Calendering thermoplastic materials

Abstract

SynopsisA general equation for the true shear rate encountered in calendering non-Newtoiiiaii fluids is derived. Based on several constitutive equations (for a power-law, a threeconstant Oldroyd. and a modified second-order Rivlin-Ericksen fluid), calendering is analyzed from the hydrodynamic point of view. The significance of dimensionless groups (the Deborah number, the Weisenberg numbers, and the viscoelastic ratio number), consisting of rheological and kinematic parameters, is discussed for scaling from prototype to production calendering. Correlation of experimental data obtained by using laboratory and production calenders is presented, and the scaling criteria obtained from the theory are examined. The onset of unstable flow, which causes non-uniform internal strain patterns (nerve) in calendered sheeting, is discussed in terms of the Weisenberg number. Good and poor calendering regions for a polymer are discussed qualitatively by using a dynamic response diagram, and the importance of the overall calendering conditions on the final sheeting quality is discussed.

Pressure distribution in a two-roll mill.

“…Figure 3 shows the calculated results for the dimensionless maximumpressure 7imax and minimumpressure 7imin which occur at £= +y/2X-2 as expected from Eq. (6). Figure 3 shows a slight increase in ;rmax and 7rmin with increasing Nca for 7Vca>100 independently of Nr.…”

“…(4), Eq. (1) is reduced to dn 3(rjR-X) d£ nl (6) The local pressure distribution can be obtained with the inlet boundary condition tt=O at the attaching point £=£0 as follows: The relationship between £0, X and £e in Eqs. (7) and (8) can be obtained by using the boundary condition in the film-splitting region.…”

Theoretical analysis of the exiting thickness of sheets in the calendering of FENE-P fluid

“…Chong [13] from hydrodynamic point of view for three constitutive equations namely; power-law equation, Oldroyd-B equation and a modified second-order equation. Sofou and Mitsoulis [14] provided numerical results for the viscoplastic calendering of sheets.…”

Nonisothermal nip flow in calendering operations

“…Perturbation around the first-order solution (Walters, 1972;Davies and Walters, 1972) provides insight in the problem but is not amenable to extrapolation for strongly nonlinear fluids. Dimensional analysis could eventually be used if sufficient insight and data were available (Tokita and White, 1966;White and Tokita, 1967;Chong, 1968). Petrusanskij et al (1971) seem to have been the first to tackle the nonisothermal case.…”