High speed wire coating by withdrawal from a bath of viscoelastic liquid

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Abstract
Data are presented for the thickness H ∞ of liquid coating entrained by continuous withdrawal at speed U of a wire of radius R from the free surface of a large bath. For Newtonian fluids of viscosity μ, density ρ and surface tension σ, the data are carried out to coating speeds beyond the applicability of current theories, to Capillary numbers of nearly one hundred. In the high speed range the data, which cover several orders of magnitude in viscosity, can be well represented by the equation for U μ/σ = N ca > 3. All data presented are at an essentially constant Goucher number of 0.08, where N Go ≡ R (ρ g /2σ) 1/2 . Data for viscoelastic fluids show phenomena quite distinct, qualitatively and quantitatively, from Newtonian observations. In particular, strongly elastic fluids show a markedly reduced ability to be entrained onto the wire. Further, the coating thickness appears to become independent of Capillary number at high speed.