Screw Simulator

Thompson, M.R., Rahim, S., and Alotaibi, A.S., Cohesion-Driven Recirculation of a Polymer Solids Bed in a Screw Simulator, SPEANTEC Tech. Papers, 55, 142 (2009)... 

Screw Simulator [45-47]. The Screw Simulator was discussed in Sections 4.3.1 and 4.4. 

The Screw Simulator was also used to measure the melting flux of TPU resins at conditions similar to those expected in the melting section of the screw. At these conditions, the melting flux was measured at 0.2 kg/(m s). This melting flux is relatively low. For example, the melting fluxes [11] for linear low-density polyethylene (LLDPE) and low-density polyethylene (LDPE) resins are 0.3 and 0.4 kg/(m2- s), respectively. The relatively low melting flux for TPU resins is a contributor to the solid polymer fragments in the extrudate. 

The stress at the sliding interface was measured using a Screw Simulator as outlined in Section 4.3.1 for the LDPE resin and is shown in Fig. A5.17 at a pressure of 0.7 MPa and shown in Fig. A5.18 at a pressure of 3.4 MPa. At temperatures of less than about 110 °C, the stress at the interface is due to a frictional force mechanism. At temperatures higher than 110°C, the forces are from a viscous mechanism. The coefficients of friction were reported as stresses so that the data from both mechanisms can be reported on the same figure. The coefficient of friction is related to the stress at the interface r as follows ... 

Resulting in access to process technology with extruder machinery Figure 6.15 Screw simulation (3D) Results... 

Equation 7.165 is comparable to Eq. 7.131 both equations are closed-form analytical solutions. However, Eq. 7.165 is more compact and easier to use. A word of caution is in order. Equation 7.165 has been experimentally verified with the screw simulator. The results of the screw simulator may not fully apply to actual melting in a single screw extruder. For instance, the screw simulator uses a molded solid polymer sample of one cubic inch. The solid bed in the extruder consists of compressed, partially sintered, polymeric particles. It is clear that an actual solid bed, as occurs in the melting zone of an extruder, may have different characteristics in terms of heat transfer properties and deformation behavior, as compared to a molded solid block of the same material. 

---