Patent Application
20190210188
The present invention relates to an apparatus for water jet cutting and in particular to an apparatus in which the water jet comprises water and dispersed abrasive particles. The invention also relates to a method for performing the water jet cut by means of the aforesaid apparatus.
Water jet cutting is a technology used to cut and/or shape workpieces made of various types of materials, making use of a very high pressure jet of water. This type of technology is commonly known as “Waterjet”.
Within this scope, the term “water” should not be understood as limited to pure water (H2O) as working fluid. In this context, the term water refers to any fluid, if necessary mixed with solid particles, capable of flowing through a tube or an orifice of a nozzle.
Apparatus used for water jet cutting are generally provided with a cutting head capable of delivering, through a specific nozzle, a very thin jet of water, with a diameter between 0.1 mm and 0.4 mm, at very high pressure, up to 6,000 bar and more. To cut hard materials, such as metals, stone, marble, glass, etc., abrasive particles are dispersed in the water to increase the erosive capacity of the water jet.
These known apparatus are divided mainly into two categories as a function of the type of technology applied: “Abrasive water jet” (AWJ) apparatus and “Abrasive Suspension Jet” or “Abrasive Slurry Jet” (ASJ) apparatus.
In the former, i.e., AWJ apparatus, the high pressure fluid, typically water, and the abrasive, in the form of dry powdery particles, are conveyed separately into a nozzle comprising a mixing chamber where the two aforesaid elements are mixed before flowing out.
These apparatus, although effective and reliable, have some limits. For example, the presence of air dispersed in the jet delivered from the nozzle means that this type of apparatus cannot be used in some applications, such as cutting potentially explosive objects or submerged objects. Moreover, with this technology, a non-negligible part of the kinetic energy accumulated by the water accelerated in the nozzle is dispersed through the chaotic movement of the abrasive particles in the focusing tube of the nozzle. Moreover, this also causes rapid wear of this tube that, generally, must be replaced after a few dozen hours of use.
Another disadvantage linked to this type of apparatus consists in the need to use dry abrasive particles. This means that it is impossible to recover and reuse in the same machining cycle the part of wet abrasive particles that, after a first use, are still sufficiently large to be used for further machining operations.
For this reason, at the state of the art, the wet abrasive particles are collected and sent to recovery centers equipped with systems dedicated to the filtration, selection and drying of the reusable particles.
On the contrary, in ASJ apparatus the abrasive and a fluid are mixed, obtaining a suspension (called “slurry”). In general, the fluid comprises water and additives to form a suspension that maintains the abrasive particles suspended in said fluid for a given period of time. With this arrangement, the particles are prevented from precipitating downward and accumulating with the risk of blocking the apparatus.
This suspension is then pressurized and conveyed toward the nozzle.
In general, in these apparatus only a part of the total flow of water of the apparatus is mixed with the abrasive to form a first flow (slurry). The first flow and the remaining part of water, conveyed in a second flow, are pressurized and sent toward the nozzle.
In some of these apparatus, the two flows are mixed upstream of the nozzle, while in others they are mixed directly in the mixing chamber of the nozzle.
Although apparatus thus configured partly overcome the limits of AWJ systems, they also have some drawbacks. Among these, the most consistent problem concerns high wear caused by the flow of abrasive in suspension on the various components of the apparatus and in particular on the valves and on the pumping means. For this reason, these systems are not widely used today, above all in the machine tool sector.
In this context, the object of the present invention is to propose an apparatus and a method for water jet cutting that overcome the problems of the prior art described above.
Therefore, an object of the present invention is to propose an apparatus for water jet cutting that can be used without limitations in a wide range of applications.
Another object of the present invention is to propose an apparatus, and a related method, that guarantees an improved penetration capacity in hard materials and at the same time an improved finish of the machined surface.
Another object of the present invention is to propose an apparatus for water jet cutting that is simple to produce, therefore inexpensive, and that requires limited maintenance.
A further object of the present invention is to provide an apparatus and a method for water jet cutting that allow the operating cost of the machining operations to be greatly reduced.
Besides the aforesaid objects, a further object of the present invention is to produce an apparatus and a method for water jet cutting that enables the environmental impact of the waste materials to be reduced.
These and other objects are achieved by an apparatus for water jet cutting comprising:
According to the invention, the source of abrasive material in suspension is in communication with said cutting head by means of an abrasive inlet channel. The cutting head is instead configured to generate a vacuum pressure that draws the abrasive material in suspension through said abrasive inlet channel toward the mixing chamber.
On the contrary to known ASJ systems, the abrasive material in suspension is not pumped at very high pressure toward the nozzle, but is only transported, preferably at atmospheric pressure, toward the mixing chamber in which it is intercepted by the high speed water jet before entering the focusing tube. This suction is caused by the Venturi effect that is created in the mixing chamber when the flow of pressurized water is made to pass through a narrow orifice before flowing into the aforesaid mixing chamber.
In this way, the components of the apparatus are subject to much less wear relative to the wear that characterizes known ASJ systems.
Moreover, due the introduction into the mixing chamber of the abrasive particles in a fluid suspension, the energy loss caused by the disorderly movement of said abrasive particles, when intercepted by the pressurized water jet, is reduced. This makes it possible to increase the distance for which the jet of water and abrasive delivered from the nozzle remains cohesive, i.e. maintains a substantially constant width. Tests carried out by the applicant show that the apparatus thus configured guarantees, with the same water pressure and the same type and amount of abrasive material, an increased cutting depth and improved surface finish (i.e., less roughness) relative to a conventional system of AWJ type. Moreover, the more orderly flow of the abrasive particles inside the focusing tube allows a reduction of the wear of this component relative to an aforesaid AWJ system.
According to an aspect of the invention, the inlet channel of the abrasive material can be equipped with flow regulating means of the abrasive material in suspension.
According to another aspect of the invention, the abrasive material in suspension comprises abrasive particles dispersed in a liquid or, preferably, gelatinous substance. Advantageously, said gelatinous substance comprises at least water and a gelling agent.
According to another aspect of the invention, in the abrasive material in suspension the volume ratio between the abrasive particles and the liquid or gelatinous substance is preferably from 1:3 to 1:7.
According to another aspect of the invention, said cutting head comprises a focusing tube of the jet (or nozzle) with a diameter preferably between 0.5 mm and 1.3 mm. The nozzle has a length preferably between 100 mm and 200 mm. The nozzle thus structured guarantees a greater cohesion of the water jet and abrasive delivered, up to a distance of around 60 mm, i.e., around five times higher than that of a conventional AWJ system.
According to another aspect of the invention, the flow regulating means are mounted at an outlet of the abrasive material of the aforesaid tank. Said flow regulating means can comprise, for example, an opening, through which the abrasive material in suspension can flow, and a moving partition, associated with control means, adapted to obstruct or partly or totally free the aforesaid opening. This system, particularly simple, allows rapid dosing of the amount of abrasive material present in the water jet delivered. The regulating system thus produced allows rapid calibration of the apparatus as a function of the material of the object to be processed and of its dimensions.
According to another aspect of the invention, the apparatus can comprise a mixing device to mix the water, the gelling agent and the particles of abrasive material to form the abrasive material in suspension. Said mixing device is preferably equipped with pumping means to transfer the abrasive material in suspension into the tank.
According to another aspect of the invention, the apparatus can comprise dosing means, associated with said mixing device, to dose the water, the gelling agent and the particles of abrasive material to form the abrasive material in suspension.
The apparatus thus configured is particularly effective to carry out continuous or, in any case, lengthy machining operations, as it allows an abrasive material in suspension with constant properties to be fed to the source throughout the whole of the machining process.
According to another aspect of the invention, the apparatus can further comprise:
In this way, the apparatus allows the abrasive material still usable to be recycled and re-introduced into the machining process. This recycling step of the abrasive material allows a significant reduction in the operating costs of the apparatus, both of those for purchasing the abrasive material and of those for its disposal.
The abrasive material most widely used for water jet cutting is garnet, well known to those skilled in the art. While on the one hand this material guarantees excellent performance, due to its high level of hardness and resilience, on the other hand it is particularly costly. In fact, it is estimated that, on average, the costs for purchasing garnet abrasive can represent up to 40%-60% of the operating cost of the apparatus.
Given that after a machining operation a large percentage of the abrasive particles discharged is still sufficiently large to be used in a new machining cycle, recycling of the aforesaid particles is without doubt desirable. This percentage varies in general between 30% and 70%, as a function of the hardness and thickness of the material being processed.
Known systems for abrasive recycling are provided with means to separate and eliminate, from the material collected, both particles with a size below a given threshold, which can comprise powdered particles of abrasive and of the material of the processed workpiece, and particles with a size above a given threshold, which generally comprise only material of the processed workpiece.
The particles of the correct size, which are therefore recyclable, are dried and stored to be re-introduced into the machining cycle.
In some systems this drying step precedes the separation step and is carried out on the whole mass of abrasive material collected from the collection tank. In other systems, separation of the recyclable abrasive particles instead takes place before the drying step.
Examples of these systems are described in WO 9817439 A2 and U.S. Pat. No. 6,328,638 B1.
Recycling systems thus produced are characterized by very high energy consumption, due mainly to the particle drying step. In fact, this energy consumption makes the recycling step particularly costly, to the extent that the cost of the recycled abrasive is substantially the same as that of the material purchased from the manufacturer.
In the apparatus of the present invention, the mass of recyclable abrasive material can be re-introduced into the apparatus still wet, eliminating the need for the drying step.
According to a preferred aspect of the invention, the recovery and recycling system is equipped with pumping means to convey said wet mass of reusable abrasive particles into the mixing device.
The objects are also achieved with a method for generating a water jet cut with an apparatus for water jet cutting, which comprises the following steps:
According to an aspect of the invention, the step of preparing the abrasive material in suspension comprises the stage of mixing the fluid and the abrasive particles to disperse them homogeneously therein. Said mixing is preferably carried out in a tank comprising agitator means.
According to another aspect of the invention, the step of preparing the abrasive material in suspension comprises a further stage, preceding the mixing stage, consisting of dosing the fluid and the abrasive particles.
According to another aspect of the invention said fluid is a gelatinous substance. According to this variant, the method comprises the stage of mixing water, at least one gelling agent and particles of abrasive to form said gelatinous substance.
The method can then comprise a further stage, preceding the mixing stage, consisting of dosing the water, the gelling agent and the abrasive particles.
According to the invention, the abrasive material in suspension prepared is, preferably, pumped into a tank from which it is then conveyed into the mixing chamber. The fact of dispersing the abrasive particles in a gelatinous substance offers the advantage of being able to store the abrasive material in the tank for many hours without the particles precipitating downward, i.e., depositing on the bottom of the tank. The apparatus thus has a stock of material in suspension ready for use that allows it to be started immediately and at any time.
The step of dosing and subsequent mixing of the water, of the gelling agent and of the abrasive particles, carried out in the mixing device, ensures that said abrasive material in suspension has the exact concentration of abrasive particles desired, guaranteeing constant quality and repeatability of the cutting operations.
According to another aspect of the invention, the method also comprises the following steps:
According to this last variant, the step of preparing the abrasive material in suspension comprises the mixing of water, at least one gelling agent, said wet or dry abrasive particles, or both wet and dry abrasive particles.
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 water jet cutting illustrated schematically in the accompanying
With reference to the FIGURE, the reference number 1 indicates as a whole an apparatus for water jet cutting. As mentioned above, within the context of the present invention the term water must be interpreted extensively, hence with reference to any liquid and, even more generally, fluid, solid or combinations thereof, provided that it is suitable to be treated (compressed, transferred, conveyed) with the normal devices used for a fluid and in particular suitable to be forced inside an orifice of small size, such as the focusing nozzle of the apparatus.
The apparatus is then supplied with a water source 2 to supply the aforesaid process water to the apparatus. The water source 2 can comprise a tank or a continuous feed line. The source 2 can be equipped with water treatment devices to treat the process water to make it more suitable for use in high pressure pumping apparatus. These treatment devices are well known to those skilled in the art and shall not be described in more detail. A water line 3 connects the water source 2 to pumping means 4.
Said pumping means 4 can comprise a common waterjet pump, for example an intensifier pump, a reciprocating pump, a direct-drive pump or a servo-electric pump.
Said pumping means are generally configured to convey the process water at a pressure typically between 3000 and 6000 bar.
A water infeed line 5 places said pumping means 4 in communication with the cutting head 10 of the apparatus.
The apparatus 1 further comprises a source, indicated as a whole with 20, of an abrasive material in suspension 21. In the variant illustrated, the source of abrasive material in suspension 20 (hereinafter also only “abrasive material”), comprises a tank 22 in which the abrasive material in suspension 21 can be deposited. An abrasive inlet channel 23 places the tank 22 in communication with the cutting head 10.
According to the invention, said abrasive material in suspension comprises a liquid or, preferably, gelatinous substance in which particles of abrasive material are dispersed. Examples of abrasive materials that can be used in the apparatus of the invention are garnet, glass, metal grits based on aluminum or the like.
A gelatinous substance is particularly advantageous as it allows the abrasive particles to remain suspended, and hence dispersed homogeneously, for several hours, preventing them from precipitating through gravity and accumulating at the bottom, mainly, of the tank 22.
The abrasive material in suspension can therefore be prepared and stored in a tank of the apparatus ready for use.
Preferably the suspension is formed with a water-based gelatinous substance.
More in detail the suspension comprises water and a gelling agent.
The volume ratio between the amount of abrasive material and of the liquid or gelatinous substance is preferably from 1:4 to 1:8 and more preferably from 1:5 to 1:7.
According to the invention, the cutting head 10 comprises a body 11 in which a mixing chamber 12 is provided. The mixing chamber 12 is in fluid communication with the water infeed line 5 and with the abrasive inlet channel 23.
The pressurized water is forced into an orifice 13 from which it flows, at a very high speed, into the mixing chamber 12. The high speed generates a vacuum pressure in the mixing chamber 12, which in turn draws the abrasive material in suspension 21 from the tank 22 through the abrasive inlet channel 23. The abrasive material in suspension 21 and the water jet are then mixed in the mixing chamber 12 and, subsequently, conveyed into the focusing tube 14 from which a jet 15 of water and abrasive material is delivered.
A suitable cutting head is, for example, the model Dialine manufactured and marketed by Hyperterm Inc. or the model Slice Two manufactured and marketed by Diamond Technology Innovations.
Advantageously, according to the invention, this nozzle is equipped with a focusing tube of the jet with a length preferably between 100 mm and 200 mm and more preferably between 140 mm and 160 mm. The nozzle thus configured creates a jet of water and abrasive material capable of remaining cohesive for a greater distance relative to that of a conventional AWJ system, allowing a greater depth of this jet with the same material processed.
According to a preferred variant, said focusing tube comprises two portions of tube joined together by a removable connection means (not illustrated). In this way, it is possible to use, as portions, focusing tubes of smaller standard length, which are more widely available and less costly. Moreover, as the portion closest to the outlet of the jet is subject to greater wear, said portions can be disassembled and reversed after a given period of operation, thereby advantageously extending the life of the focusing tube before replacement.
Suitable focusing tubes are, for example, the models Roctec 100 or Roctec 500, manufactured and marketed by Kennametal Inc.
To regulate the amount of abrasive material in suspension 21 introduced into the mixing chamber 12, the apparatus is equipped with flow regulating means 27. Said flow regulating means 27 preferably comprise a moving partition positioned on the abrasive inlet channel 23 or, preferably, directly on the abrasive outlet on the tank 22.
The moving partition, by widening or narrowing the section of the opening for the flow of abrasive material to pass through, regulates the flow of this material conveyed toward the mixing chamber as a result of the vacuum pressure.
The moving partition can be moved either manually or by means of an electric or pneumatic actuator associated therewith.
In a preferred variant of the invention, the apparatus is equipped with a mixing device 24 provided with agitator means to mix the abrasive particles and the liquid or gelatinous substance to form the abrasive material in suspension 21. Advantageously, said mixing device 24 is in communication with the tank 22.
A pump 25, if provided, can directly feed the abrasive material in suspension into said tank.
According to another mode of embodiment of the invention, the apparatus comprises dosing means 26 associated with said mixing device 24 to dose at least the water, the gelling agent and, optionally, the particles of abrasive material to form the abrasive material in suspension.
Preferably, the gelatinous substance is prepared by mixing water and the gelling agent, this latter being between 0.05% and 5% of the volume of the water used, and more preferably around 3%.
According to another variant of the invention, the apparatus is equipped with a recovery and recycling system of the abrasive material, indicated as a whole with the reference number 30.
According to the invention, this recycling system comprises a recovery device 32 configured to receive a wet mass of abrasive particles and of waste material from a collection container 31, positioned in an area below the nozzle. The process water and the abrasive material of the jet 15, as well as the waste material from processing, are collected in this container 31. A suitable recovery device is, for example, described in U.S. Pat. No. 6,299,510 B1.
According to the invention, the recycling system 30 also comprises separation means 33, adapted to separate the wet mass of reusable abrasive particles from the wet mass of non-reusable abrasive particles and from the waste material.
In particular, these separation means 33 are configured to separate particles with a size greater than a given value, comprising processing waste from the workpiece, and particles with a size below a given threshold, comprising both processing waste and crushed particles of abrasive. These products are conveyed into a waste container 36 to be disposed of correctly.
Typically, the separation means 33 comprise a cyclone device 34, if necessary associated with a filter device 35.
These devices are well known to those skilled in the art and therefore will not be described in more detail.
The wet mass of reusable abrasive particles can then be stored in a collection tank 37 or, preferably, conveyed toward the source of the abrasive material in suspension 20, for example by means of an auger or equivalent pumping means.
Advantageously, this wet mass of reusable abrasive particles can be conveyed directly into the mixing device 24 for the production of other abrasive material in suspension to be used in the machining process.
According to this variant, further dosing means are preferably provided to control the amount of recycled abrasive material introduced into the mixing device 24.
Therefore, also in this case the apparatus guarantees that the abrasive material in suspension prepared has the correct percentage of dispersed abrasive particles. Moreover, with this system it is also possible, if necessary, to introduce new dry abrasive particles into the mixer and to dose their amount relative to the amount of recovered wet particles.
With the recycling system thus configured it is possible to recycle between 30% and 70% of the abrasive material used, as a function of the hardness of the material and of the thickness of the machined workpiece.
Due to the re-introduction of the wet mass of reusable abrasive particles, the recycling system is particularly advantageous from the point of view of operating costs, making recovery and recycling profitable also for users of apparatus for water jet cutting.
Said recovery operations of the abrasive material can be implemented continuously during operation of the cutting apparatus. If the amount of abrasive particles recovered is not sufficient to guarantee the correct flow of abrasive material in suspension, new dry particles can be mixed with the recovered wet particles, the water and the gelling agent.
The invention has been described purely for illustrative and non-limiting purposes, according to some preferred embodiments. Those skilled in the art may find numerous other embodiments and variants, all falling within the scope of protection of the claims below.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102016000097457 | Sep 2016 | IT | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2017/055964 | 9/28/2017 | WO | 00 |
