BFR2100: A Remote Controlled Capillary Rheometer

BFR2100: A Remote Controlled Capillary Rheometer from Aptifirst

By: Aptifirst  23/07/2013
Keywords: extrusion, High Pressure, process solutions

The BFR2100 was a version of our ACR2100 Capillary Extrusion Rheometer modified for use with hazardous materials, namely explosive and propellant compositions. The instrument design was carefully vetted to ensure that there were no "blind holes", incompatible materials or metal-on-metal contact that could give a spark. All possible electronics and control systems were located in the control room (photo), with intrinsically safe Galvanic barriers being used to ensure that no instrumentation cables could generate a spark if cut or shorted. Limit switches were double-banked as a precaution. A capillary extrusion rheometer is a highly accurate, instrumented piston-based extrusion press, with a servo-drive system being used to control the piston speed over a very wide speed range of about 60,000:1. A melt pressure transducer is fitted in the barrel wall just above the entrance to the die (capillary), and a load cell was fitted as a precaution on top of the piston, as some materials can stress-crystallize or bridge with the result that the pressure transducer registers little load, but there is full load upon the piston. The maximum pressure of the instrument was 30,000 psi (2,100 bars), the maximum piston load 10 tonnes, and the maximum piston speed was >1,000 mm/minute. Electrical heating was used, with an independent "policeman" fail-safe temperature monitor to ensure that the temperature of the barrel did not exceed a pre-set maximum. The instrument was used to determine and study the rheology or flow properties of a range of highly-filled, multiphase pastes, with the data aiding with formulation and die design, and with the development of new processes. The experiment is basically to extrude the test material at a series of controlled speeds through a precision-machined die of known geometry; a plot of, in essence, speed against pressure gives a characteristic rheogram for the material. Extrusion through a series of dies allows corrections for machine geometry to be applied, and also allows an estimate of the extensional viscosity to be made as well as the shear viscosity. The extensional viscosity depends on tensile forces, and is important in high-extension processes such as extrusion, wire coating and injection moulding. Additional information may be deduced by measuring die swell - the tendency of extruded materials to swell after they have passed through the die, using an adapted laser micrometer, and also by measuring the surface temperature of the extrudate by used of a close-focus infra-red pyrometer. The BFR2100 also had a manual drive shaft which passed through the wall of the extrusion chamber into the control room so that, in the event, for example, of a power failure, the piston could be raised manually and remotely and thus avert the potential danger of a confined mass of energetic material. One feature of capillary extrusion rheometers which is worthy of note is that they are excellent process mimics and can be used to extrude test samples for further testing and evaluation.

Keywords: Business Process Solutions, Die Swell, elongational flow, explosive, extrusion, High Pressure, high shear rate, highly filled, instrinsically safe, process solutions, Propellant, rheometer, viscous heating,