Method of binding dust

In rock drilling, the dust-laden flushing air from the borehole is drawn through a coarse dust separator and a filter unit. A mixing apparatus is screwed to the bottom of the filter unit and in accordance with this invention the dust that falls from the filter unit is fed in batches to a mixing chamber of the mixing apparatus in which it is mixed with a liquid binder. The dust from the coarse dust separator is directly dumped on the ground and the fine dust from the mixing apparatus is also dumped on the ground.

BACKGROUND OF THE INVENTION 
The present invention relates to a method of binding dust created when 
drilling rock, in which the dust is mixed is at present collected in 
plastic bags. The use of plastic bags or sacks, however, is encumbered 
with a number of disadvantages, both with respect to the necessary 
handling of these bags and to the cost thereof. Further, if a bag should 
break, the dust contained therein swirls up, creating a still greater 
health risk. 
It has previously been proposed to bind dust with the aid of a liquid 
comprising of water and a suitable binder, to agglomerate the dust into a 
form in which it is no longer harmful to health. The dust should be bound 
immediately as it is created during drilling, since the freshly cut 
surfaces of the dust particles are then physically active, which provides 
a good binding effect. It is important, however, for purposes of 
efficiency that the dust can be bound in a manner which does not 
necessitate the interruption of a drilling operation. 
Consequently, it has previously been considered sufficient to successively 
bind dust created by drilling at the rate in which it is generated. 
Different apparatus have been proposed to achieve this goal. One such 
apparatus is described in the Swedish Pat. No. 7404759-8. One of the 
disadvantages with such apparatus, however, is that the amount of liquid 
binder supplied must be continuously adapted to the amount of dust 
created. This is very difficult to achieve, and often impossible, since 
the amount of dust created varies greatly, for example, in dependence upon 
the hardness of the rock and the wear on the drill crown or bit. 
SUMMARY OF THE INVENTION 
A principle object of the present invention is to provide a method and 
apparatus which permit the liquid binder to be dispensed to the dust in 
given quantities, in a precise and simple fashion, while being mixed 
carefully with dust without interrupting the drilling operation, thereby 
eliminating the aforementioned disadvantages. 
This object is achieved, in accordance with one aspect of the present 
invention, by mixing the dust batchwise with a liquid binder, the batches 
being of a predetermined magnitude, for example a magnitude corresponding 
to the amount of dust obtained per length of drilling rod section. 
Treatment of one batch thus takes place while a subsequent batch of dust 
is being collected. The ready-mixed batch is discharged from the apparatus 
before the following batch is complete. 
A method according to the invention is characterized in that the dust is 
collected in the bottom of a dust-separating collector and is supplied in 
batches of given size to a mixing chamber to which a liquid binder is also 
fed in an amount related to the size of the batch in question. The dust 
and liquid are mixed by stirring while a further batch of dust is 
collected in the separating collector. The resultant mixture is then 
discharged before the next batch of dust is fed to the mixing chamber. 
Preferably, the liquid binder is fed to the mixing chamber prior to a batch 
of dust being introduced thereinto, and the dust batch is passed to the 
mixing chamber gravitationally via a bottom valve arranged in the 
separating collector. Preferably, the bottom valve is pressure controlled, 
and is operated in response to the pressure difference between the 
collecting chamber and the mixing chamber. 
According to another aspect of the invention, an apparatus for binding dust 
obtained when drilling rock, by mixing dust with a liquid, comprises a 
mixing chamber connected to a dust-separator. Batchwise feeding to the 
mixing chamber of dust collected in the separator is effectuated. A supply 
of a liquid binder is provided to the mixing chamber in an amount 
dependent upon the amount of dust in each batch. A mixer is arranged in 
the mixing chamber for mixing dust and liquid by stirring. Finally, a 
discharge device releases the resultant mixture before the next batch of 
dust is supplied to the mixing chamber. 
Examples of the method and apparatus of the invention will now be described 
with reference to the accompanying drawing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In FIG. 1, number 1 is a cyclone to which air containing dust is passed via 
a line 2 extending from a drill hole. The cyclone 1 is combined with a 
filter element 3 in a conventional manner. Element 4 is an ejector 
arranged to create a subatmospheric pressure in the cyclone 1 and the 
filter unit 3, and the outlet of the ejector communicates with the 
surrounding atmosphere. Arranged in the bottom of the cyclone 1 is a 
pressure-controlled valve 5 via which the cyclone can be placed in 
communication with a mixing chamber 6. In the illustrated embodiment, the 
valve 5 comprises a so-called "rubber valve," which in its simplest form 
comprises a readily compressible rubber hose. When a pressure below 
ambient pressure prevails in the cyclone 1, because of the action of the 
ejector 4, the rubber hose will collapse as a result of the pressure 
prevailing in the mixing chamber 6, thereby closing the valve. When the 
ejector 4 is disconnected, the hose is opened due to the equalization of 
pressure between the cyclone 1 and the chamber 6. 
The mixing chamber 6 is provided with an agitator which includes an 
agitator element 8 and which can be rotated via a shaft 7. The chamber 6 
is angled so that the shaft 7 can be driven via a gear drive located on 
the outside of the chamber. This obviates the need for bevel-gear drives 
or the like. The lower end of the chamber 6 is closed by means of a 
closing element 11 operated by a double-acting air cylinder 10. Element 12 
is an inlet for binding liquid, while the number 13 identifies a vibrator. 
The mode of operation of FIG. 1 will now be described. When carrying out a 
drilling operation, the ejector 4 is rendered operative, whereas air laden 
with dust is drawn by suction into the cyclone 1. The bottom valve 5 is 
closed as a result of the under-pressure prevailing in the cyclone. Dust 
separated in the cyclone 1 and the filter unit 3 falls down onto the 
bottom of the cyclone, where it is collected. When a distance 
corresponding, for example, to the length of one drilling rod has been 
drilled, and a further drilling rod is to be assembled, so to lengthen the 
drill, the ejector 4 is cut-off. The pressure in the cyclone 1 will then 
rise and the valve 5 is opened, so the batch of dust collected in the 
cyclone 1 falls down into the mixing chamber 6. 
In conjunction herewith, the filter incorporated in the unit 3 is suitably 
vibrated, so that dust held in the filter also falls down into the mixing 
chamber 6. Prior to this, a given amount of a liquid binder, comprising 
water and some percent by volume of a suitable organic binder of known 
kind, has been introduced into the mixing chamber. The amount is 
determined in dependence upon the size of the batch of dust passed to the 
mixing chamber. In the described embodiment, the amount of binding liquid 
added has been determined in dependence upon the length of a drillingrod 
section and the diameter of the drilling crown or bit. 
The dust is mixed with the liquid in the mixing chamber 6, whose bottom 
flap 11 is closed, by means of the rotary agitator means provided with 
said agitator element 8. This mixing operation can be continued while the 
next drill length is drilled, and fresh dust is collected on the bottom of 
the cyclone 1, the bottom valve 5 of said cyclone being reclosed as a 
result of the action of the reconnected ejector 4. Thus, since mixing of 
the dust with the binding liquid can be continued for a relatively long 
time, for example, several minutes, a highly homogenous mixture in which 
substantially all dust is bound is thereby obtained. Further, only a 
minimal amount of liquid is required, in the order of magnitude of 15 cl 
per litre of dust. The readymixed mass, which now has a doughy 
consistency, is discharged by opening the flap 11 by means of the air 
cylinder 10. This can be effectuated immediately prior to reconnecting the 
ejector 4 in conjunction with changing a drilling rod and/or vibrating the 
filter. To facilitate discharge of the ready-mixed mass there can be used, 
for example, a vibrator 13 which is connected to the wall of the mixing 
chamber 6. 
As soon as the ready-mixed mass has been discharged from the apparatus, the 
bottom flap 11 is reclosed and a further amount of liquid binder is 
supplied via the inlet 12. This amount is adjusted to the amount of dust 
collected on the bottom of the cyclone 1 and enters the mixing chamber. 
The binding liquid is suitably fed at such a pressure, about 6 
atmospheres, and with such a spread to clean out the mixing chamber 6 as 
the liquid is injected thereinto. The mixing arrangement may be driven, 
for example, by means of a hydraulic motor which, as beforementioned, can 
be effectuated without the use of bevel-gear drives or the like, owing to 
the fact that the mixing chamber 6 is angled. This enables the drive 9 
arranged on the shaft 7 to be reached from outside the apparatus. 
As will be understood from the description of this embodiment, binding of 
the dust in accordance with the invention does not affect the drilling 
operation, since both the mixing of a batch of dust and the supplying of 
the binding liquid for the subsequent batch are carried out during a 
drilling operation. Transfer of dust collected in the cyclone 1 to the 
mixing chamber 6 is accomplished when it is necessary to interrupt the 
drilling operation, for the purpose of changing a drilling rod or the like 
measure. No other form of interruption is necessary when binding dust in 
accordance with the invention. 
Further, as mentioned, the binding liquid can be metered to the apparatus 
very precisely, since the amount of dust generated per length of drilling 
rod can be readily calculated with knowledge of the length of the drilling 
rod and the diameter of the drill bit. Thus, it is not necessary to vary 
the amount of liquid metered to the apparatus during a drilling operation 
in dependence of whether hard or loose rock is being drilled and in 
dependence on the condition of the drill bit. Further, it is essential 
that mixing of the dust and binding liquid can be continued for a length 
of time such as to ensure positive binding of substantially all the dust. 
Referring now to FIGS. 2 and 3, a second embodiment is shown. In FIG. 2 a 
complete dust collecting system is shown whereas in FIG. 3 only the 
filtering and mixing apparatus thereof is shown. The dust collecting 
suction system, shown in FIG. 2 generally similar to that described in 
U.S. Pat. No. 4,223,748, comprises a hood 21 located over the mouth of a 
borehole 22, a separator 23 for coarse dust and filter unit 24 with an 
ejector 25. A drill stem 26 for drilling the borehole extends through the 
hood 21 that has a rubber seal 27 that seals against the drill stem 26. In 
place of the ejector 25 an electric fan may be used in locations where 
there is a supply of electricity. 
When the suction system is used for example on crawler drill wagons, both 
the separator 23 and the filter unit 24 can be mounted on the frame of the 
crawler wagon. The hood 21 can then either be a loose hood or it can be 
mounted on the feed beam for the rock drill that operates the drill stem 
26. Since the drilling apparatus itself is not part of the invention, only 
the drill stem 26 of the drilling apparatus is illustrated. 
The hood 21 has two fittings 28, 29 for flexible hoses 30, 31 which have 
their other ends coupled to two fittings 32, 33 on the coarse dust 
separator 23. A hose 35 leads from an outlet on the top of the separator 
23 to the filter unit 24. The separator 23 is provided with a container 36 
that has a door 37 with a counterweight. 
A mixing apparatus 38 is screwed to the hopper-like bottom 39 of the filter 
unit 24. The filter unit 24 and the mixing apparatus are shown in more 
detail in FIG. 3. In the filter unit, shown in FIG. 3, there are a 
plurality of flat filter bags 41 that have long narrow mouths. The filter 
bags 41 are mounted in a partition 42 and they have interior wire cages 
that prevent them from collapsing. Similar to the mixing apparatus of FIG. 
1, the mixing apparatus of FIg. 3 comprises a mixing chamber 6, an 
agitator 8 mounted on a shaft 7, a door 11, a power cylinder 10 for 
operating the door, an inlet 12 for a liquid binder and a vibrator 13. A 
motor 43 is shown which is coupled to rotate the shaft 7. A rotating 
positive displacement feeder 44 is used instead of the feeding valve 5 in 
FIG. 1. The feeder 44 is rotated by a motor 45 shown in FIG. 2. A sensor 
46 is coupled to detect the amount of dust in the hopper 39. 
During drilling, the ejector 25 (or fan depending on availability of 
electricity) draws air from the filter unit 24 so that there will be 
subpressure in the entire system, and, as a result, the dust-carrying 
flushing air that flows out of the borehole, is drawn through the coarse 
dust separator 23 and the filter unit 24. 
The coarse dust separator 23 can preferably be of the kind described in 
U.S. Pat. No. 4,223,748 and it will therefore not be described in detail. 
It separates coarse dust that is not hazardous to the health and the 
collected coarse dust can be dumped on the ground without previously being 
treated with a binder. More than 50%, usually more than 70%, of the dust 
can be separated as coarse dust. It is advantageous to have a coarse dust 
separator since this component reduces the load on the filter unit and 
mixing apparatus 38. It is also advantageous since it reduces the amount 
of binder necessary to mix with the dust. The binder is usually a water 
solution of a hygroscopic salt. The reduction depends mainly on the 
reduction in the amount of dust. However, a smaller percentage of liquid 
is needed when there is only fine dust as compared to a mixture of coarse 
and fine dust. The apparatus of FIG. 1 can also be alternatively coupled 
directly to a suction hood or indirectly to a suction hood via a separate 
coarse dust separator of the kind described with reference to FIG. 3. 
The filter bags 41 are cleaned by the use of repeated air pulses each time 
the drilling is interrupted so that a batch of dust falls from the 
filters. The apparatus of FIG. 3 is advantageous over the apparatus of 
FIG. 1 in that the batches of dust fed to the mixing chamber 6 may be 
smaller than the dust batches falling from the filter bags since the 
feeder 44 is able to feed the dust also when there is suction in the 
collecting system. Also, more than one mixing cycle can be carried out 
during one drilling cycle. Thus, the mixing apparatus can be smaller.