COLD-FEED EXTRUSION

Understand the critical properties of the mixed compound that affect processability. It should be understood that the properties and acceptable operating values of those properties, which control the compound processability, are dependent on the processes under consideration, e.g., hot or cold feed extrusion, compression or injection molding. 

The cold-feed extruder had shallow screw channels and a much longer length/diameter ratio. The original cold-feed extruder produced extrudates which had large temperature distributions and became distorted as they emerged from the die. The issue in cold-feed extrusion of rubber was to produce a thermally homogenized product in the extruder screw which would yield thermally uniform extrudate that does not distort. From the 1960s, there have been several improvements in cold-feed extruders. First, Maillefer [M6]... 

The first rubber extruders were built for hot feed extrusion. These machines are fed with warm material from a mill or other mixing device. Around 1950, machines were developed for cold feed extrusion. The advantages of cold feed extruders are thought to be ... 

When used only as a compoimding unit to provide strip for later cold feed extrusion or injection moulding, the throughput of the MVX became more acceptable. 

In the two typical shaft seal manufacturing processes shown in Fig. 2, the extrusion process is only required if the compression molding process is being used. There are basically two types of extruders in general use, the cold feed and the hot feed. In both cases their role is to produce the preforms for use with compression molding. The critical issues with the preform are the shape, the dimensions, and the weight. 

Extrusion of tubes, hose, and profiles is done on standard extruders for rubber. The usual temperature pattern is a gradual increase of temperature from the feed zone to the die. The die temperature is typically 100°C (212°F), and the screw temperature is approximately the same as the temperature of the feed zone [44]. Processing aids are almost always required to improve the surface appearance and to increase the extrusion rate. Extrusion represents only a small proportion (about 10%) of the total consumption of fluorocarbon elastomers [52].Cold feed extruders typically used for extrusion of rubber stocks are also suitable for the extrusion of fluorocarbon elastomers. Extrusion should be carried out at temperatures below 120°C (250°F) to avoid scorch. In most cases a breaker plate and screen pack are used to generate backpressure on the screw and to remove foreign particles from the stock. A straight head is used for the extrusion of profiles or tubing, whereas a cross-head die is used for... 

Important processing methods mixing/compounding, injection molding, extrusion, Banbury mixer, two-roll mills, cold feed extruders, reaction injection molding... 

Either hot or cooled finished mix is fed into the extruder (as a hot strip or crumb fed to a hot-feed extruder, or a cooled strip or pellets into a cold-feed extruder). The extruder can form extruded profiles suitable as components of built-up products, such as side walls or treads of tires. The extruder can also form profiles that are vulcanized on the run by passing the endless extrudates through a heated salt bath or hot oven, either of which is long enough for vulcanization to sufficiently occur before the profile exits the oven or hot bath. Profiles of unvulcanized products, such as hoses, can be vulcanized after extrusion in a steam autoclave or hot oven. 

TABLE 6.22 Extrusion Guidelines Cold Feed Hot Feed Ram... 

Extrusion Continuous process in which the feed materials, generally refined cereal grits or flours supplemented with other ingredients, are transformed into foods such as different types of pasta products, breakfast cereals, and snacks. Cold extrusion is used for the production of pasta products, whereas thermoplastic extrusion is used for the production of breakfast cereals, snacks, and pregelatinized flours. 

Following the mixing operation polyisoprenes should have higher Mooney viscosities than equivalent natural rubber compounds but, nevertheless, will still exhibit faster flow under high shear. Compounds based on the synthetic polymer may be cold fed to extruders in which the necessary prewarming prior to extrusion is easily achieved or, alternatively, for hot feed extruders premilling should be kept to a minimum to avoid too... 

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