Method for recycling abrasive used for high pressure waterjet cutting from cutting sludge and an equipment for application of this method

Abstract

The recycling unit is the technology for the continuously controlled process of recycling and drying screened abrasive during which the intensity of batching of the abrasive is regulated according to the temperature in the drying oven. The control system continuously measures the current temperature and on the basis of this data it decides on switching the heating elements on or off or turning the batching process on or off; this control is based on the temperature hysteresis and on changing the intensity of batching of abrasive, which is subject to switching the heating elements or turning the batching process on or off.

Claims

1. A method for recycling abrasive material used for high pressure waterjet cutting from cutting sludge is characterised in that the cutting sludge is conveyed to a vibrating separator separating smaller and larger particles from the abrasive which is then deposited into a water-permeable container (17); after excess water is displaced, a wet screened recycled abrasive (A) is put into a storage tank (1) for wet screened recycled abrasive, conveyed by a screw conveyor (3) to a drying oven (4) which is heated by a heating elements (6), aerated by a heated air (E); temperature in the oven is regulated by switching off and on the heating elements (6) and a intensity of batching of the wet screened recycled abrasive (A) conveyed by the screw conveyor (3); the particles of dry abrasive (C) are conveyed through a outlet (B) for dry recycled abrasive from the drying oven (4) to a output vibrating separator (8) from which a dried abrasive material (C) is passed through the screen and put into a storage container/bulk bag (9) for the dry recycled abrasive (C).

2. The method for recycling abrasive material used for high pressure waterjet cutting from cutting sludge according to claim 1 is characterised in that the temperature in the oven (4) is regulated to stay in the range 130 C. to 170 C.

3. The method for recycling abrasive material used for high pressure waterjet cutting from cutting sludge according to claim 1 is characterised in that the heating elements are switched off when the temperature in the oven (4) exceeds 160 C. and the intensity of batching of wet screened abrasive (A) is at the same time increased by a specified step.

4. The method for recycling abrasive material used for high pressure waterjet cutting from cutting sludge according to claim 3 is characterised in that the heating elements are switched on when the temperature in the oven (4) drops below 140 C. and the intensity of batching of wet screened abrasive (A) is at the same time reduced by a specified step.

5. The method for recycling abrasive material used for high pressure waterjet cutting from cutting sludge according to claim 3 is characterised in that the specified step is 5% of the actual batching intensity.

6. The method for recycling abrasive material used for high pressure waterjet cutting from cutting sludge according to claim 1 is characterised in that the drying oven (4) is connected to the fine dust extractor (13) which extracted the residual dust (G).

7. The method for recycling abrasive material used for high pressure waterjet cutting from cutting sludge according to claim 1 is characterised in that the displaced waste water (F) was removed from the storage tank (1) by drainage (12).

8. The method for recycling abrasive material used for high pressure waterjet cutting from cutting sludge according to claim 1 is characterised in that the wet screened abrasive in the storage tank (1) was raked mechanically by the vault disrupter (2).

9. The drying unit for the recycled material for recycling abrasive material used for high pressure waterjet cutting from cutting sludge is characterised in that it consists of the storage tank (1) for wet abrasive (A) with the screw conveyor (3) connecting it to the drying oven (4), which contains at least one heating element (6), at least one temperature sensor (5), and in that it is provided with the inlet for bringing clean air (E) from the drying blower (7), the outlet (B) for dry recycled materials (C), which is connected to the vibrating separator (8), and the space under the mesh screen of the vibrating separator (8), which is connected to the container/bulk bag (9) for the dry screened recycled abrasive (C).

10. The drying unit for the recycled material for recycling abrasive material used for high pressure waterjet cutting from cutting sludge according to claim 9 is characterised in that the drying oven (4) is connected to the fine dust extractor (13) separating the dry fine dust (G) and the clean air (E).

11. The drying unit according to claim 9 is characterised in that the storage tank (1) is provided with vault disrupter (2) to remove the displaced waste water (F).

12. The drying unit according to claim 9 is characterised in that the storage tank (1) is provided with drainage (12).

13. The drying unit according to claim 9 is characterised in that the space above the mesh screen of the vibrating separator (8), which is connected to the container (10) for the dry waste (D).

14. The recycling unit for recycling abrasive material used for high pressure waterjet cutting from cutting sludge is characterised in that it consists of the flat vibrating separator (16) with a mesh screen with 3-4 mm openings and a mesh screen with 0.5-1 mm openings and the inlet for cutting sludge, and in that the space above the mesh screen with 0.5-1 mm openings of the flat vibrating separator (16) is connected to the container/bulk bag (17) for the wet screened recycled abrasive (A) and the space under the mesh screen with 0.5-1 mm openings of the flat vibrating separator (16) is used for discharging water (I) with fine waste.

Description

LIST OF FIGURES ON THE DRAWINGS

[0054] FIG. 1 Visualisation of the drying system, side view, in section

[0055] FIG. 2 Visualisation of the drying system, front view, in section

[0056] FIG. 3 Schematic diagram of the drying system

[0057] FIG. 4 Schematic diagram of the sludge separating system

[0058] FIG. 5 Schematic diagram of the separating process

[0059] FIG. 6 Table showing capacity of the drying system

[0060] FIG. 7 Graph showing capacity of the drying system

[0061] FIG. 8 Graph showing temperature in the drying oven in relation to the period of operation

EXAMPLES OF EXECUTION OF THE INVENTION

Example 1

[0062] The process of separating cutting sludge (FIGS. 4 and 5) is as follows:

[0063] From the trap 13 on the cutting table, the cutting sludge H is removed by means of a pumping unit in the sludge separating unit 14 to a screening unit 15 which consists of a vibrating separator 16 with steel screens or screens made from other materials of suitable mesh size depending on the required size of abrasive fraction which we want to obtain. The screening unit 15 will separate the cutting sludge H into the following groups: [0064] a) the usable abrasive to be reused in the cutting process, [0065] b) the mechanical particles of the size larger than the particles of the usable abrasive, [0066] c) the mechanical particles of the size smaller than the particles of the usable abrasive, [0067] d) dirty, turbid water.

[0068] This process is not energy demanding, it is mainly carried out simultaneously with the process of high pressure waterjet cutting. The reusable abrasive A is from the screening unit 15 conveyed into a suitable container, for example a bulk bag; the materials with different size of particles are taken to the other storage tanks depending on the type of their further use (for example, the material with smaller particles can be used for other purposes than abrasive waterjet cutting) or they are disposed of as waste materials.

[0069] After obtaining sufficient quantity, preferably about 1 ton, of reusable wet abrasive A from the screening unit 15 it is possible to start the process of drying this wet abrasive.

Example 2

Drying Unit for Recycled Material in Static Condition

[0070] The drying unit for recycled material consisted of the storage tank 1 for wet abrasive with the screw conveyor 3 connecting it to the drying oven 4, the drying blower 7, the fine dust extractor 13 the vibrating separator 8, the bulk bag 2 for the dry screened recycled abrasive C and the container 10 for dry coarse waste D.

[0071] The screw conveyor 3 went into the drying oven 4 which contained electric heating elements 6, inlet for air from the drying blower 7, pressure sensor 11, temperature sensors 5, outlet for dry recycled material and outlet into the fine dust extractor 13 which separated the dry fine dust G and the clean air E.

[0072] The drying oven 4 was aerated with pre-heated air E brought in by the drying blower 7, which kept the abrasive A afloat thereby speeding up the drying process. The same stream of air E was conveying the particles of dry screened recycled abrasive C through the outlet B for dry recycled abrasive from the drying oven 4 to the output vibrating separator 8 from which the dried abrasive material was passing through the screen and falling into the storage tank 9 which was a 1000 kg bulk bag; any larger particles D formed in the drying oven 4 due to high temperatures, which may cause sintering together the particles of dry material, were conveyed into a small container 10 for the waste material. The drying oven 4 was also connected to the fine dust extractor 13 which was extracting the residual dust G from the screened recycled abrasive thereby ensuring the dust-free operation of the drying unit. The storage tank 1 for the screened recycled material was provided with the vault disrupter 2 and the drainage 12 to remove the displaced waste water F.

Example 3

Drying Process in the Drying Unit for the Recycled Abrasive

[0073] The storage tank for wet abrasive 1 was filled with the recycled abrasive, specifically the almandine garnet of Australian origin, weight 1000 kg, particles size 150-300 m, 80 mesh.

1. The drying process was started, specifically the drying blower 7 of the drying oven 4 the transport blower, the output vibrating separator 8 and the heating elements 5. The system waited until the starting operating temperature, which was set to 150 C., was reached. When the set temperature was reached, the system started batching abrasive at the minimum specified intensity which was 0.4 kg per minute. When the temperature reached 160 C. the heating elements were switched off.

[0074] After introducing the first batches of abrasive, the temperature in the drying oven started decreasing; when the temperature dropped to 155 C., the heating elements were switched on again and when the temperature dropped again to 140 C., the batching of abrasive was turned off. The temperature then dropped to 138 C. As the abrasive was aerated and continued to warm up, it gradually started drying and the temperature in the oven started to rise and after 5 minutes the temperature rose to 170 C. As soon as the temperature rose to 150 C., the batching of abrasive was turned on again. When the temperature rose again to 160 C., the heating elements were switched off again.

2. After switching the heating elements on for the first time the adjusting system was turned on. This system adjusts the speed of the screw conveyor 3, thereby adjusting the intensity of batching. As the temperature in the drying oven exceeded the specified limit, i.e. 160 C., heating elements were switched off and the intensity of batching was increased by a specified percentage step, that is, by 5%. As soon as the temperature in the drying oven dropped below a specified level of 140 C., the batching process was turned off and the intensity of batching was reduced by a specified 5% of the actual batching input; when the temperature again rose above 150 C., the batching process was turned on.

[0075] As the system started the adjusting process only after the heating elements were switched off for the first time, it removed the transient stage when the temperature in the oven rises to over 160 C. despite continued adding of the very wet abrasive material (due to the presence of old dry abrasive). Without this step, the system would increase the intensity of batching too soon.

3. During the next operation such as turning off the heating elements or turning off the batching process, the system adjusted the intensity of batching according to the last operation carried out:

TABLE-US-00002 Actual operation Adjusting speed of batching Switching off Turning off Last operation heating elements batching operation Switching off heating +specified operation last change/2 elements Turning of batching operation +last change/2 specified operation

[0076] Specifically, if: [0077] a) the heating elements were switched off due to the increase of temperature to over 160 C., the intensity of batching was increased by 5% to 30.6 kg/hour, and [0078] b) the heating elements were switched off next time due to the increase of temperature to over 160 C., the intensity of batching was increased by 5% of the value applied in step a) to 31.9 kg/hour, [0079] c) the batching process was turned off due to the decrease of temperature, the intensity of batching was decreased by half of the value applied in step b) to 31.1 kg/hour, and [0080] d) the batching process was turned off next time due to the decrease of temperature, the intensity of batching was decreased by 5% of the value applied in the last batching process to 29.6 kg/hour.

[0081] In general, the system was set up as follows:

if
the heating elements are switched off due to the increase of temperature, the intensity of batching will be increased by 5%, and in the next step the heating elements are switched off next time, the intensity of batching will be increased by 5% of the value applied in step a) above;
or, if
the heating elements are switched off due to the increase of temperature, the intensity of batching will be increased by 5%, of the value applied last time, and in the next step the batching process is turned off due to the decrease of temperature, the intensity of batching will be decreased by half of the 5% value applied in previous step.
4. As in the case of the continuous repeated adjustments of the intensity of batching this value gradually decreased to zero, there had been specified a limit (0.5%) below which any adjustment becomes inconsequential. At the point when the system was required to adjust the intensity of batching due to reaching the limit below which the adjustment becomes inconsequential, the whole adjusting process was restarted with the specified percentage step (5%) applied accordingly.

Description of Operation of the Drying Unit

[0082] The primary requirement for operating the drying unit is to regulate batching of the abrasive according to the temperature in the drying oven. The control system continuously measures the current temperature and on the basis of this data it decides on the following: [0083] switching the heating elements on or offthis control is based on the temperature hysteresis, [0084] turning the batching process on or offthis control is based on the temperature hysteresis, [0085] changing the intensity of batching of abrasivesubject to switching the heating elements or turning the batching process on or off.

Example 4

[0086] Cutting sludge H was pumped from the cutting table 20 onto a flat vibrating separator 16 which separated smaller and larger particles from the 80 mesh wet screened abrasive. From the vibrating separator 16 this wet abrasive 20 was falling into the textile bulk bag 17. When this bulk bag 17 was filled with the wet abrasive A, it was hung in the open air for 3 days for the excess water to be displaced or trickle off. The content of this bag was then poured into the storage tank 1 for the wet recycled abrasive A in the drying unit.

Example 5

[0087] Cutting sludge H was removed from the cutting table 20 and put into the storage tank 18 for cutting sludge H. After filling the storage tank 18 the cutting sludge H was conveyed by the screw conveyor onto the flat vibrating separator 16 which separated the 50 mesh wet screened abrasive into two fractions: the undersize fraction, which consisted of water I with fine waste and the oversize fraction, which contained the wet recycled abrasive A. The wet recycled abrasive A was conveyed into the bulk bag 17 and water I with fine waste was taken into the bulk bag 22. The content of this bag 7, which was the wet recycled abrasive A, was then poured into the storage tank 1 for the wet recycled abrasive A in the drying unit.

Example 6

[0088] The drying unit for recycled material consisted of the storage tank 1 for wet abrasive A with the screw conveyor 3 connecting it to the drying oven 4, the drying blower 2, the fine dust extractor 13 the vibrating separator 8, the bulk bag 9 for the dry screened recycled abrasive C and the container 10 for dry coarse waste D.

[0089] The screw conveyor 3 went into the drying oven 4 which contained electric heating elements 6, inlet for air from the drying blower 7, pressure sensor 11, temperature sensors 5, outlet for dry recycled material and outlet into the fine dust extractor 13 which separated the dry fine dust G and the clean air E.

[0090] The drying process was started, specifically the drying blower 7 of the drying oven 4, the transport blower, the output vibrating separator 8 and the heating elements 5. The system waited until the starting operating temperature, which was set to 150 C., was reached. When the set temperature was reached, the system started batching abrasive A into the drying oven 4 using the screw conveyor 3 at the minimum specified intensity, which was 0.4 kg per minute.

[0091] When the temperature reached 160 C. the heating elements were switched off. After introducing the first batches of abrasive, the temperature in the drying oven started decreasing; when the temperature dropped to 155 C., the heating elements were switched on again and when the temperature dropped again to 140 C., the batching of abrasive was turned off. The temperature then dropped to 138 C. As the abrasive was aerated and continued to warm up, it gradually started drying and the temperature in the oven started to rise and after 5 minutes the temperature rose again to 170 C. As soon as the temperature rose to 150 C., the batching of abrasive was turned on again. When the temperature rose again to 160 C., the heating elements were switched off again. The drying oven 4 was aerated with pre-heated air E brought in by the drying blower 7, which kept the abrasive A afloat thereby speeding up the drying process.

[0092] After switching the heating elements on for the first time the adjusting system was turned on. This system adjusts the speed of the screw conveyor 3, thereby adjusting the intensity of batching. As the temperature in the drying oven exceeded the specified limit, i.e. 160 C., heating elements were switched off and the intensity of batching was increased by a specified percentage step, that is, by 5%. As soon as the temperature in the drying oven dropped below a specified level of 140 C., the batching process was turned off and the intensity of batching was reduced by a specified 5% of the actual batching input; when the temperature again rose above 150 C., the batching process was turned on

[0093] As the system started the adjusting process only after the heating elements were switched off for the first time, it removed the transient stage when the temperature in the oven rises to over 160 C. despite continued adding of the very wet abrasive material (due to the presence of old dry abrasive). Without this step, the system would increase the intensity of batching too soon. During the next operation such as turning off the heating elements or turning off the batching process, the system adjusted the intensity of batching according to the last operation carried out:

TABLE-US-00003 Actual operation Adjusting speed of batching Switching off Turning off Last operation heating elements batching operation Switching off heating +specified operation last change/2 elements Turning of batching operation +last change/2 specified operation
The stream of air E was conveying the particles of dry screened recycled abrasive C through the outlet B for dry recycled abrasive from the drying oven 4 to the output vibrating separator 8 from which the dried abrasive material was passed through the screen and fell into the storage tank 9 which was a 1000 kg bulk bag; any larger particles D formed in the drying oven 4 due to high temperatures, which may cause sintering together the particles of dry material, were conveyed into a small container 10 for the waste material. The drying oven 4 was also connected to the fine dust extractor 13 which was extracting the residual dust G from the screened recycled abrasive thereby ensuring the dust-free operation of the drying unit. The storage tank 1 for the screened recycled material was provided with the vault disrupter 2 and the drainage 12 to remove the displaced waste water F.

LIST OF REFERENCE SYMBOLS

[0094] A. Wet screened recycled abrasive [0095] B. Output of dry recycled abrasive from the drying oven [0096] C. Dry screened recycled abrasive [0097] D. Dry coarse waste [0098] E. Air [0099] F. Waste water [0100] G. Dry fine waste [0101] H. Cutting sludge [0102] I. Water with fine waste [0103] J. Clean water (for rinsing) [0104] 1. Storage tank for wet screened recycled abrasive [0105] 2. Vault disrupter [0106] 3. Screw conveyor [0107] 4. Drying oven [0108] 5. Temperature sensor [0109] 6. Heating elements [0110] 7. Drying blower [0111] 8. Output vibrating separator [0112] 9. Bulk bag for dry screened recycled abrasive [0113] 10. Container for dry coarse waste [0114] 11. Pressure sensor [0115] 12. Storage tank drainage [0116] 13. Fine dust extractor (with trap) [0117] 14. Sludge separating system for the cutting table [0118] 15. Screening unit [0119] 16. Vibrating separator [0120] 17. Bulk bag for wet screened recycled abrasive [0121] 18. Storage tank for cutting sludge [0122] 19. Vertical screw conveyor [0123] 20. Cutting table [0124] 21. Pump [0125] 22. Bulk bag for wet fine waste

INDUSTRIAL APPLICABILITY

[0126] High pressure waterjet cutting, accessories for CNC machines for the high pressure waterjet cutting. Recycling the abrasive materials used for the high pressure waterjet cutting.