|Title of Invention||
RECOVERY AND REUSE OF ABRASIVE AND VEHICLE FROM WIRE SAW SPENT SLURRY
|Abstract||A simple, elegant, economical method for the recovery of abrasive and vehicle from the used slurry of w saw. The important feature of the method is to dilute the highly viscous used slurry with the same vehi from which the slurry was originally prepared to bring down the viscosity to the desired value. Separati this slurry into thick sludge and thin slurry. The thick sludge is dispersed in the same vehicle and made with fresh abrasive to prepare a slurry suitable for use in the wire saw. The thin slurry is subjected separation of the solid as a thick cake and a clear vehicle, which is reused for preparing the slurry aga Extracting the remaining vehicle from the thick cake using suitable procedures and discarding the soli containing the kerfs and other impurities with some small quantity of abrasive and vehicle as a waste.|
BACKGROUND OF THE INVENTION
Wire sawing is the most preferred technique for producing wafers and slices of hard materials like glass, quartz, sapphire, silicon, rare-earth magnets, piezoelectric ceramics, etc., because of its high production rates, low material loss and less mechanical damage on the cut surface. It is also capable of cutting bigger size ingots of 300 mm and more, which cannot be cut with the conventional inner diameter diamond saws. As a result of such advantages, a large number of wire saws are in operation throughout the world. The technique of wire sawing is therefore well known and would not be dealt with further in detail here.
One important factor in wire sawing is the requirement of consumables for sawing. The two most important consumables are the abrasive and the vehicle. As the abrasive has to be of specified particle size distribution, the cost of the abrasive is high! Similarly, the vehicle used is also expensive. If these consumables are not recovered and reused, the cost of wire sawing becomes high. Also, disposal of the spent slurry poses serious environmental problems. Various workers have therefore developed methods for recovery and reuse of the spent slurry. The results of such methods have not been completely satisfactory and do not approach the results obtained by the present invention.. The main reason for such unsatisfactory performance of tiiese patents is improper or not controlling the viscosity of the spent slurry before attempting to separate the abrasive and the vehicle from the kerfs and impurities.
In a typical wire sawing operation for silicon ingots slicing which would be described as a typical
application throughout, slurry is prepared by dispersing 100 kg of silicon carbide grains of suitable
grade silicon carbide in appropriate quantity of a vehicle. Such slurry is used for three sets of slicing
operations each set consisting of cutting two round ingots of 100 mm diameter and 400 mm length at
a time. Alternatively such a slurry is used for two sets of slicing operations of two numbers of 125
mm pseudo square single crystal ingots of silicon, After the three processes or two processes as the
case may be the slurry contains about 13 per cent to 18 per cent of silicon kerfs. The viscosity of the
slurry would have also become high. This can be seen clearly from Figure 1, which depicts the
increase in viscosity with time of cutting. The viscosity increases from about 200 cPs to about 600
cps. If this slurry is used for cutting further ingots, the cutting operations will not be satisfactory as
the silicon kerfs interfere with the cutting action of the abrasive grains. Hence, at such stage, the
slurry is discarded. The grains of abrasives themselves would not have been subjected to degradation
The specific gravity of silicon carbide is about 3.12 and that of silicon is 2.33. As the two have different sizes, silicon being too fine, it should be possible to separate the two by some physical processes. One process that has been reported is filtration using a filter element, which will pass fine silicon particles and retains the coarser silicon carbide (U.S.Patent 5,161,533). However, those who are familiar with the principles of filtration would know that such a process is not practical since the filter element is soon coated with the coarser particles even when agitated with ultrasonic waves and further passing of fine particle is prevented.
, Attempts have been made to bring out the separation of the two solids by exploiting the difference between the specific gravities of the two components by using centrifugal separation. Many patents like U.S.Patent 6,161,533, 6,113,473, Japanese Patentl 1172237 describe the recovery of spent slurry, using either a decanter centrifuge or a cyclone separator. In such cases, however, the separated silicon carbide would be contaminated with substantial concentration of silicon because of the high viscosity of the slurry. It has been found that if the slurry is directly centrifuged with out any dilution, the silicon concentration comes down by about half in the abrasive grains, whatever process parameters are used for the centrifugation. This is shown clearly in Figure 2. Realising such difficulties, some other patents have attempted to pre-treat the slurry by either dilution with water or volatile organic solvents like methanol e.g. U.S.Patent 6,001,265, or by heating the slurry to a higher temperature so that the viscosity is reduced e.g. U.S.Patent 6,231,628. However, in such cases, the recovered abrasive will be contaminated with water or solvent, which has to be removed by using evaporation techniques. Further, in recovering the vehicle, agglomerating agents have to be added before filtering the slurry. Then the recovered vehicle would also be contaminated with water or other solvent used for dilution and has to be subjected to evaporation or distillation to remove water or the solvent. Thus the process becomes complicated and expensive. Some patents describe recovery of only the abrasive and not the vehicle (U.S.Patent 6,113,473). This leads to limitations in operation as the recovered abrasive will still have substantial portion of the kerf, and the disposal of the vehicle contaminated with solids is a problem.
In any recovery operation, it is desirable to remove the kerf from the abrasive to the maximum extent possible so that the slurry prepared by re-dispersing such abrasive could be used for the same number of wire sawing operations as with fresh abrasive slurry; for example, three runs of 100mm silicon ingot pair. In case the recovered abrasive slurry has appreciable kerf which happens when the spent slurry is directly centrifuged as taught in the U.S. Patents 6,113,473, or 6,161,533, the slurry prepared using this recovered silicon carbide abrasive can be used for only two processes. Then, the spent slurry has to be subjected to more frequent recovery operations, which adds to cost, labour and loss of valuable material at each stage. Hence, there is a need for a simple recovery process, which does not have the shortcomings of the existing patents.
The present disclosure addresses the above problems and describes a simple process for the recovery of both the abrasive and the vehicle from spent wire saw slurry, to prepare recovered slurry whose properties are almost similar to fresh slurry. It has only a few steps, involves simple unit operations, uses standard equipment, does not (require any additive or chemical in processing and is economical.
DESCRIPTION OF THE FIGURES:
Fig. 1 shows the relation between the viscosity of the slurry and cutting time.
Fig. 2 shows the relation between the silicon content of the starting slurry and the silicon content of the recovered abrasive.
Fig. 3 shows the effect of dilution with vehicle on the silicon content of the recovered abrasive against the silicon content of spent slurry.
Fig. 4 shows the particle size distribution of fresh slurry of silicon carbide measured with Malvern Laser Particle size Analyser.
Fig. 5 shows the particle size distribution of spent slurry showing the peaks of silicon carbide and silicon kerfs.
Fig. 6 shows the particle size distribution of the centrifuged sludge indicating the peak due to silicon carbide and peak due to silicon kerfs.
Fig. 7 shows the particle size distribution of the slurry made up from recovered silicon carbide and recovered vehicle.
Fig. 8 shows the particle size distribution in the thin slurry from the centrifuge.
Fig. 9 is a flow diagram of the recovery process according to the present disclosure.
DETAILED DESCRIPTION OF THE INVENTION.
In the wire sawing operation, it is desirable to recover the spent slurry of wire sawing from the point of view of economy and environmental impact. In a typical wire saw, wire is wound on a set of four rollers to form a web. Two tables are provided to hold two ingots, which can be cut at the same time using the two horizontal portions of the web. Generally, 400mm long ingots can be cut, as the web length is about 420mm. The size and shape of the ingot can vary depending on the application of the cut wafer. In a typical photovoltaic application, two 100 mm round ingots are mounted one on each of the tables. Slurry of 100 kg of silicon carbide of FEPA 500 grit size is dispersed in appropriate quantity of a suitable vehicle and this slurry, after conditioning overnight by circulation and agitation is used for the wafering operation. The slurry is placed in a tank located close to the wire saw. It is pumped on to the top of the web by means of pumps provided in the tank at rates required by the process. The web is moved at high speed in too and fro motion. The tables are moved down to make the ingots press against the iweb. The abrasive grains are carried along the wire web by the vehicle and rub against the ingot. Due to the rubbing action, cuts are produced on the ingots. When the ingot passes out of the web, the entire ingot is converted into wafers. The detailed operation of the wire sawing is known to those well versed in the art. During the cutting process, fine particles of the material of the ingot (in the present case, silicon) get added to the slurry. Some particles of the wire material, which is generally high-tensile steel, also get added to the slurry but in much smaller proportions. The slurry returns to the slurry tank by means of collection means provided in the saw and is again pumped to the web. Thus the slurry is in constant circulation. Its temperature is maintained at a desired range by means of heat exchangers. After the cutting process is over, the cut ingots are removed, a new set of ingots is fixed in the tables and the cutting process is repeated. In this way three consequent runs can be made with this slurry .for 100 mm round ingots. The silicon content increases gradually and by the end of the third process, it would be around 13 to 15 per cent. If 125 mm pseudo square ingots were cut, (hen after two runs, the silicon content of the slurry would be about 14 to 18 percent. At this stage, the slurry would be no longer able to cut the ingots smoothly. Such spent slurry is replaced with fresh slurry and the wafering process is continued. It should be apparent that the wafering is essentially a batch operation and the machine has to be
stopped after each cutting process to remove the cut ingots and putting fresh ingots. Further, the • wire also gets used and the used wire spools have to be replaced with fresh wire spools. The changing of the spools and slurry are done together such that the down time of the machine is minimized.
The spent slurry is not able to cut further smoothly because of the presence of the large concentration of the kerfs. The silicon carbide abrasive itself would not have undergone noticeable degradation. This is clear from the study of the particle size distribution of the fresh and spent slurries given in Fig 4 and Fig. 5. In Fig. 4, the particle size distribution of the freshly prepared slurry is shown. A peak due to Silicon carbide abrasive is seen. In Fig. 5, the particle size distribution of the spent slurry is shown. Here, the original peak due to silicon carbide can be seen. The size distribution pattern is very similar to the one in Fig.4 for fresh slurry. However, there are additional peaks in the range of 0.1 to 2-micron, which are due to the presence of fine particles of silicon present as kerf in the spent slurry. If the kerfs were removed, the slurry would have a particle size distribution very close to Fig. 4,. Such a slurry could be reused for further wafering operation.
The process of removing the kerfe and recovering the slurry is described with reference to Fig. 9. The spent slurry from the wire saw 1 (one wire saw is indicated for ease of presentation; more saws can be present and the recovery process is not affected except for the quantities involved) is taken into a spent slurry-receiving tank 2. From here, the spent slurry is taken by means of a pump or other transfer means to the accelerated settler 3, which can be a decanter centrifuge or hydrocyclone. Here the slurry is subjected to separation of the abrasive as thick sludge 4. The kerfe along with the vehicle and other impurities are taken out as thin slurry 5. The thick sludge is made to fall directly into a mixing tank 6, which is provided with agitation. Also, required quantity of the vehicle is fed to tank 6 prior to the start of the operation and the vehicle is kept well stirred so mat when the ttiick sludge falls into the tank, it is immediately dispersed in the vehicle. The tliin slurry is taken for recovery of the vehicle and remaining abrasive. This step will be dealt with a little later.
i The spent slurry can be fed to the accelerated settler directly. However, then, the silicon content would be high—roughly, half of the silicon kerfs in the original slurry will pass into the thick slimy as shown in Fig 2. This is because the spent slurry has a high viscosity. Further, the kerfs are present in fine size of about 0.1 to 2.0 micron and hence would be sticking to the surfaces of the bigger grains of the abrasive. Hence, when the abrasive is separated, some silicon is also separated along both by dragging due to high viscosity and by adherence due to surface tension forces. For economic recovery, however, the silicon content should be as low as possible. In this disclosure, this is achieved by adding the same vehicle used for dispersing the abrasive to the spent slurry to dilute it and to reduce the viscosity. The effect of addition of the vehicle to the spent slurry is well illustrated in Fig. 3 where silicon content of the thick sludge obtained from the settler is plotted against the volume of vehicle added to the. spent slurry. It may be noted that the silicon content comes down with addition of the vehicle. Though in principle, a large volume of the vehicle could be added to the spent slurry to bring down the silicon content to the lowest value, it has been observed by practice that this is not necessary. It is desirable to have a certain minimum concentration of kerf of about 2 to 3 percent in the recovered slurry. With such slurry, it has been found that tire quality of the cut is better than with fresh slurry. Based on this finding, it is recommended that the addition of the vehicle to the spent slurry be restricted to such a quantity, which will result in the thick sludge containing about 3 to 4 per cent silicon kerf.
The success ofthis procedure hinges very much on the possibility of recovery of the vehicle. If the vehicle were not recovered, this procedure would not be successful since adding vehicle to the spent slurry would entail additional cost. The present disclosure has the advantage that it describes an efficient method of recovery of the vehicle and reuse for it,
The advantage of dilution of the spent slurry with the vehicle itself in contrast to water or other solvent proposed in earlier patents is that the slurry recovered is not contaminated with any other liquid like water or solvent and hence can be straightaway used for wafering. Further, the recovered vehicle can also be used straightaway for the preparation of the slurry without requiring to be purified by evaporation or distillation. This has the added advantage that there is no necessity for heating the slurry to bring down the viscosity of the slurry to improve the efficiency of separation.
Required quantity of vehicle is added to the spent slurry in tank 2, which is provided with a rnixing.arrangement. The diluted slurry is then fed to the accelerated settler. Though a hydrocyclone can also be used, it has been found that a horizontal decanter centrifuge would be most suitable for the separation of the abrasive from the kerf. The main advantage of such a centrifuge is that it has high capacity, and can discharge consistently thick sludge of the abrasive and thin slurry rich in the vehicle. The fear of wear out of the centrifuge parts, particularly the conveyor, is minimized, as the slurry is still viscous enough to minimize such wear and tear. It has been observed that the wear and tear on the centrifuge parts is minimum even after prolonged use of the equipment for the separation.
What happens during centrifugation can be explained by a study of the particle size distribution of the various streams involved in the process. Figure 5 shows the particle size distribution in the spent slurry clearly indicating the presence of the silicon carbide peak and the kerfs as two shallow peaks. Figure 6 shows the particle size distribution in the centrifuged sludge, Here, the silicon carbide peak has become sharp and intense. The peaks due to kerfs are very much reduced in size, indicating that their concentration is much lower than in the spent slurry. Fig. 7 shows the particle size distribution in the made up slurry using the recovered sludge, which is similar to fig. 6 as expected. For comparison, the particle size distribution of the thin slurry is illustrated in fig. 8. Here, the peaks due to kerfs have attained prominence. Still the peak due to silicon carbide is seen.
The thin slurry can be subjected to a solid-liquid separation using many known techniques. However, investigation has revealed that this is best-done using a filter press. This is a very simple device but gives consistently clear vehicle without any difficulty. The thin slurry is pumped into the well-assembled filter press using a suitable pump at a pressure needed for filtration at a reasonable rate. The filter element can be obtained from regular commercial sources. Elements made of cotton textiles or synthetic materials could be used. It has been observed that a combination of a textile cloth overlapped by a synthetic, particularly polypropylene filter cloth, is advantageous. However, it is also possible to use a single filter element and still get good and consistent results. The material of the filter press can be polypropylene. However, for withstanding higher temperatures, which are required in further operations, cast iron or oilier metallic material could be used with advantage. The size of the filter press and the number of plates used in the press are decided by the quantity of the slurry to be handled at a time. To reduce labour, automated filter presses could be used. Alternatively, when the quantity of the slurry handled is high as happens when there are many wire
saws in operation, a vacuum drum filter can be used. This has the advantage of continuous operation and possibility of washing the cake with a solvent to recover further vehicle from the cake.
In - figure 6, solids separator 7 is fed with the thin slurry. The clear filtered vehicle is taken to dilution tank 2, slimy preparation tank 6 and/oi to the make-up tank 8 as required. Some times, during the initial stages of filtration, particularly when new filter elements are used, the filtrate may not be fully clarified. Such filtrate could be advantageously used for dilution of the spent slurry. The 'quality of the filtrate improves within a short time to the desired clarity. It has been found that the filter elements last long and require changes at long intervals.
As some quantity of the abrasive and vehicle are lost in the filter cake, required quantity of fresh vehicle and silicon carbide are added to the slurry preparation tank from the respective holding tanks 8 and 9 so that the slurry is brought to the proper consistency, which is well known to Those familiar with the art. Testing of prepared slurry is also conducted by methods, which are known to those familiar with the art. The slurry prepared thus contains required abrasive and vehicle and also a small quantity of the kerf, which will give ensure better cutting performance of the slurry in the wire sawing operation, as explained earlier.
It is possible to recover the abrasive at more than 90 % level by suitably adjusting the process parameters of the centrifuge. However, it has been found by experience that it is advantageous to recover about 2/3rds of the abrasive from the spent slurry and make up with about l/3rd of fresh abrasive. By doing this, the surface quality of the wafer is ensured to be very good.
The solid retained in the filter contains un-recovered abrasive along with the kerf and other impurities. This cake also retains considerable quantity of the vehicle. There'is no limitation for the recovery of the vehicle. In fact, it is advantageous to recover as much vehicle as possible. In order to achieve this, the cake in the filter press, after completion of the regular filtration, is pressurized with compressed air. This process allows recovery of a good amount of the retained vehicle. The vehicle thus recovered can be combined with the filtrate and used for make up and other purposes. For further recovery of the vehicle from the remaining cake, steam is passed through the cake, provided the vehicle is soluble in water. (This would not work very well with vehicles that are based on organic lubricants.) This results in steam condensing inside the pores of the cake and extracting the vehicle along with condensed water. Steam can be passed till such time that the condensate does not contain appreciable quantity of the vehicle. The condensate thus collected is evaporated preferably in a vacuum evaporator to drive away the moisture and the dry vehicle left in the retort is taken out for further use. By using these techniques, more than 85 per cent of the vehicle could be recovered.
It is possible to recover the abrasive remaining in the filtered cake. For this, the cake is dispersed in water (water recovered from the vacuum evaporation process can be used for this purpose) in a cake dispersion tank 9 so that thin slurry is made. This slurry is then passed through two hydrocyclones properly designed for separation of the heavy abrasive particles from the fine silicon and steel kerf. The abrasive comes out as the underflow of the first hydrocyclone. The overflow of the first cyclone is collected in the collection tank. The underflow from the first hydrocyclone is again passed through another hydrocyclone. The underflow of the second hydrocyclone contains abrasive as easily settling slurry. This slurry is allowed to settle, the supernatant water is decanted out and the
The thin slurry coming out of the centrifuge was collected in a tank. It was taken for filtration in the filter press. Filtration was carried out for about 6-7 hours. Total liquid collected from the direct filtration was about 320 litres. Then air was passed through the press for about 5 hours and about 125 litres of liquid was further collected. At this stage, the collection efficiency was about 67 per cent. Further, steam was passed through the filter press for about 8 hours and about 150 litres of condensate was- collected. On evaporation of the water from this liquid, about 50 litres of vehicle was further collected. This was also taken for regular processing. The overall efficiency of the recovery was about 85 per cent taking into account, the vehicle that was already present in the thick slurry.
The solid cake was dispersed in water in an agitated mixer to a dilution of about 10 per cent solids and was passed through two hydrocyclones, which were rubber-lined. The underflow of the first hydrocyclone contained most of the abrasive along with about 3 to 5 per cent of silicon. This was passed through the second hydrocyclone and the underflow collected in a shallow tank. The supernatant water was removed and the solid was dried in a oven at about 150 ~ 200 °C overnight. The dried solid had a silicon concentration of less than 1 per cent,
Thus,, it can be seen that with the present disclosure, the abrasive and vehicle from spent wire saw slurry can be recovered with high efficiency using only a few steps and simple equipment.
It is understood that the procedure described above has been made with water-soluble vehicle as example; the same can be used with organic oil based vehicles also with equal results. However, steam leaching of filter cake and recovery of abrasive from tire solid cake may be difficult with oil based slurries.
WE CLAIM .-
1. A method for recovery snd reuse of abrasive and vehicle from wire
saw spent slurry comprising of steps and sequence as herein :-
slurry using en accelereted settler such that the said sludge comprising of bulk of abrasive and said thin slurry comprising of bulk of kerf, vehicle some abrasive and other Impurities.
(c) reusing the said sludge by preparing fresh slurry comprising of
(c 1) dispersing the said sludge In the said vehicle to adjust viscosity.
(c 2} adding make-up abrasive.
(d) filtering the thin slurry comprising of sub-steps :-
(d 1) filtering wlth a filter device to get bulk of said vehicle as
dear fittrate, residual cake containing abrasive, kerf and other Impurities.
(d 2} further recovery of vehicle from the residual cake by passing compressed air to get additional extract of vehicle.
(d 3} further recovery of vehicle comprising of sub steps :-
( I. passing steam through residual cake in the filter press to form a condensate. II. Evaporation of condensate to yield more vehicle.
(d 4} recovery of further abrasive from the said cake comprising of sub-steps :-
i, dispersing the said cake In water.
II. further hydro-cyclone separation In two stages.
2. A method for recovery and reuse of abrasive and vehicle from wire saw spent slurry, as claimed in claim 1 wherein In step (a) the spent slurry viscosity is reduced by the addition of the same vehicle as used in the preparation of fresh slurry.
3. A Method for recovery and reuse of abrasive and vehicle from wire saw spent slurry, as claimed In claim 1 wherein in step (a) the viscosity of spent slurry within the range of 650 to 1100 cp.
4. A method for recovery and reuse of abrasive and vehicle from wire saw spent slurry, as claimed in claim 1 wherein step (a) the spent slurry viscosity Is reduced to a level of 165 cp approximately.
5. A method for recovery and reuse of abrasive and vehicle from wire saw spent slurry, as claimed In claim 1 wherein step (a) Is conducted by adding the vehicle to the spent slurry.
6. A method for recovery and reuse of abrasive and vehicle from wife saw spent slurry, as claimed In claim 5 wherein the said vehicle Is an organic oil or a water compatible liquid.
7. A method for recovery and reuse of abrasive and vehicle from wire saw spent slurry, as claimed in claim 5 wherein the said vehicle Is poly ethylene glycol.
8. A method for recovery and reuse of abrasive and vehicle from wire saw spent slurry, as claimed in claim 1 wherein step (a) Is conducted under constant mixing.
9. A method for recovery and reuse of abrasive and vehicle from wire saw spent slurry, as claimed in claim 1 wherein step (b) Is carried out with accelerated settler.
10. A method for recovery end reuse of abrasive and vehicle from wire saw spent slurry, as claimed In claim 9 wherein the accelerated settler means a decanter centrifuge or a hydro cyclone.
11. A method for recovery and reuse of abrasive and vehicle from wire saw spent slurry, as claimed In claim 1 wherein in step (b) the spent slurry is separated such that sludge is comprising of mainly abrasive and
sew spent slurry, as claimed (n claim 1 wherein tn step (b) wherein the said sludge being reused in the preparation of fresh slurry.
14. A method for recovery and reuse of abrasive and vehicle from wire saw spent slurry, as claimed In claim 1 wherein In step (b) after separation the sludge Is directly fed Into the slurry preparation tank.
15. A method for recovery and reuse of abrasive and v«hicia from wire
saw spent slurry, as claimed In claim 14 wherein the said slurry
preparation tank is provided with agitation.
16. A method for recovery and reuse of abrasive and vehicle from wire
saw spent slurry, as claimed in claim 1 wherein In step (c) the required
quantity of fresh silicon carbide and vehicle are added to slurry
preparation tank such that slurry so prepared contains required abrasive
and vehicle and also a small quantity of kerf which enhances cutting
performance of slurry.
17. A method for recovery and reuse of abrasive and vehicle from wire
saw spent slurry, as claimed in claim 1 wherein (n step (d) wherein bulk
of vehicle Is recovered by filtration.
19. A method for recovery ond reuse of abrasive and vehicle from wire saw spent slurry, as claimed in claim 1 wherein In step (dl) wherein the
filter element is cotton textile or synttiettc, or a combination of textile overlapped by synthetic element and filter element Is made of cast Iron.
20. A method for recovery and reuse of abrasive and vehicle from wire saw spent slurry, as claimed In claim 18 wherein the synthetic element means polypropylene filter cloth.
21. A method for recovery and reuse of abrasive and vehicle from wire saw spent slurry, as claimed In claim 1 wherein in step (dl) said filter vehicle being reused In spent slurry dilution tanic, slurry preparation tank and or in make-up tank.
22. A method for recovery and reuse of abrasive and vehicle from wire saw spent slurry, as claimed In claim 1 wherein In step (di) said filter vehicle when not fully clarified being used In spent slurry dilution tankfor diluting the spent slurry.
23. A method for recovery and reuse of abrasive and vehicle from wire sawspent slurry, as claimed in claim 1 wherein In step (dl) the said filter vehicle when not fully clarified being recycled repetitively until fully classified.
24. A method for recovry and reuse of abrastva and vehicle from wire saw spent slurry, as claimed In claim 1 wherein In step (d3) evaporation means vacuum evaporation.
25. A mettiod for recovery and reuse of abrasive and vehicle from wire saw spent slurry, as claimed In claim 1 wherein In step (d4) the cake Is dispersed In water In a cake dispersion tank to form a thin slurry.
26. A method for recovery and reuse of abrasive and vehicle from wire saw spent slurry, as claimed In claim 1 wherein In step (d4) the separation means hydro cyclone separation including the following sub-steps.
a. the thin slurry Is passed through first hydro cyclone.
b. abrasive Is collected as underflow.
c. overflow Is collected in collection tank.
d. Passing the first stage underflow abrasive through thesecond
e. Underflow of second hydro cyclone containing easily settling
f. The slurry Is allowed to settle.
g. Supernatant water Is decanted out,
h. Wet abrasive is dried In an oven.
I. Dried abrasive Is free flowing powder.
27. A method for recovery and reuse of abrasive and vehicle from wire saw spent slurry, as ctatmed tn claim 26 wherein the recovered dried abrasive being used for refractory manufacture.
28. A method for recovery and reuse of abrasive and vehicle from wire saw spent slurry, as claimed In claim 26 wherein the recovered dried abrasive being reused in sawing.
29. A method for recovery and reuse of abrasive and vehicle from wire saw spent slurry, as claimed in claim 26 wherein the overflow from the two hydro cyclones Is filtered to recover clear water which Is reused for preparing slurry.
30. A method for recovery and reuse of abrasive and vehicle from wire saw spent slurry, as claimed In claim 26 wherein the solid content is discarded as waste.
31. A method for recovery and reuse of abrasive and vehicle from wire saw spent slurry, as claimed In claim 26 wherein In step (b) underflow of first hydro cyclone comprises most of abrasive olong with 3-5 % of silicon.
32. A method for recovery and reuse of abrasive and vehicle from wire saw spent slurry, as claimed In claim 26 wherein In step (e) the underflow from second hydro cyclone is being collected in a shallow tank.
33. A method for recovery and reuse of abrasive and vehicle from wire saw spent slurry, as claimed In claim 26 wherein In step (h) wherein the wet abrasive being dried in an oven at about 150-200 degree centigrade for 12-15 hours.
34. A method for recovery and reuse of abrasive and vehicle from wire saw spent slurry, as claimed in claim 26 wherein in step (i) the said dried abrasive having the silicon concentration of less than 1%.
35. A method for recovery and reuse of abrasive and vehicle from wire saw spent slurry, as claimed in claim 1 wherein the vehicle being water soluble.
36. A method for recovery and reuse of abrasive and vehicle from wire saw spent slurry, as claimed In claim 1 wherein the vehicle being organic oil based vehicle, the recovery process is the same except for steam teaching process and recovery of abrasive from solid cake.
37. A method for recovery and reuse of abrasive and vehicle from wire
saw spent siurry, and as substantially described in the complete
38, A method for recovery and reuse of abrasive and vehicle from wire
saw spent slurry, and as Illustrated In the accompanying drawings.
|Indian Patent Application Number||973/MAS/2001|
|PG Journal Number||30/2009|
|Date of Filing||03-Dec-2001|
|Name of Patentee||M/S. CHEMPLAST SANMAR LIMITED|
|Applicant Address||9, CATHEDRAL ROAD, CHENNAI 600 086|
|PCT International Classification Number||N/A|
|PCT International Application Number||N/A|
|PCT International Filing date|