Rosand Twin Bore Principle

Malvern was the first manufacturer to introduce the twin bore measurement principle in a commercially available rheometer unit. Simultaneous measurements can therefore be made on both long and short dies to determine the inlet pressure drop at the die, and therefore absolute viscosity, using the Bagley method. More commonly, Rosand 'zero length' dies are used to directly measure the inlet pressure drop and measure the extensional viscosity using the Cogswell method. The twin bore rheometer technique gives obvious experimental advantages including improved throughput since both experiments are preheated simultaneously. Alternatively, the software can be configured to run a two material test, thus measuring the apparent viscosity of two different materials simultaneously.

Rigid 'H' frame design

The 'H' frame design principle gives a vertical frame stiffness well in excess of that achievable with cantilever or 'C' frame designs. The frame design is effectively rigid at loads many times in excess of the 100kN measurement limit. This is an important consideration in transient tests such as PVT, which rely upon compliance free measurement for accurate volume determination.

Bi-Modal speed control.

Malvern has developed a bespoke Bi-Modal digital speed control technology to control the latest generation of capillary rheometers. The technology uses different speed control algorithms suited to high and low speed rheometer operation in order to optimize performance. This gives the rheometer units an impressive dynamic range in speed control. In practice, the lower limit is determined only by long experimental times at low shear rates but a dynamic range in speed of in excess of 400:000:1 is available if required. This greatly enhances the rheometer's flexibility and means that a greater range of shear rates can be covered using a particular die.

Integral fume chamber with extraction

For operator safety, the RH7 and RH10 capillary rheometers are equipped with a safety interlocked fume chamber with fan extraction of the gases to a vent at the back of the rheometer unit. An extractor fan is also situated below the rheometer barrel.

Floor standing design

The floor standing design affords the rheometers with an open architecture below the barrel and heater assembly. This space can be used to accommodate other experimental options such as die swell measurement, a slot die, haul-off (melt strength) and a haul-off (post-extrusion) oven.