Claims:WE CLAIM

1. A method for the treatment of the erosion resistant nodular cast iron blades of Induced Draft (ID) fans using Laser Surface Melting (LSM) with line laser beam to increase their surface hardness, comprising:
operating laser source capable of generating power up to 3 kW, in continuous wave mode to surface melt the blade;
transferring laser beam using a fiber optic cable to the scanning head coupled with a 6-axis robot end arm that is programmable to make multi-dimensional movement;
harnessing the transferred laser beam output using an optical head;
falling of the defocused laser beam coming out of the optical head on the blade surface and movement of laser line beam along a specified path over the blade surface;
overlapping the track at ratio of 2-5% to cover larger surface area;
creating an inert atmosphere;
supplying pressurized air parallel to the focusing lens to protect the optics from sparks and fumes.

2. The method for the treatment of the erosion resistant nodular cast iron blades of Induced Draft (ID) fans as claimed in claim 1, wherein the scan speed and laser power are varied between 50-300 mm/min and 200-350 watts.

3. The method for the treatment of the erosion resistant nodular cast iron blades of Induced Draft (ID) fans as claimed in claim 1 or 2, wherein the laser beam output transferred through the fiber optic is harnessed using an optical head which has a ˜160 mm focal length and is kept at ( +5 mm - +30 mm) defocus to avoid vaporization.

4. The method for the treatment of the erosion resistant nodular cast iron blades of Induced Draft (ID) fans as claimed in the claims 1-3, wherein the inert atmosphere is created using argon as the shroud gas and is laterally fed at 0.6 MPa.

5. The method for the treatment of the erosion resistant nodular cast iron blades of Induced Draft (ID) fans as claimed in claims 1-4, wherein the fiber optic cable is of ˜ 300-micron diameter.

6. The method for the treatment of the erosion resistant nodular cast iron blades of Induced Draft (ID) fans as claimed in claims 1-5, wherein the laser source is having power of 100-500 W operated in continuous wave mode that is used to melt, process and modify the blade surface.

7. An improved erosion resistant nodular cast iron blade for Induced Draft (ID)fans of thermal power plants of required surface area treated with Laser Surface Melting (LSM) process with optimised line laser beam parameters for improving the surface hardness, comprising: leading edge (1), trailing edge (2), blade tip (3) and blade root (4).

8. The improved erosion resistant nodular cast iron blade for Induced Draft (ID) fans as claimed in claim 7, wherein the nodular cast iron blade has lesser fan balancing problems compared to those having sacrificial coating and has improvement in service life by 44% compared to that of untreated nodular cast iron blades.
, Description:EROSION RESISTANT NODULAR CAST IRON BLADES OF FANS AND METHOD FOR TREATMENT THEREOF

FIELD OF THE INVENTION:
[001] This invention is directed to the development of improved nodular cast iron blades of Induced Draft (ID) fans and method for treatment thereof.

[002] This invention more particularly relates to the treatment of blades using Laser Surface Melting (LSM) with line laser beam to increase their surface hardness and having improved service life against erosion in handling dust laden flue gas.

BACKGROUND/PRIOR ART OF THE INVENTION:
[003] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.

[004] In the present power scenario, reduction in periodical shutdowns and improving the performance of power plants are very much felt essential. Also, customers of supercritical thermal power plants demand for a minimum service life of 25000 hrs between replacements of eroded fan blades.

[005] The nodular cast iron blades of Induced Draft (ID) fans of thermal power plants erode while handling dust laden flue gas and require periodic replacements. Induced Draft (ID) fan running with unevenly eroded blades is subjected to unbalance and the fan trips. Induced Draft (ID) fan trip calls for boiler shut down leading to loss in power generation.

[006] The present invention provides a solution to the erosion problem and meets the current market requirement by providing nodular cast iron blades of Induced Draft (ID) fans specially treated using Laser Surface Melting (LSM) with line beam with optimised parameters (patent applied by the present inventors) to increase their surface hardness and in turn improve their service life against erosion in handling dust laden flue gas.

[007] JP2010209913A 2010-09-24 titled EROSION AND CORROSION RESISTANT TURBINE COMPRESSOR AIRFOIL AND METHOD OF MAKING THE SAME describes that an erosion-resistant and sacrificial turbine compressor airfoil has a modified airfoil surface. The airfoil surface has an airfoil coating which includes a sacrificial coating including a layer of Al, Cr, Zn, an Ni-Al alloy, an Al-Si alloy, an Al-based alloy, a Cr-based alloy, a Zn-based alloy, an Al polymer composite, or a combination thereof, or a layer of a conductive undercoat and an overcoat which is disposed on the undercoat and has a plurality of ceramic particles and conductive particles embedded in an inorganic matrix binder. One of the sacrificial coating or an erosion-resistant coating is disposed on the airfoil surface, and the other of a corrosion-resistant coating or the erosion-resistant coating is disposed on the one, and the sacrificial coating is more anodic than the airfoil surface or the erosion-resistant coating.

[008] The above invention is applicable for turbine compressor air foil of stainless steel material and involves additional sacrificial coatings.

[009] In view of the above, there is requirement to devise a treatment method of the nodular cast iron blades of Induced Draft (ID) fans of power plants in which the surface hardness is improved without any sacrificial coatings which can address the aforesaid shortcoming(s). Hence, the present invention has been introduced.

OBJECTS OF THE INVENTION:
[0010] An object of the present invention is to develop improved erosion resistant nodular cast iron blades for ID fans of thermal power plants and method for treatment thereof.

[0011] Another object of the present invention is to provide erosion resistant nodular cast iron blades without the need for additional sacrificial coatings.

[0012] Still another object of the present invention is to provide an erosion resistant nodular cast iron blades specifically treated with line beam based laser surface melting process.

[0013] Yet another object of the present invention is to provide an erosion resistant nodular cast iron blades for improving the surface hardness and in turn improving the service life of Induced Draft (ID) fan blades made of nodular cast iron.

[0014] These and other objects and advantages of the present invention will be apparent to those skilled in the art after a consideration of the following detailed description taken in conjunction with the accompanying drawings in which a preferred form of the present invention is illustrated.

SUMMARY OF THE INVENTION:
[0015] One or more drawbacks of conventional systems and process are overcome, and additional advantages are provided through the apparatus/composition and a method as claimed in the present disclosure. Additional features and advantages are realized through the technicalities of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered to be part of the claimed disclosure.

[0016] Improved erosion resistant nodular cast iron blades specifically treated with line beam based laser surface melting process with optimised parameters (patent applied by the present inventors) for improving the surface hardness and in turn improving the service life of Induced Draft (ID) fan blades made of nodular cast iron has been developed. The erosion tests carried out at different angles (15º, 30º, 45º, 60º and 75º) of impact on both base and laser treated samples indicate that the laser treated sample shows around 44% improvement in service life when compared with the base sample. The Laser Surface Melting (LSM) surface had crater depth lower than the base material similar to weight loss exhibiting their suitability for the desired application for the Induced Draft (ID) fans of thermal power plants.

[0017] However, this arrangement will work in negative pressure or balanced draft locations of steam generator zones. Thus the observation port mounted access door assembly has been conceived.

[0018] The present invention is achieved by the features of independent claims and subsequent claims.

[0019] Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.

[0020] It is to be understood that the aspects and embodiments of the disclosure described above may be used in any combination with each other. Several of the aspects and embodiments may be combined to form a further embodiment of the disclosure.

[0021] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
[0022] The illustrated embodiments of the subject matter will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. The following description is intended only by way of example, and simply illustrates certain selected embodiments of devices, systems, and processes that are consistent with the subject matter as claimed herein, wherein:-

[0023] Figure 1 shows the top view of the erosion resistant nodular cast iron blade.

[0024] Figure 2 shows the front view of the erosion resistant nodular cast iron blade displaying Induced Draft (ID) fan blade possessing the shape (5) (full line) before it is subjected to erosion and obtained the shape (6) (dashed line) after affected by erosion.

[0025] Figure 3 shows the comparison of Mass loss at different angles of impingement for base and Laser Surface Melting (LSM) treated nodular cast iron.

[0026] Figure 4 shows the White Light Interferometer (WLI) Images for (a) base material (b) Laser Surface Melting (LSM) at 15° angle of impingement.

[0027] Figure 5 shows the White Light Interferometer (WLI) Images for (a) base material (b) Laser Surface Melting (LSM) at 30° angle of impingement.

[0028] Figure 6 shows the White Light Interferometer (WLI) Images for (a) base material (b) Laser Surface Melting (LSM) at 45° angle of impingement.

[0029] Figure 6 shows the White Light Interferometer (WLI) Images for (a) base material (b) Laser Surface Melting (LSM) at 60° angle of impingement.

[0030] Figure 6 shows the White Light Interferometer (WLI) Images for (a) base material (b) Laser Surface Melting (LSM) at 75° angle of impingement.

[0031] Figure 7 shows the comparison of Crater depth at different angles of impingement for base and Laser Surface Melting (LSM) treated nodular cast iron.

[0032] The figures depict embodiments of the disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT(S) OF THE PRESENT INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS:

[0033] While the embodiments of the disclosure are subject to various modifications and alternative forms, specific embodiment thereof have been shown by way of example in the figures and will be described below. It should be understood, however, that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternative falling within the scope of the disclosure.

[0034] The present invention makes a disclosure regarding a treatment method pertinent to an improved erosion resistant nodular cast iron blades for Induced Draft (ID) fans of thermal power with leading (1) and trailing edges (2) of required surface area treated with Laser Surface Melting (LSM) with optimised line laser beam parameters.

[0035] Now reference may be made to Figure-1 illustrating the top cross section of Induced Draft (ID) fan blade showing leading edge (1) and trailing edge (2).

[0036] Now referring to Figure-2 illustrating the front view of full length Induced Draft (ID) fan blade with blade tip (3) and blade root (4). The Laser Surface Melting (LSM) treated Induced Draft (ID) fan blade was possessing the shape (5) (full line) and untreated Induced Draft (ID) fan blade was possessing the shape (6) (dashed line) when subjected to erosion. The average surface area per blade of Induced Draft (ID) fan prone for erosion is around 0.34 m2.

[0037] The Present invention relates to the treatment of the blades with line laser beam in such a way that the surface hardness value is increased as a result of very fine microstructure of austenite dendrites with an inter-dendritic network of carbides and the formation of ? Face Centered Cube (FCC-Fe3C) from Body Centered Cube (BCC- a Fe) due to high self-cooling rate during solidification under optimised process parameters for nodular cast iron.

[0038] In present invention a laser source having power ranges 100-500 W operated in continuous wave mode is used to melt the blade surface, process and modify the blade surface. The laser unit is capable of generating power up to 3 kW. The laser beam is transferred using a fiber optic cable of ˜300-micron diameter to the scanning head which is coupled with a 6-axis robot end arm. The robot arm is programmable to make multi-dimensional movement. The laser beam output transferred through the fiber optic is harnessed using an optical head which has a 160 mm focal length and was kept at +5 mm to +30 mm defocus to avoid vaporization. The defocused laser beam coming out of the optical head falls on the blade which is placed on the working table or fixture. The laser line beam (10 x 2 mm) moves along a specified path over the blade surface which needs preferential melting. To cover larger surface area, the track was overlapped at a ratio of 2-5%. The coverage of area without overlapping might lead to discontinuous surface treatment.

[0039] The scan speed and laser power are varied between 50-300 mm/min and 200-350 watts, respectively to find the optimal laser parameters. Argon is used as the shroud gas to create an inert atmosphere and is laterally fed at 0.6MPa. A pressurized air is supplied parallel to the focusing lens to protect the optics from sparks and fumes. The pilot experiments were performed using single laser track and their cross-section was studied individually before performing multi-track surface melting on real blades.

[0040] Erosion test on as-received and Laser Surface Melting (LSM) treated blade sample were conducted at 200 °C using a hot air erosion testing equipment and procedure as per ASTM G-76. The erosion tests were carried out at five different angles of impact (15º, 30º, 45º, 60º and 75º) by changing the orientation of the sample with respect to the stream of the impinging particles. The erodent particle of alumina of size 40-50 µm were prepared through sieving process and accelerated on to the nodular cast iron test surfaces. Dried air was used for accelerating these particles. The as-received, Laser Surface Melting (LSM) samples were subjected to erosion at an average particle velocity of 100 m/s for a period of 10 min.

[0041] As observed in Fig. 3, the Laser Surface Melting (LSM) treated samples indicate lower erosion rate compared to the base metal at all angles of impingement (15º, 30º, 45º, 60º and 75º). A White Light Interferometer (WLI) based topographical analysis was made to measure the depth and spread of the eroded craters. The topography of the Laser Surface Melting (LSM) surface and that of the base material for different impingement angles are shown in Fig. 4 to 8 and are compared in Fig.9.

[0042] As seen in Fig. 4 to 9, the Laser Surface Melting (LSM) surface had crater depth lesser than the base material surface depth indicating best erosion resistant property of Laser Surface Melting (LSM) surface and also it contributed to lower material loss as shown in Fig. 3. The Laser Surface Melting (LSM) surface had lowest crater depth of all other surfaces compared to the base material at all angles of impact (15º, 30º, 45º, 60º and 75º).

[0043] The laser can be used to treat the blades of larges shapes with aero-foil profiles.
[0044] The advantage of the present Invention is that the micro hardness of the laser treated surface is improved up to 920.8 HV0.3 for depths up to 1 mm which is 4.2 times higher than that of base material and it does not require any additional surface coating material and hence the expenditure for the optimised Laser Surface Melting (LSM) treatment is 3.5 times lesser than the commercially available High Velocity Oxy Fuel thermal spray coating. The treated surface blade will have lesser fan balancing problems compared to those having sacrificial coating and also it will have improvement in service life by 44% compared to that of untreated nodular cast iron blades.

[0045] The material above has been given as an example without restricting scope of the invention to the same. Thus, other materials readily apparent to a person skilled in the art are within scope of the invention.

[0046] Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the "invention" may in some cases refer to certain specific embodiments only. In other cases, it will be recognized that references to the "invention" will refer to subject matter recited in one or more, but not necessarily all, of the claims.

[0047] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all groups used in the appended claims.

[0048] It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particulars claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogues to “at least one of A, B and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B”.

[0049] The above description does not provide specific details of manufacture or design of the various components. Those of skill in the art are familiar with such details, and unless departures from those techniques are set out, techniques, known, related art or later developed designs and materials should be employed. Those in the art are capable of choosing suitable manufacturing and design details.

[0050] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. It will be appreciated that several of the above-disclosed and other features and functions, or alternatives thereof, may be combined into other systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may subsequently be made by those skilled in the art without departing from the scope of the present disclosure as encompassed by the following claims.

[0051] The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others.

[0052] While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.