Flat punch displacement

A standard IPT Type B tooling was used with a f " round flat tool tip. Tablets were made one at a time, and the compression force as well as the upper punch displacement and lower punch displacement were recorded. Tablet weight, thickness, and breaking hardness were measured for each tablet. 

Mechanical Definitions of dwell and contact times disregard material properties and concentrate on press and punch geometry (Fig. 17). Contact time can be defined as the time the punch is in contact with the compression wheel. Dwell time is defined as the time the flat portion of punch head is in contact with the compression wheel (time at maximum punch displacement, or time when the punch does not move in vertical direction). In dwell time calculations, the length of the punch head flat and horizontal component of punch speed (as determined by RPM and pitch circle diameter) are used. In case of a round head tooling, the dwell time, as defined here, is zero. But it should be kept in mind that mechanical definition is given here as a convention, a yardstick, or a common measure, to compare press speeds for different presses, and its absolute value is meaningless. A proposed convention to quantify linear speed of a press is to use an... 

In practice, theoretical and actual punch displacement profiles on a rotary press have very little in common because the theoretical profile does not account for several mechanical factors, such as punch head flat. Moreover, the punch movement equation was derived for a punch moving in and out of an... 

Compact density and its distribution is also strongly influenced by interactions between the solid particles and of the particulate mass with equipment features (e.g. die walls, punch surfaces, roller press pockets, etc.). If a perfectly lubricated particulate solid (i.e. featuring no interparticle friction) were compacted in a cylindrical die with frictionless walls, it could be expected that the force exerted by the smooth, flat punch is transmitted through the entire volume of material resulting in uniform pressure and, therefore, uniform density throughout the compact. In reality, the presence of frictional and shear forces leads to a non-uniform pressure distribution and irregular particle movement (displacement) causing variations in compact density. 

The case of an axisymmetric flat punch of radius a on an elastic half-space was solved by KendalK7) by evaluating the elastic energy = iPb and the potential energy Up = —from the elastic displacement under the load P ... 

Here, E and v are the Young s modulus and Poisson s ratio of the half space material. The indentation of a flat punch on an elastic half-space is proportional to the applied load. The contact area stays constant independent of load. We obtain a linear relation between load and displacement with an effective spring constant of E a/(l — v ) = E a. The vertical surface displacement Az(r) of the elastic half-space is given by... 

The vertical displacement outside the contact area is the sum of the displacement of a Hertzian contact under load Ti and a flat punch under a tensile force of Fi-Fl-... 

Calculate the adhesion force Tadh and critical displacement 6c at which separation between flat punch of steel with a diameter of 5 cm and a PDMS half-space occurs. The Young s modulus of steel is 200 GPa and its Poisson s ratio is 0.27. For PDMS, a Young s modulus of 2 MPa and a Poisson s ratio of v = 0.5 are assumed. The adhesion energy iVadh between the steel punch and the PDMS is assumed to be 50 mj m . ... 

Figure 1 shows tablets (300 mg) of native dextran obtained from Leuconostoc mesenteroides B-512F (Sigma) with a 10% water (w/w) punch in an eccentric machine (Manesty) at 15 kN with tablet side (flat-flace diameter) 10mm. Axial displacement of water was observed according to the change in color. 

An observed penetration depth rewritten as 8=8h+(8-Sh) corresponds to the addition of a vertical displacement 5-6h at constant radius of contact ou, that is to say to the addition of the vertical movement of a flat rigid axi-symetrical punch inducmg a strong divergence of the normal stresses on the border of the contact area. 

Figure 8.5 Radial displacements -Ar/6 for different values ofthe Poisson s ration for indentation of an elastic half-space by a flat cylindrical punch with contact radius a.

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