ebb 220/3 polymer processing methods.  the beauty of polymeric compounds  it can be shape to...

Download EBB 220/3 POLYMER PROCESSING METHODS.  The beauty of polymeric compounds  it can be shape to the desirable shape with the desirable characteristics

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  • The beauty of polymeric compounds it can be shape to the desirable shape with the desirable characteristics. There are three things that involved in all basic processing methods: 1. Mixing of the compound ingredient to get the physical forms that can be shape. 2. Changes the compound shape to the desirable shape and size. 1. To ensure the products retained their shape and dimension after shaping process. Introduction
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  • Types of Mixing Process Based on 2 basic mixing functions; Blending Compounding Blending mixing is used when the fabrication process will be followed by compounding process (pigments must be mix into granules/powder followed by injection molding process), thermosetting powders and fillers are often blends which disperse upon fusion of the resin during molding Compounding mixing is used when accurate distribution & dispersion of ingredients is required (e.g. in rubber compounding, 4-5 additives have to act together for efficient cross-linking of the rubber)
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  • Blending Stirring together/blending of a number of solids, e.g.polypropylene powder, pigment, antioxidant, etc. The results is a mixture of powders; the individual powder remain and can be separated (in principle)
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  • Compounding Involves more intimate dispersion of the additives into the polymeric matrix It requires; A physical change in the component High shear force to bring about the change The polymer to be in the molted or rubbery state during mixing
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  • Some Processes and Machine (Blending) Vary from the simplest to sophisticated high speed machine The simplest- is to tumble together dry ingredients, e.g. using a twin-drum tumbler Twin-drum tumbler
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  • High speed mixer More sophisticated & rapid machine for blending Widely used for PVC dry blends, drying, incorporated pigments, antioxidant, etc. Run at several thousand rpm, and form a circulating powders which becomes heated by friction (150-200C) Mixing tank can be single wall or jacketted for temp. control Some Processes and Machine (Blending) High Speed Mixer Mixing tank
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  • Ball Mill Comprises of cylindrical vessel containing large number of steel or ceramic balls It rotates, the balls tumble inside together with the powder Agglomerates of powder are broken down by the grinding action of the tumbling balls Some Processes and Machine (Blending) Ball Mill
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  • Involve high shear process & much more powerful machinery The simplest technique is two-roll mill Some Processes and Machine (Compounding)
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  • Two roll mill consists of two adjacent, smooth, hardened-steel rolls set horizontally. They rotate in opposite directions (i.e towards each other) produce friction or grinding action between them. The ratio between the operating speed of the front and back roll is referred to as friction ratio. Mixing was achieved by the shearing action induced in the space between the roll which is adjustable. During the mixing operation, cutting and blending is carried out in order to obtain a thorough and uniform dispersion of the ingredients in the polymer mix Two roll mill
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  • Consists of an enclosed chamber and two rotors with small clearance between them and the enclosing wall. The rotors rotate in opposite directions. The mixing chambers can be cooled by circulating water or heated by steam. Widely used for masticating rubbers and incorporating other ingredients. The mixed batch is dropped from bottom of internal mixer onto a sheeting mill and taken off for storage until further processing. Internal mixer fast, clean and works to mixed the large quantity of compounds. Internal Mixer
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  • There are various methods to form the polymeric materials. Methods that can be used to polymeric materials depends on various factors : 1. Whether the materials is thermoset, themoplastic or elastomer 2. If themoplastics the temperature at which it softens 3. The atmospheric stability of the materials being formed 4. Geometry and size of the finished products. There are numerous similarity between some of the techniques and those utilized for fabricating metals and ceramic Forming techniques
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  • The production of polymeric materials normally done at elevated temperature and pressure. Thermoplastic : Normally been form at temperature above the Tg to form polymeric products As maintained during cooling process to maintained the shape. The advantages it can recyclable. Scrap from thermoplastics can be melt and reshape to new shape
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  • Thermoset : Involved two stages of production 1. Preparation of linear polymer (prepolymer) liquid form with low molecular weight 2. The liquid form then will change to the hard and rigid products with desirable shape Curing process will start during heating or with addition of catalyst with pressure. During curing chemical and structural changes occur crosslinking or structural network were formed. It can not be recycle, not melting and can be used at high temperature compared with thermoplastics.
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  • Plastic Molding Methods
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  • The calender is a machine equipped with two, three or more heavy internally heated or cooled rolls usually placed above each other The rolls rotate in opposite directions and operate at even or uneven speeds as the applications requires The calender is used essentially for producing rubber sheets of various lengths and thickness. It is also widely used for frictioning or skin coating of fabrics including shower curtains, tablecloths, laminating film Forming techniques: Calendering
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  • Calendering process
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  • Common roll configurations for four roll calenders
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  • Alternate method for making sheets or flat film In this process, the extrudate is extruded directly into the nip area between two rolls. The roles have small gap between them, and plastics is forced through this gaps by the counterrotating of the rolls. Forming techniques: Extrusion & Calendering
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  • Extrusion is the continuous semi-finished product with uniform cross section. The range of products extends from simple semi-finished products tubes, sheets and film to complicated profiles. In principle the extrusion process comprises the forcing of molten material through a shaped die by means of pressure. Forming techniques:Extrusion
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  • What is extrusion? The word extrusion comes from Greek roots-means push out Continuous process Process which forcing a molten materials (plastic) through a shaped die by means of pressure- e.g. melting of plastic resin + adding mixing fillers In this process, screws are used to progress the polymer in the molten or rubbery state along the barrel of the machine Single screw extruder is widely used, however twin screw extruder are also used where superior mixing is needed Forming techniques:Extrusion
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  • Typical extrusion line showing major equipment Materials fed into hopper, falls through a hole in the top the extruder (feed throat) Onto the screw. The screw moves the molten plastic forward until the end of the Extruder barrel to which die has been attached. Die gives shape to molten plastics, Cooled in water tank.
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  • Main features of a single Screw extruder The channel depth decreases from feed end to die end Solid polymer is fed in at one end, inside the polymer melts and Homogenizes and molten extrudate emerges from the other There are 3 zones; feed zone, compression zone and metering zone
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  • The screw extruder has one or two flights spiraling along its length. The diameter of the flight is constant along the length channel varies in depth to allow close fit in the barrel The root or core is varying diameter and so the spiraling channel varies in depth ( the channel depth decreases from feed end to the die end) A consequences of the decreasing channel depth increasing pressure along the extruder and drives the melt through the die. Screw Extruder
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  • There are three zones whose functions as follows: 1. Feed zone Function to preheat the polymer and convey it to subsequent zones 2. Compression zone Function to expels air trapped between the original granules Heat transfer from the heated barrel walls is improved as the materials thickness decreases The density change during melting is accommodated 3. Metering zone The functions is to homogenize the melt and hence to supply to the die region materials which is of homogeneous quality at constant temperature and pressure
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  • The principle of the compression molding can be outlined as follows: The mould is held between the heated platens of the hydraulic press A prepared quantity of molding compound is placed in the mold and the mould placed in the press The press closes with sufficient pressure to minimize flash at mould parts line The compounds softens and flows to shape, chemical cure then occurs as the internal mould temperature becomes high enough The press is opened and the molding removed. Forming techniques: Compression Molding