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(11) | EP 0 962 294 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Device for feeding powders to a ceramic tile forming press |
| (57) Device for feeding powders to a ceramic tile forming press, comprising a small feed
hopper positioned to overlie a loading carriage provided with a loading compartment
containing a grid, and traversing between a position in which the compartment lies
below the small hopper and a position in which the compartment lies above the mould
impression, a powder distributor moving with reciprocating movement above the mouth
of the small hopper, and one or more large vessels or silos positioned upstream of
the distributor to feed it with one or more types of powder, comprises upstream of
the distributor tube and downstream of the powder feed silos a rotary mixer which
receives powders from one or more of said silos. |
[0001] This invention relates to the manufacture of ceramic tiles produced by a multi-colour mixture of clay-based single-colour powders.
[0002] The most recent developments in tile manufacturing technology concern a type of product, known as porcellainized stone, which is prepared by pressing atomized clay-based powders, then firing at very high temperature.
[0003] The powders used derive from mixing various components, which differ from each other by their particle size and colour, to enable tiles to be obtained having a large variety of typical appearances.
[0004] A common characteristic of said tiles is their bulk coloration, ie coloration throughout the entire tile thickness or through a substantial layer of it.
[0005] Based on the number of constituent single-colour powders of the mixture, their proportions and their mixing criteria, an indefinite number of aesthetic or decorative types can be obtained.
[0006] Each type involves different proportions and mixing criteria, currently satisfied by specific powder mixing plants.
[0007] In known processes the powders are mixed largely while being fed to the impressions in the forming press mould, hence it is immediately apparent that if the type of product is to be changed, the press feed devices must currently be modified, often to a substantial extent.
[0008] These devices generally comprise a small feed hopper positioned to overlie a carriage provided with a loading compartment containing a grid, and traversing between a position in which the compartment lies below the small hopper and a position in which the compartment lies above the mould impressions.
[0009] The small hopper is fed by a powder distributor which moves with reciprocating movement above its mouth in a to-and-fro manner and is either continuous or discontinuous depending on circumstances, with the purpose of maintaining in the small hopper that powder level necessary for the proper success of the manufacturing process.
[0010] The distributor collects the powders by flexible tubes from one or more large vessels or silos located upstream.
[0011] The aforesaid devices are common to ceramic technology, and will therefore not be described in detail.
[0012] The invention specifically relates to those devices positioned between the powder containing silos, each of which contains a determined type of powder, and said small hopper, these being the devices which substantially determine the grade, the mixing criteria and the component percentages of the various powders and hence the final appearance of the finished product.
[0013] The object of the invention is to provide a feed device able to satisfy mixing criteria within an extremely wide range, so enabling many types of product to be manufactured without requiring modifications to the plant.
[0014] This object is attained according to the invention by a device having the characteristics defined in the claims.
[0015] The merits and the functional and constructional characteristics of the invention will be more apparent from the ensuing detailed description of a preferred but not exclusive embodiment thereof, given reference to the accompanying drawings.
Figure 1 is a partial plan view of the invention.
Figure 2 is a section on the plane II-II of Figure 1.
Figure 3 is a section on the plane III-III of Figure 2.
Figure 4 is an enlarged view of a different embodiment of the invention.
[0016] Said figures show the working surface 1 of a press carrying a mould 3 with three impressions 31, 32 and 33 for receiving the dies 131, 132 and 133 extending from the underside of the movable crosspiece 13 of the press.
[0018] The carriage 5 comprises three feed compartments 51, 52 and 53 each provided with a usual grid, and is driven with reciprocating movement by a usual crank mechanism indicated by 6.
[0019] Above the carriage there lies the small feed hopper 7 supported in a fixed position by a frame, not shown, resting on the ground.
[0020] The lower mouth of the small hopper 7 is closed in the usual manner by the continuous upper surface of the carriage 5 which extends forwards and rearwards of said compartments 51, 52 and 52.
[0021] These latter have no base and are closed, except in correspondence with said impressions, by the underlying working surface 4 on which the carriage 5 traverses, and by the press operating surface 1.
[0022] On the opposite side of the small hopper 7 to that facing the press there is a fixed frame 8 provided with two guides 81 and 82 positioned transversely to the direction of travel of the carriage and extending along the entire length of the press.
[0023] The frame 8 also comprises an electric motor 9 of controlled advancement and speed, its shaft being connected possibly via a step-down gear to one of the two reversing wheels 91 about which a chain or belt 92 passes. Said wheels are positioned to the sides of the carriage travel surface 4.
[0024] On the guides 81, 82 there slides a carriage 20 engaged with said chain or belt 92 such as to be driven with to-and-fro movement.
[0025] On the carriage 20 there is located a distributor tube 21, of which the lower end lies above the small hopper 7, into which it is partially inserted, its upper end being shaped as a funnel 22.
[0026] Into the funnel 22 there dips a frusto-conical rotary mixer 23, which is supported by the carriage 20 via a thrust bearing, not shown.
[0027] The mixer 23 is rotated by an electric motor 24 connected to the rotating part of the thrust bearing by a worm transmission, possibly via a step-down gear.
[0028] Two projecting frames 30, fixed to the floor to the sides of the surface 4, each support three dispensers 35, 36 and 37, 35a, 36a and 37a, via a cylinder-piston unit 34, 34a of vertical axis.
[0029] Said dispensers, six in number, three on each side of the surface 4, are each connected by a respective flexible tube to an overlying silo, not shown, containing a determined type of powder to be mixed in desired quantities with one or more of the powders contained in the other silos.
[0030] Each of the dispensers 35, 36 and 37, 35a, 36a and 37a comprises a closure gate 38 operated by an independent cylinder-piston unit 39.
[0031] In the variant shown in Figure 4, at the base of the distributor tube 21 there is positioned at least one mixer screw 210 rotated by an electric motor 211 supported by the said tube 21.
[0032] The operation, combined and timed in the desired sequence, is controlled by a microprocessor programmable as required, this not being shown as it is of usual type well known to the expert.
[0033] By said combination of means, all possible mixing criteria can be satisfied, to hence achieve the required powder distribution within the mould impressions, without the need to replace or modify parts of the powder feed means, as is often necessary in the known art.
[0034] The operation of the invention is explained hereinafter with reference to a certain number of possibilities, which however are given by way of non-limiting example as the programming possibilities are practically unlimited.
[0035] The distributor tube 21 which traverses with to-and-fro movement along the mouth of the small hopper 7 is closed, when in its end-of-travel positions, by a plate 70 located at the ends of the small hopper.
[0036] In the illustrated example there are six different types of powder available, three at one end of the small hopper 7, dispensed by the dispensers 35, 36 and 37, and three at the other end, dispensed by the dispensers 35a, 36a and 37a.
[0037] Each time the carriage 20 with the distributor tube 21 halts at one end of the small hopper, the overlying group of dispensers descends by the action of the cylinder-piston unit 34, 34a into the mouth of the rotary mixer 23 and, depending on the composition of the tile mixture to be obtained, one or more of the dispensers opens for a time determined by the microprocessor program.
[0038] The powder falls into the mixer which rotates under the control of the microprocessor at a mixing speed equal to or greater than zero.
[0039] The mixing speed determines a greater or lesser extent of mixing within the powder columns falling from the dispensers, in an arrangement varying from initially straight-line (with the mixer at rest) to helical, to provide essentially a certain determined powder distribution within the underlying small hopper 7.
[0040] It is apparent that if the mixer is stationary, or rotates at low speed, for example a few revolutions per minute, the distribution within the small hopper 7 will be in the form of transverse single-colour veining partially mixed at their interface and twisted together to a greater or lesser extent.
[0041] As the mixer speed is progressively increased, the resultant mixture becomes gradually more homogeneous until the horizontal veining in the small hopper 7 disappears.
[0042] Hence the resultant tiles will have an appearance simulating marble veining which as the mixer speed is increased becomes increasingly less evident until it disappears.
[0044] When the mixer rotates at low speed or is stationary, operating the screw 200 at low speed, for example a few revolutions per minute, results in a powder distribution containing defined compact blobs of single-colour powder distributed within the overall mass.
1. A device for feeding powders to a ceramic tile forming press, comprising a small feed
hopper positioned to overlie a loading carriage provided with a loading compartment
containing a grid, and traversing between a position in which the compartment lies
below the small hopper and a position in which the compartment lies above the mould
impression, a powder distributor moving with reciprocating movement above the mouth
of the small hopper, and one or more large vessels or silos positioned upstream of
the distributor to feed it with one or more types of powder, characterised by comprising
upstream of the distributor tube and downstream of the powder feed silos a rotary
mixer which receives powders from one or more of said silos.
2. A device as claimed in claim 1, characterised in that the rotary mixer has a frusto-conical
body of vertical axis with its minor base lying above the mouth of the distributor
tube.
3. A device as claimed in claim 1, characterised in that the rotary mixer and the distributor
tube are mounted on the same carriage, to which the rotary mixer is connected via
a thrust bearing, an electric motor of programmed speed being provided for rotating
said rotary mixer.
4. A device as claimed in claim 3, characterised in that the carriage slides on two transverse
guides dragged by an endless flexible element extending between two reversing wheels,
one of which is connected to an electric motor of programmed speed.
5. A device as claimed in claim 4, characterised in that said flexible element is a belt.
6. A device as claimed in claim 4, characterised in that said flexible element is a chain.
7. A device as claimed in claim 1, characterised by comprising in proximity to at least
one end of the small hopper a group of dispensers arranged to overlie the upper mouth
of the rotary mixer, each being closed by an independent gate and being connected
to one of the silos.
8. A device as claimed in claim 7, characterised in that said group of dispensers is
stationary.
9. A device as claimed in claim 7, characterised in that said group of dispensers is
associated with means which lower it when it overlies the rotary mixer and raise it
when the rotary mixer begins to traverse along the mouth of the small hopper.
10. A device as claimed in claim 1, characterised in that a mixing screw driven by an
electric motor of programmed speed is positioned inside the distributor tube.
11. A device as claimed in the preceding claims, characterised by comprising a programmable
microprocessor which controls said electric motors of programmed speed, said dispensers
and said means for raising the dispenser groups.