Extruders, Cold-Feed

Cold feed extruders use compounds in a strip form. The strip is generally made during the take-off process in mixing a series of cutters are used on the blending mill... 

There are two types of cold feed extruders, the standard screw design type (Fig. 15) and one with a screw feed using a ram action to feed the extruder. In both... 

There are two types of hot feed extruders, one similar to the screw type cold feed extruder, except that the strip feeding the extruder is taken directly off the two-roll mill. The mill is used to further blend and heat the compound. It is then taken off the mill in strip form and fed directly into the extruder. The second type of hot feed extruder is based on the action of a ram being used to feed the compound into the extruder die (Fig. 16). The compound is placed on a two-roll mill to further blend and heat rubber. It is then taken off the mill in pig form to fill the extruder chamber. 

In both cases, the preforms are produced using the rotating cutter system as described for the cold feed extruders. The preforms are also cooled the same way. 

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... 

Cold feed extruders (Figure 14.25) have much larger length-to-diameter ratios because of the requirements of reducing green compound plasticity, heat buildup in the compound, and pressure buildup required to produce the extruded profile. The length-to-diameter ratio is typically 24 1. The modem cold feed extruder is also computer controlled, which enables adjustment of the compound temperature profile through the barrel, pressure control, flow rate, and feed rate. This provides accurate control over die swell, extrudate surface quality, and buildability of the extruded product. 

The factory system based on internal mixers, screw extruders, calenders, and vulcanization presses has remained basically unchanged in the past half-century. Internal mixers have had major improvements, e.g., intermeshing rotors proposed by Francis Shaw and Company [C16] and Werner and Pfleiderer [L3], and variable intermeshing clearance rotors [PI] proposed by Pomini-Farrel SpA. Sophisticated computer control systems have been introduced. The early single hot-feed extruders have been replaced by cold-feed extruders with increasingly sophisticated design including pin barrel extruders [G7, H12, H13, M18, W16] as well as complex control systems. 

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]... 

Cold feed extruders (Fig. 25) have much larger length-to-diameter ratios because of the requirements of reducing green compound plasticity, heat... 

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. 

EPDM rubber sheet can also he made using the hot or cold feed rubber extruder machine of 20-30 cm screw diameter. For a hot feed machine the L/D ratio of the screw should be 5 1 and for the cold feed extruder 20 1. 

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 extruding CSM compounds a cold feed extruder is best, but a hot feed one will also work, but uniform warming of the compound is essential for dimensional stability. Higher die temperatures are needed for a smooth surface and lower feed zone temperatores provide better back pressure for air removal. Operating temperatures of the equipment for both cold and hot feed extruders are... 

USE OF NFMIDDON COLD FEED EXTRUDER AND NOVEL LOW TEMPERATURE CURING EPDM TO REDUCE PROCESSING AND CURING ENERGY CONSUMPTION... 

Silica filler is often used together with carbon black as a reinforcing filler [7]. However, it is usually a minor component of the filler. This section explores the use of silica as a major component (67% or 100%) of the total filler in NR. In order to overcome the mixing difficulty a coupling agent is used. The control compounds contained silica in amounts of 0 or 33% of total filler. A wide ribbon of rubber was extruded from a Monsanto hot-feed extruder and then, the ribbon was fed into an NRM cold feed extruder to test extrudability through a profile die [8]. 

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