Celsum Technologies - Instrumentation for rheology, strain gages, pressure transducers, load cells, temperature control, sapphire window optical probes, precision extrusion dies, and much more.

Die Swell, more correctly called Extrudate Swell or the Barus Effect, is a result of the viscoelastic properties of a material. As the material is, for example, extruded out of a rheometer barrel through an extrusion die, there is often insufficient time for the long-chain molecules to relax into their new geometry and so, when the confinement of the die is escaped, the molecules recover in part some of their original positions, which results in the diameter of the extruded material being greater than the die diameter. The ratio of extrudate diameter to the die diameter is referred to as the Die Swell Ratio, often quoted as a percentage. Another effect of interest, for example in blow moulding, is the Draw Down Ratio, a measure of the change in the extrudate diameter as it is pulled downwards by the weight of extrudate previously extruded from the rheometer die.

CADS, above right, Celsum's new state-of-the art Advanced Die Swell monitor, is easy to set up, maintenance free, will measure consistently to an accuracy of 2 microns (0.00008"), has a high repeatability of ± 0.15 microns ( 0.000006") and can read at speeds in excess of 2 kHz.

Celsum has CEST, a Combined Extrudate Swell and Temperature system which combines the CADS optical micrometer with the CIRP Infra-Red Pyrometer, together with custom-designed mounts and a computer system with purpose-written software.

These figures are a factor of two better than conventional laser micrometers, yet CADS does not use a laser, but a very stable, low power, collimated green light source, which lends itself to applications where lasers are not permitted. The field of view is 30 mm (1.18"), and the smallest detectable object is 0.3 mm (0.012").

Additionally, the system is self-calibrating and automatically compensates for any changes in ambient temperature. The associated instrumentation package, which communicates with our rheometer software, has many features including edge-detecting logic for measuring transparent samples. We have selected this system as the transmitter and receiver may be placed quite a distance apart compared to conventional laser micrometers, and this allows plenty of room for changing the die and cleaning your rheometer without having to move your optics, and without the danger of your hot extrudate sticking to the optical windows!

CLDS, right, is our general-purpose, lower-priced on-line optical micrometer system. CLDS uses an infra-red semiconductor laser to provide a collimated light fan to illuminate the sample. In the receiver, which is physically separate from the light source, the light beam is focussed onto a light-sensitive receptor which produces an output voltage proportional to the amount of incident light.

When a target object is in the beam, the amount of light falling on the receptor is reduced proportionally to the size of the target object. Care must be exercised if the CLDS is used with transparent targets, and the system must be calibrated with a "standard" target at the working temperature, a procedure which is easily accomplished using the appropriate routine in our software suite. The field of view is 30 mm (1.18"), repeatibility is 10 microns (0.0004"), accuracy is 5 microns (0.0002") and the smallest detectable target is 0.2 mm (0.008").