Extrusion, Education, Plastics
Extrusion Definitions Clertral
Go to link - 2005-03-02Advanced Single-Screw Polymer Extrusion and Screw Design
Go to link - 2005-03-01The 10 (11) key principles of extrusion
Go to link - 2005-03-01Extrusion Processes
Go to link - 2005-03-01Extrusion Process Handbook
Go to link - 2005-02-07Extrusion Definitions
Go to link - 2004-11-24Extrusion definitions by Tangram Technology Ltd
Go to link - 2004-07-29Advanced Single-Screw Polymer Extrusion and Screw Design-Chung
Go to link - 2003-11-19Plastic Extruders Data
Go to link - 2003-11-11Twin Screw Report-Training-Leistritz
Go to link - 2003-11-11Extrusion welding of plastics
Extrusion welding of plastics (September 2000)Extrusion welding is an established technique for the fabrication of assemblies made from thermoplastics. The process is typically used in the manufacture of large fabrications, such as chemical storage vessels. In these applications, where walls are thick, it is more economical than hot gas welding. Extrusion welding is a manual process. Weld quality is dependent upon the skill of the person operating the welding gun. Training and Certification are generally recommended in order to maintain high standards of fabrication. Extrusion welding is generally only used for polyethylene and polypropylene. Some applications of the process have used nylon, but care must be taken to dry the welding rod to prevent voids occurring in the weld. Other applications include the fabrication and repair of liners for refuse tips and lakes.
The process involves continuously extruding molten thermoplastic material into a weld preparation on the plastic component or structure which is being joined. The equipment is based upon an electric drill with a mini extrusion barrel attached to the front. The extrusion barrel is heated along its length, either by cartridge heaters or hot air. A thermoplastic rod or granule feedstock is fed into the rear of the extrusion barrel and the material is heated as it is drawn through the barrel by the rotating extruder screw. Molten thermoplastic is continuously ejected through a PTFE shoe attached to the front of the extrusion barrel. The PTFE shoe is shaped to match the profile being welded, and defines the shape and size of the final weld. At the leading edge of the PTFE shoe, hot gas is used to heat the substrate material in front of the area where the molten bead is to be laid. This ensures that there is sufficient heat in the substrate material to form the weld. Typical welding speeds are 0.5-1.0 m/min.
To apply extrusion welding successfully, operators need a practical understanding of fabricating thermoplastic assemblies using the hot gas welding process. Typically, the welding procedure consists of assembling the sheets of material being welded and tacking them together using a hot gas welding tacking nozzle. A single run of hot gas weld (using the same thermoplastic material as the substrate) is placed at the base of the weld preparation to ensure that there is adequate root penetration. An extrusion weld is then used to fill the remainder of the joint, again using the same thermoplastic material as the substrate. Generally, no further work is required to complete the joint unless a flush finish is required, for example, in a butt weld.
Further information on extrusion welding of plastics can be found via the Weldasearch literature database.
Copyright © 2000, TWI Ltd
TWI WORLD CENTRE FOR MATERIALS JOINING TECHNOLOGY - 2003-10-26
Principles of Single Screw Extrusion
Go to link - 2003-10-13Extrusion definition #2
ExtrusionMore plastic resin has processed through the extrusion process than through any other plastics manufacturing technique. This fact, however, is misleading. Very big amounts of plastics are processed by extrusion into pipes, films, sheets, coatings and so on. Extrusion is also used for producing pellets of thermoplastic materials. Therefore, the majority of plastic material produced in the world today has had at least one extrusion through an extruder. Then those materials will be used in other plastic processing methods, like injection moulding, blow moulding and other melt processing methods, including the extrusion.
Extrusion is a typical method to produce continuous products (pipes, sheets, films, coatings) of different kinds of materials. The first extruders were developed for food and building materials industry. Nowadays very many materials can be extruded into products. In the area of technical materials the polymeric materials are the most common ones.
During extrusion, a polymer melt is pumped through a shaping die into the final profile form. The first extruders were ram-type extruders and the first extruders were built in 1797 to extrude seamless lead pipes. The first ram-type extruders for rubber industry were designed 1845. In 1846 a patent for cable coating was filed for trans-gutta-percha and cis-hevea rubber and the first insulated wire was laid across the Hudson River for the Morse Telegraph Company 1849. The first screw extruder was patented 1879 for wire coating. The extrusion of thermoplastic polymers started in 1935.
Ram and screw extruders are both used to pump high viscous polymer melts through a die to form a continuous profile. They are based on different principles which are illustrated in figure 1.
The extrusion process
The extruder is a melt pump. In the first stage the polymeric material is melted and then the melted material is forced via the die into the final form.
Today nearly all extruders are so called screw extruders, earlier there were different kinds of development stages. The most important step is the melting and homogenization of the polymeric materials. It can also be carried out with calenders. Multiscrew extruders have been developed for special purposes, especially for different kinds of mixing applications. One of the newest developments is the cone extruder, which will have many applications in pipe extrusion and other applications.
The extrusion process is best understood, when it is divided into key steps:
1. Pretreatment of extruded material. This includes drying of materials, feeding of additives, preheating.
2. Material is fed into the extruder through the throat, an opening that links the material hopper into the extruder barrel
3. Forced feeders, if the feeding of materials is difficult or it is important that the material feed is very constant
4. Inside the cylinder the raw material is conveyed from the feeding zone to the die. In this case it is very important that the friction between the cylinder is higher than the friction between the screw.
5. The screw can be divided into three parts and a conventional screw is presented in fig. 11. The zones are: feeding zone, compression zone and homogenisation zone.
6. The die. The melted material is pumped through the die into the final form.
7. Calibration of the extrudate in the final dimensions and form
8. Postprocessing of extrudates
The melting of viscoelastic polymeric material is carried out by external heating (outside the barrel by electricity or heated fluids) and internal heating (internal friction, molecular relaxations). The internal heating is the most important heating method in today’s extruders and its part of the heating energy is 80 - 100 %.
The melting process in the screw channel is presented in figure 5. There has been many attempts to intensify the melting process. Figure 6 presents the melt flow in the extruder cylinder.
A modern extruder consists of different parts and the most important parts are:
The screw
The screw has the following tasks:
* feeding of raw material from the feeder to the die
* compression of the material
* melting of the material
* homogenization of the material
* pressurising the material
A typical screw for rubber extrusion is presented in figure 7. Lots of studies have been made to develop more efficient screws for different applications. Nowadays the development of screws is based on the rheological facts of polymeric materials.
extrusion applications
The extrusion cylinder
The extrusion cylinders are normally significantly longer than in injection moulding. The cylinders are covered with heating (cooling) systems and the heating is made electrically or with heated liquids. The cooling is arranged normally with liquid or air.
The cylinders are made normally by using a bimetallic material which has high abrasion resistance. In many cases it can also be coated to increase the abrasion resistance.
The screen pack and breaker plate
The function of the screen pack is to filter out all possible contaminations from the polymer melt.
The breaker plate provides a controlled amount of back pressure for the extrusion process.
Gear pumps
Gear pumps are used in the extrusion process to provide a constant flow rate and pressure for the extrusion die. Figure 10 presents a conventional gear pump structure.
Tooling for extrusion
In the case of special products the tools are easiest to make. In the case of nonsymmetric products some die characteristics have to be taken into consideration.
Die swell. The extrudate is greater than the orifice from which it came. The die swell will also change the form of the extrudate .
Flow surfaces. The surfaces which are in direct contact to the melt in the die have to be very smooth.
Heat. Dies are usually externally heated and this will eliminate the solidification of material in the die.
Earlier the extrudates were monolayer structures, but nowadays there are dies for different kinds of multilayer structures (there can be even 10 - 15 layers in one extrudate).
Types of extrudates (products)
* films
* sheets
* profiles
* pipes
* filaments
* coatings
* co-extrudates
Extrusion definition #2 - 2003-09-07
THE PLASTICS EXTRUSION OPERATING MANUAL
Go to link - 2003-07-31COMPUTER-AIDED POLYMER PROCESSING
RECENT PROGRESS AND FUTURE CHALLENGESIN COMPUTER-AIDED POLYMER PROCESSING
ANALYSIS AND DESIGN
J. Vlachopoulos
Centre for Advanced Polymer Processing and Design (CAPPA-D)
Department of Chemical Engineering
McMaster University
Hamilton, Ontario, Canada L8S 4L7
Presented at the ATV-Semapp Meeting
Funen, Odense, Denmark
February 1998
COMPUTER-AIDED POLYMER PROCESSING - 2003-07-31
Principles of Single Screw Extrusion
This two-and-one-half-day seminar will be targeted for engineers, managers, and extrusion practitioners who want a fuller appreciation and knowledge of the inner workings of single screw extruders. The seminar will use algebraic formulas developed from the engineering analysis of extrusion mechanisms to obtain a physical interpretation of the developed extrusion theory and what controls an extruder's performance. The formulas will also be used to make basic feeding, melting, and metering calculations for comparison with experimental performance characterization results.Principles of Single Screw Extrusion - 2003-07-31
Twin-Screw Extrusion Training Programs
On-site training programs are customized to YOUR equipment, YOUR products and are scheduled at YOUR convenience. This is a cost-effective method to boost your productivity as well as provide operating staff with the right "tools" to perform their jobs efficiently.Twin-Screw Extrusion Training Programs - 2003-07-31
Extrusion, description of,
Extrusion process can be divided into following categories:* Extrusion of semi-finished product
* Extrusion compounding
* Blown film extrusion
Extrusion, description of, - 2003-07-31
