Pressing Parameters Series - Filling Coefficient and Compression Ratio

1. Definition: filling coefficient: is the ratio of the particle density and compact density; compression ratio: refers to the height of powder grain filling to block height; filling coefficient and compression ratio is equal in value.

2. Influencing factors:
1) mixture particle size
The main factors to effect filling coefficient or the compression ratio is the packing density of powder, the powder density in the mold cavity is slightly greater than that of its bulk density. The smaller the particle size of the mixture, the smaller the bulk density and the larger the loading volume, the greater the fill factor or compression ratio. In fact, the effect of particle size composition on the bulk density of the powder is not single value, and is often determined by two roles of particle filling, voids and bridging. If the later is the main, then the powder loose density decreased, if the former is the main, then the powder loose density increased. The bulk density is usually measured with Hall flowmete, as shown in the following figure

2) particle morphology of mixture
There are many factors affecting the density of powder such as particle shape, size, surface roughness and particle size distribution. Generally, these factors are obviously different because of the different methods of making powders and their technological conditions. Generally speaking, the density of powder loose decreases with the increase of the non spherical coefficient of particles and the increase of surface roughness. In order to obtain the required density of powder, the reasonable grading and batching is a feasible method besides considering the above factors.

3. The meaning of filling coefficient or compression ratio:
The compression ratio is an important parameter to determine the height of the mold cavity. In production, the single weight control of the pressing blank requires the participation of the compression ratio parameter, and the weight of the compact can be given by the following formula:
M=ρloose •S die cavity • h • n
In formula:
M - the piece weight of blank
Ρ- bulk density of loose mixture
S die cavity - the sectional area of die cavity
H - height of pressing blank
n - compression ratio

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