Crush strength, powder

For the two explosive loading systems used, the initial pressure wave into the powder is relatively low, varying from perhaps 1.5-4 GPa. In such cases the most relevant compression characteristic of the powder compact is its crush strength , i.e., the pressure required to compress the porous compact to solid density. In the simulations, this strength can be varied over a wide range with the P-a model. The wavespeed of the initial waves was modeled on the basis of shock-compression data on rutile at densities from 44% to 61% of solid density [74T02]. 

The influence of crush strength on mean-bulk temperature achieved in one-dimensional compression of powders has been extensively investigated... 

Fig. 6.8. The peak mean-bulk temperatures predicted in one-dimensional numerical simulation are investigated for powder compacts of different crush strengths. For the explosive loadings of the Bear fixtures, no difference in temperature is predicted for crush strengths up to about 2 GPa. This value is about that of the initial loading wave into the samples. Above that pressure the crush strength has a strong effect on temperature. The predicted behavior can be understood in terms of the various loading paths.

The mechanical strength of a tablet plays an important role in the development and control procedures. Crushing strength is the most widely used test of mechanical strength. It is defined as the compression force that, when applied diametrically to a tablet, just fractures it. Tablet hardness depends on the weight of material and the space between the upper and lower punches at the moment of compression. Inconsistent hardness values are likely to result from variation in these parameters. The fundamentals of powder compression are given in a report by Leuenberger and Rohera. ... 

The basic powder compression operation of a rotary tablet press is rather simple and is essentially the same from machine to machine (Fig. 14). The powders are compressed by passing the upper and lower punch between two rollers (or cams), thus mechanically driving punches towards one another to a specified target tip separation. The distance between the rollers can be adjusted to control the maximum degree of powder consolidation within the die (i.e., minimum tip separation), which has a direct influence on final tablet properties, such as thickness and crushing strength. 

Compaction simulators are most commonly used to replicate the compaction process of a rotary tablet press. Manufacturing parameters, such as production speed, dwell lime, compression force, precompression force are often studied using a relatively small quantity of bulk powder. These parameters can significantly affect tablet crushing strength, friability, and disintegration time. The relationship among compaction pressure. 

Compression force is the major driving force in the powder densification process. The rate and extent of the applied force on the powder bed not only affects the way panicles physically deform but also determines the integrity of the compact formed (crushing strength/tensile strength). 

Figure 51. Comparison of the tensile and crushing strengths of spherical green agglomerates made from differently sized limestone powders...

A simple, low-cost fibrous binder component that is available everywhere can be obtained by grinding waste paper. Fig. 8.25 is the flow diagram of a plant for the production of paper fluff from, for example, old newsprint as a binder for use in a roller press briquetting plant. This cellulosic material mixes quickly and uniformly with dry powders in any kind of blender. Even small percentages (2 %) result in a marked increase in (crushing) strength if compared with two other common binders (Fig. 8.26) [8.2.1]. 

Fig. 8.27 Cold crushing strength of briquettes from metal-bearing dust and sludge containing different amounts ofd lignosulfonate binder (called sulfite waste powder ) with and without reinforcement by the addition of swarf [B.48, B.97]...

A dental cement has been prepared by mixing an acrylic acid-maleic acid copolymer 7500 (44 parts), water (44 parts), and tetrahydrofuran-2,3,4,5-tetracarboxylic acid (169) (12 parts). This mixture (1 g) when mixed with denM cement powder (1.4 g) had a setting time of 4-6 min and a crushing strength of 1490 kg cm as compared with 4- min and 700 kg cm" for regular cement... 

---