MICROWAVE FORMING OF ARTICLES IN A CONTINUOUSLY OPERATING MICROWAVE OVEN

Abstract: A method and apparatus is described for forming an article by placing incoherent material to be consolidated to form an article into contact with a microwave-heatable mould, die or former and heating the mould, die or former by exposure to microwave radiation whereby the incoherent material is consolidated to form the article; the method comprising the steps of: at a first station (1), placing the incoherent material in contact with the mould, die or former; passing the mould, die or former and incoherent material through first gate means (4) into a continuously operating microwave oven (6); exposing the mould, die or former and incoherent material to microwave radiation in the continuously operating microwave oven (6) whereby the incoherent material may be consolidated to form the article; passing the mould, die or former and incoherent material through second gate means (7) out of said continuously operating microwave oven; at an article removal station (1), removing the article from contact with the mould, die or former; returning the mould, die or former to said first station (1),whereby articles may be formed in a continuous process.

Description: MICROWAVE FORMING OF ARTICLES IN A CONTINUOUSLY OPERATING MICROWAVE OVEN This invention relates to the microwave forming of articles in microwave ovens. It also relates to apparatus, and methods of materials handling, that are applicable in fields other than microwave forming of articles in microwave ovens. Microwave ovens are increasingly being used, not only in domestic catering, but also in commercial catering and industrial processing of articles and materials. Microwaves are particularly useful for heating and/or drying articles and materials. The applicant's European Patent No. 0231588, for example, shows use of microwave radiation in the at least partial sintering of materials; the applicant's International Patent Application No. WO88/09092 shows use of microwaves in the curing of dip coated materials. Heretofore microwave treatment of articles and materials has generally been undertaken on a batch basis. Materials are introduced into an enclosure (referred to hereinafter as a microwave oven) ; a door to the enclosure is closed ensuring a complete seal against escape of microwave radiation; the microwave oven is switched on; then the microwave oven is switched off; the door opened and the article removed from the oven. Batch processes are known to be less time- and cost-efficient than continuous, production line, processes. However up to now the only use of continuously operated microwave ovens has been for the treatment of articles having one dimension of less than approximately 5 cm so that they may be passed on a conveyor through a microwave choke. (For examples of this type of process see US 4839485; US 3674422; GB 2156640; GB 1392488; GB 1207281; GB 851109). A microwave choke comprises an assembly of spaced pins, grooves, or other protuberances or indentations arranged so as to cause the decay of microwave radiation passing thereby. For the wavelengths commonly used in industrial microwave applications the maximum distance between opposed microwave chokes through which an ob-ject may pass is 5 cm. There have been described chokes of particular construction for exposing larger articles to the inside of a continuously operating microwave oven (See for example GB 1467384 ) . The applicants have realised that there is a pressing need for apparatus that will allow the continuous microwave treatment of large objects ( over 5 cm) by microwave radiation. Accordingly the present invention provides a method of forming an article by placing incoherent material to be cons ol i dated to f orm an arti c l e into contact with a microwave-heatable mould, die or former and heating the mould, die or former by exposure to microwave radiation whereby the incoherent material is consolidated to form the article characterised in that the method comprises the steps of : - at a first station , placing the incoherent material in contact with the mould, die or former ; pass ing the mould , die or f ormer and incoherent material through first gate means into a continuously operating microwave oven ; exposing the mould , die or f ormer and incoherent material to microwave radiation in the continuously operating microwave oven whereby the incoherent material may be consolidated to form the article ; passing the mould , di e or f ormer and incoherent material through second gate means out of said continuously operating microwave oven; at an article removal station , removing the article from contact with the mould, die or former; returning the mould , die or f ormer to said f irst station whereby articles may be formed in a continuous process . By incoherent material ' is meant any material that does not self adhere and is divisible with little external force , non-limitative examples include a powder , liquid , sol or a wet gel . The invention further provides apparatus comprising: - i ) an input chamber for the temporary accommodation of moulds , dies or formers and incoherent material to be treated by microwave radiation ; ii) a microwave oven in which moulds, dies or formers and incoherent material may be treated by microwave radiation, iii) an output chamber for the temporary accommodation of moulds, dies or formers and incoherent material treated by microwave radiation; iv) transfer means operative to transfer moulds, dies or formers and incoherent material from the input chamber, through the microwave oven, and to the output chamber; v) gate means operatively associated with each of the input and output chambers to enable, sequentially as far as a given mould, die or former and incoherent material is concerned:- a) a given mould, die or former and incoherent material to be received in the input chamber from outside the apparatus; b) the input chamber to be closed against reception of further moulds, dies or formers and incoherent material; c) the input chamber to be opened to allow the transfer means to transfer a given mould, die or former and incoherent material from the input chamber, through the microwave oven, and to the output chamber; d) the output chamber to be closed against reception of further moulds, dies or formers and incoherent material from the transfer means; e) removal of moulds, dies or formers and incoherent material from the output chamber to outside the apparatus; said gate means being disposed and operable so as to ensure that significant amounts of microwave radiation may not escape-while the microwave oven is on; whereby the microwave oven may be operated continuously. The invention further provides apparatus for use as gate means for preventing escape of microwaves from microwave ovens; and also provides methods and apparatus for conveying materials. Further details of the invention are made apparent from the claims and are disclosed in the following description with reference to the drawings in which:- Fig. 1 shows schematically a machine for the microwave moulding of sintered articles; Fig. 2 shows a mould and associated apparatus for use in the machine of Fig. 1; Fig. 3 is a plan view of a part of the apparatus of Fig. 1; Fig. 4 is a part sectional view of a funnel for filling the moulds of Fig. 2; Fig. 5 is a part sectional elevation of a rotary microwave choke for use in the apparatus of Fig. 1; Fig. 6 is a part plan section of the rotary choke of Fig.5; Fig. 7 is a part sectional view of a microwave oven as used in the apparatus of Fig. 1; Fig. 8 is a part sectional view of the apparatus of Fig. 7 and transverse to the view of Fig. 7; Fig. 9 is a part plan section of a .further form of rotary choke. Fig.10 is a schematic view of a further machine for microwave moulding of articles. Fig. 1 shows schematically a machine for microwave moulding of sintered articles. The integers of the machine are described below first in general terms and then in detail. A moulding/demoulding carousel 1 comprises a turntable that may be rotationally indexed to allow various operations to be performed on moulds held on the carousel. A stacking conveyor 2 and transfer chute 3 lead from the rotary carousel to an input drum 4 which may be rotated to allow moulds to be extracted from the drum by a walking beam 5 into a microwave oven 6. The walking beam 5 moves the mould through the microwave oven to an outlet drum 7. The outlet drum 7, after rotation, allows the mould to be extracted via an exit chute 8 to a conveyor 9 in a hot air dwell zone to allow a sinter temperature -soak' treatment. From the conveyor 9 the moulds are delivered to a transfer slide 10 and pushed onto a conveyor 11 running through a cooling zone in which forced air cooling brings the moulds down to a temperature at which the sintered articles may be stripped from their moulds without damage to either article or mould. From the conveyor 11 the moulds are delivered to a cooling zone/carousel transfer slide 12 and are pushed onto the carousel by an actuator. Once on the carousel the article is stripped from its mould, the mould is re-assembled, and then is ready for filling again. Fig. 2 shows a form of mould that may be used for making generally cylindrical articles such as dye cores. The mould comprises cylindrical male 13 and female 14 moulds formed of a recrystallised silicon carbide material available from Ibiden of Ogaki City, Japan. It is found that for best performance the silicon carbide should have a resistivity in the range 3,000 - 70,000 Ω cm. The moulds are mounted and spaced on a spacer ring 15 of e.g. a silicone rubber which has annular grooves 16,17 to locate the male 13 and female 14 moulds respectively. The ring 15 is mounted on a stand (indicated generally as 24) of aluminium comprises an annular disc base 18 and a hollow cylindrical mast 19. This arrangement provides stability for the mould; allows forced air cooling of the male mould by passing air through the central aperture 20 of the base 18 and through venting apertures 21 in the walls of the mast 19; and provides a convenient x fingerhole' in the aperture 20 for handling equipment as will be made clear later. The male 13 and female 14 moulds and the raised area 22 of the spacer ring 15 lying between the annular grooves 16,17 between them form a moulding cavity 23. Fig. 3 shows in greater detail the moulding/demoulding carousel 1 of Fig. 1 for use with the moulds of Fig.2. The carousel l has eight stations (27-34) defined by radially disposed restraining bars 25 secured to the surface of the carousel and disposed at 45° intervals. Each stand 24 is restrained against movement towards the centre of the carousel by the radial arrangement of the restraining bars; and is restrained against vertical movement away from the face of the carousel 1 by lips (not shown) on the restraining bars 25 which engage with the top surface of the annular base 18 of the stand 24. Radially inward of each station is a post 26 the purpose of which will be explained below. The carousel is arranged to be rotationally indexable by intervals of 45° . The sequence of operations may be conveniently described by commencing with delivery of a moulded article, in its mould, on its stand, from the cooling zone/carousel transfer slide 12 to station 27. Delivery is by way of a pneumatic actuator (not shown) which acts against the annular base 18 of a stand 24 to slide the stand 24 and associated mould into engagement with the restraining bars 25 of station 27. The carousel is then indexed through 45° to present the stand 24 and associated mould to station 28. At station 28 the female mould 14 is grasped by a pneumatic clamp (not shown) raised so as to clear the moulded article in the moulding cavity 23, moved radially inwardly of the station, and placed on the post 26 associated with station 28. To prevent the male mould and moulded article lifting from the stand 24 a plunger (not shown) may be pressed against the surface of the male mould while the female mould is raised. Ordinarily the moulded article will have shrunk away from the female mould 14 on cooling and so usually only light pressure on the plunger will be required at this stage. Optionally additional stations may be provided to test and ensure that release of the moulded article from the male or female mould has occurred by e.g. moving the mould slightly relative to the moulding. After removal of the plunger and pneumatic clamp the carousel is indexed through a further 45° to present the stand 24 to station 29. At station 29 the male mould 13 and associated moulded article is gripped externally by pneumatic clamp (not shown) and raised. A stripping head (not shown) is moved under the male mould 13 and the mould 13 and associated moulded article is then placed on the stripping head. The stripping head comprises a base having a central aperture of a sufficient diameter to allow the male mould 13 to pass but to retain the -moulded article. A plunger is applied to the head of the male mould 13 which is forced through the stripping head to come to rest on the original stand 24 and retained in the groove 16 of the spacer ring 15. The moulded article then may be removed from the stripping head and passed on for packaging or further processing as may be required. The carousel 1 can then be indexed a further 45° so that stand 24 moves to station 30. At station 30 a further pneumatic clamp grips the female mould 14 and moves it from the post 26 back to its position surrounding the male mould 13 and engaged with groove 17 of the spacer ring 15. Carousel 1 can then be indexed through a further 45 ° so that stand 24 is at station 31. At station 31 the mould may be filled using a filling head as shown schematically in Fig. 4. The filling head comprises a central plunger 35 spring-mounted in an outer skirt 36. The plunger 35 has a chamfered lip 37 for engagement with the top end of the male mould 13 and the peripheral skirt 36 has an inner chamfered edge 38 for engagement with the top of the female mould 14. Concentricity of the male 13 and female 14 moulds may be adjusted by means of adjustment screws passing through the wall of the skirt 36 and bearing against the plunger 35. The material to be moulded, such as plastics powders e.g. polypropylene, is passed to the mould cavity 23 through the annular feeding channel 39 defined by the plunger 35 and its skirt 36. The mould may be vibrated during this filling process. The stand 24 can then be indexed stepwise past stations 32 and 33 which optionally may be used to provide additional filling stages such as when a layered product is required. On indexing to station 34 the mould is transferred to stacking conveyor 2 by a pneumatically actuated arm acting on the base 18 of the stand 24. This leaves station 24 unoccupied and so on indexing through a further 45° an empty position is presented at station 27 for reception of the next moulded article. From the above it would be clear that between each indexing step of the carousel 1 a stand 24 will enter the carousel at station 27;. a stand 24 will leave the carousel at station 34; and that at each of stations 28-33 a stand 24 will be present while the demoulding/moulding operation is in progress. From the moulding/demoulding carousel 1 the stands 24 are accumulated on a conveyor 2 and an infra-red detector at the end of the conveyor remote from the carousel 1 is used to provide signals to control delivery of stands 24 so as to ensure that a stand is always available for transfer by transfer chute 3 to the input drum 4 of the microwave oven. The input drum 4 is shown in partial cross-section in Fig. 5 and in sectional plan view in Fig. 6. The drum, generally indicated as 4, comprises a cylindrical body 40 rotatable about an axle 41 passing through the long axis of the cylinder. The body 40 has three recesses 42 into which an object may be slid. The base of each recess has a slot 43 through which pins may pass from below to engage with the aperture 20 of a stand 24 enabling the stand 24 to be drawn out of the recess 42 or drawn into the recess 42. Surrounding one half of the drum 4 is a microwave choke indicated generally as 44. The microwave choke comprises end panels 45 and 46 joined by two arcuate side panels 47, 48 which define between them a generally half-cylindrical cavity in which the body 40 sits and which has an aperture 49 leading to the microwave oven. The end panels 45,46 and side panels 47,48 are of aluminium and bear a large number of pins on their surfaces, the spacing of the pins being related to the microwave frequency used in operation. For example with a microwave frequency of 2460 MHz a pin spacing of 17.5mm is suitable. The distance between ends of the pins and the body 40 is some 3mm and under these conditions, with a drum of diameter 490 mm, and with greater than seven rows of pins between the aperture 49 and the open mouth of the generally half-cylindrical cavity remote from the aperture 49 the microwave flux can be reduced from that present inside the microwave oven to effectively zero outside the microwave oven. Fig. 6 shows the drum in position for a stand 24 to be drawn out of the aperture adjacent opening 49 and for a stand 24 to be inserted into the drum at aperture 42. A pin on a sweep arm may be- raised through a gap in transfer chute 3 to engage with an aperture 20 at the base of a stand and to draw the stand 24 into aperture 42, the pin passing along the slot 43 and then being retracted downwards once the stand 24 is in place. The outlet drum 7 is of substantially the same construction, drawing out of a stand from the aperture adjacent to opening 49 will be described below with reference to Fig. 7 of the drawings. Fig. 7 shows the microwave oven 6 and walking beam 5. The walking beam comprises a beam 51 of polytetrafluoroethylene (PTFE) covered aluminium bearing pins 52 of insulating, non-microwave receptive material such as polyethyl- ether ketone (PEEK) . The beam 51 is pivotally connected at 53 to an arm 54 of insulating material (e.g. PEEK) connected to a pneumatic actuator (not shown) . The arm 54 passes through a microwave choke 55 which comprises a pair of opposed plates bearing pins such as are used in the microwave choke end plates 45,46 of the drum 4. A pin-to-pin clearance between the plates of less than 5mm will suffice to effectively prevent escape of microwave radiation. The arm 54 may be operated to slide the beam 51 in saddles 56 formed of PTFE covered aluminium and mounted on actuator arms 57 of PEEK. The actuator arms 57 pass through microwave chokes 58 of the same general form as that shown at 55. Actuator arms 57 can be raised and lowered to raise and lower the saddles 56, and hence the arm 51. In operation alternately; one end of the walking beam 51 extends into the microwave choke 55 at the outlet end of the microwave oven 6; and the other end of the arm 51 extends into a microwave choke 59 at the other end of the microwave oven adjacent the input drum. The microwave chokes 55,59 join with the end plates 46 of the input and output drum 4,7 and the plates 46 have a slot 50 disposed so that the pins 52 may pass through the slot 50, through the slot 43 in the recess 42, and so engage the aperture 20 in the appropriate stand 24. It can be seen that on raising saddles 56 the arm 51 can be raised so that the pin 52 immediately adjacent the input drum 4 can pass upwards to engage with the aperture 20 in the stand waiting in recess 42. On actuating arm 54 the beam 51 can be drawn towards the outlet direction of the microwave oven drawing the stand from aperture 42 into the body of the microwave oven. The saddles 56 can then be lowered by actuators 57 and the arm 54 can then be operated to push the beam in the input direction so as to present it ready to accept the next stand. It can also clearly be seen that while one stand is being drawn out of aperture 42 that the inlet end of the microwave oven another stand 24 will be pushed into corresponding aperture 42 in the outlet drum of the microwave oven. Inside the microwave oven 6 the stands 24 are supported on shelves 60 and below cap 61 which are shown in longitudinal section in Fig. 7 and in transverse section in Fig. 8. The shelves 60 are formed of PTFE coated aluminium and are formed of generally U-section channels so that the base 18 of each stand 24 is both supported from below and restrained from tilting in the channels. Between the shelves 60 a gap 62 is left wide enough for the arm 51 and pin 52 to be raised and lowered into the gap. At periodic intervals along one of the shelves 60 brake blocks 63 are disposed which serve, as a stand is being drawn past by the pin 52, to brake one side of the stand so that it rotates as it passes. This assists in ensuring even heating of the stands and their associated moulds. Use of this walking beam apparatus, or any other apparatus which maintains a fixed relationship between objects passing through the microwave oven, has many advantages over the use of conveyors. The prime advantage is that with a conveyor there is possibility of slippage between object and conveyor which results in uneven spacing between objects and so added complication to the control mechanism so as to ensure that objects are properly delivered to the input and output devices for the microwave oven. If slippage occurs there has to be some way of ensuring that objects do not jam in the input and output devices. Additionally operation in this manner ensures that for most of the time there is a constant number of moulds within the oven and this assists in even heating of the moulds. The susceptibility of moulds to microwave radiation varies from mould to mould, and additionally there will in operation be variations in temperature owing to the interaction of moulds with the outside air during their demoulding/filling cycle. To assist in control it is advantageous to have a pyrometer or some other form of temperature sensor directed to a position to which a mould will be indexed in operation of the machine. Preferably this position is inside the microwave oven. Ly appropriate feedback circuitry the measured temperature of the moulds as they are indexed to, wait at, and pass away from the indexing station can be used to control the power to the microwave oven and thereby control the temperatures of the moulds. Because the susceptibility to microwave radiation can vary it is also useful to measure this susceptibility beforehand and to sequence the moulds in the machine so that there are no sudden changes in susceptibility from mould to adjacent mould. In other words the moulds are ranked so that the susceptibility rises and falls smoothly and so that, for example, while the moulds with highest susceptibility are passing through the microwave oven the moulds with lowest susceptibility are passing, say, through the moulding/demoulding carousel. Each mould and its neighbouring mould in the sequence have closely similar susceptibility. By adopting this strategy one reduces the risks of one mould among those passing through the microwave oven either overheating or underheating due to its differing susceptibility from its neighbours. Because of *end-effects' it is found that uneven heating of moulds may occur towards the top end of the mould. To counteract this a cap 61 is disposed the length of the microwave oven and this serves to limit the amount of radiation reaching the ends of the cap. The cap 61 is formed of PTFE covered duraluminium and mirrors the geometry of the shelves 60 and bases 18 of the stand 24. Such longitudinally extending shielding means also allow the controlled effect of microwave radiation on the object. For example, particular parts of the mould may be shielded so as to provide a lessened effect of microwave radiation adjacent the shield; or particular parts may be shielded where due to varying material in the moulds a lessened sintering effect is required. The arrangement of walking beam and shelves shown means that a stand 24 will progress in stepwise fashion from the inlet drum 4 to the outlet drum 7, with a partial rotation each time the stand passes a brake block 63. Once the stand reaches the outlet drum 7 and the beam 51 has been dropped clear of the slot 43 of the outlet drum then the inlet drum and the outlet drum can be rotated simultaneously, the inlet drum to present a new stand 24 for microwave heating, the outlet drum to remove a heated stand 24 from the microwave oven. The heated stand 24 in the outlet drum 7 can be extracted from the outlet drum 7 via SUBSTITUTE SHEET an exit chute 8 using a swinging arm and pin mechanism directly analogous to that used to transfer the stand from the stacking conveyor to the inlet drum 4. The heated stand 24 and associated mould are transferred to a conveyor 9 and are conveyed through a hot air zone as has already been described. It should be noted that the conveyors 9,11 and 2 should be capable of resisting the temperatures involved in processing the materials of choice. Suitable conveyors comprise silicone rubber conveyors as may be provided by Aldrich Transmissions, Swansea, South Wales. Transfer from one conveyor to another can be any suitable means but a preferred method is by using a pneumatic actuator acting on the base 18 of a stand 24 to slide the stand 24 and associated mould from one position to its next working position. All of the above description has been in relation to the manufacture of generally cylindrical objects. It is clear however that the process and procedure described above can readily be adapted to form other, more complicated, objected such as e.g. blind cups. Further it is clear that any large object can be transferred through a continuously operating microwave oven in the manner shown provided that inlet and outlet drums having suitable sized apertures 42 are available to receive the object. By its nature the apparatus described above operates in a stepwise manner and because of this detailed control is required to ensure that an object or stand 24 is available at each point in the apparatus where transfer of objects is required. For example infra-red or other sensors can be provided at the following places:- The junction of a stacking conveyor 2 and transfer chute 3. At the junction between hot conveyor 9 and transfer slide 10. At the junction between cooling conveyor 11 and cooling/carousel transfer slide 12. The control could ensure that articles are moved into and out of mounting/demounting carousel 1 and input and output drum 4,7 in synchronisation. The above, stepwise, apparatus can be used for large articles. For smaller articles, say of thickness less than 5mm, an alternative geometry may be used which provide a simple arrangement for microwave heating of objects. This is shown in Fig. 9, this drawing shows in plan section apparatus for microwave treatment of generally flat articles. A microwave oven 70 (not shown) has an aperture in its wall through which protrude part of the periphery of a disc 71 the surface of which comprises an electrically insulating material. Escape of microwaves from the continuously operating microwave oven 70 to the outside is prevented by a microwave choke which could be considered as a flattened version of the microwave choke shown in Figure 5. The microwave choke comprises an upper plate (not shown) , a lower plate 72 and generally arcuate side plates 73 which bear pins arranged to choke off microwave radiation. The clearance between the pins and the surface of the disc 71 can be up to, e.g. 5mm. In that portion of the disc 71 which is accessible to the outside loading and unloading operations can be performed. It will be clear to the reader that other geometries could be contemplated within the spirit of the invention. For example the drum 40 could be a complete cylinder with recesses accessible from the axial rather than the radial direction. Any geometry will do provided that no path from oven interior to exterior is provided that allows the escape of significant amounts of microwave radiation. The rotating drum geometry is not the only geometry capable of acting as an "air lock". For example a similar effect can be achieved by using a body incorporating a chamber for the accommodation of objects and reciprocable within a microwave choke conforming to at least part of the swept surface of movement of the chamber and having apertures communicating respectively with the inside of the microwave oven and the outside of the microwave oven. By movement of the body the chamber can be alternately presented to the inside of the microwave oven and the outside of the microwave oven. Figure 10 shows schematically moulding apparatus incorporating materials handling apparatus that can be used to pass objects through a microwave oven (indicated generally at 100) having at either end conventional microwave chokes 101, 102. The apparatus comprises a plurality of stations disposed in an array and indicated schematically as square boxes in Figure 10. The stations are capable of receiving carriers (not shown) which are indexable about the array by means of actuators (shown schematically) as arrows A-H) which may be electromechanically, hydraulically, pneumatically or otherwise operated. Such actuators are conventionally known in the field of materials handling and may act by pushing or drawing the carriers as may be appropriate in a given machine environment. The carriers in this example may be considered as generally square trays of the same overall dimensions as the stations so that adjacent carriers are in contact. Several stations (103-105, 107-110, and 112-113) are indicated in the drawings by a symbol of a small square box. These stations are ones that in one manner of operation of the apparatus may be alternately vacant or occupied by carriers as described below. The moulding apparatus, in addition to the microwave oven, incorporates a hot air dwell zone (indicated generally as 114) , a cooling zone 115, de oulding stations 116,113, mould assembly station 117 and filling stations 118-120. The apparatus thus has all of the integers for a continuous moulding apparatus as described above with reference to Fig. 1. In operation in a first mode all of the stations initially bear carriers except for stations 104, 107, 108, and 112. Operations may be sequentially as shown in Table 1 below which indicates which actuator is operated and the results of this actuator in terms of which station are vacated and which subsequently occupied. For example if actuator A pushes on the carrier at station 103 this results in the movement of the entire column of carriers between 103 and that at the remote end of hot air dwell zone 114 so that the station 103 is vacated and station 104 is occupied. Similarly actuator C can move a carrier at station 105 and hence 106 so that station 105 is vacated and station 107 becomes occupied. Actuator F is a double throw actuator, i.e. it can either act on carriers at stations 109, 110 and 111 so as to vacate station 109 and occupy station 112; or it can act on carriers at stations 110 and 111 so as to vacate station 110 and occupy station 112. Actuator E is a double width actuator capable of acting on carriers at stations 107, 108 and carriers in the cold zone 115 so as to vacate stations 107, 108 and occupy stations 109, 110. Table 1 shows a complete sequence which has the net effect of:- advancing a carrier at station 103 through the microwave choke 101 and to the first station 121 inside the microwave oven; and restoring the geometry of vacant stations to that prevailing at the outset of the sequence. By repetition of the sequence it is clear that a given carrier and its associated objects may be advanced through the moulding apparatus in a complete cycle. It can be seen that for every step of a given carrier through the cooling zone 115 another given carrier will move two stations through the microwave oven. Table 2 shows a sequence that allows carriers to move through faster by eliminating some steps. It can be seen that for each repetition of the sequence of Table 2 for every step that a given carrier takes through the cooling zone 115 another given carrier will take one step through the microwave oven 100. The row of stations between stations 108 and 109 may be empty or occupied by empty carriers during this sequence and by varying the sequencing it is possible to switch from the sequence of Table 1 to that of Table 2. Naturally the sequencing of movement of carriers about this apparatus has to be coordinated with the sequencing of the demoulding, reassembly, and filling or the moulds. It will be clear that by adjustment of sequencing, number of vacant stations, and array layout the relevant duration of stay of a given carrier at a given station may be varied so giving flexibility to the materials handling apparatus described and to the materials that may be treated in a microwave oven incorporating such materials handling apparatus. The above description has related to the forming of articles but it will be clear to the person skilled in the art that the apparatus described can be used in the treatment of objects and also that the individual integers, such as the gate means, can be separately used. The present invention extends to such uses and integers. SUBSTITUTE SHEET TABLE 1 STEP ACTUATOR STATIONS VACATED STATIONS OCCUPIED 1 A 103 104 C 105 107 F 109 112 2 B 104 105 D 107 108 H 113 103 3 A 103 104 C 105 107 G 112 113 4 B 104 105 F (DOUBLE THROW) 110 112 H 113 103 5 E (DOUBLE WIDTH) 108, 107 109,110 G 112 113 TABLE 2 STEP ACTUATOR STATIONS VACATED STATIONS OCCUPIED 1 A 103 104 C 105 107 F (DOUBLE THROW) 110 112 2 B 104 105 E 107 110 H 113 103 3 G 112 113 SUBSTITUTE SHEET

Claims: CLAIMS 1. A method of forming an article by placing incoherent material to be consolidated to form an article into contact with a microwave-heatable mould, die or former and heatin'g the mould, die or former by exposure to microwave radiation whereby the incoherent material is consolidated to form the article characterised in that the method comprises the steps of:- at a first station, placing the incoherent material in contact with the mould, die or former; passing the mould, die or former and incoherent material through first gate means into a continuously operating microwave oven; exposing the mould, die or former and incoherent material to microwave radiation in the continuously operating microwave oven whereby the incoherent material may be consolidated to form the article; passing the mould, die or former and incoherent material through second gate means out of said continuously operating microwave oven; at an article removal station, removing the article from contact with the mould, die or former; returning the mould, die or former to said first station whereby articles may be formed in a continuous process. 2.. A method as claimed in claim 1 in which said moulds, dies or formers and incoherent material are indexed through a continuously operating microwave oven on carriers whereby the relative spatial relationship of said moulds, dies or formers and incoherent material is assured so that operations may be carried out on said moulds, dies or formers and incoherent material without the necessity of adjusting their position. 3. A method as claimed in claim 1 or 2 in which the moulds, dies or formers being treated with microwaves are measured for their susceptibility to microwave radiation prior to treatment and are sequenced according to their microwave susceptibility so that each mould, die or former and its neighbouring moulds, dies or formers in the sequence have closely similar susceptibility. 4. A method as claimed in any preceding claim arid utilising apparatus comprising:- i) an input chamber for the temporary accommodation of moulds, dies or formers and incoherent material to be treated by microwave radiation; ii) a microwave oven in which moulds, dies or formers and incoherent material may be treated by microwave radiation, iii) an output chamber for the temporary accommodation of moulds, dies or formers and incoherent material treated by microwave radiation; iv) transfer means operative to transfer moulds, dies or formers and incoherent material from the input chamber, through the microwave oven, and to the output chamber; v) gate means operatively associated with each of the input and output chambers to enable, sequentially as far as a given mould, die or former and incoherent material is concerned:- a) a given mould, die or former and incoherent material to be received in the input chamber from outside the apparatus; b) the input chamber to be closed against reception of further moulds, dies or formers and incoherent material; c) the input chamber to be opened to allow the transfer means to transfer a given mould, die or former and incoherent material from the input chamber, through the microwave oven, and to the output chamber; d) the output chamber to be closed against reception of further moulds, dies or formers and incoherent material from the transfer means; e) removal of moulds, dies or formers and incoherent material from the output chamber to outside the apparatus; said gate means being disposed and operable so as to ensure that significant amounts of microwave radiation may not escape while the microvave oven is on; whereby the microwave oven may be operated continuously. 5. A method a claimed in claim 4, the method comprising the steps of:- i) Repeatedly inserting moulds, dies or formers and incoherent material into the input chamber, closing the input chamber against reception of further moulds, dies or formers and incoherent material, opening the input chamber to communication with the microwave oven, drawing a given mould, die or former and incoherent material from the input chamber for transfer through the microwave oven; ii) Transferring moulds, dies or formers and incoherent material through the microwave oven to the output chamber; iii) Repeatedly placing moulds, dies or formers and incoherent material in the output chamber, closing the output chamber against reception of further moulds, dies or formers and incoherent material from the transfer means, removing moulds, dies or formers and incoherent material from the output chamber to outside the apparatus; said steps taking place on a continuous basis whereby a plurality of moulds, dies or formers and incoherent material may be accommodated in the apparatus at any given time. 6. A method as claimed in claim 4 or claim 5 in which one or both of the input or output chambers and associated gate means comprises .a body incorporating a chamber for the temporary accommodation of moulds, dies or formers and incoherent material and movable between a first position in which the chamber is open to the inside of the microwave oven and a second position in which the chamber is open to the outside of the microwave oven, the body being movable within a microwave choke conforming to at least part of the swept surface of movement of the body and having at least two apertures communicating respectively with the outside of the apparatus and the microwave oven whereby moulds, dies or formers and incoherent material carried in the chamber 21 may be alternately presented to the outside of the microwave oven and the inside of the microwave oven. 7. A method as claimed in of claims 4-6 in which one or both of the input or output chambers and associated gate means comprise a body capable of carrying moulds, dies or formers and incoherent material and rotatable about an axis within a microwave choke conforming to at least a part of the surface of rotation of the body about said axis the microwave choke having at least two apertures communicating respectively with the outside of the apparatus and the microwave oven, whereby moulds, dies or formers and incoherent material carried by the body may be alternatively presented the outside of the microwave oven or the interior of the microwave oven without escape of significant amounts of microwave radiation. 8. A method as claimed in any of claims 4-7 in which the transfer means are adapted to ensure that moulds, dies or formers and incoherent material being transferred remain in fixed relative spatial relationship in their passage through the microwave oven. 9. A method as claimed in any of claims 4-8 in which the transfer means comprise a slide upon which moulds, dies or formers and incoherent material may be drawn along a sliding axis, and a reciprocable beam having a component of motion, when in use, parallel to the sliding axis, and bearing grasping means operable to grasp a mould, die or former and incoherent material, draw the mould, die or former and incoherent material along the slide, and release the mould, die or former and incoherent material, whereby on successive operation of the grasping means the mould, die or former and incoherent material may be indexed along the slide. 10. A method as claimed in claim 9 in which synchronising means are provided to operatively connect the reciprocable beam with the gate means such that the grasping means is movable to grasp a mould, die or former and incoherent material only while the associated gate means is open. 11. A method as claimed in claim 9 or claim 10 in which the grasping means comprise a plurality of pegs extending transversely of the reciprocable beam, the reciprocable beam having a component of motion transverse to the sliding axis, whereby on a first movement of the reciprocable beam transverse to the sliding axis a given peg may engage a co-operating member on the mould, die or former and incoherent material, and on movement of the reciprocable beam parallel to said sliding axis the peg may draw said mould, die or former and incoherent material parallel to the sliding axis, and on a second movement of the reciprocable beam transverse to the sliding axis the peg may disengage from the co-operating member. 12. A method as claimed in any of claims 4-11 in which the transfer means has associated turning means operable to rotate the mould, die or former and incoherent material as the mould, die or former and incoherent material is transferred. 13. A method as claimed in claim 12 as dependent on claim 9 in which the turning means comprise braking means associated with the slide acting preferentially on one side of the mould, die or former and incoherent material as it passes. 14. A method as claimed in any of claims 4-13 in which shielding means are provided extending substantially parallel to the path of transfer of moulds, dies or formers and incoherent material from the input chamber, through the microwave oven, to the output chamber, the shielding means serving to assist the controlled effect of microwave radiation on the mould, die or former and incoherent material. 15. A method as claimed in any preceding claim in which:- a temperature sensor is disposed so as to monitor the temperature of moulds, dies or formers and incoherent material in the microwave oven; and control means are used capable of receiving information from the temperature sensor and controlling power to the microwave oven; so that the temperature of moulds, dies or formers and incoherent material may be controlled during the course of forming the articles. 16. A method as claimed in any preceding claim in which apparatus is used comprising:- a plurality of stations disposed in an array; a plurality of carriers for moulds, dies or formers and incoherent material the carriers being indexable from station to station and the number of carriers being less than the number of stations; and, indexing means capable of moving one or more carriers so that simultaneously a number of the carriers may move from occupied stations to previously vacant stations and said number of carriers may move from occupied stations to leave vacant stations; so that by successive operation of the indexing means the carriers may be transported about the array. 17. A method as claimed in claim 16 in which the carriers for moulds, dies or formers and incoherent material comprise trays and the stations are spaced such that carriers on adjacent occupied stations are in contact. 18. A method as claimed in claim 17 in which the indexing means comprise a plurality of actuators capable of directly contacting and moving, in an actuator direction of movement, one or more carriers so that carriers adjacent in the actuator direction of movement to said one or more carriers are also moved on action of the actuator. 19. Apparatus adapted for use in the method of any preceding claim. SUBSTITUTE SHEET

Inventors: CHARMAN KEITH, DAVIDSON RODERICK IAIN, CHARMAN, KEITH, DAVIDSON, RODERICK, IAIN
Applicants: POROUS PLASTICS LTD, POROUS PLASTICS LIMITED
Application year: 1991
Main classification: B29C39
IPC codes: B29C33, B29C35, B29C39, B29C67