Extruders, capacities

The extruder capacity versus diameter is given by the following equations.37... 

Fig. 11. Pressure/flow-rate characteristics of extruder (capacity versus pressure drop across the head) in processing of polypropylene filled by 10 % (by mass) of chalk (a) and 20 % (by mass) of asbestos (b) at a temperature in the head equal to 210 °C and amplitude of reciprocatingrotary vibration of the core, degr.— 0 2 — 4 3 — 11.5 — 22.3...

In the flight depths illustrated in Figure 12.12, a distinction is made between standard screws and shallow-flight screws. Shallow-flight screws pick up less material and, as a result, the residence time is the plasticizing unit is shortened. This can be advantageous when utilizing thermally sensitive additives, such as colorants, or when the part production rate is a small compared with extruder capacity. 

FIG. 21-183 Determination of extruder capacity or throughput based on the intersection of screw and nozzle (die face) characteristics. From Pietsch, Size Enlargement by Agglomeration, Wiley, 1992.)... 

Standard sizes of single-screw extruders are I /i, 2, 2 /i, 3 /, 3 /i, 4 /2, 6, and 8 in., which denote the inside diameter (ID) of the barrel. As a rough guide, extruder capacity Q , in pounds per hour, can be calculated from the barrel diameter in inches, by the empirical relation [15]... 

Another estimate of extruder capacity can be made by realizing that most of the energy needed to melt the thermoplastic stems fi-om the mechanical work, whereas the barrel heaters serve mainly to insulate the material. If we allow an efiiciency from drive to screw of about 80%, the capacity Q (Ib/h) can be approximately related to the power supplied Hp (horsepower), the heat capacity of the material Cp [Btu/lb °F], and the temperature rise fi-om feed to extrudate AT (°F) by... 

The production speed of blow-molded parts is generally limited by one of two factors extruder capacity or cooling time in the mold. Cooling of mold is accomplished by a water circuit into the mold. Flood cooling and cast-in tubes are most common in cast molds drilled holes and milled slots are the norm in machined blow molds. 

The components of a pipe extrusion line include an extruder, annual die, calibration system, cooling system, puller, wind-up unit or stacker, and auxiliary equipment. The extruder typically has anL/D of 24 1 or greater and the screw design depends on the material. Conical twin-screw extruders are often used for poly(vinyl chloride). The diameter of the annular dies is 25 to 100 percent of the extruder diameter. However, the output of a pipe extrusion line is limited by the ability of the downstream equipment to cool the product and hold tolerances. Since extruder capacity is often underutilized, the same die may be used for a range of pipes of differing diameter and wall thickness. IVpically, a number of adapters and replaceable components are used with the same rear section of die. Dies with multiple outlets are employed when large-diameter extruders are used for small-diameter pipe. 

More expensive internal cooling systems are ofi en not justifiable with to-daj s equipment because most blow-molding machines do not have the additional extruder capacity to support the high production rate. This is particularly true for the heavier bottles that would benefit most. As a result, only the low cost air-exchange systems have been accepted. 

A standard thermoplastic extruder design, built using special materials of construction, with a length to diameter (E/D) ratio of 20 1 to 30 1 can be used to extrude fiuoropolymers. High E/D machines are required to obtain sufficient contact surface area for heat transfer to melt the resin. Eower E/D results in a lower output, and barrel temperatures would have to be raised which can lead to an increase in the polymer degradation. Table 8.4 shows the relationship between diameter, output, and motor size for different extruders. Restriction of flow imposed by the sizing die usually reduces the extruder capacity. 

Nanocomposites prepared with Cloisite 30B and polyvinylidene fluoride [39] provide an unexpected perspective of the mechanical properties of polymer-montmorillonite nanocomposites. Polyvinylidene fluoride has geminal fluorines on alternate carbons of a polyethylene chain. The polyvinylidene fluoride (PVDE Kynar 721 manufactured by Atofma Chemical Co.) was premixed as a powder with Cloisite 30B at 5 wt.% with a Elack-Tek DAC-150EV speed mixer. The extrusion of the melt-compounded composite was accomplished with a small DSM twin-screw extruder (capacity 5 cm ) that was utilized with the SMA and SAN meltblending work earlier. The temperature of the extruder was 200 °C. 

Polydispersity index Probability of mole fraction of x-mer Gas permeahOity coefficient in a polymer Constant in Price—Alfrey scheme Volumetric flow rate, melt flow rate Average volumetric flow rate Extruder capacity... 

---