Power extrusion

Foaming extrusion Foaming-in-place beads Foaming power Foam inhibitors... 

However, for the high strain rates appropriate for the analysis of typical extrusion and injection moulding situations it is often found that the simple Power Law is perfectly adequate. Thus equations (5.22), (5.23) and (5.27) are important for most design situations relating to polymer melt flow. 

Kalyan et al. [56] have also studied the effect of alpha-olefin comonomers on the rheological properties and processing of LLDPE. The characteristics of the resins are shown in Table 2. It is found that 1-octene-based LLDPE has the lowest shear viscosity as compared to 1-butene- and 1-hexene-based polymers (Fig. 9). Decrease in power consumption, pressure before the die, temperature in the die, and increase in output has also been found according to shear viscosities of the polymers during tubular film extrusion. 

For filled thermoplastics (30-40% by mass of chalk, ash or asbestos), complex shear may, as reported in [235], provide an increase of apparatus productivity by 40-80%, or if the flow rate is to be constant, the pressure in the molding instrument may be reduced by at least 20-30%. It is to be noted that while some extra power is required to create the complex shear conditions, the total power consumption of the apparatus as a whole may be reduced, on the power per unit of product basis, due to the high extrusion rates [233]. 

Considering that the filler increases matrix viscosity, it is necessary to use processing equipment of high power permitting the development of higher extrusion and... 

Performing numerical simulations of the extrusion process requires that the shear viscosity be available as a function of shear rate and temperature over the operating conditions of the process. Many models have been developed, and the best model for a particular application will depend on the rheological response of the resin and the operating conditions of the process. In other words, the model must provide an acceptable viscosity for the shear rates and temperatures of the process. The simple models presented here include the power law. Cross, and Carreau models. An excellent description of a broad range of models was presented previously by Tadmor and Gogos [4]. 

The availability of power and torque to the shank of the screw is extremely important to the success of an extrusion process, especially if modifications to the line are planned to increase the rate. That is, the proper level of power must be available at the proper screw speed. Thus, the motor size and speed, belt sheaving if used, and gearbox reduction must be specified to provide enough power to the screw to plasticate and pump the resin at a high rate. 

Extrusion processes are often rate limited by motor power or torque, discharge temperature, or the melting capacity of the screw. Other root causes associated with the design of the screw can limit rates as shown in previous sections. The problems, however, are typically associated with other defects such as flow surging or resin degradation. Chapters 11 and 12 discuss process defects associated with resin degradation and flow surging, respectively. Rate limitations due to inadequate motor power and torque are common problems for commercial plants. Two case studies are presented in the next sections that show rate limitations due to the lack of torque and motor power. 

The scale-up factors depend on the specific event being scaled-up in extrusion. The cube rule for mixing (23) states that at constant screw speed, output and power consumption increase with ct when H/D ratio is constant. The square-root rule for conveying (24) of material states that when channel depth is increased and screw speed decreased with x/d, the output rate increases with S, while power consumption increases by One could obtain... 

A common indicator in an extruder console is the power, E, consumed by the motor drive in transporting material from feed to product exit. A higher power consumption could mean greater friction during product movement or an overloaded chamber. The torque of extrusion (F) is the energy expended by the motor drive in rotating the screw(s) and is expressed as... 

Particle size and size distribution mixing, amperage, power consumption) Torque or pressure of extrusion... 

Among the formulation variables that control extrudability of a product, several studies (25,26,33-35) point to the fluid or moisture content of the wet feed material being more critical than others. The force or torque of extrusion and power consumption are often inversely proportional to moisture content of the extrudate as seen from Figures 11 and 12 (26,36-38), while the particle size of pellets increases linearly with water content when extruded with gravity feed basket and roll extruders (33). Using instrumented gravity feed and radial screw extruders, a three- to fourfold decrease in the force has been noted, with a 10% increase in water content of feed material (37). 

Figure 12 Influence of the amount of water on the extrusion forces (gravity feed extruder) and power consumption (twin screw extruder) on extrusion of MCC. , gravity feed extruder (N) , twin screw extruder (W). Source From Ref. 37.

A gravity feed extruder with L/D = 2 recorded (28) higher forces, compared to power generated from a twin-screw extruder with L/D = 0.9, upon extrusion of mixtures of MCC with either lactose or DCP. The extrudate from the basket extruder was denser with a smoother surface than that from the screw extruder. Similarly, material extruded through a screen with L/D = 4 in a basket extruder was denser than that with L/D = 2 (37). However, a smaller L/D ratio is preferred in an axial extruder. An improper L/D ratio could result in a loosely bound extrudate with large surface defects (37), resulting in a formulation less amenable to pelletization, as seen from Figure 14. Since the mean diameter of the pellet often approximates the diameter of the die used in extrusion, choice of the latter is also dictated by desired pellet size. 

The addition of tellurium has a deoxidizing action and confers on lead useful work and precipitation-hardening properties. It also improves resistance to wear, vibration, and mechanical breakdown. These properties, along with improved corrosion resistance, are utilized in the sheathing of power communication and marine cables, in chemical equipment (especially those exposed to sulfuric acid), or where resistance to fatigue is important. Tellurium has successfully replaced tin (1—3% Sn) in the sheathing. Thinner sheaths can be extruded, and the extrusion pressure for 0.05% Te-beafing lead is about the same as for a 3% Sn alloy. 

---