GB2303323A - Continuous casting - Google Patents

Description

CONTINUOUS CASTING APPARATUS In the conventional process for large volume production of aluminium alloy sheet and strip, the process steps include melting, melt conditioning etc in a holding furnace, casting direct chill ingots, scalping the ingots to remove surface defects, heating the ingots to rolling temperature, hot rolling the ingots from their initial thickness of about 500mm to about 25mm in a reversing mill, followed by in line hot rolling in three or more mills in tandem to a reroll gauge of about 2 to 3 mm, at which gauge the strip is coiled, cooled to room temperature and cold rolled etc to finished gauge.

The objective of this invention is to provide a strip casting machine which can be used in lieu of the direct chill ingot casting step, at an operating cost which is at most a few times that of the ingot casting step and which produces wide strip suitable for conversion to the final product by cold rolling etc. The strip gauge will be about three times that of the reroll strip from the conventional process but the cost of reducing the cast strip gauge to that of the hot line product will be modest, so that large investment, energy and other costs are avoided when a strip casting machine achieves this objective.

It is known to cast metal strip between two thin metal belts, usually steel belts, which follow substantially parallel plane paths, separated by the intended strip thickness, and which are efficiently water cooled, so that they become the two major faces of a water cooled mould, the minor mould faces being provided by side dam units which close the mould cavity at its two edges. The term twin belt casting is used hereafter to describe this casting process.

The principal invention of this disclosure is a novel belt carriage system for twin belt casters which is applicable to long moulds for casting at high rates but is especially attractive for short moulds for casting at reroll gauge at lower, but still very attractive, production rates. A modification of the short mould system described in BP 1,387,992 is one such system. It is convenient to describe this short mould before describing the new belt carriage system.

BP 1,387,992 recognised the critical importance of precision belt path control as the first step to attainment of the above objective and prescribed a mould system in which two steel belts were constrained to conform to sliding contact supports which had been ground to a planarity tolerance of a few microns in the critical casting direction. The constraint was effected, and the belts were very efficiently cooled, by directing high velocity water jets on to the belts between their supports with the water at sub-atmospheric pressure. The two controlled belt paths converged under a limit loading system such that the actual belt convergence was dictated by the behaviour of the freezing strip. Long freezing range alloys were cast successfully for the first time between twin belts using this mould system.

BP 1,589,241 recognised that the objective of the BP 1,387,992 mould design could be defeated if parts of the strip width, notably the strip edges, became strong enough to sustain the half mould preload before the rest of the strip reached a like stage in the freezing process and substituted local limit loading resilience of the belt path control system for the half mould resilience of BP 1,387,992. BP 1,589,241 also substituted high pressure water layer supports for the sliding contact supports of BP 1,387,992.

The present invention recognises that the design and method of assembly of the limit loaded water film supports of BP 1,589,241 does not readily satisfy the belt path planarity target and achievement of BP 1,387,992 and that appropriate application of the local limit loading belt support resilience concept can retain the planarity objective and assures satisfactorily low wear rate and life of the sliding contacts of BP 1,387,992.

The present invention also recognises that the hard support of the sliding contact system is better able than the soft support of the water film system to cope with off-flatness in the belts and prefers to retain that system mainly for this reason but also because the much lower water pressures of the system have some attraction in a casting shop context.

According to a first aspect, the present invention provides a mould system in which two thin metal belts are constrained to follow two initially plane and convergent paths by sub-atmospheric pressure cooling water which attracts the belts into sliding contact with a series of belt supports extending across the mould width and spaced along the mould length at intervals, such that the belts do not substantially sag between the supports, each of said supports being sustained in limit-loaded and predetermined positions by a plurality of hydraulically loaded columnar elements.

Preferably, the supports are provided in the form of narrow and discontinuous bars, whilst the hydraulically loaded columnar elements may be aligned with the bars and spaced at close intervals along the length of the bar.

Conveniently, said hydraulically loaded columnar elements are housed in the water drain tubes of a tube and plate mould structure of the kind described in BP 1,387,992. The system allows precision grinding of the operating faces of the support bars while they are held in their limit loaded and preset positions by appropriately pressurising the hydraulic pads for all belt supports,said hydraulic pads being pressurised partially flattened tubes urging the columnar elements towards the bar supports with the same limit load per unit bar length across the mould width, which limit load can be subsequently preset and maintained at the same value for all of the bar supports or at different levels for each bar to obtain the optimum cast strip quality.In a preferred arrangement the limit loading of all the bar supports in each half mould is the same but the level for one is higher than that for the other so that when the freezing /stBecomes strong enough to change the preset belt convergence to a lower value the belt path changes occur in only one belt path, leaving the other plane.

In the simplest form of this preferred arrangement the belt support bars for one half mould are all fixed,and resilient bar supports are provided on the plane path of the other half mould. The preset limit loads exerted by the hydraulic pads exceed that required to sustain the belt loading by the sub-atmospheric pressure cooling water by modest amounts, holding the columnar elements and hence the bar supports in their preset positions until the freezing strip exerts additional pressure, of the order fifty to a hundred mm of mercury, on the belt,these total loading levels then assuring long life of the low friction bar supports and low friction between the belts and the casting, given the smooth belts of the BP 1,387,992 invention. The water cooling system of BP 1,387,992 is also modified to maximise the water flow rate through the system while retaining the 5mm dia.

cooling jets, thereby minimising the water temperature change in its passage through the mould and hence minimising thermal expansion effects in the mould structure, this while retaining the low probability of even temporary blockage of a jet. A convenient solution is to provide an overhead supply tank with a head pressure sufficient to give a coolant flow rate of not less than about two litres per square centimetre of belt area per minute, the maximum flow rate suggested in BP 1,387,992, when the negative pressure on the drain side of the belt cooling system is about 150mm of mercury. The overhead tank capacity can be made sufficient to maintain flow to the belts for about a minute, as a useful aid to safe emergency abortion of a cast in the event of failure of some other feature of the system.

According to a further aspect of the invention, there is provided a belt carriage apparatus for use in continuous belt casting, which comprises first and second structural members on whose periphery are arranged a plurality of belt supports which together define a continuous belt path, and displacement means for effecting relative displacement between the structural members to enable the path of the belt to be altered.

Preferably, the displacement means is pneumatic and may comprise a pair of inflatable bags interposed between the two structural members and sequentially arranged thereby to facilitate pitching of each member about an axis transverse to the belt path.

According to a still further aspect of the invention, there is provided a mould side-wall enclosure for a belt used in continuous belt casting which comprises a pair of refractory material members arranged on either side of the belt, and means for applying oscillatory movement transverse of the belt path to each member, to bring each member into intermittent periodic contact with material carried by the belt.

An embodiment of each aspect of the present invention will now be described, by way of example and with reference to the accompanying drawings, in which: Figure 1 is a side sectional view of the mould unit of this invention Figure 2 is a series of sectional views of the resilient belt supports of the mould unit Figure 3 is a plan view showing the layout of the coolant jet and drain tubes in which the resilient belt supports are housed Figure 4 is a general arrangement drawing of the Hazelett caster showing the belt drive and steering arrangements of its belt carriage system Figure 5 shows the adaptation of the Hazelett belt carriage system to the twin belt caster of BP 1,387,992 Figure 6 is a general arrangement drawing of the Alcan BP 1,589,571 caster showing the configuration of its belt carriage system.

Figure 7 is a part side cross sectional view of the belt carriage system of the present invention showing the provision of pneumatic mattresses to urge apart the two structural components such that the roller supports around their peripheries capture and convey the belts around a short path from mould exit back to mould entry Figure 8 is a part elevation cross sectional view of the present belt carriage system showing features of the main structural part of the present belt carriage system which make it the coolant flow and return facility for its half mould unit, including features facilitating removal and replacement of the mould unit for scheduled maintenance and also showing features of the secondary structural part on which the belt driving equipment is mounted Figure 9 is a diagrammatic elevation view showing the arrangement of the drive gear assemblies which drive the belts by driving most of their roller supports on the peripheries of the secondary structural part Figure 10 is a part side cross sectional view of the mould entry end of the present mould system showing some features of the metal containment system of the present invention Figure 11 shows side cross sectional views of the side dam system of the present invention In a wide reroll caster designed with these features the mould length would be about 250mm, width would be about 2000mm, and the casting speed for 7mm reroll would be about 5m per minute. Design details are shown in Figs 1, 2 and 3.

In Fig 1 the section through the upper mould unit shows the positions of the resilient transverse belt supports 1 defining the plane belt path about 5mm distant from the plate 2; the supports on the curved mould profile, at mould entry and exit, being fixed. The resilient belt supports are attached to columnar elements housed in the drain tubes 5 and are held there in preset limit loaded positions by those elements until the freezing strip develops enough coherence to exert pressure on the converging belt surface sufficient to displace the support from its preset position.The positive pressure in the flow conduit 7 plus the negative pressure in the return conduit 8 provides the high velocity required through the jets 4, the lower velocity in the drain tubes 5 ensuring that the water pressure in the space between the belt 3 and the plate 2 is at the prescribed negative value.

Seals 9 confine coolant to the mould unit.

The part section drawings in Figs 2a, b, c & d illustrate a preferred form of the lightly limit loaded and resilient belt support element in its preset position. The cruciform section 10, shown in the part section drawing Fig 2d on XX of Fig 2b, is made by assembling and brazing together the two lmm thick hard steel strips shown in Fig 2c. The strip widths and edges in the cruciform parts are such that these slide accurately but easily in the lOmm bores of their housing drain tubes 5 and the lengths of the cruciform parts are such that their two ends do not reach the bottoms of the slots 11 and 13 in plates 2 and 6.These slots are about 3mm wide and about 7mm deep and they provide easy sliding fit alignment housings for parts of the low friction reinforced PTFE mouldings wh, are adhesively bonded to the shaded parts of the longer strip in Fig 2c, in the following assembly sequence. Moulding 12, about 16mm wide, across the casting direction, is secured to the 14mm wide part of the longer of the two strip parts in Fig 2c with the shoulder face B in Fig 2c protruding about lmm from the moulding 12, so that the 3mm thick part of moulding 12 is housed to a depth of 6mm in the slot 13 in plate 6 when the belt path reference shoulder face B is pushed on to the base of the slot 13 by activating the hydraulic pad 14 of Fig 2b, this after assembling the parts 10, 12, 14, 15 and 16 as shown in Figs 2a and 2b, and installing them in tubes 5,parts 15 being bars sustaining the thrust of the hydraulic pads 14 when anchored to the plate 6 by the brackets 16. The resilient belt support units are completed in situ by cementing the 20mm by lOmm by 3mm low friction mouldings 1 to the parts C of the columnar units 10 in Fig 2c,with the slot depth in the mouldings 1 and the length D in Fig 2c being so related to the distance between the bottoms of the slots in plates 2 and 6 that the moulding 1 is housed to half its lOmm depth in the slot 11 in plate 2.With the assemblies in their preset and loaded positions the working faces of the belt supports 1 are lightly ground to the planarity required and parallel plane surfaces are ground on parts of the plate 6, outside the part of the plate used in the mould assembly, these robust surfaces providing precision references for locating the two half moulds with respect to one another when they, in effect, carry their respective belt carriage systems.

The position references for the resilient belt supports can be made in the drain tubes near to the operating faces of the belt supports but the easier provision described above is satisfactory because the very small thermal stresses arising in the mould assembly from the temperature difference between the flow and return water are sustained by the tube-in-plate assemblies as compressive strains in the affected drain tubes, near mould entry, and the increases in the lengths of the parts 10 inside those tubes is only a few microns and merely reduces slightly the preset belt bath convergence for the reroll caster, which is of the order of one hundred microns or more.

Fig 3 is a part plan view showing the layout of the drain tubes in the plate 6 and indicating the relative positions of the jet cooling orifices in the underlying plate 2. A backing bar 15 is shown extending across the mould width and the casting direction, shown by the arrow, and secured to the plate 6 at intervals by the clamps 16, The dotted lines within one bar outline shows the positions of the 3mm slots 11 and 13 in the plates 2 and 6.

In operation the 3mm wide belt support faces sustain loads imposed by the pressurised partially flattened tubes 14 which are modest fractions of the permissible intensities cited for the low friction material sliding on smooth steel in water at the speed required in the caster, and the precision loading arrangement of Figs 2a, b, c and d ensures a low wear rate compatible with scheduled maintenance at acceptable frequency.

The mould units have other features designed to allow mould removal and replacement with much the same equipment and practice as is used for work roll changing. Details are included in the description of the belt carriage system.

The long used azelett twin belt caster uses idling pulleys at the entry end of the mould which contain part of the belt cooling system and belt driving pulleys at the mould exit which have adjustable axes for belt steering, Fig 4. That arrangement was used to drive and steer the belts in the BP 1,387,992 caster, Fig 5. In the Alcan BP 1,549,571 caster, Fig 6, belt driving and steering is by driven pulleys beyond mould exit, with differential expansion of the two ends of the pulleys for belt steering; the idling pulley at the front end of the caster was replaced by a hydraulic hover bearing compatible with the new belt path control and cooling system of the caster.

All of these belt carriage arrangements entail use of longer belt loops than are required to convey the belts from mould exit back to mould entry via paths involving given bend radii causing high but tolerable bending stresses in the belts. When the belts are made thinner, by a factor of about two, for the reason given in BP 1,387,992, belt making and handling problems are aggravated unless the belt loops are made smaller.

The present invention provides a belt carriage system in which the belt is conveyed from mould exit back to mould entry by the shortest practicable route involving given bend radii, thy belt path approximating to circular.

The belt enters and leaves the mouldgshort paths tangentially, linking the curved profiles at mould entry and exit and the similarly curved parts of the belt conveyance means, whch means is a plurality of discontinuous rollers disposed in closely packed arrays creating the desired belt path profile when they are appropriately mounted on the outer surfaces of two carriage structural compoents.The two structural parts have half cylindrical and near half cylindrical shapes, with equal diameter where they meet to form a near circular support surface to which journals carrying the rollers are secured in journal bearings, each such journal carrying an array of the rollers extending across the casting direction and along the length of the belt loop. çieans are provided to urge the two structural parts apart, thereby causing the rollers to exert radial pressure on the belt loops and the means for such urging is differentially adjustable across the casting direction and along the length of the belt loop at the dictate of a belt edge position sensor, for belt steering.The mean radial pressure exerted on the belts is small and the resulting belt hoop stress is correspondingly small; slightly resilient rollers are provided to ensure that dimensional errors in the rollers and/or in their dispositions on the structural elements cause only small and acceptable variations in the radial thrusts of the rollers. Means are provided to drive the belts by driving some of the roller arrays but alternative means are possible.

The mould unit is effectively integral with its belt carriage assembly when operational but it is made separable and means are provided for removal and replacement of the mould system, complete with its resilient belt support limit loading and monitoring facility, for routine scheduled inspection and maintenance, this using equipment and practice akin to that used for work roll changing in current rolling practice.

One of the structural parts of the belt carriage system is the prime part, comprising both a belt path roller system support but also two conduits for supply of coolant to and withdrawal of coolant from the mould, said conduit for the withdrawal function having an aperture to which the mould coolant withdrawal system makes sealed joints when the mould is linked to its belt carriage unit in the mould operational position.

Conventional arrangements are made for temporary separation of the two mould / carriage assemblies for belt changing and mould inspection or maintenance.

The belt carriage system is described in more detail by illustrations and text for a short mould system for reroll casting but it is to be understood that similar design features would meet requirements for a long mould slab caster.

Fig 7 is a part cross section of a mould and belt carriage assembly in which the prime structural carriage part 18 is seen to have plate enclosures 19 separating the flow space 7 from the return space 8.

These conduits have roughly equal cross-sectional areas. The mould coolant exit part 6 has a shallow tray extension which is sealed to an aperture in the return conduit, the aperture extending along the mould length, when the mould unit is lifted into its operating location in the prime carriage part 18. The tray also seals to an end plate of the mould unit, shown later in Fig 8, and the tray and sealing provisions allow withdrawal of the mould system with its resilient belt support and monitoring system intact.

For a 250mm long mould, about 200mm occupies the plane mould path and the rest is in a 300mm radius path at mould entry to provide a tangential path between the mould entry curvature and the preceding roller defined path.

The radius of the prime carriage part 18 is made about 250mm to allow 40mm dia. rollers 23 and their low friction half shell bearings 25 to be appropriately located on the outer surface of 18. The discontinuous and slightly resilient rollers are in arrays at about 42mm centres around the belt paths and the rollers are staggered with respect to those in adjacent arrays. Like arrangements apply at mould exit. After less than a quarter circle path on these rollers on part 18, like arrays of rollers continue the roller defined path around the semi-circular path provided on the secondary carriage part 20. Part 20 is slidably mounted on and aligned with the part 18 at 21, preferably with a linear bearing there to provide low friction movement for belt steering.Durable elastomer bags 22 are interposed between 20 and 19, as shown, to urge 20 and 18 apart and tension the belt loops. Two such bags occupy the space, one extending from the operating and the other from the non-operating end of the carriage to the carriage mid-width. Differential inflation of these provides belt steering. The separation force so exerted between parts 18 and 20 exerts a radial pressure on the belt loop of about one fifth of a kg per square cm. The thinner than usual belts of BP 1,387,992 are retained for the reason given in that disclosure and the present belts are about half a millimetre thick.The radial expansion of the belt loops is therefore only of the order thirty microns, a dimension of the same order as the likely departures of the profiles of the roller surfaces from their nominal profiles when the roller system is made and assembled by normal workshop practice. The belt loop stresses and strains are so small that the belts could sustain such departures without damage but when the rollers are made of a durable elastomer of appropriate hardness, such that the rollers flatten at the belt/roller junctions to the extent of about three hundred microns, the assembly and other errors are absorbed and the belts are protected from dent damage by detritus on the rollers. The roller and journal assemblies and the reinforced PTFE half shell bearings for the journals are shown in the inset section drawing.The rollers 23 are cemented to their 15mm dia. journals 24 and the latter are carried in the push fit half shell bearings 25.

Fig 8 shows a part section on the axis of the mould/carriage assembly, viewed in the casting direction. It shows the plate 26 secured to the operating end of the mould lunit which covers and seals an aperture in the end closure plate 27 of part 18, through which the mould unit can be extracted horizontally after it is lowered slightly to release the seal between the tray of 6 and the conduit 8. It also shows the plate 28 covering part of 27 and carrying the gears and drive parts for the driven rollers on part 20. A like plate 29 is secured to the non-operating end of 20 on which drive equipment duplicates thedrive at the operating end without presenting a belt changing problem.

Groups of about five of the belt support roller units on the structural part 20 have gear wheels keyed to extensions of their journals which extensions protrude through the plates 28 and 29. Several such groups are arranged around the periphery of the part 20 on both the operating and nonoperating ends of the part 20. The diameters of the gear wheels are slightly less than those of the belt support rollers such that the gear peripheries are within half cylinder profiles of the belts. In Fig 9 these gear wheels 30 are driven by the lay gear wheels 31 which are in turn driven by the motorised reduction gear 32 and 33. Several such drive arrangements for the several groups of rollers spaced around the semicircular periphery of the part 20 at both its operating and non-operating ends have soft drive features such that they collectively provide a smooth belt drive system.

The near edge faces of the mould plate 2 which adjoin the rectangular aperture in the prime carriage part 18 are ground plane surfaces substantially parallel with the mould plane reference surfaces described earlier and their mating surfaces on part 18 are also ground plane, so that when plate 2 is secured to 18 with a resilient seal at the junction the mould plate 2 retains its shape unchanged and becomes one of the two caster parts whose relative positions define the aperture and convergence of the mould cavity. The prime,8mSCiFflit 18 18 for the lower mould unit, with its coolant flow and return system for the lower mould, is fixed so that the lower mould unit is in a position fixed by its belt carriage system.When the upper mould unit, with its attached belt carriage system, is located on and secured to the lower mould unit, through the plane reference surfaces on the length-wise extensions of the two plates 2, the upper mould unit effectively carries its belt carriage system, the coolant flow and return linkages of the upper mould to the fixed system of the lower mould having the required freedom of movement.

In conventional twin belt casting practice the mould axis is slightly inclined downwards, as in Figs 4 and 6. This practice entails temporary closure of the mould entry with the belts stationary until liquid metal is released from the supply tundish to the metal delivery spout of the mould system and also entails operator co-ordination of the release of metal and initial movement of the belts.

Conventional practice also uses a moving chain of blocks to seal the side wall of the mould cavity and the engineering requirements of the device militate against the use of insulating blocks. Premature freezing of the edge parts of the cast strip has undesirable effects on near strip edge quality. The present invention proposes novel metal containment equipment and practice to improve start up, and termination, of the casting operation and to reduce heat extraction through the mould sidewall closures.

The first named objective is achieved by inclining the mould axis upwards to a degree limited by metallurgical and engineering considerations but yet sufficient to eliminate temporary closure of the mould entry and to permit a start up procedure in which the belts are moving at the desired casting speed when metal is released to the feed spout.

The second objective is achieved by providing a mould sidewall closure which is stationary in the casting direction but has a vibratory motion across the casting direction of frequency and amplitude such that the initially liquid and later liquid plus solid walls of the casting are supported by their intermittent and low heat transfer contact with the side dam.

W A Baker, Journal of the Institute of Metals, 1945, p165, describes and explains the effects of the two volume changes which occur during the solidification of castings and which tend to cause the appearance of unacceptable defects in castings. Among other things, this publication demonstrates that the effect of metallostatic head pressure in urging liquid flow within the freezing casting is insignificantly small after the outer layers of the casting have become coherent, this when about half of the metal, in the surface layers, has frozen: thereafter, atmospheric pressure, and surface tension forces at the solid and liquid phase interfaces, dominate the flow of residual liquid from the hotter to the colder parts of the casting.This being so, the useful function of the metal head at mould entry is retained when the mould axis is inclined upwards to a limit defined by the requirement that the liquid metal level at mould entry be at or above the level in the upper surface of the casting where the cast surface acquires coherence, this being about a half of the mould length from mould entry. The permissible upward inclination is thus dependent on the metal head and the mould length, the latter being dependent on the rate of heat extraction through the mould walls and by the desired casting rate and the former being dependent on metallurgical and engineering considerations attending the design and successful use of the novel side dam now proposed.

Rubbing contact between the spout and side dam parts and the belts is obviously unacceptable in long duration production casting operations but small gaps between the metal containment parts and the belts suffice to contain the metal by surface tension constraint if the metal head is low enough to be compatible with the surface tension of the metal and the size and accuracy of maintaining the belt/containment system clearances.

For aluminium and aluminium alloys metal heads above the lower mould surface not exceeding about twenty millimetres will permit gaps of the order one tenth of a millimetre such as can be located and sustained by the precision reference planes of the proposed mould system. In passing it is to be noted that these considerations make the permissible upward inclination of the mould axis so small when casting at slab rather than reroll gauges that the upward inclination is of little value but in the reroll casting case it is sufficient to achieve the cited objective.

Fig 10 is an approximately full size section of the entry end of the mould system outlined in Fig 1. The upper half diagram shows a cross section through the slender refractory supply spout 34 required if the metal is delivered to the mould at the transition from the curved to the plane profile of the belt path, at A. The lower half shows a section through the relatively robust spout 35 which delivers the metal on the curved belt path about twenty millimetres ahead of the plane belt path. This spout can be located and supported accurately in relation to the belt by carrying it on the low expansion metal part 36 which is in turn fixed precisely in relation to the belt by registering it on the reference plane of plate 2. These design features enable the spout component of the metal containment system to be initially fixed and then maintained in close proximity to the belt.The guard 36 is of course an essential feature of the mould system, designed to freeze metal reaching its tip, adjacent to the water cooled part of the belt, in the event of spout failure.

Figs 11a and 11b illustrate the features of the side dam part of the metal containment system. In Fig lia the side wall 37 of the spout 35 ends at the spout tip plane and the vibrating side dam 38 continues closure of the side of the mould aperture with a small gap at B like that between the spout tip and the belt. Like gaps are between the remainder of the side dam and the belts along the length of the side dam. Fig 11b is a part plan view on XX in Fig ila showing the inductor core 39, attached to the side dam 38, and the energising coil 40 attached to the side wall 37 of the spout 35. The side dam part is preferably made of a strong and thermally shock resistant refractory, like silicon nitride, with a durably very smooth surface presented to the metal in the vertical face of the casting.This face of the side dam preferably diverges from the casting direction as indicated and at the exit end of the mould the side dam is located and secured, relatively to the belts, by a hinge link to the reference plane of plate 2.

Belt assembly and start up of the belt path and belt cooling system call for no special comment but before casting begins the following dry test is desirable. With the resilient belt support elements in their preset and limit loaded positions and with the belts in motion, the subatmospheric pressure in the coolant return space 8 is lowered still further until the force exerted on the belts exceeds the preload and the belt position sensors confirm that this critical part of the mould system is functioning normally. Start up follows with release of metal to the spout after the pressure in space 8 has been restored to normal. Normal, or emergency shut down, is conventional by opening a large metal escape vent in the supply tundish.

Claims (1)

1. (1) A belt carriage apparatus for use in continuous belt casting which comprises first and second structural members on whose periphery are arranged a plurality of belt supports which together define a continuous belt path and displacement means for effecting relative displacement between the structural members.

   (2) An apparatus according to claim 1 in which the displacement means is preferably pneumatic and may comprise a pair of inflatable bags interposed between the two structural members and sequentially arranged thereby to facilitate pitching of each member about an axis transverse to the belt path.

   (3) A belt carriage apparatus according to claims 1 and 2 for use in continuous casting of metal strip in which the half mould unit for each of the two endless belt loops is carried on or by the primary structural member which member also has parts providing ducts for coolant flow to and from the mould unit the ducts occupying most of the available space between the assembled primary and secondary structural parts.

   (4) A belt carriage apparatus according to claim 1 in which the belt supports on the periphery of the primary and secondary members are a multiplicity of discontinuous and slightly resilient rollers in a series of arrays parallel to the belt loop axis the rollers of each such array being secured to a common journal whose parts between adjacent rollers are carried in low friction bearings mounted on the external surfaces of the two members.

   (5) A belt carriage apparatus according to claimS1 in which the secondary member conveniently accommodates a preferred belt driving means comprising multiple drive motor and gear assemblies driving most of the roller/journal assemblies on the secondary member at both ends of said member.

   (6) An apparatus according to claims 1 to 5 with a mould system in which two thin metal belts are constrained to follow two initially plane and convergent paths by sub-atmospheric pressure cooling water which attracts the belts into sliding contact with a series of belt supports extending across the mould width and spaced along the mould length at intervals such that the belts do not substantially sag between the supports each of said supports being sustained in limit-loaded and predetermined positions by a plurality of hydraulically loaded columnar elements and having their sliding contact belt support surfaces precision ground to lie in plane arrays while the support parts are in their predetermined limit loaded positions; preferably the supports are provided in the form of narrow and discontinuous bars whilst the hydraulically loaded columnar elements may be aligned with the bars and spaced at close intervals along the length of the bar.

   (7) An apparatus according to claims 1 to 6 in which the belts enter their half mould units by leaving their adjacent belt carriage paths tangentially to join similarly curved extensions at the entry ends of their otherwise plane and slightly convergent paths in the mould units and similarly rejoin their

   belt carriage paths at mould exit being support(in the curved parts of their mould paths on continuous narrow bar supports in fixed positions but on resilient limit-loaded multipart supports in their plane paths each such narrow multipart transverse support comprising a series of bar elements of length about the same as the support bar spacing lengthwise of the mould and held in alignment across the mould width by housing grooves in the prime plate component of the mould each such bar element being carried on a resilient columnar element housed in a drain tube of the coolant system all said columnar elements being urged towards the belts until parts of them register on limit-loaded stops under which condition the multipart transverse support surfaces are precision ground to the high planarity required the said urging being effected by substantially equal hydraulic thrusts on each element sufficient to sustain the force exerted on the belt by the sub-atmospheric pressure coolant plus an additional small preload the said thrusts deriving from an.adjustable pressure in partially flattened thin walled tubes bearing on platens attached to the columnar elements and loading the array of belt supports comprising each multipart transverse support bar said tube pressure having the same or different value for each multipart support a preferred arrangement using the same preload for all supports in each mould half but a larger preload for one than for the other with the movement of fluid from each flattened tube to its hermetically sealed and constant total volume system being monitored to show the movement of the columnar elements when they are moved from their preset positions.

   (8) An apparatus according to claims 1 to 7 in which there is provided a mould side-wall enclosure comprising a pair of refractory material members arranged on either side of the mould cavity and means for applying oscillatory movement transverse of the belt path to each member to bring each member into intermittent periodic contact with material in the cavity edges.

   (9) An apparatus according to claim 8 with a metal containment system in which the minor faces of the mould closing the gaps between the belts at the two sides of the mould cavity are preferably made of a strong but poorly conducting material whose smooth faces closing the gaps diverge from the casting direction and have low friction hinge supports near mould exit which hold them in a desired close proximity to the moving belts at the exit end of the cavity and at their mould entry ends are movable in the horizontal plane while they too are held in a desired close proximity to the moving belts said holding being effected by securing the entry ends of the side dams to the cores of solenoid coil units which are in turn secured to the stationary sidewalls of the conventional feed spout intermittent energising of the coils then causing the entry ends of the side dams to move in cyclic motion towards and away from the material at the edges of the mould cavity making intermittent and poorly conducting contact with said material the close proximity of the side dams to the belts being a clearance of the order of one tenth of a millimetre such that the surface tension of the liquid metal prevents leakage through the gap when the metallostatic head in the feed spout is no more than about twenty millimetres such as suffices to feed liquid metal into the mould at the required rate and to press the initially liquid and later partly solid outer layers of the casting into conformity with their mould faces even when the mould axis is inclined slightly upwards provided that the head pressure does not decay to zero before the half mould length position is reached.