Blown Film Extrusion Introduction

Blown Film Extrusion Introduction
Blown film extrusion is a technology that is the most common method to make plastic films, especially for the packaging industry. The process involves extruding a tube of molten polymer through a die and inflating to several times its initial diameter to form a thin film bubble. This bubble is then collapsed and used as a lay-flat film or can be made into bags. Usually polyethylene is used with this process, and other materials can be used as blends with these polymers. A diagram of a polyethylene chain is shown in Figure 1 to the right.
Background Theory on Polymers

In the cooling step of blown film extrusion, the amorphous, transparent melt crystallizes to form a translucent, hazy, or opaque film. The point where opacity begins in the bubble is known as the frost line. 
Fig 1: Model of polytheylene chain frompolyethylene Wikipedia article.The frost line height is controlled by several parameters: the air flow, film speed, and temperature difference between the film and the surroundings. Properties of the film, such as tensile strength, flexural strength, toughness, and optical properties, drastically change depending on the orientation of the molecules. As the transverse or hoop direction properties increase, the machine or longitudinal direction properties decrease. For instance, if all the molecules were aligned in the machine direction, it would be easy to tear the film in that direction, and very difficult in the transverse direction.

The Film Blowing machine Process

Fig 2: Schematic of set-up from User:J.Chiang.

Typically, blown film extrusion is carried out vertically upwards, however horizontal and downward extrusion processes are now becoming more common. Figure 2 shows a schematic of the set-up for blown film extrusion. This procedure consists of four main steps: The polymer material starts in a pellet form, which are successively compacted and melted to form a continuous, viscous liquid. This molten plastic is then forced, or extruded, through an annular die. Air is injected through a hole in the center of the die, and the pressure causes the extruded melt to expand into a bubble. The air entering the bubble replaces air leaving it, so that even and constant pressure is maintained to ensure uniform thickness of the film. The bubble is pulled continually upwards from the die and a cooling ring blows air onto the film. The film can also be cooled from the inside using internal bubble cooling. This reduces the temperature inside the bubble, while maintaining the bubble diameter. After solidification at the frost line, the film moves into a set of nip rollers which collapse the bubble and flatten it into two flat film layers. The puller rolls pull the film onto windup rollers. The film passes through idler rolls during this process to ensure that there is uniform tension in the film. Between the nip rollers and the windup rollers, the film may pass through a treatment centre, depending on the application. During this stage, the film may be slit to form one or two films, or surface treated. Advantages Blown film generally has a better balance of mechanical properties than cast or extruded films because it is drawn in both the transverse and machine directions. Mechanical properties of the thin film include tensile and flexural strength, and toughness. The nearly uniform properties in both directions allow for maximum toughness in the film.
Blown film extrusion can be used to make one large film, two smaller ones, or tubes that can be made into bags. Also, one die can make many different widths and sizes without significant trimming. This high level of flexibility in the process leads to less scrap material and higher productivity. Blown films also require lower melting temperatures than cast extrusion. Measured at the die opening, the temperature of cast film is about 220 C, where as the temperature of blown film is about 135 C. Furthermore, the cost of the equipment is approximately 50% of a cast line.

Blown Film Extrusion Disadvantages Blown film has a less effective cooling process than flat film. Flat film cooling is done by means of chill rolls or water, which have significantly higher specific heat capacities than the air that is used in the blown film cooling process. The higher specific heat capacity allows the substance to absorb more heat with less change in the substance temperature. Compared to cast film, blown film has a more complicated and less accurate method to control film thickness; cast film has a thickness variation of 1 to 2% versus the 3 to 4% for blown film. The resins used for casting typically have a lower melt flow index, which is the amount of polymer that can be forced through a standard die in 10 minutes according to a standard procedure. The melt flow index for cast film is about 5.0 g/10 min where as for blown film it is about 1.0 g/10 min. Consequently, the production rates for cast film are higher: cast film lines can reach production rates of up to 300m/min where as blown film lines are usually less than half this value. And finally, cast film has better optical properties, including transparency, haze, and gloss.

Common Problems Air entrapment between film layers and rollers – this may cause film scratching or wrinkling, or processing problems when winding up the film due to reduced friction. Possible solutions to this is using a vacuum to remove entrapped air or by using winding rolls with a diamond shaped groove in the rubber cover to increase surface area and decrease amount of entrapped air in the film. Large output fluctuations from the die – this causes thickness variations, and can be prevented by keeping the extruder clean and by using more consistently shaped pellets in the extruder. Melt fractures – these appear as roughness or wavy lines on the film surface, and can be eliminated by lowering the viscosity of the polymer melt. This can be done by increasing the melting temperature or by adding an internal lubricant to the material composition. Thickness variations in the film – this can be avoided by centering the die in the extrusion line before every run, adjusting the air speed of the cooling system, or by using heated die lips. Die lines on the surface of the film – this defect reduces the aesthetic appeal of the film, reduces optical properties, and weakens mechanical properties such as tear strength. This can usually be avoided by routinely cleaning the inner surfaces of the die and by refinishing scratched or roughened flow surfaces. Gels – these defects are small, hard globules encapsulated in the film or stuck on the film surface and reduce the aesthetic appeal of the film and cause stress concentration points which may result in premature failure. These are caused by overheating to the point of polymer degradation in the die, and can therefore be avoided by cleaning the inner surfaces of the die on a regular basis. Optimization of the Process Coextrusion One way to improve the line efficiency of blown film extrusion is to implement coextrusion. This is the process of extruding two or more materials simultaneously through a single die. The orifices in the die are arranged such that the layers merge together before cooling. This process saves time because it extrudes two or more layers at the same time, and it provides a method with fewer steps to produce multilayer films. The production rate for a coextruded multilayer film of three layers is about 65m/min, and the production rate for a single layer of blown film is about 130m/min. Thus, in order to produce 10 000m of a three layer multilayer film, it would take almost 4 hours using a single layer blown film process, and only 2 and a half hours using the coextrusion process. Furthermore, the film produced from the single layer process would require an extra step to glue the layers together using some sort of adhesive. Coextrusion is the least expensive means of producing layered films and the coextrusion system is capable of quick changeovers to minimize production line down time.

Minimizing the Melt Temperature
The efficiency of blown film extrusion can be improved by minimizing the temperature of the polymer melt. Reduction of the melt temperature causes the melt to require less heating in the extruder. Normal extrusion conditions have a melting temperature at about 190 C despite the fact that the temperature of the melt only needs to be about 135 C. However, it is not always practical to decrease the melting temperature by that much. By decreasing the melt temperature 2 to 20 C, the motor load can be decreased by about 1 to 10%. Furthermore, reduction of the melt temperature causes less need for cooling, so there is a reduced use of the cooling system. Moreover, removing heat from the bubble is usually the rate-limiting factor in this extrusion process, so by having less heat in the polymer to remove, the rate of the process can be increased, thus yielding higher productivity. A way to maintain the melt temperature at a minimum is to choose an extruder that is matched to the specific processing conditions, such as the material of the melt, pressure, and throughput.

Heated Extrusion Die Lips
Typically, solutions to melt fractures involve decreasing the output or increasing the melt temperature to decrease the shear stress in the extruder. Both of these methods are not ideal because they both reduce the efficiency of the blown film line. Heated extrusion die lips can solve this problem. This targeted heating method allows for film extruders to be run at higher production rates with narrower die gaps while eliminating melt fractures. Direct heat is applied to the surface of the polymer melt as it exits the die so that viscosity is reduced. Therefore, melt fractures, which are caused when trying to extrude too much of the polymer at one time, will no longer act as a limiting factor to increasing the production rate. Furthermore, heated die lips use less energy than increasing the melting temperature because only the surface of the melt is heated and not the bulk of the liquid. Another benefit of using heated die lips is that thickness variations can be controlled by adding heat to certain areas along the die circumference to make the film at that position thinner. This would ensure that no excess material is used.
Determine how much energy each of these processes can save per given volume of material. 

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Athens – What To See And How To See It


There are so many aspects of current civilization that were birthed in ancient Athens. Among these are theatre, philosophy, democracy, classical art and even the Olympic games. Athens is located on the southern coast of Greece and has existed for over 7,000 years providing a rich culture expressed in a diverse setting. The term diverse fits as you will find ancient relics and sites in some of the same areas where there are trendy boutiques and sidewalk cafes all mixed in together. This mixture of the very old and the new create a very unique experience provided nowhere in the world like it is provided in the ancient city of Athens. You will need to be sure your passport is up to day so if you need to add passport pages, be sure to go online and access a passport site to help you with this so you can be on you way.

World travel requires a passport but computers have simplified all passport needs. Even if you have to get an emergency passport, an online passport is available to help you. No one plans to have their travel documents lost or stolen but if this happens, help is as close as the nearest computer.

Athens is a city that contains many sites that make history come alive so this is certainly the ideal place for lovers of history to visit. High on top of the Acropolis you will find the Parthenon. This famous sight has earned the honor of being named as a World Heritage Site by UNESCO. Investigating these ruins takes you back to sights names in Greek Mythology related to gods and goddesses, the titans and many other mythological characters. Admission to this site also opens the Theatre of Dionysus, the Roman Agora and the Temple of Olympian Zeus to the traveler.

Being the birthplace of the performing arts, it is no wonder that the arts and culture are very important to the Athenians. While the National Gallery is certainly large and well known, many smaller art galleries populate the city. Athens is also host to approximately 148 theatres so if you are in the mood for a show, the difficult part will be which performance to see. Among the theatres is the famous Herodes Atticus Theatre.

Using a bike or even walking around this city is a wonderful way to see the sights. Green space is always welcome when you travel to big cities and the National Garden of Athens provides an exceptional treat. Within it can be found a small zoo, ponds with ducks, colorful flowers and beautiful landscape with no shortage of a shady tree to relax under and consider the sights of the day.

For those who would like to shop till your drop, your experience will be a little different in Athens. Rather than large malls and strip centers, you will find street vendors selling custom crafts rather than name brand items. Some of the most visited markets are found on Plaka, Kolonaki and Ermou Street. You will find endless selections of shoes, purses and jewelry if you visit here and the quality will certainly not disappoint you.

Authentic cuisine is always interesting in a foreign city and Athens is no exception to this rule. Known for their souvlaki, which is comprised of grilled meat, veggies and a special yogurt sauce, this Athenian staple is considered a treat by all who try it.


Athens – Church of Agioi Theodoroi


Crossing Odos Dragatsaniou, in the end stands the attractive medieval church of Agioi Theodoroi (St. Theodore), built on the site of a church founded in the ninth century, but in its present form dating from between 1050 and 1075. This small cruciform church with its high narrow dome, multiple roofs that lend it an air of rhythmic grace, narrow mullioned windows and decorated central door surmounted by arches, is a precious gem of eleventh century Byzantine architecture.

The earliest form of Byzantine churches was that of the basilica, a long rectangle divided by two or four ranges of columns into three or five naves. Later, during the 11th and 12th centuries, the plan changed to that of a Greek cross within a square, dominated by a dome constructed in brick and often combined with one or more subsidiary domes. The exterior walls consist of square-cut stone with thin brick surrounds and are enriched by bands of decoration, carving and the use of color. Few of these churches were large. Apart from St. Theodore, typical examples are the churches of Kapnikarea and St. Eleutherios.

The glory of the Byzantine church lies not so much in the architecture as to the ethereal beauty of its mosaics or frescoes. From the center of the principal dome Christ looks down upon the faithful and below Him are the Apostles. The Virgin appears in the half dome, while around the sanctuary are symbolic figures and emblems connected with the Eucharist. On the West wall opposite the chancel is the Last Judgement. Colored marble and similar material in the lower walls add to the resplendent beauty of the interior.

The liturgy of the Greek Orthodox Church requires separation of the altar from the laity. The altar is placed in a chancel screened from the congregation by the iconostasis, i.e. the screen dividing the sanctuary from the church proper. This is adorned with pictures of Christ, the Virgin, and Saints, and generally has three doors, the curtains of which are lowered while Mass is being celebrated. The chancel is flanked by the Prothesis, where the bread and wine for the Eucharist are prepared, and by the Diakonikon, or vestry.

In St. Theodore one can also notice the influence of the East on Byzantine art, which was prominent in the period from the mid-9th to mid-11th centuries, when Byzantine artists used a variety of Oriental motifs in their designs. It is probable that the design of pseudo-kufic characters (the script perfected during the 7th century by calligraphers in the city of Kafa, in present-day Iraq) that decorate the terracotta panel below the windows of the facade was inspired by the work of Arab craftsmen.


The Acropolis – Athens, Goddess Athena


Archaeologists tell us that the original city of Athens was situated on the Acropolis. Even in classical times, the Athenians still referred to this area as “the City.” The city of Athens and its patron goddess emerge into the light of history as inseparably coupled. In Mycenaean times each city was built around a central palace, and each palace was under the protection of its patron goddess. Athena was the goddess of the palace on the Acropolis. The names of the city and its goddess are essentially the same: Athena was Athens, and Athens was Athena. She was “The Athenian.” The ancient Athenians seem to have exhibited, during much of their history, precisely those virtues which they traditionally attributed to her. This may be because, when the Athenians imagined their goddess, they did so in their own image.

According to the myth, Zeus fell in love with a beautiful titaness, Metis (“Cunning Intelligence”). Although she repeatedly changed her shape to avoid his unwelcome attentions, as was his way, he persisted. In the end he caught up with her and raped her.

An oracle then announced that Metis would bear Zeus two children: first a daughter then, a son, and the son would be mightier than his father. Just as Zeus had once overthrown and dispossessed his own father, Chronos, so he was destined in his turn, to be overthrown by his own son. In a desperate attempt to avoid sharing his father’s fate, Zeus gave Metis a potion of drugged ambrosia, and then swallowed her whole.

Some time afterwards a terrible headache came upon him. In great pain, he sought the advice of Hermes, whose only suggestion was that Hephaestos, the smith of the gods, should open his head in order to allow the cause of his pain to escape. Zeus was so desperate that even this drastic remedy was preferable to doing nothing, and Hephaestos was duly summoned to cleave open Zeus’ head with his mighty axe. When he did so, to the astonishment of all the immortals, Athena sprang out with a great war-cry, fully-formed, wearing armour and bearing arms.

Zeus’ daughter not only became the patron of many arts at that time normally considered masculine preserves, such as ceramics, she was also credited with a distinctly unfeminine warlike nature. When the Olympian gods were faced with a titanic struggle against the giants, Athena played a major role in the war, defeating the giant Enkelados in single combat. She came to be depicted not merely as a virgin goddess, but, as an ancient Roman writer put it, as a virago: as a female capable of playing a leading role in a world dominated by men.

It came to be said that the reason for the birth of this goddess lay in a wager between Zeus and his consort, Hera, as to which of them could generate the better progeny entirely alone and unaided. By herself, Hera managed to produce only the crippled god, Hephaestos and a monster; while Zeus was able to bring forth, in Athena, one of the greatest of the Immortals.

This seems to have been a picturesque reference to a widespread belief, which was to appear later in the works of the philosopher Aristotle: that the father alone is responsible for generating his children, and for providing them with their inherited characteristics, and that their mother affords them nothing more than a temporary shelter and sustenance in her womb during her pregnancy.

This is a striking example of the strong climate of male chauvinism which dominated the early classical period in ancient Greece, which is very evident in myth and legend.


Meeting the Potential Seller: Can it be a Good Idea?

Checking the documents of the possible buy or sell is a must. If you want to ensure the method goes somewhat flawlessly, this has to be done before contract signing. One more issue that prevents problems would be to talk with the particular owner on a much more personal level. It really is easy to make a deal with a agent, but several frauds are employed because folks undergo an agent in order to catch the unwary. Employing an real estate broker is a must unless you want to be caught off-guard. You will find additional resources here or by getting in contact with your regional adviser.

At that time of closing, the existing proprietor should be obtainable as this is just where their documentation is confirmed in effectiveness. By understanding the owner as well as checking their particular documentation, you can also discover additional issues like knowing their particular marital position. If they are married, you should talk to the husband or wife since their own name is going to be required for someone buy of the house. Be worried about the situation if barriers are usually put in place to meet the spouse.

Beware of attributes sold at a cost well below market. Everybody is looking for a very good bargain — especially when, such as the case associated with property, the values are usually extremely high. But when the price is too very good, you should suppose a scam. And also you’re right to be on your guard. Numerous men and women tend to sell the home well below the market simply because they want to get rid of it at any cost, either since there are structural issues or even lawful problems. Occasionally, scammers buy the property or home at an affordable and then market it in a higher price – but still less than industry. If you need help or to find more information, contact your nearby real estate agent.

Features of a Great Real Estate Agent

Being a great real estate adviser needs more than receiving a license. It involves commitment, integrity and a ability to hard work. Choosing the right agent might mean almost everything when it comes to a sale or investment. Among the the features required to look for when you want to see this home are:

  • Getting focused on customer care. This is a occupation that constantly deals with the general public. Your estate agents should like speaking with individuals and want to see satisfied customers.
  • It requires recurrent phone conversations, acquiring the ability to answer calls or perhaps answer emails on time, and be patient.
  • Investing in a house is actually a big financial choice that most customers think about carefully. Hardly ever is it carried out on behavioral instinct, as is the case with other things purchased.
  • Have sales capability.

The key to this particular career is knowing how to market. Even if they will devote their particular time to serving buyers and not sellers, their particular capacity to sell their providers can make the difference between accomplishment and failing. Being convincing is one of the capabilities that they should develop as well as having the capacity to near the deal, i.e. agreements. Real estate agents must assure that will their consumer comprehends that she or he is the very best option and therefore are trained to enable you to achieve your goal, whether buying, selling or renting. This is essential while closing the sale, which is the last part of the process, and it depends on both an individual and the real estate agent. These people should keep on taking courses to develop into much better informed and offer better services.

Someone is Excited to Learn More About Purchasing Your Property

If you have been thinking of promoting your house, there’s a good chance that you don’t fully realize where to start. You do understand that you need to sell it quickly so as to proceed with your way of life. However, you don’t fully realize the way to determining the right client. If this describes something you are preoccupied through, take the time to navigate here for this website.

It is possible to express with your friends and family members, I Was Reading This write-up which taught me how to get started using the approach to getting a realtor. Your current real estate professional is going to begin with advertising and marketing your house on their site. This way, numerous people are able to find out more on that which you offer.

You’ll want to spend some time and correct things up all over your property. Should you choose this, it’s going to be more inclined which other folks should consider purchasing it. Ensure that you tend to be inquiring a practical amount of cash for your household. You will also have to be sure that you are ready to leave immediately. If you do these things, your property may well be more irresistible to potential house buyers. Accomplish your best to obtain your property in a position to home sale. In this way, obtaining a buyer is not hard. Your own real estate professional will certainly direct you.

Somebody May Help You With This Particular Method

Beginning the whole process of investing in a residence is usually very exciting. However, it can also be very stress filled. It is very helpful to rely on someone else to help you to find the proper home. As opposed to cruising out searching for something great, take time to talk with someone who usually takes someone to visit some sort of 2 bedroom house. This will give the actual chance to have a look at a few of the homes plus think about what you would like in your dream home. Be aware of items that you like and also points that aren’t necessary.
A real estate broker features a number of stunning houses that might be perfect for you. Should you not notice something that you enjoy, make sure that you tell the adviser in order to carry on searching for many different houses. You will end up surprised at the wide variety from houses that can be regarded. The real estate agent is aware that this can be one of the biggest decisions that you will at any time help to make. Because of this , they will show patience plus explain to you exactly what you need to understand. A representative is able to try to make factors correctly and they’re will make confident that you happen to be happy with your investment.

Optimize Your Home Hunting Time Through Looking Online

Once there was a time when individuals seeking a whole new home were required to look at the paper advertisements, circling those that intrigued them, and next walking over the area (or maybe the region) to be able to actually scrutinize just about every house to determine if it lived up to its newspaper description. Usually, these kinds of journeys ended in disappointment, given that the specifications often seemed to be blown up and the customers often went home with dejection. It seemed to got lots of research and much shopping, generally speaking, to find a place that was truly suitable. Nowadays, luckily, the means exists to view dwellings on the web, which in turn will save people unknown quantities associated with time, money as well as effort.

If you want to find out how to buy a home online, then you can search for a site Like This and find out if perhaps something pleasing for you is provided. By utilizing the energy the Internet, a home buying guide, and the networks involving dwelling sites that have long been developed within the last ten years or so, it’s now easy for customers to set up an on the web property consultation with the estate agent regarding their own option. They could see extensive movies from the properties available, and also high-res images. They can also talk to agents online in real time, even with the opportunity to see each other because of interaction software programs such as Skype.

Consult with friends who may work in property management, or even that have just lately obtained a house these people acquired online. There are a variety of house preserving tips and tricks that will help one arrange the particular homes that will interest them. Do the preliminary buying as well as questioning on the net. That way, you’ll be able to narrow the sheer number of properties you really visit to a achievable quantity. Right now, many people are generally growing to be mindful that by simply considering homes via the Internet, it is possible to get rid of the substantial majority involving all those which basically really don’t allure, while at precisely the same moment, permitting those which to so they will stand out from the bunch. By making use of such strategies as this, real estate purchasing turns into a simpler job, overall.

Buying a Property Using These Kinds of Tips

Purchasing home owners insurance is crucial. When you tend to be a renter, this particular can always be an eye-opening knowledge in phrases of expenses. Make certain that a person understand typically the difference among insuring typically the structure as well as insuring the actual contents. Along with if anyone are purchasing property in which is shut to h2o, make certain that anyone have a great agent who have can aid you register in the particular national ton insurance plan. What else really should one know when purchasing cheap houses or even lots for sale?

Is considered helpful for you to start typically the residence process together with an eyes to the actual future. In the event that you’re relocating within the particular next several years, a person might need to order a property requiring any minimal purchase for fixes and servicing. If you are setting lower longer origins, then experience free for you to look in properties using an eyes towards reconstruction and some other improvements.

Help make sure a person use powerful online house finder resources to maintain you knowledgeable of the actual current market place. You will certainly want in order to research additional homes throughout the region in your own price collection. Consult along with your Real estate agent and possess them manage a evaluation market research to help make sure which the home supports typically the asking cost. A fine agent can easily help inform you inside this feature of the particular home acquiring process.

Zero one understands your nearby market a great deal better than the professional genuine estate consultant. Having a good agent which you experience comfortable using and is usually looking out and about for your own best fascination is 1 of typically the smartest techniques you could make whenever you tend to be buying the home. In the market will be important to be able to understand your current credit ranking so anyone can meet the requirements for while much property as achievable. Talk to be able to your actual estate agent for the referral for you to a loan broker to be able to get prequalified and understand the precise amount associated with loan a person will be eligible for.

Offer as significantly information regarding your desires and demands as a person can for you to your Real estate professional, such since local facilities, transportation, colleges, shopping, and many others. This technique your Real estate agent can locate your ideal home which matches most of your own criteria. Whenever making a offer upon a residence, it is usually a very good idea in order to make your own personal offer it all depends on typically the home assessment conducted by simply independent experienced inspector. Right Here are a few additional ideas.