SLIP CASTING

Abstract: A slip casting method and machine are described wherein a stirring station (18) is provided either coincident with or separated from and downstream (considered in relation to mould travel) from a filling station (17), each mould (13) which has been filled at station (17) being stirred by a stirrer assembly (27) during and/or subsequent to filling.

Description: * SLIP CASTING This invention relates to a slip casting method and a machine. The machine and method have particular application in relation to casting larger items from bone china and porcelain. The invention is, however, by no means limited to such applications. In the slip casting of larger items, particularly of bone china or porcelain, and particularly when of a generally smooth-walled form, such as of cylindrical form, a problem can arise when a mould is filled with slip from an automatic filling head and then passes along the slip casting machine through the conditioning and conventional subsequent processing. It has been found that with a stationary mould and a relatively immobile filling head, there is an unevenness in the surface of the slip body formed in the mould which, although it is not always noticeable in the cast article becomes evident after firing. In manually operated slip casting machines, it has been conventional to overcome this problem of "wreathing" by placing the mould on a turntable and manually spinning it during filling. This has been found to eliminate the problem. When trying to construct an automatic J machine, this approach has problems. If a single spinning platform is provided at the filling head position, the mould has to be transferred, after filling, from the turntable to the conventional conveyor. This cannot be effected very conveniently. Mechanical lifting would require complicated machinery, and a sliding movement tends to damage the base of the mould and possibly cause slip to slop over the top edge of the mould. To provide a chain of turntables, each of which can be spun at the filling position and not thereafter, is possible, but this results in a very large bulky and costly machine, a turntable having to be provided for every mould position. Apart from the expense, this makes the machine very inflexible in that the spacing between moulds is set at the spacing between the turntables. Even when a comparatively small mould is being used the spacing between the moulds would be fixed by the turntable spacing and remains large. This means that such machines could not operate efficiently of a number of moulds of different sizes had to be used and could not optimise the use of floor space. It is an object of the invention to provide a slip casting machine wherein the above described advantages are obviated or reduced. According to the invention, there is provided a slip casting machine having a filling station and a stirring station at which slip introduced into mould at the filling station can be agitated. The filling and stirring can occur at the same station. For example a filling head assembly and a stirring head assembly could be arranged to operate on moulds at one station sequentially, or simultaneously. In the simultaneous operation, the filling head assembly could include a plurality of filling heads each incorporate a stirrer capable of being immersed in and stirring slip during and/or after filling and capable of being removed after stirring to permit mould movement. Alternatively, a filling head assembly and a stirring head assembly could each be movable between an operative position in register with moulds at the station and a remote storage position. As a further possibility, the stirring can be effected by means acting on the mould rather than directly on the slip in them. For example means could be provided for stirring the slip by vibration of the moulds or a support or supports therefor. The vibration could be linear or part-rotary. Vibration through a vibrating support could be replaced or supplemented by a mould shaking and/or tilting assembly. In the case of stirring actually in the slip rotary, pivotal and other forms of stirring can be used, for example a vibrating probe or oscillating or flapping stirrer could be used. The invention also provides a method of slip casting wherein after the mould has been filled the slip is stirred to reduce or eliminate wreathing. In the past, it has been thought that rotation of the mould during filling, or immediately thereafter was essential. However, we have found that the problem of wreathing can be successfully overcome by having a stirrer at a station downstream of a filling station. Typically, time for a machine to index between two such stations can be about one minute. We have surprisingly found that stirring even one minute after filling is, in fact, sufficient to agitate the slip so that the surface structure being formed in the slip which causes wreathing is, in fact, eliminated or destroyed by such stir. However, stirring simultaneously with and/or immediately after filling on an automatic machine fall within the scope of the invention. A separate stirring head can be moveable in its position longitudinally of the machine so that the distance between itself and the filling head can be varied depending on the size of moulds used. Whatever size of moulds are used on the machine, they can be placed almost side by side, and the index distance adjusted accordingly. This allows maximum use of conveyor space, particularly when all the moulds are being used. The stirring head can include a support which mounts a body for vertical movement, the body mounting a stirrer and including or consisting of a drive. The drive can be a shaft from a remote power source, but desirably is a power source incorporated within the body such as a pneumatic or electric motor. The body can, in fact, be a gear box connecting a motor to the stirrer. The stirrer can rotate about a vertical axis. The support can be a pneumatic cylinder arranged to move the stirrer into and out of the moulds in a generally vertical direction. The stirrer can be a central shaft with lateral blades. The blades can be solid or hollow depending on the nature of the slip and the type of moulds being used. Desirably, the rate of stirring can be varied by altering either the speed of the stirrer and/or the depth of the immersion of the stirrer to suit different conditions. The slip casting machine incorporating the stirring station can be a linear machine, in which moulds pass in a general straight line from a filling to a tip and drain turntable and then return via a drying and conditioning conveyor, or can be a circular machine wherein a single operator position serves all functions. Indeed, the slip moulding machine can have any convenient configuration with the stirring station being provided at one index position downstream of the filling station. A combined filling and stirring head assembly can be provided including free nozzels and stirrers mounted to move into operative relationship with a mould at the filling station. In such a case the filling and the stirring can be effected simultaneously or the stirring can be commenced part way after filling, or can start during filling and finish after filling has been completed.If desired, the filling nozzle and/or a stirrer support one on the same item or incorporated together to allow both functions to be carried out efficiently. Instead of a combined filling and stirring head separate filling and stirring heads can be provided, each being movable between the rest position and an operative position and movable sequentially into engagement with a mould at a single station The invention will be described further, by way of example, with reference to the accompanying drawings wherein:- Fig. 1 is a plan view of a preferred slip casting machine in accordance with the invention; Fig. 2 is a fragmental cross-section view on line 22 of Fig. 1; Figure 2A shows a detail of a stirrer of the machine; Fig. 3 is a schematic plan view illustrating a second slip casting machine, also in accordance with the invention. Figure 4 is a view similar to figure 2 but showing a third machine; and Figure 5 is a view similar to figure 2 but showing a fourth machine of the invention. Referring now to Fig. 1, it will be seen that a slip casting machine 10 is generally conventional including a pair of conveyors 11 and 12. Each of conveyors 11 and 12 is a triple conveyor in that it can convey three rows of moulds 13, 14 and 15. On conveyor 11 each row of moulds 13, 14, 15 proceeds from a position station 16 at which the mould is positioned by an operative. Thereafter, indexing of the conveyor moves the mould to a filling station 17 and thereafter to a stirring station 18 which will be described later. Downstream of the stirring station the filled moulds go through conventional operations such as standing, tip and draining and conditioning. At a discharge station 19 an operative strips the moulds, passes the goods for further processing and returns the moulds to the positioning stations 16. Reference will now be made to Fig. 2 which shows part of the slip casting machine of Fig. 1 in vertical longitudinal cross-section. The position station 16 is now shown but the filling station 17 and stirring station 18 are described in some detail. Conveyor 11 carries moulds 13 shown as 13a in the filling station, 13b in the stirring station and 13c subsequently. When the mould 13a reaches the filling station after an indexing step of the conveyor 11, a filling nozzle 20 (connected to a supply of slip by a flexible hose 21) is carried downwards by a carriage 22 sliding along a pneumatic cylinder 23. When a feeler 24 detects the mould a filling valve (not shown) is opened for a predetermined time sufficient to fill the particular mould concerned. Alternatively, filling of the mould can be detected by other means and the valve closed when a desired level of slip in the mould has been reached. Operation of the filling station is entirely conventional, and as indicated by the arrow 25, its position along the machine can be varied depending on the size of the mould employed. The separation between the indexing positions can vary. For medium size moulds a separation D is usual, whereas the separation can actually vary from a larger value Dl to a smaller value D2 as indicated. It will be appreciated that the distance between the stations 16, 17 and 17, 18 has to be one indexing step. In a similar way, a support in the form of a pneumatic cylinder 26 is provided at the stirring station 18 and mounts a stirring assembly 27 for vertical movement. The support 20 can be moved longitudinally as indicated by the arrow 28 to adjust the indexing distance. The stirring assembly 27 can include a carriage 29 carried by the support 26. The carriage 29 can support, for example, a gear box 30 driven by a pneumatic or electric motor 31. Alternatively, of course, the carriage 29 can simply connect a drive from a remote position to the assembly. Depending from the gear box 30 is a shaft 32 which carries stirring blades 33. In a preferred embodiment, the shaft 32 is some 22mm in diameter, and each of the blades 33 is constituted by a rod of comparative diameter attached to the shaft 32 and rotatable therewith. It should be emphasised, however, that loop type blades, two or more in number, or plain sheet like blades, or perforated blades can be used. No limitation is placed on the type of stirrer. Referring now to Fig. 3, it will be seen that the invention is equally applicable to a slip casting machine 34 which has a circular two or one lane conveyor 35 and an operator position 36. Here, movement of the moulds 37 is in a circular or other closed loop path and following a filling station 38 is a stirring station 39. The essential constructions of the filling and stirring stations can be similar to those described in relation to Figs. 1 and 2. We have found, surprisingly, that it is not essential that agitation of the slip has to be carried out simultaneously with filling (as has been previously thought) , but can be effectively carried out at a subsequent indexed position yet still effectively deal with the problem of wreathing. Referring now to figure 4, there is illustrated a third machine according to the invention (or at least a filling head part of such a machine) . The rest of the machine can be in the same form as shown in figure 1 or generally of the form shown in figure 3. A combined filling and stirring assembly (40) includes a plurality of filling heads (41) . As shown in figure 1 these may be three in number, but any convenient number can be provided extending transversely of the machine conveyor (42) . Each head is carried by a support (43) whereby it can be raised and lowered. The support (43) can be a beam extending transversely of the conveyor and supported by a plurality of pneumatic or hydraulic rams (44) for movement into and out of engagement with the mould (45) . Alternatively, an individual support (43) can be provided for each head (41) and each individual support (43) can be carried by an individual ram (44) . In each head a supply nozzle (46) is mounted and there is a position sensing feeler (47) . Alternatively a tight beam mould location system can be used. Alongside the nozzle (46) is mounted a stirrer shaft (48) which carries a paddle or like stirrer (49) which in the operative position of the support (43) is immersed in slip (50) of the mould (45) . The upper end of the stirrer shaft (48) is connected by a gear box (51) to a motor (52) which can be either electric or hydraulic or pneumatic. Of course, shaft (48) could be directly driven if required. In this embodiment of machine the need for a filling station followed by a stirring station is eliminated. Stirring can be carried out during and/or after filling has taken place. The degree of stirring can be varied by arranging for the depth of emersion of the paddle (49) to be variable or by arranging for the speed of rotation of shaft (48) to be changed. Figure 5 illustrates a fourth possible machine again wherein there is a single filling and stirring station. However, there are separate filling and stirring head assemblies (53) and (54) . Each of head assemblies (53) and (54) is movable between an operative position and a storage position. The operative position is indicated by the numeral suffix A and the rest position is indicated by the numeral suffix B. The filling head assembly (53) includes a plurality of filling heads (56). As described above in relation to figure 4 and figure 1, the heads (56) can be separably mounted for movement but are conveniently interconnected. To this end they can have a common support (57) in the form of a beam which at each end is connected to a pivotable link (58) which is movable between the two illustrated positions by means of pneumatic or hydraulic rams (63) or a like, mechansium means being provided to maintain the general vertical orientation of filling nozzle (59) during such movement. In a similar manner the stirring head assembly includes a plurality of stirring head (60) which can have either individual or a common support such as a beam (61) . The beam (61) is mounted by a pair of pivotal links (58) and is again moveable between its two position by means of a pair of rams (62) . A stirring shaft (63) carries a paddle (64) and the shaft (63) can be rotated by means of a motor (65) . In the operation of the fourth machine, filling is carried out with the filling heads in their operative position and the stirring heads in their storage position. After filling the filling heads are removed and the stirring heads moved into position to carry out the stirring. Whilst the stirring can not be carried out during filling, it can be carried out immediately afterwards. This can be advantageous in some circumstances. Variations are, of course, possible in the above. For example in all the embodiments rotary or pivotal stirring can be replaced by linear oscillating or vibratory stirrers. In the embodiment of figure 4 the filling nozzle and the stirring shaft can be identical or combined. For example the two shafts could be concentric, the filling nozzle being central and stationery and an outer stirrer shaft surrounding the nozzle and being rotatable mounted relatively thereto. THe stirrer shaft would be open at its lower end to allow slip to emerge from the nozzle and a stirrer blade on the lower part of the stirrer shaft could be arranged to travel around the slip issuing from the nozzle during filling so that stirring can occur during filling without undue splashing. As a further example the type of stirrer can vary widely depending on the circumstances, moulds and slip being used and the stirring action can be rotary, vertical or in any other combination of direction. The drive for the stirrer can be of any convenient form, and the amount of stirring is desirably variable, either by varying the speed of stirring or by varying the depth of the immersion of the stirrer or both stirring can be effected by means engaging the moulds or the carrier such as a conveyor beneath the moulds at the filling or stirring station. Rams could vibrate the conveyor, or a beam could carry probes or clamps which could engage the moulds and either vibrate them or apply cyclic tilting or like movement thereto. The invention is, of course, applicable to slip casting apparatus of any form. Many other variations are possible within the scope of the claims.

Claims: CLAIMS 1. A automatic slip casting machine having a filling station and/ a stirring station at which slip introduced into a mould at the filling station can be stirred. 2. A machine as claimed in claim 1, wherein the filling station and the stirring station are one and the same.. 3. A machine as claimed in claim 2, wherein there is provided a combined filling and stirring head assembly. 4. A machine as claimed in claim 3 wherein the assembly includes a number of filling nozzles and each has a stirrer associated therewith. 5. A machine as claimed in claim 4 wherein each nozzle is surrounded by a stirrer shaft. 6. A machine as claimed in claim 2, wherein there is provided a filling head assembly and a stirring head assembly each assembly being movable between an operative position and a storage position. 7. A machine as claimed in claim wherein the stirring station is downstream of the filling station. 8. A machine as claimed in claim 7 wherein the spacing between the stirring station and the filling station can be varied. 9. A machine as claimed in claim 8 wherein the filling station is fixed and the stirring station is movable. 10. A machine as claimed in any preceding claim wherein a stirring assembly has a number of stirring heads, each of which includes a support mounted for vertical movement, the support mounting a stirrer and including or consisting of a drive. 11. A machine as claimed in claim 10 wherein the drive includes a shaft driven from a remote power source. 12. A machine as claimed in claim 10 wherein the drive is a power source incorporated with the body. 13. A machine as claimed in claim 12 wherein the power source is a pneumatic or electric motor. 14. A machine as claimed in any of claims 10 to 13 wherein the support includes a gear box connecting a motor to the stirrer. 15. A machine as claimed in any of claims 1 to 14 wherein the stirrer can pivot about a vertical axis. 16. A machine as claimed in any of claims 10 to 15 wherein a ram arrangement can to move the stirrer into and out of the moulds in a generally vertical direction. 17. A machine as claimed in any preceding claims wherein the stirrer is a shaft with lateral blades. 18. A machine as claimed in any preceding claim wherein the rate of stirring can be varied by altering either the speed of the stirrer and/or the depth of immersion of the stirrer. 19. A machine as claimed in any preceding claim and being a linear machine, in which moulds pass in a generally straight line from a filling station to a tip-and-drain turntable and then return to the filling station via a drying and conditioning conveyor. 20. A machine as claimed in any of claims 1 to 18 and being a closed loop machine wherein a single operator position serves all functions. 21. A slip casting machine substantially as described with reference to figures 1, 2 and 2A or 2, 2A and 3 or 1 and 4 or 1 and 5 of the accompanying drawings. 22. A method of slip casting wherein during after and/or filling of a mould filled with slip it automatically stirred to reduce or eliminate wreathing. 23. A method as claimed in claim 22 wherein filling and stirring take place at the same station. 24. A method as claimed in claim 22, wherein stirring takes place at a downstream stirring station and at a time later than filling. 25. A method as claimed in claims 22, 23 or 24 wherein the stirring is effected by engagement of the slip. 26. A method as claimed in claims 22, 23 and 24 wherein stirring is effected by engagement with the moulds. 27. A method as claimed in claims 25 or 26 wherein the stirring is rotary/pivotal. 28. A method as claimed in claims 25 or 26 wherein the stirring is vibratory. 29. A method as claimed in any of claims 22 to 28 wherein the stirring is varied to suit different conditions. 30. A method of slip casting substantially as described with reference to figures 1, 2 and 2a or 1 and 4 or 1 and 5 of the drawings. 31. Ware produced by the machine of any of claims 1 to 21 or the method of any of claims 22 to 19.

Inventors: BERRISFORD TREVOR, WATERS FRANK SAMUEL, BERRISFORD, TREVOR, WATERS, FRANK, SAMUEL
Applicants: CENTRAL CERAMICS SERVICES LIMI, CENTRAL CERAMICS SERVICES LIMITED
Application year: 1992
Main classification: B28B1
IPC codes: B28B1