INTRODUCTION TO PLASTICS PROCESSING CORPORATE TRAINING AND PLANNING

INTRODUCTION TO PLASTICS PROCESSING CORPORATE TRAINING AND PLANNING

1. 0 INTRODUCTION ü Plastics – The unique class of wonder materials – came into existence by virtue of their superior performance and cost effectiveness over to conventional materials. ü Over the years the applications spectrum of plastics have been widened with the advent of new generation Polymers, blend alloys and composites ü. 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. ü This inturn necessitates the need for different types processing methods and machinery to produce quality plastics products at affordable cost ü Today a host of processing methods and machinery are available to manufacture plastics products meeting stringent quality requirements and cost to performance CORPORATE TRAINING AND PLANNING balance.

1. 1 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 CORPORATE TRAINING AND PLANNING Semi-finished or Finished Products

In a more technocrate way we may say “Get the Shape and set the Shape”. Technique to get the shape and Set the shape varies depending on Process and Material employed. Principles: ü Deformation of a polymer melt (ex) Injection, Extrusion, Blow Moulding etc ü Deformation of a polymer in Rubbery state Ex: Thermoforming Vacuum Forming Pressure Forming ü Deformation of a Suspension Ex: PVC Plasticsol Processing / Coating ü Deformation of a Solution Ex : Solvent Casting of CN Film ü Deformation of a low melt polymer / monomer Ex: Acrylic Sheet Casting ü Preparation of GR Laminates ü Machined Structures Secondary fabrication operation CORPORATE TRAINING AND PLANNING

1. 2 CLASSIFICATION OF PROCESSING METHODS 1. Primary Processing Methods: u More importance by virtue of o Extent of utilisation for Varied applications o Growth Potential Ex: Injection Moulding, Extrusion, Blow Moulding, Compression / Transfer Moulding, 2. Secondary Processing Methods u Lesser extent of utilisation u Acts as supplementary to primary operation Ex: Roto Moulding, Thermoforming, Coating, Casting, FRP Fabrication CORPORATE TRAINING AND Methods, Calendaring, etc. , PLANNING

1. 3 PROCESSING FUNDAMENTALS Performance Requirements Practical Approach Engineering Approach Material Selection Properties Process Cost Ideal Choice Product Manufacture : A TRAINING Simplified Flow Diagram CORPORATE AND PLANNING

The process selection depends on several interrelated factors: (1) Designing a part to meet performance and manufacturing requirements at the lowest cost; (2) Specifying the plastic; (3) Specifying the manufacturing process, which requires ü Designing a tool ‘around’ the part, ü Putting the ‘Proper Performance’ fabricating process around the tool, ü Setting up necessary auxiliary equipment to interface with the main processing machine ü Setting up ‘Completely integrated’ controls to meet the goal of zero defects; (4) Purchasing equipments and materials, and warehousing the materials. CORPORATE TRAINING AND PLANNING

COMPETITIVE PROCESSES S. No Product Inj. Moulding Extrusion Thermo forming Blow Moulding Comp. / Transfer Moulding Roto Moulding 1 Narrow neck container - - - 1 - - 2 Oil Barrels Upto (200 ltrs) - - - 1 3. Tanks (20000 ltrs) - - - 1 4. Films, Profiles, Pipes - 1 - - 5 Housing, Auto parts 1 - 2 2 2 - 6. Wider Neck parts 1 - - - 7. Hallow Containers - - - 1 1. Best Process CORPORATE TRAINING AND PLANNING 2. Supplementary Process

Parameters that help one to select the right options are 1. Setting up specific performance requirements; 2. Evaluating material requirements and their processing capabilities; 3. Designing parts on the basis of material and processing characterstics, considereing part complexity and size as well as a product and process cost comparison 4. Designing and manufacturing tools (Moulds, Dies, etc) to permit ease of processing; 5. Setting up the complete line, including auxliliary equipment; 6. Testing and providing quality control, from delivery of the plastics, through production, to the product 7. Interfacing all these parameters by using logic and experience and / or obtaining a required update on technology. CORPORATE TRAINING AND PLANNING

1. 4 PROCESSABILITY: ü Processability means generally the ease or difficulty with which a plastic can be handled during its fabrication into film, moulded products, pipe, etc. ü A plastic with good processability possesses the properties necessary to make it easy to process the plastics into desired shapes. ü The main characterstics or properties which determine a plastic’s processability are molecular weight, uniformity, additive type and content, and plastic feed rates. CORPORATE TRAINING AND PLANNING

1. 5 PROCESSING METHODS: ü 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. ü 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. ü 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. CORPORATE TRAINING AND PLANNING

PROCESSING METHODS – An Overview: Depending upon the configuration of the part, economic viability and the part tolerance, etc the process can be selected. Machine Operation Terminology in the plastics industry regarding the operation of machinery is as follows: ü Manual Operation Each function and the timing of each function is controlled manually by an operator. ü 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. ü 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. CORPORATE TRAINING AND PLANNING

BLOW MOULDING : Description : An extruded parison tube of heated thermoplastic 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. 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. CORPORATE TRAINING AND PLANNING

BLOW MOULDING CORPORATE TRAINING AND PLANNING

INJECTION MOULDING : Description : Very widely used. High automation of manufacturing is standard practice. Thermoplastic or thermoset 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 resin undergoes solidification rapidly. The mould is opened, and the part ejected, Injection Moulding is growing in the making of glass reinforced parts. 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. CORPORATE TRAINING AND PLANNING

INJECTION MOULDING CORPORATE TRAINING AND PLANNING

EXTRUSION : Description : Widely used for continuous production of film, sheet, tube, and other profiles; also used in conjunction with blow moulding. Thermoplastic moulding 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. 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. CORPORATE TRAINING AND PLANNING

EXTRUSION CORPORATE TRAINING AND PLANNING

COMPRESSION MOULDING : Description : Thermoset compound, usually preformed, is positioned in a heated mould cavity; the mould is closed (heat and pressure applied) and the material flows and fills the mould cavity. Heat completes polymerization and the part is ejected. The process is sometimes used for thermoplastics, e. g. Vinyl phonograph records. Little material waste is attainable; large, bulky parts can be moulded; process is adaptable to rapid automation. Limitations: Extremely intricate parts containing undercuts, side draws, small holes, delicate inserts, etc. ; very close tolerances are difficult to produce. Time consuming process. CORPORATE TRAINING AND PLANNING

TRANSFER MOULDING Description : Widely used to produce Thermoset products with part complexity. 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. 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. CORPORATE TRAINING AND PLANNING

CALENDERING : Description : 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. Low cost, and sheet materials are virtually free of moulded in stresses. Limitations: Limited to sheet materials and very thin films are not possible. CORPORATE TRAINING AND PLANNING

ROTATIONAL MOULDING Description : 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. Low mould cost, large hollow parts in one piece can be produced, and moulded parts are essentially isotropic in nature. Limitations: Limited to hollow parts; production rates are usually slow. CORPORATE TRAINING AND PLANNING

ROTATIONAL MOULDING CORPORATE TRAINING AND PLANNING

THERMOFORMING Description : 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. 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. CORPORATE TRAINING AND PLANNING

THERMOFORMING CORPORATE TRAINING AND PLANNING

CASTING Description : 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. CORPORATE TRAINING AND PLANNING

CENTRIFUGAL CASTING: Description : Reinforcement is placed in mould and is rotated. Resin distributed through pipe; impregnates reinforcement through centrifugal action. Utilized for round objects, particularly pipe. Limitations: Limited to simple curvatures in single axis rotation. Low production rates. COATING Description : Process methods vary. Both thermoplastics and thermosets widely used in coating of numerous materials. Roller coating similar to calendaring process. Spread coating employs blade in front of roller to position resin on material. Coatings also applied via brushings, spraying, and dipping. Limitations: Economics generally depends on close tolerance control. CORPORATE TRAINING AND PLANNING

FILAMENT WINDING : Description : Excellent strength to weight. Continuous, reinforced filaments, usually glass, in the form of roving are saturated with resin and machine wound onto mandrels having shape of desired finished part. Once winding completed, part and mandrel are cured; mandrel can then be removed through porthole at end of wound part. High strength reinforcements can be oriented precisely in direction where strength is required. Good uniformity of resin distribution in finished part; mainly circular objects such as pressure vessels, pipes, and rocket cases. Limitations: Limited to shapes of positive curvature; openings and holes can reduce strength if not properly designed into moulding operations. CORPORATE TRAINING AND PLANNING

LAMINATING : Description : Material, usually in form of reinforcing cloth, paper, foil, metal, wood, glass fibre, Plastic etc. , preimpregnated or coated with thermoset resin (sometimes a thermoplastic) is moulded under pressure greater than 1000 psi (7 Mpa) into sheet, rod, tube, or other simple shapes. Excellent dimensional stability of finished product; very economical in large production of parts. Limitations: High tool and die costs. Limited to simple shapes and cross sections. CORPORATE TRAINING AND PLANNING

MATCHED DIE MOULDING : Description : A variation of the conventional compression moulding, this process employs two metal moulds possessing a close fitting, telescoping area to seal in the plastic compound being moulded and to allow trim of the reinforcement. The mat or preform reinforcement is positioned in the mould and the mould is closed and heated under pressures of 150 – 400 psi (1 3 MPa). The mould is then opened and the part is removed after curing. Limitations: Prevalent high mould and equipment costs. Part often require expensive surface finishing. CORPORATE TRAINING AND PLANNING

SLUSH MOULDING : Description : 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. CORPORATE TRAINING AND PLANNING

Effect of polymer properties on Process Technique CORPORATE TRAINING AND PLANNING

1. 6 EFFECT OF POLYMER PROPERTIES ON PROCESS TECHNIQUE When processing thermoplastic melts the following factors should be taken into account in order both to process efficiently and obtain quality products. (1) (2) (3) (4) (5) (6) (7) (8) 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. CORPORATE TRAINING AND PLANNING

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

Actions Necessary 1. Use granules as soon as the bag is opened. 2. Pre drying ovens, Hopper drier, Dehumidifying drier can be used. 3. For PC Dehumidifying drier preferable Physical form of Raw Material ü Powder form, granular form, lumpy/slab form ü Slab Form Calendering, Compression Moulding ü Granular Form – Preferred Uniform pellet size ensures even and faster feeding. ü 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. CORPORATE TRAINING AND PLANNING

Thermal stability of polymers ü 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. ü PMMA, POM upon depredation liberates MMA & formaldehyde respectively MMA volatilize and cause bubbles Formaldehyde gas causes “eye irritation”. ü PVC & POM (acetal) should never be processed one after the other. This may lead to explosion Adhesion of melt to metal: ü 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. ü PC has a strong adhesion to metal. It can take away the skin of the barrel if not properly purged CORPORATE TRAINING AND PLANNING

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. CORPORATE TRAINING AND PLANNING

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. CORPORATE TRAINING AND PLANNING

FROZEN-IN ORIENTATION ü 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. ü 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. ü Some orientation is thus “Frozen in” the product. Such stressed parts are very weak. Hence annealing is must. CORPORATE TRAINING AND PLANNING

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. CORPORATE TRAINING AND PLANNING

With the availability of host of plastic raw materials and a wide range of plastic processing methods and technologies, it is a difficult task for the processor to select a suitable cost effective process for a specific product. Although in some cases one or more processes may be suitable for producing a specific plastics product A plastics processor can select a specific process keeping in mind the key parameters such as cost, quality and cost/performance balance. In this presentation, a few selected case studies were made for the benefit of plastic processors. CORPORATE TRAINING AND PLANNING

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 CORPORATE TRAINING AND PLANNING

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. CORPORATE TRAINING AND PLANNING

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. CORPORATE TRAINING AND PLANNING

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, 000 ltrs) will have to be produced by Roto moulding inspite of higher initial cost on plant & machinery. CORPORATE TRAINING AND PLANNING

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. 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 CORPORATE TRAINING AND PLANNING

Hence accumulator type blow moulding process can be selected. 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. 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 Material : PMMA Process : 1. Casting 2. Extrusion CORPORATE TRAINING AND PLANNING

Since optical properties are very essential based on cost/performance & quality casting process is best. CORPORATE TRAINING AND PLANNING

Quality Mainly due to quality reasons, inspite of higher cost of manufacture, certain products are produced by a specific process only. Case: 1 PVC gramaphone records even today produced by compression moulding. 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 CORPORATE TRAINING AND process is selected. PLANNING

Case: 3 Product : Plastic float Material : PP/HIPS Processes: 1. Roto Moulding 2. Injection Moulding Two halves and then joining by vibration welding. CORPORATE TRAINING AND PLANNING

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