Extrusion

In the extrusion ( cast out of Latin extrudere =,- drive ) or extrusion are squeezed solid to viscous curable compositions under pressure continuously from a shaping orifice ( also referred to as a nozzle or die tip ). This body forms with the cross section of the opening in theory any length.

• 4.1 Plastics Industry 4.1.1 Pipe and Profile Extrusion
• 4.1.2 Blown Film Extrusion

Method

Products of extrusion technology can be found in numerous application areas again. Depending on the properties of the material to be processed, the print production and the desired result can be distinguished different methods. Wherein the cold extrusion is at low pressures, temperatures, and shear forces, work at the hot extrusion at higher temperatures and the hot extrusion to both high pressures and temperatures.

Types of extruder

Ram extruder

In this design, the pressure is generated by a piston (English ram extrusion ). Ram extruders are mainly used when the material to be processed can not be processed by means of screw extruders or frequent product changeovers to be performed.

Ram extruders are frequently used for ceramic materials. Screw extruder in the ceramic production have the serious disadvantage that wear out the screw by the highly abrasive ceramic mass quickly. Other materials that are sensitive to high shear forces, are by ram extrusion better producible. Ram extruder can be cleaned quickly and have little contact area to the extrusion mass.

By employing large diameter piston and the cylinder length, a semi-continuous production can be used. Also, the parallel connection of two Kolbe extruders can optimize this yet.

Screw extruder

In this design, the pressure by means of an auger, also called worm generated. It is in the so-called screw cylinder, whose nominal diameter is equal to the outer diameter of the screw. At the front end of the worm cylinder is located, the outlet opening forming. At the rear end of the cylinder, the drive, in most cases an electric motor with gear unit, which provides for the rotation of the screw.

The materials to be processed are of the screw usually fed continuously via a hopper from above. Decisive is the exact and reproducible dosing in several components. It differs depending on the control mechanism between gravimetric and volumetric doses. Other components may be incorporated into the screw cylinder on side feeder, needle valves etc.. In plastics processing are described, for example, masterbatches ( colorant), reinforcing fibers, antioxidants or plasticizers.

The worm itself is generally divided into three zones, which take on different tasks. In the rear area of the screw cylinder is called the feed zone. This is the material to be extruded, which is present as a solid in the form of granules or powder, for example, a hopper fed ( " feeding " ) and optionally melted ( thermoplastics ). By the rotation of the auger, the material is conveyed. To this, the compression zone follows, in which the material is compressed by the reduced channel depth of the screw, and thus further the required for the discharge pressure is built up in the tool. Finally, the metering or metering ensures a homogeneous material flow towards the tool.

The shape or design of the screw determines the properties.

• Barrier screw

In the barrier screw, an additional web is at the beginning of the barrier section is mounted, the height of which is less than that of the main web. This web is called a barrier wall. Through the barrier wall of the screw channel is divided into the melt and solid channel. The gap width is so small that no solid particles may pass over the bridge in the underlying melt channel. The separation of melt and solid state be a better melting process is guaranteed, since no solid islands in the melt can swim around. In the discharge zone of a barrier screw homogenization are as shearing and mixing parts available. Towards the end of the barrier zone of the solids channel smaller and the melt channel increases. Thus, the remaining solids are forced by dissipation to go into melt.

• Twin-screw extruder (direct or the opposite )
• Much screw extruder

Other types

• Cascade extruder
• Planetary roller extruder

Advantages of the extrusion process

The advantages of the method are the possibilities to create and process brittle or soft material complex shapes.

Complex structure of an extruded WPC profile

Applications & Products

Products of extrusion technology are found in numerous applications such as back Construction industry (Building Construction and Civil Engineering ), automotive industry, aerospace industry, medical equipment, furniture industry (especially kitchen or office furniture), exhibition, packaging, agricultural use, hose applications and granulation.

Examples of products which are produced by extrusion

• Tubes, rods ( semi-finished )
• Profiles such as window frames, cable ducts or seals
• Casings, such as for electric cables
• Hoses
• Plates by means of T-die which can be formed after the production, if necessary by means of thermoforming.
• Films (via die or slot die and downstream calender)
• Treads of car tires
• Smaller car parts ( interior door panels, rear-view mirror versions )
• Squeegee the windshield wiper
• Bicycle rims
• Wedge belts and timing belts by supplying copper wire through the extruder head
• Door seals
• Extruded polystyrene rigid foam panels (XPS )
• Ceramic, perforated bricks and foundry mold
• Precursors for soap manufacture
• Stearinkerzen
• Noodle pasta, snacks, biscuits, processed meat
• Manufacture of chemical fibers
• Heatsink

Plastics industry

Plastic and plastic granules, including compound granules

By extruding seamless sheets, tubes and profiles with a constant cross-section over the length can be prepared for example. , Plastic containers, such as bottles, cans or the fuel tanks are produced by extrusion. An extruded tube is enclosed by a mold and blown by means of compressed air to the tool wall. In this case one speaks of extrusion blow molding. The most important product of wood-plastic composite ( WPC) decking boards are.

In addition to the food industry, the plastics industry is a major consumer of extruder. Here in addition to the above-mentioned construction will be attached to the heating strips screw cylinder that the filled plastic granules or powder melting ( plasticize ). Extruder must not only be heated. Some procedural tasks also make cooling the plasticized plastic necessary. This is done either by the cooling fan or to the cylinder of the extruder is worked cooling channels, which are provided with a cooling medium, eg water under pressure, flows through. Depending on the nature of the plastic used is further necessary equipment, for example for pumping gases, the bubbles would be left in the final product. The material used is also a decisive factor in the form of the screw. Thus, the gradient, the number of turns and the width of the screw threads, depending on the plastic material can be completely different.

In general, more machines are needed for the production of plastic products according to the nozzle.

For this purpose, the plastic or the extrudate (also called screw press ) is first melted and homogenized by means of heating and internal friction through an extruder. Furthermore, the need for the through flow of the nozzle pressure is built up in the extruder. After emerging from the nozzle of the plastic solidifies mainly in a water-cooled calibration. The application of vacuum causes the profile is pressed against the wall of the caliber and therefore the shaping is completed. Following it often follows a cooling section in the form of a chilled water bath. The cross-section of the resulting geometric body corresponding to the nozzle or calibration used. The possible production tolerances are in the range of ± 0.05 mm. An analog, based on the same original form principle method is to use in the hot- forming of metals is known as continuous casting.

The merging of similar or strange materials before leaving the profile nozzle is also called co-extrusion. Here a distinction is single-stage and two-stage process:

• Single-stage method

In the single-stage process, also called direct extrusion, for example, be the wood particles and the plastic pellets for wood-plastic composites at the same place at the same time fed to the extruder. Usually conical, counter-rotating twin -screw extruders are used for single-stage, fulfilling the task of intensive mixing and a required pressure build-up for the extrusion time.

• Two-stage process

In the two- step extrusion process plastic pellets and wood particles ( compounders ), heating cooling mixers, or pelleting presses are first mixed and compacted in parallel twin-screw extruders. The actual extrusion then takes place in another, directly coupled or spatially and temporally separate unit. Generated in the two-stage process WPC intermediates can be used in addition to the extrusion and in injection molding, rotational molding or the plate reduction press equipment.

Pipe and Profile Extrusion

In the tube or profile extrusion, the extruded material must then be kept in a calibration table in the mold until it is cooled. Otherwise it slumps down and deforms. The heart of calibrating the calibration sleeve, which serves primarily the shape retention of the tube or profile. It is installed directly behind the nozzle of the extruder. It comprises a metal block having exactly inside the cross-section of the tube or profile. The extruded tube or profile so it runs through the calibration sleeve. For the shape retention of the profile is carried out inside the sleeve, especially with vacuum. Vacuum ports at different locations in the sleeve along the cross section suck the profile to the interior walls, water around and flushed while the profile until it has cooled. The nature and form of the calibrating addressed this very after being extruded plastic product. Especially with complex profiles, such as window frames, here a lot of know- how is required, so that the profile is not collapses and deformed during cooling in itself.

A trigger behind the calibrating ensures the transport of the tube or profile. It consists of two or more crawlers, whose surfaces are pressed against each other. The extruded tube or profile is then placed and set by the movement of the chains under train between these treads. So the trigger pulls the extruded plastic product from the extruder and through the calibration table. The speed of the trigger determines the speed of the extruder together with the relevant speed of the profile or pipe.

Behind the deduction is usually still a cutting edge facility that been cut to length, the endless tube or profile accordingly. A collection table collects the cut to length tubes or profiles. The machine operator can bundle and pack the finished tubes or profiles here.

The combination of extruder, calibration table, trigger, cutting machine and collecting table is " extrusion line " because each machine after the other the production process according to an axis.

Blown Film Extrusion

Extruders are also part of a blown film. Here the plasticized material is not brought into the form of a profile, but blown up to a very thin film bubble. For this, the melt is deflected in the vertical direction and brought into the form of a tube by spiral mandrel dies. By annular array of up to nine extruders and bring together the different melt streams in spiral mandrel die multilayer films can be produced in this way. To bring the melt tube exiting the usual today thicknesses of several hundredths of a millimeter, the tubes are subsequently stretched. This is done by blowing air centric, not only mechanically stretched the hose, but also cools down and therefore fixed in shape. The film tube is calibrated, folded and wrapped by a basket.

Common materials processing are:

• PVC: Polyvinyl chloride
• PE: polyethylene
• PP: Polypropylene
• PA: polyamide
• HDPE: High Density Polyethylene
• LDPE: Low Density Polyethylene
• ABS: acrylonitrile-butadiene- styrene copolymer
• PC: polycarbonate
• SB: styrene
• PMMA: polymethylmethacrylate
• PU: polyurethane
• PET: polyethylene terephthalate
• PSU: polysulfone

And innovative biomaterials such as

• Thermoplastic starch, starch
• CA: cellulose acetate
• PLA: Polylactic acid
• PHB: polyhydroxybutyric
• WPC: Wood -Plastic Composite

See also wood extrusion.

Feed and food industry

In the feed and food industry preconditioning example, be integrated heating and vapor deposition processes in the context of the open grain ingredients, for example, and do with it digestible.

• Chewing gum and chewy candy
• Pasta ( Noodles )
• Many snack products: potato Products
• Erdnussflips

During hot extrusion quite a hydrous dough (ground) under enormous pressure in a compression screw (similar to a meat grinder ) heated. At the nozzle, the pressure drops, so that the water evaporates and the product is greatly relaxed. Here, the already gelatinized starch, the gas attitude ( similar to a fire ground) support and hold at fixed pores. Often a drying or roasting station is still downstream. Typical products include peanut puffs, onion rings and other snack items. But even some breads ( eg flat bread or bread chips) and biscuits are produced in this process.