CA1073621A - Method of solidifying molten material - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

In a process for solidifying molten materials by pouring onto a substrate and cooling, silicone fluids or kerosene are incorporated in the solidifying melt to promote the formation of amorphous material and provide increased hardness on aging. Undesired cryst-allinity is also avoided by first forming a solidified skin on the melt surface by carefully controlled air cooling or dusting with powdered material before more vigorous cooling by air or water directed against the solidified skin. When using an endless belt as substrate, the plain surface may be modified by superposing a skeleton framework to form tablet orbar moulds. The process is particularly applied to the solidification of molten sulphur.

Description

0'~.36Zi.

This invention is concerned with the solidification of molten materials, especially sulphur.
:The e~tracti.on of sulphur ~rom naturally occurring deposits usually results in the sulp~ur being obtained in :molten form. For ease o~ st~rage and handling the molten . S sulphur is solidi~ied. Other normally solid materials ~- .that are brought to a molten state while processi~g and are subsequently solidi~ied are thermoplastic materialæ
..such as synthetic resins, e.g. polystyrene~ bitume~ and pitch.
.~ 10 Previously, the solidii~ication of sulphur took place on a large ssale in so-called "vats~. Th~ problem~ ln recovering.the sulphur ~or ~urther use have led to the ~ development of processes in which sulphur is continuously :;. cast onto movi~g endless belts (Canadian Patent No.~9,6~2 ) .~
' .15 or turntables ~U.S. Patent No.2~g~3s).
.. In these latter processes one problem is providing .. ~ a substrate which will withstand conti~uous working at the .1 temperature of molten sulphur and which has a surface which will allow the solidi~ied sulphur to be stripped without : 20 adhesion ~o the bel~.
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, To overcome these problems,, I have previously proposed .~ that molten materials should be cast onto ~arious substrates which I have ~ound to be non-bonding to the soldified material (U.S~ Patent No. 3,819,793). In another approach I have proposed pouring the molten material on to "pour strips"
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to the substrate (Canadian Pate~t Application No. 184,901).
In another proposal I have provided an anti-adhesion coating o~ (e.g. for molten sulphur) sulphur dust.
. Another problem associated with prior solidi~ication . proces~es, particularly with sulphur, is the formation of pockets o~ crystallinity in. the solidified material.
. m ese orystalline regions embrittle the resulting solid, . . causing dust problems and pro~iding sites for water occlusion both in water-coo~ing procedures and on exposed stockpiles. It has been proposed to overcome this problem : . by casting sulph~r in thin layers and immediately plunging . the layer in a water bath and building up the thickness by . . ~urther superimposed castings. miS reduces crystallinity . . and moisture entrainment only where the solidifying ~ `
. 15 temperature ls obtained below 95C~ (The transformation . temperature from monoclinic to orthorhombic sulphur.) The . . pressure o~ monoclinic sulphur directly encourages . moisture and contaminates ocslusion and overall, substantially ': weakens the end product~
. 20 I have previously proposed (U.S. Patent No. 3,819,793 . which was mainly concerned with avoiding adhesion between solidi~ying sulphur and a mould or belt sur~ace) to avoid water occlusion by first air-cooling molten sulphur at least to ~orm a sur~ace skin thereon and only then applying ~l water cooling.

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I have now discovered that incorporating an organo-polysiloxane or ke~sene in the molten material promotes the formation of a dense or close-grained vitreous or amorphous solidified material o~ solidification and results in a stron-ger solidified product. The reason for this effect is not yet entirely understood.
I have also discovered that to avoid undesired cry-stallinity it is important that the initial surface skin should be formed with no substantial disturbance of the mol-ten surface. This condition may be achieved either by direc-ting a steady stream of air against the molten material in such a manner that negligible rippling of the surface is caused, until at least a solidified skin is formed, or by applying powdered solidified material to the molten surface until at least a solidified skin is formed.
. The organopolysiloxanes that are particularly e-fective are dimethyl and phenyl-methyl "silicone fluids"
(dimethyl and phenylmethyl polysiloxanes), the latter having ~ better heat resistance, having viscosi.ties up to 100,000 cen-:. 20 tistokes. Specific fluids which have been successfully used are those manufactured by Dow Corning under the references Da710 and DC556, also DC550 and DC510. These are found to be effective at additive quantities of about 5 ppm and above, for example, 0.~5 gm. silicone fluid per 50 kg sulphur.
Above about 30 ppm no increase in beneficial eect is achieved. Kerosene may be used in ..........................

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similar quantities separateIy or as a solvent aid for the silicone fluid. Of the specific fluids mentioned above, kerosene is compatible with DC550 and 510 but not DC710 and 556.
The preferred substrate ~or casting molten materials according to the present invention is an endless belt of stainless steeI, for example the type of belt known by the trade mark "Sandvik". This provides good heat exchange from the cooling material through the metal belt which is sprayed by water jets on its undersîde. Direct cooling to the molten material is preferably provided by a hood extending longitudinally of the belt and positioned a few inches above : .~
the melt surface. Transverse slotted outlets may be provided to control the air flow so as to avoid disturbing the melt surface. Once the initial surface solidified skin has been formed, cooling may be by more vlgorous air blasts , or by water jets, the latter preferably in the form of an atomised water spray which evaporates from the solidified surface giving additional evaporative cooling and avoiding water occlusion.
The feed of molten material onto a moving substrate, ,~l which may be in the form of an endless belt, or a drum or a turntable, may be by means of a weir overflow from a trough, preferably steamjacketed, positioned transversely to the direction of movement of the substrate. Alternatively the feed from the trough may be by a plurality of gulleys . . . .. . . .
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¦ providing a plurality of streams of molten material which impinge individually on the substrate be~ore merging to cover the substrate. This ~orm o~ feed is especially advantageous if the substrate has been treated with water prior to ~eeding to reduce the substrate temperature. As S described in my Canadian Patent Application No. 184,901, in such circumstances the use of indi~idual streams ; minimises watèr occlusion ~rom the substrate sur~ace.
To allow the molten material to build up a satis~actory thickness on the substrateg rubber retaining strips may be provided at the substrate edges. When the substrate is an endless belt the strips must be o~ sufficient flexibility to pass continuously over the curvature of the terminal pulleys. The rubber must also withstand continuous operation at the temperature of the molten material. As a result, ~ilicone rubber (partlcularly phenyl-silicone rubber) would be the preferred material but I have founa it possible to operate satisfactorily with neoprene strips ~hich ha~e been dressed with a silicone ~luid.
When the substrate has a plain surface, the solidified product is obtained in slab or "slate" ~orm. On an endless stainless steel belt su~ficiently solidified material of sufficient thic~ness, i.e. above ~ inch, comes away from the belt as it begins to traverse the termlnal pulley and breaks after approximately 40 to 5O cms of deflection. I~ the interior oi t e slab has not ~ully soli~ified at this timo, ' .

-~-. ~ 2 r or is above 95C, the~ the exposed material will solidify in monoclinic crystalline ~orm. Accordingly either the belt should be of sufficient length to ensure complete solidification before removal o~ the solidi~ied material9 or else the partially solidi~ied material should be passed, S unbroken, from the belt on which inltial oooling has taken place to another belt to complete the cooling~ This latter process is particularly suitable for operation with .~
an endless stainless steel belt as the casting becomes ~ree o~ the belt surface before it is solidified throughout.
As the belt returns around the terminal pulley the casting may be maintained in the horizontal plane supported by ~ bridging rollers and led onto another con~eyor ~or further ., .
cooling under natural or forced conditions. Because of the initial cooling that has taken place on the steel belt in solidifying the outer portions of the casting9 the ;, second conveyor may use a belt o~ conventional construction, e.g. rubber, canvas, and can be o~ a grade which could not .~
have been used to receive molten material. Thus the length of expensive stainless steel belting required can be minimised. The second conveyor is pre~erably slightly wider than the ~eeder belt and operates at the same speed.
Further cooling means may be provided at suitable intervals.
On the second conveyor the slab can again be broken on pass~ng over the terminal pulley, or a pro~iled roller or other breaker may be brought into contact with the slab ; ' . . - 7 -.' . ;
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10736Zt -¦ as it passes along the con~eyor, In the case of drums or tur~tables combinations of scraper blades and/or brea~er rollers may be required to remove solidi~ied material.
The ~ecessity to break the slab o~ solidified material ca~ cause problems of air-borne dust with resultant pollution and f1re hazards and causes large quant~ties of . unwanted fine~. Also, the slates break into ra~dom shapes and sizes. I have already proposed in Canadl~n Patent ~pplications Nos~ 184,gO1 and 184,902 that molten material should be solidified in the ~orm of unlform ~ablets or cubes. The -~ 15'' '.' ' , . . /
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_ considerations o~ the present invention may equally be applied to the prodt:~ction o:e sulphur in these ~orms.
These forms may be aohieved by moulding suitable recesses into a convent~onal rubber conveyor belt sur~aced with a suitable heat resistant mate~ial, or provided with suitably shaped tiles bonded to the belt ~urfaee, preferably o~ phen~l silicone rubberO However, such belts restrict the thickness of cast sulphur products due to their inherent heat resistant property, and in the ~irst-mentioned case, is basically un~uitable as in a comparati~ely short ~ength of time its hea~ resistant surfacing is dissolved by conti~uous contact with molten sulphur. However, such materials may more suitably be . used on drums and tuFntables where M exing is avoided. It .would be possible to impress suitable recesses into the : 15 steel belts now favoured but this would severely if not wholly i~pair their flexibility.
I now propose to adapt steel substrates9 or other plain substrates capable of withstanding the working . conditions, by positioning thereon a skeleton framework .'20 which defines the sidewalls of a tablet mould, the surfaoe o~ the steel or other substrate forming the floor of the ;mould. In one form the framework may be of silicone rubber bonded to the substrate with a suitably hea~ resistant adhesive~ In another ~orm, the framewor~ is made up at least longitudlnally from a plurality of metal sections9 _ g_ ..
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¦ each section being linked by metal wire, or by inherent mag~etisation, or being individually spot welded to the metal substrate to allow the substrate to flex as it passes around the pulleys of a conveyor belt installation.
Transversely there is no flexing and so it is not necessary S that the metal ~ramework is broken into s~ctions.
In the wire linked or magnet~cally linkable ~orms, the ~ramework is removable so that the substrate may be used i~ its plain for~. The linked ~orms may be retained on the substrate ~y magnetisation and to increase the adhesive e~fect and for greater speed of addition and removal are pre~erably formed into modules containing a num~er of recesses.
- Alternatively, the linking wire may be passed through through-bores in the indi~idual sectio~s and the wire tensioned around the terminal pulleys of the belt over ; the belt surface9 the ends of the wire being welded or clamped together. In this way problems of adhesion of the sectio~s to the belt are a~oided. Similarly, a silicone ~rubber ~ramework can be bonded to steel wire cable or - 20 tape and stressed and secured in position o~ a plain belt.
The e~posed ~oint is covered by a ~gaiter" of similar material, which ma~ be cured in situ to bond to the already positioned rubber and wire.
m e sidewalls of each framework should preferably

2~ be of triangular cross-section with the apex lying above .
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. . ` ~73621 the substrate being rounded.to allow easy release o~ the solidi~ied material. In addition, the sidewalls are . preferably dressed with a silicone fluid be~ore use.
In casting molten material into such a ~ramewor~ lt . is preferable to allow the molten material to ri~e slightly (e.g. ~ inch) above the sidewalls. This allows . . the solid material to be remo~ed as a slab, ensuri~g that all the tablet recesses are emptied. I~ ~ubseque~t . handling the slab breaks cleanly into tablets or smaller . . slabs along the lines of weakness formed by the thin . 10 layer o~ material above the impression lef~ by each sidewallO
. The resulting appearance of sulphur solidi~ied in this . manner has given rise to the name "candy-bar'l sulphur.
¦ In an alternati~e form the transverse pro~iles may be ! omitted so that solidified material may be obtained in ..1 lS bar form.
; The temperature at which molten material is poured onto the substrate should not be so close to its melting point as to produce premature uncontrol~ed solidification possibly in an undesired crystalline ~orm, or so high as : 20 to require an excess of cooling capacity. In the case of molten sulphur a temperature o~ 145 - 150C is . convenient, this being the approximate range at which freshl~ mined molten sulphur exits from degassing equipment ; in which H2S is removed. In certain climatic conditions ; 25 it may be desirable to cool the molten sulphur to below ':
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. ., ~36~1 . this temperature range but the temperature should preferably remain above 125~C.
If it is cooled to say 120 - 1 25C and air cooling . is used, it is found that the surface of the molten . sulphur quickly solidii~ies in the undesired monoclinic struc ture with a rough crater like appearance. me sulphur slate obtained looses strength after a few ~lay~
and crumbles and breaks easily. However9 if the - Ireshly poured molten sulphur is not treated to air coolin~
but is dusted with fine sulphur particles (fine enough lû not ~o Iorm a rough sand paper-like end surface ~inish on solidifying) no such monoclinic transformation occurs.
On stabilising the melt sur~ace as described, ~so that no further surface ~usion of the sulphur dust particles occurs) followed by either water spray cooling, or air 15 blasts, or a combination o~ both, or contact with a water soaked sponge cloth roller for evaporative cooling, it is found that the sulphur casting on break up is suitably dense and close grained and equally if not harder than that o~tained with continuous air cooling at higher melt feed temperatures, i~e. say from about 135 - 150C. It has been found that such a sulphur dusting system operates with equall~ good results from 120C - 150C, although ; more dust is required as the mel-t temperature is increased.
The preferred particle size range for sulphur dusting is about 100% minus 90 mesh BSS, the upper tolerance being .
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. _ pre.~erahly no particles exceeding 1/64~. 1/32" and above will provide a coarse sand paper sur~ace e~fect, which will ~orm dust on attrition and is therefore undesi~able.
Coarser sized particles can only be used when a sufflciently higher melt temperature is to be treatedt i.~. say ~ro~
. S about 135 to 150C, but then only as to avoid making : an over-rough end sur~ace effect, o~ about say 1~64~l to 1J32" particle sizing range, although up to about 1~16"
- has been used in practiceO
The application o~ sulphur dust to the melt sur~ace ; 10 is in some ways preferable to the use of controlled air cooling to stabilise the melt surface by skin ~ormation, since with the latter there is always the risk that some disturbance o~ the melt sur~ace will occur resulting ; in the ~ormatio~ of undesired monoclinic crystals, though of course some degree of such crystalli~ity may be tolerated~ It will of course be appreciated that in some circumstances the presence o sulphur dust will not be ~acceptable although the application points may be suitably hooded, and subsequently the ~ust is ~used into ~ 20 the solidified material.
.. If cooling o~ the melt is required it may advantageously be per~ormed by aerating the melt using a~ impeller-type . aerator. This provides ideal conditions for introducing a silicone or kerosene additive ~o the melt. These additives require to be well-dispersed throughout the melt "~
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_ before casting and preferably a "conditioning't time of at least 4 minutes i.s allowed to elapse before casting.
Using the controlled air cooling process of the present invention with a silicone additive it has been . fou~d possible to obtain amorphous sulphur "slate" oi - S adequate thickness, e.g. up to 5/~" in a ~ingle pour of molten sulphur onto a stai~less steel Sa~d~ik*belt.
. However, it is possible to build up a thicker layer by : using multlple pour points and a laminating technique : i~ desired9 pro~ided that the above described cooling precautions are observed a~ter each pour.
Some specific embodiments o~ the present in~ention will now be descrlbed with reference to the accompanying dra~wings, in which:
FIGS. 1 a~d 2 are respec~ively side and plan views -' of an installation ~or solidifying sulphur with controlled .~ air cooling, . FIGS. 3 and 4 are respectively side and plan views . of an installation for produoing "cand~-bar" sulphur, FIG. 5 is a view o~ an installation for pro~ucing bar sulphur~
.; . FIGS. 6 and 7 are respectively a transverse section and plan view showing in detail a portion of the belt used in Figs~ 3 and 4, FIGS. 8 and 9 are respecti~ely side and plan views of an installation for solidifying sulphur using sulphur * Trade Mark . , . ,............ . ..
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10~3621 dust to stabilize the melt surface.
Re~erring to Figs. 1 and 2, the installation comprises a stainless steel endless belt 1 tensioned between terminal pulleys 2 and 3. Enclosed water ~ets 4 are positioned to impinge on the under surface of the upper ~ strand o~ the stsinless steel belt. Drainage means are \ provided so that water is continuously circulated. Molten sulphur is ~ed from storage via a pipe 6 to a trou~h 7.
From the trough it over n ows a weir edge 8 via a distribution plate 9 onto the belt 1. Air cooling is provide~ by a hood 10 which is in the ~o~m of a closed box ha~i~g air inlet 11 and outlets indicated at 12 in the form of transverse slotsO A movable baffle 13 allows the air to be directed preferentially to either end of the hood so that variable air pressure on the melt surface may be obtained. Water cooling is provided by an atomised water spray 14 directed at the upper sur~ace o~ the belt. Molten sulphur is ; prevented from running o~ the edge of the belt by rubber retaining strips 15~ A further strip may be required transversely behind the trough 7 to prevent backflow. Slab sulphur leaving ~he belt 1 is passed over bridging rollers 16 to a further conveyor 17 on which further cooling takes place, A5 a specific example of this apparatus, tests were carried out on a Sandvlk stainless steel belt tgrade 12R11) , o~ 500 mm width running between 500 mm pulley centres and ha~ing an ef~ective cooling length of 4000 mm. The edge retaining strips were of neoprene rubber bonded to the ., ,, ' ' ' " , " ' ~ ' ~ : :'. :' .. ... . ..
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10~3~Zl . _ belt. The strips were dressed with silicone f~uid be~ore casting. The hood 10 was 2000 mm in length and had 17 slots 12 approximately 8 mm in thioknessO The bottom v~
. . the hood was 55 mm above the belt sur~ace.
; In one test molten sulphur contai~ng 7.5 ppm o~ eachof Dow Corning silicone fluids DC710 and DC556 was cast . onto the abo~e belt moving at 0.8 mlmin. to a dep~h o~
13 mm. The rate of throughput of the sulp~ur was 210 kg/m~h~
The feed ~emperature was 148C and air was ~ed to the cooling hood at ~uch a pressure that the air emerging ~rom the slots oaused only the slightest r~ppling of the sur~ace.
The temperature o~ the water feed to the under-sprays was 10C. The sulphur emerging from beneath the hood had a ~ .
: solidified skin and was then subjected to an a~omiqed water epray. As the solidiiied sulphur reached the end . of the helt all the water had evaporated and the solid r sulphur was at a temperature of 70C. The sulphur was ~reed from the belt and allowed to break under its own weight . as it passed over the terminal pulley. Examination of this solidified sulphur showed it to be substantially amorphou~
and free from monooli~ic c~ystalss . A similar test was conducted using sulphur treated ~ with 5 ppm of each of the same ~luld~ under the same ;- conditions except that the belt speed was 0.7 m/min. and the throughput was 21g kg/m2h. Again a 13 mm thick slab ~` 25 of amorphous sulphur was obtained.
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In similar tests in which the pressure o~ air was such -that disturbance o~ the sur~ace was caused, the solidified slabs were ~ound to contain monoclinic crystals extending down from the air-oooled sur~ace. Crystallinity also occurred in tests with no air cooling and no silicone addi1;i~e.
It ~as found that solid~.ed sulphur containing silicone additives hardened on ageing, as opposed to that obtained without additive which tend to lose strength and become brittle.
10FigsO 3 and 4 show similar views to that of Figs. 1 and 2 for an installation ~or producing "candy-barl' sulphur under the same conditions. Similar parts have ; been given the same reference numerals as in Figs. 1 and 2. Optional additional features, apart from the structure o~ the belt which is described below with reference to Figs. 6 and 7, include the provision of an additional ~eed trough 7 as one trough may not provide suf~icient ~eed to fill the tablet moulds to the required depth a~d an additional water spray 14 in view of the possibi~ity of increased casting depth compared ~o slate production.
On its return path the belt may optionally be treated with water or water/kerosene mixture from spray poin~ 18 bo-th ~or cooling the belt and reducing adherence o~ the castings to the belt, and also optionally with sulphur dust ~rom delivery point 19 ~or a release coating as .' ~ 17 -' :: ~...,) ;'.: , . - ~ : . . : ..... .. :
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_ described in Canadian Patent Application No. 184~902.
The solidi~ied material will brea~ up into individual tablets or slabs o~ several tablets as it pas~es over the terminal pulley 3 but they may not always releasP
~rom the moulds u~der their own welght. Removal is S accomplished by a roller 20 having a surface o~ rubber suction caps which are pressed against the tablets as they traverse the terminal pulley. A water spray 21 provides further cooling and assists the operation o~
the suction capsO
10Referring to Figs. 6 and 7, the tablet mould framework used in Figs. 3 and 4 is made up from longitudinal - phenyl silicone rubber profiles 22 and trans~er profiles ~3 of similar material. Each of the profiles has a triangular cross-section with a rounded apex. The lS longitudinal pro~iles 22 ha~e a core 24 o~ steel wire cable which is stressed around the endless belt 1 and then ~ree ends welded or clamped together. The join is covered by a !'gaiter" of similar material moulded in situ. The retaining edge portions 15 may with advantage be positioned in the same manner as shown in Fig. 6 as the ef~ects of continuous high temperature worX~ng reduces the strength o~ the adhesives used hitherto. I~ addltional bondlng is requlred the core cables 24 may be split welded to the metal ,.
belt 1 at intervals. The transverse profiles 23 need not contain core cables and they are practically unaf~ected ~.
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by flexing of the belt on traversing the terminal pulleys, ; they may be bonded directly to the belt or merely but-bonded to the adjacent longitudinal profiles 22.
In the example shown in Fig. 6, the side portions 15 are appro~imately 1 inch high and the profi.les apprsximately inch high. As shown in Fig. 6, the pour of molten ~ulphur from the fir~t trough 7 fill~ the moulds to the region of the ap~x of the profile~ and the second trough provides a further ~ inch overall cover. ~his allows the ~olidified material to be removed ~ore easily-in - ~lab~ o several tablet~. In initial handling, i.e.
pa~age to a stockpile, the~e break along the lines of weakness forme~ by the profiles to form individual uniform tablet~. The use of the silicone additive described earlier cau~os the tablet~ to increase in hardness with :
aging so that sub~equent handling causes nagligable further breakage.
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.: Fig. 5 shows a modification o~ the installation de~cribed with respect to Figs. 3, 4, 6 and 7 in that only longitudinal profile~ 22 are provided. In this ca~e it is not necessary that the molten sulphur should extend above the apex of the profiles, and the result ''~I
.~ i8 the formation of rod or bar solidified sulphur.
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can be allowed to break and release under their own weight as they traverse the terminal pulley.
m e feed ~rom the ~irst feed trough 7 may b~ by gullies feeding directly into the spaces between the S longitudinal profiIes 22. The second ~rough ~s available if an overall cover o~ sulphur is required as in the case . of the tablets shown in Flg. 6.
: Figs. 8 and 9 show an installation comparable to that of Figs. 1 and 2 but with the replacement o~ air hood 10 by spreaders 26 ~or supplying sulphur dust to the molten surface to solidi~y and stabilize the surface.
Again similar parts are given the same reference numerals . as used in Figs. 1 and 2.
The spreaders 26 are enclosed in hood 27 fitted with 1~ ex-traction equipment to remove air-borne dust. Spreaders of the type used in agricultural dusting are suitable.
Apart from the use o~ the dust spreaders 26, operation . . of this installation is as described ~or Figs. 1 and 2. ~n optional alternating arrangement o~ water sprays 2~ and - 20 air jets 2g is shown for cooling the s~in solidi~ed molten sulphur. The air ~ets 29 increase the rate of evaporative cooling from water applied by the preceding sprays 28.
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Claims (12)

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

1. A method of solidifying molten material comprising pouring the molten material onto a substrate and cooling it, wherein an organopolysiloxane or kerosene is incorporated in the molten material as an additive for promotion of amorphous solidification and improved hardness on aging.

2. A method according to Claim 1, wherein the organopoly-siloxane is a dimethyl- or a phenyl-methyl-polysiloxane fluid.

3. A method according to Claim 1, wherein the substrate is an endless belt, a drum or a turntable.

4. A method according to Claim 3, wherein the substrate is an endless steel belt cooled on its underside by water-sprays.

5. A method according to Claim 1, wherein after the molten material has been poured onto the substrate a solidified skin is formed on the molten material on the substrate by cooling with air jets at a pressure which causes negligible rippling of the melt surface, and the material is subsequently cooled on the substrate by water sprays and/or more vigorous air jets directed against the solidified skin.

6. A method according to Claim 5 wherein the molten material is molten sulphur poured at a temperature of 130° to 150°C.

7. A method according to Claim 1, wherein after the molten material has been poured on the substrate a solidified skin is formed on the molten material on the substrate by treating the molten surface with powdered material, and the molten material is subsequently cooled on the substrate by water sprays and/or air jets directed against the solidified skin.

8. A method according to Claim 7 wherein the molten material is molten sulphur poured at a temperature of 120°
to 150°C.

9. A method according to Claim 7 or 8, wherein the powdered material has a particle size not exceeding 1/64 inch.

10. A method according to any one of Claims 1 to 3, wherein the molten material is molten sulphur.

11. A method according to Claim 1 wherein the molten material is poured onto an endless belt having a plain surface on which is positioned a skeleton framework of longitudinal or longitudinal and transverse profiles to define bar or tablet moulds on the belt surface.

12. A method according to Claim 11, wherein the longitudinal profiles comprise silicone rubber strips of triangular cross-section having a steel wire core, the strips being tensioned around the endless belt and the free ends of the steel wire welded or clamped together.