3 1 extrusion machinery

POLYMER PROCESSING

MODULE - III

SPRING 2015

VI Semester BE (Chemical Engineering Plastics)

POST EXTRUSION MACHINERY & PRODUCT TESTING

Plastics are superior to many conventional materials, in both their physical propertiesand the variety of ways in which they can be processed.Molding during processing owes its simplicity to the basic characteristics ofthermoplastic resins, that they change reversibly from the solid to the molten state, thatpermits the molding operation to be shifted from the raw material producer to theprocessor.Machine manufacturers have the task of developing extrusion lines for the processorsspecial requirements.Extrusion lines consist of a logical in-line arrangement of the machines, auxiliaryequipment, and measuring and control instruments that are required for the productionof semi-finished and finished products from thermoplastics.All extrusion lines are based on the principle of transforming a polymer by means ofan extruder from the solid to easily moldable plastic state, then through an extrusion diein a predetermined cross-sectional shape, solidifying it by cooling, possibly drawing itor subjecting to further treatment and stacking it as semi-finished product or winding orpacking it as finished product.The rapid growth of the industry produced many suppliers of extrusion lines and led tostrong competition, involving a wealth of innovations.

POST EXTRUSION MACHINERY & PRODUCT TESTING

Topics to be discussed in this module:

Downstream equipments of PIPE/TUBE & Product testingDownstream equipments of BLOWN FILM & Product testingDownstream equipments of CO-EXTRUDED FILMS & Product testingDownstream equipments of WIRE COATING & Product testingDownstream equipments of CAST FILM/SHEET & Product testingDownstream equipments of ORIENTED FILMS & TAPES & Product testingDownstream equipments of MONOFILAMENTS & Product testing

EXTRUSION LINEOF PIPE/TUBE & WIRECOATING

Extrusion of thermoplastic pipes hold second place in market after films.This production line has broken into the following products: Pressure pipes (PVC,PE),Cable and elctro conduit pipes (PVC, PE), drainage pipes (PVC, PE, PP), gas pipes(PCV,PE), water spray pipes (PE), domestic drinking water pipes (PE), Brake and fuelpipes for the automobile industry (PA) etc.,Pipe production line consists of an extruder which is equipped with a die depending onthe end product and also a calibration device. After the extruder, the material is runthrough a cooling pool, nip rolls and a cutting saw.Biggest production of pipes is made out of PVC, PE and PP.During the manufacturing process of pipes, the molten plastic from extruder is led to acircle die towards the calibration device, where the final shape and size are determined.Pipe calibration can be carried out either in high or low pressure.Haul-off unit function is to pull the calibrated product towards the cooling pool, whichis then cut into desired length.Flexible tubes, such as PE-LD are often wound into a roll. Rigid pipes are cut tolength.

EXTRUSION LINEOF PIPE/TUBE & WIRECOATING

Extrusion line of thermoplastic pipes consists of:Extruder with die head Calibration unit Cooling unitHaul-off CutterWinding, discharge and socketing

EXTRUSION LINEOF PIPE/TUBE & WIRECOATINGExtruder with die head

Twin screw extruders are used for PVC and single screw extruder for polyolefins andother thermoplastic materials.For the processing of powdered Rigid PVC, counter-rotating intermeshing twin screwextruders are used exclusively and superior to SSE, because:Friction independent and constant raw material supplyGentle heating and plasticatingReliable degassing of volatile raw material constituentsExcellent homogenous int erms of heating and mixingHigh output at low screw speeds Favourable ratio of capital cost to outputOptimum pressure build-upDepending on the output range, the counter-rotating TSE are divided into: Extruderswith conical and extruders with parallel twin screws.Advantage of CTSE are: increased feed volume, small overall length due to shortplasticating unit and compact drive units.PTSE are advantageous of manufacture of cylindrical screws are less costly, variablebarrel and screw lengths, variable geometry screw allowing adaption to the rawmaterial.

EXTRUSION LINEOF PIPE/TUBE & WIRECOATINGSSE are used for producing polyolefin pipes due to:High torques for obtaining high outputHigh and pulsation free melt throughputHigh output rates at low screw speedsOptimum melt temperatureHigh flexibility and minimum wear.Co-rotating intermesing TSE for producing filled polyolefin pipes. Fillers such ascalcium carbonate, talc, barium sulfate etc., are added to pure polymers to providematerials for products with specific property profile and considering economical tocarryout compounding and extrusion in one operation.Co-rotating TSE are advantages in direct extrusion for the reasons of:Easy conveyance of poor-flowing, powderised materialsHigh, pulsation free throughputsExcellent dispersion and homogenization for a constant, good quality productsHigh flexibility in the processing of various material components.Control of the mass temperature.

EXTRUSION LINEOF PIPE/TUBE & WIRECOATINGPipe die head

Processing of PVC, which is thermally unstable demands perfect flow channels and itis met by dies with a spider mandrel retainer.PVC melt comes from the extruder through a narrow inlet channel and then it fills outthe relatively large volume of the die head and flows around the mandrel which issupported by a ring of spokes (Spider leg).Spider dimensions must be that they can absorb the pressure on the mandrel.In addition to dividing the melt it must also fulfill the task of reducing thermalinhomogeneities of the melt from the twin screws in a strained state can relax.Further, it is necessary that the diameter and cross-section of the flow channel in themandrel retainer area are made larger than the die diameter and also reducing theannular area of the flow channel enables the melt that has been divided into ringsegments and create buildup in die pressure that force the melt streams to converge,minimize weld or spider lines.After the melt is rejoined, itmoves into the last section of the die, called the land.The land that has a constant cross-sectional area and reestablishes a uniform flow andallows the final shaping of the melt and also allows a certain amount of relaxation time.The land can adversely affect the surface finish of the pipe if it is too short in length.Typical land lengths are 15 to 20 times the annular spacing.

EXTRUSION LINEOF PIPE/TUBE & WIRECOATINGPipe die head

By changing the die insert and mandrel, pipes of varying wall thickness & diametercan be produced.Another design is the perforated ring as a retarder disk developed to normalizes themelt flow and reduces the effect of flow disturbance through the spider. The moltenpolymer is forced through a perforated sleeve or plate, which contains hundreds ofsmall holes. Polymer is then rejoined under pressure as a round profile. The perforatedsleeve, which is also called a screen basket, eliminates spider leg lines.

EXTRUSION LINEOF PIPE/TUBE & WIRECOATINGPipe die head for wire coating

The extrusion line comprises an extruder which is equipped with crossed head.Coated wire is pulled in a certain angle towards a cross headed extruder.The cross head will cover the wire or cable with molten plastic.After exiting the cooling pool, the solidified plastic and cable are rolled.Plastic materials that are most common for cable coating are PVC and PE.

EXTRUSION LINEOF PIPE/TUBE & WIRECOATINGCalibration Unit

The tube of thermoplastic melt from the die head must be cooled and calibrated byshaping for exact dimensions and for stresses in the pipe wall.Inner and outer calibration methods are used. Although inner calibration leads to amore favourable distribution of stress within the pipes, but it is complicated anddifficult to handle.External calibration unit are used by sizing from outside and it is classified intoVacuum tank calibration and internal air pressure calibration.Due to easier and safer handling, vacuum sizing has been generally accepted andproved for pipes with OD of upto 2000 mm.Upon entering the vacuum tank the still soft and deformable pipe is subjectedimmediately to moderate cooling on its surface over a length of several centimetres.Then it enters the sizing sleeve where it is intensively cooled by water and vacuum iscreated in the calibration unit.After the pipe exits the vacuum sizing tank, it is moved through a second vacuum tankor a series of spray or immersion cooling tanks.The primary requirement is to cool the pipe periphery as uniformly as possible to avoidovalities or sink marks.

EXTRUSION LINEOF PIPE/TUBE & WIRECOATINGCalibration Unit

Calibration with the help of internal air pressure is an old fashioned method but stillused for processing larger PVC and PO pipes.A sizing sleeve is placed centrally and at a small distance behind the pipe die head anda sealing plug with flexible sealing lips is attached to the pipe die head at a fixeddistance inside the pipe.An excess pressure is produced in the space b/w die and plug by compressed air, whichpresses the pipes outer wall against the inner side of the water cooled sizing sleeve.

EXTRUSION LINEOF PIPE/TUBE & WIRECOATINGCooling Unit

For either the vacuum or pressure sizing technique, the pipe must be cool enough sothat it maintains its circularity before it exits the cooling tank.Various methods of cooling are utilized to remove the residual heat out of the PE pipe. Depending upon the pipe size, the system may use either total immersion or spraycooling.Spray cooling is usually applied to large diameter pipe where total immersion wouldbe inconvenient.Smaller diameter pipe is usually immersed in a water bath.Cooling water temperatures are typically in the optimum range of 40 to 50F (4 to10C).The total length of the cooling baths must be adequate to cool the pipe below 160F(71C) in order to withstand subsequent handling operations.The required length of cooling bath is calculated with the help of Fourier number.

Fo = t/X2

Where is temperature conductivity mm2/sT cooling time W/mK

X pipe wall thickness m

EXTRUSION LINEOF PIPE/TUBE & WIRECOATINGCooling Unit

The cooling length l is:l = vab.t

where vab is haul-off speedwe obtain

1.l1/vab1.X12 = 2.l2/vab2.X22

where subscript 1 : known case and 2 is case to be designedThe cooling behavior of a PE-HD pipe with diameter 110mm, wall thickness 10mmwith vab = 2.2 m/min and a cooling length of 22m is known. What cooling length isrequired for a pipe with half the wall thickness at the same melt throughput ie twice thehaul off speed.

l2 = l1 . 1/ 2 . vab1/ vab2 . X22/ X12

1/ 2 = 1 vab2/ vab1 = 2 X2/ X1 = 1/2l2 = 22 . 1. 2 . = 11m

EXTRUSION LINEOF PIPE/TUBE & WIRECOATINGHaul-off Unit

The puller must provide the necessary force to pull the pipe through the entire coolingoperation without jerking.It also maintains the proper wall thickness control by providing a constant pulling rate. The rate at which the pipe is pulled, in combination with the extruder screw speed,determines the wall thickness of the finished pipe.Increasing the puller speed at a constant screw speed reduces the wall thickness, whilereducing the puller speed at the same screw speed increases the wall thickness.Belt type and caterpillar type haul-off units are used.Belt type units are mainly used for sensitive, thin-walled pipes and tubes in the lowerdiameter range. Evenly distributed pressure on the product is applied by two flat beltsmoving at synchronised speed.Caterpillar units with rubber gripping pads are used for medium-sized and largediameter pipes. The contact pressure can be kept as low as possible in order to preventdeformation of the pipe.

EXTRUSION LINEOF PIPE/TUBE & WIRECOATINGCutting Unit

Most smaller pipes can be coiled for handling and shipping convenience. This isadvantageous when long uninterrupted lengths of pipe are required - for example, wheninstalling gas and water pipes.Large diameter pipes is usually cut into specified lengths for storage and shipping.The selection of appropriate cutting units depends on:The cut form and the quality of cut requiredPipe diameter and wall thicknessType of raw materialCut-off lengthPlanetary saws are used for large diameter pipesParting automatic radial saws are used for cutting small and medium diameter pipes.These units are travelling systems, retained by clamping jaws and a slide is carriedalong by the pipe and returned after the cutting operation either pneumatically or bymotor.The most important requirement of cutting units are: a low noise level, safe chipextraction, cleaning of pipe ends from chips in cutting operations, easy and quickresetting when changing pipe dimensions.

EXTRUSION LINEOF PIPE/TUBE & WIRECOATINGWinding, Discharge and Socketing Unit

Winding will be done to those plastic materials which do not undergo permanentdeformation through bending should be wound. A variety of automatic winders isavailable for high speed extrusion.Pipes in fixed lengths generally upto 6m are discharged into a tilting channel.Socketing is used to vary the diameters at the end of the pipe to fix with other pipes.

EXTRUSION LINEOF PIPE/TUBE & WIRECOATINGCorrugated Pipes

Advantages of corrugated pipes are high pressure resistance with good flexibility, highimpact strength .

PIPE PRODUCT TESTINGDimensions of pipes:Pipes are checked for outside diameter and thickness with the help of ball endedmicrometer.Visual Appearance:The pipes shall be reasonably round. The internal and external surface of pipes shall besmooth and clean, reasonably free from grooving and other defects. The end shall becleanly cut and square with the axis of the pipe.OpacityThe wall of the pipe shall be not transmitting more than 0.2% of visible light falling onthem. This is easily done with the help of electric lamp, photoelectric cell andgalvanometer.Short term Hydraulic Test:This method was developed to determine the ability of a plastic pressure vessel to resistrupturing when it is pressurized for a short period of time. Surging is a commonphenomenon in a fluid transfer system. Surging is a pressure rise in a pipeline caused bya sudden change in the rate of flow or stoppage of flow in the line. A sample of pipeequal to 10 times the nominal size of pipe (not less then 35 cms or more then 75cms)shall withstand a circumferential stress of 360 kg/cm2 for at last 1hr. at 27+10C withoutany sing of leakage or weeping.

PIPE PRODUCT TESTINGLong- Term Hydraulic Test:Pipe passing the short-term hydraulic test may be continued under test to burst within 1-10 hours, the results may then be plotted as part of the long term test. The extrapolatedcircumferential burst stress at 50 years shall bet be less then 90 kg/cm2.Reversion Test:A 20 cm piece of pipe on which two marks are made 100 mm apart, is immersed inethylene glycol at 150+20C for 15 minutes, after cooling the distance between twomarks shall not go below 95mm. In other words, pipe should not shrink by more then5%.Alternatively, this test could be performed in an air oven at 1500C for 1 hour.Impact Strength at 00C:30 cm pipe pieces are cut and conditioned at 00+10C for 1 hour. Specimens shall betested on falling weigh machine within 10 secs, of removal from the bath.

EXTRUSION LINE OF ORIENTED FILMS

The manufacture of oriented film starts with the extrusion of a primary film from a slitdie or an annular-gap die and then the film is oriented by stretching.To improve physical properties like strength, elongation, shrinkage, tear resistance,rigidity & transparency are orienting the film and to utilize these improved properties inmany applications.In order to achieve an operationally reliable orienting process nowadays, ones uses theprinciple of optimization of individual process steps and is carried out in a dedicatedline element.This increases the number of independently controllable factors, and the overallprocess itself becomes more controllable.Hence, this principle demands an extremely high standard of design, and a largenumber of units connected in series to form the complete line.The materials used for producing oriented films are PP, PET, PE, PA, PS and PVC.Applications are packaging, photographic film, capacitor film, audio/video film,electric insulating film etc.,

EXTRUSION LINE OF ORIENTED FILMSProcesses for manufacture of Oriented Films

The dried pellets are supplied to the extruder. In the extruder, the pellets are conveyed,melted, compressed & homogenized, mixed and discharged as melt.Then the melt passes through a filter to remove contaminant particles and then itpasses to a film die on to the casting roll.Then it is cooled & solidifies as it carried around the chill roll.Passes through a thickness gauge & is stretched first longitudinally b/w two roll setsand then transversely in an oven.Then followed by further thickness measurement & trimming of the edges.The edge trim is chopped up at once & fed back to the extruder inlet pneumatically.The oriented film is then cut into usable widths & wound up.

EXTRUSION LINE OF ORIENTED FILMSProcesses for manufacture of Oriented Films - Sequential

EXTRUSION LINE OF ORIENTED FILMSProcesses for manufacture of Oriented Films - Simultaneous

EXTRUSION LINE OF ORIENTED FILMSLines for Production of Oriented Films

Most of the film drawing lines are based on the same principle, the various processsteps can be carried out in different ways. The process steps are:A) Extruder: Single screw extruderB) Filtering: Long life filterC) Casting/cooling: Cast film die, chill roll, water bathD) Temp. Conditioning: thermostated rolls, hot air furnaces, heat radiators.E) Stretching: bi-axial lines (two step or simultaneous)F) Winding: central winder, multipurpose winderG) Waste return: chopping mills, waste-metering units

EXTRUSION UNIT: In this unit, the material is melted and mixed uniformly withadditives & filtered & evenly extruded as single layer film.Extruder used are single screw extruder. Screw diameter depends on output & may be60 to 350 mm with screw lengths of 27 to 33D for o/p of upto 6000 kg/hr.

EXTRUSION LINE OF ORIENTED FILMSLines for Production of Oriented Films

EXTRUSION DIE and COOLING UNIT: Slit dies are used for flat film. The thicknessrange is 15 to 500 m. Coextruded films can be produced in multichannel dies.Before film stretching process, the material must be cooled to below its melting point.Cooling must be fast and even in order to obtain homogeneous crystalline structure.Chill roll principle has proved to be the best method for this purpose. For efficientremoval of heat from the melt, casting roll have a diameter of 50 to 2500mm dependingon the film thickness & take off speed.TEMP CONTROL of FILM: Before stretching, the film must be heated to its optimumorienting temp. It is carried out by contact with oil-heated rolls or by air transfer in theheating oven or be means of heat radiators.STRETCHING UNIT: In order to achieve film properties, the primary film is stretchedby a tension applied in the required direction, by this the film changes shape. It canstretched first longitudinally and then transversely or it is stretched simultaneously inboth directions.The stretching tension is applied by draw rolls and sliding caliper clips on a tenterframe. The film is heated to temp. below the crystalline melting point by roll contact orhot air. Different roll arrangements are used and it goes to four to six stretching rollsdriven at different speeds

EXTRUSION LINE OF FILM TAPESLines for Production of FILM TAPES

Film tapes are uniaxially oriented thermoplastic semi-finished products with a highwidth to thickness ratio which can be converted into twins, ropes, knitted or wovenfabrics.The first step is to produce flat film from polymer pellets.Cooling method includes the use of water baths, chill rolls or air jets.The film is then drawn, slit lengthwise into strips and then wound into spools or filmpackages.The field of applications are sacks, tapes, wall paper & home textiles, outdoor carpets,decorative tapes etc.,


Tape grade thermoplastic pellets are fed to the extruder. In the extruder, the material ismelted, compressed and homogenesied and extruded as films at constant massthroughput.The film is solidified by cooling in contact with a chill roll, then the film is cut into agroup of tapes with the blade spacing determining the tape width.The tape is then stretched b/w roll sets which run at increasing surface speeds. In orderto improve orientiation the tapes are heated in an air stream.Then settings & edge trim takes place.


EXTRUSION: Single screw extruders are used.CASTING: The film is formed by casting from the flat film die into a water bath orinto a chill roll.SLITTING: The quenched films are cut into a group of individual tapes prior tostretching, so slitting operation is used by large number of blades arranged next to eachother slit the pre-tensioned film.FEEDING OF TAPES: The film tapes must be stretched to many times their originallength to achieve the required properties. It is generally takes place by the speeddifferences between the first and second godet units.HEATING: The tapes are heated externally in the stretching process. Hot air oven, hotwater baths, hot plates or internally heated godet rolls are used for heating.STRETCHING: Stretching unit is similar in its arrangement to the feed units. Speedrange & drive power for the stretching rolls are set to give the required stretch ratio &stretching force.FIBRILLATING: Similar to embossing on the film. If the stretched tapes are fibrillateby means of needle, pin or knife rollers which slice into the oriented. For eg., net likesplit tape.WIND UP: the film tapes are wound onto wind up tubes.

EXTRUSION LINE OF FLAT FILMLines for Production of FLAT FILM

EXTRUSION: Single screw extruders are used.CASTING: The film is formed by casting from the slot die. The die outlet width mustbe larger than the width of film to be produced for edge trimming purpose.CHILL ROLL TAKE OFF UNITS: The extruded film is cooled on the casting rollwhich ensures even cooling of the film.FILM GUIDANCE & DOWNSTREAM EQUIPMENT: After leaving the chill rollunit, the film passes through several guide elements such as idler rolls, thicknessscanner, surface treatment unit before it reaches the windup station.

EXTRUSION LINE OF FLAT FILMLines for Production of FLAT FILM

EXTRUSION LINE OF MONOFILAMENTLines for Production of MONOFILAMENT

Monofilament are wire like polymer strands whose tensile properties are achieved bystretching. They usually have a circular cross-section.A range of applications are ropes, nets, tennis racket strings etc.Polyethylene, polypropylene, nylon and polyesters are commonly used raw materialsfor making monofilaments.The process essentially consists of the following steps Extrusion: Single screw extruders are used. Monofilament dies usually have 180 to200 holes which are even distributed on 2 or 3 pitch circles. These holes are preciselymachined to get a smooth and uniform monofilament surface. FormingThe monofilaments emerging from the die are taken into a quench bath. The quenchmedium is water which is maintained at around 25-35C. The purpose of quenching isto have a finer crystallite size which will facilitate stretching to produce high tenacityfilament. The filaments are taken over a deflecting roll in the quench bath and aredrawn continuously by Godet I.

EXTRUSION LINE OF MONOFILAMENTLines for Production of MONOFILAMENT

DrawingThe drawing zone of a monofilament line consists of the first godet, a hot air oven and afast godet (2nd godet). Stretching is effected by the speed differential between the 1stand IInd godet. The filaments are heated to just below their softening point in the hot airoven (145-160C) and drawn.WindingIn most of the extrusion lines, the filaments are wound individually on separate spoolsor bobbins.

EXTRUSION LINE OF BLOWN FILMBasic ConceptExtrusion through an spiral die & the tubular film will be formed which is stretchedand inflated by an air stream flowing inside the die which create a bubble consists ofmolten plastic.The bubble is cooled by an air jet flowing from an air ring towards its outward surfacegives cooling at a certain distance from the die exit.Beyond the crystallization line, there is the freeze line where the bubble boundariesbecome parallel to the centreline.Beyond the freeze line, the deformation of the bubble is practically zero.Eventually, the cooled film passes through the collapsing frame & nip rolls ( where thebubble is flattened by a set of guide rolls) before being taken off to storage drums.Nip rolls may be either constant speed or constant torque.Finally, the film is wound onto cylinders and sold as lay flat.Major advantage is the ease with which biaxial orientation can be introduced into thefilm.The pressure of the bubble determines the blow-up and this controls thecircumferential orientation (Transverse direction).

EXTRUSION LINE OF BLOWN FILMBasic ConceptAxial orientation (Machine direction) may be introduced by increasing the nip rollspeed relative to the linear velocity of the bubble. It is referred as draw down ratio.Mechanical properties of blown film are nearly uniform in both directions as a result ofbiaxial orientation. Thats why flat films is produced by the film blowing process aswell as economy & speed of production.

EXTRUSION LINE OF BLOWN FILMLines for Production of BLOWN FILM

The main line elements of blown film are:ExtruderDie unitCooling & calibration unitHaul-off unitWind-upRaw materials used are LDPE, LLDPE, HDPE, HIPS, PP, PA6.Applications are General Packaging films, lamination films, surface protection films,green house films, barrier films for food packaging, etc.,


The main line elements of blown film are:Extruder: Single screw extruder are mainly used for blown film production. Screwdiameter is 40-200 mm & screw length will be 20-30D.Die: Spider type dies & Spiral type dies are used.


The main line elements of blown film are:Cooling Unit: External cooling and Internal cooling of blown films are used.External Cooling: It is carried out by air emerging from a cooling ring mounted on dieoutlet. Air volume, air speed & direction of air stream determine the effectiveness ofcooling. Cooling rings are operated with blowers.Internal Cooling: It is done by internal air exchange. Cooling system is equipped withpressure blower for bringing fresh air & suction blower for pulling air into the bubblethrough a tube mounted axially inside it as well as removes volatiles from inside thebubble.


The main line elements of blown film are:Calibration Unit: Basket like construction with free-running rollers with support arms.Dimensional constancy is achieved by calibration. Calibration basket is set at a heightthat the frost line always lies below the first set of rolls.


The main line elements of blown film are:Haul-off Unit: It includes collapsing frame and haul-off or squeeze rolls.The collapsing frame is constructed from two or more wedge shaped, angularlyadjustable surfaces made of either wood or free running rollers.Two haul-off rolls are either rubberized steel or a combination of rubber & steel rolls.The pressure of the unit is adjustable so as to avoid inversion breaks in the side foldregion.


The main line elements of blown film are:Winders: Contact winders and central/contact winders.Contact winders also called circumferential surface or drive roll winder. Rubber orchromed roll is used. The axis of the winding shaft lies parallel to that of the contactroll. Manufacture of heavy duty films, thin films contact winders are used.Disadvantage is low tension wound rolls cannot be produced.Central/contact winders also called axial or direct winders. It is used to produce softrolls of wound film at very low tension. Winders are expensive. The axis of thewinding shaft does not lie parallel to the contact roll.

EXTRUSION LINE OF CO-EXTRUSIONLines for Production of BLOWN FILM

It is the process for making multilayer blown films in one operation.It operates with separate melt channels, so different viscosities are easier to combine.No of extruders depends on the film combination.Two layer dies, three layer, five layer and seven layer dies are used.

EXTRUSION LINE OF CO-EXTRUSION

Diagram of the coextrusionhead for extrudates of asimple cross-section area: 1 supplyingcomponent, 2 connectingcomponent, 3 extrudingcomponent (co-extrusion head), 4 inlet channel, 5 distributingchannel, 6 co-extrusion head

Diagram of the co-extrusion head fortwo-layer film: 1 inlet channel of thefirst polymer, 1a inlet channel of thesecond polymer, 2 distributingchannel, 3 coextrusion head die, 4 adjusting bolt, 5 co-extrusion headbody, 6 choker bar, 7 flexible lip

FILM BLOWING ANALYSIS

The important outcome of a film blowing process is the size or diameter of tubular film defined by the dimensionless blow-up ratio, BR and draw down ration, DR.

BR = final tube radius, Rf / Initial tube radius, Ro = Db / Dd

DR = Take up speed / die extrusion speed = V / o

Orientation in machine direction, OMDOMD = Length of bubble, Lb / Length of die, Ld

Orientation in Transverse direction, OTDOTD = Dia. Of Bubble, Db / Dia. Of die, Dd

FILM BLOWING ANALYSISSince the volume flow rate is the same for the plastic in the die and in the bubble, then

for unit time.

DdHdLd = DbHbLb

DdLd / DbLb = Hb / Hd

1 / BRDR = Hb (thickness of bubble) / Hd (thickness of die)

DR = Hd / Hb*BR = OMD

Ratio of OMD/ OTD = Hd / Hb *(BR)2Dimensionless freeze point, X = freeze line above the die, Z / radius of die, RoDimensionless thickness, Ho / Hf = Thickness of die / thickness of filmDimensionless pressure, P = *Ro3*P / QDimensionless take up force, F = Ro*fz / QWhere =Newtonian viscosity, Ro=Initial Radius of extruded tube, Q=volumetricthroughput, P=pressure difference across the film, fz=film take up force

FILM BLOWING ANALYSISAn LLDPE film is blown to a thickness of 50 m from a 25 mm diameter annulardie with 1mm thick slit. Determine the required bubble pressure and take upforce for an extruder mass throughput of 100 kg / hr and draw down ratio of 4.The freezing point is 200 mm above the die exit. The polymer is assumed to beNewtonian with a viscosity of 1000 pa s and the density is 920 kg / m3.Given Data: Z=200mm, Ro=25mm = 12.5mmHo=0.001m, Hf=50x10-6m, DR = 4X=200/12.5=16Ho/Hf=0.001/50x10-6BRDR=Ho/HfBR=20/4=5From graph of X=10 & X=20X=10=P=0.08 and F=1.95 & X=20=P=0.055 and F=1.50Interpolate, X=16 = P=0.065 and F=1.68Bubble pressure, P=319Pa= 0.065*1000*(100/60*60)*(1/920) / *(0.00125)3Take up force, fz=4.06N= 1.68*1000* *(100/60*60)*(1/920) / 0.0125

Analysis of Flow in ExtruderThe output from the extruder as consisting of three components - drag flow, pressureflow and leakage.The derivation of the equation for output assumes that in the metering zone the melthas a constant viscosity and its flow is isothermal in a wide shallow channel. Theseconditions are most likely to be approached in the metering zone.(a) Drag Flow: Consider the flow of the melt between parallel plates.

For the small element of fluid ABCD the volume flow rate dQ is given bydQ= V * d y * dx

Assuming the velocity gradient is linear, then

Analysis of Flow in Extruder

Fig. 4.8 shows the position of the element of fluid and (4.2) may be modified toinclude terms relevant to the extruder dimensions.

For example Vd = DNCOSwhere N is the screw speed (in revolutions per unit time).

Analysis of Flow in ExtruderThe output, Q, of a Newtonian fluid from a die is given by a relation of the form


POLYMER PROCESSINGSlide Number 2Slide Number 3Slide Number 4Slide Number 5Slide Number 6Slide Number 7Slide Number 8Slide Number 9Slide Number 10Slide Number 11Slide Number 12Slide Number 13Slide Number 14Slide Number 15Slide Number 16Slide Number 17Slide Number 18Slide Number 19Slide Number 20Slide Number 21Slide Number 22Slide Number 23Slide Number 24Slide Number 25Slide Number 26Slide Number 27Slide Number 28Slide Number 29Slide Number 30Slide Number 31Slide Number 32Slide Number 33Slide Number 34Slide Number 35Slide Number 36Slide Number 37Slide Number 38Slide Number 39Slide Number 40Slide Number 41Slide Number 42Slide Number 43Slide Number 44Slide Number 45Slide Number 46Slide Number 47Slide Number 48Slide Number 49Slide Number 50Slide Number 51Slide Number 52Slide Number 53Slide Number 54Slide Number 55Slide Number 56Slide Number 57Slide Number 58Slide Number 59Slide Number 60

3 1 extrusion machinery

Documents