Pellets compression testing

D.S. Cahn and J.M. Karpinski, Compression testing of green and dry iron ore pellets, Trans. Amer. Inst. Mining Eng., 241 (1968) 475—481. 

Compression testing of coated pellets has recently received attention in the pharmaceutical literature, as researchers compress these pellets into the more tamper-resistant tablet dosage form. " " Methods to quantify the compression properties of coated pellets have been discussed elsewhere. " "" The compres-sional forces used during tableting are critical and, if... 

Pellet crushing tests can determine compression strength. 

Breakdown by confined compression can be tested in a compression cell similar to that in compaction tests, except that the normal forces used are greater here. A British Standard method59 packs a sample of specified quantity and size grade into a steel cylinder, 150 mm nominal diameter a plunger is inserted into the open end of the cylinder and the whole compressed in a compression testing machine. The load is slowly increased up to 400 kN and the product is then sized. A similar test has been used in assessing friability of pellets and coal. 

The pellets physical property and metallurgical performances are shown in Table II which were tested by the relevant standard of COREX. Pellets with 2670 N pellets compressive strength have a porosity of 22.27%. The reduction degradation and reduction swelling indexes are low. The softening temperature is 965"C. Thus it can be seen that self-fluxed pellets can meet the requirement of raw materials for COREX. 

We can also resort to a diametric compression test, also known as the Brazilian test, for evaluating the tensile stress [CLA 70]. This test, which is particularly suitable for raw materials or for bars (non-sintered products), consists of compressing a pellet monoaxially (diameter D , thickness t) following a diametric direction. The breaking stress is then deduced from the mpture load using the following relationship ... 

The average elastic stiilhess of this waU-peUet-wall-systems results from sequence contacts (Antonyuk et ah, 2010). Hence, the equivalent contact stifBiess (fen.d.p). usually measured by a compression test, equals half the stiff"-ness of a pellet (fen.ei,p) ... 

The particle deformation and breakage behavior can be illustrated by means of the measured force-displacement curves. A typical force-displacement curve for the investigated sugar pellets is shown in Fig. 9. The force F characterizes the contact force between stamp and particle. The distance 5 shows the corresponding displacement of the particle. AH compression tests were carried out up to a compressive strain of 20%. 

To predict the real interactions of the particles in the FB, their material properties were obtained experimentally and used as parameters of DEM contact model. The deformation and breakage behavior of pellets were obtained with the help of single particle compression tests. The energy loss during the collisions was obtained by means of free-fall impact tests. 

Stmcture is usually measured by a void volume test such as the absorption of dibutyl phthalate (DBPA) (15), or by bulk density measurements of the carbon black under compression. In order to eliminate the effects of pelletizing conditions the DBPA test has been modified to use a sample that has been precompressed at a pressure of 165 MPa (24,000 psi) and then broken up four successive times (24M4) (16). This procedure causes some aggregate breakdown and is claimed to more closely approximate the actual breakdown that occurs duting mbber mixing. 

In the method, a weighed portion of a sample of coke dried at 110°C (230°F) and crushed to pass a No. 200-mesh sieve, mixed with stearic acid, and then milled and compressed into a smooth pellet. The pellet is irradiated with an x-ray beam and the characteristic x-rays of the elements analyzed are excited, separated, and detected by the spectrometer. The measured x-ray intensities are converted to elemental concentration by using a cahbration equation derived from the analysis of the standard materials. The K spectral lines are used for aU the elements determined by this test method. This test method is also apphcable to the determination of additional elements provided that appropriate standards are available for use and comparison. 

The mechanical properties (compression strength and % compression) are determined by Instron Universal Testing Machine using a pellet of 20mm x 20mm pressed at a pressure of 1000kgcnf2 similar to the method used for plastics [68]. 

In this method it is possible to det the blow or pressure developed by an expl over a small measurable interval of time and this is a measure of the violence(brisance) it exhibits. The principle on which the determination of the pressure is based depends on the fact that when a chge is fired against the end of a cylindrical steel bar, bal-listically suspended, a wave of compression travels along the bar and is reflected at the far end as a wave of tension. For details of measuring pressure by this method see B.Hopkinson,PhiITrans 213A,437(1914) and Vol 1 of this Encyclopedia, p XVI. Following are results of tests by this method expressed as pressure in tons per inz in 0.5 10 5 sec(with constant pellet interposed) ... 

He found hexanitrodiphenylamine to be slightly less sensitive in the drop test than tetryl and tetranitroaniline. When 1 pound of the explosive was loaded into a 3.5-inch cubical box of cardboard or tin and fired at with a U.S. Army rifle from a distance of 30 yards, hexanitrodiphenylamine gave no detonations in the cardboard boxes, and 7 detonations and 1 failure in tin TNT gave no detonation in cardboard, fire and detonation in tin and tetryl and tetranitroaniline gave detonations in every case with either kind of container. Marshall reported the velocity of detonation of hexanitrodiphenylamine to be 6898 meters per second at density 1.58, and 7150 meters per second at density 1.67. Pellets of the explosive, mixed with 1 per cent of stearic acid, compressed at 5000 pounds per square inch, had a density 1.43, at 10,000... 

A series of pulsed electron beam tests were conducted on dextrinated and RD-1333 Pb azide pellets by Avrami et al (Ref 232), From the limited data in Table 14 it can be seen that sample ambient pressure, sample thickness and type of Pb azide are all important factors in the sensitivity of initiation by pulsed electron beam The question arises as to what mechanism can explain the observed pressure, thickness and type of Pb azide dependence. A purely thermal initiation mechanism or a compressive shock initiation resulting from nearly instantaneous energy deposition can account for some of the observations but not all... 

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