CA1162160A - Skips and flasks - Google Patents

Abstract

ABSTRACT

This invention relates to a skip or loading flask which has a body defining a storage chamber and a sloping bottom. A
discharge opening is defined in the body adjacent to the sloping bottom, and a door for closing the discharge opening is openable to allow material to be discharged from the chamber.
The body includes at least one pair of opposed walls arranged so that the storage chamber widens downwardly within the body as a wear-reducing factor. The door may be operable by at least one door-operating mechanism such as over-centre mechanisms, arranged for normally holding the door closed.
For example, over-centre mechanisms may at least partly extend alongside the opposite sides of the body and, in a skip, may be operable by movement of a follower along a cam track to open the door, more complex locking mechanisms thus being avoided. The door can be pivotable about an axis for closing the discharge opening, and the sloping bottom and the door may then have supporting surfaces meeting at a junction substantially extending along said axis to restrict passage of material between the surfaces.
A loading flask of the invention can be used with a feeder chute located to guide material discharged over the door and having a feeder surface at a steeper slope than the door when the door is in its fully open position.

Description

1 ~6216() T~IIS INVENTION relates to skips and to loading flasks of similar basic construction to such skips.
~ ccording to the invention, there is provided a unit in the form of a skip or loacling flask for receiving, containing and di.scharging material, the unit comprising a body defining a downward]y extending storage chamber and having an integral sloping bottom beneath a part of the chamberi a discharge opening beneath a further part of the chamber and defined in the body adjacent to the integral sloping bottom; and a door locatable in a closed position beneath the further part of the chamber for closing the discharge opening, the door being openable by pivoti.ng downwardly to an open position to allow material to be discharged from the chamber through the opening, the door forming a chute beneath the opening and extending downwardly and away from the sloping bottom in the open position of the door, wherein the body includes at least one pair of spaced opposed walls diverging downwardly along at least a substantial part of the height of the chamber whereby the storage chamber widens downwardly within the body, the substantial part of the height of the chamber being greater than the spacing between the opposed walls immediately above the opening.
The body may be substantially square or substantially rectangular in horizontal cross-section along at least a substantial part of its height and it may then have two opposed pairs of walls, both of which can diverge downwardly along at least a substantial part of the height

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l 162~6P `
of the chamber. The walls preferably diverge downwardly along the whole height of the chamber as the provision of the downwardl.y diverging wal].s and thus a downwardly widening chamber can help to eliminate wear on side, back and front walls of the skip or loading flasX as material moves downwardly within the skip or flask.

- 2a -1 l62l6n An over-centre mechanism may be provided for holding the door of the skip or flask closed. In one embodiment, the skip or flask may have over-centre mechanisms with over-centre means at opposite sides of the body and operable to open and close the door, the mechanisms being movable to over-centre positions to releasably lock the door in its closed condition.
With suitable over-centre mechanisms, the load on the door, the weight of the door itself, and optionally the weight of any operating means provided for operating the door may be used to biased the mechanisms -to their over-centre positions.

Each mechanism may include an arm pivotally connected to the door, a lever having one region pivotally connected to the body and one region connected to the arm to provide for over-centre means, and operating means pivotally connected to the lever to move the arm and release the ovex-centre mechanism from its closed condition and then to move the door to its open position when the lever is pivoted in a predetermined direction. The mechanism will then be arranged to move the door to its closed condition and the over-centre mechanism -to its over-centre condition when the lever is moved in the other direction. Such a lever having a pivotal connection to the body, a pivotal connection to an arm connected to the door, and a connection to an operating means such as a follower or ram, is herein referred to generically as a bell crank lever for ease of reference, whether the bell crank lever is, for example a single V-shaped or substantially triangular member or comprises lever arms spaced from one another along a pivot axis but movable together about the pivot axis.

1 16216fl The over-centre mean~ may be such that a line extending between the pivotal connections of the arm to the door and of the arm to the lever is on one side of the pivot axis o~ the lever when the mechanism is i~ its over-centre condition and on the opposite side when the mechani~m i5 moving the doox to its open condition. Any reaction forces applied to the lever from the closed door will then extend along such line and will serve to retain the mechanism in its over-centre condition until the arm is pivoted.

The control of the door may be particularly important for a moving skip, and in one embodiment the operating means for the mechanism may include a follower for engaging a cam track, the mechanism being operable ~y movement of the follower along the cam track to open the door. The cam track may be any suitable tipping path provided in the head gear of a mine, for example, and the follower may move into the path and engage to the cam track as the skip moves upwardly to the head gear.

In contra~t, the mechanism for a loading flask can be relatively ~imple and can be controlled, for example, by a single pneumatic or hydraulic ram.

In~one embodiment, the over-centre mechanisms of the skip may be largely arranged closer to one side of the skip, for example towards the front of the skip closest to the feed side. A bottom cross-head may then be arranged 21Bn so that its weight is largely on the opposite side of the skip and ~o that it helps to balance the loaded skip. The skip design may be further modiEied to compensate for normal unbalanced loads in the s]cip. If it is found that the material in the skip adopts an angle of repose such that more material will normally be received on the side of the skip cloiest to the feed side, the sloping bottom may then be aLranged on the oppo~ite side of the skip and the door control mechanism and cross-head may be largely arranged to help balance the loaded skip. This can help to eliminate wear on shoes, guide rollers, and guides for guiding the skip as it is raised and lowered.

Material is normally discharged into -the skip from a loading flask, and loading flasks often direct material from the feed side of the skip by providing a feeder chute. This can result in undue wear on the opposed wall of the ~kip.

In order to help reduce this wear, a loading flask assembly including a loading flask according to the invention may have its door for closing the discharge opening movable to a fully open position to define a chute surface extending from the opening; and a feeder chute can be located to guide material discharged over the door, the feeder chute preferably being at a steeper slope than the door when the door is in its fully open position.

-6- 116216~

If the feeder chute is at a steeper angle than the door, the material flowing from the flask is able to follow a more natural path so that material is more likely to fall downardly into the ski.p rather than to be projected at the opposite side of the skip.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which, Figure 1 is a front view of a skip in a Job's bridle;
Figure 2 is a side view showing the skip and bridle of Figure l;
Figure 3 is a front view of a bridle-less skip;
Figure 4 is a side view of the skip of Figure 3;
Figure 5 is a plan view of the skip of Figure 3;
Figure 6 is a front view of a loading flask;
Figure 7 i9 a side view of the loading flask of Figure 6, schematically illustrating the position of a feeder chute;
Figure 8 is a side view of a feeder chute for use with the loading flask of Figure 6;
Figure 9 is a front view of the feeder chute;
Figure 10 is a front view of an alternative loading flask;
Figure 11 is a side view of the loading flask of Figure 10 also illustrating a discharge position with respect to a feeder chute;

Figure 12 is a front ~iew of a further skip;

1 lB2161~

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Figure 13 shows the skip of Figure 12 in its closed condition;
: Figure 14 is ~ detail of a side of the skip of Figure 12;
Figure 15 is a plan view of the skip;
Figure 16 is a detailed rear view of part of the skip;
Figure 17 is a schematic detail showing the junction between a door and a sloping bottom with the door in its closed condition;
Figure 18 is a view similar to that of Figure 17 but with the door open;
Figure 19 illustrates the application of a rubber lining to the door and bottom;
Figure 20 is a front view of a further skip in a Job's bridle;
Figure 21 is a side view showing the skip and bridle of Figure 20;
Figure 22 is a side view illustrating the removal of the ~kip from its bridle;
Figure 23 is a side view illustrating the operation of the door of the skip;
Figure 24 is a front view of a further loading flask;
Figure 25 is a side vlew of the loading flask of Figure 24;
Figure 26 is a side view of the loading flask illustra-ting the operatio~ of the door of the loading flask;

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Figure 27 is the front view of yet another skip;
Figure 28 is a side view of the skip of Figure 27; and Figure 29 is a detail of a side of the skip of Figure 28, illustrating the operation of the door of the skip.

Throughout the drawings, like reference numerals are used to refer to similar parts, where practical.

Referring firstly to Figures 1 and 2, a skip 10 is mounted in a Job's bridle 12 on a pivot shaft 14 and is prevented from swinging within the bridle by means of a lock 16. The bridle may be of a conventional construction and may be capable of receiving a man cage shown i,n solid lines at 18 in place of the ~kip, in the manner illustrated.

The bridle has suitable guides 20 for co-operating with a guide assembly in a mine shaft to guide the bridle for movement in a vertical direction. The skip 10 is mounted relatively high in the bridle for overrun in the head gear so that the head gear can be as low as possible.

The skip has a body 22 comprising a front wall 24, a rear wall 26, and side walls 28, and is of substantially rectangular cross-section in plan view along the major part of its leng~h. At its upper end the body is provided with a feed opening 30 for receiving material from a loading flask 32 and a feeder chute 34 (see Figures 6 to 9) .

9 1 162I6~

Instead of being mounted in the ~ob's bridle 12, the skip could be a bridle-less skip, as shown in Figures

3 and 4. This ski~ has a carrier 36 secured to its upper end and is provided with guide shoes 38 secured to the skip by suitable brackets, the guide shoes being arranged for co-operating with the guide assembly 38.1 (Figure 5) of a mine shaft for guiding the skip. Apart from these differences, the skips of Figures 1 and 2 and Figures 3 and 4 are of similar construction and like reference numerals are used to refer to like parts.

The bottom of each skip is partially closed by a sloping bottom 40 which is inclined downwardly at a suitable angle with respect to the walls and extends over approximately half of the width area of the bottom of the skip. A discharge opening is defined between the lower region of the sloping bottom 40 and three walls of the body and is normally closed by a door 42.. The door and body can be provided with wear plates 44 in a suitable manner.

The door 42 of each skip is normally held in its closed condition by a door control mechanism 46 including over-centre mechanisms 48 and followers SO in the form of tipping wheels. As shown in the drawings, each over-centre mechanism comprises an arm 52 which is fast with the door or with a shaft 52.1 secured to the door for movement with the door; a bell-crank lever 54 pivotally mounted on a bracket 56 carried by the sloping bottom 40 1 1621~) of the qkip, and a connecting link 58 pivotally connected to the arm 52 and the bell-crank lever 54. A stop (not shown) is provided for limiting the pivotal movement of the levers 54 in an anti clockwise direction as seen in Figure 4 50 that the lever cannot pivot beyond the posi-tion shown in Figure 4. Each follower 50 is rotatably mounted on the opposite end of the respective bell-crank lever to the link 58.

Each over-centre mechanism is such that, with the door in its normal closed condition shown in Figure 4, it i9 held in an over-centre position by the weight of and on the door and the weight of the follower 50.

Each ikip is arranyed to be used with a skip head which includes a cam track provided in a t.ipping path so that when the ~kip moves upwardly the follower 50 moves into the tipping path and along the cam track. This causes the over-centre mechanism to be moved from its over-centre position and to allow the door to open. The cam track is designed so that the follower will return the over-centre mechanism to its over-centre position and close the door when the skip moves downwardly in the shaft after material has been discharged from the skip.

In order to feed a suitable quantity of material into the skip of Figures 1 and 2 or 3 to 5, the loading flask 32 and feeder chute 34 are provided. The loading flask is of similar construction to the skip of Figures 3 1 16216n and 4 and like reference numerals are used to refer to like parts. The flask thus has downwardly diverging walls and a door control mechanism including an over-centre mechanism similar to that in Figure 3 to 5, although the over-centre mechanism is a composite mechanism operated by pneumatically controlled ram 60 instead of tipping wheels because the loading rlask is not moved in the same way as the skips.

Material can be supplied into the loading flask from a conveyor 62 or in any other suitable manner and the door 42 of the flask is held closed until surficient material is received in the loading flask. Once sufficient material is in the loading flask and a skip has been located in a position where its feed opening 30 is beneath the lower end of the feed chute 34, the door 42 can he opened by means of the ram ~0 to allow material to flow from the loading flask and down the feeder chute into the skip.

The door moves to a fully open position (represented in chain lines 64 in Figure 7) and supplies material into the feeder chute. The feeder chute (Figures 8 and 9) then guides the material into the hopper, the feeder chute being at a steeper angle than the door over at least the major part of its length. This has the advantage that material flowing from the loading flask and across the door will be able to follow a relatively natural path into the skip being filled, rather than all -12- l 16216~

being directed by the.feeder chute against the opposed wall o~ the skip. Rai~s 66 (Figures 8 and 9l help to prevent undesirable-escape of material from the feeder chute.

Instead of the loading flask of Figures 6 and 7, the loading fla~k 70 of F.igures lO and ll may be used.
This loading flask has a body of almost identical construction to that of Figures 6 and 7 and is filled in the same way.

The loading flask 70 has a door 72 mounted on door trunnions 74 to enable the edge of the door to be located close to the sloping bottom of the flask~ thus restricting escape of material, whether the door is in its open or its closed condition las described in more detail with reference to Figures 17 to l9).

Locking plates 76 are mounted on side plates 78 of the door and are engageable by locking pins 80 carried by pi~tons in pneumatic locking cylinders 82. The door is movable by drive cylinders 84 having pistons connected to connecting rods 86 which are themselves connected to drive pins 88 on the plates 78, the rods containing slots 90 to allow limited lost motion.

The cylinders 82 have small diameter pistons which are relatively rapidly acting, and the cylinders 84 have larger diameter pistons ~hich move relatively slowly.

-13- l~6216n The pistons are operable by a pneumatic control valve system (not shown) of suitable form. When the valve system is initially- operated, the pins 80 are withdrawn rapidly from the locking plate and the rods 86 take up the lost motion provided by the slots 90 while this is happeni,ng. The cylinders 84 then move the rods until the door 72 is fully open, as shown at 92. The loading flask thus discharges its contents into the chute 34, where it follows a relatively natural discharge path in the manner described above with reference to Figures 6 to 9.

When material is fed into a skip from either of the loading flasks described above, it will adopt an angle of repose which depends to some extent on the manner in which it is supplied into the skip. However, its upper surface 68 will normally be inclined to the horizontal.
This has the disadvantage that it causes the skip to try to pivot within the guide assembly of the shaft in which the skip is moving. This results in wear on the shoes, guide rollers, brackets, or other parts used for guiding the skip. To help reduce this wear, the sloping bottom 40 is arranged so that it is below the side of the material which is lowest in the fully loaded skip, and the door control mechanism is partly mounted below the sloping bottom and is thus also at or below the side of the material which is lowest in the skip. The mass of the door control mechanism can therefore help to balance the loaded skip and this can help to reduce unnecessary wear.

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It will be appreciated that the skip, loading flask and feeder chute described above can therefore help to reduce wear in the skip and in the guide assemblies for the skip, as in the loading flasks.

Referring now to Figures 12 to 16, a skip 94 has a body which is similar to that of Figure 4, although the number of guide shoes 38 ma~ be different. A door 96 having side plates 98 is mounted on the bod~y by trunnions lO0, allowing edges of the sloping bottom of the skip and of the door to lie adjacent to one another whether the door i5 open or closed, as described in more detail for Figures l7 to l9. The trunnions also enable the base and door to form a substantially continuous discharge surface when the door is open.

The door 96 and the sloping bottom of the skip are rubber-lined, the lining covering the junction hetween the door and bottom.

The door is held in position by a door locking mechanism 102 including locking arms 104 pivotally mounted on pivot shafts 106 on each side of the skip. The arms carry locking shoes 108 which, in operation, engage wedges llO on the side plates 98. The shoes 108 and wedges llO

engage in generally vertical planes which are slightly inclined to the axis of the skip to prevent jamming.

-15- ~ 182~6n The locking arms are in the form of bell crank levers and carry monkey wheels 112 for engaging monkey rails 114 (Figure 14). The monkey wheels engage the monkey rails when in the locked position and, as the skip is raised, come to engage a curved part of the rail to pivot the arms 104 and release the locking shoes 108 from the wedge~ 110. The locking mechanism is thus released as the skip moves to the position shown in Figure 14.

Tipping rollers 116 are provided on the side plates 98 and move into tipping paths 118 when the skip is raised sufficiently. Thus, when the locking mechanism 102 is released, the door 96 is not able to swing freely to its open position but instead is restrained by the rollers 116 in the tipping paths.

As shown in Figure 14, the lower part of each tipping path defines a guide 118.1 for guiding the respective roller into the path and, after an initial straight surfaces 118.2 corresponding to the position where the locking mechanism is released, the inner surface of the tipping path is curved sharply at 118.3 to allow the door to open. By suitably curving the paths in this way, it is possible to ensure that the door moves smoothly to its open position. The inner surface of the tipping path then continues straight upwards at 118.4 initially to hold the door in place and to inhibit oscillations of the door.

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When the skip moves downwardly, the wheel 116 moves down~ardly onto a curved platform 115 of the outer surface of the tipping path which supports the wheel 116 as the skip moves downwardlv. When the skip has moved down to a sufficient extent the wheel 116 moves between surfaces 118.2 so tha-t the door is closed and is held closed by the tipping ~heels and tipping paths until the locking mechanism serves to lock the door once more.

In order to prevent the action of the tipping paths on the tipping wheels from,pressing the guide shoes 38 hard against the shaft guide and causing undue wear and inaccurate operation of the skip, guide wheels 120 can be provided on the skip body for engaging the monkey rail, or on the shaft for engaging suitable members on the skip body. These guide wheels serve to keep the skip aligned in the shaft.

As with the skip of Figures 3 and 4, the positioning of the components, including the locking mechanism, can help to balance the skip.

In each embodiment, the bottom and the door are mounted on trunnions and have plates 122 providing upper supporting surfaces 124 (Figures 17 to 19) for supporting material in the flask or skip. A trunnion 126, a door 128 and a bottom 130 are shown in Figures 17 and 19 to exemplify this arrangement. As shown, the door and bottom have strengthening members 132 and the trunnions at 1 l62lsn opposite sides of the door are connected to these members to allow the door to pivot about -the axis of rotation of the trunnions. The adjacent edges of surfaces 124 meet at the axis 134 so that, when the door is pivoted from the closed position of Figure 17 to the open position of Figure 18, the adjacent edges remain substanti.ally in contact to prevent passage o~ material between the surfaces 124. A liner 136 of suitable rubber can cover the surfaces 124 and the junction between them as illustrated in Figure 19.

The skip of Figures 20 to 23 is similar to that of Figures 1 and 2. The skip 10 is mounted in a ~ob's bridle 12 on a pivot shaft 14 in seats 15 and is prevented from swigning within the bridle by means of a releasable lock 16.
The bridle may be capable of receiving a man cage in place of the skip, by pivoting the skip to bank level in the manner .
illustrated in Figure 22, lifting the shaft 14 from seats 15, and locating a man cage shaft in the seats 15 in place of the shaft 14. The bridle may be extended down-wardly to receive a multi-deck cage if desired.

Figures 27 to 29 show a bridle-less skip similar to that shown in Figures 3 to 5.

The doors 42 of the skips of Figures 20 and 27 are normally held in a closed condition by composite door con-trol mechanisms each including over-centre mechanisms 48 on opposite sides of the respective body. These mechanisms -18- 1 16216n each include a follower 50 in the form of a tipping wheel, an anll 52 which is pivotally connected to a respective bracket on the door for moving the door, and a plate forming a bell crank lever 54 having one ena region pivotally mounted on a trunnion 138 carried by a respective side 2~ of the skip. The opposite end portion of each lever 54 is connected to the respective arm 52 and the central portion of the lever carries the respective follower 50.

In each of these two skips, the extent of movement of the lever 54 once the mechanism moves to its over-centre position may ~e limited in any suitable manner, for example by slightly cranking the arm 52 at 140 so that, with the door in its normal closed condition, it rests against the supporting shaft 142 of the trunnion 138. The arm is cranked to such an extent that an imaginary line 144 joining the pivotal connections of the arm to the door and to the lever 54 is on the opposite side of the pivot axis of the trunnion 138 to that which it normally is in when the door is opening. Forces applied to the closed door to open the door thus provide a reaction along the imaginary line and increase the locking effect of the mechanism.
To open the door it is necessary to move the imaginary line 144 from the position of Figure 21 or 28 to the opposite side of the pivot axis of the trunnion by pivoting the lever 54.

To pivot the levers 54, each skip is thus used with a skip head which includes cam tracks 146 shown in chain lines and each providing a tipping path for engagement by a respective follower 50 so that when the skip moves upwardly the follower -19- 1 1621~n 50 moves into the tipping path and along the cam track. This causes the over-centre mechanisms to be moved from its over-centre position in the direction of arrow 148 and to open the door and the rollers follow the outside -tracks 146.1 until the door is fully open.

The cam tracks 146 control the whole opening operation of the door and cause the door to move from position 150 to position 152 while the followers are in the cam tracks.
The cam tracks will guide the followers to return the over-centxe mechanisms to the over-centre position and close the door when the skip moves downwardly in the shaft after material has been discharged from the skip.

In order to feed a suitable quantity of material into these two skips, the loading flask 32 of FigurPs 24 to 26 and a feeder chute 34 are provided. The loading flask is of sim.ilar construction to that of Figures 6 and 8 and like reference numerals are used to refer to like parts. The flask thus has downwardly diverging walls and a door control mechanism, although the door control mechanism is operated by a pneumatically controlled ram 154 as the loading flask is not moved in the same way as the skip.

Material can be supplied into the loading flask from a conveyor or in any other suitable manner and the -20- ll621~n door 42 of the flask is held closed until sufficient material is received in the loading ~lask. Once su~ficient material is in the loading flask and the skip has been located in a position where its feed opening is between the ]ower end of a feed chute associated with the flask, the door 42 of the flask can be opened by means of the door control mechanism to allow material to flow from the loading flask and down the feeder chute into the skip.

The apexes of bell crank levers 54 at opposite sides of the body of the flask are each pivotally mounted on pivot pins 156 carried by brackets and a shaft 158 on the body of the flask and one end of each lever 54 is pivotally connected to a connecting link 140 extending from the ram 154 by a shaft 162. Each lever 54 may be a single cranked element or a composite lever comprising a lever arm adjacent to the side of the flask and a further lever arm fixed on a common shaft with the first lever arm but located closer to the centre of the flask. The door is itself pivotally connected to the opposite ends of the bell crank levers to the link 160 by connecting rods 164.
The rods 164 in Figure 25 are shown in an over-centre position with a line 166 between the pivots for the rod 164 on the opposite side of the pivot axis of the lever 54 to that which is normally adopts while the door is opening.
Load applied to the door will thus tend to increase the locking effect of the door control mechanism~

-21- ~16216n The ram 154 has a suitably large diameter piston which moves relatively slowly and is operable by a pneumatic control valve system (not shown). When the valve system is initially operated, the ram 154 moves the link 160 to pivot the levers 54. This initially moves the rods 164 from their over-centre positions and line 166 moves across the axis of rotation of the levers 54 and then continues to move the rods until the door is fully open as shown in Figure 26. The loading flask thus discharges itscontents into the chute which guides it into the skip.

The basic features of the skip of Figures 27 to 29 and its operation have been described in general terms together with reference to the skip of Figures 20 to 23. However, because the skip is bridle-less and the over-centre mechanisms are located closer to the front 24 of the skip than to rear 26, the bottom cross-head 168 of the skip is eccentrically mounted so that its load is applied largely towards the rear of the skip to balance the skip.
Furthermore, in the embodiment of Figures 27 to 29, deflectors 170 are mounted so that they extend over the major parts of the over-centre mechanisms without preventing the tipping wheels from entering the cam tracks 146. These deflectors can help to prevent dirt from falling onto the mechanisms.

-22~ t 16216() In each of the skips and flasks shown in the drawings, the opposed pairs of walls, i.e. the opposed front and rear walls and the opposed side walls, diverge down-wardly so that the chamber widens dGwnwardly to facilitate downward flow of material within the skip and to eliminate undue wear on the walls as the material flows downwardly within the skip to be discharged from the skip.

Claims (17)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A unit in the form of a skip or loading flask for receiving, containing and discharging material, said unit comprising a body defining a downwardly extending storage chamber and having an integral sloping bottom beneath a part of the chamber; a discharge opening beneath a further part of the chamber and defined in the body adjacent to the integral sloping bottom; and a door locatable in a closed position beneath said further part of the chamber for closing the discharge opening, the door being openable by pivoting downwardly to an open position to allow material to be discharged from the chamber through said opening, said door forming a chute beneath said opening and extending downwardly and away from said sloping bottom in the open position of said door, wherein the body includes at least one pair of spaced opposed walls diverging downwardly along at least a substantial part of the height of the chamber whereby the storage chamber widens downwardly within the body, said substantial part of the height of the chamber being greater than the spacing between said opposed walls immediately above said opening.

2. A unit according to claim 1, wherein the body is substantially square or substantially rectangular in horizontal cross-section along at least a substantial part of its height and has two opposed pairs of walls, both of which diverge downwardly along at least a substantial part of the height of the chamber.

3. A unit according to claim 2, wherein the walls diverge downwardly along substantially the whole height of the chamber.

4. A unit according to claim 1 and having at least one door-operating mechanism for holding the door of the unit closed, and operating means for operating said mechanism to open the door.

5. A unit according to claim 4, wherein the mechanism includes a least one over-centre mechanism with an arm fixed to the door, a lever pivotally connected to the body, a link pivotally connected to the arm and the lever, the operating means being operable to pivot the lever to release the over-centre mechanism and open the door.

6. A unit according to claim 4, wherein the mechanism includes over-centre mechanisms having over-centre means at opposite sides of the body and operable to open and close the door, the over-centre mechanisms being movable to over-centre positions to releasably lock the door in its closed condition.

7. A unit according to claim 6, wherein each over-centre mechanism includes an arm pivotally connected to the door, and a lever having one region pivotally connected to the body to pivot about a pivot axis, and one region connected to the arm to provide the over-centre means, and wherein the operating means is connected to the lever to move the arm and release the over-centre mechanism from its closed condition and then to move the door to its open position when the lever is pivoted in a predetermined direction.

8. A unit according to claim 7, wherein each over-centre mechanism is such that a line extending between the pivotal connections of the arm to the door and of the arm to the lever is on one side of the pivot axis of the lever when that over-centre mechanism is in its over-centre condition and on the opposite side when that mechanism is moving the door to its open condition.

9. A unit according to claim 6, wherein the over-centre means at least partly extends alongside the opposite sides of the body.

10. A skip comprising a unit according to claim 4, wherein the operating means for the door-operating mechanism includes a follower for engaging a cam track, the door-operating mechanism being operable by movement of the follower along the cam track to open the door.

11. A skip according to claim 10, wherein the operating means comprises followers arranged so that they do not project forwardly or rearwardly beyond the opposite sides of the body when the door is closed.

12. A skip according to claim 10, wherein deflectors are provided at least partly to prevent falling material from falling against the door-opening mechanism.

13. A unit according to claim 1, wherein the door is pivotable about an axis for closing the discharge opening, and wherein the sloping bottom and the door have supporting surfaces meeting at a junction substantially extending along said axis.

14. A unit according to claim 13, wherein the door is connected to the body by suitable trunnions at opposite sides of the door to provide the necessary movement of the door while keeping the edges of the bottom and door at said junction suitably close together for substantially preventing passage of material between the surfaces at the junction.

15. A unit according to claim 13, wherein said door is movable to provide a substantially planar chute surface co-planar with said sloping bottom when the door is open.

16. A unit according to claim 15, wherein a flexible liner is fixed to the bottom and the door and covers the junction.

17. A loading flask assembly including a loading flask comprising a unit according to claim 1 and having its door for closing the discharge opening movable to a fully open position to define a chute surface extending from the opening; the assembly including a feeder chute located to guide material discharged over the door and having a feeder surface at a steeper slope than the door when the door is in its fully open position.