Rubber cold feed

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. 

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... 

In the 1930s, Paul Troester Maschinenfabrik [W12] introduced the cold-feed screw extruder to which cold strips of rubber compound were added. 

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]... 

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 ... 

Cold feed rubber extruders, nowadays, do not differ too much from thermoplastic extruders. Some of the differences are ... 

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]. 

The feed characteristics of cold rubber compounds differ considerably from those of hot compound to the extruder and a number of devices were developed to overcome this problem. However, the productivity of the early machines was not as high as for the hot-feed machines. 

This cell design illustrates several inherent features the ease of sealing to a rubber connector in the cold zone, the high thermal shock resistance which allows the electrolyte tube to go through the thermal insulation into the hot zone, the feasibility for carrying out some fuel processing upstream of the cell region, and the ease of combustion at the exit of the tube. Typically, the gas feed... 

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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