The second edition of Extrusion is designed to aid operators, engineers, and managers in extrusion processing in quickly answering practical day-to-day questions. The first part of the book provides the fundamental principles, for operators and engineers, of polymeric materials extrusion processing in single and twin screw extruders.
The next section. Extrusion is a very popular manufacturing process, especially because of its versatility in terms of materials and shapes. Representing the vast and multifaceted field of extrusion, this book contains write-ups on latest developments from experts in the field. Part A on Metal Extrusion contains chapters on spur gear manufacturing, stiff.
Plastics extrusion is a high volume manufacturing process in which raw plastic material is melted and formed into a continuous profile. There are fundamentally two different methods of extruding film, namely,. This first comprehensive overview of reactive extrusion technology for over a decade combines the views of contributors from both academia and industry who share their experiences and highlight possible applications and markets.
They also provide updated information on the underlying chemical and physical concepts, summarizing recent developments in terms of. Addressing the two major unit operations-mixing and extrusion-fundamental toprocessing elastomers and plastic materials, this reference summarizes design equationsthat can be employed effectively in scaling up product performance parameters, andcontains a thorough survey of rheological principles.
In addition, the book provides awealth of practical information, relating molecular and compositional properties ofpolymers. Offering complete and in-depth data and information on plastics extrusion, this practical handbook presents the technology of the subject rather than the theory. Presents an overview of extrusion technology as applied to the operation of extrusion systems and the design of tooling and equipment for use in the process.
Download or read online Selected problems of polymer extrusion written by Janusz W. Sikora, published by Unknown which was released on Share This Paper. Background Citations. Methods Citations. Results Citations. Figures and Tables from this paper. Citation Type.
Has PDF. Publication Type. More Filters. Evaluation of particle and fibre degradation during processing of wood plastic composites WPC using dynamic image analysis. The aim of … Expand. Highly Influenced.
View 6 excerpts, cites background. View 2 excerpts, cites background. Over the last years, the use of high performance thermoplastic materials increased significantly especially in aviation applications. Thus, the processing of these high temperature polymers became … Expand.
View 1 excerpt, cites background. A multi-objective model predictive control for temperature control in extrusion processes. In this paper, we consider the temperature control problem of an extrusion process with both heaters and coolers. For the purpose of energy saving and avoiding frequent switch between the heaters and … Expand. The seven papers were pub- lished in Ind. Tadmor, Polym. Maddock, SPE Journal, 15, Hensen, W. Knappe, and H. Potente Eds.
Xanthos Ed. Rauwendaal Ed. Manas-Zloczower and Z. Tadmor Eds. Butler and E. White and H. Noriega and C. Campbell and M. The main dis- tinction between the various extruders is their mode of operation: continuous or discontinuous. The latter type extruder delivers polymer in an intermittent fashion and, therefore, is ideally suited for batch type processes, such as injection molding and blow molding.
As mentioned earlier, continuous extruders have a rotating mem- ber, whereas batch extruders have a reciprocating member. A classification of the various extruders is shown in Table 2. The single screw extruder is the most important type of extruder used in the polymer industry. The extruder screw of a conventional plasticating extruder has three geometrically different sections; see Fig. The first section closest to the feed opening generally has deep flights.
The material in this section will be mostly in the solid state. This section is referred to as the feed section of the screw. The last section closest to the die usually has shallow flights. The material in this section will be mostly in the molten state. This screw section is referred to as the metering section or pump sec- tion. The third screw section connects the feed section and the metering section. This section is called the transition section or compression section.
Later, it will be shown that this compression, in many cases, is essential to the proper functioning of the extruder. Obviously, the very large machines are much less common than the smaller extrud- ers. Some machines go up in size as large as 35 inches. These machines are used in specialty operations, such as melt removal directly from a polymerization reactor.
In Europe, the standard extruder sizes are 20, 25, 30, 35, 40, 50, 60, 90, , , , , , , , , , and millimeters. Most extruders range in size from 1 to 6 inches or from 25 to mm. Extruders used for extraction of volatiles vented extruders, see Section 2. Table 2. Material enters from the feed hopper. Generally, the feed material flows by gravity from the feed hopper down into the extruder barrel. Some materials do not flow easily in dry form and special measures have to be taken to prevent hang-up bridging of the material in the feed hopper.
As material falls down into the extruder barrel, it is situated in the annular space between the extruder screw and barrel, and is further bounded by the passive and active flanks of the screw flight: the screw channel.
The barrel is stationary and the screw is rotating. As a result, frictional forces will act on the material, both on the barrel as well as on the screw surface. These frictional forces are responsible for the forward transport of the material, at least as long as the material is in the solid state below its melting point. Feed section Compression Metering section Figure 2. When the temperature of the material exceeds the melting point, a melt film will form at the barrel surface. This is where the solids conveying zone ends and the plasticating zone starts.
The boundaries of the functional zones will depend on poly- mer properties, machine geometry, and operating conditions. Thus, they can change as operating conditions change. However, the geometrical sections of the screw are determined by the design and will not change with operating conditions. As the material moves forward, the amount of solid material at each location will reduce as a result of melting.
When all solid polymer has disappeared, the end of the plasticat- ing zone has been reached and the melt conveying zone starts. In the melt-convey- ing zone, the polymer melt is simply pumped to the die. As the polymer flows through the die, it adopts the shape of the flow channel of the die. Thus, as the polymer leaves the die, its shape will more or less correspond to the cross-sectional shape of the final portion of the die flow channel. Since the die exerts a resistance to flow, a pressure is required to force the material through the die.
This is generally referred to as the diehead pressure. It is important to understand that the diehead pressure is caused by the die, and not by the extruder! The extruder simply has to generate sufficient pressure to force the material through the die. If the polymer, the throughput, the die, and the temperatures in the die are the same, then it does not make any differ- ence whether the extruder is a gear pump, a single screw extruder, a twin screw extruder, etc.
Thus, the diehead pressure is caused by the die and by the flow process, taking place in the die flow channel. This is an important point to remember. A vented extruder is equipped with one or more open- ings vent ports in the extruder barrel, through which volatiles can escape.
Thus, the vented extruder can extract volatiles from the polymer in a continuous fashion. This devolatilization adds a functional capability not present in non-vented extrud- ers. Instead of the extraction of volatiles, one can use the vent port to add certain components to the polymer, such as additives, fillers, reactive components, etc. This clearly adds to the versatility of vented extruders, with the additional benefit that the extruder can be operated as a conventional non-vented extruder by simply plug- ging the vent port and, possibly, changing the screw geometry.
A schematic picture of a vented extruder is shown in Fig. One of the main problems that vented extruders are plagued with is vent flow. This is a situation where not only the volatiles are escaping through the vent port, but also some amount of polymer. Thus, the extruder screw has to be designed in such a way that there will be no positive pressure in the polymer under the vent port extraction section. It is somewhat like two single-stage extruder screws coupled in series along one shaft.
The details of the design of two-stage extruder screws will be covered in Chapter 8. Vented extruders are used for the removal of monomers and oligomers, reaction products, moisture, solvents, etc. The devolatilization capability of single screw extruders of conventional design is limited compared to twin screw extruders.
A draw- back of such a design is that the length of the extruder can become a problem. This creates a problem in handling the screw, for instance when the screw is pulled, and increases the chance of mechanical problems in the extruder deflection, buckling, etc. If substantial amounts of volatiles need to be removed, a twin screw extruder may be more cost- effective than a single screw extruder.
However, some vented single screw extruders of more modern design have substantially improved devolatilization capability and deserve equal consideration; see Section 8. Industrial machines for rubber extrusion were built as early as the second half of the nineteenth century. Some of the early extruder manufacturers were John Royle in the U. One of the major rubber extruder manufacturers in Germany was Paul Troester; in fact, it still is a producer of extrud- ers. Despite the fact that rubber extruders have been around for more than a cen- tury, there is limited literature on the subject of rubber extrusion.
Some of the hand- books on rubber [1—5] discuss rubber extrusion, but in most cases the information is very meager and of limited usefulness. The few publi- cations on rubber extrusion stand in sharp contrast to the abundance of books and articles on plastic extrusion. Considering the commercial significance of rubber extrusion, this is a surprising situation.
These machines are fed with warm material from a mill or other mixing device. Around , machines were developed for cold feed extrusion. As a result, hot feed rubber extruders are still in use today.
Cold feed rubber extruders, nowadays, do not differ too much from thermoplastic extruders. The viscosity of rubbers is gener- ally very high compared to most thermoplastics; about an order of magnitude higher [5].
The reduced length keeps the temperature build-up within limits. This is another reason for the short extruder length. The length of the rubber extruder will depend on whether it is a cold or hot feed extruder. Cold feed extruders range from 15 to 20D. Vented cold feed extruders may be even longer than 20D. Rubber extruders used to be heated quite frequently with steam because of the rela- tively low extrusion temperatures.
Today, many rubber extruders are heated like thermoplastic extruders with electrical heater bands clamped around the barrel. Oil heating is also used on rubber extruders and the circulating oil system can be used to cool the rubber.
Many rubber extruders use water cooling because it allows effec- tive heat transfer. The feed section of the rubber extruders has to be designed specifically to the feed stock characteristics of the material. The extruder may be fed with either strips, chunks, or pellets. If the extruder is fed from an internal mixer e. The feed opening can be undercut to improve the intake capability of the extruder. This can be useful, because the rubber feed stock at times comes in rela- tively large particles of irregular shape.
Material can also be supplied in powder form.
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