Extrusion moulding


Rubber extrusion. moulding 0.48 Tiles and mosaic 0.61  [c.766]

The mix is formed by extrusion, moulding or hydrostatic pressing into a green artifact.  [c.863]

Industrial polymer processing encompasses a wide range of operations such as extrusion, coating, mixing, moulding, etc. for a multiplicity of materials carried out under various operating conditions. The design and organization of each process should therefore be based on a detailed quantitative analysis of its specific features and conditions. The common - and probably the most important part in the majority of these analyses is, however, the simulation of a non-isothermal, non-Newtonian fluid deformation and flow process.  [c.287]

ISO/DIS 1874-2, Plastics Polyamide (PM) Moulding and Extrusion Materials, Part 2 Preparation of Test Specimens and Determination of Properties, International Standards Organization, Geneva, Switzedand, 1994.  [c.277]

Fig. 24.3. (a) Extrusion polymer granules ore heated, mixed and compressed by the screw which forces the now molten polymer out through a die. (b) Injection moulding is extrusion into a mould. If the moulding is cooled with the pressure on, good precision and detail ore obtained.  [c.258]

There are certain differences between the properties of a polymer crystallised under conditions of high nucleation/growth ratios as compared with those made under the opposite conditions. In the latter case the polymer develops large crystal structures which may be sufficiently large to interfere with light waves and cause opacity. It may also be somewhat brittle. In the former case the polymer mass, with smaller structures, is generally more transparent. The properties of the polymer will also depend on the time available for cooling. In the case of a polymer such as the bis-phenol A polycarbonate (Chapter 20) the glass temperature is about 140°C. There is in this case little time for crystallisation to develop in cooling from the melt after injection moulding and extrusion and transparent polymers are usually obtained.  [c.51]

Deformation of a polymer melt—either thermoplastic or thermosetting. Processes operating in this way include extrusion, injection moulding and calendering, and form, in tonnage terms, the most important processing class.  [c.158]

The principles of thermoplastic melt processing can perhaps best be illustrated by reference to Figure 8.1 illustrating extrusion, injection moulding, bottle blowing and calendering operations. In order to realise the full potential of the process it is necessary to consider the following factors  [c.159]

Figure 8.1. (a) Extrusion—material is pumped, in the above ease with a screw pump, through a die to give a product of constant cross-section, (b) Injection moulding—material is pumped by a screw pump to the front end of the injection cylinder with the screw moving to the rear in order to provide space for the material the screw then moves forward as a ram injecting molten material into a relatively cool mould into which the material sets, (c) Extmsion blow moulding—the extruder tube is inflated in the mould while still above softening point, (d) Calendering—softened material is flattened out into sheet between rolls  [c.160]

The setting of these materials after shaping occurs via a chemical process, that of cross-linking. The most common process is moulding but some extrusion, sintering and other miscellaneous processes are also used. A typical compression moulding process is illustrated in Figure 8.12.  [c.176]

Melt elasticity is of considerable importance in understanding much of the behaviour of polyethylene when processing by film extrusion techniques and when blow moulding. The complex relationships observed experimentally here have been summarised by the author elsewhere.  [c.223]

Although the tonnage consumption is small compared with the amount of polyethylene consumed in injection moulding or extrusion, polyethylene is widely processed using a powder as the starting material. This powder can be made either by precipitating the polymer by cooling a solution or by grinding processes. The former method gives the finest powder whilst the latter is more economic.  [c.237]

Poly-(4-methylpent-l-ene) is a highly pseudoplastic material and in the usual processing range is of low melt viscosity. There is a narrow melting range and the viscosity is highly dependent on temperature. In injection moulding this results in the use of cylinder temperatures of the order of 270-300°C, mould temperatures of about 70°C and the use of restricted nozzles to prevent drooling . In extrusion, high-compression screws with a sharp transition from feed to metering zone are recommended. Melt temperatures of about 270°C are required for many operations.  [c.273]

A major difference between SBR and natural rubber is that the former does not break down to any great extent on mastication. The synthetic material is supplied at a viscosity considered to provide the best balance of good filler dispersability (requiring a high viscosity) and easy flow in extrusion, calendering and moulding. This provides savings in both energy consumption and time, and hence on costs. Since the viscosity changes little with working it is much easier to work re-worked stock into a compound. In many other respects the processing behaviour of SBR is not as good as natural rubber. Mill mixing is generally more difficult, and the synthetic material has lower green strength (i.e inferior mechanical properties in the unvulcanised state) and does not exhibit the characteristic of natural tack which is so useful in plying together or otherwise assembling pieces of unvulcanised rubber.  [c.293]

Converting the fluxed product into a suitable shape for further processing, e.g. granulating for injection moulding or extrusion.  [c.347]

Extrusion blow moulding of bottles has been successfully accomplished in reeent years by attention to the points mentioned above. It is to be noted here that UP VC has a much lower average specific heat between the proeessing temperature and room temperature than polyethylene and, being essentially amorphous, no latent heat of fusion. This leads to much less heat needing to be removed on cooling of mouldings and very short cycle times are possible.  [c.350]

Injection moulding and extrusion may be carried out at temperatures in the range of 300-380°C. The polymer has a high melt viscosity and melt fracture occurs at a lower shear rate (about 10 s ) than with low-density polyethylene (about 10 s ) or nylon 66 (about 10 s ). Extruders should thus be designed to operate at low shear rates whilst large runners and gates are employed in injection moulds.  [c.373]

The advantage of being able to injection mould and extrude these copolymers has perhaps had a less marked effect than might have been expected. This is because the fabrication of PTFE has been developed by firms closely related to the engineering industries rather than by the conventional plastics fabricators. The PTFE fabricators, because they do not normally possess conventional injection moulding and extrusion machines, would see no obvious advantage in melt processability. At the same time the conventional plastics fabricators, if they wished to enter the field of fabricated fluorine-containing thermoplastics, would have to modify their existing machinery in order to cope with the processing temperatures and high melt viscosity. In spite of these retarding influences the use of FEP copolymers has grown steadily.  [c.373]

PFA fluoropolymers may be proeessed by injection moulding, extrusion, extrusion blow moulding and transfer moulding. All machine parts coming into contact with the melt should be made from highly corrosion-resistant high nickel content alloys. Processing melt temperatures can be as high as 420°C and mould temperatures may be in the range 50-250°C.  [c.378]

Because of its high cold flow, poly(vinyl acetate) is of little value in the form of mouldings and extrusions. However, because of its good adhesion to a number of substrates, and to some extent because of its cold flow, a large quantity is produced for use in emulsion paints, adhesives and various textile finishing operations. A minor proportion of the material is also converted into poly(vinyl alcohol) and the poly(vinyl acetal)s which, are of some interest to the plastics industry.  [c.386]

The average molecular weight of most bulk polymerised poly(methyl methacrylates) is too high to give a material which has adequate flow properties for injection moulding and extrusion.  [c.404]

Cast material is stated to have a number average molecular weight of about 10. Whilst the Tg is about 104°C the molecular entanglements are so extensive that the material is incapable of flow below its decomposition temperature (approx. 170°C). There is thus a reasonably wide rubbery range and it is in this phase that such material is normally shaped. For injection moulding and extrusion much lower molecular weight materials are employed. Such polymers have a reasonable melt viscosity but marginally lower heat distortion temperatures and mechanical properties.  [c.405]

Processing in the melt state such as by injection moulding and extrusion.  [c.409]

The melt viscosities at the processing temperatures employed are considerably higher than those of polystyrene, polyethylene and plasticised PVC. This means that the equipment used must be robust and capable of generating high extrusion and injection pressures. The injection moulding of polyfmethyl methacrylate) (PMMA) has been made much easier by the widespread use of the reciprocating screw in-line injection moulding  [c.409]

The polymer may be prepared by mass, suspension, solution, and emulsion methods, the first two being the most important. Mass polymerisation has the advantage of apparent simplicity and gives a polymer of high clarity and very good electrical insulation characteristics. There are, however, severe problems due to the exothermic reaction and the product has a broad molecular weight distribution. Polymerisation in solution reduces the exotherm but may lead to problems of solvent recovery and solvent hazards. The solvent may also act as a chain transfer agent and cause a reduction in molecular weight. Suspension polymerisation avoids most of these problems but there is some contamination of the polymer by water and the suspension agent. Furthermore the polymer must be dried and aggregated before being sold as pellets suitable for injection moulding and extrusion. Emulsion polymerisation techniques are seldom used with polystyrene since the large quantities of soap used seriously affects clarity and electrical insulation characteristics. This process is therefore used only for the production of polystyrene latex.  [c.429]

ABS is more hygroscopic than polystyrene. (It will absorb up to 0.3% moisture in 24 hours.) It must therefore be dried carefully before moulding or extrusion.  [c.447]

Polymers of a-methylstyrene have been marketed for various purposes but have not become of importance for mouldings and extrusions. On the other hand copolymers containing a-methylstyrene are currently marketed. Styrene-a -methylstyrene polymers are transparent, water-white materials with BS softening points of 104-106°C (c.f. 100°C for normal polystyrenes). These materials have melt viscosities slightly higher than that of heat-resistant polystyrene homopolymer.  [c.453]

Polystyrene and closely related thermoplasties such as the ABS polymers may be proeessed by sueh techniques as injection moulding, extrusion and blow moulding. Of less importance is the processing in latex and solution form and the  [c.455]

Being either brittle or soft, these resins do not have the properties for moulding or extrusion compounds. These are, however, a number of properties which lead to these resins being used in large quantities. The resins are chemically inert and have good electrical insulation properties. They are compatible with a wide range of other plastics, rubbers, waxes, drying oils and bitumens and are soluble in hydrocarbons, ketones and esters.  [c.471]

Acetal resins may be processed without difficulty on conventional injection moulding, blow moulding and extrusion equipment. The main points to be considered are  [c.542]

Extrusion blow moulding  [c.564]

Structurally viscous grades are based on branched polymers (branching being effected by the use of tri- or higher functional phenols). These polymers exhibit a sharp decrease in viscosity with increasing shear rate which makes them particularly suitable for extrusion and blow moulding and also, it is claimed, in reducing drip in case of fire.  [c.564]

Another moulding process based on the extruder is extrusion moulding. Molten polymer is extruded into a mould where it sets. Since satisfactory mouldings can be produced using low moulding pressures, cheap cast moulds can be used. The process has been used to produce very large objects from polyethylene. The techniques of screw-preplasticising with injection moulding can be considered as a development of this process.  [c.233]

Other, more recently developed, uses include microwave oven parts, transparent pipelines, chemical plant pumps and coffee machine hot water dispensers. One exceptional use has been to produce, by an extrusion moulding process, very large rollers for textile finishing for use where cast nylons cannot meet the specification. Also of growing interest are medical equipment applications that may be repeatedly steam-sterilised at 134°C, filtration membranes and cartridges for ink-jet printers.  [c.602]

In these problems, flow geometry is not known a priori and some sections of the domain boundary may change with flow. This situation arises in a variety of polymer processes such as injection moulding and mixing in partially filled chambers. Free surface flow regimes are also encountered in extrusion and wire coating operations where die swell is a common phenomenon. Various techniques for the modelling of free boundary flow regimes have been developed in the last two decades. Some of these methods are process specific, or they were developed in conjunction with particular numerical schemes and cannot be regarded as general simulation tools.  [c.101]

The coagulated rubber was a highly elastic material and could not be shaped by moulding or extrusion. In 1820 an Englishman, Thomas Hancock, discovered that if the rubber was highly sheared or masticated, it became plastic and hence capable of flow. This is now known to be due to severe reduction in molecular weight on mastication. In 1839 an American, Charles Goodyear, found that rubber heated with sulphur retained its elasticity over a wider range of temperature than the raw material and that it had greater resistance to solvents. Thomas Hancock also subsequently found that the plastic masticated rubber could be regenerated into an elastic material by heating with molten sulphur. The rubber-sulphur reaction was termed vulcanisation by William Brockendon, a friend of Hancock. Although the work of Hancock was subsequent to, and to some extent a consequence of, that of Goodyear, the former patented the discovery in 1843 in England whilst Goodyear s first (American) patent was taken out in 1844.  [c.3]

In addition to the deliberate monoaxial or biaxial orientation carried out to produce oriented filament or sheet, orientation will often occur during polymer processing whether desired or not. Thus in injection moulding, extrusion or calendering the shearing of the melt during flow will cause molecular orientation. If the plastic mass sets before the individual molecules have coiled then the product will contain frozen-in orientation with built-in, often undesirable, stresses. It is in order to reduce these frozen-in stresses that warm moulds and fast injection rates are preferred in injection moulding. In the manipulation of polyfmethyl methacrylate) sheet to form baths, light fittings and other objects biaxial stretching will frequently occur. Such acrylic products produced by double curvature forming will revert completely to the original flat sheet from which they were prepared if they are heated above their glass transition temperature.  [c.49]

A second persistent processing problem is that of shrinkage. During extrusion and moulding, polymer melts are normally subject to intense hydrostatic pressures which tend to cause compression. For example, in injection moulding the melt is under compression at the moment following mould filling. If the mould was suddenly opened at this stage the moulding would expand (slightly) and also distort gruesomely. However, during cooling molecular movement becomes less and the pressures exerted on the mould cavity walls decrease. In most cases not only do they fall to zero but in addition the moulding shrinks. In the case of amorphous polymers the shrinkage is very small and is about 0.005 cm/cm.  [c.176]

Injection moulding of unplasticised PVC was only really made possible by the advent of the in-line screw preplasticising machines. As with extrusion the main points to bear in mind are the high melt viscosity, the need to avoid overheating and steel corrosion by hydrochloric acid evolved during processing. In practice this demands good control of operating conditions, short runners, reasonably generous gates and mould cavities which, preferably are either ehrome or gold plated. Although it is possible to extrude rigid PVC sheet, it is commonly made by compression moulding techniques, either by laminating hide from a sheeting or mixing mill or by moulding granules. Such sheet may be welded using hot gas welding guns to produee ehemical plant and other industrial equipment. The sheet may be shaped by heating and subjecting it to mechnical or air pressure. The methods used are similar to those originally developed to deal with poly(methyl methacrylate).  [c.350]

The high crystallinity which develops on cooling results in a shrinkage of about 0.020 cm/cm. Because of the low glass transition temperature, crystallisation can take place quite rapidly at room temperatures and aftershrinkage is usually complete within 48 hours of moulding or extrusion. In processing operations injection moulds, blow moulding moulds and sizing dies should be kept at about 80-120°C in order to obtain the best results.  [c.543]

Both homopolymers and copolymers are available in a range of molecular weights (Af 20000-100000). The materials are normally characterised by the melt flow index using basically the same test as employed for polyethylene. For general purpose work polymers with an MFI of about 9 are employed but high-precision work and complex mouldings polymers with MFIs as high as 27 (viz. lower molecular weight polymers) may be used. For extrusion and thick-walled mouldings a polymer with MFI about 2.5 (M, ca 45 000) is often employed although for extrusion blow moulding the special polymers used have MFIs of about 1.0.  [c.543]

In the usual range of moulding and extrusion materials an increase in molecular weight leads to comparatively small improvements in such properties as tensile strength. It does, however, lead to the usual steep increase in melt viscosity and to an increase in impact strength. This is indicated in Table 20.2, which also indicates the recommended processing method. Polymers with number average molecular weights below 20000 are generally unsuitable as plastics wjulst those with molecular weights above 50 000 (particularly those in range of = ca 70000) are mainly processed into film by solution casting methods.  [c.564]


See pages that mention the term Extrusion moulding : [c.13]    [c.178]    [c.317]    [c.52]    [c.172]    [c.253]    [c.410]    [c.457]   
Plastics materials (1999) -- [ c.159 , c.160 , c.233 , c.350 ]