Precision extrusion dies for quality assessment

Celsum Technologies can supply a wide range of precision extrusion dies for laboratory rheometers and extrusion lines, as well as for pilot extrusion plants

Recently, Celsum has provided a set of complex dies with bi-hyperbolic profiles (ie, hyperbolic profiles on the entry and exit section of the die), and with a sub-miniature pressure transducers only 3mm in diameter embedded in the die wall.

These are being used to study the flow behaviour of muds and slurries in an especially-built rheological test rig.

Celsum has also supplied regular hyperbolic-profile dies for a range of commercially available capillary extrusion rheometers, where they are useful for analysing the elongational or extensional flow properties of materials.

Such materials include polymer melts, rubbers, ceramic pastes, pharmaceuticals, foods, cosmetics, explosives, and others, although the latest batch of dies are being used to optimise processing geometry for polymers filled with wood-flour in a major recycling project aimed at developing the next generation of building materials.

Celsum also supplies regular parallel-profile precision dies for laboratory rheometers including its own BFR 2100 and Eta 2100 instruments, in a range of materials including tungsten carbide, tool steel and stainless steel.

Typically, a set of dies with the same diameter bore but different bore lengths is used to determine the Bagley End Correction, by plotting the pressures required to maintain extrusion at a series of constant extrusion rates.

When extrapolated to zero length, there is still a finite residual pressure, and this is used to correct the shear stress values (the Bagley Correction).

This zero-length pressure is used also in most analyses, such as Cogswell's and Rides's, to estimate the extensional viscosity of the fluid - that is, the viscosity when considered in tension rather than in shear.

Materials with similar shear viscosities can have widely different extensional viscosities, which can cause severe processing difficulties.

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