Note: Descriptions are shown in the official language in which they were submitted.
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BALANCED VENTILATION DOORS
[0001] This invention relates to doors, of the kind as used in
underground tunnels and passageways for the control of ventilation.
[0002] Traditionally, the door apparatus is provided as a pair of
door-sections, which are hinged one to the left: side-wall and the other
to the right side-wall of the passage. The door-sections operate like
canal-lock gates, i.e the door-sections extend each halfway across the
passage to close off the passage to airflow, and the door-sections open
both together, to lie flat against the side-walls of the tunnel, to
allow traffic to pass through.
[0003] When the doors are being opened or closed, the traditional
design requires the door-sections to open either both against, or both
with, the flow of air passing through the passage. Mine ventilation
doors can be large, for example each door-section may be three metres
high and three metres wide. Even a small pressure difference across
the doors creates an enormous force tending to blow the doors open, or
closed, and the door actuation system must provide enough force to
overcome the pressure differential.
[0004] Providing a means, down a mine, for exerting such large
forces is not only inconvenient, but can lead to safety problems. It
is not unusual for mine-workers to be injured by ventilation doors. In
order to close the doors against the air pressure, the actuators have
to be so powerful they cannot even detect the presence of the worker.
Precautions must be taken to prevent the door-sections being blown open
or closed, in case the power supply to the actuator should fail.
[0005] One proposal has been to provide two pairs of door-sections,
arranged in an air-lock configuration. The force needed to open or
close one pair of door-sections of course is much less if the passage
is already closed by the other pair of door-sections. However, the
ventilation fans are usually not switched off simply to enable the
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passage is to be changed from being open for ventilation to being
closed (or vice versa); since the ventilation status of the passage
still has to be changed while the fans are on, one of the door-section
pairs has to open or close against the full airflow. Arranging mine
doors in an air-lock configuration, besides doubling the cost, in fact
does not allow the designer to provide a less powerful actuation
system.
GENERAL FEATURES OF THE INVENTION
[0006] The invention provides a door apparatus in which the door-
sections open, not in the manner of lock-gates, but in the manner
whereby one door-section opens upstream while the other door-section
opens downstream. Thus, one door-section opens against, while the
other opens with, the air pressure. Thus, one door-section is being
urged to blow open, while the other door-section is being urged to blow
closed.
[0007] In the invention, the door apparatus includes a mechanical
linkage, which couples and connects the door-sections, and transfers
forces between the door-sections. Theoretically, the door-sections can
be exactly balanced: i.e the force tending to blow the upstream door-
section closed is exactly balanced by the force tending to blow the
downstream door-section open. That being so, the force required to
actuate the door apparatus from the open condition to the closed
condition (and vice versa) is minimal. Because the force required from
the actuator is so small, the power of the actuator now can be light
enough not to cause injury to a worker who might have fallen between
the door-sections.
[0008] The actuation force is, at least theoretically, independent
of the magnitude of the air pressure differential acting on the door.
In practice, a large pressure differential puts larger forces onto the
door hinges and the linkage, and the increased friction would be
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reflected in an increase in the force needed to open and close the
door.
[0009] Since the actuator only need provide a small force, the
actuator can be a wholly electrical unit. This is preferred because,
increasingly, below-ground operations must have the ability to be
powered and controlled remotely from the surface, and electrical
devices are much more convenient than pneumatic or hydraulic
force-actuators in this regard. With traditional pneumatically-
operated doors, often the door-actuators are the only below-ground
machines that require compressed-air lines to be run down from the
surface. Also, an all-electric actuator can be powered by stand-by
batteries in emergencies.
[0010] For vehicular traffic, the actuator should be provided with a
signal sensor, enabling the driver to remain with the vehicle while
operating the doors. But, as mentioned, by the use of the invention,
the door-sections can be balanced sufficiently that the worker can pull
the door-sections open by hand, walk through the gap, then close the
door-sections, again by hand. The worker might be discomforted by the
wind draft that then blows through the gap, but at least the worker
can, if required, control the opening and closing of the doors by hand
action, even in the event of power failure. Preferably, the actuator
should be of the type that permits the door-sections to be moved when
the actuator is not being supplied with power, whereby the worker does
not have to dismantle the actuator in order to open and close the doors
by hand.
[0011] With the invention, there is no need for the traditional
small man-door to be let into the ventilation-door. Indeed,
traditional man-doors have been subject to slamming or blowing open,
violently enough to cause injury to an unwary worker. However, a man-
door may be provided, if desired. In fact, one field for applying the
invention is to replace the (dangerous} man-doors in existing
traditional ventilation-doors by a pair of half-doors which are
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operated in the force-balanced, one-upstream-one-downstream, manner of
the invention.
[0012] The invention provides a manner of operating mine
ventilation-doors which, though safer and more convenient, can be
significantly less expensive than traditional systems. As will be
described, the linkage connecting the door-sections can be cheap to
manufacture, and need not require sophisticated set-up and adjustment.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0013] By way of further explanation of the invention, exemplary
embodiments of the invention will now be described with reference to
the accompanying drawings, in which:
[0014] Fig 1 is a pictorial view of a mine tunnel, having a
ventilation door apparatus that embodies the invention.
Fig 2 is a diagrammatic plan view of the door apparatus of Fig 1,
showing the doors in a closed position.
Fig 3 is the same view as Fig 2, but shows the doors in a wide-open
position.
Fig 4 is a diagrammatic plan view of the door apparatus of Fig 2, which
shows a mechanical linkage and actuation system of the apparatus,
and shows the doors in a partially-open condition.
Fig 5 is a plan view from underneath the door apparatus of Fig 1, and
shows a door-lintel of the apparatus.
Fig 6 is a diagrammatic plan view corresponding to Fig 4 of another
door apparatus that embodies the invention, and shows the doors
in a partially-open condition.
Fig 7 is a view of a strut of the door apparatus of Fig 6.
[0015] The apparatuses shown in the accompanying drawings and
described below are examples which embody the invention. It should be
noted that the scope of the invention is defined by the accompanying
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claims, and not necessarily by specific features of exemplary
embodiments.
[0016] The manner in which the doors open and close is shown in Figs
1-3. Door-section 20A opens towards the upstream side and door-section
20B opens towards the downstream side. The door-sections are hinged,
at 22A,22B, to jambs 23A,23B of the door frame. The jambs 23A,23B and
lintel 24 of the door frame are concreted into the side-walls 25A,25B
and roof of the passage.
[0017] When the doors are open, there is a clear passage between the
door-sections for a vehicle 26 to pass through. It may be noted that,
generally, tunnels in mines are only one vehicle-lane wide, so the
door-sections have to open in such a manner as to provide a clear space
between the door-sections. If the door-sections were hinged, not to
the side-walls of the tunnel, but to a central post, for example, one
of the door-sections, by itself, would have to open wide enough for the
vehicle to pass through. This would be quite .inappropriate in most
mine situations.
[0018] Fig 4 shows the mechanical linkage that ensures the door-
closing force on door-section 20A is transmitted to door-section 20B,
and the door-opening force on door-section 20B is transmitted to door-
section 20A. The linkage constrains the door-sections to move in
corresponding (preferably equal) arcs. The door-sections have
respective lever-arms 27A,27B, which are fixedly integrated into the
body of the respective door-sections. Both lever-arms extend towards
the upstream side, so the lever-arms are of different shape, as shown,
to accommodate the hinging motion around the jambs 23A,23B.
[0019] The lever-arms 27A,27B carry respective arm/link-attachment-
points 28A,288. A connecting-link 29 is mounted between these points.
The linkage, including the connecting-link 29 coupled between the two
lever-arms 27A,27B, constrains both door-sections to rotate in the same
sense, i.e both clockwise or both anticlockwise. Lines joining the
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pivot axes of the respective hinges 22A,22B to the respective
arm/link-attachment-points 28A,28B preferably are equal in length, and
parallel, but other geometries may be used. Often, the door-sections
are required to open a few degrees more than ninety degrees. The
designer must see to it that the linkage can accommodate the full arcs
of movement of the door-sections.
[0020] The connecting-link 29 is of such a structure that it can be
adjusted in length (e.g by the use of left- and right-hand threads at
its ends), whereby the linkage installation can be accurately matched
to the particular door.
[0021] One of the lever-arms 27B has an actuator-connection-point
30, and an actuator 31 is mounted between the point 30 and a mounting
bracket 32 which is fixed to the lintel 24 of 'the door frame. The
actuator 30 is of the recirculating-ball screw-jack type, and the
actuator is operated by an electric motor. Such actuators are
economically obtainable at force-ratings up to a few hundred pounds,
which is all that is required of the actuator for a door-operating
mechanism of the invention, when properly designed.
[0022] Preferably, the cut-out that is provided on such actuators
may be set at about seventy pounds, on the basis, the designer may
note, that, if the actuation force rises above that level, probably
something is interfering with the movement of the doors, and movement
of the doors should cease, to avoid injury or damage to personnel or
equipment.
[0023] In the invention, the actuator 31 supplies only the
difference in force between the upstream door-section 20A and the
downstream door-section 20B, and is not sensitive to the actual
magnitude of the forces on the door-sections, since those forces cancel
each other out. In a well-engineered system, the difference between
the force on door-section-A and the force on door-section-B comes from
such comparatively minor sources as friction in the hinges and pivots
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of the linkage. On the other hand, especially when the doors are
almost closed, i.e when air rushes through the (narrow) gap at high
speed, it can happen that the swirling air currents can lead to
vigorous aerodynamic effects which cause the door-sections to
experience differences of wind force, and the actuator should be rated
to accommodate this.
[0024] Sometimes, the designer may prefer to build in (slight)
differences between the door-sections - to bias the doors closed, for
example. However, preferably, and especially in cases where the
ventilation air can blow either way along the passage, the door-
sections and the linkage should be designed to be symmetrical, i.e
balanced, as to the air-pressure forces acting on the door-sections.
[0025] Door-stops 34A,34B are provided underneath the lintel 24 of
the door-frame, as shown in Fig 5. The door-stops comprise angle-
strips, welded to the lintel, which the tops of the door-sections can
abut against when fully closed. The door-sections are not sealed, so
when the doors are closed wind can still leak 'through around the edges,
so the designer should arrange the manner in which the door-sections
actually close together to minimize direct drafts.
[0026] Fig 6 shows another type of mechanical linkage, which is
effective to utilise the blow-open force on the downstream door-section
to balance and cancel out the blow-closed force on the upstream door-
section.
[0027] In Fig 6, the door-sections 36A,36B are identical, the two
connecting-links 37A,37B are identical, and the actuation-bar 38 is
symmetrical. This simplifies installation and assembly. Lever-arms
39A,39B are attached to the respective door-sections. Connecting-links
37A,37B connect the lever-arms to bar/link-attachment-point-A 40A and
bar/link-attachment-point-B 40B on the central actuating-bar 38. The
actuating-bar 38 is pivoted to the underside of the lintel 24. The
recirculating-ball screw-jack 43 actuator acts between the actuating-
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bar 38 and the doorframe.
[0028] The arrangement as shown in Fig 6 makes it easy for the
designer to ensure that the pivoting components remain always in
geometrically-favourable sectors of their arcuate movements. It may be
noted that the difference in force on the door-sections varies with the
degree of door-opening. When the doors are fully open, there is hardly
any difference in air-pressure force. It is only when the doors are
starting to close together that the pressure differential increases.
Therefore, the designer preferably should ensure that the most
favourable arcuate sectors occur as the doors are coming together.
[0029] Thus, the designer preferably should arrange that the angular
rate of pivoting of the doors, per unit of travel of the actuator,
should be smaller when the doors are together, and larger when the
doors are fully open. Another benefit of this arrangement occurs when
drivers operate the door remotely from their vehicle as they approach
the door. Most drivers try to judge the opening swing of the door so
they can pass through without stopping, and the driver would be more
likely to make a misjudgment resulting in the 'vehicle hitting the door-
section if the door-section that pivots towards the vehicle were to
swing open quickly at first, and then slow down as the door-section
opened wider.
[0030] The door-section 36A is made actually in two halves, 36AL and
36AR. Door-section 36B is in two halves 36BL and 36BR. In many mines,
it simplifies the task of transporting the door-sections to the door
site if the door-sections are in two halves, the halves being bolted
together at the door site.
[0031] The door halves each comprise a frame of spars and a skin 44
attached thereto. It will be understood that the effect of the wind is
different, whether the wind blows towards the plain-skin side of the
half or towards the open-frame side. The open-frame side may be
compared with a scoop, which collects the wind, whereby a larger force
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acts on the open-frame side than on the plain-skin side. This
difference may be harnessed, and the difference utilised to bias the
door to the closed position. Thus, the open-frame side should face
upstream. Of course, when the door is fully c:Losed there is no
airflow, and no difference between the forces on the respective door-
sections; but if the door should start to open, whereby air does start
to flow, the force difference arising from the scoop effect will apply
(slightly) more force to the upstream-facing door-section, whereby the
door closes again. Thus, if the door should open slightly, a restoring
force is created tending to close it again. Since the door is biassed
to remain closed, no latch is needed to hold the door closed. This
aspect can be important in the case where the ventilation doors are
opened remotely from a vehicle, where it would be inconvenient if the
driver also had to operate a latch.
[0032] As shown, only the outboard halves 36AR and 36BL of the doors
present the open-frame or scoop side to the airflow, since not much
difference in force is needed to keep the door closed. It will be
understood that the scoop effect holds the door closed, whichever way
the wind blows along the passage.
[0033] Fig 7 shows another safety aspect that may be incorporated.
The strut 45 fits in place of the connecting-link 37A of Fig 6.
Sometimes, when blasting is carried out in the mine, a pressure wave
from the blast can travel along the tunnels and passages, and can blow
the doors open - often with accompanying damage to the doors, hinges,
actuators, etc, and perhaps injury to workers. In Fig 7, a sheer pin
46 is arranged to break if the (momentary) force on the door should
become too large. Once the sheer-pin has broken, the door can fly open
without damaging the actuator. A spring 47 catches the swinging door,
and absorbs the violence of the movement. In fact, depending on the
forces involved, the designer might find it possible to dispense with
the sheer pin, and, when the force on the actuator exceeds the setting
of the spring, simply allow the door to open against the spring.
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[0034] As depicted, the linkage for transmitting and balancing the
forces between the two door-sections is mechanical, and includes simple
fixed-length struts, as shown. An alternative is to actuate the doors
by hydraulic ram, and to balance the forces hydraulically.
[0035] In alternative installations, the linkage may be more complex
and sophisticated. Springs or weights may be 'used to further balance
the door-sections, or to bias the door-sections to a closed or open or
partially-open position.
[0036] Because the forces on the door-sections are balanced, sensors
may readily be provided to measure any differences between the door-
sections. It is usually a requirement that the position of ventilation
doors be controlled from the surface, or at least that it be possible
to tell from the surface whether the door is closed, open, or partially
open. The fact that the door-sections are balanced simplifies this
remote sensing and operation.
[0037] Preferably, the door-sections are identical, but they need
not be. Preferably, each door-section is, at least for operational
purposes, a single solid panel; however, the door-sections may include
each more than one panel, which articulate for operation. This can be
useful for example if space restricts the full swing of a single-panel
door-section.
[0038] The linkage mechanism is depicted as fitting above the door;
alternatively, the linkage may be placed in the floor underneath the
door.
