Feed throat

Eig. 1. Parts of an extmder A, screw B, barrel C, heater D, thermocouple E, feed throat E, hopper G, thmst bearing H, gear reducer 1, motor , deep channel feed section K, tapered channel transition section and L, shallow channel metering section (15). 

The feed must be nonabrasive with a hardness of 1.5 or less. The miU is capable of taking 2-cm ( A-in) feed material, depending on the size of the feed throat, and reducing it to a product substantiaUy aU able to pass a No. 200 sieve. For producing materials in the fine-size range, it may be operated in conjunction with external air classifiers. Such an arrangement is shown in Figs. 20-12 or 20-42. A number of machines have internal air classifiers. 

During extrusion, the blend components are fed into the feed throat of the extruder. Compounding extruders are starve fed. This means that material is conveyed away from the feed throat more rapidly than the raw materials are fed into the barrel. Therefore the volume of raw material introduced is always less than the total available volume of the flights... 

Sakai and Hashimoto (33) presented experimental results on devolatilization of a mixture of octane/hexane in linear low density polyethylene (LLDPE) from 10% to 0.01%, as well as a rubber slurry of 42% chloroprene and of 58% slurry in carbon tetrachloride in a JSW TEX 65 counterrotating, intermeshing, TSE. The LLDPE mixture was prepared in SSE upstream, where the octane/hexane was added to the melt with a plunger pump, which maintained constant concentration and was fed directly under pressure into the feed throat of the counterrotating, vented, TSE. 

Fig. 10.32 Cross-sectional view of the feed throat region of a CRNI TSE.

Fig. 10.57 Typical 4 LID Co-TSE barrel segments, (a) Feed throat (b) melting (c) downstream feed section (d) mixing (e) devolatilization (f) pumping and limited pressurization. [Courtesy of P. Andersen Coperion Wemer and Pfleiderer, Ramsey, NJ.]...

It is worth noting that the method used by Vergnes et al. in experimentally obtaining the relative viscosity equation parameters, a and ft in Eq. 10.3-6. They worked with two almost identical PP homopolymers, one in 4-mm mean pellet diameter form, and the other in the form of small, 750-pm-diameter beads (Solvay Eltex HL 101). A 21-mm Co-TSE was fitted with a rheometric slit of length L = 52 mm, width w = 28 mm, and an adjustable gap spacing 1.5 < h < 2.5 mm. The polypropylene in pellet form was fed at the feed throat and melted. Just before the die, a second feed port introduced the PP in bead form at various rates, resulting in different effective values. Two pressure transducers at the die were used to record the slit pressure drop AP(relative viscosity was then expressed as... 

Fig. 14.23 Typical blow molding die A, choke adjusting nut B, mandrel adjustment C, feed throat D, choke screw E, die head F, plastic melt G, die barrel H, heater band /, choke ring J, centering screw K, clamp ring L, die heater M, die N, mandrel. [Reprinted by permission from J. D. Frankland, A High Speed Blow Molding Process, Trans. Soc. Rheol., 19, 371 (1975).]...

When an empty hopper is not the cause of machine output failure, plastic might have stopped flowing through the feed throat because of screw bridging. An overheated feed throat, or startup followed with a long plasticator operating delay, could build up sticky plastics and stop flow in the hopper throat. Plastics can also stick to the screw at the feed throat or just forward from it. When this happens, plastic just turns around with the screw, effectively sealing off the screw channel from... 

Some types of thermal processing equipment, such as a Banbury, are designed to perform the preliminary mixing before the extrusion step. In this case, a weighed-out formula batch is directly added to the feed throat of the equipment. 

In the newest plants, the sealed mixing chamber would be directly connected to the feed throat of the thermal processing equipment before it is opened. When the vessel is emptied, it is again closed and sent to a special equipment wash bay for cleaning. This enclosed system virtually eliminates dust emissions throughout the thermal encapsulation process. 

The barrel is a hollow cylinder extending from the end of the feed throat to the tip of the screw (Figure 14-8). The exit end of the barrel is referred to as the head. Coating the entire inside surface of the barrel is a very... 

The polysiloxane network is formed during part fabrication. In injection molding, the acetylenic alcohol, which acts as a fugitive inhibitor of the vinyl-addition reaction, is volatilized at low temperature as the pellets enter the feed throat. The platinum complex is activated at the process temperature of the urethane (170-185 °C). The vinyl-addition reaction is initiated by the melt state, and the parts generated demonstrate mechanical properties consistent with the formation of a silicone IPN. The fabricated parts are translucent. The physical properties of this formulation (PTUE 205) are given in Table 1. 

Liquid additives are mostly added downstream of the plastification section because they tend to lubricate the pellets or cause powders to agglomerate in the feed throat. If a significant amount of liquid is to be incorporated, it can be added at several locations. The most effective method for low viscosity liquid incorporation is to inject into a fully filled distributive mixing section. This requires a pressure injection valve and positive displacement pump. For small amounts of compatible liquid, non-pressurized injection into a low degree of fill area of the screw configuration may also be acceptable. 

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