Compression and Wafering of Hay. (I)

Compressibility and Power Requirements

Abstract

From the experiments of the compression and wafering of hay or pasture (ladinoclover and orchardgrass) by the piston and cylinder type compression tests, the following results were obtained:
1. Some sap ran off and the compression force requirements increased steeply when the final density of hay exceed over a limit.
2. The characteristics of compression of hay or pasture were just like powder, and the following linear equation was obtained in relation between σ and σ/ε,
σ=a+bσ/ε
where σ is stress, ε is strain, a and b is constant.
3. The maximum strain value of 23.5% moisture contents ladinoclover and 19.6% moisture contents orchardgrass were 0.8 and 0.808, in each sample, at this time the stress increased infinitely.
4. The compression stress p for the equal strain value of orchardgrass were larger than that of ladinoclover, perhaps because the more fiber content and stronger stiffness of the former than the latter.
5. The compression ratios of samples were 4-6 at a low moisture contents and 3-5 at a high moisture, but the difference of the compression ratio between ladinoclover and orchardgrass was very little. They increased linearly with increase of final dry weight density ρd.
6. Pasture and hay showed rheological characteristics.
The degree of stress relaxation increased with increase of sample moisture contents and that of orchardgrass was smaller than ladinoclover and disappeared after about two minutes.
7. The compression force P increased exponentialy with increase of final dry weight density ρd, which of orchardgrass was larger than ladinoclover at low ρd, but their relations were inverted at high ρd.
8. The compression force P and stress P increased as the height and volume of the formed wafer increased if sample moisture, ρd and diameter of formed wafer were equal, with the exception of high moisture samples.
9. When the kind of hay, moisture contents, ρd and forming height were the same, to decrease the diameter of formed hay gave an increase in the compression stress p, and the difference of compression stress between rations diameters increased as ρd increased; therefore, it was supposed that the ratio of friction between wafer and cylindrical chamber wall was relatively large.
10. As for the same kind and the same moisture content of hay, the force P requried to compress from a certain initial volume to a certain ρd decreased with the decrease of the diameter, especially in case of low moisture contents, therefore, it was sujested that the slender forming of hay is desirable from the view point of the power requirements.
11. The Compression force P was constant or reduced as the forming height of hay increased at a high moisture contents.
It was considered that the facts in the above three items depended on the rheological characteristics and ununiform compression of hay.