polymer processing ppt

polymer

1. Polymer Processing I Introduction to Polymer Processing

2. INTRODUCTION Plastics – The unique class of wonder materials – came into existence by virtue of their superior performance and cost effectiveness over to conventional materials. Over the years the applications spectrum of plastics have been widened with the advent of new generation Polymers, blend alloys and composites Every day newer and newer application are being promoted in all the key sectors of Indian Economy viz. Automobiles, Agriculture, Aerospace. Building & Construction, Infrastructure, Telecommunication, IT, Medical & Bio Medical engineering, Packaging, etc. This in turn necessitates the need for different types processing methods and machinery to produce quality plastics products at affordable cost Today a host of processing methods and machinery are available to manufacture plastics products meeting stringent quality requirements

3. Definition Plastics Processing – in a simple layman’s language – can be defined as the process of converting the plastic raw materials into Semi-finished or finished products Raw Materials (Powder/granules) Processing Semi-finished or Finished Products

4. Classification of processing methods 1. Primary Processing Methods: Injection, Extrusion, Blow, Compression and transfer moulding . 2. Secondary Processing Methods: Rotational molding, Thermoforming, Coating, Casting, Fabrication and Calendaring etc. 3. Tertiary Processing Methods: Cutting, Drilling, Welding and Bending etc.

5. Fundamentals of processing Performance Requirements Engineering Approach Practical Approach Material Selection Properties Process Cost/Performance Ideal Choice

6. The process selection depends on several interrelated factors: Designing a part to meet performance and manufacturing requirements at the lowest cost; Specifying the plastic; Specifying the manufacturing process, which requires Designing a tool ‘around’ the part, Putting the ‘Proper Performance’ fabricating process around the tool, Setting up necessary auxiliary equipment to interface with the main processing machine Setting up ‘Completely integrated’ controls to meet the goal of zero defects; Purchasing equipments and materials, and warehousing the materials.

7. Setting up specific performance requirements; Evaluating material requirements and their processing capabilities; Designing parts on the basis of material and processing characterstics , considereing part complexity and size as well as a product and process cost comparison Designing and manufacturing tools (Moulds, Dies, etc) to permit ease of processing; Setting up the complete line, including auxliliary equipment; Testing and providing quality control, from delivery of the plastics, through production, to the product Interfacing all these parameters by using logic and experience and / or obtaining a required update on technology. Parameters that help one to select the right options are

8. PROCESSABILITY: Processability means generally the ease or difficulty with which a plastic can be handled during its fabrication into film, moulded products, pipe, etc. A plastic with good processability possesses the properties necessary to make it easy to process the plastics into desired shapes. The main characteristics or properties which determine a plastic’s processability are molecular weight, uniformity, additive type and content, and plastic feed rates.

9. PROCESSING METHODS: The type of process to be used depends on a variety of factors, including product shape and size, plastic type, quantity to be produced, quality and accuracy (Tolerances) required, design load performance, cost limitation, and time schedule. Each of the processes provides different methods to produce different products. As an example, extrusion with its many methods produces films, pipe,sheet, profile, wire coating, etc. Almost all processing machines can provide useful products with relative ease, and certain machines have the capability of manufacturing products to very tight dimensions and performances. The coordination of plastic and machine facilities these processes.

10. PROCESSING METHODS – An Overview: Machine Operation Terminology Terminology in the plastics industry regarding the operation of machinery is as follows: Manual Operation Each function and the timing of each function is controlled manually by an operator. Semiautomatic Operation A machine operating semi automatically will stop after performing a complete cycle of programmed moulding functions automatically. It will then require an operator to start another complete cycle manually. Automatic Operation A Machine operating automatically will perform a complete cycle of programmed moulding functions repetitively; it will stop only for a malfunction on the part of the machine or mould, or when it is manually interrupted. Depending upon the configuration of the part, economic viability and the part tolerance, etc the process can be selected.

11. Plastic Materials Thermoplastics start as regular pellets or granules and can be re-melted. Thermosetting materials start as liquids/syrups, often called "resins", as powders or partially cured products (" preforms ") which need heat for the shaping phase. The shaping is accompanied by a chemical reaction, which means that the material does not soften on reheating. The reaction may be exothermic (giving heat out), in which case cooling is required.

12. Plastic Processing Methods Extrusion Injection Moulding Blow Moulding and Stretched Blow Moulding Thermoforming and Vacuum Forming Compression Moulding Transfer Moulding Rotational moulding Casing and Slush Moulding Calendaring Reaction Injection Moulding

13. Extrusion Widely used for continuous production of film, sheet, tube, and other profiles; Types of products: Films, Pipes, Strapping, Sheets, Multilayer films, Profiles etc. also used in conjunction with blow moulding . Thermoplastic molding compound is fed from a hopper to a screw pump where it is heated to plasticate then pumped out through the shaping orifice (die) to achieve desired cross section. Production lines require input and takeoff equipment that can be complex. Advantages: Low tool cost, numerous complex profile shapes possible, very rapid production rates, can apply coatings or jacketing to core materials (Such as wire). Limitations: Usually limited to sections of uniform cross section.

14. EXTRUSION

15. Injection Molding Very widely used process Most versatile for Fast production Intricate design is possible High automation and robotics can be adopted Thermoplastic or thermoset both can be moulded Plastic granules or powder is heated to plasticate in cylinder at controlled temperature, then forced under pressure through a nozzle into sprue , runners, gates, and cavities of mould. The plastic or resin undergoes solidification rapidly by cooling or heating. The mould is opened, and the part ejected, Injection Moulding can be used for glass-reinforced plastic materials Advantages: High production runs, low labour costs, high reproducibility of complex details, and excellent surface finish are the merits. Limitations: High initial tool and die costs; not economically practical for small runs.

16. INJECTION MOULDING

17. Blow Moulding Used or hollow products with Neck to Bottom diameter less than one Used for thermolpastics Types of Products: Bottles, Containers, Air ducts, Panels, Portable toilets, Arm rests, tanks, gas tanks A parison or tube formed by extrusion or injection moulding heated parison is positioned between two halves of an open split mould and expanded against the sides of the closed mould via air pressure. The mould is opened and the part ejected. Advantages: Low tool and die costs, rapid production rates, and ability to mould fairly complex hollow shapes in one piece. Limitations: Generally limited to hollow or tubular parts; some versatile mould shapes, other than bottles and containers

18. Types of Blow moulding machine: 1.Extrusion Blow moulding Extrusion Blow moulding : In extrusion blow molding (EBM), plastic is melted and extruded into a hollow tube (a parison ). This parison is then captured by closing it into a cooled metal mold. Air is then blown into the parison , inflating it into the shape of the hollow bottle, container or part. After the plastic has cooled sufficiently, the mold is opened and the part is ejected. 2. Injection Blow moulding The process of injection blow molding (IBM) is used for the production of hollow glass and plastic objects in large quantities. The blow molding process begins with melting down the plastic and forming it into a parison or in the case of injection. The parison is a tube-like piece of plastic with a hole in one end through which compressed air can pass. 3. Stretch Blow moulding Stretch Blow moulding : In the stretch blow molding (SBM) process, the plastic is first molded into a " preform " using the injection molding process. the preforms are heated (typically using infrared heaters) above their glass transition temperature, then blown using high pressure air into bottles using metal blow molds. The preform is always stretched with a core rod as part of the process. In the single-stage process both preform manufacture and bottle blowing are performed in the same machine.

19. Thermoforming Thermoplastic sheets are used Heat-softened thermoplastic sheet is positioned over male or female mould; air is evacuted between sheet and mould, forcing sheet to conform to contour of mould. Variations are vacuum snapback, plug assist, drape forming, etc. Advantages: Tooling costs are generally low, large part production with thin sections possible, and often comes out economical for limited part production. Limitations: Limited to parts of simple configuration, high scrap, and limited number of materials from which to choose

20. Thermoforming air pressure and plug assisted forming of the softened sheet. -invariably automated and faster cycle times only thermoplastics sheet can be processed by this method. The largest application is for Food Packaging. Other industries include Toiletries, Pharmaceuticals and Electronics Food related applications such as Meat Trays, Microwave & Deep Freeze Containers, Ice Cream and Margarine Tubs, Snack Tubs, Bakery and Patisserie packaging, Sandwich Packs and Vending Drink Cups Manufacturing Collation trays, Blister packaging and Point of Sale display trays.

21. THERMOFORMING

22. Compression Moulding Usually Used for Thermoset compound, Molding powder or a preformed, is positioned in a heated mould cavity; the mould is closed with the application of heat and pressure the material flows and fills the mould cavity. Heat completes polymerization and identification the part of ejected . Types of Products: Plugs, sockets, handles, Engine Casing switches, cistern etc. Heat completes polymerization and the part is ejected. The process is sometimes used for thermoplastics, e.g. Vinyl phonograph records. Advantages: Little material waste is attainable; large, bulky parts can be moulded ; process is adaptable to rapid automation. Imitations: Extremely intricate parts containing undercuts, side draws, small holes, delicate inserts, etc.; very close tolerances are difficult to produce. Time consuming process.

23. Advantages of compression molding (compared with injection molding) -Low scrap arisings -Low orientation in the moldings -well distributed fibrous fillers -low residual stress product -retained mechanical and electrical properties -low mold maintenance -low capital and tooling costs

24. Transfer Moulding Widely used to produce Thermoset products with part complexity. Types of Products: Plugs, Sockets, Handles, Engine Casing Switches, Cistern etc. Thermoset moulding compound is fed into transfer chamber where it is then heated to plasticate ; it is then fed by a plunger through sprues , runners, and gates into a closed mould where it cures; mould is opened and part ejected. Advantages: Good dimensional accuracy, rapid production rate, and very intricate parts can be produced. Limitations: High mould cost; high material loss in sprues and runners; size of parts is somewhat limited.

25. Rotational Molding A predetermined amount of powdered thermoplastic material is poured into mould; mould is closed, heated, and rotated in the axis of two planes until contents have fused to the inner walls of mould; mould is then opened and part is removed. Limited to hollow parts; production rates are usually slow.

26. Casting Liquid plastic which is generally thermoset except for acrylics is poured into a mould without pressure, cured, and taken from the mould. Cast thermoplastic films are produced via building up the material (either in solution or hot-melt form) against a highly polished supporting surface. Advantages: Low mould cost, capability to form large parts with thick cross sections, good surface finish, and convenient for low-volume production Liquid plastic which is generally thermoset except for acrylics is poured into a mould without pressure, cured, and taken from the mould. Cast thermoplastic films are produced via building up the material (either in solution or hot-melt form) against a highly polished supporting surface. Low mould cost, capability to form large parts with thick cross sections, good surface finish, and convenient for low-volume production. Limitations: Limited to relatively simple shapes. Most thermoplastics are not suitable for this method. Except for cast films, method becomes uneconomical at high volume production rates.

27. casting -cast hollow plastic parts with few restrictions regarding size or complexity Very stable parts - no molded in stresses Low tooling cost for large parts Suited for low volume production Can produce complex part geometries Can mold in metal inserts and graphics

28. Slush Moulding Liquid thermoplastic material ( Plastisol ) is poured into a mould to capacity; mould is closed and heated for a predetermined time in order to achieve a specified buildup of partially fused material on mould walls; mould is opened and excess material is poured out; and semifused part is removed from mould and fully fused in oven. Low mould costs and economical for small production runs. Limitations: Limited to hollow parts; production rates are very slow; and limited choice of materials that can be processed

29. Calendaring Dough-consistent thermoplastic mass is formed into a sheet of uniform thickness by passing it through and over a series of heated or cooled rolls. Calenders are also utilized to apply plastic covering to the backs of other materials. Types of products: Rain boots, Shoes, Hollow toys, Balls, large pipes and tubes etc. Types of Products: Luggage, Rain wear, Tank lining, Credit cards, Trays, Helmet liner etc.

30. Reaction Injection Moulding RIM is a specialized subset of the injection molding technique that chemically bonds two or more plastics into a polymer before they are introduced into the mold. The most important feature of this process is the plastic polymerization during molding which can yield properties distinct from those of the base materials.  RIM utilizes chemical reactions to produce stronger, tougher, more lightweight, more complex and more customizable parts in a significantly more cost-efficient manner than standard injection molding RIM can also fabricate large parts with complex shapes, making it well-suited for industrial applications that require bulky components. Likewise, issues of cost-efficiency, production cycle rates, and machinery design can influence the decision to employ this technique.

31. Effect of polymer properties on Process Technique

32. CORPORATE TRAINING AND PLANNING 1.6 EFFECT OF POLYMER PROPERTIES ON PROCESS TECHNIQUE Water absorption of Raw materials, Physical form of raw material, Thermal stability of polymer, Flow properties, Adhesion of melt to metal, Thermal properties affecting, Heating and cooling of melt, Compressibility and shrinkage, Frozen in Orientation. When processing thermoplastic melts the following factors should be taken into account in order both to process efficiently and obtain quality products.

33. Water / Moisture is the greatest enemy for processing of plastics.    Hygroscopic Materials Absorption phenomena - Ex: Nylon, POM, PC.    Adsorption phenomena - Ex: HIPS, PS, ABS.    All these materials should be pre-dried.    Non-Hygroscopic material - Ex: PVC, Polyolefins, etc.    Need not be predried. Except when completely wet during monsoon. WATER ABSORPTION

34. CORPORATE TRAINING AND PLANNING   Actions Necessary Use granules as soon as the bag is opened. Pre-drying ovens, Hopper drier, Dehumidifying drier can be used. For PC - Dehumidifying drier preferable          Physical form of Raw Material Powder form, granular form, lumpy/slab form Slab Form - Calendering,Compression Moulding Granular Form – Preferred - Uniform pellet size ensures even and faster feeding. Powder Form - Difficulty in feeding - But savings in cost because of the ability to avoid pelleting stage - Special feeder attachment essential to ensure proper feeding.

35. Thermal stability of polymers PVC thermally sensitive material - ­Little higher melt temp. may lead to depredation - HCL is released - ­This can leads to corrosion and harmful to human being. PID Temperature controller can be used. PMMA, POM upon depredation liberates MMA & formaldehyde respectively - MMA volatilize and cause bubbles - Formaldehyde gas causes “eye-irritation”. PVC & POM (acetal) should never be processed one after the other. This may lead to explosion Adhesion of melt to metal: Wetting of the polymer melt against the metal wall of processing equipment can lead to strong adhesion of polymer to metal. Ex: difficulty in removing PVC - Mix from two roll mill. PC has a strong adhesion to metal. It can take away the skin of the barrel if not properly purged

36. THERMAL PROPERTIES AFFECTING HEATING AND COOLING In the case of polymer melts the specific heat varies with temperature. For crystalline polymers such as POM, NYLON etc. latent heat of fusion and sp.heat should be taken in to account. i.e Total heat content (Enthalpy) =LH of fusion + sp.heat. POLYMER PROCESS TEMP 0  C ENTHALPY / KJ / KG PS 200 310 LDPE 200 500 HDPE 260 810 PP 260 670 Because of higher enthalpy PP requires more cooling time than LDPE and PS.

37. COOLING SHRINKAGE AND COMPRESSIBILITY When polymers are in molten stage the vibrations of the molecules results in the polymer chain being pushed apart so that the volume occupied by a given polymer mass is higher than when the material is solid. POLYMER DENSITY AT 20 C(G/CC) DENSITY AT PROCESS TEMP (G/CC) LDPE 0.923 0.746(210  c) PP 0.905 0.765(210  c) PMMA 1.180 1.105(210  c) SPVC 1.48 1.390(190  c) Because polymer melts are compressible moulding shrinkage is much less than the above fig.

38. FROZEN-IN ORIENTATION When polymer melts are being shaped by either injection moulding or Extrusion the long polymer chains tend to be elongated or uncoiled in the direction of flow. After shaping, the melt is usually cooled rapidly and there is seldom time for the oriented molecules to return to a random coiled shape by the process known as relaxation. Some orientation is thus “Frozen-in” the product. Such stressed parts are very weak. Hence annealing is must.

39. PROCESS SELECTION CRITERIA FOR PLASITC PRODUCTS Introduction: With the advent of New Generation Polymers, blends alloys and composites, over the last decade, the application spectrum of plastics has been widened. Today with the result, the plastics have penetrated deeply in all the key sectors of economy which includes Automobiles Telecommunication Aerospace Defence Biomedical Building & Construction etc In the liberalized economy the survival of plastic industries largely depends upon timely delivery, quality, cost and cost / performance balance of plastics products.

40. Process Selection Criteria The following parameters play a key role in selecting the best suited process to produce a specific product for a specific application. 1. Material Processibility - Limitations 2. Volume of production 3. Size & shape of the product (configuration) 4. Cost to performance balance 5. Quality

41. Material Processibility Limitations If a specific material is suitable for a particular application, then material processibility will decide the specific method of Processing / Production. Case :1 Product : PET bottle Process : Blow Moulding Specific process : Injection stretch Blow moulding Not possible by : Extrusion Blow moulding or Extrusion Stretch blow moulding Reason: PET material used today does not have the required hot melt strength to hold/self support a parison.

42. Case: 2 Product : PTFE sheets Process : Compression moulding following by sintering process.-The sintered sheets are subsequently machined to the required dimension. Other Conventional Process : Extrusion - Not possible. Reason : PTFE exhibits - very high melt viscosity above its melting temperature. Hence only best suited process is compression moulding followed by sintering.

43. Configuration of Product - Size & shape governs the process selection. Case 1: Narrow neck containers like Shampoo bottles, Pharmaceutical containers, soft drink bottles will have to be produced by Blow moulding only. Case 2: Hollow containers such as Tanks (20,000ltrs) will have to be produced by Roto moulding inspite of higher initial cost on plant & machinery.

44. Case 3: Product : FRP Boat Raw materials : Fiber glass material, Polyester resin and other additives Process : 1. Hand lay-up 2. Spray up Most suitable process : If volume of production is less then hand lay up. If more then spray up technique. Spray up technique calls for higher initial investment.

45. Quality Mainly due to quality reasons, in spite of higher cost of manufacture, certain products are produced by a specific process only. Case:1 PVC – sheets by calendaring Reason : Stress-free moulding Case:2 Product : PP Blown film Process : Only downward extrusion process should be used instead of upward blown film process. Reason : PP, being a crystalline polymer,in order to get transparency, the film emerging out of die lips needs to be quenched.The best /economical way of quenching is to dip in water which is possible only in downward extrusion. So due to quality reason this process is selected.

46. Since optical properties are very essential based on cost/performance & quality casting process is best.

47. CORPORATE TRAINING AND PLANNING Cost / Performance Balance If more than one process is suitable for producing a product based on performance, then cost plays a crucial role in process selection . Case: 1 Product : 200 litres chemical container Material : HDPE Process : 1. Blow Moulding 2. Roto Moulding

48. CORPORATE TRAINING AND PLANNING Case - 2 Product : FRP pipe Material : Glass fiber, Polyester resin & other additives Process : 1. Limited lengths & high strengths - Filament winding 2. Continuous lengths & high strength - pultrusion 3. Centrifugal casting - Batch process If medium strength and relatively stress free pipes are required with better optical properties, then centrifugal casting is the best method.

49. CORPORATE TRAINING AND PLANNING Case: 3 Product : PVC Flexible sheet Material : Compounded PVC with additives such as plasticizer, stabilizer, colourants etc. Process : 1. Calendering 2. Extrusion Suitable process : Calendering Reason : Wider width, cost effectiveness Case: 4 Product : Acrylic sheet Materia l : PMMA Process : 1. Casting 2. Extrusion