Gieseler plastometer

Plasticity can be studied using a device known as the Gieseler plastometer. A constant torque is appHed to a shaft with rabble arms imbedded in coal in a cmcible heated at a fixed rate. The rate of rotation of the shaft indicates the duidity of the coal and is plotted as a function of the coal temperature. These curves, as shown in Figure 8, have a well-defined peak for coking coals usually near 450°C. Softening occurs at 350—400°C. At a normal heating rate of 3°C/min, the duid hardening may be complete by 500°C. 

Fig. 8. Plasticity curve obtained using the Gieseler plastometer. Heating rate is 2°C/min.

Testing with a Gieseler plastometer (ASTM D-2639) gives a semiquantitative measurement of the plastic property, or apparent melting of coal when heated under prescribed conditions in the absence of air. The chemical nature of the constituents that account for a coal s plastic properties is not known. The material thought to be responsible for the plastic properties of coal has been removed from coal successfully by solvent extraction, leaving a nonplastic residue. Such residue has been rendered plastic by returning to it the extracts obtained by the solvent extraction. No definite relationship has been established between the amount of extract and the plastic properties of the coal. 

The values normally determined with the Gieseler plastometer are ... 

ASTM D-2639. Test Method for Plastic Properties of Coal by the Constant-Torque Gieseler Plastometer. 

Data usually obtained with the Gieseler plastometer are (1) softening temperature (the tanpera-ture at which stirrer movement is equal to 0.5 dial divisions per minute) which may be characterized by other rates but if so the rate must be reported, (2) maximum fluid temperature (the temperature at which stirrer movement reaches maximum rate in terms of dial divisions per minute), (3) solidification temperature (the temperature at which stirrer movement stops), and (4) maximum fluidity (the maximum rate of stirrer movement in dial divisions per minute). 

Plastic properties of coal, as determined by the Gieseler plastometer, appear to be sensitive to oxidation, which can have a maiked effect in decreasing the maximum fluidity. In fact, prolonged oxidation may completely destroy the fluidity of a coal. To reduce oxidation, samples should be tested soon after collection or, if delay is unavoidable, storage under water or in a nonoxidizing atmosphere such as nitrogen is advisable. 

ASTM. 201 Ih. Method of Test for Plastic Properties of Coal by Gieseler Plastometer (ASTM D1812). Annual Book of Standards, American Society for Testing and Materials, West Conshohocken, PA. 

Test for Plastic Properties of Coal by the Gieseler Plastometer Test for Expansion or Contraction of Coal by the Sole Heated Oven Test for Plastic Properties of Coal by the Constant Torque Gieseler Plastomer Definition of Terms Relating to Lithologic Classes and Physical Components of Coal Preparing Coal Samples for Microscopical Analysis by Reflected Light Microscopical Determination of the Reflectance of the Organic Components in a Polished Specimen of Coal... 

Some of the most common methods to evaluate the suitability of a coal or coal blend for coke production are the free-swelling index test, Gray-King assay, Roga assay, various dilatometer tests, and Gieseler plastometer test. In addition, research using larger amount of coal sample is also performed by means of a pilot coke oven. 

The measurement of the fusibility (melting) of a coal (it becomes plastic rather than liquid on heating) is a difficult operation and use is made of a Gieseler plastometer shown in diagrammatic form in Figure 2.25. The plastometer heats the coal in an inert atmosphere in a crucible in which is located a stirrer, the energy supplied to whieh is kept constant. As the coal becomes fluid, the speed of rotation of the stirrer increases to a point of maximum... 

Figure 2.26 is a typical plot of fluidity, measured as ddpm (quite an arbitrary unit, but one which is established within the industry). Bituminous coals, used for active carbon production, have to be tested in this way. The Gieseler plastometer has proved to be a reliable instrument over many years for measurements of coal fluidity. There is one disadvantage, for which there is no answer, and that is the tedious operation of cleaning the stirrer and crucible after each testing. 

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