Historical review of die drool phenomenon during plastics extrusion

Musil, Jan; Zatloukal, Martin

doi:10.1063/1.4802600

Cited by 3 publications

(2 citation statements)

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“…[4,5,8,27] Our work includes this possibility as a special case. For instance, when the die drool is found to have a lower molecular weight than the bulk, [9] we think this is probably caused by polymer thermal degradation through scission (such as is common for polypropylene), and specifically, when the temperature given by Equation (39) exceeds the degradation point for the polymer.…”

Section: Resultsmentioning

confidence: 99%

“…This accumulation can then interfere with the extrusion, scratching imperfections into the extrudate surfaces called die lines. [1] This die face buildup, called die drool, costs plastics manufacturers by requiring chemical engineers to shutdown the operation for die cleaning [2][3][4][5][6][7][8][9] (see section 8.3.3.3 of Dealy and Wang). [10] No single governing dimensional parameter has been identified to control die drool, and since changing a system property, such as increasing melt temperature, can result in either an increase or decrease in die drool rate, solving die drool problems is clearly a complex matter (see Result column in Table 1 of Schmalzer and Giacomin).…”

Section: Introductionmentioning

confidence: 99%

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Slip heating in die drool

Gilbert

Giacomin

2015

Can J Chem Eng

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When molten plastic is extruded from a die, it can collect on the open die face. Called die drool, this phenomenon costs plastics manufacturers by requiring shutdown for die cleaning. This has been attributed to cohesive failure within the fluid at an internal surface, where the fluid slips on itself; the corresponding isothermal analysis led to an analytical solution for the drool rate (Schmalzer and Giacomin, J. Polym. Eng. 2013, 33, 1). In this paper, we account for the frictional heating at the cohesive slip interface, which we call slip heating. We focus on slit flow, which is used in film casting, sheet extrusion, curtain coating, and in many other chemical engineering unit operations. In slit flow, the magnitude of the heat flux from the slipping interface is the product of the shear stress and the slip speed. We present the solution for the temperature rise in pressure‐driven slit flow subject to constant heat generation at the cohesive slip interface. We solve the energy equation in Cartesian coordinates for the temperature rise, for both the transient and steady temperature profiles, in both the drool layer and the bulk polymer. We then evaluate the effect of this temperature rise on the rate of die drool. For this simplest relevant non‐isothermal problem, we neglect viscous dissipation and convective heat transfer in the melt and we model viscosity as an Arrhenius function of temperature. We conclude with three worked examples showing the relevance of slip heating in determining die drool flow rates. We find that slip heating diminishes die drool. We arrive at two sufficient dimensionless conditions for the accurate use of our results: Br ≪1 or Gi ≪1.

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