Overwind conveyance drop protection

Abstract

A hoist system for hoisting a conveyance from a mineshaft, comprising: a head frame mounted over the mineshaft; a hoist connected to the conveyance by an elongate flexible hoisting element so as to be operable to hoist the conveyance from the mineshaft by winding the hoisting element; an upper crash barrier located on the head frame so as to be engageable by the conveyance to prevent upward movement of the conveyance beyond the crash barrier in an overwind condition; and an upper conveyance retarder to retard upward movement of the conveyance as it approaches the crash barrier.

Claims

1. A hoist system for hoisting a conveyance from a mineshaft, wherein the conveyance is a skip, the system comprising: a head frame mounted over the mineshaft; a hoist connected to the conveyance by an elongate flexible hoisting element so as to be operable to hoist the conveyance from the mineshaft by winding the hoisting element; an upper crash barrier located on the head frame so as to be engageable by the conveyance to prevent upward movement of the conveyance beyond the crash barrier in an overwind condition; and an upper conveyance retarder capable of retarding upward movement of the conveyance, by undergoing plastic deformation, as the conveyance approaches the crash barrier.

2. The hoist system as claimed in claim 1, further comprising a conveyance catcher to catch the conveyance from free fall downward movement if the conveyance engages the upper crash barrier and the hoisting element fails.

3. The hoist system as claimed in claim 2, further comprising a lower conveyance retarder located below the upper conveyance retarder and the conveyance catcher, the lower conveyance retarder for retarding free fall of the conveyance in the event that the conveyance catcher fails to catch the free falling conveyance.

4. The hoist system as claimed in claim 3, further comprising a lower crash barrier having an open condition in which to allow upward and downward movements of the conveyance from and into the mineshaft, and a closed condition to prevent debris from falling into the mineshaft.

5. The hoist system as claimed in claim 4, wherein upward movement of the conveyance triggers release of the lower crash barrier to move to its closed condition.

6. The hoist system as claimed in claim 5, wherein upward movement of the conveyance triggers release of the lower crash barrier prior to engagement of the conveyance with the upper crash barrier.

7. The hoist system as claimed in claim 2, wherein the conveyance catcher is a jack catcher.

8. The hoist system as claimed in 7, wherein the jack catcher comprises pivoting jack catches on the headframe engageable with lugs on the conveyance to catch the conveyance against downward movement.

9. The hoist system of claim 3 comprising a lower crash barrier having an open condition in which to allow upward and downward movements of the conveyance from and into the mineshaft but releasable upon upward movement of the conveyance toward or into engagement with the upper crash barrier to a closed condition to prevent downward movement of the conveyance into the mineshaft if the lower conveyance retarder fails to stop a free fall of the conveyance.

10. The hoist system as claimed in claim 3, wherein the upper conveyance retainer and the lower conveyance retarders are energy absorption devices.

11. The hoist system as claimed in claim 3, wherein the lower conveyance retarder is an energy absorption device.

12. The hoist system as claimed in claim 3, wherein the lower conveyance retarder is capable of retarding free fall of the conveyance by undergoing plastic deformation.

13. The hoist system of claim 4 wherein the conveyance catcher is arranged to catch the conveyance from free fall downward movement if the conveyance engages the upper crash barrier and the hoisting element fails.

14. The hoist system as claimed in claim 5, wherein when activation of the upper conveyance retarder is active to retard upward movement of the conveyance, release of the lower crash barrier is triggered.

15. The hoist system of claim 1 comprising: a conveyance catcher to catch the conveyance from free fall downward movement in the event that the conveyance engages the upper crash barrier and the hoisting element fails; a lower conveyance retarder located below the upper conveyance retarder and the conveyance catcher, the lower conveyance retarder for retarding free fall of the conveyance in the event that the conveyance catcher fails to catch the free falling conveyance; and a lower crash barrier having an open condition in which to allow upward and downward movements of the conveyance from and into the mineshaft but releasable upon upward movement of the conveyance toward or into engagement with the upper crash barrier to a closed condition to prevent downward movement of the conveyance into the mineshaft in the event that the lower conveyance retarder fails to stop a free fall of the conveyance.

16. The hoist system as claimed in claim 15, wherein the conveyance catcher is a jack catcher.

17. The hoist system as claimed in claim 15, wherein one or both of the upper conveyance retarder and the lower conveyance retarder is an energy absorption device.

18. Apparatus for removing excavated material from a mineshaft during formation of the mineshaft, comprising: a material conveyance moveable up and down within the mineshaft intermittently to receive discrete loads of material excavated during formation of the mineshaft and transport that material to the top of a mineshaft for discharge, wherein the conveyance is a skip; and a hoist system as claimed claim 1 installed at the top of the mineshaft and operable to hoist said material conveyance.

19. Apparatus for removing excavated material from a mineshaft during formation of the mineshaft, comprising: a material conveyance moveable up and down within the shaft intermittently to receive discrete loads of material excavated in the formation of the shaft and transport that material to a top of a mineshaft for discharge, the material conveyance being a skip; and a hoist system installed at the top of the mineshaft and operable to hoist said material conveyance, the hoist system comprising: a head frame mounted over the mineshaft; a hoist connected to the conveyance by an elongate flexible hoisting element so as to be operable to hoist the conveyance from the mineshaft by winding the hoisting element; an upper crash barrier located on the head frame so as to be engageable by the conveyance to prevent upward movement of the conveyance beyond the crash barrier in an overwind condition; and an upper conveyance retarder capable of retarding upward movement of the conveyance, by undergoing plastic deformation, as the conveyance approaches the crash barrier.

20. A hoist system for hoisting a conveyance from a mineshaft, the conveyance being a skip, the hoist system comprising: a head frame mounted over the mineshaft; a hoist connected to the conveyance by an elongate flexible hoisting element so as to be operable to hoist the conveyance from the mineshaft by winding the hoisting element; an upper crash barrier located on the head frame so as to be engageable by the conveyance to prevent upward movement of the conveyance beyond the crash barrier in an overwind condition; an upper conveyance retarder capable of retarding upward movement of the conveyance, by undergoing plastic deformation, as the conveyance approaches the crash barrier; and a lower crash barrier having an open condition in which to allow upward and downward movements of the conveyance from and into the mineshaft, and a closed condition to prevent debris from falling into the mineshaft; wherein upward movement of the conveyance triggers release of the lower crash barrier to move to its closed condition.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In order that the invention may be more fully explained one particular embodiment will be described in detail by way of non-limiting example only, with reference to the accompanying drawings in which

(2) FIGS. 1 to 4 illustrates a hoisting system constructed in accordance with the invention at various stages of operation during an overwind event; inset FIGS. 2A and 2B show magnified details of the conveyance catcher and conveyance retarders, respectively, of FIG. 2; inset FIGS. 3A and 3B show magnified details of the conveyance catcher and conveyance retarders, respectively, of FIG. 3;

(3) FIG. 5 is a close up view of the conveyance catcher (jack catchers) and conveyance (skip);

(4) FIGS. 6 to 8 show progressive stages of the conveyance being engaged by the conveyance catcher;

(5) FIG. 9 is a close up view of the upper and lower conveyance retarders;

(6) FIGS. 10 to 12 show progressive stages of the conveyance being engaged by the conveyance retarders; and

(7) FIG. 13 shows diagrammatically the sequence of operations during overwinding events.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(8) The drawings show part of a mineshaft head frame 11 fitted with a hoisting system for raising and lowering a pair of conveyances, each presently embodied by a skip 12, along parallel vertical paths from and into a mineshaft. While the illustrated embodiment shows the use of two such conveyances or skips 12, it will be appreciated that 1, 3 or any other number of conveyances or skips may be used as appropriate.

(9) The skips 12 are operated in tandem so that as one skip 12 is raised to the top of the mineshaft to discharge excavated material the other is lowered to the bottom of the mineshaft to be filled with further excavated material. The head frame carries one set of protection devices per skip 12, each set of protection devices being effective to arrest a respective skip 12 following an overwind event and subsequent hoist rope failure. The operation of the arresting system appearing at the left hand side of the drawings will be described but it is appreciated that a duplicate system is provided for the skip at the other side of the drawings.

(10) Each skip 12 is raised and lowered by winding a rope 20 about a hoist drum (not shown). In general, the skips 12 will travel upwardly from a work stage to the top of the mineshaft. In this circumstance, each skip 12 may run along guides that ensure correct orientation of the skip 12 during filling and discharge of material. A hoist motor (not shown) moves the hoist rope, thereby providing the motive force to raise/lower each skip 12, whereas the guides serve only to prevent rotation and lateral swinging of the skip 12 during hoisting. The guides may include a variable length guide (e.g. stage ropes) extending down to the work stage. The variable length guide may extend into the head frame 11. Alternatively, fixed guides may be provided in the head frame 11 as shown, with each skip 12 transitioning onto the fixed guides during upward travel.

(11) Guides and guide systems are discussed in Australian patent application No. 2013903212, entitled Skip and Crosshead and filed on 23 Aug. 2013), the entire content of which is incorporated herein by reference.

(12) In normal operation the skip 12 is brought to rest at a discharge position within the head frame 11 and its contents are discharged before the skip 12 is lowered back into the mineshaft. The contents of the skip 12 may be discharged or otherwise deposited on the ground, onto a conveyor or in a bin or other receptacle, as necessary for storage or conveyance of the mined material after extraction of that material from the mineshaft.

(13) In an overwind event the skip 12 is hoisted above its normal discharge position until it hits an upper crash barrier in the form of a horizontal crash beam 14 fixed to the head frame 11. A conveyance arrest system then prevents free fall of the skip 12 back down the mineshaft. The conveyance arrest system comprises upper and lower conveyance retarders 15, 16, a conveyance catcher 17 and a lower crash barrier 18.

(14) The upper and lower conveyance retarders 15, 16 may include technogrids of the kind marketed by the Horne Group and affiliated companies in South Africa, United States and Canada. Each technogrid is a deformable steel grid section. On impact the individual elements of the grid are deformed in controlled bending which converts the kinetic energy into strain energy that is safely dissipated in the form of low grade heat.

(15) The upper conveyance retarder 15 is fixed in position so as to retard upward movement of the skip as it approaches the upper crash barrier 14.

(16) The upper conveyance retarder 15, as shown in FIG. 9, is in the form of a pair of technogrid assemblies 26.

(17) There are two technogrid assemblies 26 for each conveyance.

(18) The technogrid assemblies each comprise a pair of technogrids 28.

(19) The technogrids 28 of each assembly 26 are connected to each other at the top by a lateral connector 30, so as to form a substantially U-shaped body 32 as shown in FIG. 2.

(20) When operating normally, the technogrids 28 are as shown in FIG. 10. When a skip 12 enters an overwind condition and continues to travel upwardly, the skip 12 travels between the technogrids 28 of the U-shaped bodies 32, and impacts the lateral connectors 30. The respective technogrids 28 then plastically deformelongating under strainas shown in FIG. 11. This plastic deformation absorb kinetic energy from the skip 12, thereby slowing the skip 12. If the upper conveyance retarder 15 fails to absorb all of the kinetic energy of the skip 12, and the skip 12 continues upward, then the skip 12 will impact the upper crash beam 14. At this point, upward movement of the skip 12 will cease.

(21) Once the skip 12 has ceased travelling upward, it will descend under gravity. The first safety system used to stop the conveyance during descent is the conveyance catcher 17.

(22) Attention is drawn to FIGS. 2A and 3A. Conveyance catcher 17 is in the form of one or more jack catchers each comprising a vertical column of pivoting catchers 22 fixed to the head frame 11 and a co-operating set of projecting lugs or teeth 24 mounted on the skip 12 at any appropriate position, including the skip body. The jack catchers 22 have an extended, normal condition as shown by jack catcher 22a in FIG. 5, and a retracted condition as shown by jack catcher 22b. The jack catchers 22 remain in the extended condition under gravity. In this condition, the jack catchers 22 bear against respective retaining lugs 27 that prevent the jack catchers 22 from rotation past the extended condition as shown. The jack catchers 22 pivot upwards from the extended condition and into the retracted condition when impacted by the projecting lugs 24 of the skip 12, permitting upward movement of the skip 12 past the jack catchers 22. The jack catchers 22 then drop back to the extended condition, behind the projecting lugs 24, under gravity. When the skip 12 attempts to fall downwardly, the jack catchers 22 catch the teeth or projections 24 on the skip 12 as shown in FIG. 8, to arrest movement of the skip 12. Preferably there are at least two vertical columns of jack catchers 22. The columns in the present example are disposed on opposite sides of the skip 12.

(23) The process of a skip 12 moving past the jack catchers 22, and coming to rest against the column of jack catchers 22 is shown sequence in FIGS. 6 to 8. In FIG. 6, the projecting lugs 24a, 24b of the skip 12 impact against jack catchers 22c, 22d. This impact pivots jack catchers 22c, 22d into the retracted condition.

(24) FIG. 7 shows the skip 12 once it has stopped its upward movement during an overwind condition. The top projecting lug 24a has moved past the uppermost jack catcher 22e.

(25) In FIG. 8, the skip 12 has descended until projecting lug 24a bears against jack catcher 22e, thereby halting movement of the skip 12. If the skip 12 impacts the jack catchers 22 with sufficient force, the jack catchers 22 will break and thus the lower technogrids and crash doors (discussed below) will attempt to stop downward movement of the skip 12.

(26) Notably, for traditional blasting and mucking operations, a bucket or kibble is used. As discussed above, the bucket or kibble is round so that its ability to be loaded and dumped is unaffected by rotation of the bucket or kibble. Since the bucket or kibble may have rotated before entering the head frame, the precise orientation of the bucket or kibble is unknown.

(27) Accordingly, teeth or projections, such as those provided on the skip 12 of the present disclosure, would not be provided on the bucket or kibble since it is uncertain whether those teeth or projections will align with the jack catchers.

(28) The conveyance catcher 17 of the present disclosure prevents freefall downward movement of the skip 12 along the mineshaft, in the event that the hoist rope fails as the result of an overwind condition. The conveyance catcher 17 therefore acts as part of a safeguard against conveyance freefall, constituting part of a hoist system for hoisting a conveyance from a mineshaft.

(29) Such a safeguard could include an upper conveyance retarder 15 that retards upward movement of the conveyance 12 in case of an overwind event of said conveyance 12 (discussed further below), and/or a lower conveyance retarder 16 located below the upper conveyance retarder 15 and the conveyance catcher 17 to retard freefall of the skip 12 in the event that the conveyance catcher 17 fails (discussed further below).

(30) The lower conveyance retarder 16 has technogrid elements 34 and technogrid arms 21 attached to each technogrid element 34 through a linkage 36. Each technogrid arm 21 is generally in an open condition. This condition is shown in FIGS. 9 and 10 in which the technogrid arm 21 is held out of the path of skip 12 so as to allow upward movement of the skip 12 toward the upper crash barrier 14.

(31) Attention is drawn to FIGS. 2B and 3B. During upward movement of the skip 12 in an overwind condition, the skip 12 engages a trip mechanism 19. The trip mechanism 19 is in the form of a pair of pivotally connected bars that extend to respective ones of the technogrid arms 21. They trip mechanism 19 may be engaged by a hook or other mechanism, mounted on the skip 12. Activation of the trip mechanism 19 causes the technogrid arms 21 to move to a closed condition as shown in FIG. 11. In the closed condition the technogrid arms 21 are positioned beneath the skip 12 such that they will engage the skip 12 upon descent, and the technogrid elements will retard subsequent downward movement of the skip 12.

(32) A ratchet bar 38 is connected to one of the technogrid arms 21, and a bolt 40 is connected to the other of the technogrid arms 21. The ratchet bar 38 and bolt 40 engage to hold the technogrid arms 21 together.

(33) As the arms 21 come together, the bar 38 of one arm 21 rides along a lug 42 on the other arm 21. Once the arms 21 are sufficiently close, the bolt 40 will fall into the teeth of the ratchet bar 38. An angled rear surface of each tooth enables the bolt 40 to continue to slide over the teeth to allow the arms 21 to approach, but the curved front face of each tooth engages the bolt 40 to prevent the arms 21 from subsequently moving apart.

(34) FIGS. 10 to 12 show progressive stages in the engagement of the lower conveyance retarder 16. FIG. 10 shows the arms 21 of the lower conveyance retarder 16 in an open condition, permitting upward passage of the skip 12 therebetween. FIG. 11 shows the upper conveyance retarder 15 having been engaged and plastically extended, the arms 21 closed beneath the skip 12, and the ratchet 38 and bolt 40 engaged to prevent the arms 21 from reopening. FIG. 12 shows the lower conveyance retarder 16 after engagement by the skip 12, with the technogrid elements 34 plastically extended to absorb kinetic energy of the falling skip 12.

(35) The technogrid elements 34 plastically deform and strain harden to absorb the kinetic energy of the descending skip 12, and to transfer energy form the skip 12 to the head frame 11.

(36) The lower crash barrier 18 is in the form of a crash door having an upwardly hinged retracted position to allow free passage of the conveyance into and out of the mineshaft. In an overwind condition, the conveyance travels toward the upper crash barrier, triggering the lower crash barrier door to drop to a closed position to prevent free fall of the skip and/or debris back into the mineshaft.

(37) The lower crash barrier 18 is spring loaded so that spring force initiates closure of the lower crash barrier 18, after which gravity takes over and completes closure of the lower crash barrier 18.

(38) It will be appreciated that when the system acts as a safeguard against skip 12 freefall, the means for retarding that freefall (namely retarders 15 to 18) may be individually selected according to the particular requirements of a mining project, and the mass of the conveyance 12 when loaded.

(39) A loaded conveyance (i.e. skip 12) may have a total weight of 6 or 8 t for smaller systems or, for larger systems, a total weight in the order of 20 tonnes or more. If the conveyance were to experience an overwind event and consequently descend in freefall back towards the mineshaft, the lower crash barrier 18 would need to have sufficient strength to withstand the force of the fully loaded conveyance moving at potentially high speed. The lower crash barriers 18 would therefore need to be very heavy, and heavy duty.

(40) In the present case, the rate of descent of the conveyance can advantageously be considerably reduced by the conveyance catcher 17 and conveyance retarders 15, 16. Consequently, the lower crash barrier 18 need only be as strong as necessary to stop a fully loaded conveyance moving at a reduced speed (i.e. with reduced kinetic energy) when compared with the case where no conveyance catcher 17 or conveyance retarders 15, 16 are provided. In other words, it may be possible to design the lower crash barrier 18 to have a strength less than would be required to completely arrest movement of a conveyance that has traveled in freefall from immediately after an overwind event.

(41) Operation of the illustrated hoist system is indicated diagrammatically at FIG. 5. On the occurrence of an overwind event the skip 12 is hoisted upwardly toward the upper crash barrier 14. As the skip approaches the crash barrier (see FIG. 1) the upper conveyance retarder 15 is impacted to retard and slow the skip so as to reduce rebound energy. As the skip approaches the crash barrier (see FIG. 2) and is slowed by the upper technogrid the lower technogrid trip mechanism is tripped by the upward movement of the skip to cause the lower technogrid arms 21 to be brought inwardly into an operative position beneath the skip 12, and the final upward movement of the skip 12 also triggers release of the lower crash barrier 18 so that it moves to the closed condition.

(42) The system and safeguard of the present disclosure advantageously allow the presence of workers under the suspended load of the conveyance, for example within the mineshaft, thereby increasing the safety and efficiency of the shaft sinking process.

(43) If an overwind event is experienced during upward movement of the skip 12, the skip 12 will impact the upper barrier 14. If that impact is sufficient to cause the hoist rope 20 to fail, the skip will begin to fall downwardly. It is then anticipated (FIG. 3 and scenario A in FIG. 13) that the jack catchers of the conveyance catcher 17 will engage to stop the skip 12. In the event that the jack catchers fail to engage successfully to stop the skip (FIG. 4 and scenario B in FIG. 13) the skip falls so as to impact the technogrid arms 21 of the lower conveyance retarder 16 that then engage to stop the skip 12. In the event that the lower conveyance retarder fails to arrest the skip 12 (scenario C in FIG. 13), the skip 12 impacts the crash door of the lower crash barrier 18 so as to be stopped from falling into the mineshaft. In all three scenarios the crash door of the lower crash barrier 18, having closed prior to downward movement of the skip, is effective to contain any spills and debris from the skip during rebound and falling movement.