EFFECT OF COTTON PREPARATION ON AFIS AND HVI MEASUREMENTS - 2
As the micronaire is used to calculate the beard mass (function of optical density and micronaire) for the strength test, any positive micronaire bias will lead to a negative HVI strength bias (Figure 2). In addition, the drawing process is similar in effect to an increase in the brushing time (or force) on the HVI combs. Taylor (TRJ, 1986, 93-102) has shown the effect of increasing brushing force on HVI strength readings. In his experiment two sample preparations were tested, hand brushing and HVI brushing (harder brushing than by hand). The results show an increase by 1.9 g/tex when using the HVI brushing device. In our case, we think that the drawing sliver samples have a lower optic density (for a given number of fibers in the comb) than the raw cotton. This results in a lower calculated mass of the sample to be broken. As the HVI strength is calculated by dividing the force applied to break the sample by the
As expected, the AFIS nep counts (Figure 3) increase with passage of the fibers through the opening line. The Mono- cylinder increases the average nep count by 75, then the first ERM (operating at 850 rpm) by 136 and the second ERM (operating at 950 rpm) by 240; that is 451 neps in total. The card removes 540 neps and the drawing frames have no effect.
The HVI reflectance (Figure 4) increases slightly after each cleaning stage. The drawing seems to also have an effect on the reflectance readings. This is not due to trash removal but more likely to an artifact because the paralleled fibers are not reflecting the light the same way as the randomly oriented fibers.
The changes in yellowness (Figure 5) are quite small but significant. The most important change is due to the drawing. This is, as for the reflectance, probably due to an artifact.
Combing affects AFIS Upper Quartile Length, Mean Length, Short Fiber Content and HVI Upper Half Mean Length and Uniformity Ratio. As expected the fiber length parameters all increase when the cotton is combed, with the exception of the Short Fiber Content. The drawing also affects the length parameters; as discussed before, it is probably an artifact. It is interesting to note that combing increases the length by 0.006 inch (minimum noil settings) and that the first drawing increases it by 0.027, i.e. nearly five times more. The artifact effect seems to be much more important than the real mechanical effect. The combing process seems to have no effect on the fiber diameter (Figure 6). The drawing, as discussed before, decreases the diameter (artifact). The HVI micronaire (Figure 7) increases when combing is applied, mainly because the removal of short, weak and immature fibers during the combing process increases the average maturity level. As discussed before the drawing has a positive effect on micronaire (artifact effect).
FIG:7 HVI STRENGTH:
The HVI strength (Figure 8) also increases with combing, because of the removal of short fibers. The drawing, as discussed before, increases the apparent HVI strength (artifact effect).
FIG:8 HVI STRENGTH
The AFIS neps (Figure 9) are removed during the combing process as expected (-62% for the minimum noil setting to -91% for the normal noil setting).
The combing also removes trash and dust. The decrease in trash is (Figure 10) nearly 60% for both types of settings. The decrease in dust (Figure 11) is about 40% for the minimum noil setting and 60% for the normal noil setting. As these are removed the HVI reflectance increases as expected and the yellowness decreases. The drawing effect on both parameters is an artifact, as discussed before.
FIG:11 AFIS DUST
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