This invention concerns improvements in or relating to apparatus for, and a method of, drying ware, and to automatic ware forming machines.
In a conventional automatic ware forming machine, such as for making mugs, clay is supplied into a plaster of paris mould. The mould is subsequently moved to a making machine where the clay is pressed into the required shape to form ware. The mould is then passed under a plurality of streams of hot air or gas to dry the ware prior to the removal thereof from the mould for subsequent processing. A plurality of such moulds are generally carried on the machine by an endless chain or belt, or on a carousel.
DE 3104499 discloses a drying oven including a chamber in which a large number of ceramic articles can be located. An air flow is provided through the chamber such that reduced pressure is provided therein.
According to the present invention there is provided ware drying apparatus comprising a mould upon which ware can be carried, the mould defining a chamber for the ware, selectively operable means for substantially closing the chamber, means for producing below ambient pressure in the chamber, and means for applying heat therein, characterised in that the apparatus is arranged such that ware is locatable between the heat applying means and the mould.
Preferably the apparatus includes means for providing a flow of gas through the chamber. The gas flow may be of air or any other suitable gas or mixture of gases.
The closing means may comprise a cover engageable with an upper part of the chamber.
The cover and/or chamber may be movable relative to each other in a substantially vertical direction between a lowered position of the cover engaging the chamber and a raised disengaged position.
One or more apertures may be provided in the apparatus through which the flow of gas may enter into the chamber. The or each aperture may be provided in the cover.
The apparatus may also comprise means for sealingly closing a hole in a lower part of the chamber. The lower hole closing means may be operable by virtue of below ambient pressure being produced in the chamber.
The lower hole closing means may comprise a closure member movable between a position closing said hole and a position clear from said hole, the position preferably being spaced beneath the hole.
The heat applying means is preferably constructed so as to be locatable within hollow ware when the chamber is closed. Alternatively the heat applying means may be locatable substantially adjacent flatware within the chamber.
The heat applying means may comprise an electrical heating element which may be mounted on the cover. The heating element preferably provides radiant heat and is desirably controllable. The heating element preferably comprises a plurality of heating zones which may be separately controllable. The heating element may be an infra red radiation source.
One or more of the apertures permitting gas to enter the chamber may be provided adjacent the heat applying means such that gas entering the chamber is warmed.
The means for producing below ambient pressure may comprise a vacuum pump in communication with the interior of the chamber, preferably through the cover.
The communication with the vacuum pump may provide an outlet from the interior of the chamber through which the gas may flow. Preferably the means for producing below ambient pressure substantially causes the gas flow through the chamber.
Alternatively, the means permitting gas to flow through the chamber may be provided by pores in the mould structure. A coating may be applied to the mould to reduce the porosity to a suitable value.
Also according to the present invention there is provided an automatic ware forming machine including drying apparatus according to any of the preceding thirteen paragraphs.
The ware forming machine preferably comprises a plurality of moulds movable along an endless path. Certain of the moulds are arranged to locate in part of the endless path at any one time, and the drying apparatus is preferably in operative relationship with the moulds when the latter are in said part of the path, preferably providing a drying unit for each mould in said part of the path. Said part of the endless path is desirably positioned between a location where clay can be shaped in moulds to form ware and a location where shaped ware can be removed from the moulds.
Said part of the endless path may comprise zones such that different drying conditions may be applied to the moulds in each zone.
The machine may include means for introducing warm air on to the moulds subsequent to removal of the shaped ware and prior to filling with clay. The warm air introducing means is preferably in communication with an arrangement for warming air by passing air over the heat applying means of the drying apparatus not located in moulds.
The drying apparatus may be mounted on a movable carrier located above said part of the endless path and selectively lowerable to engage with respective moulds on the path and the carrier may comprise a rotatable carousel.
The machine may be operable on any of hollow ware, flatware, cast ware, moulded ware, and pressed ware.
Further according to the present invention there is provided a method of drying ware in a mould, the method comprising substantially closing the mould, producing below ambient pressure in the closed mould, and applying heat, characterised in that the ware is located between the heat applying means and the mould.
A flow of gas may be provided through the mould.
The below ambient pressure may be produced during only a part of the drying method. The below ambient pressure may be ceased when the percentage of water in the ware has been reduced to a predetermined percentage, which may be in the range 2-6%.
Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings in which:-
A plurality of pairs of mould carriers 24 are respectively movably located on the rails 14, 16 with the outer carrier 24A mounting a guide wheel 26 and the inner carrier 24B being mounted on the chain 18. Mounted between each pair of the carriers 24 is an open ended frusto conical mould casing 28. A suitably shaped plaster of paris mould 30 is carried in the casing 28. A passage 32 is provided through the base of the mould 30 to permit air to be sucked therefrom during the locating and shaping of clay therein. A washer 34 mounted on a vertically movable spindle 36 is located within a cavity 38 below the passage 32 such that in a raised position the washer 34 closes the lower end of the passage 32.
Provided at the downstream end, of the second part 22 of the track relative to the direction of movement of the chain 18, is a making machine 40 which shapes clay into ware within the moulds 30. Immediately upstream of the making machine 40 is a clay extruder 42 for supplying a required amount of clay into the moulds 30. Upstream of the extruder 42 is an area 44 where warm air can be blown onto the moulds 30 when empty to provide drying thereof prior to filling with clay. At the upstream end 46 of the second part 22 is a product transfer device (not shown) for removing ware after drying from the moulds 30 by for example means of suction.
Coaxially mounted above the first part 20 of the track is a carousel 48 which mounts around the perimeter a plurality of vertically aligned rams 50. A cap 52 is provided on the lower end of each ram 50. A downwardly pointing lip 54 is provided around the periphery of the cap 52 with an annular seal 56 on its lower edge. The cap 52 is dimensioned to sealingly close the upper end of a respective one of the mould casings 28, when lowered thereonto, and hence close the respective mould 30 within a chamber C. A cylindrical heating element 58 extends coaxially beneath the cap 52, and is of a size to fit within an item of ware 60 in the mould 30. An electric lead 62 extends through the cap 52 from the element 58. A passage 64 also extends through the cap 52 and connects via flexible piping 66 to a vacuum pump.
In use, the chain 18 and carousel 48 are driven and indexed relative to each other. As a mould 30 passes beneath the extruder 42 a required amount of clay is supplied therefrom. The making machine 40 subsequently presses the clay into the required shape against the sides of the mould 30 to form an item of ware. As the clay is being supplied into the mould 30 and shaped therein air is sucked through the hole 32 by a further vacuum pump (not shown) to assist these processes. As a mould 30 moves on to the first part 20 of the track it passes beneath the carousel 48 which is indexed to lower a cap 54 thereonto by the action of a respective one of the rams 50. When a cap 54 is thus fitted suction is applied through the piping 66 and passage 64. The reduced pressure created within the mould 30 causes the washer 34 to rise and thus close the passage 32. Simultaneously heat is applied internally of the mould 30 by the element 58. Heat and suction are applied as the mould travels around the first part 20 until the second part 22 of the track is reached whereat the ram 50 raises the cap 52 off the mould 30. The ware 60 is subsequently removed from the mould 30 by the product transfer device and warm drying air blown onto the mould 30 at the area 44. The warm drying air may have been heated by passing over the heating elements 58 which are in a raised position.
In a second embodiment as shown in Fig. 4, relatively narrow inlet passages 63A are provided extending through the heating element 58. The inlets 63A connect the interior of the mould 30 with inlet passages 63B extending through the cap 52 to the exterior thereof. The suction of the vacuum pump draws air into the chamber C from outside through the inlets 63A,B. As air flows through the inlets 63A,B it is heated by the element 58. The air flows from the inlets 63A,B, through the chamber C and exits through the passage 64. This flow of warm air facilitates the drying of the ware by assisting the removal of the relatively wet atmosphere within the chamber C, through the passages 64 and replacing it with warm dry air. The warm air flow enables the temperature in the chamber C, to be reduced whilst still achieving effective drying. This is energy efficient and may help prolong the life of moulds. Instead of using air a supply of a specific gas or mixture of gases may be connected to the inlets 63B.
It is to be appreciated that the dimension and numbers of inlets 63A,B are predetermined relative to the capacity of the vacuum pump and the degree of reduced ambient pressure required in the chamber C. The making machine 40 can be used in forming and drying cast ware, moulded ware and pressed ware, including hollow ware and flatware.
Fig. 5 shows a part of a ware forming machine according to a third embodiment of the present invention, for drying flatware. The machine includes a mould casing 128 mountable between a pair of carriers (not shown) similar to the carriers 24A,B. A plaster of paris mould 130 is carried in the casing 128. A passage 132 is provided in the base of the mould 130 to permit air to be sucked therefrom during the locating and shaping of the clay therein. A washer and spindle arrangement (not shown) may be provided to close the end of the passage 132, to be operable in a similar manner to the washer 34 and spindle 36 described above.
A cap 152 is provided on the lower end of each ram on the carousel 48. The cap 152 has a downwardly extending wall 154 around its periphery which seals with the casing 128 on its lower edge, in a similar manner as hereinbefore described, to form a chamber C₂. A planar ceramic heating plaque 158 extends beneath the cap 152 to a position directly above the ware in the mould 130. The heating plaque 158 includes a plurality of coaxial heating elements arranged in annular zones to enable the heating effect of the plaque 158 to be varied across the radius thereof. For example, if the ware is of relatively small diameter, (a saucer) then the heating effect may be required less towards the periphery of the casing 128 and more towards the centre. Consequently the zones towards the centre of the plaque 158 only would be activated. Electric leads 162 extend through the cap 152 from the plaque 158 to a heating control (not shown). The plaque 158 is an infra red radiation source, but any other suitable heating means may be used.
A passage 164 extends through the cap 152 and connects to a vacuum pump. One or more further passages 163 extend through the wall 154. These passages 163 provide inlets into the chamber C₂. Air is drawn into the chamber C₂ through the inlets 163 under the influence of the suction provided by the vacuum pump. The air flows through the chamber C₂ and exits through the passage 164. As it flows through the chamber C₂ the air is warmed by the plaque 158. The flow of air through the chamber helps the removal of water in the atmosphere of the chamber and thereby facilitates drying of the ware. Insulation 165 may be provided on the underside of the cap 152 to help reduce heat loss through the cap 152.
Fig. 7 Shows a ware forming machine 200 according to a fourth embodiment of the present invention, for drying flatware. The machine 200 has an endless track 212 which is substantially rectangular but one end of the rectangular extends outwardly to define an elbow 222. The track may take any conventional form such as illustrated in Figs. 1-3 and will thus not be described in any detail. A plurality of mould casings 128 bearing moulds 130, of the type illustrated in Fig. 5, are movably located on the track, their movement being precisely indexed.
Each side of the rectangle has a section 270 defining positions for ten adjacent casings 128. Between the respective sides of the rectangle are defined four further sections 272 of ten positions for the casings 128. Means are provided for moving the casings 128, normally all ten simultaneously on each section, between respective sections. Such moving means may comprise pivoting lift bars (not shown).
A cap 152 (Fig. 5) is provided above each of the positions of the sections 272. The cap 152 is movable by a ram to engage or disengage a casing 128 provided there beneath to permit drying of an article of flatware held in the casing.
A ware making machine 240 is provided at the apex of the elbow 222. Upstream of the making machine 240 are mould cleaning and mould conditioning equipment (not shown). Further upstream from this equipment is a stage (not shown) where the ware is unloaded from the casings 128. The unloading stage may connect to a similar apparatus for white drying the ware. In such similar apparatus the ware is obviously not mounted in mould but suitable shape closable containers are provided in which the ware is supported. The white drying apparatus may subsequently connect to a kiln.
In use, the track 212 rotates in a clockwise directions as shown is Fig. 7. Movement of the track is precisely indexed to ensure that the casings 128 thereon move at precisely the required time and move to the exact required position. When ten casings 128 fill each of the positions in the section 270 the casings will be moved at a required time by pivoted arms to the respective positions in the lowermost (as shown in Fig. 7) section 272. In the section 272 caps 152 are lowered onto the casings 128 to provide a first drying at a required temprature for a required period. It has often been found advantageous in the first heating section 272 to only apply heat and not reduced pressure, thereby stabilising the ware. At the required time the casings are moved to the next section 272 where a further drying process is applied this time under reduced pressure. Two further such drying stages are carried out in the further section 272 and the casings 128 are finally moved onto the upper run of the track 212. The casings are then moved, again precisely indexed, to the unloading station where the ware is removed for subsequent drying and firing. The casings 128 and moulds 130 therein are thereafter cleaned and conditioned.
There are thus described automatic ware forming machines with a number of advantageous features. The provision of reduced pressure in the mould lowers the boiling point of water thus providing for enhanced drying. The suction from the vacuum pump and where provided the flow of gas through the chamber remove the steam and water vapour created away from the ware further enhancing drying. Closing the mould provides for more localised and thus efficient heating of the ware. Locating the heating element within the ware for hollow ware, and closely adjacent the ware for flat ware, and the ware being located between the heating element and the mould provides for less heating of and thus damage to the mould. Accordingly the required drying can be carried out more efficiently and quickly
With the described machines the drying times have been reduced to 50-55 seconds from 90-100 seconds for hollow ware and from 19-20 minutes to 3-4 minutes for flatware. Accordingly it has been possible to make a machine with twenty-eight moulds rather than the conventional fourty-five which thus reduces the floor space required which is often of a premium. This machine is ideally suited for relatively small runs, in that gas is not required nor is the removal of burnt waste gases.
The drying process hereinbefore described refer primarily to the drying stage commonly termed "mould release". This is a state of dryness which when reached allows the ware to be removed from the mould. The percentage of water in the ware at this stage is usually in the range 10-15%
Often the next stage is to further dry the ware, subsequent to removal from the mould, until the percentage of water in the ware is in the range 1-2%. This is commonly termed "white drying". The present invention may readily be used to "white dry" ware. In this instance the ware is placed on a support such as a perforated plate, within a substantially sealed container. An outlet to a vacuum pump and a heating element is provided within the container substantially as hereinbefore described. Gas inlets may also be provided in the container as described above. During operation, the pump causes an atmosphere in the container of below ambient pressure and also, if applicable, a flow of gas through the container as above. The vacuum pump may be turned off before the ware has been finally dried perhaps when the water content is in the order 3-5%. The removal of below ambient pressure prior to final drying has been found to reduce the likelihood of the dried ware cracking.
Various other modifications may be made without departing from the scope of the invention as defined in the accompanying claims. For example, as illustrated in fig. 4, the washer for closing the passage through the mould may be replaced by a short stroke ram 70 which closes the bottom surface of the mould casing 28 and hence mould 30. The moulds and/or caps may be moved by different means and the caps could be raised and lowered other than by the described rams, or the moulds could themselves be raised and lowered rather than the caps.
Also, the cap 52,152 and the corresponding lip 54 and wall 154 may seal directly onto the mould 30,130. This makes the provision of the casing 28,128 unnecessary. In such cases, the inlets for the gas may be provided by the pores in the structure of the mould. Further, a coating may be applied to the mould to reduce the porosity of the mould to a suitable value such that the drying process as hereinbefore described will function. Alternatively or additionally moulds of material other than plaster of paris may be used.