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Cast vs. Blown Film
Blown films, sometimes 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.

In October 2004, the German processor Orbita Film (Weissandt G?lzau) started production with a new, fully automated five-layer stretch cast film line supplied by Austrian machine producer SML Maschinengesellschaft (Lenzing). It has an output of 2250 kg/h and production speed of 600 m/min. This line can increase a processor''s output from 100,000 to 112,000 tonnes/yr.

Cast film is traditionally produced in either polyethylene (PE) or polypropylene but can also include EVOH and/or nylon for barrier in multilayer materials. It is not limited to these resins. Materials can also be vinyl, or polyester, although PE offers the best economies of scale. In 2004, the stretch-wrap market in Europe showed 5% to 7% growth with an annual production quantity of about 1 million tonnes. This market is divided into 40% hand wrap, 48% machine wrap, and 12% power stretch. These applications generally cover a thickness range from 12 to 50 μm.

Film layer structure is moving toward more uniformity. Europe has traditionally stuck to three-layer stretch-wrap structures, while in North America five to seven layers dominate. Market observers say five-layer lines may be becoming the global norm. Multiple layers also offer a plywood effect said to provide better strength and bonding power.

Processors also are headed toward a more unified approach to resins used. North American processors have traditionally processed cheaper butene (C4) LLDPE with a blend of hexene (C6) to get the right stretch retention, clarity for barcode reading, as well as gloss and cling-all at low prices. European processors tend to concentrate on octene (C8), very low-, ultralow-density PE, and metallocene (mPE) grades.

But some processors say there aren''t substantial benefits to using expensive mPE today compared to new C8 grades. Also mPE tends to cut poorly. Alternatives are coming onto the market that offer processors property benefits as well as lower costs. One such product is a recently introduced super hexene LLDPE grade for Super Power stretch (270-350% prestretch used to machine-wrap odd-shaped objects). It gives the mechanical performance of C8 and mPE grades, but better processability than metallocene and at lower costs.

Another growth market is cast polypropylene (CPP), which is finding a niche as competition to biaxially oriented polypropylene (BOPP) film. The equipment investment for CPP is substantially less than the machinery needed for tenter frame-processed BOPP.

What Are The Characteristics Of Film Blowing Machine

Basic characteristics

The group is suitable for blown polyethylene (LDPE), high-density polyethylene (HDPE), and linear (LLDPE) plastic films. It is widely used in fruits and foods, clothing, textiles, strain cultivation, daily necessities, etc. package.

Design Features

The film blowing machine is mainly composed of an extruder, a die head, a die head, a cooling device, a foam stabilizer, a herringbone plate, a traction roller, a winding device and the like.


The extruder is mainly composed of a screw, a barrel, a hopper, a reducer and a drive motor; a belt-driven reducer drives the screw to rotate in the barrel; the screw adopts a special structure, that is, a certain section of the screw is equipped with a special The mixing device relies on the surrounding plastics to support and center when working. The axial force of the screw shaft is borne by the 7310 or 7614 bearing installed between the reducer and the screw. It is sent away between the screw grooves to ensure the conveying capacity and stable extrusion quality.


The machine head is composed of three parts: filter screen, filter plate and machine head gland. In order to adapt to the production of plastic materials containing more impurities, the unit adopts a right-angle machine head structure with a large filtering area. At the same time, high pressure, low pressure, and mixing are considered. The material and reclaimed material have a large power viscosity, a reasonable choice of the material flow channel design, and the use of an extruder drive motor to extrude the filter plate, so it can adapt to a separate screen change operation.

Die head

The die head adopts advanced spiral die head structure. Based on the special characteristics of high pressure, low pressure, mixed material, and recycled polyethylene materials, the spiral angle, backslope angle, setting angle length, and die opening are designed. The parameters are selected and optimized through multiple comparative tests. It has the advantages of large internal pressure, stable and uniform extrusion, good film strength performance, and good matching of the non-sewn line with the extruder of the unit. At the same time, exchange of high and low pressure polyethylene and blending It is not necessary to replace the die head when blowing film production with the ratio of raw materials and recycled materials; various die heads can be prepared according to user needs, and the replacement operation can be completed by one person, which is simple, safe, convenient and fast.

Cooling device

Composed of cooling air ring, blower, etc. The cooling air ring is an externally cooled adjustable air ring, which can adjust the opening degree of the inlet air outlet, which is convenient to operate and is beneficial to the control of film thickness and uniformity.

Stable bubble stand

This unit adopts adjustable ring and fixed rod structure to stabilize the bubble holder, which has a large adjustment range, convenient operation and adjustment, stable bubble tube, and creates conditions for the coiling tube to be flat.

Traction auxiliary machine

The traction auxiliary machine is composed of traction frame, herringbone, traction roller, winding mechanism and traction motor. The traction motor of this unit adopts an electromagnetic slip motor, which drives the two pairs of traction rollers through the deceleration part, and at the same time drives the winding. machine. The herringbone is fixed on the fixed frame under the traction roller. The angle can be adjusted freely according to the thickness of the blown film. The two pairs of traction rollers are composed of rubber rollers and steel rollers, which can effectively prevent gas from leaking out and ensure coiling. Smooth progress, the traction frame adopts the assembled structure, which is convenient for disassembly and assembly, which is conducive to transportation and loading and unloading. The winding device adopts an effective winding mechanism with constant tension. The device drives the friction plate by the sprocket, the large gear by the friction plate, and then the winding shaft, thereby ensuring that the winding diameter changes from small to large. The size can be controlled by adjusting the spring force.

Air compression

The compressed air output from the air compressor and the storage tank enter the spiral mandrel hole of the die through the outlet valve of the storage tank. The die head is equipped with a pressure regulating valve. The gas volume and pressure are adjusted according to the size of the product. Tube-shaped, blown extruded plastic into a bubble-shaped film.

Electrical Control

Electrical control is equipped with a unit operation cabinet. The main power button is connected to the main power and the motor switch is turned on. The electric heating of the fuselage, tee, and die can be controlled by push button switches. The key parts adopt thermocouple automatic temperature measurement and automatic temperature controller. During normal production, the temperature can be automatically controlled to ensure the stable production process. reliable.

Step-By-Step Multi-Wall Paper Bag Manufacturing Process

Multi-wall paper bags are used to transport and store dry flowable bulk materials. The paper shipping sack originated over a century ago. Today billions of units are produced and filled each year. Variations of the industrial paper bag include the pasted valve bag, pinch bottom open mouth bag, self opening satchel bag, and the sewn open mouth bag.

There are two basic types of paper bag: Open Mouth and Valve. An open mouth bag is a tube of paper plies with the bottom end sealed. The bag is filled through the open mouth and then closed by stitching, adhesive, or tape. Valve bags have both ends closed (pasted) and are filled through a valve.

Multi-wall bags are made up of 2-6 layers (plies) of paper and film. Paper plies are generally kraft or extensible paper. For bags requiring moisture or grease protection, a layer of plastic film may be added to the paper plies. The paper itself can also be coated with a thin layer of film.

The following information demonstrates the basic steps in manufacturing a multi-wall paper bag.

Step 1: Printing

Flexographic Printing - A flexographic press uses photopolymer plates, either digital or conventional, mounted on a printing cylinder.

This process uses very fluid, fast drying solvent or water-based inks. It is especially adaptable to high speed, low cost, in-line printing.

Step 2: Tubing

The initial production of a paper bag occurs on a tuber, a machine which takes several rolls of paper and other materials and combines them over a rigid former into a flat or gusseted tube (a tube with creases or folds in the sides not found in flat tube bags), bonded together with adhesives. Tuber speeds typically run from 150 to 250 feet per minute.

Step 3: Bottoming

The tubes are then taken to the bottom-forming operation as required by the particular specification of bag they will become. The tubes are placed in bundles on automatic feeders which deliver them one at a time at speeds of 30 to 50 bags per minute.

The valve bag is pasted closed at both ends during manufacture with only a corner opening or valve at one end, through which the bag is filled.

Step 4: Palletizing/Drying

Finished bags travel through a metal detector to assure the absence of contaminants. Bags are then palletized and dried prior to final shipment.

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