IT201600097457A1 - APPARATUS FOR WATER JET CUTTING - Google Patents

Description

"APPARATUS FOR WATER JET CUTTING"

The present invention relates to an apparatus for water jet cutting, or water cutting, and in particular to a plant in which the water jet comprises water and dispersed abrasive particles.

Water jet cutting is a technology used to cut and / or shape pieces in various types of materials, using a very high pressure water jet. This type of technology is commonly referred to as “Waterjet”.

In this context, the term "water", as well as the corresponding "water", must not be understood limited to pure water (H2O) as an operating fluid. In this context, the term water refers to any fluid, possibly mixed with solid particles, capable of flowing through a duct or an orifice of a nozzle.

The devices used for water cutting are generally equipped with a cutting head capable of delivering, through a special 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 beyond. To cut hard materials such as metals, stones, marble, glass, etc., abrasive particles are dispersed in the water to increase the erosive capacity of the water jet.

Such known apparatuses are mainly divided into two categories according to the type of technology applied: "Abrasive water jet" (AWJ) apparatuses and "Abrasive suspension Jet" or "Abrasive Slurry Jet" (ASJ) apparatuses.

In the former, the AWJ apparatuses, 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 aforementioned elements are mixed before flowing to the 'external.

These devices, although effective and reliable, have some limitations. For example, the presence of air dispersed in the jet delivered by the nozzle makes this type of apparatus not usable in certain applications such as for example the cutting of potentially explosive objects or submerged objects. Furthermore, with this technology, a non-negligible part of the kinetic energy accumulated by the accelerated water in the nozzle is dispersed due to the chaotic movement of the abrasive particles in the nozzle locating duct. This, however, also causes rapid wear of this duct which, in general, must be replaced after a few tens of hours of use.

On the other hand, in the ASJ apparatuses the abrasive and a fluid are mixed in a suspension (called "slurry"). Generally, the fluid comprises water and additives to form a suspension which keeps the abrasive particles suspended in said fluid for a certain time to avoid that, by precipitating downwards, they can accumulate with the risk of blocking the apparatus.

This suspension is then pressurized and conveyed towards the nozzle.

Generally, such apparatuses foresee that only a part of the total water flow rate of the apparatus is mixed with the abrasive to form a first flow (slurry). The first flow and the remaining part of water, which has flowed into a second flow, are pressurized and sent towards the nozzle.

In some of these apparatuses the mixing of the two flows occurs before the nozzle, in others directly in the mixing chamber of the nozzle.

Devices configured in this way partially overcome the limitations of AWJ systems but, however, also have some disadvantages. Among these, the most consistent problem concerns the 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 very common today, especially in the machine tool sector.

In this context, it is an object of the present invention to propose an apparatus for water jet cutting which overcomes the aforementioned drawbacks of the known art.

It is therefore an object of the present invention to propose an apparatus for water jet cutting which can be used without limitations in various applications.

Another object of the present invention is to propose an apparatus for water jet cutting which guarantees a better ability to penetrate hard materials and at the same time a better finish of the machined surface.

Another object of the present invention is to propose an apparatus for water jet cutting which is simple to manufacture, therefore inexpensive, and which requires limited maintenance.

A further object of the present invention is to provide an apparatus for water jet cutting which allows to significantly reduce the operating costs of the apparatus.

In addition to the aforementioned purposes, the aim of the present invention is also to provide an apparatus for water jet cutting which allows to reduce the environmental impact of waste materials.

These and other purposes are achieved by a water jet cutting apparatus comprising:

- a source of water;

- pumping means, in communication with the water source, for generating a high pressure water flow;

- a source of an abrasive material in suspension;

And

- a cutting head in fluid communication with said pumping means and said source of the suspended abrasive material, said cutting head comprising a mixing chamber for mixing the water and the suspended abrasive material.

According to the invention, the source of suspended abrasive material is in communication with said cutting head by means of an abrasive inlet channel. The cutting head, on the other hand, is configured to generate a depression which drags the abrasive material in suspension through said inlet channel of the abrasive towards the mixing chamber.

The abrasive material in suspension, unlike the known ASJ systems, is not pumped at very high pressure towards the nozzle but is only transported to the mixing chamber where it is intercepted by the jet of water at high speed before entering the focusing duct. This suction is caused by the Venturi effect which is created in the mixing chamber when the flow of water and pressure is made to pass through a narrow orifice before flowing into the aforementioned mixing chamber.

In this way the components of the apparatus are subjected to a very low wear compared to that which characterizes known ASJ systems.

Furthermore, thanks to the introduction into the mixing chamber of the nozzle of the abrasive particles in a fluid suspension, the dispersion of energy caused by the disordered movement of said abrasive particles, when intercepted by the jet of pressurized water, is reduced. This allows to increase the distance in which the jet of water and abrasive leaving the nozzle remains cohesive, that is to say it maintains a substantially constant width. From tests carried out by the applicant, the apparatus thus configured guarantees, with the same water pressure and the same abrasive material, a higher depth of cut and a better surface finish (less roughness) than a traditional AWJ system. The more orderly flow of the abrasive particles inside the localizer duct, moreover, allows to reduce the wear of this component compared to the aforementioned AWJ system.

According to an aspect of the invention, the inlet channel of the abrasive material can be equipped with means for adjusting the flow of the abrasive material in suspension.

According to another aspect of the invention, the abrasive material in suspension can comprise abrasive particles dispersed in a liquid or, preferably, gelatinous substance. Advantageously, said gelatinous substance can comprise at least water and a gelling substance.

According to another aspect of the invention, the volume ratio between the abrasive particles and the liquid or gelatinous substance in the suspended abrasive material is preferably from 1: 3 to 1: 7.

According to another aspect of the invention, said cutting head comprises a jet focusing duct (or nozzle) with a diameter preferably comprised between 0.5 mm and 1.3 mm, and a length preferably comprised between 100 mm and 200 mm. The nozzle thus shaped guarantees greater cohesion of the water and abrasive jet delivered, up to a distance of about 60 mm, that is to say about five times greater than that of a traditional AWJ system.

According to another aspect of the invention, the source of the suspended abrasive material comprises at least one reservoir in fluid communication with the abrasive inlet duct. In a preferred variant, the flow adjustment means are mounted at an outlet of the abrasive material of the aforesaid said tank. Said adjustment means can comprise, for example, an opening, through which the suspended abrasive material can flow, and a movable partition, associated with control means, able to obstruct or partially or completely free said opening. This particularly simple system allows you to quickly dose the amount of abrasive material present in the jet of water delivered. The adjustment system thus created allows the apparatus to be calibrated quickly according to the material of the object to be machined and its dimensions.

According to another aspect of the invention, the apparatus can comprise a mixing device for mixing the water, the gelling substance and the particles of abrasive material to form the abrasive material in suspension. Said mixing device is preferably equipped with pumping means for transferring the abrasive material in suspension in the tank.

According to another aspect of the invention, the apparatus can comprise metering means, associated with said mixing device, for metering the water, the gelling substance and the particles of abrasive material to form the abrasive material in suspension.

The apparatus configured in this way is particularly effective for performing continuous or in any case long-lasting machining operations since it allows to feed an abrasive material in suspension with constant characteristics to the source throughout the machining process.

According to another aspect of the invention, the apparatus can comprise:

- a collection container to collect the water and the abrasive material, supplied by the cutting head, and the waste material from the processing;

- an abrasive material recovery and recycling system configured for:

- taking from said collection container a moist mass of abrasive particles and waste material;

- separating a moist mass of reusable abrasive particles from a moist mass of non-reusable abrasive particles and waste material;

- imparting said moist mass of reusable abrasive particles into the source of the suspended abrasive material;

In this way, the apparatus allows the abrasive material still usable to be recycled and re-introduced into the manufacturing process. This phase of recycling of the abrasive material allows to considerably reduce the operating costs of the apparatus, both those for the purchase of the abrasive material and those for its disposal.

The abrasive material most used for water cutting is the "garnet", well known to those skilled in the art. On the one hand, this material guarantees excellent performance thanks to its high hardness and resilience, on the other hand, however, it is particularly expensive. It is estimated that on average, in fact, the cost for the purchase of the garnet abrasive can affect up to 40% - 60% of the operating cost of the device.

Since, after a processing, a large percentage of the discharged abrasive particles still has a size large enough to be used in a new processing cycle, being able to recycle the aforementioned particles is certainly desirable. This percentage generally varies between 30% and 70% depending on the hardness and thickness of the processed material.

Known abrasive recycling plants are provided with means for separating and eliminating, from the removed material, both particles with a size lower than a certain threshold, which may include pulverized particles of abrasive and the material of the worked piece, and particles with a size greater than a certain threshold that typically comprise only material of the workpiece.

The particles of the correct size, therefore recyclable, are dried and stored to be re-introduced into the processing cycle.

In some plants this drying phase precedes the separation phases and is performed on the whole mass of abrasive material taken from the collection tank. In other plants, however, the separation of the recyclable abrasive particles takes place before the drying phase.

Examples of such systems are described for example in WO 9817439 A2 and US 6328638 B1.

Recycling plants created in this way are characterized by a very high energy consumption, mainly due to the drying phase of the particles. This energy consumption, in fact, makes the recycling phase particularly expensive to the point 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 fed back into the still wet apparatus eliminating the need for the drying step.

According to another aspect of the invention, the recovery and recycling system is equipped with pumping means for conveying said moist mass of reusable abrasive particles into the mixing device.

Further characteristics and advantages of the present invention will become clearer from the description of a preferred but not exclusive embodiment of an apparatus for water jet cutting illustrated schematically in the attached figure 1.

With reference to the figure, the number 1 generally indicates an apparatus for water cutting. As mentioned above, in the context of the present invention the term water must be interpreted extensively with reference to any liquid, fluid, solid or combinations thereof, as long as it is suitable for being treated (compressed, delivered, conveyed) with the normal devices used. for a fluid and in particular suitable for being forced inside a small orifice such as the focusing nozzle of the apparatus.

The apparatus is therefore provided with a source of water 2 to supply the aforementioned process water to the apparatus. The water source 2 of the water can comprise a reservoir or a continuous feed line. Water treatment devices can equip source 2 to treat process water to make it suitable for use in high pressure pumping equipment. Such treatment devices are well known to those skilled in the art and will 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 pump for "waterjet", for example a pump with intensifier, a reciprocating pump or a direct drive pump or a servo-electric pump.

Said pumping means are generally configured to convey the process water at a pressure typically comprised between 3000 and 6000 Bar.

A water inlet line 5 puts said pumping means 4 in communication with the cutting head 10 of the apparatus.

The apparatus 1 also 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 inlet channel of the abrasive 23 puts the tank 22 in communication with the cutting head 10.

According to the invention, said abrasive material in suspension comprises a liquid or gelatinous substance in which particles of abrasive material are dispersed. Examples of abrasive materials usable in the apparatus of the invention are garnet, glass, aluminum-based metal debris or the like.

Preferably the suspension is formed in a water-based gelatinous substance. More specifically, the suspension comprises water and a gelling substance.

The volume ratio between the amount of abrasive material and the liquid or gelatinous substance is preferably from 1: 4 to 1: 8 and more preferably is from 1: 5 to 1: 7.

According to the invention, the cutting head 10 comprises a body 11 in which there is a mixing chamber 12. The mixing chamber 12 is in fluid communication with the water inlet line 5 and with the inlet channel abrasive 23.

The pressurized water is forced into an orifice 13 from which it flows, at very high speed, into the mixing chamber 12. The high speed generates a vacuum in the mixing chamber 12 which, in turn, sucks the abrasive material in suspension 21 through the inlet channel of the abrasive 23. The abrasive material in suspension 21 and the jet of water are then mixed in the mixing chamber and, subsequently, conveyed into the focusing duct 14 from which a jet 15 of water is delivered and abrasive material.

A suitable cutting head is, for example, the Dialine model produced and marketed by Hyperterm Inc. or the Slice Two model produced and marketed by Diamond Technology Innovations.

Advantageously, according to the invention, this nozzle is equipped with a jet focusing duct with a length preferably between 100 mm and 200 mm and more preferably between 140 mm and 160 mm. The nozzle configured in this way creates a jet of water and abrasive material capable of remaining cohesive for a greater distance than that of a traditional AWJ system, allowing this jet a higher depth of cut for the same material processed.

According to a preferred variant, said focusing duct comprises two portions joined together by a connecting means (not shown). In this way it is possible to use, as portions, focusers of a shorter standard length, more common and less expensive. Furthermore, since the portion closest to the outlet of the jet is subject to greater wear, said portions can be reversed after a certain working time, extending the life of the focuser before replacement.

Suitable focusers are for example the Roctec 100 or Roctec 500 models manufactured and marketed by Kennametal Inc.

To regulate the quantity of the suspended abrasive material 21 introduced into the mixing chamber 12, the apparatus is equipped with flow regulating means 27. Said flow regulating means 27 preferably comprise a movable septum located on the abrasive inlet channel 23. or, preferably, directly on the abrasive outlet on the tank 22.

The movable septum, by widening or narrowing the section of the passage opening for the flow of abrasive material, regulates the flow rate of this material conveyed towards the mixing chamber due to the effect of the depression.

The movable partition can be operated manually or by means of an electric or pneumatic actuator associated with it.

In a preferred variant of the invention, the apparatus is equipped with a mixing device 24 for mixing 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 suspended inside said tank.

According to another embodiment of the invention, the apparatus comprises metering means 26 associated with said mixing device 24 for metering at least the water, the gelling substance and, optionally, the particles of abrasive material to form the abrasive material in suspension.

Preferably, the volume percentage of the gelling substance in the water is comprised between 0.5% and 5% and more preferably it is about 3%.

According to another variant of the invention, the apparatus is equipped with a recovery and recycling system for the abrasive material, indicated as a whole with 30.

According to the invention, this recycling system comprises a recovery device 32 configured to take a wet mass of abrasive particles and waste material from a collection container 31, located in an area below the nozzle, in which they are collected the process water and the abrasive material, of the jet 15, as well as the waste material of the processing. A suitable recovery device is described for example in US 6299510 B1.

According to the invention, the recycling system also comprises separator means 33 for separating the wet mass of reusable abrasive particles from the wet mass of non-reusable abrasive particles and waste material.

In particular, these separator means 33 are configured to separate particles with a size greater than a certain value, including processing waste from the piece, and particles with a size below a certain threshold, including both processing waste and particles of abrasive material. shattered. These products are conveyed to a waste container 36 to be properly disposed of.

Typically, the separator means 33 comprise a cyclone device 34, possibly associated with a filtering device 35.

Such devices are known to those skilled in the art and will therefore not be described in more detail.

The moist mass of reusable abrasive particles can then be stored in a collection tank 37 or conveyed to the source of the suspended abrasive material 20, for example by means of an auger or equivalent pumping means.

Advantageously, this moist mass of reusable abrasive particles can be conveyed directly into the mixing device 24 for the production of other suspended abrasive material to be used in the manufacturing process.

According to this variant, further metering means are preferably provided to control the amount of recycled abrasive material introduced into the mixing device 24.

With the recycling system configured in this way, it is possible to recycle from 30% up to 70% of the abrasive material used, depending on the hardness of the material and the thickness of the workpiece.

Thanks to the reintroduction of the mass of wet reusable abrasive particles, the recycling system is particularly advantageous from the point of view of management costs, making recovery and recycling convenient even for users of water cutting equipment.

The invention has been described for illustrative and non-limiting purposes, according to some preferred embodiments. The person skilled in the art will be able to find numerous other embodiments and variants, all of which fall within the protection scope of the following claims.

Claims (13)

CLAIMS 1. Apparatus for water cutting comprising: - a source of water (2); - pumping means (4), in communication with the water source, to generate a high pressure water flow; - a source (20) of an abrasive material in suspension (21); - a cutting head (10) in fluid communication with said pumping means (4) and said source of the abrasive material in suspension (20), said cutting head comprising a mixing chamber (12) for mixing the water and the abrasive material in suspension; characterized in that said source of the suspended abrasive material (21) is in communication with said cutting head (10) by means of an abrasive inlet channel (23), said cutting head being configured to generate a depression which drags the abrasive material (21) in suspension through said abrasive inlet channel (23) towards the mixing chamber (12). 2. Apparatus according to claim 1, characterized in that the inlet channel of the abrasive material (23) is equipped with means for regulating the flow (27) of the abrasive material in suspension (21). 3. Apparatus according to claim 1 or 2, characterized in that said abrasive material in suspension comprises abrasive particles dispersed in a liquid or gelatinous substance. 4. Apparatus according to claim 3, characterized in that said gelatinous substance comprises at least water and a gelling substance. 5. Apparatus according to any one of the preceding claims, characterized in that the volume ratio between the abrasive particles and the liquid or gelatinous substance is from 1: 4 to 1: 8. 6. Apparatus according to any one of the preceding claims, characterized in that said cutting head (10) comprises a focusing duct (14) of the jet with a diameter comprised between 0.4 mm and 1.5 mm, and a length comprised between 100 mm and 200 mm. 7. Apparatus, according to any one of the preceding claims, characterized in that said source (20) of the abrasive material in suspension (21) comprises at least one reservoir (22) in fluid communication with the inlet duct of the abrasive (23 ). 8. Apparatus according to claims 2 and 7, characterized in that said flow adjustment means (27) are mounted at an outlet of the abrasive material of said tank (22). 9. Apparatus, according to claim 8, characterized in that said means for regulating the flow (27) comprise an opening, through which the abrasive material in suspension can flow, and a movable septum, associated with control means, adapted to obstruct or partially or completely free the aforementioned opening. 10. Apparatus according to claims 3 and 7 to 9, characterized in that it comprises a mixing device (24) for mixing the water, the gelling substance and the particles of abrasive material to form the abrasive material in suspension (21) . 11. Apparatus, according to claim 10, characterized in that it comprises metering means (26), associated with said mixing device (24), for metering the quantities of water, gelling substance and particles of abrasive material to form the abrasive material in suspension (21). 12. Apparatus, according to any one of the preceding claims, characterized in that it comprises: - a collection container (31) to collect the water and the abrasive material, delivered by the cutting head (10), and the waste material from the processing; - a recovery and recycling system (30) of the abrasive material configured for: - taking from said collection container (31) a moist mass of abrasive particles and waste material; - separating a moist mass of reusable abrasive particles from a moist mass of non-reusable abrasive particles and waste material; - imparting said moist mass of reusable abrasive particles into the source (20) of the abrasive material in suspension; 13. Apparatus according to claims 10 and 12, characterized in that said recovery and recycling system (30) is equipped with transport means for conveying said moist mass of reusable abrasive particles into the mixing device (24).