Figure 9. Close-up of the cutting drum.
that 360 rotation in 15 increments can be made
for six of the eight rows, with the other two rows
to the tangential position of the cutters around the
engaging 43.2 cm of the tunnel face. This resulted
axis of the shaft. The cutters are toothed, with an
in near-even loading and a smoother cut as each
11-clearance angle and a 24 top rake. Cutter ge-
series of cutters engaged the material.
ometry is based on work done by Ueda and
The original drive for the drum was a fixed-
Kalafut (1989). Due to the brittle nature of the
speed axial vane hydraulic motor with a 7.07:1
material to be machined, no chip breaker was
gear reducer (Von Ruden 25S-207-A-12). A 1-in.-
machined into the cutter. The cutters were origi-
(2.54-cm.-) pitch stainless steel roller chain (no. 80)
nally to be bolted to seats on the arms, but distor-
transferred power between a 21-tooth drive
tion during welding of the seats to the arms re-
sprocket and a 28-tooth drum sprocket. Two
Duralon bearings support the 6.35-cm-OD 1.6-
sulted in mounting difficulties, so the cutters are
tack welded to the seats. This modification has
cm-wall 4340 CD seamless hollow drum shaft. A
worked well, as the cutters are easily removed by
pivoting mechanism that allows the drum to be
rotated 90 for maneuvering the tunneler in the
grinding off the weld.
A total of 26 cutter arms are used to span the
confines of the tunnel was incorporated at the end
1.84-m-long drum. The drum is 0.6 m in diameter
of the boom.
with a maximum in-feed depth of 15 cm. In-feed
The power required to drive the drum was cal-
is limited by the flange diameter of the hubs used
culated based on the projected density of the snow
(ρ) at a depth of 10 m: 0.5 g/cm3, or 500 kg/m3
for mounting the arms. The number of arms can
be adjusted using spacers and various width cut-
(Gow and Ramseier 1964). From Mellor (1977), for
ters (Fig. 9). Three cutter widths are currently used:
efficient rotary snow plow operation:
5, 6.4, and 7.6 cm, with the 6.4-cm cutters the most
Es/σc ≈ 0.3
common. The cutters are toothed, with 1.27-cm-
(1)
wide teeth opposing nontoothed sections on the
opposite end of the same arm. This results in larger
where Es is the process specific energy for cutting,
and σc is the uniaxial compressive strength of the
disaggregation chips during machining and less
work for a given amount of material removed.
snow.
Cutter arms were originally mounted to the
At the projected conditions, the unconfined
flanges in 45 tangential increments, with arms
compressive strength of the snow should be
around 0.85 MN/m2 (Gow and Ramsier 1964). By
arranged nearly symmetrically around the center
of the drum where the drive is located. Linear en-
back-calculating, the process specific energy for
gagement along each 45 increment was 40.6 cm
cutting will be
7
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