WATER JET CONFERENCE - Waterjet Technology Association

high-velocity water jet is based on these ways the following schemes of breakage by a
water jet and a double-sided-wedge rim disc cutter are possible:
(a) a front scheme when the inter-slot pillar is broken by a disc cutter rolling directly
along the pillar in its symmetry plane (Fig. l,a);
(b) an one-sided scheme (Fig. l,b) when the pillar is broken towards its exposed surface
by the side of the wedge rim of the disc cutter thrust against the side surface of the
pillar and rolling along the slot between the pillar and the main part of the coal
massif;
(c) a two-sided scheme (see Fig. l,c) when the disc cutter breaks simultaneously both
pillars while rolling along the slot cut by a water jet between these two pillars; and
(d) an one-sided scheme of breakage with a floating attachment of the disc cutter (Fig
l,d). In contrast to the rigid attachment (Fig l,b) which allows but one degree of
freedom for the disc cutter (its rotation), the floating attachment provides for two
degrees of freedom (besides rotation the disc cutter can reciprocate).
For breaking a coal massif by a water jet and a disc cutter with single-sided
wedge rim, two one-sided schemes are possible: either the depth of the disc cutter thrust
is greater (Fig. l,e), or it is smaller (Fig. l,f) than the depth of the slot cut in the massif by
the water jet.
The main feature of the last scheme (Fig l,f) as compared with all the others is
that the disc cutter while rolling along the slot acts upon the coal massif not only by its
rim sides but also by its rim top.
Scheme of breakage, breakage parameters (depth of disc cutter thrust h, slot
cutting pitch t, depth of slot h s, distance between the disc cutter axis and the water jet
contact point with the coal massif a), geometric parameters of disc cutter (wedge rim
angle δ and wedge outside diameter (D) and physical and mechanical properties of the
coal massif constitute the main factors responsible for the combined breakage.
The schemes of the combined breakage were studied with constant velocity of
water jet and disc cutter movement, while the depth of slot (produced by different water
pressure in nozzle outlet) was assumed as a unifying hydraulic factor.
The mechanical breakage specific energy consumption H w was assumed as the
main criterion to evaluate the combined breakage scheme efficiency. Besides, this
efficiency was evaluated according to: total specific energy consumption E o including the
mechanical breakage energy consumption H w and hydraulical breakage energy
consumption E o (with V p = 2.75 m/s, d o = 2 mm); cutting force P z, forward force P y and
side thrust P x; percentage of coal grade 0-6 mm (R -6) and +25 mm (R +25) and specific
coal dust formation q.
Coal masif breakage was studied both for the levelled surface and in the
established regime. The studies of breakage from the levelled surface have made it
possible to better find out the special features of the combined breakage and to establish
its most efficient schemes. The studies in the established regime were carried out to find
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