AP840A

AP840A - Safety detaching hooks.

Info

Publication number: AP840A
Application number: APAP/P/1996/000887A
Authority: AP
Inventors: Alan Sims; Isabel Jeanette Mitchel
Original assignee: Bellambie Mining And Industrial Ltd
Priority date: 1995-12-04
Filing date: 1996-11-29
Publication date: 2000-06-01
Also published as: AP9600888A0; GB2307941A; AU709036B2; GB2307942A; AU7417396A; GB2307942B; AU7417496A; GB9625101D0; AU714836B2; AP842A; GB2307941B; GB9625102D0; AP9600887A0

Abstract

A safety detaching hook 10 includes a pair of scissor plates 12, 14 which are mounted between outer plates 28, 30 for pivotal displacement relative to one another between a normally closed condition and an open condition. The scissor plates 12, 14 each have a striking plate striking formation 16 whereby the scissor plates 12, 14 are displaceable, in use, from their closed condition to their open condition. The safety detaching hook 10 includes locking means in the form of an elongate drop element 42 extending with little clearance through complementary arcuate slots 48 in the scissor plates 12, 14. The slots 48 are configured such that in the closed condition of the scissor plates 12, 14 portions of the slots 48 are in register and portions of the slots 48 remain in register when the scissor plates 12, 14 are displaced from their closed condition towards their open condition only if the displacement of the scissor plates 12, 14 occurs simultaneously. Hence, the locking means is configured to prevent displacement of the scissor plates 12, 14 from their closed position to their open position unless the scissor plates 12, 14 are displaced simultaneously.

Description

THIS INVENTION relates to safety detaching hooks. More particularly it relates to a safety detaching hook suitable for use in connecting a mine conveyance to a winding rope.

Safety detaching hooks of which the Inventors are aware comprise a pair of 5 scissor plates mounted between a pair of outer plates for pivotal displacement about a pivot axis relative to one another between a normally closed condition and an open condition. The outer plates have registering holes therethrough towards operatively lower ends thereof whereby the safety detaching hook is connectable to a conveyance such as a skip or a cage. Each scissor plate defines a hook-like formation, a catch plate or striking plate striking formation and a catch plate engaging formation. The hook-like formations of the scissor plates are configured such that in the closed condition of the scissor plates they overlap and define an aperture whereby a winding rope is connectable, e.g. by means of a top pin and attachments, to the safety detaching hook and in their open condition the hook-like formations are spaced apart to detach the safety detaching hook, and hence a conveyance connected thereto, from the winding rope. The hook-like formations are positioned above the pivot axis. The catch plate striking formations are positioned below the pivot axis and, in the closed condition of the scissor plates, they protrude from between the outer plates laterally in opposite directions. The catch plate engaging formation of each scissor plate is positioned on the opposite side of the scissor plate to and operatively above the associated catch plate striking formation.

In use, in the event of an overwind, the safety detaching hook is drawn upwardly through an aperture in a catch plate mounted on the head frame or head gear. The aperture in the catch plate is dimensioned such that at least an upper portion of the safety detaching hook can pass therethrough with clearance. As the upward displacement

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ο of the safety detaching hook continues, the upper surfaces of the catch plate striking formations abut the lower surface of the catch plate. Further upward displacement of the safety detaching hook relative to the catch plate results in the scissor plates being pivotally displaced from their closed condition towards their open condition. This in turn serves to displace the hook-like formations away from one another and simultaneously to displace the catch plate engaging formations outwardly such that they protrude from between the outer plates laterally in opposite directions. The scissor plates are configured such that by the time that the hook-like formations are spaced sufficiently far apart for the safety detaching hook to become detached from the winding rope, the catch plate engaging formations are positioned above the catch plate and protrude sufficiently far from between the outer plates such that they prevent downward displacement through the aperture in the catch plate. In this way, the conveyance is disconnected from the winding rope and is suspended from the catch plate.

A problem with safety detaching hooks of this type is that debris such as rocks and the like falling down the mine shaft could strike the catch plate striking formations which under certain circumstances could lead to the safety' detaching hook and hence the conveyance detaching from the winding rope. The Inventors believe that the present invention will at least alleviate this problem.

According to one aspect of the invention, there is provided a safety detaching hook which includes a pair of scissor plates which are mounted for pivotal displacement relative to one another between a normally closed condition and an open condition, at least one of the scissor plates having a striking plate striking formation whereby the scissor plate is displaceable, in use, from its closed condition to its open condition; and locking means configured to permit displacement of the scissor plates from their closed condition to their open condition only if displacement of the scissor plates occurs simultaneously.

The locking means may include an elongate drop element extending with little clearance through complementary arcuate slots in the scissor plates, the slots being

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AP Ο ο 0 g 4 ο configured such that in the closed condition of the scissor plates portions of the slots are in register and portions of the slots remain in register when the scissor plates are displaced from their closed condition towards their open condition only if the displacement of the scissor plates occurs simultaneously.

The arcuate slots may be oppositely disposed in the scissor plates, each arcuate slot curving outwardly and downwardly such that in the closed condition of the scissor plates upper end portions of the slots are in register and in the open condition of the scissor plates lower end portions of the slots are in register. Each arcuate slot may have a radius of curvature of 30 -70 mm when the safety detaching hook has a carrying capacity of 5 - 35 tonne. A safety detaching hook with a carrying capacity of 5 tonne may have a radius of curvature of 40 mm. A safety detaching hook with a carrying capacity of 30 tonne may have a radius of curvature of 53 mm.

The safety detaching hook may include a pair of spaced apart outer plates provided with complementary elongate longitudinally extending apertures and a pivot pin extending between the outer plates on which the scissor plates are pivotally mounted, the drop element being in the form of a drop pin which is mounted on and extends between the outer plates and which is longitudinally slidable relative to the outer plates in the longitudinally extending apertures, the drop pin extending through the arcuate slots in the scissor plates so that, in use, the drop pin inhibits displacement of the scissor plates from their closed condition towards their open condition unless the scissor plates are displaced simultaneously. Accordingly, the drop pin may have a diameter of sufficient size to inhibit displacement of the scissor plates from their closed condition towards their open condition except when the scissor plates are displaced simultaneously. In other words, the drop pin may be mounted on and extend between the outer plates, being longitudinally slidable relative thereto, thereby to inhibit or prevent displacement of the scissor plates when only one of the striking plate striking formations is subjected to a displacement force.

The drop pin may have a diameter of about 25 - 100 mm when the safety detaching hook has a carrying capacity of 5 - 35 tonne. In addition to resisting independent displacement of the scissor plates, the drop element may be configured to be connectable c:/data/specs/3/banana.cs/cb 27 November 1996

AP/P/ 96/0 0887 ο ο 8 4 ο to a conveyance. The drop pin of a safety detaching hook having a 20 tonne carrying capacity may have a diameter of about 25 - 50 mm, e.g. 38 mm, when it serves solely to inhibit independent displacement of the scissor plates and a diameter of about 40 - 100 mm, e.g. 86 mm, when it serves both to inhibit independent displacement of the scissor plates and as a connection for a conveyance.

It will be appreciated that the drop pin is manufactured from a metal or metal alloy of sufficient hardness to inhibit or resist shearing thereof. Accordingly, the drop pin may be manufactured from a metal or metal alloy having a hardness of at least 250 HB, e.g. a metal alloy BS 970 826M40 Condition U.

Clearance or spacing between the arcuate slots and the drop pin may be selected to inhibit or resist initial displacement of the scissor plates towards their open condition and, when required in use, to permit simultaneous displacement of the scissor plates from their closed condition to their open condition. The clearance between each arcuate slot and the drop pin may be less than 0,6 mm, preferably 0,1 - 0,5 mm, e.g. 0,1 mm, 0,25 mm or 0,5 mm. A safety detaching hook with a carrying capacity of 20 tonne having a drop pin with a diameter of 38 mm may have a clearance of 0,5 mm.

The safety' detaching hook may include a shear pin extending between the outer plates through registering holes in the scissor plates thereby to retain the scissor plates releasably in their closed condition to resist initial displacement of the scissor plates towards their open condition, in use.

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Each scissor plate may have a catch plate engaging formation. In one embodiment of the invention, each scissor plate may be provided with a striking plate striking formation and a catch plate engaging formation, the striking plate striking formation being positioned at an operatively higher level than the catch plate engaging 25 formation, with the striking plate striking formation being adapted to engage a striking plate and the catch plate engaging formation being adapted to engage a catch plate.

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The striking plate striking formation in the closed condition of the scissor plates may slope downwardly outwardly and define together with a longitudinal centre line of the safety detaching hook an included angle of not greater than 45°. Preferably, each scissor plate has a striking plate striking formation having an upper striking plate engaging surface which, in the closed condition of the scissor plates defines, together with the longitudinal centre line of the safety detaching hook, an included angle of not greater than 45°.

Preferably, the included angle is not greater than 30°, more preferably the included angle is between 12° and 20°, e.g. 16° or 19°.

The safety detaching hook may include a retaining member positioned at an operatively higher level than the striking plate striking formation(s) so as to resist initial displacement of the scissor plates towards their open condition. The retaining member may be in the form of a band, the band being configured to deflect falling debris away from the striking plate striking formation(s). Preferably, each scissor plate has a striking plate striking formation and the retaining band is configured to protect both of the striking plate striking formations from falling debris.

The invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which:

Figure 1 shows a schematic three-dimensional view of a safety detaching hook according to the present invention;

Figure 2 shows an exploded three-dimensional view of certain components of the safety detaching hook of Figure 1;

Figure 3 shows a schematic front elevation of the safety detaching hook in its closed condition in relation to part of a catch plate and part of a striking plate forming part of a winding installation;

Figure 4 shows the safety detaching hook of Figure 3 in its partially opened condition;

Figure 5 shows the safety detaching hook of Figure 3 in its fully open condition and releasing a top pin and attachments connected to a winding rope;

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Figure 6 shows the safety detaching hook of Figure 3 in its fully open condition supported on the catch plate;

Figure 7 shows a schematic three-dimensional view of another embodiment of a safety detaching hook according to the present invention;

Figure 8 shows an exploded three-dimensional view of certain components of the safety detaching hook of Figure 7;

Figure 9 shows a schematic front elevation of the safety detaching hook of Figure 7 in its closed condition in relation to part of a catch plate and part of a striking plate forming part of a winding installation;

Figure 10 show's the safety detaching hook of Figure 9 in its partially open condition;

Figure 11 shows the safety detaching hook of Figure 9 in its fully open condition and releasing a top pin and attachments connected to a winding rope;

Figure 12 shows the safety detaching hook of Figure 9 in its fully open condition 15 supported on the catch plate;

Figure 13 shows a schematic front view of another embodiment of a safety detaching hook according to the present invention;

Figure 14 show's a schematic front view of a scissor plate of the safety detaching hook of Figure 13; and

Figure 15 shows a schematic front elevation of the safety detaching hook of Figure in its fully open condition in relation to part of a catch plate and part of a striking plate forming part of another embodiment of a winding installation.

In Figures 1 - 6 of the drawings, reference numeral 10 generally indicates a safety detaching hook in accordance with the invention. The safety detaching hook 10 has a carrying capacity of 20 tonne and includes a pair of spaced apart outer plates 28, 30 and a pair of scissor plates 12, 14 which are positioned between the outer plates 28, 30.

. The scissor plates 12, 14 are mounted for pivotal displacement relative to one another between a normally closed condition (see Figures 1 and 3) and an open condition (see

Figures 5 and 6). The scissor plates 12, 14 each have a striking plate striking formation

16 having an upper striking plate engaging surface 18. In the closed condition of the scissor plates 12, 14, the striking plate striking formations 16 protrude in opposite

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AP Ο Ο Ο 8 4 Ο directions from between the outer plates 28, 30 and the striking plate engaging surfaces 18 slope downwardly outwardly (see Figures 1 and 3). Each surface 18 defines together with a longitudinal centre line 20 of the safety detaching hook 10, an included angle A (see Figure 3). The included angle A will not be greater than 45° and typically will be about

16°. It is to be appreciated, however, that the optimum angle A for a particular application can be ascertained by routine experimentation.

Each scissor plate 12, 14 defines a hook-like formation 15. The hook- like formations 15 of the scissor plates 12, 14 are configured such that in the closed condition of the scissor plates 12, 14 they overlap and define an aperture 17 whereby a winding rope (not shown) is connectable by means of a top pin and attachments, part of which is indicated by reference numeral 19 (see Figures 3, 4 and 5) to the safety detaching hook 10 and in the open condition of the scissor plates 12, 14, the hook-like formations 15 are spaced apart to detach the safety detaching hook 10 from the top pin and attachments 19 and hence from the winding rope.

The safety detaching hook 10 also includes a rectangular retaining band'24 mounted on the outer plates 28, 30 and positioned above the striking plate striking formations 16 so as, in use, to retain the scissor plates 12, 14 in their closed condition and to deflect falling debris away from the upper striking plate engaging surfaces 18 of the striking plate striking formations 16. The band 24 is secured to the outer plates 28, 30 by means of shear pins in the form of bolts or pins (not illustrated). In another embodiment, the band 24 is mounted on the outer plates 28, 30 by means of a frictional press fit. The band 24 has an aperture 25 therethrough shaped to receive the upper portion of the outer plates 28, 30 in a snug fit and hence, as mentioned above, serves to retain the scissor plates 12,14 in their closed condition.

25. The scissor plates 12, 14 are provided with catch plate engaging formations

26. The catch plate engaging formation 26 of each scissor plate 12, 14 is positioned on the opposite side of the scissor plate 12, 14 to and at a level which is below the level of the associated striking plate striking formation 16.

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AP0008AQ

The safety detaching hook 10 includes a pivot pin 32, extending between the outer plates 28, 30 on which the scissor plates 12, 14 are pivotally mounted. The pivot pin 32 extends through registering apertures 33 (see Figure 2) provided in the outer plates 28, 30 and the scissor plates 12, 14 and is secured in position by lock nuts 34.

A pair of spacing studs 62 extend between the outer plates 28, 30. Threaded end portions of the spacing studs 62 protrude through apertures 60 in the outer plates 28, 30 and nuts 64 are mounted thereon to secure the spacing studs 62 in position. The spacing studs 62 and pivot pin 32 serve to retain the outer plates 28, 30 in the desired spatial relationship.

The hook-like formations 15 of the scissor plates 12, 14 are positioned above the pivot pin 32. The striking plate striking formations 16 are positioned at lower levels than the level of the pivot pin 32 and, in the closed condition of the scissor plates 12, 14, they protrude from between the outer plates 28, 30 laterally in opposite directions (see Figures 1 and 3). The outer plates 28, 30 are provided with slots 35 at upper ends thereof for receiving or releasing the top pin and attachments 19 connected to the winding rope (see Figure 2).

The safety detaching hook also includes a shear pin 36 which extends between the outer plates 28, 30 through registering holes 40 (see Figure 2) provided in the outer plates 28, 30 and the scissor plates 12, 14 to resist initial displacement of the scissor plates 12, 14 to their open condition. The shear pin 36 is retained in position by nuts 38 mounted on protruding ends thereof.

Furthermore, the safety detaching hook 10 includes locking means configured, in use, to permit displacement of the scissor plates 12, 14 from their closed . condition to their open condition only if displacement of the scissor plates 12, 14 occurs simultaneously. The locking means includes a drop pin 42 with a diameter of 38 mm which is mounted on and extends between the outer plates 28, 30 and is longitudinally slidable relative to the outer plates 28, 30 in longitudinally extending apertures 46. The drop pin 42 is held captive by means of nuts 44 mounted on protruding ends thereof. The

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ΑΡ Ο Ο Ο Β 4 Ο drop pin 42 extends through complementary oppositely disposed arcuate slots 48 (see

Figure 2) in the scissor plates 12, 14, with a clearance of 0,5 mm between the drop pin 42 and the arcuate slots 48, so that, in use, the drop pin 42 inhibits independent displacement of the scissor plates 12, 14 from their closed condition towards their open condition but permits displacement of the scissor plates 12, 14 when they are displaced simultaneously to shear the shear pin 36. Each arcuate slot 48 has a radius of curvature (designated r in Figure 4) of 53 min. The arcuate slots 48 are configured such that in the closed condition of the scissor plates 12, 14, portions of the arcuate slots 48 are in register and portions of the arcuate slots 48 remain in register when the scissor plates 12, 14 are displaced from their closed condition towards their open condition only if displacement of the scissor plates 12, 14 occurs simultaneously. More particularly, the arcuate slots 48 are oppositely disposed in the scissor plates 12, 14, each arcuate slot 48 curving outwardly and downwardly such that in the closed condition of the scissor plates 12, 14 upper end portions of the arcuate slots 48 are in register and in the open condition of the scissor plates 12, 14 lower end portions of the arcuate slots 48 are in register. Hence, the registering portions of the slots 48 move progressively from the upper end portions to the lower end portions as the scissor plates 12, 14 move progressively from their closed condition to their open condition.

The outer plates 28, 30 have registering holes 50 which are in register with arcuate slots 52 provided in the scissor plates 12, 14 whereby, in use, the safety detaching hook 10 is connectable to a conveyance (not shown) such as a skip or a cage.

The safety detaching hook 10 is also provided with registering holes 54 in the outer plates 28, 30 and slots 56 (see Figure 2) in the scissor plates 12, 14 for receiving a lowering shackle or link (not shown).

25- The scissor plates 12, 14 will typically be manufactured from 1,5% manganese steel BS 2772 part 2 1989 Group 2 150 M19 British National Coal Board Standards. The drop pin 42 will typically be manufactured from a metal alloy B5970 826M40 condition U. The drop pin 42 has a minimum hardness of 250 HB.

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The safety detaching hook 10 is intended for use with a winding installation, part of which is generally indicated by reference numeral 65 (Figures 5 and 6). The winding installation 65 includes a head gear positioned above a mine shaft (not shown), the striking plate 66 (see Figures 3-6) mounted on the head gear has an aperture 68 therethrough through which the winding rope can extend, and an arrestor or catch plate 70 mounted on the head gear below the striking plate 66. The catch plate 70 has an aperture 72 therethrough which is in register with the aperture 68 in the striking plate 66. As shown, the aperture 72 in the catch plate 70 is larger than the aperture 68 in the striking plate 66.

Referring to Figures 7 - 12, the same reference numerals will be used to indicate the same parts as in Figures 1-6, unless otherwise indicated. The safety detaching hook of Figures 7 - 12 has a carrying capacity of 20 tonne. The main difference between the safety detaching hook 10 illustrated in Figures 1-6 and the safety detaching hook 10 illustrated in Figures 7 - 12, is that the locking means of the safety detaching hook

10 of Figures 7-12 includes a bottom drop pin or drop rod 74 forming part of a clevis (not shown). The drop rod 74 is of relatively large diameter (the diameter being 86 mm) compared to the drop pin 42 of Figures 1-6 and serves the dual function of inhibiting independent displacement of the scissor plates 12, 14 in the same manner as the drop pin 42 and connecting a conveyance to the safety detaching hook 10. As can be seen from

Figures 7 - 12, the drop pin 42, the apertures 46, the arcuate slots 48, the holes 50 and the arcuate slots 52 of the safety detaching hook 10 of Figures 1-6 have been combined into a more simplified arrangement with fewer components as described below. The drop rod 74 is mounted on and extends between the outer plates 28, 30 and is longitudinally slidable relative to the outer plates 28, 30 in longitudinal apertures 76. The drop rod 74 extends through complementary oppositely disposed arcuate slots 78 (see Figure 8) in the scissor plates 12, 14 with a clearance of 0,5 mm between the drop rod 74 and the arcuate slots 78 . so that, in use, the drop rod 74 inhibits independent displacement of the scissor plates 12, 14 from their closed condition towards their open condition but permits displacement of the scissor plates 12, 14 when they are displaced simultaneously. Each arcuate slot 78 has a radius' of curvature (designated r in Figure 9). It is to be appreciated that the radius of curvature r may vary depending inter alia on the dimensions of the rod 74 and the slot 78.

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The optimum radius of curvature for a particular application can be ascertained by routine experimentation. Furthermore, in use, the safety detaching hook 10 is connected to the conveyance by means of the clevis of which the drop rod 74 forms part. The included angle A in Figure 9 is typically about 19°.

The drop rod 74 will typically be manufactured from a metal alloy B5970

826M40 condition U. The drop rod 74 has a minimum hardness of 250HB.

Referring to Figures 13 - 15, the same reference numerals will be used to indicate the same parts as in Figures 1 - 12, unless otherwise indicated. The main difference between the safety detaching hook 10 illustrated in Figures 13 and 15, is that the scissor plates 12, 14 are each provided with a striking plate engaging formation 82 in addition to the catch plate engaging formation 26. The striking plate engaging formations are positioned at an operatively higher level than the catch plate engaging formations **** GO

26. The striking plate engaging formation 82 of the scissor plate 12 is most clearly qq illustrated in Figure 14. The included angle A of the safety detaching hook 10 is typically o

about 22°. Furthermore, as can be seen from Figure 15, the striking plate 66 is thicker than the striking plate 66 illustrated in Figures 3-6 and Figures 9-12. iO

In use, the safety detaching hook 10 is connected to the cage by means of Q· a securing pin (not shown) extending through the holes 50 and the slots 52 provided in the outer plates 28, 30 and the scissor plates 12, 14 respectively, and to a winding rope (not shown) by means of the top pin and attachments 19.

The cage is then ready to be raised or lowered by means of the winding installation 65 in a hoistway or shaft of a mine. As mentioned above, the striking plate striking formations 16 with the upper striking plate engaging surfaces 18 slope downwardly and outwardly at a relatively shallow angle A in relation to the outer plates 28, 30. The striking plate striking formations 16 are configured in this manner to minimise or prevent accidental actuation of the safety detaching hook 10 by way of falling debris striking the striking plate engaging surfaces 18. In other words, the upper striking plate engaging surfaces 18 are angled, as described above, to minimise the possibility of debris such as ::/data/specs/3/banana.cs/cb 27 November 1996

APO ο ο 8 4 Ο

rocks striking the striking plate striking formations 16 and thereby actuating the safety detaching hook 10. The angled striking plate striking formations 16 thereby provide a reduced striking surface area to vertically falling debris and, if struck by debris, the sloping angle of the striking plate striking formations 16 facilitates deflection of the debris off the upper striking plate engaging surface(s) 18 without actuation of the safety detaching hook 10 since the component of force acting to displace the striking plate striking formation 16 inwardly, i.e. towards the open condition of the scissor plates 12, 14 is relatively low. The band 24 also functions to protect or shield the striking plate striking formations 16 from falling debris. Accordingly, the retaining band serves the triple function of retaining the scissor plates in their normally closed condition, deflecting falling debris away from the striking plate striking formations 16 and to urge the scissor plates 12, 14 into their open condition when the band 24 comes into contact with the striking plate 66. Furthermore, the locking means, i.e. the drop pin 42 or the drop rod 74 together with the arcuate slots 48 only permit displacement of the scissor plates 12, 14 from their closed condition to their open condition if displacement of the scissor plates 12, 14 occurs simultaneously. In other words, if falling debris strikes one of the striking plate striking formations 16, the locking means resists displacement of the scissor plates 12, 14 from their closed condition to their open condition.

During normal use, the safety detaching hook 10 will be below the catch plate 70. However, referring specifically to Figures 3 - 6, in the event of an overwind, the safety detaching hook 10 is drawn upwardly through the aperture 72 in the catch plate 70 mounted on the head frame or head gear. The aperture 72 in the catch plate 70 is dimensioned such that the safety detaching hook 10 and the band 24 can pass therethrough with clearance. In Figures 3-6, only one of the scissor plates, i.e. scissor plate 14, is indicated in broken lines through the outer plate 28 and in Figures 4 - 6 not all the components have been numbered for the purpose of clarity. As the upward displacement . of the safety detaching hook 10 continues, the upper end of the safety detaching hook 10 passes through the aperture 68 of the striking plate 66 as shown in Figure 3 and the band comes into contact with the peripheral edge of the striking plate 66 defining the aperture

68. The aperture 68 in the striking plate 66 is dimensioned such that only the upper portion of the safety detaching hook 10 can pass therethrough with clearance, the band 24

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AP 0 Ο ο 8 4 Ο and the lower portion of the safety detaching hook 10 being too large to pass through the aperture 68 of the striking plate 66. As the upward displacement of the safety detaching hook 10 continues, the upper striking plate engaging surfaces 18 of the striking plate striking formations 16 come into contact with the peripheral edge of the band 24 defining the aperture 25 as shown in Figures 3 and 4 respectively. The upward displacement of the safety detaching hook 10 relative to the striking plate 66 results in the shear pins securing the band 24 to the outer plates 28, 30 being sheared and the band 24 being pushed downwardly along the upper portion of the safety detaching hook 10. The upward displacement of the safety detaching hook 10 relative to the band 24 and the striking plate

66 results in the peripheral edge of the band 24 defining the aperture 25 coming into contact with and exerting an inwardly directed force on the upper striking plate engaging surfaces18 of the striking plate striking formations 16 thereby resulting in the scissor plates 12, 14 being pivotally displaced from their closed condition towards their open condition, with the shear pin 36 being sheared by the scissor plates 12, 14 as they pivot towards their open condition. This pivotal displacement of the scissor plates 12, 14 relative to one another serves to displace the hook-like formations 15 away from one another and simultaneously to displace the catch plate engaging formations 26 outwardly such that they protrude from between the outer plates laterally in opposite directions as shown in Figure 5. Upward displacement of the safety detaching hook 10 continues until the scissor plates

12, 14 are in their open condition in which the hook-like formations 15 are spaced sufficiently far apart for the safety detaching hook 10 to release the top pin and attachments 19 as shown in Figure 5 of the drawings. As the safety detaching hook is displaced upwardly and the scissor plates 12, 14 are pivotally displaced from their closed condition towards their open condition, portions of the arcuate slots 48 continuously come into register thereby allowing the drop pin to be displaced along the length of the arcuate slots 48 while simultaneously being displaced longitudinally downwardly in the apertures 46 of the outer plates 28, 30. In other words, because the arcuate slots 48 are oppositely . disposed in the scissor plates 12, 14 with each arcuate slot curving outwardly and downwardly, upper end portions of the arcuate slots 48 are initially in register in the closed condition of the scissor plates 12, 14, different portions of the slots 48 continuously come into register as the scissor plates 12, 14 are pivotally displaced towards their open condition until finally the lower end portions of the slots are in register when the scissor plates 12,

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APO 0 0 8 4 Ο are in their open condition, the drop pin 42 abutting the lower end portions of the slots 48 serving to lock the scissor plates 12, 14 in their open condition. Accordingly, the drop pin 42 is displaced and slides longitudinally downwardly in the apertures 46 of the outer plates 28, 30 while simultaneously being displaced in the arcuate slots 48 in the scissor plates 12, 14 until the drop pin 42 abuts the lowermost edge of the apertures 46, thereby locking the scissor plates 12, 14 in their open condition. The drop pin 42 permits displacement of the scissor plates 12, 14 relative to one another only if the scissor plates 12, 14 are displaced simultaneously. It will be appreciated that, if falling debris strikes the striking plate engaging surface 18 of, for example, the scissor plate 12, the force imparted to the scissor plate 12 to displace it towards its open condition is resisted or inhibited by the drop pin 42, the shape of the arcuate slot 48 inhibiting the drop pin 42 from being displaced longitudinally downwardly in the apertures 46 of the outer plates 28, 30 by virtue of the fact that the second scissor plate 14 remains in its closed condition. In other words, as a result of the scissor plate 14 remaining in its closed condition, the arcuate slot 48 of the scissor plate 14 remains stationary thereby resisting or inhibiting movement of the scissor plate 12 via the drop pin 42 when a force is directed on the upper striking plate engaging surface 18 of the scissor plate 12. Furthermore, the clearance of 0,5 mm between the drop pin 42 and the arcuate slots 48 is small enough to resist or inhibit initial displacement of the scissor plates 12, 14 towards their open condition but large enough to allow displacement of the scissor plates 12, 14 towards their open condition when the band 24 comes into contact with and exerts an inwardly directed force”on the upper striking plate engaging surfaces 18 of the striking plate striking formations 16. Referring specifically to Figures 9 - 12, the safety detaching hook 10 of Figures 9-12 functions in the same manner as the safety detaching hook 10 of Figures 3 - 6 described above except that in

Figures 9 - 12, the drop rod 74 is displaced and slides longitudinally downwardly in the apertures 76 of the outer plates 28, 30 while simultaneously being displaced in the arcuate slots 78 in the scissor plates 12, 14 until the drop rod 74 abuts the lowermost edge of the . apertures 76, thereby locking the scissor plates 12, 14 in their open condition. The drop rod 74 permits displacement of the scissor plates 12, 14 relative to one another only if the scissor plates 12, 14 are displaced simultaneously. Accordingly, the drop rod 74 functions in the same manner as the drop pin 42 of Figures 1-6 when a force is imparted to only one of the upper striking plate engaging surfaces 18 of the scissor plates 12, 14. The drop

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APO Ο Ο 8 4 Ο rod 74 functions both to lock the scissor plates 12, 14 in their open condition and to suspend the conveyance from the safety detaching hook 10 by means of the clevis. The catch plate engaging formations 26 are positioned above the catch plate 70 and protrude sufficiently far from between the outer plates 28, 30 such that as the conveyance and safety detaching hook 10 fall under the influence of gravity, the catch plate engaging formations 26 come into contact and abut an upper surface of the catch plate 70 as shown in Figures 6 and 12 to prevent downward displacement of the safety detaching hook 10 through the aperture 72 in the catch plate 70, thereby suspending or supporting the cage by means of the safety detaching hook 10 on the catch plate 70 in the head gear. Referring specifically to Figures 13 and 15, the safety detaching hook 10 functions in the same manner as the safety detaching hook 10 of Figures 3-6 described above except that in Figure 15, when the catch plate engaging formations 26 are displaced outwardly such that they protrude from between the outer plates 28, 30 laterally in opposite directions, the striking plate engaging formations 82 are simultaneously displaced outwardly such that they also protrude from between the outer plates 28, 30 laterally in opposite directions at a higher level than the catch plate engaging formations 26 as shown. As the conveyance and safety detaching hook 10 fall under the influence of gravity, the catch plate engaging formations 26 come into contact and abut an upper surface of the catch plate 70 while simultaneously the striking plate engaging formations 18 come into contact and abut an upper surface of the striking plate 66 as shown in Figure 15 to prevent downward displacement of the safety detaching hook 10 through the aperture 68 of the striking plate 66 and through the aperture 72 in the catch plate 70, thereby suspending or supporting the cage by means of the safety detaching hook 10 on the striking plate 66 and on the catch plate 70 in the head gear. The cage can be removed from the head gear or reattached to the winding rope via the shackle

19 by means of the lowering link (not shown) positioned in the slots 54, 56 in a conventional manner. For the safety detaching hook of Figures 7 - 12, the conveyance needs to be supported in order to enable the drop rod 74 and the band 24 to be returned to their original positions illustrated in Figure 9. A new shear pin 36 will then be secured in position before returning the safety detaching hook 10 to service.

It is to be appreciated that the safety detaching hooks 10 can be used without the retaining band 24, displacement of the scissor plates from their closed to their open

AP/P/ 9 6 I 0 0 8 87 :/daia/specs/3/banana.cs/cb 27 November 1996

APO Ο Ο 8 4 Ο positions then being effected by the surfaces 18 abutting the portion of the striking plate 66 defining the aperture 68.

The Applicant believes that the safety detaching hook in accordance with the invention will minimise or prevent accidental actuation of the safety detaching hook by 5 debris such as falling rocks. The arcuate slots in the scissor plates in conjunction with the drop pin or drop rod retain the scissor plates in their closed condition until displacement of the scissor plates occurs simultaneously. Furthermore, the retaining band can be used on the safety detaching hooks in accordance with the invention to minimise or prevent actuation of the striking plate striking formations by falling debris or can be used on 10 existing safety detaching hooks for the same purpose. Accordingly, the retaining band serves the triple function of retaining the scissor plates in their normally closed condition, deflecting falling debris away from the striking plate striking formations 16 and to urge the scissor plates 12, 14 into their open condition when the band 24 comes into contact with the striking plate 66.

Claims

1. A safety detaching hook which includes a pair of scissor plates which are mounted for pivotal displacement relative to one another between a normally closed condition and an open condition, at least one of the

5 scissor plates having a striking plate striking formation whereby the scissor plate is displaceable, in use, from its closed condition to its open condition; and locking means configured to permit displacement of the scissor plates from their closed condition to their open condition only if displacement of the scissor plates occurs simultaneously.

10

2. A safety detaching hook as claimed in Claim 1, in which the locking means includes an elongate drop element extending with little clearance through complementary arcuate slots in the scissor plates, the slots being configured such that in the closed condition of the scissor plates portions of the slots are in register and portions of the slots remain in register when the scissor plates are displaced from their closed condition towards

15 their open condition only if the displacement of the scissor plates occurs simultaneously.

3. A safety detaching hook as claimed in Claim 2, in which the arcuate slots are oppositely disposed in the scissor plates, each arcuate slot curving outwardly and downwardly such that in the closed condition of the scissor plates upper end portions of the slots are in register and in the open condition of the scissor plates lower end portions of the

20 slots are in register.

4. A safety detaching hook as claimed in Claim 2 or Claim 3, in which each arcuate slot has a radius of curvature of 30 - 70 mm when the safety detaching hook has a carrying capacity of 5 - 35 tonne.

5. A safety detaching hook as claimed in any one of claims 2 to 4 inclusive,

25 which includes a pair of spaced apart outer plates provided with complementary elongate longitudinally extending apertures and a pivot pin extending between the outer plates on which the scissor plates are pivotally mounted, the drop element being in the form of a

AP/P/ 9 6 / 0 0 887 e:/data/specs/3/banana.cs/cb 27 November 1996 drop pin which is mounted on and extends between the outer plates and which is longitudinally slidable relative to the outer plates in the longitudinally extending apertures, the drop pin extending through the arcuate slots in the scissor plates so that, in use, the drop pin inhibits displacement of the scissor plates from their closed condition towards their

5 open condition unless the scissor plates are displaced simultaneously.

6. A safety' detaching hook as claimed in Claim 5, in which the drop pin has a diameter of 25 - 100 mm when the safety detaching hook has a carrying capacity of 5 35 tonne.

7. A safety detaching hook as claimed in any one of Claims 2-6 inclusive, in 10 which, in addition to resisting independent displacement of the scissor plates, the drop element is configured to be connectable to a conveyance.

8. A safety detaching hook as claimed in any one of Claims 2-7 inclusive, in which clearance between each arcuate slot and the drop element is less than 0,6 mm.

9. A safety detaching hook as claimed in Claim 8, in which the clearance 15 between each arcuate slot and the drop element is 0,1 -0,5 mm.

10. A safety detaching hook as claimed in any one of the preceding claims, which includes a shear pin extending through registering holes in the scissor plates to retain the scissor plates releasably in their closed condition.

11. A safety detaching hook as claimed in any one of the preceding claims, in 20 which each scissor plate includes a striking plate striking formation and a catch plate engaging formation, the striking plate striking formation being positioned at an operatively ' higher level than the catch plate engaging formation, with the striking plate striking formation being adapted to engage a striking plate and the catch plate engaging formation being adapted to engage a catch plate.

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APO 0 0 8 4 0

12. A safety detaching hook as claimed in any one of the preceding claims, in which the striking plate striking formation in the closed condition of the scissor plates slopes downwardly outwardly and defines together with a longitudinal centre line of the safety detaching hook an included angle of not greater than 45°.

5

13. A safety detaching hook as claimed in Claim 12, in which each scissor plate has a striking plate striking formation having an upper striking plate engaging surface which, in the closed condition of the scissor plates defines, together with the longitudinal centre line of the safety detaching hook,.an included angle of not greater than 45°.

14. A safety detaching hook as claimed in any one of the preceding claims, 10 which includes a retaining member positioned at an operatively higher level than the striking plate striking formation(s) so as to resist initial displacement of the scissor plates towards their open condition.

15. A safety detaching hook as claimed in Claim 14, in which the retaining member is in the form of a band, the band being configured to deflect falling debris away

-15 from the striking plate striking formation(s).