Claims:WE CLAIM:

1. A device (10) for clearing blockages using cavity machining, according to the present invention comprising:
a mounting plate (20);
an assembly plate (30);
an extension plate (40); and
holding sleeves (50);
characterized in that mounting plate (20) is detachable attached with the assembly plate (30) using locating pins and threaded bolts;
the extension plate (40) is detachably attached with the assembly plate (30) with the help of bolts and nuts; and
the extension plate (40) Is detachably attached with the holding sleeves (50) using the threaded portion on the top side of the sleeves (50).
2. The device (10) as claimed in claim 1, wherein the device (10) is made from EN24, Stainless steel, aluminium.
3. A method for clearing blockages using cavity machining, according to the present invention comprising steps of:
Mounting the device (10) on a 4 axes CNC controlled EDM machine;
Holding an impeller (100) on a machine work table using three jaw self-centring chuck (110);
Inserting a graphite electrode inside the impeller channel, specifically in the vane cavity;
Moving the graphite electrode 1 mm below in z – direction and rotating 4 degrees about z – axis.
4. The method as claimed in claim 3, wherein the impeller is firmly held, using a self-centring chuck and placed on the bed table of the CNC EDM machine.
5. The method as claimed in claim 3, wherein the complete impeller with machine bed plate is then immersed in a kerosene tank.
, Description:FIELD OF THE INVENTION
[001] This invention relates to narrow gap impellers used in a centrifugal compressor. The present invention in particular relates to a device and method for cavity machining of narrow gap impellers used in a centrifugal compressor.

BACKGROUND OF THE INVENTION

[002] Centrifugal compressors, sometimes called radial compressors, are a sub-class of dynamic axisymmetric work-absorbing turbomachinery.

[003] They achieve a pressure rise by adding kinetic energy/velocity to a continuous flow of fluid through the rotor or impeller. This kinetic energy is then converted to an increase in potential energy/static pressure by slowing the flow through a diffuser. The pressure rise in the impeller is in most cases almost equal to the rise in the diffuser.

[004] In the case where flow passes through a straight pipe to enter a centrifugal compressor the flow is straight, uniform and has no vorticity, ie swirling motion, so the swirl angle a1 = 0°. As the flow passes through the centrifugal impeller, the impeller forces the flow to spin faster as it gets further from the rotational axis. According to a form of Euler's fluid dynamics equation, known as the pump and turbine equation, the energy input to the fluid is proportional to the flow's local spinning velocity multiplied by the local impeller tangential velocity.

[005] In many cases, the flow leaving the centrifugal impeller is travelling near the speed of sound. It then flows through a stationary compressor causing it to decelerate. The stationary compressor is ducting with increasing flow-area where energy transformation takes place. If the flow has to be turned in a rearward direction to enter the next part of the machine, e.g. another impeller or a combustor, flow losses can be reduced by directing the flow with stationary turning vanes or individual turning pipes (pipe diffusers). As described in Bernoulli's principle, the reduction in velocity causes the pressure to rise.

[006] The key component that makes a compressor centrifugal is the centrifugal impeller which contains a rotating set of vanes (or blades) that gradually raises the energy of the working gas. This is identical to an axial compressor with the exception that the gases can reach higher velocities and energy levels through the impeller's increasing radius. In many modern high-efficiency centrifugal compressors the gas exiting the impeller is traveling near the speed of sound.

[007] Impellers are designed in many configurations including "open" (visible blades), "covered or shrouded", "with splitters" (every other inducer removed) and "w/o splitters" (all full blades). Most modern high efficiency impellers use "backsweep" in the blade shape.

[008] Euler's pump and turbine equation, plays an important role in understanding impeller performance.

[009] Impellers of varying sizes and varying vane profiles are used in Centrifugal Compressor. The impeller is having two parts i.e., Disc and counter disc. Vanes are machined on Disc (refer Fig 1) and weld grooves are machines on counter disc (refer Fig 2). These two parts are welded using a qualified welding process. However, for narrow gap impellers where the channel width (refer Fig 3) is just 4 to 5 mm, the channel passages are sometimes blocked due to inclusion of weld fusion material, deep penetration, shrinkage and distortion during welding process. These blockages are to be removed, otherwise causes turbulence in fluid flow and efficiency loss will occur. Since, the clearance (channel width) available is very less and aerofoil profile of the impeller vanes, it is very difficult to clear the passage using hand grinding tools.

PRIOR ART AND ITS DISADVANTAGES:

[0010] US 4441004A, US 4603391A, US 3604884A, US 4992639A, US 4335436A, US 4029929A were found to have discrete information either related to drilling using EDM process or cutting with wire electrode . But there is no mention of special fixtures, graphite tooling which are used to make a cavity machining of narrow gap impellers. The narrow gap impellers channel width is 4 to 5 mm only. The vane profile is an aerofoil shape. IT is difficult to clear these passages using manual grinding tools, as tool cannot go inside and clear the passage. If the blockages are not cleared, it creates turbulence in fluid flow and causes drop in efficiency.

[0011] To address this issue, a method has been established to clear the passages using Electrical Discharge machining (EDM) process. This invention is giving a way to design and develop a fixture, tooling and method to clear the blockages using cavity machining with the help of a 4 axis CNC controlled Electrical Discharge Machining (EDM) process.
OBJECTS OF THE INVENTION
[0012] The principal object of the present invention is to design a device for clearing blockages of the impellers using cavity machining.
[0013] Another objection of the present invention is to develop a method for clearing blockages of the impellers using cavity machining.

SUMMARY OF THE INVENTION
[0014] According to the aspect of the invention, a device and method for clearing blockages of the impellers is disclosed.
[0015] A device (10) according to the present invention is disclosed. The device (10) is designed particularly to hold graphite tool/electrode. The device (10) comprises of mainly 4 components: a mounting plate (20), an assembly plate (30), an extension plate (40) and holding sleeves (50).
[0016] The device (10) is mounted on a 4 axes CNC controlled EDM machine, which is having controlled motion in X, Y and Z directions as well as rotation about Z axis. The impeller (ref Fig 5) is held on the machine work table using a three jaw self-centring chuck. The work offset for the impeller is set in such a way that the origin reference point is on the centre of the impeller. The electrode is inserted inside the impeller channel and moved as per the developed CNC program. The electrode is moved 1 mm below in Z direction and rotated 4 degrees about z axis. With this, the electrode comes in contact with the side wall of the channel groove and material is removed due to electric discharge. The same operation is carried out for all the channel openings and blockages, if any are cleared. With this development, the flow will be laminar and desired losses due to turbulence are reduced. The efficiency of the compressor shall improve.

BRIEF DESCRIPTION OF DRAWNGS
The proposed invention will be better understood by the following description with reference to the accompanying drawings:

[0017] Figure 1: Disc vanes as machined on Disc.

[0018] Figure 2: Weld grooves as machines on counter disc.

[0019] Figure 3: A narrow gap impeller.

[0020] Figure 4: A device according to the present invention to hold graphite tool/electrode.

[0021] Fig. 4a: Mounting plate top view

[0022] Fig. 4b: Assembly plate

[0023] Fig. 4c: Extension plate

[0024] Fig. 4d: Holding sleeves

[0025] Figure 5: The device according to the present invention holding the impeller.

[0026] Fig. 6: Designed graphite electrode which is fixed to the fixture

[0027] Fig. 7: Vane Profile

[0028] Fig. 8: Three jaw self-centring chuck

DETAIL DESCRIPTION OF THE INVENTION
[0029] It should be appreciated by those skilled in the art that any block diagrams herein represent conceptual views of illustrative systems embodying the principles of the present subject matter. Similarly, it will be appreciated that any flow charts, flow diagrams, state transition diagrams, pseudo code, and the like represent various processes which may be substantially represented in computer readable medium and executed by a computer or processor, whether or not such computer or processor is explicitly shown.
[0030] In the present disclosure, the word "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any embodiment or implementation of the present subject matter described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments.
[0031] While the present disclosure is susceptible to various modifications and alternative forms, specific embodiment thereof has been shown by way of example in the drawings and will be described in detail below. It should be understood, however that it is not intended to limit the present disclosure to the particular forms disclosed, but on the contrary, the present disclosure is to cover all modifications, equivalents, and alternative falling within the spirit and the scope of the present disclosure.
[0032] The terms “comprises”, “comprising”, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a setup, device or method that comprises a list of components or steps does not include only those components or steps but may include other components or steps not expressly listed or inherent to such setup or device or method. In other words, one or more elements in a system or apparatus proceeded by “comprises… a” does not, without more constraints, preclude the existence of other elements or additional elements in the system or apparatus.
[0033] In the following detailed description of the embodiments of the disclosure, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration specific embodiments in which the disclosure may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the disclosure, and it is to be understood that other embodiments may be utilized and that changes may be made without departing from the scope of the present disclosure. The following description is, therefore, not to be taken in a limiting sense.
[0034] The present invention will be described in detail below with reference to an embodiment as shown in the drawing.
[0035] Referring to Fig. 4, a device (10) according to the present invention is disclosed. The device (10) is designed particularly to hold graphite tool/electrode. The device (10) comprises of mainly 4 components: a mounting plate (20), an assembly plate (30), an extension plate (40) and holding sleeves (50).
[0036] The mounting plate (20) is detachable attached with the assembly plate (30) using locating pins and threaded bolts (not shown). The extension plate (40) is detachably attached with the assembly plate (30) with the help of bolts and nuts and the extension plate (40) Is detachably attached with the holding sleeves (50) using the threaded portion on the top side of the sleeves (50).
[0037] The device (10) is mounted on a 4 axes CNC controlled EDM machine, which is having controlled motion in X, Y and Z directions as well as rotation about Z axis. The impeller (ref Fig 5) is held on the machine work table using a three jaw self-centring chuck (110). The work offset for the impeller is set in such a way that the origin reference point is on the centre of the impeller. The electrode is inserted inside the impeller channel and moved as per the developed CNC program. The electrode is moved 1 mm below in Z direction and rotated 4 degrees about z axis. With this, the electrode comes in contact with the side wall of the channel groove and material is removed due to electric discharge. The same operation is carried out for all the channel openings and blockages, if any are cleared. With this development, the flow will be laminar and desired losses due to turbulence are reduced. The efficiency of the compressor shall improve.
[0038] The device (10) is designed in such a way that the electrode can smoothly enter the groove of the impeller by rotating the C-axis of the machine (rotation about Z), to which the device (10) is mounted.
[0039] The graphite electrode is designed and machined as per the profile of the impeller vane. The impeller vane passage consists of arc type of construction as shown in Fig. 7. The passage clearance is just 4 – 5 mm (channel width in Fig. 3). During the welding process of disc and counter disc (refer fig 1 and 2), to make them as a single piece called “impeller”, sometimes the passage gets chocked with weld fusion material and causes fluid flow obstruction. This affects the performance of the impeller. There is no other method readily available to clean these passages (less clearance and curved path) the same was done using EDM Process. In the EDM process, an electrode or tool (generally graphite) is used to generate spark using electric discharge. Material is eroded from the work piece by a series of rapidly recurring current discharges between electrode and work piece (impeller vane). In order to do so, the electrode is designed and manufactured as per the vane profile.
[0040] The method to use the device (10) for cavity machining of narrow gap impellers using EDM process is disclosed as follows:
[0041] The impeller is firmly held, using a self-centring chuck and placed on the bed table of the CNC EDM machine.
[0042] The complete impeller with machine bed plate is then immersed in a kerosene tank. EDM process requires an electrolyte. Without this machining /material removal will not take place. Kerosene is used as an electrolyte commonly
[0043] Next, the profiled graphite electrode/tool, which is mounted to the z-axis of the machine using the device (10), is rotated into the impeller channel passage.
[0044] The profiled graphite electrode/tool rotates in a particular motion to cause erosion in the channel passage to clear the channel passage.
[0045] The device (10) is made from EN24, Stainless steel, aluminium.
[0046] It should be noted that the description and figures merely illustrate the principles of the present subject matter. It should be appreciated by those skilled in the art that conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present subject matter. It should also be appreciated by those skilled in the art that by devising various assembly that, although not explicitly described or shown herein, embody the principles of the present subject matter and are included within its spirit and scope. Furthermore, all examples recited herein are principally intended expressly to be for pedagogical purposes to aid the reader in understanding the principles of the present subject matter and the concepts contributed by the inventor(s) to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. The novel features which are believed to be characteristic of the present subject matter, both as to its organization and method of operation, together with further objects and advantages will be better understood from the aforementioned description when considered in connection with the accompanying figures.
[0047] These and other advantages of the present subject matter would be described in greater detail with reference to the following figures. It should be noted that the description merely illustrates the principles of the present subject matter. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described herein, embody the principles of the present subject matter and are included within its scope.
[0048] It will be further appreciated that functions or structures of a plurality of components or steps may be combined into a single component or step, or the functions or structures of one-step or component may be split among plural steps or components. The present invention contemplates all of these combinations. Unless stated otherwise, dimensions and geometries of the various structures depicted herein are not intended to be restrictive of the invention, and other dimensions or geometries are possible. In addition, while a feature of the present invention may have been described in the context of only one of the illustrated embodiments, such feature may be combined with one or more other features of other embodiments, for any given application. It will also be appreciated from the above that the fabrication of the unique structures herein and the operation thereof also constitute methods in accordance with the present invention. The present invention also encompasses intermediate and end products resulting from the practice of the methods herein. The use of “comprising” or “including” also contemplates embodiments that “consist essentially of” or “consist of” the recited feature.
[0049] Although embodiments for the present subject matter have been described in language specific to structural features, it is to be understood that the present subject matter is not necessarily limited to the specific features described. Rather, the specific features and methods are disclosed as embodiments for the present subject matter. Numerous modifications and adaptations of the system/component of the present invention will be apparent to those skilled in the art, and thus it is intended by the appended claims to cover all such modifications and adaptations which fall within the scope of the present subject matter.