Plant for creating pre-compacted ceramic powder blanks and for feeding them to the forming cavity of a press

Abstract

 Plant for creating precompacted ceramic powder blanks and feeding them to the forming cavity of a press, comprising a conveying line for at least one mould, along which there are provided a powder loading station, a precompacting station and a discharge station positioned along said conveyor, means within said loading, precompacting and discharge stations to drive the mould parts, means for removing the precompacted blank from the mould, means for transferring said blank onto the forming cavity of a press and means for transferring said at least one mould from that end to the other end of said conveyor.

Description

[0001] This invention relates to the manufacture of ceramic tiles by pressing powders in suitable moulds.

[0002] The crude tiles obtained in this manner are then subjected to a firing cycle at very high temperature to give rise to the finished product.

[0003] The invention relates in particular to the powder pressing operation.

[0004] The pressing operation takes place within the cavity of a press consisting of a vertically movable lower die, a die plate within which the lower die is permanently inserted, and an upper die fixed to the upper crosspiece of a press, and which in cooperation with the die plate and the lower die defines the powder pressing cavity.

[0005] The powder is pressed at pressures between 150 kg/cm² and 400 kg/cm² according to the type of material used and the tile quality to be obtained.

[0006] One of the problems presented during pressing is the need to evacuate the air contained in the soft powder, this air constituting about one half the volume of this latter.

[0007] Air evacuation is more difficult the larger the tile surface as the air is discharged between the die plate and the dies, those tile portions distant from the edge hence being the most difficult to deaerate.

[0008] In the known art deaeration is facilitated by subjecting the tile, while within the cavity, to at least two successive pressing actions separated by a slight raising of the upper die.

[0009] This procedure presents however a series of drawbacks which range from an increase in production time to wear of the peripheral parts of the die plate and dies due to abrasion by the powder entrained by the air, until it becomes impossible to create formats exceeding certain dimensions.

[0010] An increase in tile format is made possible by the increased capacity of modern presses, which can easily reach thousands of tons, but deaeration represents an insurmountable obstacle.

[0011] This problem has been solved by using pressing cycles comprising a precompaction operation, performed at pressures of the order of 50 kg/cm², followed by the actual pressing.

[0012] Precompaction is generally effected by means which act on the powder extended with constant thickness on a surface such as a belt, and which can consist of an upper belt associated with a pressing plate.

[0013] The result of precompaction is a relatively fragile blank having a thickness of 65-75% of the initial powder thickness, and is a substantially deaerated product which can undergo final compaction in a single pressing.

[0014] This procedure presents however serious homogeneity problems in proximity to the tile perimeter arising from the difficulty of laterally constraining the powder, these problems manifesting themselves during firing as cracks in the finished product in said regions.

[0015] Plants are known, such as that described in Italian patent 1260974, in which the powder is laterally constrained by a die plate which descends from above onto a conveyor on which the powder layer lies, and by an upper die which descends to become inserted into the die plate.

[0016] This solution to the lateral powder constraining problem has however created, in said plant, a series of subordinate problems that have virtually prevented its large scale use.

[0017] In this respect, the lack of a lower die movable relative to the die plate makes it difficult to extract the precompacted tile, which inter alia is much more fragile than the blanks after final compaction.

[0018] The objects of the present patent are to provide a powder compacting plant which is free from said drawbacks, which can be associated with already existing normal presses, which presents considerable format flexibility, and enables different materials to be applied to the surface of the blank before final pressing.

[0019] Said objects are attained by a plant having the characteristics defined in the claims.

[0020] More precisely, the objects are attained by a plant comprising a conveyor for at least one mould, a powder loading station, a precompacting station and a discharge station positioned along said conveyor, means within said loading, precompacting and discharge stations to drive the mould parts, means for removing the precompacted blank from the mould, means for transferring said at least one mould from that end to the other of said conveyor and means for transferring said blank over the forming cavity of a press. Finishing stations can also be provided.

[0021] The constructional and operational merits and characteristics of the invention will be apparent from the ensuing detailed description of a preferred but non-limiting embodiment of the invention with reference to the accompanying drawings.

[0022] Figure 1 is a side view of the plant according to the invention.

[0023] Figure 2 is an enlarged view of that end of the plant distant from the press.

[0024] Figure 3 is an enlarged view of that end of the plant close to the press.

[0025] Figure 4 is a schematic side view of a plant component.

[0026] Figure 5 is a partial section through the component of Figure 4.

[0027] Figure 6 is a partial section through an alternative version of the component of Figure 5.

[0028] Figure 7 shows an enlarged portion of Figure 1.

[0029] Figure 8 shows a further enlarged portion of Figure 1.

[0030] Figure 9 shows a second embodiment of the pusher for the tile to the mould cavity.

[0031] The figures show a normal powder compacting press 1, in front of which a first conveyor belt 2 is located.

[0032] The conveyor belt 2 is driven stepwise by an electric gearmotor 21 controlled by an encoder 22.

[0033] Between the belt 2 and the press there is positioned a first elevator device 3, the upper platform of which when in its raised position is coplanar with the conveyor 2, and when in its lowered position is coplanar with the active branch of a second conveyor 4 positioned below the first conveyor and having the same length.

[0034] A second elevator 5 similar to the first is positioned at that end of said conveyors distant from the press.

[0035] In the illustrated example, both the upper conveyor and the lower conveyor are constructed for convenience in two separate portions positioned one following the other.

[0036] On the upper conveyor there are positioned eight equidistant movable moulds 7 which are described in detail hereinafter.

[0037] With those ends of said conveyors close to said elevators there are associated transfer means 6, the function of which is to transfer the moulds 7 from the conveyors to the elevators and vice versa.

[0038] Each mould (Figure 4) comprises a base 71 in which there is inserted a vertically movable die plate 72 rigid with six columns 73 which support it by friction by being inserted into six corresponding seats 74 rigid with the base 71.

[0039] From the base 71 there upwardly extend a number of lower dies 77 equal to the number of die plate cavities, into which they are inserted.

[0040] The friction occurs between the column and the hole in a slide block associated with the base by electromagnetic or pneumatic means.

[0041] More specifically, with reference to Figure 5 in correspondence with each of the holes in the base 71 which receive the columns 73 there is fixed a member 74 provided with a cylindrical hole 740 within which a piston 741 sealedly slides. The piston 741 presents a diametrical hole which receives the column 73, and is subjected on one side to the thrust of a spring 742, and on the opposite side to the action of compressed air fed by 76.

[0042] The spring maintains the column locked except when compressed air is fed.

[0043] With reference to Figure 6, this shows a magnetic variant of the locking device, in which corresponding parts are indicated by the same numerals.

[0044] In this version the piston presents a rod 743 subjected to the magnetic field of a coil 744, the spring being dispensed with.

[0045] Energizing the coil 744 causes locking of the piston rod 73.

[0046] Said electromagnetic means are energized from the outside.

[0047] The vertical movements of the die plate 72 are produced by lifting devices 9 disposed in the various stations along the upper conveyor.

[0048] Specifically, on the upper conveyor there is positioned at least one loading section 8, three loading stations 81, 82 and 83 respectively being provided in the illustrated example.

[0049] Each loading station is associated with usual powder loading means, for example a carriage feeder with a sliding distributor of classical type, well known to the expert of the art and therefore not shown.

[0050] Loading preferably takes place in a direction perpendicular to the conveyor axis.

[0051] In correspondence with the loading stations, under the conveyor there are positioned means 9 to drive the die plate by making it translate vertically and locking it by friction as stated.

[0052] The means 9 comprise six cylinder-piston units 91 of controlled advancement arranged to act on the base or, as will be apparent, on the top of the columns 73, and an electrical or pneumatic connector 92 which, when the die plate 7 is present in the station, becomes connected to the electromagnet electrical circuit 774 or to the pneumatic circuit 76.

[0053] The die plate 7 arrives at the first station 81 where it is raised by a device 9 to receive a first layer of powder; it is further raised by the respective devices 9 in the stations 82 and 83, by an amount sufficient to create the space for a second and a third layer of powder.

[0054] In passing from the second to the third station, the die plate 72 is subjected to the action of a scraper blade 10 which removes the excess powder and causes it to fall into an underlying collector 11.

[0055] Immediately downstream of the loading station 83 there is a press 12 able to exert a pressure of the order of 10 to 25 kg/cm² sufficient to precompact the powder.

[0056] The press crosspiece supports a pressing plate 120 of greater dimensions than the surface of the die plate 72 so that during the pressing action the plate acts on the die plate to urge it downwards and overcome the friction which maintains it in position.

[0057] Downstream of the press 12 there are two finishing stations 13, indicated schematically, in which decorative materials are applied to the smooth and structured surface of the precompressed blank.

[0058] Downstream of the stations 13 there is the tile removal station 14, overlaid by a device 9 similar to that already described, but positioned inverted on the upper part of the conveyor.

[0059] The device 9 lowers the die plate 72 to expose the tile.

[0060] The mould 7 comprising the movable die plate 72 is then pushed by the means 6 onto the elevator 3 with the die plate perfectly flush with the press working surface.

[0061] A double pusher 15 associated with the press pushes the blank into position over the press forming cavity, while at the same time removing the tile already pressed during the preceding cycle.

[0062] The pusher 15 is aided by a sucker 16 which slightly raises the precompacted blank to facilitate its sliding onto the mould of the press where the blank receives its final pressing.

[0063] After the action of the pusher 15 the elevator 3 is lowered to the level of the lower conveyor 4, onto which the mould is pushed to be transported to the beginning of the conveyor 2.

[0064] A station 17 for removing defective blanks is located on the lower conveyor 4.

[0065] The means for the stepwise advancement of the conveyor 2 are not shown.

[0066] In place of the conveyor 2 an equivalent known conveyor line could evidently be used.

[0067] The conveyor 4 could likewise evidently be positioned to the side of the conveyor 2, in which case the elevators would be in the form of lateral transfer means.

[0068] A second embodiment of the pusher for the tile is shown in Fig.9, in which corresponding parts are indicated by the same numerals.

[0069] In Fig.9 it can be seen the mould comprising the base 71 in which there is inserted the vertically movable die plate 72 rigid with six columns 73 which support it by friction by being inserted into six corresponding seats rigid with the base 71.

[0070] From the base 71 there upwardly extend a number of lower dies 77 equal to the number of die plate cavities, into which they are inserted.

[0071] The friction occurs between the column and the hole in a slide block associated with the base by electromagnetic or pneumatic means, not shown and similar to those disclosed with reference to Fig. 5.

[0072] More specifically, with reference to Figure 5 in correspondence with each of the holes in the base 71 which receive the columns 73 there is fixed a member 74 provided with a cylindrical hole 740 within which a piston 741 sealedly slides.

[0073] The second embodiment of the pusher indicated with 150 in Fig.9 comprises a plate 151 having a lower rectangular cavity 152.

[0074] Near and parallel to the sides of the cavity 152 there are located four shafts 153. Each shaft is connected to the adjacent shafts by a conical gear, so that the shafts rotate together in both directions.

[0075] At least one of the shafts 153 is connected by a cylindrical gear 154 to a rack 155 that is operated by an usual linear actuator 156.

[0076] Each shaft 153 supports, through suitable brackets 157, a bar 158 that, depending from the rotation of the shaft is positioned in a lowered substantially vertical position in which the bars of each shaft are adjacent to realise a frame surrounding the blank positioned onto the lower die 77, or in a raised position in which the bars are located over the blank.

[0077] The pusher 150 is associated with the press, and comprises a frontal bar 159.

[0078] The pusher 150 reciprocates between a first position in which it is positioned over the blank with the bars 158 in raised position.

[0079] The blank is located onto the die 77 and the vertically movable die plate 72 is lowered.

[0080] The four shafts are rotated to position the bars 158 in lowered position, to embrace the blank, and the pusher pushes the blank into position over the press forming cavity, while at the same time the bar 159 removes the tile already pressed during the preceding cycle.

[0081] The four bars are raised and the pusher returns back over the die 77 to receive the further blank.

Claims

1. A plant for creating precompacted ceramic powder blanks and feeding them to the forming cavity of a press (1), characterised by comprising a conveying line (2) for at least one mould (7), along which there are provided at least one powder loading station (81, 82, 83), a precompacting station (12) and a discharge station (14) positioned along said conveyor, means (9) within said loading, precompacting and discharge stations to drive the mould parts, means (14) for removing the precompacted blank from the mould, means (15, 150) for transferring said blank onto the forming cavity of the press (1) and means (4) for transferring said at least one mould from that end to the other end of said conveyor.

2. A plant as claimed in claim 1, characterised in that at least one finishing station (12, 13) is provided between the precompacting station and the press.

3. A plant as claimed in claim 1, characterised in that said at least one mould (7) comprises a flat base (71) with an associated at least one fixed lower die (77), a movable die plate (72) drawn vertically over said die, and means (73) for supporting said movable die plate by friction relative to said base.

4. A plant as claimed in claim 3, characterised in that said support means comprise a base (74) within which there slides a piston (741) provided with a diametrical hole which receives the column (73) rigid with the die plate (72).

5. A plant as claimed in claim 4, characterised in that said piston (741) is associated with electromagnetic means (744).

6. A plant as claimed in claim 4, characterised in that said piston (741) is associated with pneumatic means.

7. A plant as claimed in claim 1, characterised in that the precompacting station comprises a press (12), the pressing plate of which presents plan dimensions such as to interfere with the die plate of the underlying mould or moulds.

8. A plant as claimed in claim 1, characterised in that the means for transferring at least said one mould from one end to the other of said conveying line (2) comprise transfer means(3, 5) positioned at the ends of said line, means (6) for urging the mould from the line to said transfer means and vice versa, and a conveyor (4) positioned parallel to the conveying line.

9. A plant as claimed in claim 7, characterised in that said transfer means (6) are elevator means.

10. A plant as claimed in claim 7, characterised in that said conveyor (4) is positioned below the conveying line (2).

11. A plant as claimed in claim 1, characterised in that said conveying line (2) is a stepwise operated conveyor.

12. A plant as claimed in claim 1, characterised in that the means for transferring said blank onto the forming cavity of a press comprise a reciprocating plate (151) supporting four rotating shafts (153) operatively connected each other to rotate together in both directions, at least one of the shafts (153) being connected to an actuator (156), each shaft (153) supporting, through suitable brackets (157), a bar (158) that, depending from the rotation of the shaft is positioned in a lowered substantially vertical position in which the bars of each shaft are adjacent to realise a frame surrounding the blank, or in a raised position in which the bars are located over the blank.

Drawing