Title of Invention

A METHOD FOR OBTAINING WEAR RESISTANT EXHAUSTER HOUSING

Abstract

A methods for obtaining wear resistant exhauster housing comprising identifying wear prone zones of the exhauster housing; providing covering/lining of wear resistant plates of wear resistant high Cr iron hard facing alloy deposit on a mild steel base plate for said wear prone regions of said exhauster housing; and installing said prefabricated wear plates on said wear prone regions of said housing to thereby obtain the wear resistance exhauster housing. In the above method, the said wear resistant plates are prefabricated based on the required contour for installation in the wear prone regions of the exhauster housing. The method is also applicable for reclamation of worn-out surfaces of sinter plant exhauster. Also disclosed is an exhauster housing comprising covering wear prone regions of said exhauster housing by lining with wear plates of wear resistant high Cr. Iron hard facing alloy deposit on a mild steel base plate. The method also provides for obtaining a wear resistant exhauster housing, with extended and effective life span could be obtained. The method also provides a wear resistant exhauster housing which has better wear resistivity and thus longivity as compared to prior art exhauster housings.

Full Text

FIELD OF THE INVENTION The present invention relates in general to a method for obtaining wear resistant exhauster housing and an exhauster housing obtained therefrom and also to a method for reclamation of worn-out surface of exhauster housings. The exhauster housing of the present invention finds use in sinter plants. BACKGROUND OF THE INVENTION Exhauster housings of sinter plants are involute shaped cast housing made of St-20 grade steel. It forms a chamber for rotor blade assembly. Basically, this assembly acts as a huge air-sucking pump. Air is sucked through the hot sinter bed for making sinter for blast furnace. While sucking air through hot sinter, fine sinter and other abrasive particles are also carried with the air into this exhauster-housing chamber at great velocities. Due to this impinging of abrasive particles on the walls of exhauster housing at glancing angle, erosion of top-layer of the housing takes place. Exhauster housing thickness is normally about 50 mm. However, with time it gets thinner and at certain locations get punctured, resulting in inefficient air sucking. This enhanced the need to develop an appropriate technology for preventing the exhauster housings from wearing by reclamation of different areas of the exhauster housing. In the technology known in the art, different processes were adapted for reclamation of the different areas of the exhauster housing depending on the degree of wear. The salient features of the technology known in the art were as follows: In areas of the housing wall where surface had eroded to the extent of 5-8mm or less reclamation by direct hard facing or build up by normal low heat input electrodes followed by final hard facing the area were adopted. 2 When direct hard facing was employed without any build up of welding area, first the area was cleaned properly to remove non-metallic particles. Thereafter, the welding area was heated to a temperature of 200-250°C followed by hard feeing with high alloy Cr-Mo-W iron type electrodes. Areas suffering from high degree of wear were first build up with low H2, low input variety of electrodes. These areas were first cleaned and preheated to 100-150°C and thereafter build up was achieved by 2-3 runs of interpass cleaning. Final hardfacing was done after cleaning of the top surface of build up area without much delay to restrict the thermal shock of the pool. At locations of housing where wear was excessive to the range of near puncture, it was essential to make initial repairs with mild steel plates. Prior to installation of mild steel plates, such locations were first cleaned properly, if needed by gouging. Steel plates were installed by welding, taking care of smooth matching of edges with the housing wall. Plate thickness and its fitting procedure were adopted taking care of the provisions of final hard faced coating to be given on it. In a nutshell, prior art techniques essentially consisted of localised reclamation of worn-out exhauster housing by applying the various techniques as contemplated before, specifically at physically visible worn-out areas of such exhauster housings. Such repairing used to last only for a maximum period of two months, and problems shooted up, as further wearing of the exhauster housings took place, i.e. with gradual increase in the area of wearing zone. Need for welding of larger area increased with successive repair, frequently causing distortion of the whole housing. At this stage further repair by local welding became impossible resulting in severe wear of certain regions, even to the extent of puncturing of the wall. So, replacement of whole housing with a new one became inevitable. Besides the above defects, prior art techniques applied resin bonded cold setting compound based on Al203 and SiC. They were applied with welded wire mesh on wear prone areas. Also, ceramic tiles made of AI203 and SiC were overlayed on 3 mild steel plates. Although AI203 and SiC had extremely high hardness (>8 in Moh's scale), the strength of bonding the materials amongst the particles was not that high. Hence the individual particles were detached. Accordingly, such materials have been found to be unsuitable for prevention of erosive wear. OBJECTS OF THE INVENTION It is a basic object of the present invention to provide a method for obtaining a wear resistant exhauster housing, whereby the disadvantages of the prior art technique, as contemplated hereinbefore, are obviated. It is yet another object of the present invention to provide a wear resistant exhauster housing which has better wear resistivity and thus longivity as compared to prior art exhauster housings. It is a further object of the present invention to provide an exhauster housing having better wear resistivity and thus longivity as compared to prior art exhauster housings. SUMMARY OF THE INVENTION Thus according to the present invention there is provided a method for obtaining wear resistant exhauster housing comprising; identifying wear prone zones of the exhauster housing: providing covering/lining of wear resistant plates of wear resistant high Cr iron hard facing alloy deposit on a mild steel base plate for said wear prone regions of said exhauster housing ; and installing said prefabricated wear plates on said wear prone regions of said housing to thereby obtain the wear resistance exhauster housing. Preferably, in the above disclosed method, the said wear resistant plates are prefabricated based on the required contour for installation in the wear prone regions of the exhauster housing. 4 According to another aspect of the present invention, there is provided the method of reclamation of worn-out surfaces of sinter plant exhauster housing comprising covering the worn out regions of said exhauster housing by lining with wear plates of wear resistant high Cr. Iron hard facing alloy deposit on mild steel base plate, wherein said lining is effected by prefabricating the said wear plate segments according to the possible contour of worn out housing and installing said prefabricated wear plates on said wear prone regions of said housing. According to another preferred embodiment, the present invention also provides a method as described hereinbefore, wherein said wear plates are manufactured by depositing said hard layer of wear resistant high Cr-iron hardfacing alloy on said mild steel base plate by weld deposition. According to another preferred embodiment, the present invention also provides a method as described hereinbefore, wherein said wear plates are manufactured by depositing said hard layer of wear resistant high Cr-iron hardfacing alloy on said mild steel base plate by casting. According to a further preferred embodiment, the present invention also provides a method as described hereinbefore, wherein two adjoining said wear plates are welded after installing them on said housing wall. In accordance with another aspect of the present invention, there is also provided an exhauster housing comprising covering wear prone regions of said exhauster housing by lining with wear plates of wear resistant high Cr. Iron hard facing alloy deposit on a mild steel base plate. In said exhauster housing, the lining is obtained of prefabricated wear plate segments according to the possible contour of wear prone zone of the housing. The present invention thus discloses providing exhauster housing having improved wear resistance characteristics for durable and extensive life span especially for use in sinter plants. This technology is thus different from the 5 localised repairing technology of prior art, where repairing was done specifically at physically visible worn out areas of the exhauster housings. Importantly, the present invention provides for advantageous use of selective wear plates made of high iron-Cr hard facing alloy deposited on steel base plate and avoides the use of AI2O3 and SiC based material due to their disadvantages. BRIBF DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS The objects and working of the present invention will be better understood on perusing the following non-limiting description in relation to the accompanying drawings wherein, Figures 1(a) & (b) illustrate typical photomicrographs of high Cr-iron alloy in accordance with the invention magnified 200 times and 500 times respectively. Fig.2 illustrates a schematic lay out of the sinter plant incorporating exhauster housing in accordance with the invention. Fig.3(a) illustrates an exploded view of exhauster housing in accordance with the invention. Fig.3(b) illustrates a top view of exhauster housing in accordance with the invention. Fig.4 illustrates a profile and sectional view of the exhauster in accordance with the invention. Fig.5 illustrates a developed drawing of the internal housing surface where wear plates are to be laid in a pre-designed fashion. Fig.6 illustrates a large single bend wear plate emplaced in central portion of the exhauster housing in accordance with the invention. 6 Fig.7 illustrates a double curvature wear plate emplaced in lateral portion of exhauster housing of the invention. Fig.8 illustrates a methodology of welding of wear plates in accordance with the invention. Fig. 9 illustrates a map of hardfacing alloys used in the wear plates of the invention. Fig. 10 illustrates amount of surface roughness after welding of wear plates. Figures 1(a) & (b) show a uniform distribution of hard chromium carbides in a hard martensitic martix leading to an ideal situation to minimise wear in an exhauster housing wall. Fig.2 illustrates the different elements in a sinter plant incorporating the exhauster housing in accordance with the invention. The sinter plant comprises proportioning bins (1), mixing cum balling drum (2), raw mix hopper (3), sinter max charging system (4), hearth layer hopper (5), hot sinter screen (9), sinter cooler (10), cold sinter screen (11), wind boxes and wind legs (12), wind main (13), dust cleaning system (14), exhauster housing (15) and chimney (16). Fig. 3(a) shows the exhauster housing in detail. It has an overall involute shape having a rotor (11). This assembly acts as a huge air sucking pump. Air is sucked through the hot sinter bed for making sinter for blast furnace. While sucking air through hot sinter, fine sinter and other abrasive particles are also carried with the air into the exhauster housing chamber thus giving birth to worn out layer (21) along both top housing (31) and bottom housing (41). Fig.3(b) shows a top view of exhauster housing shown in Fig. 3(a), housing focussing the zones of severe wear. 7 Fig. 4 shows the profile and sectional view of the exhauster housing. Due to complicated contours of the housing and limitation of bendability of the high chromium iron wear plate, it is required that the required internal surface be divided into segments. Regions where the curvatures are acute further smaller segments are to be adopted. Fig.5 shows the developed drawing of the internal housing surface where wear plates are to be laid in a pre-designed fashion. The wear plates are designed in accordance with the contour of the housing. Central portion of housing has more or less flat surface with single curvature. Here large wear plates with single bend needs to be accommodated as shown in Figure 6. Lateral portions of the housing contour has double curvature. Here, the wear plate tiles are required to be adjusted with proper careful bending of tiles as shown in Figure 7 Shape and size of the wear plates may be estimated with a CAD tool. Figure 8 shows the methodology to be used for proper welding of two adjoining wear plates after fixing these plates on the housing wall. This figure 8 shows high chrome alloy hard deposit (51), high chrome alloy matching hard deposit (6), mild steel base plate (71), LH. electrode (81) and S.S. electrode (91). A wear plate basically contains a hard wear resistant high Cr iron hard facing alloy deposit on mild steel base plate. Deposition of hard layer can be achieved either by weld deposition or by casting obtaining strong bonding with the base plate and uniformity of thickness. In both these cases, the manufacturing parameters are controlled by computerized system. Depending on the requirement of carbides and its nature to withstand temperature condition, the composition of hardfacing alloys forming the wear plates may vary in respect of carbon and chromium content principally with some variation of alloy content. Preferably, composition of high Cr irons of two basic types used in the wear plates of the invention are shown in Table-I. 8 Table-I Hardfacing Alloys type Chemical Composition (Wt%) Hardness (*HRC) 1 C 3.0 Cr 26.0 Mo 4.0 W 2.0 Ni 0.25 Nb 1.50 V 0.25 Fe Balance 55-57 II 5.5 23.0 2.0 2.0 - 7.0 1.50 Balance 59-61 * Hardness in Rockwell C-Scale. Further, as illustrated in accompanying figure 9 and Table - II below, the invention further identifies the wt% of alloy : carbon : iron which can be selectively used depending upon the degree of wear resistacnce, quality of wear resistance and the hardness required. Table-II Degree of Wear **Alloy (%) by Wt. Carbon (%} by Wt. Iron Severe abrasive 8.0% to 35.0% 4.0% to 7.0% Balance Impact abrasive wear 1.8% to 35.0% 2.0% to 4.0% Balance Couging & impact wear 1.8% to 30.0% 0.35% to 1.2% Balance Rolling & Sliding wear 1.0% to 20.0% 0.05% to 0.7% Balance ** Alloys include Cr, Mn, Mo, Ni, W, Nb, V, Ti, A1 Figure 10 shows amount of surface roughness after welding of wear plates wherein like reference numerals represent like features as in Figure 8. In particular, when two adjacent wear plates are welded on their edges the final top weld beads are always protruded above the plate levels. This gives rise to unevenness of the surface at the joined edge of the plate. To ensure proper joining of two wear plates adequate molten weld metal is ensured in the joints and therefore protrusion occurs. However, control/shill has to be exercised during welding to avoid excessive weld metal to result in high protrusion. A protrusion of 2-3 mm relative to wear plate surface with smooth blending at locations shown in Fig. 10 are tolerable for the exhauster housing surface. It shows that the surface smoothness is acceptable even after welding of wear plates. The present invention has been described with reference to some preferred embodiment and the accompanying drawings, but in no way is limited to such preferred embodiments and drawings and it is to be understood that various modifications of the invention is possible within the purview of what has been described hereinbefore are claimed in the appended claims. 9 We Claim: . 1. A method for abtaining wear resistant exhauster housing comprising; -providing an exhauster housing - identifying wear prone zones of the exhauster housing: - providing covering/lining of wear resistant plates of wear resistant high Cr iron hard facing alloy deposit on a mild steel base plate for said wear prone regions of said exhauster housing, said hard facing deposit comprising 1.0%-35% alloy, 0.05%-7% carbon and balance iron by wt.; wherein the hard facing alloy has composition selected from C-3%, Cr-26%, Mo-4%, W-2%, Ni-0.25%, Nb-1.50%, V-0.25%, the balance - Fe, all by weight when hardness of the alloy is between 55-57 HRC; and C-5.5%, Cr-23%, Mo-7%, W-2%, Nb-7%, V-1.50%, the balance - Fe, all by weight when hardness of the alloy is between 59-61 HRC; and installing said prefabricated wear plates on said wear prone regions of said housing to thereby obtain the wear resistance exhauster housing. 2. A method for obtaining wear resistant exhauster housing as claimed in claim 1 wherein said wear resistant plates are prefabricated based on the required contour for installation in the wear prone regions of the exhauster housing. 3. A method for obtaining wear resistant exhauster housing as claimed in any one claims 1 to 3 wherein said wear plates are manufactured by depositing said hard layer of wear resistant high Cr-iron hardfacing alloy on said mild steel base plate by weld deposition. 4. A method for obtaining wear resistant exhauster housing as claimed in any one claims 1 to 3 wherein said wear plates are manufactured by depositing said hard layer of wear resistant high Cr-iron hardfacing alloy on said mild steel base plate by casting. 2. 10 5. A method for obtaining wear resistant exhauster housing as claimed in any one of claims 1 to 5 wherein two adjoining said wear plates are welded after installing them on said housing wall. 6. A method as claimed in any preceding claim, wherein said hardfacing alloy deposit in said wear plates comprises 8.0% to 35.0% of alloy and 4.0% to 7.0% of carbon, the balance Fe all by weight, said wear plates being suitable for resisting severe abrasive wear. 7. A method as claimed in any preceding claim, wherein said hard facing alloy deposit in said wear plates comprises 1.8% to 35.0% alloy and 2.-0% to 4.0% of carbon, the balance iron all by weight, said wear plates being suitable for resisting impact and abrasive wear. 8. A method as claimed in any preceding claim, wherein said hard facing alloy deposit in said wear plate comprises 1.8% to 35.0% of alloy and 0.35% to 1.2% of carbon, the balance iron all by weight, said wear plates being suitable for resisting gouging and impact wear. 9. A method as claimed in any preceding claim, wherein said hard facing alloy deposit in said wear plate comprises 1.0% to 20.0% of alloy and 0.05% to 0.7% of carbon, the balance iron, all by weight, said wear plates being suitable for resisting rolling and sliding wear. 10. A method as claimed in any preceding claim, wherein two adjoining said wear plates are welded after installing them on said housing wall. 11. A method as claimed in any preceding claim, wherein in central portion of said housing, larger wear plates with single bend are installed. 12. A method as claimed in any preceding claim, wherein in lateral portion of said housing, small wear plates with double curvature bending are installed. 12. 11 13. A method as claimed in any preceding claim, wherein bending of said wear plates are done in stages in a bending machine. 14. A method for obtaining wear resistant exhauster housing, substantially as herein described, particularly with reference to the accompanying drawings. 15. A restored exhauster housing having been abtained by the method as claimed in any preceding claim comprising wear prone regions of said exhauster housing covered by lining with wear plates of wear resistant high Cr. Iron hard facing alloy deposit on a mild steel base plate comprising wear plate segments that are prefabricated according to the possible contour of wear prone zone of the housing and selective wear plates made of high iron-Cr hard facing alloy deposited on steel base plate. Dated 7th day of March, 2001. S. MAJUMDAR OF S.MAJUMDAR&CO. Applicant's Agent A methods for obtaining wear resistant exhauster housing comprising identifying wear prone zones of the exhauster housing; providing covering/lining of wear resistant plates of wear resistant high Cr iron hard facing alloy deposit on a mild steel base plate for said wear prone regions of said exhauster housing; and installing said prefabricated wear plates on said wear prone regions of said housing to thereby obtain the wear resistance exhauster housing. In the above method, the said wear resistant plates are prefabricated based on the required contour for installation in the wear prone regions of the exhauster housing. The method is also applicable for reclamation of worn-out surfaces of sinter plant exhauster. Also disclosed is an exhauster housing comprising covering wear prone regions of said exhauster housing by lining with wear plates of wear resistant high Cr. Iron hard facing alloy deposit on a mild steel base plate. The method also provides for obtaining a wear resistant exhauster housing, with extended and effective life span could be obtained. The method also provides a wear resistant exhauster housing which has better wear resistivity and thus longivity as compared to prior art exhauster housings.

Documents:

00136-cal-2001-abstract.pdf

00136-cal-2001-claims.pdf

00136-cal-2001-correspondence.pdf

00136-cal-2001-description(complete).pdf

00136-cal-2001-drawings.pdf

00136-cal-2001-form-1.pdf

00136-cal-2001-form-18.pdf

00136-cal-2001-form-2.pdf

00136-cal-2001-form-3.pdf

00136-cal-2001-pa.pdf

136-cal-2001-granted-abstract.pdf

136-cal-2001-granted-claims.pdf

136-cal-2001-granted-correspondence.pdf

136-cal-2001-granted-description (complete).pdf

136-cal-2001-granted-drawings.pdf

136-cal-2001-granted-examination report.pdf

136-cal-2001-granted-form 1.pdf

136-cal-2001-granted-form 18.pdf

136-cal-2001-granted-form 2.pdf

136-cal-2001-granted-form 3.pdf

136-cal-2001-granted-letter patent.pdf

136-cal-2001-granted-pa.pdf

136-cal-2001-granted-reply to examination report.pdf

136-cal-2001-granted-specification.pdf