CA1064459A

CA1064459A - Integrated slide gate valve

Info

Publication number: CA1064459A
Application number: CA291,179A
Authority: CA
Inventors: Ludwig Walther; Josef Lothman
Original assignee: USS Engineers and Consultants Inc
Current assignee: USS Engineers and Consultants Inc
Priority date: 1976-11-19
Filing date: 1977-11-18
Publication date: 1979-10-16
Also published as: FI61420C; PT67280B; FI773485A; PL108866B1; TR21004A; CH624034A5; NZ185692A; PH15410A; JPS6362308B2; HU178127B; GR62640B; BR7707648A; NO773957L; AR215031A1; JPS5386642A; NL7712753A; FR2371260A1; MX146330A; IN147574B; IT1087219B

Abstract

A B S T R A C T

A sliding gate valve assembly for pouring liquid metal is described in which the frame that mounts the sliding plate is attached directly to oppositely spaced motor apparatus of particu-lar design. Thus, in addition to imparting motion to the slide frame, the motor apparatus also serve to slidably mount the frame thereby eliminating the need for a housing enclosure about the slide frame. According to one aspect of the invention, the frame is movable longitudinally by motor apparatus on two opposed sides of the frame. According to another aspect of the invention, the frame is movable both longitudinally and transversely by pairs of motor apparatus rectangularly disposed about the four sides of the frame. Motor apparatus that is mechanically, electrically or fluid operated can be employed.

Description

' The present invention ~elates to a sliding qate valve for pourLng molten metal, as for example, from the bottom of a receiving vessel such as a ladle or tundish. The valve of the invention includes a slide plate having at least one outlet port and being contained in a movable frame. The slide plate is ;spring-biased upwardly against a head plate located above the slide plate. The head plate contains an opening that communicates with the vessel interior and cooperates with that in the slide plate to pass molten metal from the receiving vessel when the openings are vertically aligned. The head plate is held by a mounting member connected to the bottom of the receiving vessel and the slide gate frame is held by a support device equipped with tensioning means for pressing the frame and its contained slide plate agal;nst the head plate.
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In known sliding gate valves of the described type, the 1~ frame slides inside a housing forming part of the support device.
¦~ Usually the housing is hinged to the mounting plate, and can be ` !- pressed against the mounting plate by means of suitable tensioning apparatus, including springs that are compressed between the !, 20 frame and the slide plate, and thus force the slide plate up against the head plate. A pressure cylinder, operative to move ~, the frame and slide plate relative to the head plate, laterally penetrates the housing to connect with the frame.
, ., :, The use of an essentially closed housing as a support device has several disadvantages. A serious drawback is that even minor-quantities of escaped liquid metal or other contami-nants, for example, tar or sand, can obstruct the free motion of the relatively movable parts, so that the frame and the slide \

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plate contained within it cannot be moved satisfactorily. The resultant operational disruptions can have far-reaching conse-quences. Furthermore, the fabrication and installation of the housing, the sliding members within it, and the pressure cylinder require considerable constructional effort and expense.
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- Therefore, it is the aim of the invention to further develop the above-described type of sliding gate valve in such a manner that the troublesome and structurally cumbersome houslng is eliminated, and the drive for moving the frame is improved and 10 simplified.

~j To achieve this aim ehe invention proposes to modify ¦ the above-described type of sliding gate valve so that the support for the slide plate is derived from the motor means that are also ¦~ used for moving the slide plate relative to the head plate.
- ~ Desirab}y, two motor units are located at opposite sides of the frame containlng the slide plate and disposed parallel to its long dimension, with the components of these units, that are movable with respect to the vessel in the longitudinal direction ~-' of the frame, being connected with the frame.
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1 20 In the sliding gate valve of this invention, the .,,.1 ~
supporting housing and the glide arrangements contained within it are replaced by the motor units located on both sides of the frame, whereby these units also serve as supporting members as , .
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well a~ dr~ves for imparting mot~on to the frame. ~he eliminat$on ; of the bous~ng regult~ ~n a structure that ~- open on ~ iae~
o th~t $t cannot be ~mmed by liquid metal or other contaminants and thereby operate~ trouble-free. Furthermore, the tot~l con-truction effort ~nd expense i- obviously reduced by a considerable umount. ~he motor apparatus proposed by th- invention as~ume the function of the housing and its sliding support for the frame, a~
well as the function of driving the frame.

An especially advantageous further development of the sliding gate valve according to the invention provides for the upport device to have addition~l motor me~ns for impartinq transverse motion to the frame. These additional motors ~re desirably located on opposite sides of the frame parallel to its transver~e dimension. The stationary components of the units are rigidly conne~ted with respect to the vessel, and the components that are moYable in the transverse direction of the frame support 1,~
the~stationary components of the motor means used for the longi--~ ~ tudinal motion of the fr~me, thereby the frame can be moved l ~ ~ selectively not only $n its longitudinal direction, but also k ~ :
transver eIy to it. This ~rrangement is especially ~dvantaqeous ., in that several pouriDg port~ can be incorporated in the slide plate by arranqing the ports, for example, in two rows staggered . , .
ln the longitodinal direction.

~h- advantage- arising from such an arrangement are - obvious. ~he variou~ port~ may have different di~meters, so that the metal pouring rate can be varied without changing the ~lide . , - , ~064459 plates. Also, an increase in the number of ports increases c~rrespondingly the expected service life of each slide plate.
Moreover, the ability to move the frame sideways permits adjustment of the location of the ports in the pouring stream so that the very intensive wear at the edges can be distributed uniformly around the perimeter of each port. A transverse motion of the frame, while maintaining exact guides in the longitudinal as well as in the transverse direction, is not possible with the closed housing constructed in accordance with the known state of tech 10 nology. Only the open construction using motor apparatus as supporting, guiding and motion imparting drive means proposed by the invention offers this opportunity.

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; To achieve favorable load relationships and a compact construction, it is further proposed that each motor unit utilized to impart longitudinal motion to the frame according to a preferred form of the invention, shall comprise a centrally located pressure-active cylinder and the connecting rods attached to a piston ., ' within the cylinder extending from both ends thereof, whereby the respective cylinders are connected with the frame and the free ~ 20 ends of the connecting rods are connected with the vessel mounting J plate or with the components of the valve that are movable trans-versely of the frame, these components being part of the piston-cylinder units supported by the mounting plate and serving for ~ ~ transverse movement of the frame.
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Similarly, each piston-cylinder unit for transverse motion of the frame may comprise a centrally located cylinder and , ~O~i4455~

connectinq rods extending from both ends of the cylinder, whereby the cylinders are attached to the mounting plate and the free ends of the connecting rods are connected with the componentS
i that are movable in the longitudinal direction of the frame, ; these components being part of the piston-cylinder units for the longitudinal movement of the frame.

Various forms of tensioning apparatus can be employed in the operation of the gate valve of the present invention. In ~ ; one form the tensioning apparatus can be located between the ,! 10 cylinder components for the longitudinal motion and the frame in a manner well known in the art. In this form the apparatus, on one side, includes a tensionable hinge joint and on the other ` side a tensionable releasable latch joint. Manually operated tensioning rods, such as those commonly used with gate valves having housings, may be employed in the present gate valve arrange-ment.

In another form, the tensioning device is located at the junctures between the motor units for the longitudinal motion of the frame and mounting plate, or between the motor units for the transverse motion of the frame. The tensioning device contains eccentric bushings that are rotated by an appropriate lever system to increase or decrease the tension. The lever system is moved in one or another direction by the longitudinal motion of *he frame, as required.
` -.., ~or a better understanding of the invention, its operating advantages and the specific objectives obtained by its .

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use, reference should be made to the accompanying drawings and .
description which relate to a preferred embodiment thereof.
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; The invention is further described, by way of example, . with reference to the accompanying drawings, in which:

. FIGURE 1 is a vertical section taken along line 1-1 of Figure 3 illustrating a first embodiment of thé sliding gate ! ' valve of the present invention;
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FIGURE 2 is a schematic plan view of the slide plate . ~: used in the sliding gate-valve shown in Figure l;

¦ 10 FIGURE 3 is an isometric view of the sliding gate valve shown in Figure 1:

. FIGURE 4 is a schematic representation of the hydraulic system employed in the operation of the sliding gate valve of ! ~ Figure 3;
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FIGURE S is a vertical sectional representation taken along line 5-5 of:Figure 3;
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~ : FIGURE 6 is a sectional view illustrating the sliding ~ ~:
:: gate valve in its unlatched position;
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FIGURE 7 is an isometric view illustrating a simplified embodiment of the sliding gate valve in which transverse mobility of the frame is omitted;
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` ~0644S9 `,~ FIGURE 8 is an isometric view, similar to Flgure 7, illustrating the sliding gate valve with an alternative form of tensioning means;

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FIGURES 9 and 10 are illustrations of eccentric bushings .. . .
utilized in the embodiment of Figure 8;

FIGURE 11 is an isometric view, similar to Figure 7 illustrating the sliding gaee valve having an alternative form of motor means;

FIGURE 12 is a partial sectional view of the motor means 10' of Figure 11; and FIGURE 13 is a plan view of the sliding gate valve equipped with~yet another alternative form of motor means.

In Fi~gure 1,~ the boteom of a receiving vessel such as a ladle ls indicatéd by the reference numeral 11. A mounting ,plate 12 is attached to the ladle bottom 11. Below the mounting plate lies a refractory head plate 13, secured by bolts 14 against ' horizontal motion. The ladle bottom 11, the mounting plate 12, , :
and the~head plate 13 are penetrated by a pouring port 15, which is lined inside witb appropriate inserts 16. Adjacent to the lower surface of the head plate 13 is located a slide plate 17, which is also made of a refractory material.

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-~: The slide plate 17 contains ~ever~l apertures 18, which ~re extended downward by tubes 19. The slide plate 17 is biased ~.
upwardly against the head plate 13 ~y means of springs 20. The ~prings 20 are supported by the frame 21, which is movable in the horizontal direction together with slide plate 17 contained within $t.
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The frame 21 is supported by a support device, which is lndicated generally by the reference numeral 22. The support device also serves to move the frame 21 in the horizontal direc o tion. Figure 3 shows the construction and attachment of the support device 22 at the mounting plate 12, which, in Fiqure 3, is shown detached from the ladle bottom 11.
i. ~ , ~ The support device 22 contains two piston-cylinder .
units 23 located parallel to the long.dimension.of the frame 21 t opposlte sides of it, only one unit beinq visible in Figure .3...
Each piston-cylinder unit 23, for the longitudinal motion of the frame 21 comprises a centrally~located cylinder 24, which iS
connected~ with the frame 21 as hown in Fiqure 5. Connectinq rods 25 extend from opposite ends of a pi&ton 2S'(Figure 4) , ~ .
~ 20~ enclosed within the cylinder and are operatively connected to ; ~ .
.~ ; the mounting plate 12. Toward this end, thc free ends of :: .
connecti~g rods 25 are joined with the free ends of two further connecting rods 26 of the pi~ton-cylinder units 27 located parallel to the lateral dimension of the frame 21 ~nd operative to move the frame 21 in the transverse direction as hereinafter described by connector ~locks 2~ disposed at the four corners of .: .

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~Q64gS9 the support device 22. The piston-cylinder unit 27 for the transverse motion of the frame 21 is constructed similarly to the piston-cylinder unit 23, for the longitudinal motion of the frame 21, but its cylinder 29 is rigidly connected with the mounting plate 12 by means of upright supports 30. Thus, the -~
piston-cylinder units 23 and the piston-cylinder units 27, serve to jointly support the frame 21. The piston-cylinder units 23 and 27 can be supplied with a pressurizing agent in a known ; manner, and therefore can move the frame 21 in its longitudinal .0 and/or transverse directions as described in more detail herein-after.
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To move the frame 21 in the direction of the head plate 13 and to force the frame against the head plate, with consequent compres-ion of the springs 20, the embodiment according to Figure 3 provides for a tensioning device locatDd between the cylinder 23~and the frame 21 and indicated in its entirety by the reference numeral 31. This tensioning device 31 is constructed as a known latch joint. _ ~

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20, As shown in Figures 3, 5 and 6, it comprises an ~: : , . ...................... . . .:
rticulated lever 32, one member 32a of which is connected with the cylinder 24 and a notch 32b' in the other member 32b engages a horizontal bar 33, whereby the articulated joint 32c i5 movable . -, , ; beyond the dead-center as is indicated in Figure 5 by the arrow 34. The a~ticulated joint 32c is moved by a locking bar (not shown), which is inserted into ~ 60cket opening 35' in boss 35 on the lever 32b. In a similar manner, the hinge, located on the :: .

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` ~ 10644S9 opposite side of the frame 21 between the frame and the cylinder '24, can be~tensioned. This hinge connection, on the opposite ide of the~frame 21, is of identical construction except that the lever~member 32b ic permanently pivotably fixed by pins 32d to the~frame. In principle, this mechanism is constructed similarly:to the hinged joint used in conjunction with a slide gate~housing. This~construction permits the housing to swing away from the ladle:bottom as shown in Figure 6, after unlocking tbe latcb, for example, to insert a new slide plate 17.

~ ~ 10~ :The~fluid System employed to effect movement of the ~`
frame 21 with respeot:to the mounting plate 12 is as~shown in.
Figore~4,: That portion of:the~system wbich is operative in conjunction~with the motor unitJ 23 to move :the frame 21 longi-tudinally~of the mounting~plate;l2, shown:in:phantom:in the drawing, compris-J'oppositély actlng pairs of parallely-connected eJ SOa~,;SOb,~and~Sla,~Slb.that~connect between a~fluld source '(not~:~shown)~:~and~the~inter:ior of~the:~cylinders 24. As shown in th-~figure~the lines are conveniently formed~;through the connecting:rodJ :25~:~and~ 26 'and eonnecto'r~blocks 28. Lines 50a~
and~50b~are~:~caused~:to~communicate:~at~one end with fluid port 52 .and extend:~each to~one~of::the respective cylinders 24, communi-cating therewith~adjacent carr-sponding~-ides of the respective piston- 25':. ~Lines Sla~:a~nd;Slb, on~the other hand, are similarly e~onstructed -nd extènd~between port 53 and the cylinders 24, communicating therewith on the~`other corresponding sides of the piston:s 25'. It will be appreciated that witb the pistons 25', being effectively fixed with respect to the mounting plate 12, ,' . .
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: ' in order to move the frame 21 with respect thereto in the upward direction as it appears in the drawing figure, ~perating fluid is admitted by means of appropriate valving apparatus (not shown) through port 52 and lines 50a and 50b to the interior of the cylinders 24 on the upper sides of the respective pistons 25'.
Simultaneously therewith, fluid from the lower sides of the pistons is released from the cylinders through lines 51a and 51b and port 53 to be returned to the source. The effect is to pro-!~ ~duce a resultant movement of the cylinders 24 and of the attached frame 21 longitudinally with respect to the mounting plate 12 in the upward direction as it is viewed in Figure 4. When it is desired to move the frame 21 in the opposite direction, the described procedure is reversed.
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That portion of the fluid system that is operative to move the frame laterally with respect to the mounting plate 12 :
comprises oppositely acting lines indicated as 56 and 57 formed ;interiorly of the thickness of the mounting plate 12. The lines 56 and 57 each connect at one end with the ports 58 and 59 `~ ~ respectively, that are attached to the mounting plate and which 20 communicate with a source of operating fluid that is independent of the previously described source. The lines 56 and 57 have feeders offset therefrom, indicated by the subscripts a and b :."
which communicate with oppositely spaced cylinders 29 of the motor units 27. In construction these offsets extend interiorly of the upright supports 30 which attach the cylinders 29 to the mounting plate 12. Feeders 56a and 56b communicate with the cylinders 29 on corresponding sides of the pistons 26', here .

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;44sg .... ... . .. . . .... .. ... .. ...
~ shown as being the:l-ft side ther-of, which feeders S7a and 57b ~. . ~
communicate with the cylinders 29 on the opposite sides of the ! ~ respective pistons. ~Thus,~since the cylinders 29 are effectively fix-d with~respece to~the~mountlng p;l-t-, ~to move the frame 21 from~left:to right as v~iewed~ln the drawing figure, operating ~:
:fluid is admitted~to line 56 through the port 58 from whence it f;lows~ through the~l;ine offsets~56a~and 56b~to the lnterior of the re~sp-ot~ive cyllnderJ 2~9 on~the l-ft side~:of the plstons 26'. At 1 ~ t~he~-ame~time,~fluid i~s:released~from th- oylinder~ on the opposite .
. ~ IO:~ ; : sides:of:the respective~:pistons~through~offsets 57a.and 57b and.. ~ port~5:9 thereby producing~a movement of the pistons.26' to the .. ~ left.: Since:~the:entire~support~structure 22 and, thereby the ~. ~ frame~:l2, is:~peratively~fixed~:to the:pistons 26' movement of the .- ~ pistOns~26~ to~ehe~left produc-s move~ènt of the fra.me coincident ~ ~ -therewith.~ ~ en:movement:of::the:~frame in the oppo~ite Iateraltl ~ h ~.direction:~;is desired,~;this~procedure is reversed. . ~:.

h- e~d nt of~ehe uppo-t~device 22' hown in `:Figure :7:does~:not~provide~for::transverse;motion of the frame 2I.
`ln this embodiment of the invéntion~the:free ends of the connecting .~ rods 25~of the~piston- y inder~units 23;ar rigldly~connected with~the~head;plate~l2~at~po-t-~;36. ~oeherwise ehe construction sho~in~Figure~7~corresponds with.~ehose~shown in Figures I and 3,~and ehe~corresponding:~componenes~are ldentlfied wieh the same reference~numeralS-~

Th-~embodiment shown in Figure 8 also does~not provide for transverse vement of the frame 21, and to this extent it , ,., , ~
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~ 13 -~! , ~Q644S9 corresponas with that shown in Figure 7. It differs fr~m the embodiment shown in Figure 7 by the construction of the tensioning device 31. The tensioning device 31' shown in Figure 8 contains four eccentric bushings 37, which can be rotated in the bearings 38 located on the underside of the mounting plate 12. Support rods 39 extend through each pair of eccentric bushings 37, and the free ends of the support rods are connected through connectors 40 with the free ends of the connecting rods 25 of the piston-cylinder units 23, for the longitudinal movemeht of the frame 21 The cylinders 24 of the piston-cylinder units 23, are rigidly connected with the frame 21. By rotating the eccentric bushings ;,. .
37 in the bearings 38 the support rods 39, the piston-cylinder units 23, and the frame 21 can be raised and tensioned (see ~ Figures 9 and 10). The eccentric bus,hings are equipped with up-,~ ward pointing levers 41. The upper ends of two levers 41 on the .~ :
~ same side of the frame are joined by a connecting rod 42, which ','~ can be~moved by the frame 21 in one or the other d',rection as . ~ .
~-~ desired. For this purpose, the connecting rod 42 contains on its "~ underside projections 43, which can be connected with the frame ~20 21 or can be disengaged from it. In this manner the frame 21 can ' move the connecting rod 42, the levers 41, and the eccentric . :, :: :
'` bushings 37 in the direction of increasing or decreasing tension.
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_. ,. -- ` - -`--' ' - ` , ' '' C `',`, Figures 11 and 13 illustrate a`lternative forms of motor means for the gate valve herein. In the embodiment of Figure 11 the sliding gate valve and support~structure are in all substantial effects the same as those shown in Figure 7 and as described in connection therewith. In this embodiment, however, the hydraulic motor units 23 of Figure 7 are replaced by electrical linear induction motors indicated generally as 60. The linear induction ; motors 60 on the opposite sides of the frame 21 each comprise a moving inductor member 61 that is fixedly mounted on a sleeve 62 that attaches one end of the frame 21 and that surrounds an elongated rod 63 forming the secondary or reaction axis of the motor. As shown, the rods 63 are caused to extend between and are fixedly attached to oppositely spaced posts 64, the latter being disposed at the four corners of the mounting plate 12. In this embodiment of the invention, movement of the frame 12 is effected by imposing an electric ~urrent through the coils of the inductor members 61 to produce an axial movement thereof along the rods 63 thereby moving the frame 21 longitudinally of the mounting plate 12.
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~-~ 20 In the embodiment of Figure 13, ~he frame 21 is driven by a reversible electric motor 70 through appropriate worm gearing and drive screws. As shown in the drawing figure the frame 21 is attached at its opposite ends to movable nut members 71. The nut members 71 are operated by drive screws 72 that extend along opposite sides of the mounting plate 12 between corner posts 73 and 74. Posts 73 contain appropriate bearings to permit rotation of the respective drive screws while posts 74 contain, in addition to the bearings, worm gear means to effect rotation of the drive screws, all as is well known in the art. The worm gears are in turn driven by a reversible electric motor 75 suspended from the mounting plate 12. The motor 75 connects with the respective worm gear apparatus through oppositely extending drive shafts 76 each of which contains clutch apparatus 77.

While the motor 75 has been described as being a reversible electric mo~or, this motor may, in some applications, preferably be a pressure-activated motor, su~h as, for example, a compressed air motor.

It will be understood that various changes in the details, materials and arrangements of parts'which have been herein described and illustrated, in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.

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Claims

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

1. A sliding gate valve apparatus for a metal pouring vessel, comprising a head plate having an aperture adapted to communicate with the vessel interior; a slide plate movable relative to said head plate and containing a pouring aperture cooperable with the aperture in said head plate to pass molten metal from said vessel interior when said apertures are axially aligned;
and means supporting said slide plate relative to said head plate;
said supporting means being operable to move said slide plate relative to said head plate and including at least one motor unit having a stationary member and a movable member; means attaching said stationary member with respect to said head plate; and means attaching said movable member to said slide plate so as to support the slide plate.

2. An apparatus as claimed in claim 1 in which said slide plate is mounted in a frame movable with said slide plate and having spring means for biasing said slide plate against said head plate, said frame being attached to said movable member of the motor unit.

3. An apparatus as claimed in claim 1, having two parallel motor units arranged for simultaneous activation and disposed on opposite sides of said slide plate.

4. An apparatus as claimed in claim 3 in which said slide plate is mounted in a frame movable with said slide plate, one side of said frame being hingedly connected to one of said motor units and the other side of said frame being releasably latched to the other of said motor units.

5. An apparatus as claimed in claim 1 including a mounting plate for attachment to said vessel and se-cured to said head plate, and support posts depending from opposite ends of said mounting plate, said stationary member comprising a connecting rod extending from opposite ends of said movable member and connected to said posts, said movable member being movable along said connecting rod.

6. An apparatus as claimed in claim 1 in which said means attaching said stationary member with respect to said head plate comprises an additional motor unit disposed transversely of the first motor unit or units, said additional motor unit including a stationary member and a movable member, means attaching said stationary member with respect to said head plate, and means attaching said movable member with respect to the stationary member of said first motor unit or units whereby said slide plate is movable in both the longitudinal and transverse directions.

7. An apparatus as claimed in claim 6, having two parallel transverse motor units arranged for simultaneous activation and disposed on opposite sides of said slide plate.

8. An apparatus as claimed in claim 6 including a mounting plate for attachment to said vessel and secured to said head plate, the movable member of the or each additional motor unit comprising a connecting rod extending from opposite ends of the stationary member and the stationary member of the or each first motor unit comprising a connecting rod extending from opposite ends of the movable member, means attaching the stationary member of the or each additional motor unit to said mounting plate and means joining the adjacent free ends of said connecting rods.

9. An apparatus as claimed in any one of claims 1, 6 and 7, in which the or each motor unit comprises a fluid pressure activated piston-cylinder unit.

10. An apparatus as claimed in claim 5 in which the motor unit comprises a fluid pressure activated piston-cylin-der unit having a piston rod which constitutes said connect-ing rod and which has a passage for the introduction of pressurized fluid into the cylinder.

11. An apparatus as claimed in claim 8 in which each motor unit comprises a fluid pressure activated piston-cylinder unit having a piston rod which constitutes a said connecting rod and which has a passage for the introduction of pressurized fluid into the cylinder.

12. An apparatus as claimed in any of claims 1, 6 and 7, in which the or each motor unit comprises a linear induction motor.

13. An apparatus as claimed in any one of claims 1, 6 and 7, in which the or each motor unit comprises a screw-threaded rod operably connected to a reversible rotary motor and a screw-threaded nut in screw-threaded engagement with said rod.

14. An apparatus as claimed in any one of claims 1, 6 and 7, in which the or each motor unit comprises a screw-threaded rod operably connected to a reversible rotary motor and a screw-threaded nut in screw-threaded engagement with said rod and said rotary motor is a fluid pressure activated motor.

15. An apparatus as claimed in any one of claims 1, 6 and 7, in which the or each motor unit comprises a screw-threaded rod operably connected to a reversible rotary motor and a screw-threaded nut in screw-threaded engagement with said rod and said rotary motor is an electric motor.

16. An apparatus as claimed in claim 6 or claim 7, in which the slide plate has a plurality of pouring apertures disposed in staggered relation.