Extrusion of Thermoplastics Sheet Essays

Extrusion of Thermoplastics Sheet Essays Extrusion of Thermoplastics Sheet Essay Extrusion of Thermoplastics Sheet Essay 1. Abstract Sheet bulge is an of import procedure particularly in boxing industries. In this experiment, Nova Innovene Polystyrene with Grade Empera 416N ( MFI 18 ) and Grade Empera 622N ( MFI 4 ) would used to measure the difference in end product, die caput force per unit area under different processing conditions. Through sheet bulge experiment, it shows that addition in mass end product as die caput force per unit area increased. MFI 18 produced more end product than MFI 14 as the prison guard velocity decreased from high to low. By utilizing the unfastened discharge informations at screw velocity 2RPMto secret plan graph against with experimental consequences, it can foretell the maximal end product at different die caput force per unit area without making proving. As screw velocity additions, emphasis rate addition, which leads to increase in screw velocity, and so increase in thickness. Web rupture will happen with the velocity of the axial rotation stack and extruder increased quickly. W hen die spread is more than concluding sheet, thicknesses, cervix in, pull down will happen and besides bring forth a batch of molecular orientation. Draw down causes die swell, sharkskin and melt break. Sentmanat extensional rheometer is used to mensurate the extensional emphasis. . A movie of polymer is wound on two revolving membranophones, which apply changeless or variable strain rate extensional distortion on the polymer movie. The emphasis is determined from the torsion exerted by the membranophones. Tear trial and shrinking trial were done, because it is of import for applications such as nutrient packaging. The nutrient bundle might shrivel under microwave temperature. 2. Aims * Analyze how different operating parametric quantities and conditions in a sheet bulge procedure affect dice flow features utilizing different MFI HIPS * Analyze the different procedure conditions affect the shrinking and molecular orientation 3. Experimental 1. MFI 18 HIPS Empera Grade 416N was added into the hopper. 2. The screw velocity was adjusted from 0RPM to 24RPM. 3. The end product was collected and weighted after 90seconds for 2RPM and 4RPM, 45seconds for 8,12,16,20,24RPM and repeated from 24RPM to 0RPM. 4. Actual Melt Temperature, Pressure, Motor Current and Difference in Die Head Pressure were recorded. 5. The same stairss from 1-4 were repeated for MFI 4 HIPS Empera Grade 622N, but it started from 24RPM to 0RPM. 4. Consequences and Discussion Refer to appendix for the consequences under table 1 and 2. 4.1 Die flow feature: secret plan mass end product versus die head force per unit area ( for each class of stuff ) in order to bring forth the dice flow features for each class of PS, as a map of screw velocity. From 1, which is for HIPS MFI 18, the ?P and mass end product from the diminishing curve, is higher than the increasing curve. It is because the temperature was already really high ( 168.5oC ) when the thaw was runing when the prison guard velocity was reduced to 20RPM from 24RPM.Whereas the temperature from screw velocity 20RPM to 24RPM, which was 166.9oC. Higher temperatures, faster thaw, more thaw produced. However, from 2, the prison guard velocity at 12 RPM, the increasing curve has higher end product of 0.59g/min the decreasing curve. In existent fact, the end product mass from the diminishing curve should hold more than the increasing curve. Because, the temperature at screw velocity 12RPM for the decreasing curve is higher than the increasing temperature. With mention to the dice flow characteristic equation – Newtonian ( refer to equation 1 in appendix ) , it shows that with the addition in ?P, Q will besides increase. Â µ will diminish as temperature and ?P addition together, allowing to increase end product mass. The job that causes a lessening of end product rate for 12RPM for the decreasing curve, might be the operator did non roll up the extrudate thoroughly or roll up the sample before the timer has reached 1minute. Refer to 5 in appendix ; it was the comparing bulge consequences for MFI 4 and MFI 18 were from screw velocity 24RPM to 0RPM were used to make a comparing. The end product for MFI 18 is higher compared to MFI 4 because MFI 18 has low molecular weight which gives lower viscousness and so higher end product. Whereas, MFI 4 has higher molecular weight which gives lower viscousness and so lower end product although under the same prison guard velocity. 4.2 Extruder flow characteristic relating to ‘open discharge informations for HIPS Screw speed 2RPM was used to plot the graph, because the consequences recorded from screw velocity 8RPM to 24RPM was higher than the ‘Open discharge informations. Mention to 6 in appendix for MFI 18 and 7 for MFI 4. At screw velocity 2RPM, the ‘open discharge informations was 17.7g/min for mass end product and the ?P is 0mPa. For MFI 18, the mass end product collected was 11.2g/min and the ?P is 0.8mPa. For MFI 4, the mass end product collected was 17.09g/min and the ?P is 2.4mPa. 4.3 Account the tendencies which are established, with mention to extrusion flow theory, and the effects of prison guards speed / stuff viscousness. State the relevancy of shear flow theory to the observation of non-linear extruder features. Screw Speed An addition in screw velocity will increase the volumetric and so shear rates besides increases1. Screw velocity, shear rate and end product are in direct proportion under low-shear conditions2. Shear warming occurs for polymer which will take away from additive screw speed-throughout correlations3. Melt Viscosity Refer to appendix for equations 2-Single Screw extruder feature and 3- shear flow through an opening of changeless dimension, each suggest that an addition in viscousness will diminish the gradient –dQ / d?P each feature, ensuing in increased dice caput force per unit area for an end product rate which remains comparatively unchanged4. 3.2 With mention to this theory, describe and history for the relationship between prison guards velocity and sheet thickness profiles. As the Screw velocity additions, the sheet thickness profiles besides increase. The extruder and axial rotation stack velocities simultaneously5. If the extruder increases faster than the axial rotation, polymer construct up between the dice and axial rotation stack will either wrap a axial rotation or flux back onto the die face6. If the axial rotation stack and takeoff equipment velocity is increased excessively quickly, web rupture takes place7. If the dice spread greatly exceeds the concluding sheet thickness, pulling or make outing down might go on to the concluding merchandise thickness8. It may bring forth excessively much molecular orientation9. 3.3 Explain the phenomenon of drawdown, in footings of how it occurs ( on the extruder ) and the type of distortion which the polymer is subjected to. Drawdown means to cut down the plastic s size by stretching it10. It occurs when longitudinal strain was imposed upon an extruded, partially-solidified thaw due to emphasize created by draw –off viscousness which is more than dice end product velocity11. The types of distortions are die crestless wave, sharkskin and melt fracture12. Die Swell alterations in extrudate diameter at the issue of die13. It leads to longitudinal shrinking and sidelong enlargement, which is caused by gyrating of polymer molecules after being stretched through the die14. Sharkskin is the surface abnormality of an extrudate, which is like a series of ridges perpendicular to the flow direction15. The cause of this might be the acceleration consequence on the outer bed consequences in lacrimation of the weak elastic melt16. Melt Fracture is when a rod like cross-section extrudate is twisted into a signifier of spiral, which is bambooing17. It is the cause of slow relaxation times relative to the distortion rates in which the emphasis exceeds the strength of the thaw and a break results18. It can be minimized by cut downing the dice diameter, which leads to cut down in shear emphasis and so cut down of thaw fracture19. 3.4 Suggest how a quantitative ‘extensional emphasis parametric quantity might be measured or calculated from farther instrumentality on the bulge procedure. The Sentmanat extensional rheometer ( SER ) is really a fixture that can be field installed on shear rheometers20. A movie of polymer is wound on two revolving membranophones, which apply changeless or variable strain rate extensional distortion on the polymer film21. The emphasis ( extensional ) is determined from the torsion exerted by the drums22. Refer to plot 1 for the equation of distortion under force23. Where extensional emphasis is equal to Young s modulus multiply by strain24. 3.5 Account for the consequences from the simple ‘tear trials carried out on the sheets. It is easy to rupture in the oriented way which is the y axis ; nevertheless it is hard to rupture in the un-orientated way ( x-axis ) . A nip cut at the side in the un-orientated way, helps rupturing apart easier. However, it was rupturing in the x-axis, after awhile, the lacrimation starts to rupture towards the y-axis. The ground why the lacrimation ever in favor of y-axis is due to the molecules were arranged in the y-axis way and it was cooled instantly once it passed the ice chest roller, and the molecules were frozen in that orientation. 3.6 Account for the consequences from the shrinking trial carried out on the sheets. Directional shrinking occurred in this experiment25. The grade of orientation imparted to the thaw during the mold filling procedure has a big influence on the shrinking exhibited by HIPS26. During mold filling, the polymer molecules undergo stretching those consequences in molecular orientation and anisotropic shrinking behaviour27. HIPS is a neat orientated fictile stuff, so it tend to shrivel more along the way of flow ( in flow shrinking ) 28. The cut of strips of the samples were placed in the 120oC for 10minutes. By comparing the % length shrinking for extrude velocity at 20rpm with different roller velocities ; the highest roller velocity 2metre/min with the thinnest thickness has the highest % length shrinking of 22.64 % . Whereas, the lowest roller velocity 1metre/min with the thickest thickness has the lowest % length shrinking of 9.80 % . Because of the fast roller velocity, the molecules in the movie orientation are frozen rapidly, and have no clip to rearrange. But one time, its placed in the oven, the molecules were in relaxed province, hence, shrinking occurs. By comparing the % length shrinking for roller velocity 2metre/min with different extrude velocities ; the lowest extrude velocity 12rpm with the thinnest thickness has the highest % length shrinking of 38.46 % . And the highest extrude velocity 20rpm with the thickest thickness has the lowest % length shrinking of 22.64 % . 4 Decisions * The experiment was a success * All aims were met. 5 Mentions 1-3 Extrusion Processes, Physics of Plastics: Processing, Properties and Materials Engineering, by Birley/Haworth/ Batchelor, page 127 4 Bulge Processes, Physics of Plastics: Processing, Properties and Materials Engineering, by Birley/Haworth/ Batchelor, page 119 5-9 Operation, Bulge: the unequivocal processing usher and enchiridion, By Harold F. Giles, John R. Wagner, Eldridge M. Mount, page 437 10 Extrusion Process, hypertext transfer protocol: //online.sfsu.edu/~jge/html/extrusionprocess.html ( accessed on 7th December 2009 ) 11 Bulge Processes, Physics of Plastics: Processing, Properties and Materials Engineering, by Birley/Haworth/ Batchelor, page 116 13-19 Processing of Thermoplastic, material.eng.usm.my/stafhome/ /Week % 204 % 20Processing.ppt ( Accessed 7th December 2009 ) 20-22 Rheometer, hypertext transfer protocol: //about.qkport.com/r/rheometer, ( accessed on 9th December 2009 ) 23-24 Material response to force, Practical bulge blow casting, By Samuel L. Belcher 25-28 Plastic portion design for injection casting: an Introduction, By Robert A. Malloy 6 Appendix ?P With mention to decease flow characteristic equation ( Newtonian ) : Q = g. Â µ Equation 1 ( Equation taken from: Bulge Processes, Physics of Plastics: Processing, Properties and Materials Engineering, by Birley/Haworth/ Batchelor ) , page 117 Single Screw extruder characteristic ? Q = ?N . ?P -eqn 2 Â µ ( ? and ? are invariables of screw geometry ) Taken from: Bulge Processes, Physics of Plastics: Processing, Properties and Materials Engineering, by Birley/Haworth/ Batchelor, page 107 Shear flow through an opening of changeless dimension ?P Q = K. -eqn 3 Â µ Taken from: Bulge Processes, Physics of Plastics: Processing, Properties and Materials Engineering, by Birley/Haworth/ Batchelor, page 117 Taken from Material response to force, Practical bulge blow casting, By Samuel L. Belcher Table 1: Consequences for MFI 18 Table 2: Consequences for MFI 4 Extrude velocity( RPM ) Avg. Thickness ( millimeter ) 20 0.17 16 0.15 12 0.12 Table 3: Consequences for mean thickness with different extrude velocity – refer to 8 for graph secret plan Table 4: Consequences for different extrude velocity and roller velocity, mean thickness and before and after shrinking