Melt strength is measured by pulling the extrudate as it emerges from the die and increasing the speed while measuring the force on the melt. In this test the principal data required is Force against Haul-off speed. There are two principal definitions of Melt Strength widely used :
◎The Force at failure (Speed is also recorded in this event).
◎The Force at a defined speed (less common).
Note：The stability of these processes also depends on the Extensional Viscosity of the melt.
The Imatek Melt Strength System
Great sensitivity is required to measure the small forces involved (typically a few grams), but the system must also be highly robust to survive real-life experiments. Imatek uses the unique Tragethon system (Figure 1) to provide this rare combination.
Haul-off speeds must represent those used in the processes being modelled. Rosand therefore offer the Haul-Off with an exceptional speed range from
1 to 1000 m/min to represent both the fibre-forming and blow-moulding processes.
For even greater versatility, the system can be used with
Safety Note：The Imatek Melt-Strength Option has safety systems to full CE requirements.
The system is illustrated in Figure 1. All systems are supplied complete with
◎Speed control and measurement system to provide speed ramps and set speeds from 0.5 to 1,000 m/min. Other speed ranges are available - please discuss your needs with Imatek Asia.
◎High-precision, high-sensitivity melt-tension measurement system, with support stand
2N Capacity, 0.0002N Resolution.
◎Computer interfaces to provide complete control of the test.
•Provide ramp speeds or speed steps and to monitor melt tension and diameter (when used with the diameter gauge option).
•Analyse Data, and provide the required graphs of Force vs Haul-Off speed.
◎Calibration mass for the melt tension measurement system.
Typical Haul Off Speed;
Blow molding : 0-70m/min.
Fiber Spinning : 0-300m/min
Die Swell Measurement Option
Imatek offers 2 kinds of Die Swell measurement options;
1.Laser Die Swell
2.CCD Die Swell
1) Laser Die Swell
As shown in the Figure, Imatek die swell systems are supplied with full features which provide both operation and accuracy benefits.
◎Heat shield. This allows the unit to be used as near as possible to the die exit.
◎Height-adjust support system, for measurement versatility.
◎Swing-arm to maintain convenient rheometer use when the Die swell system is not in use.
◎Independent Digital display of the diameter, conveniently mounted near the rheometer.
◎Full interfaces to the control computer.
◎Dedicated, easy-to-use Software captures the data and provides the graph as illustrated overleaf.
2) CCD Die Swell
We proud to announce the CCD Die Swell system. This system avoids the height adjustments of the Die Swell measurement system, because intelligent image analysis software determines where the biggest swell point is and records that data.
|Range of diameters (mm)
||0.08 to 30
||0.1 to 30|
p-v-T Measurement Option
The reason to measure pvT
Polymers are processed at high temperatures and pressures. An important relationship needed to model any process is the relationship between Pressure, Volume and Temperature (PVT).
Imatek Comparative PVT Method
Comparative PVT is measured in the Imatek R6000 rheometer by the following process
a)A defined volume of melt (V0) is sealed in the rheometer.
b)The volume is changed (ΔV) and the change in pressure is measured.
c)The Temperature is controlled and maintained.
d)The required curve of Pressure against volume strain ( ΔV/V0 ) is derived.
The PVT Option provides:
1.Active-seal piston tip system.
2.die deal system.
3.Software to ◎Control experiment
◎Provide defined V0.
◎Store and retrieve data
◎Produce tables and graphs
Seals in the standard PVT system are designed for use at temperatures up to 250 oC
Slit Die Option
The Slit Die System has been designed primarily as a tool for use in conjunction with extrusion processes. The benefits of slit die rheometry are that no Bagley correction is required to obtain the true shear stress since pressure is measured using three pressure transducers. For equivalent polymer volumetric flow rates the rectangular geometry will yield lower maximum shear rates than those of a capillary, but consistent with those expected in extrusion.
The Imatek slit die is a modular construction allowing easy slot dimension changes. The slit geometry is machined into a changeable insert, thus only the insert has to be changed if a change in slit height is required. This construction allows great flexibility over slit dimension and thus shear rate. The maximum and minimum slot geometry combinations are;
widthmax (bmax) =12mm
widthmin (bmin) =9mm
heightmax (dmax) =4mm
heightmin (dmin) =0.5mm
||aspect ratio (b/d)|
The system includes;
◎An independent, temperature controlled, ceramic heater.
◎Platinum Resistance Thermometer (PRT).
◎Two additional software interfaced Pressure transducers*.
◎Insert(s) with appropriate slit dimensions.