By
Tom Wake, Product Manager, Raise Boring Equipment
Since
its introduction in 1979, the Robbins 34R has developed into one
of the most versatile raise drills ever made. And it continues
to evolve as customer requirements change.
The first 34R units were made
for Falconbridge's Kidd Creek mine in Timmins, Ontario, Canada
- and have been in continuous use since they were commissioned.
The mine uses
the machines to bore 1.2 metre diameter slot raises and for down-reaming
710 mm diameter holes, which are used for dumping backfill into
empty stopes.
The Robbins 34R
has a number of special advantages: it is small, compact and powerful;
it can operate with as little clearance as 3.4 m while drilling
or reaming; and the hydraulic drive provides variable speed control
which helps the operator to maximize machine performance in varying
rock conditions.
In addition, it
can be operated by a single employee due, in part, to a number
of automatic features. These features include a sensor that automatically
shuts down the boring cycle at the end of a cylinder stroke or
at a pre-determined level of torque.
Increased capacity
Since the production of the
first two machines, the Robbins 34R's torque and thrust has been
increased and the model has been renamed the 34RH-HT (High Thrust),
reflecting its increased capacity.
In the operation
of all raise drills, it has always been necessary to pour a concrete
pad so the raise boring machine can be bolted securely to cope
with the torque and thrust of the machine. These pads are costly
items and take time to prepare.
But now our engineering
department has designed a drilling platform that utilizes levelling
jacks which, combined with stinger cylinders in the derrick columns,
eliminates the need for pads.
| Easy
positioning: The reamer head is hydraulically lifted into
place at the top of the rig, or (as pictured) swung out to
give access for servicing. |
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The Robbins 34RH-HT
has been designed to also drill box holes, which are used to excavate
raises where there is limited or no access to the upper level.
The machine is set up at the lower level and a full diameter raise
is bored upward. During boring, stabilizers are periodically added
to the drill string to reduce oscillation and bending stresses
in the string. The cuttings are carried by gravity down the hole,
deflected from the machine and removed at the lower level. Boxhole
boring can be accomplished with or without a pre-drilled pilot
hole.
Separate controls
However, a major problem with
boxhole boring has been to prevent the cuttings from covering
the machine as they fall down the bored raise. To combat this,
a muck collector is installed between the bored hole and the machine.
But the varied designs of the collectors has not always been satisfactory.
Atlas Copco Raise
Boring engineers have now designed a muck collector that connects
to the head frame of the Robbins 34RH-HT with hydraulic cylinders.
The cylinders have separate controls so that the muck collector
can be adjusted to an irregular rock face.
The top of the
collector is fitted with an inflatable air bag, which seals around
the outside of the raise and prevents muck and dust from coming
out on the outside of the collector. The design proved effective
and is now standard.
The muck collector
is designed in two halves so it can be opened by hydraulic cylinders
to allow the passage of the reamer and the stabilizers. It also
contains a seal which clamps around the drill pipe and prevents
muck and water from entering the drive box area of the machine.
The collector
also incorporates a muck chute which deflects the muck away from
the machine at any location - except where it may interfere with
the hydraulic positioning cylinders.
The reamer used
to be installed above all boxhole boring machines, which was cumbersome
and time consuming. The drilling site also had to be high enough
to allow the installation of the reamer above the machine. This
required even more time and expense for the preparation of each
drilling site.
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Born
in 1979: The 34R raise boring machine has demonstrated its
versatility at projects all over the world for nearly two
decades - and is still a favourite with customers.
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It was therefore
decided to extend the width and depth of the machine so that the
reamer and stabilizers could be installed inside it.
This also required
the redesigning of the drill pipe wrenching system into two halves
so that hydraulic cylinders opened it wide enough to allow the
passage of the reamer. This feature increased the footprint of
the machine, but did not increase the height and the overall result
was a more functional system.
Pipe economy
The first Robbins 34R units
used 20 cm drill pipe 1.22 m long. Boxhole boring requires stronger
pipe to better stabilize the reamer and to transmit the full torque
and thrust of the machine through the drill pipe to the reamer
and cutters in the compression mode. The 34RH-HT was again modified
to incorporate the use of stronger 25 cm pipe.
The stronger pipe
gives another advantage to the end user because 25 cm drill pipe
1.52 m long is the most common size in the raise boring industry.
Consequently, there is a lot of used 25 cm pipe which - although
no longer strong enough for medium-powered raise drills - can
be utilized in the lower-powered 34RH-HT. The used pipe is reworked
by refurbishing the pin end and cutting down the box end from
1.52m to 1.22m with new thread cut into it. This greatly reduces
the overall cost to the end user.
All Robbins 34R
raise boring machines are designed to utilize the well-proven
reamers and RCC Duro Cutters.
Over the years,
Atlas Copco engineers have designed standard reamers and, in many
cases, highly specialized reamers. There was some concern about
the possibility of ground squeezing during boxhole (blind) boring,
so the engineers designed a set of gage housings and cutters which
are installed on the under side of the reamer.
In the event of
the ground squeezing during boring operations, the RCC Duro cutters
would cut their way out as the reamer is withdrawn from the completed
boxhole.
All the Robbins
34R units are designed so that the machines' full torque and thrust
are available in either the pushing or pulling mode.
Continued development
The design of the 34RH-HT
continues to evolve as customer requirements change, resulting
in 360 degree drilling, no concrete pad requirement, reamer and
stabilizer installation under the head frame and an integral muck
collector.
The close co-operation
which has been built up between the engineers and the customers
has resulted in the continued development of this most versatile
raise drill.
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