Cast vs. Blown Film

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Blown filmssometimes referred to as tubular films, are manufactured by extruding molten resin vertically through a circular die. Introducing air through the center of the die creates a bubble. The air drives the bubble upward, and slowly cools the material. Nip rollers flatten the material into a tube that can be reeled for creating bags and pouches, or slit and then reeled as a flat sheet of film. Blown films are pre-stretched by virtue of their manufacturing process.

Cast films are made by extruding melted resin horizontally through a flat die to create a sheet of material that is pinned to a highly polished chilled roller by means of an air curtain or vacuum box. Additional chill rollers quickly cool the film prior to trimming and rolling. Cast films are minimally pre-stretched allowing for improved depth of drawing for thermoforming operations. Typically, cast films have an even distribution of polyolefins due to increased gauge consistency due to the manufacturing process.

What Is An Extruder, And Does Our Company Need One?

To understand what an extruder is, we must first know what the process of extrusion is. Extrusion is when a material, usually pellets, dry powder, rubber, plastic, metal bar stock or even food is heated and pushed through a die. A die is essentially a mold that shapes the material as it is forced through the small opening to the other side. It’s one of the most common ways to produce sheets and strips of stock metal, plastic and rubber shapes.

An extruder is simply the machine used to complete the extrusion process. Using a system of barrels and cylinders, the machine heats up the product and propels it through the die to create the desired shape.

Extruders can be used to create a wide variety of usable products by shaping various materials. For example, our breakfast cereals and pre-formed snacks are often made using food extruders, which use uniform, controlled pressure and temperature to create the near-identical pieces we pour into our bowls each morning.

Pet food and treats are created with food extruders for the same reason — to create a high level of consistency and quality in the meals we feed our furry family members. The Bonnot Company’s food forming extruders can be used as standalone applications or be combined with a cooking extruder for unitized cooking and cooling.

For many industries, catalyst extruder machines are used to create catalysts such as high aluminas, gels, kaolin carriers, molecular sieves and more. Whether your company requires minute pellets, solid rods, unsupported rings or another catalyst configuration, Bonnot has the extruder that can get the job done.

Rubber bales can also be extruded for a variety of purposes. For instance, rubber extruders can create extruded hydrogels, which are used to create everything from contact lenses to replacement cartilage. A rubber extruder from The Bonnot Company can break down the large, tacky bales without the use of talc or special chemicals.

Extrusion equipment is even used to create the materials that keep the air and water in our homes purified. Vacuum extruders, which were originally used in the clay industry to de-air their products, are now used to create activated carbon. The extruder de-airs the carbon to increase its adsorptive properties and prepare it for use for any number of air and water purification applications. Bonnot has worked with virtually every base material available, not just activated carbon, and can use our expertise to demonstrate how this extrusion process could work for you in our test facility.

While these are some of the most common types of extrusion supported by The Bonnot Company, other extrusion equipment manufacturers may specialized in extruders for other materials, such as plastics, clay, aluminum or other metals. For example, plastic extruders can be used to create PVC pipe. As you can see, the types of extrusion equipment and their uses are widely varied.

In short, no. First of all, many devices that are technically extruders are meant for individual, personal use and must be operated by hand. Manufacturers, however, will generally require much larger, more sophisticated industrial extruders. It all depends on the scope of your operation and the standards of your industry.

As with any other type of machinery, there are a wide variety of industrial extruders available, and each one is intended for a particular purpose or set of purposes. Some are designed to also serve a specific niche function, such as de-airing a material, de-watering it or pelletizing it.

Capacity is another differentiating factor. For large batches and maximum capacity, a company may need the High Volume Production Extruder (Terrier), for example. Meanwhile, a company that specializes in research and development would probably do well with low-volume Lab Extruders for producing and testing their products in small batches. Another company may need an entirely different solution.

What you need depends on the applications, volumes, shapes and materials required to get the job done.

Cast film extrusion covers wide range of markets

Production of cast film is a continuous process where a thermoplastic material is extruded from a slot die onto a chill roll, quenched, and wound.

The resulting film has machine direction orientation compared to a somewhat limited bidirectional orientation achieved in blown film processing. Cast film extrusion, because of the high speed and output, can be limited to dedicated applications such as lamination web, printed packaging film, and a growing market- stretch wrap.

In recent years, the ongoing move toward automatic wrapping of pallets has shown a steady increase in demand for stretch-wrap film. Due to its processing advantages, cast film today dominates the market in this sector. Equipment producers offer high-speed cast film lines for the manufacture of coextruded linear low-density PE-based films with up to nine layers. Coextrusion also allows downgauging to save raw materials costs. The processor can also manufacture a product where he determines the level and location of cling-on the inside, outside, or on both sides. Agricultural wrapping films as well as stretch film for manual wrapping applications can also be extruded on cast film lines. Another interesting market possibility is food-wrapping film, normally a blend of LDPE and LLDPE.

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