Solids conveying in screw extruders part II: Non isothermal model

ABSTRACT:Aspects of heat transfer within the solids conveying zone of a single-screw extruder were studied by using a specially constructed drum testing apparatus. Experiments were conducted with linear low-density polyethylene, polystyrene (PS), and polypropylene (PP) samples by examining their transient temperature profile while the heated drum was stationary or moving. In accordance with classic solids conveying theory, the granular beds of PP and PS remained as plugs while the drum rotated. In such cases, the dominant modes of heat transfer for these systems are conduction through the contact area of a particle and conduction through the interstitial gas. An exception to this behavior was found with PE, in which the bed temperature increased more rapidly while the drum rotated. Visual observations of the bed showed that the particles circulated in the presence of shear and that this complex flow pattern increased in velocity as the drum temperature approached the onset temperature for melting the PE material. With strong correlation between the rate of circulation and the temperature rise in the bed, the movement of particles was assumed to act in a convective heat transfer

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“…as done in our previous work, 10 or even as a continuous, homogeneous mass similar to the model of Tadmor and Broyer 4 and others.…”

Section: Advances In Polymer Technology Doi 101002/advmentioning

confidence: 70%

Cohesive‐driven particle circulation in the solids conveying zone of a single‐screw extruder

2008

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“…Friction force between the solids bed and the screw surface f s pW dz F 6 Force acting on the solids bed by pressure p ϩ dp HW (p ϩ dp) F 7 Normal force acting on the solids bed by the rear flight pHdz ϩ F* F 8 Normal force acting on the solids bed by the fore flight pHdz is D b N. Equation (2) can be rearranged with respect to the angle as follows:…”

Section: Table I Expressions Of the Forces Acting On The Differentialmentioning

confidence: 99%

“…For the solids conveying zone, Darnell and Mol 3 studied systematically the single-screw extruder in 1956, and Tadmor and Klein 4 expanded the theory further in 1970. Tadmor and Broyer 5,6 considered the anisotropic pressure acting on the solids bed and proposed a nonisothermal model. Tadmor and Kacir 7 insisted that a delay zone is formed at the end of the solids conveying zone just before the start of the steady-state melting mechanism.…”

Section: Introductionmentioning

confidence: 99%

A study on the rheological properties and processability of polycarbonate

Ahn

Kim

2002

J of Applied Polymer Sci

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ABSTRACT:The transport theory for the solids conveying zone in a single-screw extruder was applied to calculate the pressure distributions along the screw channel for several bisphenol A polycarbonate resins based on the screw revolution speed and the flow rate. The pressure distributions and the flow rates of the resins were related to the structural and rheological properties. When polymers have the same chemical structure and number-average molecular weight and the same mechanical properties, the polymer having a broader molecular weight distribution showed a lower glass transition temperature. For the polymer with broader MWD a relatively low pressure was developed along the screw channel, and an increased flow rate was observed. A relatively short melting length was also observed for this polymer and, accordingly, it was concluded that the polymer with a broader MWD has a better processability.

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“…The mathematical model has been developed with the aid of Tadmor and Broyer's theory [6] for two-dimensional, non-isothermal, non-isotropic plug flow of solid material. The ratio of normal stresses for calculating the non-isotropic pressure distribution coefficients [7] has been taken to be 0.4 according to Schneider's theory [8].…”

Section: The Solids Conveying Zone (Scz)mentioning

confidence: 99%