Title of Invention

"AN IMPROVED AIR JET SIEVE"

Abstract

The present invention relates to an improved air jet sieve. The device of the present invention helps in screening finest, lightest materials and those materials difficult to screen. With the help of the device of this invention it is possible to deagglomerate the feed material, cleaning of the screen mesh and an optimum discharge of fine product. Use of the device of this invention helps to constantly maintain and adjust various test parameters such as testing time, jet speed, volumetric gas flow rate, jet surface area. The device is based on the principle of pneumatic screening or aerodynamic sifting in which the material to be sifted is moved by air currents only. A screening chamber, enclosed under a solid housing and framed support employs two conventional analysis screens of about 200 mm diameter, with screen inserts of stainless steel construction. The screens are placed intact one above the other by means of rubber gaskets warped around the sieve drum and sealing rings, which ensure the prevention of entry of foreign air during sieving. The test material is placed on the lower screen. The test material to be taken can range from 5 to 50g. The entire transport of air comes out of two nozzles that are located one above a screen and one beneath the other screen.

Full Text

The present invention relates to an improved air jet sieve. The device of the present invention helps in screening finest, lightest materials and those materials difficult to screen. With the help of the device of this invention it is possible to deagglomerate the feed material, cleaning of the screen mesh and an optimum discharge of fine product. Use of the device of this invention helps to constantly maintain and adjust various test parameters such as testing time, jet speed, volumetric gas flow rate, jet surface area. The device is useful in simple, reliable determination and evaluation of mass proportions. The device is easy to use and operated reliably with a controlled influence of the screening process. In any food processing or mechanical processing technology particle size distribution is one of the most important parameters in the characterization of solids. Many solid food and pharmaceutical powders contain fine particles that are difficult to characterize. Pneumatic screening has gained importance in recent years for screening very fine materials. With air jets it is possible to screen the materials that are difficult to screen. Applying air jets in screening fine particles both screening efficiency and accuracy can be increased. The air jets can function as air jet cleaners simply to blow free plugged openings or they can take over the entire process of screening. The flowing air leads to deagglomeration overcoming the adhesive forces between the particles of the feed material, cleaning of the screen mesh and optimum discharge of fine product. Air jets can eliminate the danger of product damage that may occur due to the screening analyses which are time consuming. Reference may be made to Schmidt, P. Luftstrahlsiebung (in German) Aufbereitungs-Technik 7 (1980) P. 337-345 where in the importance of Pneumatic screening for very fine materials was reported. With air jet screens, it is possible to screen the finest, lightest materials i.e., those materials difficult to screen. The flowing air leads to deagglomeration of the feed material, a cleaning of the screen mesh and an optimum discharge of fine product. Applying air jets in screening considerably increase both screening efficiency and accuracy as compared to mechanical screening. The air jets can function as air jet cleaners to blow free plugged openings or they can take over the entire process as air jet screening. But the drawbacks were ; due to equipment related uncertainties such as maintaining a constant fluidization conditions of entire bulk solid undergoing sieving, volumetric flow rate, jet circulation speed, screening time, temperature and air moisture content till now it has not been possible to apply the principle of air jet screens completely, for the particle size analysis by screening. Also short circuit currents in the screening chamber can cause difficulties. In case of a turbulent mixing a stirring chamber character exists with high false particle content in the oversize. So a stirring chamber cascade with good separation of fine material in several whirling up zones has to be achieved. In Fig.1. of the drawings accompanying this specification a schematic diagram of an unidirectional air jet sieve has been shown. In the Figure the various pats are, A - Housing, B - Sieve chamber, C- Sieve drum, D - Sieve cover, E - Split nozzle, F - Air jets Reference may be made to Obering J. Bruederlein. Screening machinery - review and preview. Aufberitungs - Technik ,12(1986) P. 683 - 690 where in an useful insight into the theory of screening as well as was development in the area of particle measuring technology over the past twenty years was reported. The report concentrated mainly on optical methods, based on sedimentation, screening and classifying processes. Transmission measurements particularly scattered light measurement was also discussed highlighting some of the practical difficulties presented by many of the methods. Accordingly the drawbacks presented by many of the methods currently available are: (a) The vibration needed to get the small particles through the screen often causes abrasion and reduces the size of larger particles ( b ) Small particles ( powders ) tend to agglomerate thus distorting the true size distribution ( c ) The screens are made of fine wires, which are easily damaged with use, thus allowing particles that are larger than the stated screen size to pass through, (d) Clogging of screens reduces the opportunity of majority of bulk solids undergoing sieving or screening process resulting in improper, unreliable size representation and reduced efficiency, (e) Due to equipment related uncertainties screening analyses are very time consuming and there will be a possibility of product damage Reference may be made to Standish, N. The kinetics of sieving. Powder Technology 41 (1985) P. 57 - 67 where in a detailed study of the sieving kinetics for powder particles using batch sieving technique with continuous weighing of undersize stream was described. The drawback identified was as one of size segregation; each screen processing material of different size distribution. Reference may be made to Bruederlein, J. Siebklassierung mit Grossiebmaschinen (in German) Aufbereitungs-Technik 23 (1982) P 71 - 90 where in importance of classifying process for granular materials using sieving technique was highlighted. It was reported that despite the rapid and very interesting development over so many years, screening technology has been able to maintain its place commercially. The reasons may be attributed to easy operation, robust construction, low investment and maintenance costs, distinct allocation of particle size to mesh size of the screen panel used, simple and reliable determination and evaluation of mass proportions. The major draw back highlighted was classification by many methods require the correct selection of technical equipment and process parameters, which for their part must correlate very well with material parameters Reference may be made to Kaye, B.H. Particle Size analysis In " Chemical Engineer's handbook" (R.H. Perry and Chilton, eds pp. 8-3-8-8 McGraw-Hill New York) where in it was reported that when viewed physically, mechanical sieving comprises superposition of segregation, diffusion and passage through the screen. Screen sieving classifies particles with wire mesh screens or, below a size of about 40 µm with electroformed sieves. The size of the openings in the screen is known, and sieve analysis consists of measuring for several screens the percentage (by weight or number of particles) of a small which passes through or is retained. The specific screening performance and the sharpness of separation prove to be a measure for the quality of screening. The drawback identified was frictional and cohesive forces have to be overcome and the coarse feed material transported over the screen primarily by circular, elliptical or linear vibration. Reference may be made to P. Schmidt. Problems of fine screening Aufberitungs - Technik, 6(1976) P 322 - 324 where in problems of fine screening are discussed in detail and several fine screening machines are described regarding their mode of operation. It was reported that two phase flows, solid/fluid through screens are employed for screening and separation. Determination of pressure drop was done analytically and nondimensional characteristic numbers were found by using similarity theory. The drawbacks highlighted from this study were: (i) screening becomes problematic when the adhesion forces between the particles being screened and the screen deck exceed the forces due to acceleration and impact of the screen deck, (ii) Clogging of the screens. This occurs due to jamming at the web/particle size ratios 1 Reference may be made to Paul Schmidt. Sizing by sifting with screens Chem.-lng. -Tech 56 (1984) P. 897 - 907 where in screening of a particulate mixture on a screen decks with flip-flow systems using biviTec special flip-flow systems was reported. The drawbacks here were: (i) material was subjected to an extremely high acceleration and possibility of product damage (ii) additional self cleaning effects have to provided for the products slightly hydrophobic in nature. Reference may be made to Buckingham; Paul J, Abington MA. Rotary air jet screen cleaning device US Patent application No. 1991000685467. where in a vacuum cleaning system in which the top dome and receiving shell are separated by a screen, a screen cleaning system comprising an air knife having a coanda profile rotatably arranged in the dome adjacent the screen. The vacuum cleaning system is selectively actuated in accordance with a timed program to clean lint and debris from the screen. The major draw back here is that an effective cleaning and separation of products cannot be assured since the high velocity, high volume sheet of air is directed against the screen in a single direction there is a tendency of screen clogging due varied particle size distribution and segregation. Also since the air knife with respect to screens is at a distance entire screen surface is not exposed to air stream. The main object of the present invention is to provide an improved air jet sieve which obviates the drawbacks as detailed above. Another object of the present invention is to achieve a reproducible dry sieve analysis for test quantities of approx. 5 - 50 g according to mesh width of test screen with short sieving time as compared to mechanical sieving with single sittings. Still another object of the present invention is to screen difficult materials like electrostatically affected or tend to agglomerate. Yet another object of the present invention is to have a screening process where there is no particle size reduction. Another object of the present invention is to provide air jets to function as air jet cleaners to blow free plugged openings, whirling up of entire test material to undergo the screening process. Yet another object of the present invention is to have increased screening efficiency and accuracy as compared to mechanical screening. Still another object of the present invention is to have a two way air jet sieving device where there is possibility of fines recovery. Yet another object of the present invention is to have controlled influence of the screening process, obviating any mechanical influence such as tapping, brushing and the like. In Fig.2 of the drawings accompanying this specification is schematic diagram of the device of the present invention, has been shown. In the figure the various parts are, 1,2 - Split nozzles, 3,4 - Lower sieve and Upper sieve, 5 -Screen chamber, 6 - Sieve cover, 7,8 - Sealing rings, 9 - Housing, 10 -Outlet pipe connection, 11,12-Air inlets, 13,14-Air jets. An embodiment of the improved air jet sieve of the present invention is shown Fig. 3 of the drawings accompanying this specification. Accordingly the present invention provides an improved air jet sieve which comprises; a screen chamber (23) essentially consisting of two conventional analysis screens of 200 mm diameter (21,22) fixed facing each other with a gap of 25-60 mm in between capable of holding the material to be sieved, the said screen chamber being provided characterized in that with two bidirectional air jet nozzles (15,16) ,the said air jet nozzles being connected to one or more rotatable parallel slitted fingers(19,20) rotatably fixed to both sides of the said screen chamber, the rotatable fingers being directly connected to gear drive shafts driven by two electric motors (17,18), the said screen chamber and the said rotatable fingers being enclosed in an air tight chamber, the said chamber being provided with means for connecting to fines recovery chamber (30). In an embodiment of the present invention the means for providing air jets may be such as diaphragm compressors, rotary compressors. In another embodiment of the present invention the air jet nozzles (15,16) used may be exchangeable with nozzles of different slot geometry or multiarmed nozzles depending on the product, with parallel slot widths ranging from 1 to 6 mm, with the reversible direction of rotation of the nozzles. In another embodiment of the present invention the rotatably fixed fingers being connected to prime movers such as variable speed electric motors. In yet another embodiment of the present invention the fines recovery chamber used may be such as vacuum cleaner sack, cyclone or filter. In still another embodiment of the present invention a timer (32) may provided for control of the screening process. The present invention provides a two way air jet sieve, an embodiment of which is shown in Fig.3 of the drawings. The improved air jet sieve of the present invention comprises of two air nozzles (15,16), where the air jet passes, constructed as a slitted rotating finger with parallel slits, exchangeable with nozzles of different slot geometry or multiarmed nozzles depending on the type of product handled, of variable speed and geometry to influence dispersal capability, directly connected to gear drive shafts, driven by two direct current motors (17,18), with a regulated supply voltage where in the number of revolutions can be continuously varied by varying the pulse width, moving parallel to the screens with little space in between, provided with labyrinth seals (19,20), preventing the air flowing towards screening area, so that the entire transport of air comes out of two nozzles, exposing the whole screen surface to air jets, which are located one above and one beneath the conventional analysis screens of 200 mm diameter, (21,22) with screen inserts constructed of stainless steel, assembled one over the other, employing a screening chamber (23), covered with flat cover (24), sealed by a rubber seals (25,26), that is laid in a grove all around the chamber, a sealing ring (27) ,to prevent entry of any foreign air during screening, a housing (28) with an outlet pipe connection (29) with an extra air slide (30), a pressure gauge connection with dust cap (31) to record the differential pressure during screening, a timer (32) to vary the sieve testing time, a connection to vacuum chamber (33) where in the test material placed on the lower screen, whirls over the entire screen surface soon after the transport of air through the nozzles, passing through the top and bottom screens, flowing back through the lower screen, enabling the undersized or fine material to be collected in a vacuum cleaner sack, cyclone or filter, completed with an air inlet connection (34), a rigid framed structure (35), to support the major components like motors, screening chamber, nozzle, spindle assemblies and to obviate vibrations or any other mechanical influences that may hinder the screening process. The device is based on the principle of pneumatic screening or aerodynamic sifting in which the material to be sifted is moved by air currents only. A screening chamber, enclosed under a solid housing and framed support employs two conventional analysis screens of about 200 mm diameter, with screen inserts of stainless steel construction. The screens are placed intact one above the other by means of rubber gaskets warped around the sieve drum and sealing rings, which ensure the prevention of entry of foreign air during sieving. The test material is placed on the lower screen. The test material to be taken can range from 5 to 50 g. The entire transport of air comes out of two nozzles that are located one above a screen and one beneath the other screen.. Nozzles are constructed like rotating fingers having slits, moving parallel to the screens with only a small space in between so that the entire screen surface is exposed to air jets. The slot widths range from 1 to 5 mm. The two nozzles can be rotated clockwise or anticlockwise relative to each other. The nozzle air has pressure ranging between 100 to 1000 mm water scale (WS). After taking the test material on the lower screen and suitably securing the two sieves intact under the screening chamber by means of rubber gaskets and sealing rings, test parameters such as constant jet speed ranging between 0-60 rpm, volumetric gas flow rate, between 0 to 75 m3/ h, jet surface arua with slot widths of 1,2,3,4, 5 and 6 mm, are to be selected. After adjusting and maintaining constant the selected test parameters the device becomes ready for screening. The discontinuance criterion given as the incremental material left over on the screen surface to time corresponding to less than 0.1% per minute is adopted for obtaining characteristic or optimal screening time (dr / dt The novelty of the present invention with respect to prior art in: (i) attainment of short dry sieving times obtained by air currents constantly purging the sieve meshes, (ii) increased screening capacity as compared to single air jet, or mechanical sieving. (iii) overcoming of adhesive forces due flow forces of air jets, (iv) better accuracy of separation by overcoming agglomeration and clogging of screens; since the material to be screened is moved by air currents only agglomerates if any are broken up completely without any effect on particle size, (v) air brooming eliminating clogging of screens, since the pressurized air flowing through the screens from the slit of the nozzles beneath the screen acts as an air jet cleaning, (vi) efficient, reliable, complete screening, providing an opportunity for each particle of the feed or test material to undergo sieving process since the whole bed of material is aerodynamically or pneumatically whirls in the screening chamber due to two way air jet currents. (vii) absence of segregation phenomena, uniform quality of mixture with respect to product composition due to two way impinging streams of air jet. The following examples are given by way of illustration of the present invention and therefore should not be construed to limit the scope of the present invention. EXAMPLE -1 In this example optimal time data using calcium powder, a highly resistant abrasion resistant material by using two way air jet, normal or single air jet and mechanical sieving methods are presented. To begin with, a weighed quantity of calcium powder was divided into a number of samples using rotary sample splitter. Two conventional analysis screens of 200mm dia. are taken and the material is placed on the lower screen. The two sieve drums are placed one above the other and suitably sealed in the screen chamber by using rubber gaskets warped around the sieve drum. This is done to ensure proper alignment and to prevent any entry of foreign air during sieving. Table 1 shows the parameters selected . The discontinuance criterion according to DIN given as 'differential left over on the screen to time to be less than 0.1% per minute (dr / dt Table 1: Parameters selected for optimal time determination using calcium powder (Table Removed) S1 - Sieve (lower) S2 - Sieve (upper); P1- Pressure (bar-g) below the sieve P2 - Pressure (bar-g) above the sieve The screening time requirements carried out under the above selected parameters for two way air jet sieving along with single or normal air jet sieving and mechanical sieving are presented in Table 2. Table 2: Optimal screening time(min) for calcium powder by two way, normal (single) air jet sieving and mechanical sieving (Table Removed) S1 - Sieve (lower) S2 - Sieve (upper); PI - Pressure (bar-g) below the sieve P2 - Pressure (bar-g) above the sieve Mean value : 40.09% > 32µm 46.01 %> 50µm Standard deviation : 0.24% (32µm); 0.31% (32µm It can be seen from the table that the sieve test or screening analysis can be completed in a lesser time than normal (single) air jet and mechanical sieving thus eliminating the possible product damage. Also the low standard deviation indicates good reproducibility of results. The screening time tests were further earned out using different pressure conditions like 1.0x1.0, 1.5x1.5, 2.0x2.0 bar-gauge pressures. (Table 3). Table 3: Screening time results under different pressure conditions (Table Removed) S1- Sieve (lower) S2 - Sieve (upper); P1- Pressure (bar-g) below the sieve P2 - Pressure (bar-g) above the sieve V - Volumetric flow rate (m3/h); U - Air outlet speed (m/s) Material weight -12 g The table indicates lesser time consumption for two way air jet sieving as compared to other sieving methods thus eliminating the possible product damage or attrition. Again the tests were exerted to examine the possible influence of variation of parameters on screening time and results. A change in the number of revolutions of the nozzle showed the following results using screens of mesh size of 32 microns. (Table 4) Table 4: Screening time results for change in revolutions (Table Removed) PI - Pressure (bar-g) below the sieve, P2 - Pressure (bar-g) above the sieve Material weight - 12g EXAMPLE - 2 In this example, screening results of onion powder is presented. The screening time requirements were carried out on the two way air jet screening device with the following parameters: Volumetric flow rate : 49 m3/h Pressure conditions : P1xp2 (0.5 x2.0) (P1 - Pressure (bar-g) below the sieve, P2 - Pressure (bar-g) above the sieve) Air out let speed : 67.5 m/s Nozzle revolution : 18 r.p.m Mesh size :31µm Material weight : 12g The discontinuance criterion according to DIN dr/dT A total number of 4 samples were analysed and categorized into grades: >0.315 µm; > 250 µm; > 200 µm; > 90 µm; > 50µm; Table 5 : Screening results of onion powder (Table Removed) As seen from the table it can be confirmed that the analytical results are reproducible. The main advantages of the present invention are: 1. reproducible, dry sieve analysis for test quantities of approximately 5 -50 g according to the mesh width of the screen 2. short screening times as compared to normal (single) air jet, mechanical sieving 3. deaggiomeration of the feeo material, cleaning of the screen mesh and optimum discharge of fine product 4. increased screening efficiency 5. no product damage or particle attrition 6. elimination of any mechanical influences such as tapping, brushing and the like 7. absence of segregation phenomena 8. uniform quality of mixture with respect to product composition undergoing screening 9. controiied influence of the screening process 10. easy to use and reliable operation We claim: 1. An improved air jet sieve which comprises; a screen chamber (23) essentially consisting of two conventional analysis screens of 200 mm diameter (21,22) fixed facing each other with a gap of 25-60 mm in between capable of holding the material to be sieved, the said screen chamber being provided characterized in that with two bidirectional air jet nozzles (15,16) ,the said air jet nozzles being connected to one or more rotatable parallel slitted fingers(19,20) rotatably fixed to both sides of the said screen chamber, the rotatable fingers being directly connected to gear drive shafts driven by two electric motors (17,18), the said screen chamber and the said rotatable fingers being enclosed in an air tight chamber, the said chamber being provided with means for connecting to fines recovery chamber (30). 2. An improved air jet sieve as claimed in claim 1, wherein the air jets are provided by diaphragm compressors, rotary compressors. 3. An improved air jet sieve as claimed in claims 1 and 2 wherein the air jet nozzles (15,16) used is exchangeable with nozzles of different slot geometry or multiarmed nozzles depending on the product, with parallel slot widths ranging from 1 to 6 mm, with the reversible direction of rotation of the nozzles. 4. An improved air jet sieve as claimed in claims 1 to 3 wherein the fines recovery chamber used is vacuum cleaner sack, cyclone, filter. 5. An improved air j'et sieve as claimed in claims 1 to 4 wherein the control ofthe screening process is through a timer (32). 6. An improved air jet sieve , substantially as here in described with reference to the examples and Figures 2 and 3 ofthe drawings accompanying this specification.

Documents:

294-del-2000-abstract.pdf

294-del-2000-claims.pdf

294-del-2000-correspondence-others.pdf

294-del-2000-correspondence-po.pdf

294-del-2000-description (complete).pdf

294-del-2000-drawings.pdf

294-del-2000-form-1.pdf

294-del-2000-form-19.pdf

294-del-2000-form-2.pdf

294-del-2000-form-3.pdf