Solids conveying models

The original solids-conveying model developed by Darnel and Mol [7] assumed that the pressure (or stress) in the solid bed is isotropic. This assumption was made to simplify the mathematics and because of the lack of stress data for solid bed compacts. Previous research, however, showed that stresses in solid compacts are not isotropic [8]. Anisotropic stresses can be represented by the lateral stress ratio. It is defined as the ratio of the compressive stress in the secondary direction to the compressive stress in the primary direction, as shown in Fig. 4.7 and Eq. 4.1. 

Literature Review of Smooth-Bore Solids Conveying Models... 

Tadmor and Broyer [16, 17] produced two more solids conveying models a modified version of Tadmor s earlier model [1], which assumed isothermality [16], and a second model that allowed for thermal effects [17]. Later, a model by Strand et al. [18] was developed based on the Tadmor-Klein model for starve-fed solids conveying. 

Several solids conveying models were developed by Campbell and his students at Clarkson University [19, 20]. These models will be referred to as either the Clarkson University models or the Campbell models. They proposed that the movement of the screw flight was pushing the polymer bed as the screw turns rather than the frictional force at the barrel moving the polymer pellets down the screw. For these models, they assumed that the solid bed behaved more like an elastic fluid rather than a solid and removed the torque balance constraint. Campbell and Dontula [20] reasoned that because the solid polymer pellets more closely resemble an elastic particulate fluid, no torque balance in the bed would be necessary. They further assumed that the force normal to the pushing flight was due to a combination of the force due to the pressure in the channel and a force proportional to the frictional force exerted at the barrel by the solid bed. The Campbell-Dontula model was first published as ... 

Appendix A5 Solids Conveying Model Derivations and the Complete LDPE Solids Conveying Data Set... 

The modified Campbell-Dontula solids conveying model was based on screw rotation and a normal force at the pushing flight that was directly proportional to the frictional force between the solid bed and the barrel wall. The force balance on the slab is provided in Fig. A5.4... 

In an operating extruder the beginning of the screw can be ftilly described by the solids conveying model... 

Properties for a few polymers required in the solids conveying model are presented in Appendix B. Here it is observed that the friction coefficient between the polymer and steel is relatively independent of temperature. As the temperature approaches the melting point the friction coefficients tend to increase, but over a wide range of temperatures /b is nearly constant. Hence, it seems justifiable to use the mass flow rate and pressure rise calculated by means of the isothermal model in the nonisothermal model. 

C,2 Nonisothermal Solids Conveying Model (Tadmor and Broyer, 1972). As a result of frictional heating at the barrel and plug interface the solid plug... 

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