Lower Punch Force Research Articles

Influence of surface integrity on the plastic flow in analogous testing of 42CrMo4

Surface modification of workpieces for cold forming processes is common in industrial practice. Specific surface topographies manufactured by means of shot peening form lubricant pockets, which provide a continuous lubricating film throughout the process. Furthermore, hydrostatic as well as hydrodynamic lubrication effects emerge, which further reduce the friction during the process and protect the tool from wear effects. These effects are well researched and applied in order to enable cold forming processes. In dry forming processes, no lubricants are used, and the positive lubrication effects do not appear. Surface modifications by shot peening or knurling change surface integrity in terms of hardness, residual stresses and geometry. The effects of the changed surface integrity on the forming process are not researched. In tribometer tests, a hard and rough surface texture lead to a lower frictional shear stress, whereas a rather smooth and hard surface texture leads to a lower punch force in an extrusion process. The mechanisms between surface textures and the smoothing and forming process are unknown. Furthermore, findings of the tribometer tests cannot be fully transferred to the extrusion process. As in tribometer tests a pin is used as tool and in extrusion a whole die, a discrepancy between the most suitable surface texture for a friction reduction results out of different flow conditions. Still, the tribometer tests give a first reference on a surface pretreament. The paper deals with an investigation of surface textures in order to distinguish characteristics of surface textures respectively a friction reduction. By means of indentation tests of the quenched and tempered steel 42CrMo4 the plastic flow in dependency of different surface integrities are researched. The results show which characteristics help to lower the punch force the most, so for further investigations an optimized surface modification is set up in order to enable a dry metal forming process.

Formulation and in vitro evaluation of theophylline matrix tablets prepared by direct compression: Effect of polymer blends

The deformation mechanism of pharmaceutical powders, used in formulating directly compressed matrix tablets, affects the characteristics of the formed tablets. Three polymers of different deformation mechanisms were tested for their impact on theophylline directly compressed tablets namely Kollidon SR (KL SR, plastic deformation), Ethylcellulose (EC, elastic deformation) and Carnauba wax (CW, brittle deformation) at different compression forces. However, tablets based mainly on KL SR, the plastically deformed polymer (TN1) exhibited the highest hardness values compared to the other formulae which are based on either blends of KL SR with CW, the very brittle deformed polymer. The upper detected force for TN formulae and the lower punch force were found to dependent mainly on the powder deformation. This difference is attributed to the work done during the compression phase as well as the work lost during the decompression phase. Furthermore, the release profiles of TN from formulae TN2 and TN4 that are based on the composition (2KL SR:1EC) and (1KL SR:2EC), respectively, were consistent with different deformation mechanisms of KL SR and EC and on the physicochemical properties like the water absorptive capacity of EC. Upon increasing the weight ratio of KL SR (TN2), the release rate was greatly retarded (39.4%, 37.1%, 35.0% and 33.6% released after 8h at 5, 10, 15 and 20kN.

錠剤のスティッキングに及ぼす打錠圧力及び臼壁面圧力の影響

An eccentric-type tablet machine fitted with 8-mm-diameter flat-faced punches was used to measure the forces of upper and lower punches, die-wall pressure, tablet ejection force, and scraper pressure (SCR), a type of shear stress, to evaluate sticking behavior. The shear stress between the surfaces of the tablet and lower punch was determined using an SCR detection system. Mean surface roughness (R(a)) of tablets, measured by laser scanning microscopy, was used to estimate the magnitude of sticking. Tablet tensile strength tended to increase with compression pressure, which is consistent with previous reports. SCR decreased with increasing compression pressure for samples at all formulations (i.e., for different kinds and percentages of lubricant). R(a) associated with sticking increased with SCR, indicating that the adhesive force between the particles of the tablet surface and the lower punch surface plays an important role in sticking. Multiple linear regression analysis with SCR as the response variable was conducted. Upper and lower punch force, die-wall pressure, tablet ejection force, SCR, percentage of lubricant, and tensile strength of tablet were selected as explanatory variables. Results of this analysis indicate that the incidence of sticking decreased when either the lower punch force or die-wall pressure increased, where, of these two, increasing the lower punch force had a stronger effect on decreasing SCR.

Influence of the punch diameter and curvature on the yield pressure of MCC-compacts during Heckel analysis

The volume reduction behaviour of powders has been quantified by means of the 'in-die' yield pressure (YP) using Heckel analysis. However, because different YPs are reported for the same material, the experimental conditions influencing this material-constant were investigated. Silicified microcrystalline cellulose was compressed into flat-faced and convex tablets using a compaction simulator instrumented with load and displacement transducers. During compression, upper and lower punch force and displacement data were recorded and corrected for punch deformation. A symmetrical triangle wave compression profile was used and the instantaneous punch velocity was kept constant (5mm/s). Individual tablet height and weight were used for Heckel analysis. The influence of the 'effective compression pressure' (P(EFF)) (ranging from 10 to 350 MPa), punch diameter (PD) (4, 9.5 and 12 mm) and filling depth (FD) (4.5, 7.5 and 10.5mm) on YP was statistically evaluated using Response Surface Modelling software. A quadratic surface response equation, describing the relationship between P(EFF), PD, FD and YP, was proposed for concave (Adj R(2): 0.8424; S.D.: 14.60 MPa) and flat-faced (Adj R(2): 0.8409; S.D.: 4.49 MPa) punches. YP and tensile strength were mainly determined by P(EFF), irrespective of punch curvature. FD and PD had only a minor influence on the YP, although more pronounced for the concave punches. The method used resulted in reproducible P(EFF) and tensile strength values and the flat-faced tablets showed less weight variation. Flat-faced punches are preferred over punches with a concave surface when investigating the volume reduction behaviour of a powder by means of Heckel analysis and the experimental parameters should be reported.

Friction-actuated blank holding in deep drawing

A new method of blank holding in deep drawing has been introduced by the first author. In this method, a urethane pad between two parts of a drawing punch, when compressed by the drawing force applies lateral pressure on the tubular part of a blank holder. As the punch moves to draw the blank, friction between the urethane pad and the blank holder automatically applies the blank holding force. An experimental rig with this type of blank holding was constructed and aluminium, copper and brass cups were drawn. Tests were also conducted with constant-force blank holding for comparison. Results indicate lower punch force, modest increases in limiting draw ratios and less thickness variations when compared with cups formed under constant-force blank holding.

Tablet compaction to a constant load

In studies of tablet compaction, it is usual to work at constant tabletting force (or pressure) or to correlate the tablet properties with the force. Owing to the friction between the tablet and the die wall, different forces are obtained on the upper and lower punch and it is not obvious which of the values is the most relevant one to use. In most studies on instrumented reciprocating tablet presses, the maximum upper punch force (UPF) is regarded as the tabletting force but the mean of the UPF and the maximum lower punch force, (LPF), has also been used (e.g. by Hersey et al., 1967). The lower punch force has been claimed to be independent of the die wall friction (Lammens et al., 1980, 198 1) and would be a useful measure of the tabletting force. There seem, however, to be few experimental data supporting the choice of the different force measures or their importance in compaction studies. In a recent study (Ragnarsson and Sjogren, 1983) we compressed a number of tablets of sodium chloride, anhydrous lactose and saccharose in a die which was lubricated at the beginning of each series. No lubricant was added during the series and the die wall friction consequently increased while all other factors were kept constant, As illustrated in Fig. 1, both the UPF and the LPF were affected by the

The Physics of Tablet Compression: IV. Relationship of Ejection, and Upper and Lower Punch Forces during Compressional Process: Application of Measurements to Comparison of Tablet Lubricants

The relationship of the upper and lower punch forces and the ejection force during the process of tablet compression has been studied. Large differences may exist between the maximum force exerted by the upper punch and the maximum force obtained at the lower punch. When such differences exist, substantial forces are needed to eject tablets from the die. The magnitude of the difference between the maximum upper and lower punch force and the magnitude of the ejection force appear to be linearly dependent on the area of the tablet in contact with the die wall. The value of the ejection force and the difference between the upper and lower punch forces are both markedly affected b the presence of lubricants. With a well-lubricated granulation the force exerted by the upper punch is essentially the same as that transmitted to the lower punch and a negligible force is required to eject the tablets from the die. A quantitative method for evaluating lubricants on the basis of these observations is suggested.