Title of Invention

A CHEMICAL MILLING PLANT

Abstract

A chemical milling plant which comprises an overhead tank (1) having top inlet pipe (10) and a valve (4) with controlled bottom outlet pipe (5) leading to the bottom of a milling tank (2) fixed at a level lower than the bottom of the overhead tank (1), the said milling tank (2) being provided with a top overflow outlet pipe (7) leading into a storage tank (3) fixed at a level lower than the bottom of the milling tank (2), the said storage tank (3) having a heat exchanger or cooling coil (9) connected externally to a conventional cooling system, the said storage tank (3) being provided with a conventional chemical pump (8) which is connected to the overhead tank (1), through a pipe (10), the said milling tank (2) being provided with a mechanism ( 11,12,13,14 & 15) for vertical reciprocating movement to a work-piece (16)

Full Text

The present invention relates to a chemical milling plant The main usage of the present invention is that a chemical milling plant for the removal of material selectively from a work piece by chemical machining process. Another particular usage of the present invention is that a chemical milling plant for the production of internal or external taper chemical milling of steel tubes or metal parts on one side of the tube or on both sides of the tube and leaving a portion of desired length without any change in the original dimension at the centre of the tube. US Patent No: GB 1387458 of Armco Steel Corporation, USA describes the chemical milling method and bath for chemical milling of stainless steel and high nickel alloys. The chemical milling bath is an aqueous bath consisting of 3 to 15% by volume sulfuric acid, 3 to 15% hydrochloric acid, 2 to 6% nitric acid and 0.1 to 5% extract of Acacia Mollissima bark as an inhibitor maintained at a temperature of 80 to 90 °C. The above chemical milling bath and method was used for chemical milling of the coils of stainless steel wire and the temperature of the bath has to be heated and maintained at 90°C and the above method was not suitable for our application. US Patent No: 2762150 to Edds Richard.V of Turco Product Inc, USA describes a method of removing material from the surface of a work piece by chemical etching, which comprises impinging a stream of chemical etching solution through a spray nozzle against a portion of the said surface. By moving such surface with respect to the stream of etchant so as to change the localized area of impingement of the stream against said surface and to expose successively greater surface portions to contact with the solution by direct impingement against and drainage of said solution from said surface. The etching solution is caused to contact successively greater areas of the surface to be etched to form the desired taper, without contacting those portions of the surface which is not desired to etch. The above method is not suitable for the production of internal tapering of smaller diameter tubes and larger length of the metal tubes and it involves the use of a rotating spray nozzle wheel through which the etching solution is impinged on the inside surface of the tube. US Patent No: US 2802726 to Langsfeld William P of Turco Products Inc, USA describes a method and apparatus for selectively removing metal from a metal part for producing tapered sheets. The above method is not suitable for the internal taper chemical milling of metal tubes. US Patent No: US 4053347 to Glenn Richard C of United States Steel Corporation, USA describes a method and apparatus for forming internal taper in the walls of a sleeve-like body by a chemical machining process. This method and apparatus are particularly useful for forming a taper in the walls of a mold liner, usually copper and are of rectangular or square cross section used in continuously casting metals. The mold liner which has to be internal tapered is fixed in an upright position and inside faces of the sleeve like body is exposed to a pool of etching solution and control the configuration of the taper by controlling the rate of rise or fall of the level of pool surface through an overflow tube inside the mold liner. The above chemical machining process is not suitable for the production of internal taper chemical machining of smaller diameter tubes and longer length of the metal tubes. There are two methods available as mentioned earlier in the Prior art Patent for internal taper chemical machining of metal tubes. These prior methods are limited for internal taper chemical milling of metal tubes of shorter length and larger diameter tubes. These methods are not suitable for internal taper chemical milling of special alloy steel of stabilizer spar tube. There is no literature information available for chemical machining of special alloy steel of stabilizer spar tube. Therefore a new method and a chemical milling plant has been developed for internal taper chemical milling of Cr-Mo-V steel of special alloy stabilizer spar tube employing the chemical milling bath /described in our co-pending patent No: NF-248/02 The main object of the present invention is to provide a chemical milling plant, which obviates the drawbacks of earlier inventionsas detailed above. Another object of the present invention is to provide a chemical milling plant and a method for the removal of material selectively from a work piece by chemical machining process. Still another object of the present invention is to provide a chemical milling plant and a method for internal gradual taper chemical milling of steel tubes or metal tubes on one side of the tube or on both sides of the tube leaving a portion without any change in the original dimension at the centre of the tube. Yet another object of the present invention is to provide a chemical milling plant and a method for external gradual taper chemical milling of steel tubes or metal tubes on one side of the tube or on both sides of the tube. In the drawings accompanying this specification, figure 1 represents chemical milling plant wherein Part No. 1 is overhead tank Part No. 2 is chemical milling tank Part No. 3 is storage tank Part No. 4 is valve Part No. 5 is bottom outlet pipe Part No. 6 is distributor Part No. 7 is Overflow pipe Part No. 8 is Chemical Pump Part No. 9 is Heat exchanger or cooling coil Part No. 10 is inlet pipe to the overhead tank. Figure 2 represents Tool drive mechanism wherein Part No. 11 is AC or DC motor Part No. 12 is rotating disc with a strip Part No. 13 is pulley Part No. 14 is pulley Part No. 15 is rope connecting to the job Part No. 16 is Job or workpiece Accordingly the present invention provides a chemical milling plant which comprises as shown in Fig.l an overhead tank (1)having top inlet pipe (10) and a valve(4)with controlled bottom outlet pipe (5) leading to the bottom of a milling tank (2) fixed at a level lower than the bottom of the overhead tank(l), the said milling tank (2) being provided with a top overflow outlet pipe (7) leading into a storage tank(3)fixed at a level lower than the bottom of the milling tank^the said storage tank (3) having a heat exchanger or cooling coil (9} which is connected externally to a conventional cooling system to control the temperature of chemical milling bath, the said storage tank(3)being provided with a conventional chemical pump(8) which is connected to the overhead tank(l) through a pipe(10), In an embodiment of the present invention provides a chemical milling plant as shown in Fig.l, wherein the overhead tank(1) bottom outlet pipe(5)leading to the bottom of the milling tank (2) is provided with a distributor (6) capable of providing uniform laminar flow of chemical milling bath in the milling tank(2) In an another embodiment of the present invention provides a chemical milling plant, wherein the storage tank (3) is provided with a conventional temperature controller connected to a conventional cooling system. In still another embodiment of the present invention provides a chemical milling plant as shown in Fig.2, wherein the job or workpiece movement mechanism(ll, 12, 13, 14 and 15)capable of providing vertical reciprocating movement to a job or workpiece (16) consisting of a prime mover (l 1 )which may be AC or DC motor connected to a rotating disc with a strip(12)in such a manner so as to provide vertical reciprocating movement to a workpiece (16) through a connecting rope (l 5) via pulleys (13) and (14) In yet another embodiment of the present invention, a chemical milling plant is provided with a conventional Fume extraction system for the removal of liberated gases and fumes during the chemical milling operation. After thoroughly cleaning the inside and outside surface of the tube which has to be internal taper chemical milled for a certain length is masked completely on the outer surface of the tube with PVC insulation tape or suitable masking agent. Specially designed teflon bush is inserted into the inner surface of the tube either at the end of the tube or at the centre of the tube which acts as a maskant where the chemical machining is not required and the PVC support tube with a hook is integrated with steel tube. The job weight is noted at every stage which is before and after the complete insulation ready for chemical milling. The chemical milling bath which is described in our copending patent No: NF-248/02, is prepared and charged into the chemical milling tank and storage tank and the chemical milling bath is circulated by a chemical pump through the overhead tank and a flow distributor in the chemical milling tank. The overflow from the milling tank discharges into the storage tank and pumped back to the overhead tank. After the masking, the job is fixed to the hook with a supported mechanism for downward and upward movement of the component in the chemical milling tank. The process parameters such as chemical composition and strength of etching solution, machining rate, machining on time and off time with number of cycles per minute, the stroke length, the temperature of the etching solution and the total duration of machining time are selected and the experiment is started. The tool drive mechanism is switched on with the continuous circulation of the etching solution. The chemical machining process is a controlled dissolution of metallic materials is coupled with oxidation and reduction reactions. The reaction occurs between the etching solution and the material is exothermic which results in increase in temperature of the solution continuously. The temperature of the solution is maintained at constant value by cooling the solution with a heat exchanger and cooling system. The metal atoms reacts with the etching solution and liberates oxides of gases with oxidised product. The liberated gases and fumes are extracted and fed to a wet scrubber with Fume exhaust system. As the job moves downward and upward into the etching solution, the inside surface of the bottom tube comes into contact with solution for a longer time than the successive top portion of the inside surface of the tube for every cycle of the job movement. The job movement system may consist of a screw rod assembly driven with electrically controlled AC /DC motor by micro processor based system for variable duty cycle. The level of the etching solution in the milling tank is kept at a constant level by means of a overflow pipe leading into the storage tank. We can produce a taper of the amount required on the internal or external surface of the metal tube or a metal part by varying the suitable process parameters by this novel method. The chemical milling continues until the desired profile and the amount of metal reduction is produced. Then the workpiece is removed from the chemical milling bath, washed with water and the maskant or insulation is removed from the inner and outer surface of the metal tube. The workpiece is thoroughly cleaned, dried and final weight is noted down. The steel tube is applied with anticorrosive oil. The tapering profile have been measured in the metrology lab. The following examples are given to illustrate the invention and should not be construed to limit the scope of the present invention. For gradual tapering the internal or external surface wall of the Cr-Mo-V steel of special alloy stabilizer spar tube, the above novel chemical milling method was used. Example 1 Steel tube I.D - 35.765 mm Steel tube O.D - 39.885 mm Wall thickness - 2.06 mm Length of the tube - 110mm Temperature of the bath - 26 - 30°C Total machining time - 130min Total weight of metal machined - 86.1 gm Machining rate - 5.57µm/cm2/min I.D at the tapered end of the - 38.445 mm tube for internal tapering Example 2 Steel tube I.D - 35.765 mm Steel tube O.D - 39.885 mm Wall thickness - 2.06 mm Length of the tube - 165 mm Temperature of the bath - 26 - 30°C Total machining time - 120 min Total weight of metal machined - 145.3 gm Machining rate - 14.10 µm/cm2/min I.D at the tapered end of the - 38.185mm tube for internal tapering Example 3 Steel tube I.D - 35.765mm Steel tube O.D - 39.885 mm Wall thickness - 2.06 mm Length of the tube - 360 mm Temperature of the bath - 24-30°C Total machining time - 83 min Total weight of metal machined - 245 gm Machining rate - 12.42 u,m/cm2/min I.D at the tapered end of the - 37.895 mm tube for internal tapering Example 4 Steel tube I.D - 35.765mm Steel tube O.D - 39.885 mm Wall thickness - 2.06 mm Length of the tube - 560mm Temperature of the bath - 24-30°C Total machining time - 160 min Total weight of metal machined - 472.4 gm Machining rate - 11.47µm/cm2/min LD at the tapered end of the tube for internal tapering 38.235 mm Example 5 Steel tube I.D - 35.765 mm Steei tube O.D - 39.885 mm Wall thickness - 2.06 mm Length of the tube - 362mm Temperature of the bath - 24 - 32°C Total machining time - 166 min Total weight of metal machined - 201.6 gm Machining rate - 15.05 µm/cm2/min I.D at the tapered both end of - 37.830 mm tube for internal tapering for a and length of 150 mm at both sides 37.840 mm leaving 62 mm portion without machining at the centre of the tube Example 6 Steel tube I.D - 35.765mm Steel tube O.D - 39.885mm Wall thickness - 2.06 mm Length of the tube - 110mm Temperature of the bath - 26 - 30°C Total machining time - 180 min Total weight of metal machined - 67.6 gm Machining rate - 4.47µm/cm2/min O.D at the tapered end of the - 37.503 mm tube for external tapering Using the above chemical milling plant and the novel method of chemical milling, we can produce gradual and smooth taper without any step or line formation with a very good surface finish on the internal or external surface of the metal tube or a metal part. The main advantages of the present invention are : i. A chemical milling plant used for the removal of material selectively from a workpiece by chemical machining process, ii. A chemical milling plant and a novel method for the production of gradual and smooth internal taper chemical milling of steel tubes or metal tubes, iii. A chemical milling plant and a novel method for the production of gradual and smooth internal taper chemical milling of steel tubes or metal parts on both sides of the tube and leaving a portion of desired length without any chemical machining at the centre of the tube. iv. A chemical milling plant and a novel method for the production of gradual and smooth external taper chemical milling of steel tubes or metal parts on one side of. the tube or on both sides of the tube and leaving a portion of desired length without any chemical machining at the centre of the tube. v. A chemical milling plant, which can be used for several applications where chemical milling is necessary. As an example, this can be used for machining complicated internal taper chemical milling of stabilizer spar tube. We claim : 1. A chemical milling plant which comprises an overhead tank(l)having top inlet pipe(lO)and a valve(4)with controlled bottom outlet pipe(5jleading to the bottom of a milling tank(2jfixed at a level lower than the bottom of the overhead tank(l), the said milling tank(2)being provided with a top overflow outlet pipe (7) leading into a storage tank (3) fixed at a level lower than the bottom of the milling tank (2), the said storage tank (3) having a heat exchanger or cooling coil (9) connected externally to a conventional cooling system, the said storage lank (3) being provided with a conventional chemical pump(8)which is connected to the overhead tank(l through a pipe 2. A chemical milling plant as claimed in claim 1, wherein the overhead tank bottom outlet pipe(5)leading to the bottom of the milling tank(2)is provided with a distributor (6)capable of providing uniform laminar flow of chemical milling bath in the milling tank(2). 3. A chemical milling plant as claimed in claim 1-2, wherein the storage tank (3) is provided with a conventional temperature controller connected to a conventional cooling system. 4. A chemical milling plant as claimed in claim 1-3, wherein the mechanism (ll, 12, 13, 14 and 15)capable of providing vertical reciprocating movement to a workpiece(l 6) consisting of a prime mover(11)connected to a rotating disc with a strip (l 2) in such a manner so as to provide vertical reciprocating movement to a workpiece(l6)through a connecting rope (l5) via pulleys(l3) and(l4). 5. A chemical milling plant as claimed in claim 1-4, wherein the chemical milling plant is provided with a conventional fume extraction system. 6. A chemical milling plant substantially as herein described with reference to the examples and drawings accompanying this specifications.

Documents:

573-del-2002-abstract.pdf

573-del-2002-claims.pdf

573-del-2002-correspondence-others.pdf

573-del-2002-correspondence-po.pdf

573-del-2002-description (complete).pdf

573-del-2002-drawings.pdf

573-del-2002-form-1.pdf

573-del-2002-form-19.pdf

573-del-2002-form-2.pdf

573-del-2002-form-3.pdf