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

Kingdom Machine Co.,ltd Ruian Economic Zone,Wenzhou,China 325200
Mobile:0086-13958812663;  0086-13088651008
Tel.:0086-577-65127709       Fax:0086-577-56846789 Whatsapp:0086-13958812663

What Marketing Strategies Can Do For Organizations

Prior to your organization starts promoting a product or service, it aids to make an best client who have you need to attain with your own personal promotional supplies. Once anyone have your own personal ideal consumer, you have got a variety of strategies to choose from. The majority of of these types of are very low cost/no charge strategies as well as an individual might use diverse ones in different phases of your current business routine, or perhaps anyone may use them just about all at when from your own personal business’ beginning. We’ll seem at several of these types of strategies within more fine detail. (Do anyone have exactly what it requires to function in this particular fast-paced industry? This post will support you figure out if marketing and advertising is regarding you. Read this awesome blog post to find out more.

While you create a company, the 1st thing an individual want to be able to secure is usually a client base. Using a reasonable printer, a great answering equipment and a great average personal computer, you could put jointly a pretty extensive advertising and marketing campaign with no having in order to pay regarding space. This kind of is typically the carpet-bombing approach of low-cost advertising. A person find a great area in which you might like to be able to do company in, and also you disperse flyers for you to all the particular mailboxes in reach. Your current flyer need to be quick and to be able to the place, highlighting typically the services anyone offer and also providing make contact with information. Giving free of charge Identification solutions, promotion or discounted never affects.

Most food markets, public places and centers offer cost-free bulletin aboard space regarding Printed items and also advertisements. This kind of is any hit or even miss technique, but anyone should attempt to help make your manifesto reasonably obvious and possess removable tab that typically the customers could present intended for a lower price. Make each and every location the different shade so which you can easily get a great idea through the tab where the particular most prospects are currently being generated. In the event that there will be one spot that will be producing the particular majority associated with your potential buyers, you may better targeted your advertising campaign (flyers, advertising in reports catering to be able to those regions, cold contacting, etc.). To find out more, Visit this guide.

In the surface area, value upgrades are really similar to be able to coupons and also free evaluations, yet they will are targeted at raising consumer full satisfaction and extending the difference between a person and competitors. Common price additions consist of guarantees, special discounts for returning customers, stage cards along with referrals returns.

Specifics and Common Information Concerning Decoupled Injection Molding

Molding isn’t simply an skill anymore. Really about water and energy dynamics as well as controlling strain and stream and sustaining shot regularity. Exactly how could an individual receive your unit to create a great part every time? Here is some suggestions on precisely how you could apply research principles for you to this specific decoupled method after finishing scientific molding training.

Because the requirements of international competition along with complexity involving part models have enhanced, the particular molding course of action has created into any far far more sophisticated effort than possesses previously also been required. Brand new molding products have come to be far a lot more skilled within their capability to perform a assortment of gymnastics to create great elements. Often, nevertheless, we get that molders on the actual shop flooring have not necessarily kept rate with typically the sophistication associated with, or recognize how to be able to apply, typically the new regulates offered to injection molding training. Throughout addition, these with more mature machines tend to be discouraged simply by the wild degree regarding complexity encircling these modern controls as well as wonder just how they can easily ever remain competitive. The strategy, called decoupling, covers these problems.

In any sense, decoupling will be a group system, since opposed to be able to classic molding. Decoupling is further more broken along into different forms. Very first, it makes it possible for process capacity to end up being achieved over and above that associated with standard techniques as well as allows typically the molder in order to utilize the actual full prospective of typically the new machine. Every bit as important, decoupling on an old machine using a few quite simple upgrades) allows people with outdated equipment for you to execute with world-class quantities, thus which allows them to be able to contend properly in the actual new entire world environment. Actually, scientific molding seminars could aid folks with this.

Absolutely it noises too fine to always be true, however let’s street address just specifically what this specific issue is discussing about. To realize the variations in creating techniques, the idea is crucial to establish what many of us mean through a classic molding method, and to be able to then separate it coming from decoupled molding training. Injection evolved via a guide process inside the early 40’s, when devices were almost unsophisticated presses inside which plastic material was tautened into some sort of mold that will was personally clamped through hand. Materials was given into any cylinder, heated up by heating unit bands, along with a plunger was employed to contract the dissolved plastic directly into a frosty mold. Force was managed until typically the part solidified, and and then the mold was exposed and typically the part ended up being taken apart.

Make Certain Your Home Is Actually Secured

It really is critical for a house owner to guard their residence. Wherever they live, there is a likelihood an individual can break into their own home. This could leave them without a lot of their particular belongings and, in case they’re at home at that time, put their own life in jeopardy. As an alternative to risking all of this, they should take time to totally think of just what they’re going to have to have in order to be prepared for exactly what might take place.

Quite a few people are generally deciding on home security systems these days. Though there have been security systems used for a long time, the newest ones supply a selection of advantages that the older ones did not. A person can now select security cameras that allow them to check into the property anytime they’re not there to be able to discover what exactly is taking place. They can furthermore get warnings on their phone so they’ll be advised promptly if the police are called as a result of an alarm at their particular home. They need to additionally make sure to ensure the entrances as well as exits will be completely safeguarded in case there is a concern.

If you’re worried about the protection of your home, be sure you talk with a professional now to be able to receive advice on precisely what you are going to require to be able to fully safeguard your property. You’ll be able to click here to learn more about our services at this time.

Advantages of Organizing Your Company

Managing is almost all about trying to keep things inside proper obtain. For any kind of enterprise, corporation plays any significant function in supporting you attain your targets. Practicing successful organizational expertise will aid you privately as well as expertly, and your own good company skills can be returned in typically the completion involving new content as well as all associated with your each day duties. Company also presents you any sense regarding control along with allows intended for increased efficiency.

Productivity is possibly the biggest advantage associated with organizational abilities. An arranged professional can spend much less time repairing mistakes, seeking for details and mending any muddle. More period saved signifies more period for carrying out productive points. In a organization, organizational abilities will support you preserve track involving your company’s progress. When you spend sufficient period to putting together and saving your budget, you can easily easily inform whether your own business will be progressing. A person might consider that viewing the cash come within is plenty of indication involving success, nevertheless, if anyone spend some sort of lot regarding money with regard to advertising along with promotions without having having virtually any record associated with it, anyone could end up being losing some sort of lot involving money credited to shortage of company. Always possess a learn list to be able to show just about all activities, profits and expenses. A person could find it here.