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. 

Above article from

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Guidelines When Selecting Artificial Grass Installation Company

In the current world, there are several ways that a person can make use of artificial grass installation. Carpets can be made from artificial grass when correctly installed, roofing different things among other things. Artificial grass Installation Company would do you good if you are in need of this kind of service. It is not easy to choose a good company in artificial grass installation. This website highlights some of the factors that need to put into consideration when choosing the best artificial grass installation company.

The reputation of the artificial grass installation company is the first factor that you are supposed to consider in the selection process. Making a decision whether you will choose this company and not the other one will always depend on the status of that particular company. A solid decision is made once you get some recommendations from friends and colleagues about the best performing artificial grass installation. If you have come across a company with a biased status then you can change it and pick another one.

The second tip that you are supposed to think about is the duration that the artificial grass installation company has been in service. If you choose an artificial grass installation company that has been in operation for a long period of time then you will be better placed. It is not right that you pick a company which has just started and it is new in the market.

The other factor that you should think about is the location of the artificial grass installation company. This is one of the core factors that you are supposed to think about whenever you want to choose an artificial grass installation company. It has never been easy to operate with a company that is far away from you and so you should make sure that you go for that which is near your location. It is important that you work with a company that you will be convenient with and so advisable to opt for that which is near.

The cost of installation service for the company is the other consideration. It is important that you prepare a budget plan early in advance on the expense that you will incur once you venture in such services. It is always good that you are well prepared financially to receive the artificial grass installation services that are offered by the company that you choose.

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How to Look for a Venue

The area and size of the reception halls are essential when you are planning an event. Clearly, for bigger events, you will require a bigger office to oblige the majority of your guests. Consequently, dependably set aside some opportunity to guarantee that regardless, you can perceive with regards to the venues which may be inside your region, all which will guarantee that you can discover all that you may search for. Nonetheless, you’ll find that this will be a guarantee that in due time, you can find a place which will suit your needs. Implying that you can generally accomplish some an incentive for your cash.

Moreover, it’s optimal getting the chance to consider a portion of the services which they may have, this will enable you to find out about a portion of the immense things which you may accomplish. Besides, this will ensure that you’ll make some comparisons, all which will ascertain that eventually, you’re contented and also that you’ll be able to decide properly. For instance, the office may have a region for guests to move and blend on an outside porch. All which will be a perfect way to guaranteeing that in due time, you can make sense of which venues may be superior to the rest. The venue may have bundles that you can look over, making it less demanding to get what you need. Along these lines having the capacity to guarantee that you’ll end up even sparing more cash.

Numerous individuals realize that they will require reception halls for weddings, however these venues are likewise utilized for birthday parties, commemorations, office parties, occasion parties, graduation parties, child showers, pre-wedding parties, and other extraordinary events. This will be something which might end up being viable especially when you need to have the location for something else. Through this, you’ll be able to save some time and ensure that you’ll discern as to all the things which will work best. In any case, it’ll have the capacity to guarantee that in due time, you’ll generally know about a portion of the areas which will have the best services and furthermore sustenance.

Along these lines having the capacity to guarantee that its a social event space which you can generally depend on. On the off chance that the venue is in your general vicinity, you should endeavor to visit the venue. Visiting the reception halls will enable you to see where the venue is found. In this way having the capacity to enable you to understand with regards to the things which may work best for you. You don’t need your guests to get captured in rush hour gridlock attempting to get to your event. Implying that you can generally be placated with the esteem you wind up picking.

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How To Select The Right General Contractor

It is usually an important thing to know all the things that you should consider when selecting a general contractor to be in charge of your construction project so that you can select the right general contractor.

The first thing that you should actually do is knowing what you want exactly before hiring any general contractor so that you will be able to tell him what you want if you find him and he will know how to work from there. The first important thing that you should look at when you have found a person saying he is a general constructor is if he is licensed so that you can know that you are letting a professional constructor is in charge of your construction project.

Look at the kind of experience that the general constructor whom you want to select and hire for your construction project has and you can measure has experience by asking him for how long has he been working as a general constructor. Go for that general constructor whom you know that he will always be available in the construction site ensuring that the construction project does not have any mistake every single day and if you want to consult him about something you will find him.

Your friends, relatives and also co-workers can really be a big help in selecting the right general contractor for your construction project this is because you ca just ask them fir referrals and they will refer you to the contractor that they know or have ever hired before. You should select a general contractor who only specializes in those kinds of construction projects like the one that you have so that you will know that if you hire him he will do the work in a professional way.

It is a good thing to check the references of every general contractor that you will be coming across so that you can be able to know which one to select and you should select the one with perfect references from his previous clients. Price is another thing that can help you select t eight general contractor for your construction project meaning that you should know how much will the contractor charge you after you have hired him if he is cheap don’t choose him.

Select a general contractor who is insured against all kinds of accidents so that you will be able to know that in case he is injured while working he will use the insurance to pay for his medical charges and not you.

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Why You Need to Hire a Professional Window Cleaning Service

Whenever you will be opting to clean a home or a building with many windows then it is a time-consuming job. It is you that will not be able to get the job done right at the end of the day especially if you will do it on your own. Hiring a window cleaner is the best thing that you can do due to the reasons that have been mentioned. When you will be hiring a professional window cleaner then you will be able to experience a number of advantages and that is what we will be talking about in this article.

Your window panes are the ones that can get foggy over a period of time that. This one can get overlooked easily especially when you are busy with your work or and some other things. It can accumulate much of the dirt and can make your house look dirty. The reason why you need the help of a professional window cleaner is that when you will have situations like this one that it can get complicated. You will not be able to get the cheapest solutions out there when hiring a professional and always remember that.

Hiring a professional can give you that lasting impression especially if you have a business. Your clients are the ones that will be noticing the dirty windows that you have. When you have a dirty window that it is you and your clients that can have damaged a relationship. Your windows is all part of an establishment like restaurants and cleanliness is a priority always. By making sure that your windows are clean then it will be your clients that will notice that you are concerned about the image and reputation that you have. Allowing natural light to come in can be done when you will have clean windows. Being happy with the clean workspace that you have is what your employees will feel Being more productive and more professional at work is what they will be feeling

Window cleaning that is a task that can be dangerous when you will take a look at it. What you will get once you will be hiring a professional is that they have the knowledge and tools to do things right. These professionals will be using cleaning solutions that are eco-friendly and safe. Using techniques that are efficient and effective is what these professionals will be doing. Giving you the results that you want to achieve is what they are able to do with this one.

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Getting To The Point – Clinics

Benefits of an Aesthetic Procedure

At times your body may have changed because of the meals you take or probably because of lack of regular physical exercises and you could be interested in dealing with this issue in order for you to gain a body size and body look that you want. In order for you to achieve the kind of transformation that you would want on your body, there are quite a number of available options such as indulging in regular physical activities, transforming your eating habits or using gadgets that are designed to give you that desired change. As opposed to other kinds of techniques that you can use so as to effect the kind of transformation that you would want on your body, procedures that make use of radio frequency technology to achieve the desired changes are quite beneficial.

One of the advantages of this aesthetic procedure is that it does not require surgery hence there is no pain and furthermore you do not risk having any permanent scars on any part of your body. The other great advantage with the radio frequency technology on aesthetic procedures is the fact that this process has proven to be comfortable, very safe and highly effective and efficient in the elimination of fat cells.

At other times diets and physical exercises may not give you the results you want in some areas of your body but with the use of aesthetic procedures that employ the use of radio frequency technology, this can be easily and quickly achieved. It is through the use of this procedure that you are able to have personalized changes since the procedure can be done in a way to effectively and efficiently suit your personal requirements. There are some conditions such as skin type, treatment size and thickness of fat in some people that may be a hindrance when it comes to transforming the body shape but these do not pose any hindrance with the use of this kind of procedure.

The radio frequency technology enabled process usually entails the destruction of the fat cells which make up most of the body weight and once these fat cells are destroyed, then the desired body shape can be achieved. Another advantage of using the radio frequency technology enabled procedure to eliminate body fat is that it has been tested and certified therefore, it does not have any negative health effects on the patient. Always make sure that you are very careful in your selection so that you consult the best provider for this procedure. It is important that you check and analyze the licences and documentation of provider in order to certify that they are legal and approved by the law. The other thing to also look for is the service charge.

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Guidelines for Getting the Best Mental Health Center

The number of people having mental health issues due to various reasons, for example, stresses. Ensure you carefully pick a mental health center for your loved one to access help. Below are guidelines for selecting the right mental health center.

You should factor the experience. You do not intend to go to a mental health that will practice with your mental health. You should, therefore, select a center that has lasted for many years. Due to the many mental clients a center has helped; it can provide assistance to those suffering from complicated mental issues. In addition, they understand that no two mental conditions are the same hence provide services that are customized to meet your specific needs.

You should put the location into consideration. It is of much significance to hire a mental health center located near your site. First, you will interview numerous mental health centers face-to-face hence getting higher chances of selecting the most qualified. Secondly you can be sure of getting quality services because a local center is interested in building helpful relationships with the local customers. Moreover, you will easily go to the center in case the need arise.

You should factor the cost. Different mental health centers have different fee structures for the mental health services they provide. However, do not allow fees to be the only reason for choosing a center because you can avoid spending a few coins then end up with numerous regrets upon realizing that a center provides services of low quality. It is thus crucial to be attentive to the quality of services you will get from a center in comparison to the price they charge then make a good decision.

Pay attention to the reputation. The reputation a mental health center has should be of great concern. A mental health center with no reputation can apply measures that limit the therapy they provide during a session so that a client can have numerous sessions with them in order to pay more money. In addition, they can misuse their client in a range of ways, even taking advantage of them physically. Before making any commitment with a center make sure you have confirmed about its reputation.

You should check how qualified the staffs are. It is crucial to be assured about the qualifications of a mental health center’s employees. Ensure you take a good look at the staff’s academic papers in order to be assured they possess the skills that are needed to help your loved ones. Qualified staffs will exercise professionalism in all their deals. In addition, check whether the staffs have been awarded for any special achievement.

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How to Access the Best Online Car Resources

An online car resource is very helpful in providing insight view in getting of cars whether used or new ones. Most information is provided for the clients sake and the online resource platform gives detailed information. When it comes to buying of cars there are various steps that need to be followed as it’s a big deal. The first step is to research on auto mobiles and the features that come with it. Thus online car resource are the best platform as they give you a variety, detailed information and possible ratings from those who have. In addition to variety, online car resources give expert and owner reviews, new car deals and invoice prices.

So that individuals get a full view of the car they are interested in, lots of photo options are provided. Getting preapproved for a loan is the next step when it comes to buying of a car. Knowing the amount to afford is resulted when individuals want a preapproved loan enabling them to compare with the dealership financing. When an individual compares the dealership financing, they are only looking for one that offers the lowest annual percentage rate. Individuals then look for loans from their mobile web pages of their bank of convenience.

So that a loan is approved information such as; Employer, salary information and balances of other debt is needed. A given time period of about two weeks is given to individuals to already have bought their cars after seeking a preapproval. The reason for this regulation is to avoid the number of hard inquiries to your credit history. Planning for a trade in is the next step when it comes wanting to buy a car. Skipping of the trade in can be done as its not a must. The trade in means that if you have a car, getting of the current trade in value is important before heading to the dealership. Thus by knowing the current value an individual is able to know and limit their expectations while at the same time have a reference point to the offers they will receive.

By using a car retailer to appraise your car and then make you an offer is the other alternative when it comes to trade in. Picking a car of choice is followed by test driving then deal closing. When it comes to locating the car, testing driving the car there are certain dos and don’ts that need to be kept in mind.

Its important for individuals to keep in mind the following; verifying the car is still in stock, asking the sales person if there are any detailed installed options, scheduling an appointment for a test drive among others. While for the don’ts they include; not showing up at the dealer on a busy weekend and not feeling obligated to buy the car at the same day.

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Are You Looking For A Commercial Auto Insurance Company? Here Is What You Should Consider

It should be noted that selecting the best insurance company is not as easy as it may sound. Nowadays, there are more companies that have ventured into this field. You should note that this further complicates the scrutiny process. However, you have no option but to assess the available option before settling for the best company.

For starters, you are tasked with checking out the market status of the insurance service providers. You will note that there are experts that have gone the extra mile to ensure that you get the best services. This is indicated by the gratitude showcased by previous clients. Nonetheless, you should note that there are non-performers in this field. You should thus make a point to look at the reviews of the firm. If you are meticulous with this aspect then you will know the possible outcome of the company.

Secondly, you are supposed to look at the exposure of the company. You should not be cheated that the experience is shared among the various companies. This is important to check out especially when it comes to the services entailed here. Moreover, there are amateurs that are getting into this sector. You have the duty to pick a company that has been working for over 10 years.

Additionally, you are supposed to look at the area of operation of the company. It should be made clear that the companies are spread all over the state and nation. That is why you will find experts that are not close to your location. It should be brought to your attention that this has some significance when it comes to the flexibility of the services. You should thus make sure that you pick a local commercial auto insurance company. At the end of the day, you should ensure that you cut on expenditure when getting the insurance cover.

It is also your obligation to look at the documentation of the company. It is important that you realize that there are quacks that have infiltrated this market. Here, you should validate that the company is operating legally. Furthermore, you are encouraged not to shy away from getting the right information from the relevant authorities.

Finally, you are supposed to look at the customer support of the commercial auto insurance company. It is important that you get informed on the services that you should get from the experts. That is why you should ensure that you check the prioritization of the customer needs. Furthermore, you should ensure that there are online customer support services. All in all, you should strive to get information when needed.

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How to Bid for Government Contracts

Government often offers so many contracts but they are notoriously difficult to locate. Government contracts are often huge ones and they are well paying. There are a great number of sources throughout the internet that will enable you find the best contracts offered by the government and they are newspaper classified, government web pages, 3rd party contracted websites, public works pages and many others. The best thing to always do is to be alert and follow the internet sources that shows when these contracts are advertised.

There are those several government entities that are near your places and you should keep an eye on various sources that show their contracts offered. Those who are operating businesses that are in close proximity to the government entities can easily access the contracts offered within short times. There is no doubt that larger business operating in busy areas should go for the systems that are cost and time- effective solution to enable them win the many opportunities that present to them. When you have identified a qualified lead, it will be best for you the verify the qualifications and deadlines related to the bid document. You can also request for a proposal instead.

There are several things that you will have to ensure in your process. Start with the qualification and ensure that your company qualifies for it. Every contract will call for some specific qualification for it to be approved. There are some bids that are set aside for women, veteran- owned businesses and even the minority. Ensure that you don’t waste your time on the contracts that you don’t qualify.

After these verifications of the basic qualifications, ensure that you keep checking the websites where you found the bids posted. This will enable you to be alert on any amendment or addendums. Most entities are well aware of how important such bids are to companies and thus they will keep them updated of all changes made. However, it is important that you always keep checking on the websites to be sure.

Most entities often post sign-in sheets for a pre- bid conference or present you with a way to view past awards Such information will assist you a lot in developing a very competitive bid. You should talk to the procurement officer of the entity should the information be missing in their website. You should ask various questions from this contact, including on amendments, specifications, bid document, addenda and others. Every information you need is available in the website or the bid document bust should you find it hard to access, you should get assistance from the right support team.

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