Tables 2 and 3 summarize the data obtained in the linear cutting tests using a bit attack angle of 45°. All data points were used in computing the means; the mean for specific energy (Esp) was computed using the mean forces.

coal,

Figures 11-12 show the relationship between airborne respirable dust and Ep for each coal. The individual points show the mean values (from tables 2 and 3); the solid line is. the least-squares curve fit to all the raw data. The dashed line shows the upper 95-pct confidence limit. Of the five curvefit functions tried (power, exponential, linear, quadratic, and polynomial), the third-order polynomial gave the highest correlation coefficient. The least-squares equations and correlation coefficients (R) determined are as follows:

FIGURE 11. - Airborne respirable dust as a function of specific energy for Pittsburgh seam

1.16

11.6

116.0

g/ton

FIGURE 12.- Airborne respirable dust as a function of specific energy for Illinois No. 6 coal.

116

100.0

and Illinois No. 6 coal,

Y = -779,982.83+ 1,505,953.6X - 158,568.62x2 + 8,863.2502x3; R = 0.84,

where Y = airborne respirable dust (m3/g)

and X = Esp (j/g).

R2

= 0.71, (?)

These equations show that 71 pct of the airborne respirable dust is explained by E for Illinois No. 6 coal and 66 pct for Pittsburgh seam coal.

1.16

11.6

g/ton