Zwick improves accuracy and repeatability of melt-flow testing

Melt-flow indexers or “melt indexers” are used to determine the melt flow rate (MFR) of virgin and compounded thermoplastic resins and to evaluate incoming material and finished products. MFR is commonly used as a material-acceptance specification by processors. It also has many uses in quality control environments.

Zwick is pleased to announce its new Melt Indexer with an advanced heating system and many new and improved features for the measurement of melt flow rate (MFR) or melt volume rate (MVR) in quality control and research applications. The innovative heating and temperature control system achieves much better temperature accuracy and stability than existing products..

The melt-flow test is carried out according to ISO 1133 and ASTM D1238 and measures one point on the viscosity curve under standard conditions. Both test methods are technically equivalent but the way the test is run is different and this can lead to different results.  Zwick’s Mflow plastometer can automatically detect the most suitable parameters for MVR determination via its unique method of “parameter field programming”. The operator just selects “ASTM” or “ISO” or creates an individual parameter field.

Both test methods offer two variations of the standard melt-flow test: Method A and Method B. Method A requires relatively simple test equipment where a thermoplastic moulding mass is heated to its processing temperature and then extruded through a die of standardized dimensions under fixed load. It has a limited application range especially when the filament cutting is performed manually. The load and temperature to be used are determined by the material and the test method. The temperature is automatically controlled but all the measurements are performed by the operator.

Method B is much easier. It is based on the measurement of piston travel during the test and determines the mass volume rate (MVR) in cc/10 min. The operator simply loads the barrel with resin, starts the test and the instrument calculates the results. The main advantage of this method is that the procedure can be easily automated and the range of application is much larger. (0.08 to 600 cm³/10 min, depending on the resolution for piston travel and time measurement.)

There is no general consensus as to which procedure is the best. Zwick’s new melt indexer can be used to perform both tests. The optional motor driven filament cutter improves the accuracy of higher MFR results according to method A. The accuracy of filament cutting timing is significantly improved compared to manual cutting and measurements of MFR values higher than 10 g/10 min become achievable.

The optional travel transducer allows very accurate MVR measurements according to method B because the new digital measurement system has much higher precision than previous technology.

Another new option is the motorized lifting and lowering of the loading weight onto the piston. The optional automatic weight lift unit enables the test procedure to be entirely processor-controlled.

The Mflow Plastometer can also be used for testing without a PC, if required.

The complete system includes a PC and testXpert® II, Zwick’s software for materials testing, which enables control parameter setting and results administration to be carried out with ease. Up to 6 plastometers can be connected to one PC via USB, and connections to company IT infrastructures are possible for test result archiving and process control.  testXpert® II provides a traceable record of the gradient of temperature, position of piston and precise piston speed.

The intelligent software also detects and automatically eliminates the effects of air bubbles (gas inclusions) in the material so that they do not influence the test results and repeat tests are avoided.

Routine calibration is essential for the correct use of a melt indexer and requires the temperature and the dimensions of the barrel, piston and die to be checked. Zwick offers a comprehensive calibration service for its customers around the world.

About the Zwick Roell Group
The Zwick Roell Group is a global leader in automated materials and component testing systems.  With 150 years of testing experience and operating worldwide, it has manufacturing facilities in Germany and distribution and customer support headquarters in Atlanta, Georgia, USA, and Singapore.  As of 2006 the group has 900 employees and sells to 20 different industry sectors through a network of sales and service offices in 56 countries.   For more information see www.zwick.com