Tensile tester for assessing the tensile strength of compacted powders

AJAX Tensile Tester

1. Introduction.

A stainless steel horizontal split circular cell is fixed on one half of the machine with the other part mounted on a pivot block supported in low friction radial bearings. The assembly has a stainless steel body on which is fitted a clamping screw, to secure the cells for loading, and both a tensioning screw and an adjusting screw assembly for setting the initial null balanced loading on the cell. A counter is directly coupled to the tensioning screw for recording the precise spring extension. A filling collar and loading plug are supplied with the machine. The machine may be used with pre-weighed samples to establish the density of product when tested, or loaded by means of weight compaction.

2. Method.

A sample of material is prepared in a diametrically split cell to a predetermined state of compaction. The cell is then subjected to an increasing separating force applied by means of null balances low hysteresis springs tensioned by a lead screw. The stress at tensile failure of the sample is obtained from a counting device on the loading screw in conjunction with a calibration graph.

3. Uses.

Tensile strength is a fundamental property of a powder and provides a terminal point of the yield loci of failure for samples in differing states of compaction. The way in which material holds up in arches formed over hopper outlets, and the breaking strength of tablets and the like, are influenced by the tensile strength of the material. The results obtained from the Ajax Tensile Tester can be used in relation to the identification of properties for a variety of needs, including:

Design The results allow completion of the family of failure curves which, in conjunction with the cohesive strengths at similar compactions, will assist in the determination of the failure pattern within the material at low stresses - hence the derivation of the yield surface.

Quantification of properties For identification of material, correlation, classification and categorisation of powder samples with relation to like and dissimilar materials. Establishing the effect of major or minor changes of the primary properties of the material specification, e.g. particle size, moisture content.

Significance Tests To establish the relevance of variations in the material to behavioural characteristics or plant operation and the sensitivity of same.

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