ household -whiteware -bricks -bricks for high T ( f urnaces) - san d pa p er -cutting -polishing - comp o s i tes -structural Ad v a n ced ceramics engine -rotors -valves -bearings - sens o rs Taxonomy of Ceramics

16. Shaping of Ceramics First, the raw materials must be ground or crushed down into fine particles. Next, the particles must be mixed with additives, which include: binder- to hold particles together lubricant- to reduce friction and aid in removing from mold wetting agent- to improve mixing process (commonly water) plasticizer- to improve ease of forming mixture agents- control of foaming and sintering deflocculent- to create uniform mixture by applying like charges to all particles, causing them to repel each other Finally, the material must be shaped, dried, and fired.

17. Crushing is typically done in a ball mill, in either wet or dry conditions. Wet milling is preferred because it strengthens particle bonds and limits dust. For correct sizing, the crushed particles are passed through a sieve. Mixing Particles are then mixed with one of the additives . Crush i ng

18. Casting Slip Casting (Drain Casting)- The crushed particles are first mixed with water , then are poured into a mold. Pouring must be done properly to avoid air pockets. When some of the water has been absorbed, the remainder of the mixture is poured out of the top of t he mold . The top of the part can then be trimmed. Advantages- inexpensive components Disadvantages- limited control of dimensions & low production rate Doctor-Blade Process- Used to produce ceramic sheets thinner than 1.5mm. Ceramic mixture is forced under a blade to create a film, which is then dried in a drying chamber (usually attached to the same machine).

19. Forming and Shaping of Glass Flat Sheet and Plate Glass Float Method- Molten glass is floated over a “bath” of molten tin before it is solidified in a separate chamber. No additional finishing is necessary. Drawing Process- Molten glass is squeezed through two rolls, then moves on o two smaller rolls. Rolling Process- Similar to drawing process, but patterns are commonly imprinted from the rolls onto the glass, leaving a rough finish.

20. Glass Tubing and Rods Tubing- Molten glass is wrapped around a mandrel and taken out by two rolls. Air is blown through the mandrel to prevent the tube from collapsing into itself. Some machines manufacture 2000 fluorescent light bulbs per minute using this method. R o ds- Rods are made in exactly the same way, but without the air blown through the mandrel. This allows the glass to collapse and become solid.

21. Processes used to make discrete glass objects Blowing Pressing Centrifugal casting Sagging Discrete glass products

22. Blowing process: Blown air expands a hollow gob of heated glass against the inner walls of a mold. A parting agent (such as oil or emulsion) is usually used to prevent the glass from sticking to the mold. Blowing

23. Applications: Hollow and thin- walled glass items (bottles, vases, and flasks) Surface finish: Acceptable for most applications Blowing

24. Pressing process: A gob of molten glass is placed into a mold and pressed by a plunger into a confined shape. Molds may be one piece or split. Solidifying glass acquires the shape of the mold-plunger cavity. Similar to closed-die forging. Pressi n g

25. One-piece molds cannot be used in pressing if the plunger cannot be retracted. One-piece molds cannot be used for thin-walled items Split molds can accommodate thin-walled products Pressing

26. Pressing Pressing can produce higher dimensional accuracy than blowing. Press and blow process After a part is pressed, it is blown to further expand the glass into the mold.

27. Centrifugal casting process: The centrifugal force pushes the molten glass against the wall. TV picture tubes and missile nose cones can be made with centrifugal casting. Centrifugal Casting (Spinning)

28. Sagging process: A sheet of glass is placed over a mold and heated. The glass sags by its own weight and takes the shape of the mold. Typical applications include dishes, sunglass lenses, mirrors for telescopes, and lighting panels. Sag g ing

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