TO KNOW HOW TO EXTRUDE or TO KNOW EXTRUSION
Two years ago I wrote an article “Extrusion – Art or Science” inviting to consider the Extrusion as a science because to face extrusion problems and to interpret the functioning of the extruders complex (extruder-head), the science Rheology must be used.
Today I am returning to the same subject because I think that the improvement of the extrusion technologies cannot overlook the rheology, that teaches us the laws of flow inside the ducts (the extrusion head and die are ducts of special shape) and other physical laws, as the transformation of electrical energy into mechanical and thermal energy, that are applied when the extrusion technologies are actuated.
To know how to extrude does not mean to know the Extrusion science. .
The polymer extrusion is a process that transforms a solid polymer into a melt that is pushed by the pressure generated by the screw, through the apparatus situated forward the extruder.
To know the extrusion means to know how and why a determined quantity “Q” of solid polymer is transformed into a melt that is pushed outside the die, which actions are exerted on the polymer and which are the reactions of the polymer molecules to contrast those actions. The result is that the solid polymer is transformed, owing to the suffered work and energy accumulated, into a quantity “Q” of melted polymer having a very precise temperature and therefore into a melt that exits from the die at a very precise “viscosity”. A viscosity that cannot change during the profile production, if the working conditions are not changed, because the extrusion is an absolutely stable process.
This polymer viscosity is the “Quality” of the melted polymer exiting from the extrusion complex and therefore we can affirm that if during extrusion the viscosity, that is the melt temperature, changes there is definitely a cause and this cause can be detected.
To know the extrusion means to know rheology, that is how the melted polymer flows inside the heads, at a certain output, which is the shear rate and the shear stress at the walls and therefore which is the pressure drop required to make the polymer flow.
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To know how to extrude means to be able to find the working condition to extrude the melted polymer at the viscosity that allows to obtain the maximum output and the best profile quality.
To know how to extrude means to apply the rheology laws in order to obtain the desired quality, without knowing rheology. In fact the melt flows according to the laws of rheology independently of the will of those who extrude, because the melt knows perfectly the rheology and is able to flow only following those laws.
The expert of extrusion knows the Art but not the Science, he is guided by experience acquired doing a lot of positive trials and having always less disappointment. Unfortunately those who have only experience can increase their knowledge only doing new experiences, which rarely are successes that teach something new. In any case, this is a very slow way to learn and, in addition, to do innovative trials it is required a high predisposition to the risk of doing something wrong.
T
hose who know the extrusion and use the science are in the position to know the results without doing practical trials, but just simulating the tests with the mathematical model realised by themselves.The practical tests are used just to confirm a good choice or a good idea to improve the quality or the quantity produced. Those who know extrusion and use the science improve the machines and the technologies on paper without wasting raw material and without using lines that can be used to produce.
Those who know the extrusion iuse the production lines to find, for each line, the correlation between the variables to quantify the effects of the changes of the working conditions. In a following time these correlations will be used to determine the quality and entity of the changes, because the extrusion is a steady process that guaranties the same quality at the same working conditions.For example it is important to use the production lines to know how much the melt temperature, i.e. the quality of the melted polymer, changes for a determined pressure change at the end of the screw.
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In the article “Extrusion – Art or Science” I clarified to those who extrude that the extruder complex is a rheometer of a particular shape that uses a screw, instead of a piston, to make the polymer flow through the die and therefore we cannot think that it is possible to reason about extrusion and create an innovative technology without knowing how “our rheometers”, that extrude tons of melted polymer in our production departments, work.
In the past years the extrusion technology is improved for quantity and quality only for the skilfulness of those who know how to extrude, the incidence of those who knows extrusion has been imperceptible in production and only slightly greater in design. I also have been for many years a technician who knew how to extrude among many others that were able to extrude better than me.Therefore to improve myself as fast as possible, I constantly used rheology and now I know extrusion at such a level that when I look at an extrusion complex I see what is happening inside the cylinder, section after section, until the exit of the head. First the advancing solid, then the compacting of the solid and the melting, meantime I see the polymer accumulating heat that arrives to the die exit more or less smoking.
By this time I am a “Rheo-dependent” and when I look to an extrusion process, I do not see a profile, I see a flow, I see Poiseuille’s law, I do not see only the appearance of the melt, but rather its quality, the viscosity, and I begin to reason about the process and think about what I could do better and if I could patent it.
For many years I have been using rheology to understand some phenomena and explain them in a correct way, but only in 2008, while writing my Handbook of applied rheology “L’estrusione con parole mie” I discovered that to calculate the pressure at the end of the screw flight a corrected Poiseuille’s law must be used, not at all the one learned at the university.
I am giving this news, to let people know that it is not enough to know rheology to know extrusion, but it must be used to learn something new and solve the extrusion problems. Only continuous training in the use of rheology can light the lamp that leads to technological innovation.
When we look at an extrusion complex, we must automatically do the “process analysis” and find the cure. If the result of the analysis is “the extrusion is ok” the cure is “nothing to change”.
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The foregoing should induce factories producing extruded profiles to force their technicians, that know how to extrude, to know the extrusion , to be able to do the process analysis and to forecast the effect of any action, instead of going on with the usual trials.
The only way that allows to increase the knowledge in a fast way and to improve the processes, that is the performances of extrusion complex, is the continuous application of rheology to explain, first to himself, what happens during extrusion. Remember that there is no event or product defect that cannot be explained by science and then eliminated.
The way to face the extrusion problems is the following. The extrusion is an absolutely stable process, so if we note some instability we must seek the cause and, once we have found it, we shall be able to eliminate it along with the instability. Total confidence and determination is required. .
When we set the right number of revolution of the extruder screw we shall obtain the expected output. The extrusion line, set up in this way, will produce a melt of a certain quality. The quality will be the melt viscosity, i.e. a melted polymer at a precise temperature. We must not doubt about that. .
We must know that every time the melt exits at the same temperature the melt quality is the same and then the same profile quality is obtained. Never doubt about that..
In practice for each extrusion line a thecnitian must:
1) Find for each product the melt quality that allows to produce the best profile.
2) Know the temperature (viscosity) of the melt when the best profile is produced. Be careful, few people know that the temperature gauge that are on the market (to use with the probe into the melt) does not read the melt temperature (see “Experience n°5” in my Handbook of Rheology applied to Extrusion).
3) Set, all the time, the right working condition to get the same “quality”, no doubt that the profile will have the expected quality.
If the extrusion complex is known and one “knows extrusion” it is impossible to fail the target.
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The situation described above is the exact picture of which is the actual extrusion, the same of many years ago, for the production of plastic profiles.
Several years ago the factories had many workers that knew how to extrude and the production supervisors worked at their best to extrude the best melt quality and then to get the best profile quality at the end of the line. Generally each line had its operator and therefore there were a lot of workers trained and they knew how to extrude.
Nowadays extrusion lines have been improved and there are many lines that produce by themselves, after the start up, and the line conduction consists of filling the hoppers and unloading the profile. Since the lines have been improved, the workers learn next to nothing. The people who knows how to extrude are retired and it is difficult to find an expert to conduct the extrusion department.
In the next future I forecast that the more provident factories will impose a clever technician, that knows the extrusion to the production, with the function to learn how the extrusion complexes of the factory work, to know at which temperature the polymer exits from each die, to have for each profile the optimal quality and to state the working conditions at which it must be extruded. Every factory must have a technician that is able to analyse the process. Done the analysis the technician shall find the manual technique more suitable to have the same quality in the future profile productions. Knowing the extrusion it is quite simple.
Once the technique has been found, the technician will invent the way to obtain the same result automatically.
For example transforming the instrument panel, that nowadays is a simple reader and recorder of data, into a process control panel, having the target to maintain constant the quality of the extruded polymer, that is the melt. Knowing the extrusion complex and the “Future Extrusion” this too is quite simple.
In this new situation, that I named Future Extrusion technicians who are able to extrude will be necessary, but not indispensable, because it will be the machinery that knows how to extrude.
Personally as a rheo-dependent and an Italian I hope that the future will come soon.
HOW TO SAVE ENERGY WHILE EXTRUDING
To save energy, when any plastic Profile (Film, Sheet, Tube, Straps) is extruded, a new innovative technique must be used. This technique discovered by Mr. Mario Miani is named
“Future Extrusion”
Whatever is the Profiles produced by your factory, Mr. Mario Miani Teacher of Rheology Applied to Extrusion at CESAP Institute or in Italian and Foreign Factories, guarantiees an Energy/Kg save, that may be higher than 5%, to produce the same profile with exactly the same Quality (aspect and physical-mechanical properties) using your extrusion lines with your workers, but following the innovative strategy suggested by
The Future Extrusion
This is a strategy that, according to the Physical and Rheological Laws, guarantees that, at a stated output, the Quality of any Profile is exactly the desired one all the times that the extrusion line is started up and until the production is finished.
Moreover, this innovative strategy absolutely assures an interesting save of Energy and an important increase of output at the same screw r.p.m. How? I have a Know How that is guaranteed by physics Laws.
Everybody Knows that the extrusion is a steady process.
The Future Extrusion is the Production Strategy based on the elimination of all the instabilities (output and quality) during the production. In this way waste is produced only during the start up and the filter change because the output (at constant rpm) and the Profile Quality cannot change!
An example: the Future Extrusion suggest to keep OFF all the heaters (extruder and other devices up to the die) to avoid that the change of temperature of the walls (against which flows the melt) may cause the change of Melt Quality and then the change of Profile Quality.
That is
ZERO ENERGY CONSUMPTION TO HEAT THE LINE
Appendix 1 to my Handbook “The Extrusion according to me”
THE UNKNOWN EXTRUSION and THE FUTURE EXTRUSION
The polymer extrusion is a very well known way to process plastics and it is well known by many peoples that have never seen an extruder producing a profile of constant section and infinite length. It is therefore logical to imagine that technicians extruding plastic profiles know the extrusion process, i. e. what the polymer has to undergo, owing to the pushes of the screw, entering, solid into the extruder to exit melted through the die.
As the function of the extruder is to melt the polymer and push it through the die, it is logical to think that the technician who extrudes knows why the polymer melts and why it flows through the die. Unfortunately reality is very different, so much, that it seems unbelievable that people involved in the profile production, nevertheless they are really able to extrude wonderful profiles, do not know extrusion.
How is possible that the companies producing and selling profiles do not know extrusion, the ones conducting the extrusion lines do not know extrusion, the ones responsible of quality end of the research and development of extruded products do not know extrusion? How was possible that in 1988, when I retired after being involved for 26 years with extrusion and having used rheology to design dies, I did not know extrusion?
After 4 years by a Research Institute attending the production of polypropylene filaments, plus 4 years by an other Research Institute attending the production of PMM and ABS profiles, after 12 more years as process manager in a factory producing extrusion lines for any type of profiles and any kind of polymer and eventually 6 years in a factory producing PVC profiles, how to explain that I did not know extrusion?
What I realised, year after year, since I began to teach the extrusion, is just that: in 1988 I did not know the Extrusion. I knew what was happening during extrusion, but not the whys and wherefores.
It is evident that the knowledge of extrusion techniques is not sufficient to know extrusion, only when somebody knows why a technique works he knows extrusion and only when that technique works forever it becomes a Low of the Extrusion Science.
No doubt, at that time, I could not accept that somebody would dare say that I did not know extrusion. Today it is me who says: I did not know Extrusion. I was exactly in the situation of almost the totality of people that nowadays produce good profiles using very valid techniques, but without knowing extrusion.
If today I know the Real Extrusion I have to thank the 2000 people that, asking me lesson after lesson the whys and wherefores, pushed me to analyse and understand all what was happening into the extrusion complex, while solid polymer first, and then the melt, was going towards the die exit. I would like to know if today some of them are following the extrusion rules that I taught them and that can be found in my Handbook of applied rheology “L’estrusione con parole mie ”(Extrusion according to me). I would like to know that from those who followed my lessons during the last 10 years, that is, since when I have been conscious that I knew about everything of the extrusion process; I say about everything because on January 2009 I discovered a quite important Know How, that allow to save an appreciable quantity of energy per each kilogram of produced profile. In that day I understood how was working an extrusion technique, that I had already used many times to solve specific problems, and since then that technique became an Extrusion Low valid for the production of any profile.
Eventually conscious of the difference between to be able to extrude and to know extrusion, of the difference between the knowledge of the Art to extrude and to know Extrusion Science, being convinced that Extrusion in unknown by those who produce profiles, I decided to write this “Appendix 1” to my Manual to convince the artists of extrusion that the lack of knowledge of this Science causes economical losses, to profile producers, and waste of energy for the community, but what is worse than that, owing to a lot of wrong ideas on the extrusion process, one has not the necessary knowledge to innovate the extrusion processes.
To innovate means to find the most suitable technique and, why not, the Know How and the Patents for each production, for all extrusion complex and for all profiles.
No innovation means to be unable to reach the target desired by all profile producers.
Which “Target”?
To obtain, for each profile, the maximum production and the best quality at minimum cost.
The logic says that this target exists because we are able to distinguish a good profile from a better one and, as there is always a limit, we are able to say we cannot do anything better.
This means that when we shall state that a better profile cannot be obtained the production of that specific profile have been optimised. Moreover as the Target is obtained following the physics laws, as Galileo Galilei said before me, it will be always possible to obtain again the best profile.
Remember that the one who knows the Extrusion is always able to obtain the optimal quality.
The best quality will be very easily obtained also by those who, as nowadays happens, have difficulty to produce, today, the profile equal to the one produced the day before.
The demonstration that the Target is not achievable by people producing profiles is in the facts. After several tenths of years the Target is still an utopia for people producing profiles.
The Target is still an utopia because those who produce profiles do not know the cause of extrusion malfunctioning. We could also say, as it is exactly the same concept, that they do not know how extrusion works, owing to their lack of knowledge of the Extrusion Science.
Unfortunately the profile extrusion is still based on prejudices that are difficult to eliminate. Prejudices which should be removed to reach the “target” that, in the preface of my Manual of applied rheology “L’estrusione con parole mie”, I define, showing a lack of imagination and a lot of faith, “Future Extrusion”.
Before speaking of the Future Extrusion, that I always suggest to use to my customers and that I teach to people attending my lessons, let us see which are the ideas that I define prejudices andare wrong ideas derived by not valid scientific deductions.
For example examining the tests done before my lectures, by people having several years of extrusion experience, it results that about everybody thinks that the polymer melt temperature coincides with the set point temperature of the cylinder and head zones. But there is something worse, when the heating zones are overheated and the heaters are off, many people involved in extrusion are convinced that the polymer is heated by the heaters and not viceversa!
Should we think that with this ideas can be achieved the Target?
I know that it is difficult to accept my suggestion to change ones ideas, it is not easy for anybody to admit to be wrong, but I am sure that for all people, who will have such humility, is open the way to become technicians that never mistakes when extruding. They will become Technicians of the Future Extrusion able to optimise the production of any profile whatever be the shape, the polymer and the extrusion complex (extruder – head).
At the beginning there will be some difficulties, some deductions to review, but after a couple of months supported by always positive results and targets always reached, to be in the Future Extrusion will give a unique gratification. Believe me, I am enjoying these types of satisfactions since several years.
Before discussing about other prejudices emphasized in my Manual, let us try to understand something more about the actual production of profiles.
Why there are so many prejudices?
I think that when we give, or somebody give us, a logical answer to a question, we accept it without any analysis to know whether, besides to be logic, the answer is the right one. The consequence, for people involved in extrusion, is that, after a lot of logic, but not right, answers, everyone has his own “model”, of extrusion working, that obviously is a quite wrong model. The result is that, when an extrusion malfunction is analysed, quite often first the diagnosis and then the cares are wrong and undesired consequences for the firm and, may be, for the technicians are caused.
To avoid the prejudices, when we analyse the extrusion process we must remember that when the question or the answer regards physical phenomena, for example, forces and movements that means actions and reactions (machine functioning) or potential differences as the one that cause the flowing into the ducts (pressure differences) or the one that cause heat transfer through the walls (temperature differences) the answer must always be logical and coherent with the physical laws regulating the phenomena that we are analysing.
When I begin my lessons, to let the people understand how to face the extrusion problems and the phenomena connected to the process, I use the following example and ask: ”If we see a cyclist pedalling and I ask why he is moving, which is the right answer?”
It doesn’t matter if the attending people are qualified or not, it is unusual to have an answer!
So I suggest:
The cycle is moving because the cyclist is pedalling. Logical answer, but pedalling is a physical exercise and not a physical Law.cycle is moving because the gears and the chain are moving. Logical answer, but it is not physics.cycle is moving because while pedalling the back wheel rotates. Logical answer, but it is not physics.
When I ask: “If the cycle is on the ice, is it moving?” Eventually somebody answers that it is the friction on the land, that is the reaction forces, that makes the cycle move. Eventually I get the right answer, suggested by the physics!
To avoid prejudices, for any events regarding the extrusion process the answer must have the same logic and therefore the answer to the question: “Why the polymer advance along the screw during the extrusion?” is? Please, even if you are thinking that, do not answer: “Because the screw is rotating.”
Some other prejudices about extrusion:
The Dogma of extrusion “The extrusion is a process absolutely steady!” is not accepted, nevertheless it is indispensable to explain that any output variations have a precise cause and can be eliminated. It is not accepted that when there are rhythmic changes of profile section and weight the extrusion is stable, and we are attending a stable instability. Unstable is not the extrusion, but the quantity of polymer entering the first flight as it is demonstrated by the “Experience N° 7” in my Manual.people know that the pressure at the end of the extruder does not depend on the extruder, but on the output, the melt viscosity and the friction aganst the head walls.knows which is the Quality of the extruded polymer. This will be seen later on.a consequence nobody know why the Quality can change, or should not change, during extrusion.who do not know why the Quality can change are not able to determine the cause.
In this situation if you are not convinced to substitute the prejudices with the Extrusion Science I can only recommend that you think about it all the times you are not able to obtain the profile as good as you want. Will come the time when you too accept the Extrusion with the “E”.
Should not be convinced because you think that rheology is a science that you cannot digest, I suggest you to read at least once my Manual because, to apply the extrusion rules, the knowledge of rheology is not necessary, it is enough to apply the extrusion Laws as suggested in the Manual.
Remember also that, when the profile you are producing is perfect, the Extrusion Science teaches us that this event is not casual, but it happens because you are respecting, obviously without knowing it, The Rheology Laws!
The profile quality
Before continuing the extrusion story (extruder-head) let us go back to the profile extrusion.
How a profile is obtained? A profile is obtained solidifying the melted polymer exiting from the die.
Therefore the profile quality will depend on the physical characteristic of the polymer, on the Quality of the extruded polymer and on the cooling system and time.
If you do not doubt, that what I said is true, you cannot doubt that until the external surface is not solidified the profile is not a profile, because it has not a definite shape that does not change.
Therefore we can say that the “”extruded” polymer is not a profile, but a fluid that will become a profile, ant then its quality is very different from that of the finished profile.
To avoid any confusion we must realise that, nevertheless the “extruded” (the melted polymer coming out from the die) heavily influences the “profile” quality, the two products have in common just the raw material, because the profile production process initiate exactly at the moment that finish the extrusion process.
They are two processes completely separated where the quality of the “extruded” polymer influences the quality of the profile and not viceversa.
Facing the quality problem of the finite profile there is a big difference between those who produce profiles without knowing extrusion, as they ascribe the profile quality to the “extrusion process”, seen as something abstract and indefinite, and those that, knowing Extrusion, attributes the profile quality to the Quality of the “extruded” melt, that is something real and definite.
It is so exactly defined that we can say: “The one who knows which is the Quality of the “extruded” probably knows Extrusion, while the one who does not know it is able to extrude, but does not know Extrusion”.
The quality of the “extruded”
Extrusion is a Science because the extrusion process is the practical application of the Flow Laws that are obtained by means of a rheometer, that is the rheological curves, which tell us how the molecules are moving while the polymer is flowing into a duct.
There is no difference between a rheometer, into which the polymer flows through the die because it is pushed by the pressure generated by a piston, and an extrusion complex (extruder-head) into which the polymer flows through the die because it is pushed by the pressure generated by the flights of screw rotating into the extruder. Both are rheometer!
The extrusion is a process that takes place into the extrusion complex constituted by a machine, the extruder, and a duct, the head-die. The polymer enters solid, into the flights of the screw just under the feeding throat, and then it is pushed by the screw flights towards the end of the cylinder, to exit melted through the die.
To know extrusion means to know what happens to the polymer and why it happens into each extrusion complex.
Keeping in mind that the polymer is pushed in a different way, according to the specific characteristics of the extrusion complex by which it is processed, we have to expect that, at the same output, the quality of the extruded polymer be different, according to the specific characteristics of the extrusion complex by which it is extruded. More exactly, the Quality will not be casually diverse, but, and this is quite unknown, the Quality will be just the one characteristic of that particular extrusion complex.
To determine why that happens we must remember that the Quality is strictly connected to the forces that are exerted on the polymer by the screw flights and to the resistance ( Shear stresses) that the polymer opposes, in that complex, to the pushing forces exerted by the screw, first on the solid and then on the melt. Owing to this cause the Quality of the melt extruded will be different when the same quantity of polymer is extruded by two not identical complex.
Now let us see why the title of this work is “The unknown extrusion”. You who are reading: “Do you know which is the Quality of the extruded melt?”
To know whether you know the Extrusion or you are just able to extrude, now, you should stop reading and try to answer the following question; “Which is the Quality of the extruded?”
If you know the Quality of the “extruded”, to answer is enough a fraction of a second, if you are still thinking about it, but you want some more time, think of what is the “extruded”. When you will read again, without any doubt you will know if you are part of the people that is able to extrude and to produce wonderful profile, but does not know the Extrusion.
Now it is the time to tell you which is the Quality of the extruded melt. An only word is enough to define the quality of any non newtonian fluid or polymer melt. It is the word which characterises in an unequivocal way the melt flowing out from the die.
The Quality of the extruded melt is its Viscosity! The viscosity that has the mass of melt at the moment it is coming out from the die. Viscosity which for the polymer that you are extruding is identifiable with the temperature of the melted mass flowing through the die. However, as the extruded is a fluid, which other quality could it have besides the specific weight? Just the Viscosity.
As the viscosity is correlated to the melt temperature if someone knows the Temperature of the melt flowing through the die he knows the viscosity and therefore the Quality is known.
We just said that the Quality coincides with the Temperature, but if this is true, and it is certainly true, the Temperature, that is easily measurable, is exactly the Target that we are looking for.
Do you remember the “Target”?
The target to obtain, for each profile, the maximum production and the best quality at the minimum cost.
The right deduction is that to produce the best Quality it is enough to extrude the melt always at the same temperature, the one that the “Quality Control” has defined as the right one to obtain the Best Profile.
The Target for each profile and each extrusion complex becomes to extrude always at the same Temperature, at the output (profile velocity) chosen by the production manager!
This Temperature for each profile can be defined the Optimal Temperature.
The “Target”? is no more an utopia.
In the case that, when the profile reaches the stated velocity, the melt temperature is not the optimal one, it is enough to change in the “proper way” the working condition to have the melt exiting at the Optimal Temperature.
In my Handbook one can find which is the proper way in the only two undesired situations. First the extruded melt is colder then desired. Second the extruded melt is hotter then desired.
To search the Optimal Temperature for all profiles is the strategy to use in the next future and remember that “Strategy” means to have absolutely clear where you want to go (Montezemolo in an interview).
Unfortunately it is not simple to know the real melt temperature, because the apparatus to read it, that can be found on the market, can do mistakes up to some tenth of degrees °C (4.4.2 of my Handbook). Today to know the melt temperature we must use a particular manual technique, while in the next future I hope that an apparatus, patented by me, will be produced.
The Future Extrusion
This is the second part of the title end is the way to extrude that everybody will be compelled to use in the next year to produce profiles to be competitive and meantime innovative.
Remembering my Patents and Know How, I am confident that they who will innovate the extrusion will discover much more Patents and Know Now than I did, because I dedicated abut all my time to study extrusion instead of producing profiles.
As my trials to convince the artists to learn the Extrusion on my Handbook are finished, to avoid misunderstanding, I want to make clear that to enter in the Future Extrusion it is not enough to study how to apply the Extrusion Laws, but one must use them everyday.
It is not easy and therefore I promise you a second Appendix, in some months, to suggest you the more adequate technique to use, according to the extrusion situations, to find quickly or automatically the Optimal Temperature. All these techniques, I repeat, can be found in my Handbook “L’estrusione con parole mie”.
CAUSE – EFFECT
I like to give a philosophic interpretation of the phenomenon extrusion.
Stuart Mill assert that the CAUSE is the series of conditions without which a phenomenon could not happen; the INVARIABLE result of this antecedent facts is the EFFECT
The extrusion that I teach is based on the concept Cause-Effect
All what happens into the extruder is a consequence of the fact that the extrusion is a process that take place, into an extrusion complex, when the screw rotates inside the cylinder and into the extruder is put a polymer that is subjected by the screw to an indefinite number of forces that melt and push it through a sequence of ducts that are assembled after the screw.
The effect of the extrusion is the invariable Quality of the melt that exit from the die.
The series of conditions at which this phenomenon take place produces a fluid, usually a melted polymer, that has an invariable Quality.
Therefore this invariable Quality is the effect of all the conditions (forces and ambient) that act on the polymer during extrusion.
This extrusion law is valid for any type of extrusion (screw fed with solid or melted material) and consequently both for solid polymers and for kneaded flour mixed with water, as both are non-newtonian fluids.
The consequences? All the times the series of conditions are the same the Quality of the polymer melt remains the same while the time goes on the extrusion is effectuated, that is, the Extrusion is an absolutely stable process.
Unfortunately, few people get a benefit from this teaching because they do not deduce that any time (whenever) the Quality changes, this demonstrates that the conditions (forces and ambient) at which the extrusion phenomenon took place is changed. Few people knows that when the Quality of the melt changes certainly there is a cause and deduce that to go back to the previous steady conditions it is enough to remove the cause that made the Quality to change.
In my Manual of applied Rheology “L’estrusione con parole mie” (“My Extrusion”, not yet printed) can be found all the rules that allows to Extrude the desired melt Quality and mainly this Quality is clearly defined. About this Quality I want to point out that, having thought extrusion to several handreds of extrusion technicians, I am convinced that very few of them know which is the Quality of the extruded melt and therefore they are not able to take advantage of this knowledge.
To get the most from this knowledge, one must conduct the extrusion lines using the “Future Extrusion” namely a strategy that is not yet used in any world country. Should somebody use it I invite him to let me known , because, should we discuss our points of view, we could improve our knowledge of extrusion.
In my site “mianimario.it” one can read “The unknown extrusion and the Future Extrusion” where is described the strategy to reach a very precise Target to produce any profile always, but really always of the same quality.
Taking into account that the extrusion that I teach is based on the concept Cause - Effect, when the extrusion line malfunctions or products defects are analysed, all the reasoning must be based on the same physical principles.
That is, it is absolutely necessary to know all what happens into the extruder and why it happens, that is, which are the cause and the effects of all that series of conditions without which each phenomenon could not happen.
Therefore it is indispensable to forget those imprecise rules, often wrong, that are used by the conductors of the production lines and to devote themselves to apply, always, the right rules of the Future Extrusion.
Among these rules there is one very special that in my manual I call “La Regola” (“The Rule”) that seams incredible and is ignored by people producing profiles. This “Rule”, that is a law of extrusion, tells us that the Quality of the melt is not chosen by the line conductor, but by the polymer.
Owing to this event, that happens every time the conductor starts the production line, if one wants to produce a profile having exactly the same quality of the preceding time, he is compelled to follow a very precise strategy. More precisely he must use a strategy that makes the polymer to chose exactly the quality that he wants.
In fact the profile quality is guaranteed to be the same of the previous time only when the Quality of the melt is equal to that of the preceding production and the strategy that guarantees this result is the one that I named Future Extrusion.
This strategy guarantees the possibility of innovating the profiles produced and the profile quality constancy for any profile, any polymer and any production line.
When I say innovation I mean the possibility to find special Know How for the production of certain type of profile or, as it happened to me (2009), to discover a Know How that allows to reduce the Kw/Kg of the extruder motor and meantime to increase the production per screw revolution ant to increase the line velocity.
For a certain profile the optimal quality and the output/hour will depend exclusively on the type of line used. They will depend on how the extruder is fed (feeding throat) on the forces acting on the polymer (type of screw pushing and melting) on the equipment downstream the extruder (head, filter, static mixer, etc,) on the cooling type and pulling machine.
The extrusion laws tell us that extrusion is a stable process and therefore the melt Quality is always constant and I say “ absolutely constant” because these are laws of physics and rheology that Galileo Galilei called Lows of Creator.
We, as human people, are imperfect subjects and we must accept that extrusion is quasi-stable and the Quality is quasi-stable.
That happens because solid polymers have a granularity quasi-constant, because these polymers are processed at a number of revolutions of the screw quasi-constant, molecules melt at different times the melt is subjected at shear rates quasi-constant, and then the shear stresses are quasi-constant, the walls temperatures, against which flows the melt, have temperatures quasi-constant etc.. Obviously, nevertheless this plurality of “ quasi-constant”, the stability law remains valid, just as it is valid to think that all the molecules that flow by a polished wall have a precise shear rate, the one stated by the well known formula, nevertheless, if we look the wall with a microscope, we can see that in each wall imperfection can be hidden, absolutely steady molecules, in thousands.
The conclusion is that all people that will switch to the Future Extrusion can produce profiles of the desired quality at the minimum cost.
The Target of Plastic Profile Production
Constant Quality and Maximum Output means minimum Profile Cost
A Plastic profile is a product of constant section and indefinite length.
In order to extrude a Profile of constant section the Quantity of polymer entering into the extruder screw and the screw revolution must be absolutely constant, from the beginning until the end of the production lot.
Meantime to obtain the optimal “Profile Quality” (both constant section and physical-mechanical properties) the “Quality” of the “Raw material”, used to produce the Profile, must be absolutely constant from the beginning until the end of the Profile production.
Therefore, as the Raw material to produce any Profile is the molten polymer flowing out through the die exit, whose “Quality” is the melt Viscosity at the extrusion Temperature, the Quality of the Profile will be absolutely constant maintaining constant the melt Viscosity of the polymer from the beginning until the end of the Profile production.
What I have just affirmed is guaranteed by Physics, Rheological and extrusion Laws when the extrusion, that is a steady process, is performed at constant screw revolution and constant Output.
Obviously the Profile extrusion of a constant Quantity at constant Screw Revolutions can be defined “the Quality Certification” of any Profile.
Obviously, what I affirm, will be obtained only when the “Extrusion process” is performed in the “right way” to produce a molten polymer having an absolutely constant Quality.
The only Right Way to operate on the production line, that is Extrusion and Profile formation Processes, that I know is to extrude according the Strategy of the Future Extrusion “FE” (Estrusione del Futuro “EdF”).
A Special Offer
On the 1of November 2014, while I was about to ask a meeting to an Extrusion and Injection Moulding Lab in order to have a practical demonstration of my “Found”, I discovered and theorized a Know How that allows to eliminate Production Scraps both producing extruded Profiles and during injection moulding.
Immediately, I decided that I should have given my KHs, at very low Down Payment, to any Company producing Profiles or Injected products.
Meantime, I decided to teach them how must operate their Extrusion Complexes to eliminate any production Scrap.
Besides, as I have a personal interest to stabilize those “Extrusion Complex” to find “exemplificative problems”, whose solutions I would describe in my Operation Manual for Profile Production Lines, I propose to the Companies a Contract that allow them to innovate their technology using the EdF (Future Extrusion) Strategy, at Zero cost of Investment.
Some clearing up
Should somebody think that this Offer is not enough convenient, please tell me, I am ready to change it.
I think that, for now, I’ll chose not more than 10 Companies because I cannot attend more than 20 a year.
From now I am ready to sign a Contract that guarantees the Company that when, their own Profile Lines are operating according to the teaching of the Know How “Miani EdF”, the “Production of Scraps” (out of tolerance) can be reduced towards null. This reduction will happen since the first day of application of the KH removing any Cause of Output instability of the Extrusion Complex (Extruder-Head).
When the production will be stabilized (constant Output and Profile Quality) it will be very easy to increase the Output/hour maintaining the Profile Quality.
The obvious result will be a very important decrease of the Cost/meter of the Profile. This is guaranteed.
The Target that I guarantee is the constancy of the Section, of the Aspect and of the Physical-Mecanical Properties of any Profile produced from the beginning until the end of each production lot or bobbin when the profile is winded up.
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The path to reach the Target
The first step is to give the “Right to Use” the KH “Miani EdF” to the Company and to sign a Contract that guarantee the Company that operating on their Profile Lines according to the EdF Strategy they will reach the signed Target.
Signed the Contract the situation of the two partners, the Company and me, will be the following:
the Company has the Operators able to produce perfect Profiles, but, owing to the “usual instability” of all extrusion lines, they are not able to avoid that a certain quantity of Scraps be produced.know what have to be done to reach the Target, but I don’t know what is happening to the polymers processed into their extruders, by that screw, while they are pushed through that Head-Die.
To reach the Target the Operators must be trained to stabilize their line. I must do the Process Analysis to know what is happening to the polymer advancing through the Extrusion Complexes.
To stabilize the line it is necessary to do the “Process Analysis” of the Extrusion Complex having assembled the Head-Die to produce the chosen Profile and the Line must be driven by their Operators.
To perform the Process Analysis means to record how are changing, during the lot extrusion, the following “Process parameters”:
Screw revolution (When not Constant), Output, Melt Temperature and Pressure.
How does I teach the Operators to stabilize their Extrusion Complex?
The Operators will start the Profile production Line and reach their Standard working Conditions to produce the desired Profile. When the Profile Quality will be “the one desired”, the “Values” of all the “Process parameters” will be recorded.
Among the Values there is the Pressure that is the Parameter that changes its Value every time that change the Value of any other Parameter, according to the Poiseuille Law.
These are the Values that must be maintained constant to get the Quality of that Profile always identical when the “same Head” is used assembled with “any extruder”.
Remember! Same Line velocity (output) same head and any extruder, but each extruder at the screw revolution that makes the Melt Temperature of the “any” extruder be equal to the one recorded during the Process Analysis.
Going on the recording of the “Process parameters” at stated times, it will be found how much change the Output and the Melt temperature during the production.
Meantime, while the time goes by, I’ll teach the Operators “the right way” to go back to the Value of the first recording of the Pressure. Moreover I’ll teach how to modify the “Standard working Condition” (The one set by the Operators before beginning the stabilization of Process Parameters) to find the Cause of the Output changes and the way to eliminate them.
The main rule to stabilize the Profile production is: any instability has its Cause and it is removable.
Continuing the “Values recording” for some hours or some days all the instabilities will be removed. Therefore, when the same polymer will be extruded again, the Operators, working at the same Values of the “Process parameters”, will have just to change the bobbins or collect the perfect Profile exiting at the end of the line. No more extrusion problems.
After the experience with the first Profile, I know that the Operators will find the Values of the “Process parameters” for the others Profiles without asking me suggestions, but, may be, they will teach me some practical rules that they experienced for years.
After the experience with the first Line the Operators will be ready to stabilize a new Profile Line, that means an Extrusion Complex not jet stabilized that could have different Causes of instability and different polymers to process. This means that I and the Operators will be compelled to start from the Process Analysis and repeat the complete path for all the profile Lines
When all the Lines will be stabilized it will be the time to Optimize the Target according to the Rules of the “Khow How Miani 2009” that guarantee the extrusion of the melt at lower Melt Temperature at the same Screw Revolution.
Using KH Miani 2009, the same Profile Quality will be produced at a higher Line Velocity and consequently at a lower Cost/Kg.
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Last Note.
For the Company is important to know that, processing according the EdF Strategy, all what must be done by Operators to maintain steady the Profile Quality can be done automatically by a microprocessor!