EP3221086B1

EP3221086B1 - Apparatus for the erosion of articles of material aggregate compact

Info

Publication number: EP3221086B1
Application number: EP15726314.6A
Authority: EP
Inventors: Piero REBECCHI
Original assignee: Effegi Brega Srl
Current assignee: Effegi Brega Srl
Priority date: 2014-11-20
Filing date: 2015-04-15
Publication date: 2021-03-24
Anticipated expiration: 2035-04-15
Also published as: WO2016079599A1; EP3221086A1

Description

DESCRIPTION

The invention relates to an apparatus for the erosion of articles made of dense aggregate material, for example of powdery or damp materials.
The apparatus according to the invention applies in particular, although not exclusively, to the dental sector for the erosion or breaking up of molds for producing dental prostheses.
A typical procedure for producing dental prostheses, for example crowns or bridges, is the "lost wax" casting process. According to this procedure, the molten material, in general a ceramic or metal alloy, is poured into specific molds in which the negative forms of the prosthesis are produced.
As is known to those skilled in the art, the molds used for these applications are made from powders and/or liquids that are mixed and compacted to form a hard and solid aggregate.
Examples of typical materials are minerals, such as silicon dioxide, magnesium oxide or the like, capable of withstanding very high temperatures (around 850-1200°C) without breaking up.
After the casting process has finished, the prosthesis must be released from the compacted material of the mold surrounding it.
This operation is known as "deflasking" in the trade.
Cutting systems are disclosed in documents US 4,951,429 and US 2011/0195641 that disclose an abrasivejet nozzle assembly and a nozzle for a high pressure cutting arrangement, respectively.
The most widely used technique for deflasking is currently sandblasting.
In fact, the mechanical action of small granules (sand, glass or the like), projected at high speed onto the surface of the mold, causes gradual erosion and break-up of the compacted mass, gradually releasing the cast product.
After sandblasting has finished, the cast product must be treated with chemical products, generally liquids, to eliminate the outermost "reaction layer" that is formed after pressing of the casting material in the mold.
This step generally consists of immersing the prosthesis in a bath, typically corrosive, and subsequent fine sandblasting, at low pressure, with aluminum oxide.
However, the process described above has some problems.
In fact, erosion of the mold by sandblasting produces large amounts of very fine powder. This powder, besides soiling the workstation and the surrounding area, can be inhaled, albeit minimally, by the operator performing the operation, even if appropriately equipped with respiratory devices or the like.
Given the harmful nature of the powders used to produce the molds (especially silicon dioxide), this can be hazardous to the health of the operator and of people passing in close proximity.
Besides the aforesaid problems, deflasking by means of sandblasting is also relatively time consuming and requires particular care and ability by the operator.
In fact, the surfaces of the prosthesis can be damaged (eroded or deformed) if persistently exposed to the action of the sandblasting grains. For this reason, when the surface of the cast product starts to emerge, the operator must pay particular attention to direct the sandblasting jet precisely only at the part still covered by the mold material.
The subsequent step of eliminating the reaction layer is also relatively time consuming.
Besides this, as the bath in which the prosthesis is immersed is included in the list of hazardous chemicals, it must be disposed of in conformity with the relevant administrative provisions.
In this context, the object of the present invention is to propose an apparatus for the erosion of articles made of dense aggregate materials, which overcomes the problems of prior art mentioned above.
Document US 5,556,324 discloses an apparatus for cleaning a surface by removing coatings, surface rust, etc., the apparatus comprises all the features set forth in the pre-characterizing part of present claim 1.
More in detail, the object of the present invention is to propose an apparatus that allows the mold used to produce small ceramic or metal articles, such as dental prostheses or the like, to be eroded or broken up, limiting dispersal of powders harmful to the health of the operator.
Another object of the present invention is to produce an apparatus that allows complete removal of the material of the mold from the cast product, in a simpler and faster way with respect to prior art systems.
Yet another object of the present invention is to produce an apparatus that allows removal of the reaction layer from the cast products, without the use of harmful and polluting chemical products.
A further object of the present invention is to provide an apparatus that is practical and easy to use, even by less expert operators, that limits the possibility of damaging the cast product.
These objects are achieved by an apparatus for the erosion of dense aggregates comprising a casing that defines an operating chamber, where the casing preferably includes at least:

a) a bottom,
b) lateral walls,
c) a covering wall,
d) a hatch for accessing the chamber and allowing the insertion of an article to be eroded or broken up, and
e) at least one window for viewing the article inside the chamber;

A spraying device is housed in the chamber for dispensing a pressurized liquid and is connected to pumping means adapted to feed, to the spraying device, said pressurized liquid.
Said pumping means can be included in the casing or can be external means to which the spraying device is connected.
The apparatus also comprises first gripping means for gripping and handling, inside the chamber, the spraying device and second gripping means for gripping and handling, inside the chamber, the article to be eroded or broken up.
According to an aspect of the invention, the spraying device includes a body, in which there is produced at least one duct for passage of the pressurized liquid and at least one nozzle, in communication with said body, this latter preferably also performing the function of handle.
In another aspect of the invention, the nozzle comprises an inner channel with a first stretch and a second stretch, from which the pressurized liquid flows, which has a cross section between 0.007 mm² and 3 mm².
Preferably, the cross section of the second stretch is between 0.07 mm² and 0.30 mm².
In an aspect of the invention, the pumping means operate at a pressure preferably between 50 bar and 300 bar.
Use of the liquid to erode and break up the aggregate material prevents the formation and/or the dispersal into the air of very volatile powders, which could then be dispersed outside the chamber.
Moreover, the feed pressure of the liquid allows the nozzle, thus structured, to generate a jet capable of completely eroding and breaking up the aggregate material of the article I.
In the erosion of casting molds, the apparatus of the invention allows the cast product to be completely cleaned, also eliminating any reaction layer without having to resort to the use chemical agents or the like.
In fact, the jet of water can also be used directly on the surface of the cast object without causing erosion or deformation thereof.
In an aspect of the invention, the first stretch of the inner channel has a length between 22 mm and 42 mm and said second stretch has a length between 5 mm and 10 mm.
In another aspect of the invention the first stretch of the inner channel has a cross section between 10 mm and 30 mm.
These dimensions of the nozzle, together with the operating pressure of the pumping means, allow a liquid flow rate indicatively between 0.5 l/min and 5 l/min to be dispensed.
Preferably this flow rate is around 2 l/min.
In a further aspect of the invention, the spraying device comprises a cap, which defines a chamber around the nozzle. The cap has at least one passage, for inflow into the chamber of solid particles, and at least one duct that allows outflow from the chamber of said solid particles dispersed in the jet of liquid.
In another aspect of the invention, the second gripping means comprise a jaw, configured to grip the article to be eroded or broken up, and a control element connected at a first end to said jaw and at the opposite end to a handle positioned outside the chamber.
The operator, gripping the handle, can thus move the article inside the chamber, so that the jet can reach the whole of its surface.
The grip on the handle reduces or even eliminates the possibility of the operator injuring a limb with the jet of liquid, which has a high cutting capacity, during the operations to erode and break up the article.
In a variant of the invention, the control element comprises a rod passing through an opening produced in the casing.
Said control element can be supported on the casing by a coupling that comprises a guide ring in which there is housed a spherical element, the control element passing through said spherical element. The coupling thus configured allows the article to be moved, shifted in any direction or rotated in any sense or both of these movements, inside the chamber.
In another aspect of the invention, the control element can be supported on the casing by a flexible membrane, fitted around the control element, which blocks the opening of the casing.
According to an aspect of the invention, the first gripping means comprise a flexible membrane arranged at an opening produced in the casing, where said membrane is shaped in the form of a glove.
In another aspect of the invention, the apparatus comprises blowing means adapted to direct a jet of air onto the inner surface of the window to remove drops of liquid deposited thereon.
Said blowing means can comprise a plurality of nozzles positioned at least along one edge of the window and arranged so as to create a jet of air substantially parallel to the inner surface of the window.
In yet another aspect of the invention the apparatus comprises a vent grille positioned on the casing, a filter element being interposed between the chamber and said vent grille to retain volatile particles that could escape from said chamber.
The grille facilitates expulsion of the excess air introduced by the blowing means. The filter element thus allows passage of the air, while blocking particles such as drops of nebulized water in which powder of the aggregate material is dispersed.
Further characteristics and advantages of the present invention will become more apparent from the description of an example of a preferred, but not exclusive, embodiment of an apparatus for the erosion of dense aggregates, as illustrated in the accompanying drawings, wherein:

Fig. 1 is a perspective view of the apparatus for the erosion of dense aggregates according to the invention;
Fig. 2 is a front sectional view of a part of the apparatus of Fig. 1 according to the invention;
Fig. 3 is a lateral sectional view of a part of the apparatus of Fig. 1 according to the invention;
Fig. 4 is a sectional view of the spraying device of the pressurized liquid according to the invention;
Fig. 5 is a sectional view of the spraying device of the pressurized liquid according to a variant of the invention;
Fig. 6 is a sectional view of the apparatus according to a further embodiment of the invention.

With reference to the accompany figures, the apparatus, indicated as a whole with 1, comprises a casing 10 in which there is defined a chamber 11 for housing an article I to be eroded or broken up.
According to the invention, the apparatus is particularly suitable for eroding articles composed in particular of compacted aggregates of powdery or fluid materials, or of a mixture of these two.
As already mentioned, the apparatus is particularly effective when applied to erode and/or break up molds used for producing small articles made of metal, ceramic compounds or other materials compatible with the casting process.
Typical uses of the apparatus according to the invention are, for example, the production of dental prostheses, of jewelry or of small mechanical components with a complex shape. In these contexts, the material of the molds in general comprises silicon dioxide mixed with other minerals or chemical products that increase its consistency.
In detail, the casing 10 comprises at least one bottom 12, lateral walls 13 and a covering 14 in the upper part.
A hatch 15, preferably positioned in the upper part of the casing, closes an opening 16 that allows access to the chamber 11. Through the opening 16, an article I to be eroded or broken up can be inserted into the chamber 11. Movement of the hatch 15 from the closed to the open position and vice versa is allowed by hinge means 15a. A gasket 15b is preferably interposed between the hatch 15 and the wall of the casing 11.
The casing 10 is also provided with a window 19. The window is closed with a transparent material, preferably not colored, which allows an operator to view the article I inside the chamber 11 during execution of the work.
In a preferred variant of the invention, the window 19 is included in the hatch 15. For this purpose the hatch 15 is at least partially made of a transparent material, typically glass, polymethacrylate or polycarbonate.
In the variant shown, at least one part 14a of the upper covering 14 is sloping toward the front wall 13a of the casing 11. The hatch 15 is preferably positioned on this sloping part 14a to provide the operator with a better view of the chamber 11.
Advantageously, according to the invention erosion of the article I is performed by means of a jet of liquid, at high pressure, sprayed onto the surface of the article I.
In fact, the use of a liquid allows incorporation of the potentially harmful powders generated by erosion and prevents them from being dispersed outside the chamber 11.
A suitable liquid for this purpose is typically water or water-based mixtures.
To dispense the liquid, the apparatus is provided with a spraying device, indicated as a whole with 20, housed in the chamber 11.
The pressurized liquid is supplied to the spraying device 20 by pumping means 30, better described below.
With reference to Fig. 4, the spraying device 20 comprises at least one body 21 and at least one nozzle 22 in fluid communication with one another. The body 21 acts as handle for freely handling the device in the chamber 11 so as to direct the jet of liquid against the article I.
In the variant shown, the body 21 has a substantially cylindrical shape. However, any other ergonomic shape can advantageously be used.
In the body 21 there is produced a duct 23 for passage of the liquid towards the nozzle 22. The nozzle 22 is connected to the body, for example, by means of a threaded connector 25.
The nozzle 22 according to the invention comprises an inner channel 24 with a first stretch 24a and a second stretch 24b; the jet of liquid flows from said second stretch 42b.
The two stretches of the inner channel are typically, but not exclusively, cylindrical and coaxial to each other.
The first stretch 24a of the inner channel 24 has a cross section preferably between 10 mm² and 30 mm² and more preferably between 15 mm² and 25 mm².
The second stretch 24b of the inner channel 24 has a cross section between 0.007 mm² and 3 mm², and more preferably between 0.07 mm² and 0.3 mm².
In an example of embodiment tested by the applicant, the first stretch 24a of the inner channel 24 has a cross section of around 19.6 mm² and the second stretch 24b has a cross section of around 0.115 mm².
The first stretch 24a of the duct 24 is typically longer than the second stretch 24b. More in detail the first stretch 24a has a length between 22 mm and 42 mm and more preferably between 28 mm and 34 mm. The second stretch 24b instead has a length between 5 mm and 10 mm, and more preferably between 7 mm and 9 mm.
In the example tested, the first stretch 24a has a length of around 32 mm and the second stretch 24b has a length of around 8 mm.
A nozzle 22 with these characteristics, together with an adequate feed pressure of the liquid, allows a jet of liquid capable of rapidly eroding and breaking up the aggregate material of the article I to be generated.
In fact, the mechanical action of this jet is capable of eroding relatively soft compacted aggregates, such as chalks or the like, and tougher materials such as quartz (silicon dioxide) or mixtures based on this material.
This is particularly useful, for example, in the dental sector for breaking up molds used to produce dental prostheses.
In these contexts, a jet of liquid is particularly effective as, contrary to the case of the prior art sandblasting method, it does not damage the cast product (prostheses, crowns, bridges) even if they were to be hit by the jet for a few moments.
To obtain a good erosion efficacy, the liquid must be fed at a pressure between 50 bar and 300 bar. Optimal operating pressures are between 90 bar and 200 bar.
In these conditions the flow of the liquid dispensed by the nozzle 22 is between 0.5 1/min and 5 1/min.
This somewhat limited flow rate allows the operator to have an excellent view of the area of contact between the jet and the surface of the article I at all times.
When extracting a small and complex article from a mold, this is important in order to completely remove all residues of the mold material from the surface of the article.
According to the invention said pumping means 30 comprise at least one motor 31, preferably electric, connected to a pump 32. Advantageously, the motor 31 can be powered by an inverter (not indicated in the figure) that allows its rotation speed to be varied and, consequently, also the delivery pressure of the pump 32 to be varied. The rotation speed of the motor can be controlled, for example, by means of a pedal control (not shown) so as to leave both of the operator's hands free.
In the variant shown in Figs. 1 to 3, the pumping means 30 are enclosed in a second casing 33, separate from the casing 10. This variant allows the pumping means 30 to be positioned on the ground or under the work bench, so as to reduce the footprint in the operator's range of action.
In an alternative variant, shown in Fig. 6, the pumping means 30 are instead enclosed in the casing 10. In this variant, a bulkhead 17 separates the chamber 11 from a further chamber 18 in which the pumping means are positioned.
In both variants, a pipe 25 feeds the pressurized liquid from the pump 32 toward the spraying device 20.
In a variant of the invention, shown in Fig. 5, the spraying device 20 is configured to dispense a liquid mixed with solid particles.
This is useful, for example, when the reaction layer is particularly resistant and the action of the liquid alone is insufficient to completely clean the surface of the cast product.
According to this variant, the spraying device 20 comprises a cap 26, positioned at the outlet of the liquid from the nozzle 22, which defines a chamber 27 around the nozzle 22.
A passage 28, produced in the cap 26, allows the inflow of solid particles, such as abrasive grains or the like, into the chamber 27.
These particles are typically picked up from a container in communication with the chamber 27, directly or through a pipe, not shown in the figure.
The particles can comprise, for example, materials such as bicarbonate of soda or other substances not harmful to human health.
Transfer of the particles from the container to the chamber 27 takes place through a vacuum pressure that is created inside the aforesaid chamber when the jet of liquid flows from the nozzle 22.
A duct 29, preferably coaxial with the duct 24 of the nozzle 22, allows the outflow from the cap 26 of the solid particles dispersed in the jet of liquid. Advantageously, the cap 26 can be removably coupled to the body 21 or to the nozzle 22, for example through screw or interlocking means.
In this way, the cap 26 can be fitted to the spraying device also only to complete the last processing step, i.e. the surface finishing operation of the cast product.
According to the invention, the apparatus is provided with gripping means that allow the operator to handle the article I and the spraying device 20 inside the chamber 11.
More in detail, the apparatus comprises first gripping means 40 for gripping and handling the spraying device and second gripping means 50 for gripping and handling, inside the chamber 11, the article to be eroded or broken up.
According to the invention, the first gripping means 40 can comprise a flexible membrane 41 positioned at a first opening 42 produced in the casing 11, preferably in a lateral wall 13.
Said membrane 41 is advantageously in the form of a glove, so as to allow safe and easy gripping of the spraying device 20.
The membrane is maintained in position by a sealing ring 43 fixed at the edge of the first opening 42.
According to a preferred variant of the invention, the second gripping means 50 comprise at least one jaw 51, configured to grip the article I to be eroded or broken up.
A control element 52 is connected at a first end to said jaw 51 and at the opposite end to a handle 53. The handle 53 is advantageously positioned outside the chamber 11. The movement provided by the operator to the handle 53 is transmitted from the control element to the jaw 51.
This solution eliminates the risk of the operator injuring a limb with the jet of liquid dispensed by the spraying device 20.
In fact, this jet could possibly cut through protective equipment, such as gloves or the like, if not adequately reinforced.
The jaw 51 is advantageously separable from the control element 52. In this way, it can be replaced with others jaws to adapt to different shapes and dimensions of the articles I to be eroded.
According to the invention, the control element 52 can comprise a rod passing through an opening 54 produced in a lateral wall 13 of the casing 11.
According to a preferred variant, the control element 52 can be supported on the casing 11 by a coupling 55.
More in detail, the coupling 55 can comprise a guide ring 55a in which there is housed a spherical element 55b. The control element 52 passes through the spherical element 55b. Said spherical element 55b, being able to rotate freely in the guide ring 55a, allows the control element 52 to shift and rotate the jaw 51 inside the chamber 11. Moreover, the coupling 55, acts as seal to prevent the liquid from escaping from the chamber 11 through the opening 54.
In an alternative variant, not shown, at the opening 54 there can be provided a flexible membrane, for example made of rubber or similar materials, in turn fitted around the control element 52.
In a further variant, not shown, the second gripping means, similarly to the first gripping means, can comprise a membrane, in the form of a glove, positioned at the opening produced in a lateral wall 13 of the casing 11.
This membrane, to withstand the cutting action of the jet of liquid, is preferably made of composite materials.
For example, materials comprising a layer of fibrous material, such as Kevlar or carbon fiber, covered with a layer of plastic material, such as polyurethane or the like, are suitable to withstand the cutting action of the jet of liquid.
According to the invention, the apparatus also comprises blowing means 60 adapted to direct a jet of air onto the inner surface of the window 19 to remove drops of liquid that can deposit thereon during execution of the work.
In a preferred variant, said blowing means 40 can comprise a plurality of nozzles 61 positioned along at least one edge 19a of the window 19.
Preferably, said nozzles 61 are arranged side by side so as to create a laminar jet of air substantially parallel to the inner surface of the window 19.
The nozzles 61 are fed with compressed air from a compressor that, typically, is not included in the apparatus.
Other mechanical means, such as brushes or the like, can be used to remove residues of liquid from the inner surface of the window 19.
To allow outflow of the air introduced by the blowing means 60 into the chamber 11, the casing 10 is provided with vent grille 62. The vent grille is preferably positioned in the upper part of the casing 10, for example on the upper cover 14 or, as in the variant shown, in the top part of the rear lateral wall.
Preferably a filter element 63 is interposed between the chamber 11 and the vent grille 62 to retain the powder, dissolved in nebulized water, which could escape from the chamber 11.
The vent grille 62 is preferably connected in a removable manner to the casing 11 so as to allow removal of the filter 63 for cleaning or replacement.
To enhance the visibility of the article I during processing, the apparatus can be provided with lighting means 70 adapted to illuminate the inside of the chamber 11.
Said lighting means comprise, for example, light sources 71 positioned in a housing 72 facing the chamber 11. The housing 72 has a window 73 that allows the light to illuminate the article I in the chamber 11.
During erosion of the article I, a layer of liquid containing residues of the material of the article I is deposited on this window 73.
Therefore, the light source 71 is preferably removable from the housing 72 to be able to clean the window 73.
The invention has been described for illustrative and non-limiting purposes according to some preferred embodiments thereof. Those skilled in the art may find numerous other embodiments and variants, all falling within the scope of protection of the claims below.

Claims

Apparatus for the erosion of dense aggregates comprising:
- a casing (10) defining an operating chamber (11), where the casing (10) includes at least:
f) a bottom (12),

g) lateral walls (13),

h) a covering wall (14),

i) a hatch (15) for accessing the chamber (11) and allowing the insertion of an article (I) to be eroded or broken up,

j) at least one window (19) for viewing the article (I) inside the chamber (11);

- a spraying device (20), housed in the chamber, for dispensing a pressurized liquid;

- pumping means (30) for feeding said pressurized liquid toward said spraying device (20);

- first gripping means (40) for gripping and handling, inside the chamber (11), the spraying device (20);

- second gripping means (50) for gripping and handling, inside the chamber (11), the article (I) to be eroded or broken up;
wherein said spraying device (20) includes a body (21), which acts as handle, in which there is produced at least one duct (23) for passage of the pressurized liquid and at least one nozzle (22), in communication with said body (21), the apparatus being characterized by the fact that the nozzle (22) comprises an inner channel (24) with a first stretch (24a) and a second stretch (24b), from which the pressurized liquid flows, where said second stretch has a cross section between 0.007 mm² and 3 mm², and in which the pumping means (30) operate at a pressure between 50 bar and 300 bar.
Apparatus according to claim 1, characterized in that said first stretch (24a) of the inner channel (24) has a length between 22 mm and 42 mm and said second stretch (24b) has a length between 5 mm and 10 mm.
Apparatus according to claim 1 or 2, characterized in that said first stretch (24a) of the inner channel (24) has a cross section between 10 mm² and 30 mm².
Apparatus according to any one of the preceding claims, characterized in that said spraying device (20) comprises a cap (26), which defines a chamber (27) around the nozzle (22), with at least one passage (28), for inflow into the chamber (27) of solid particles, and at least one duct (29) that allows the outflow from the chamber (27) of said solid particles dispersed in the jet of liquid.
Apparatus according to any one of the preceding claims, characterized in that the flow rate of the pumping means (30) is between 0.5 1/min and 5 l/m.
Apparatus according to any one of the preceding claims, characterized in that said second gripping means (50) comprise a jaw (51), configured to grip the article (I) to be eroded or broken up, and a control element (52) connected at a first end to said jaw (51) and at the opposite end to the handle (53) positioned outside the chamber (11).
Apparatus according to claim 6, characterized in that said control element (52) comprises a rod passing through an opening (54) produced in the casing (10).
Apparatus according to claim 7, characterized in that said control element (52) is supported on the casing (10) by a coupling (55), said coupling comprising a guide ring (55a) in which there is housed a spherical element (55b), the control element 52 passing through said spherical element (55b).
Apparatus according to claim 7, characterized in that said control element (52) is supported on the casing (10) by a flexible membrane, fitted around the control element 52, which blocks the opening (54).
Apparatus according to any one of the preceding claims, characterized in that it comprises blowing means (40) adapted to direct a jet of air onto the inner surface of the window (19) to remove drops of liquid deposited thereon.
Apparatus according to claim 10, characterized in that said blowing means (40) comprise a plurality of nozzles positioned at least along one edge (19a) of the window and arranged so as to create a jet of air substantially parallel to the inner surface of the window (19).
Apparatus according to any one of the preceding claims, characterized in that it comprises a vent grille (62) positioned on the casing (10), a filter element (63) being interposed between the chamber (11) and said vent grille (62) to retain volatile particles that could escape from said chamber.