The effect of wall friction in the compaction of pharmaceutical tablets with curved faces: a validation study of the Drucker–Prager Cap model

Modelling Powder Compaction

The effect of lubrication in reducing net friction in warm powder compaction process

Experimental and numerical investigation of idealized consolidation: Part II: Cyclic compaction

Powder—wall friction: The effects of orientation of wall grooves and wall lubricants

The ‘pin and disc’ method has been used to measure the coefficient of friction for the following lubricants: aluminium, calcium, lithium, zinc stearates, and stearic acid. The variation of the coefficient of friction at the surface of iron compacts has been studied with respect to metal/metal contacts exposed through the lubricant film and the behaviour of the lubricant film with variations of pressures, temperature, and speed of sliding has been related to the variation in coefficient of friction for the system.The results for a range of zinc stearates are compared with those for other stearates for reduced iron powder compacts sliding against high-chromium die-steel.

The variation of coefficient of friction with temperature and compaction variables for iron powder stearate-lubricated systems*

Laboratory compaction and ejection studies have been made using a reduced iron powder mixed with a number of zinc stearates having median particle sizes between 4 and 22μm. Comparable experiments were carried out on a fully instrumented production press, which was operated at compacting pressures between 300 and 500 MN/m2 to produce compacts with true densities ranging from 5·90 to 6·70 g/cm3. Determination of ejection forces by the two methods enabled calculations of the coefficients of friction between compact and die wall to be made for mixtures containing 0·5–2·0 wt.% zinc stearate. These showed that the behaviour during compaction and ejection was comparable on both laboratory and production scales and gave very similar results. An interpretation of the results is given and values of coefficients of friction are presented which show that these are dependent on the type of zinc stearate used.

Friction coefficients between iron powder compacts and die wall during ejection using various admixed zinc stearate lubricants

A method of measuring the interparticle friction of metal powders under conditions of applied vibrational energy has been devised. With zero vibrational energy, the friction, expressed as an angle or as a coefficient, can be correlated with the basic characteristics of a powder, provided that the conditions of settling are standardized to provide consistent density values. The effect of the variation of settled density is shown. By the application of rectilinear sinusoidal vibrational energy to the powders, it can be shown how the variation and combinations of frequency and displacement effectively reduce interparticle friction, thus enhancing flow and settling of metal powders into dies offering difficult contours and restrictive sections.

D. S. Coleman

Papers

The variation of coefficient of friction with temperature and compaction variables for iron powder stearate-lubricated systems*

Friction coefficients between iron powder compacts and die wall during ejection using various admixed zinc stearate lubricants

The effect of vibrational energy on the interparticle friction of metal powders