|Title of Invention||
"A PROCESS FOR RECLAMATION OF MACHINERY COMPONENTS
|Abstract||This invention relates to a process for reclamation of worn-out machinery pomponents using plasma weld surfacing technique wherein the coated material in the form of powder or wire is melted using pilot arc maintained between nozzle and electrode and the substrate (worn-out machinery component) is heated using transferred arc maintained between electrode and substrate. And then spraying plasma of melted filler material on to the heated surface of the substrate.|
|Full Text||FIELD OF THE INVENTION
The present invention relates to the process for reclamation of machinery components.
PRIOR ART OF THE INVENTION
A large number of high cost and critical machinery components, such as brake disc of aircraft, crank shaft, camshafts, rotor shafts etc, get frequently worn-out due to fair wear and tear. Therefore, the necessity of development of process for reclaiming such costly and critical machinery components has been felt by the engineers over last few decades.
The necessity to reclaim worn-out machinery components, in general is due to requirement of improving the mean life before failure of the machinery component, to conserve the scare material resources and to impart special surface properties for enhancing the life of the machinery components and thus to save the replacement cost, which in-turn forms a major component of the maintenance cost.
The reclamation processes as known in the prior art are generally classified as thermal spraying, welding and electrop1at ing.
The main disadvantage of such known processes is that, none of these processes approach universality of applications to reclaim the worn-out machinery components. Each process has limitations of its own.
The commonly known welding processes known in the prior art, have disadvantage of leading to the warpage due to their inherent high heat input.
The thermal sparying processes, as known in the prior art, like flame, arc and plasma spraying, high velocity oxyfuel (HVOF), detonation gun etc. have disadvantage of being the cold processes, which in-turn, results in coatings
having poor bond strength, which further in-turn is due to
their mechanical bond at the coating material, referred as
deposit here-in-after and coated substrate, referred as
substrate here—in-after, interface.
The another such known processes, like electroplating processes, such as hard chrome plating, selectron process-in-situ electroplating process also have disadvantage of being the cold processes.
Therefore, the known conventional processes of reclaiming the worn—out machinery components, like welding processes, thermal spraying processes and electroplating processes, as known in the prior art and as briefed herein above, lack in one way or other in achieving properties like distortion free component and strong metallurgical banding between the deposit and substrate, which are the prerequisites for reclaimation of the critical worn-out machinery components.
The another such known technique is plasma weld surfacing technique. This technique has disadvantage of exhaustive experimentation for many aspects of parameters to control the characteristics of coating and of interface between deposit and substrate and of the metallurgical bonds formed between coating material and the substrate material.
The disadvantages of the Plasma Weld Surfacing Technique, here in after referred as PWST, are that it requires control of various aspects of operating parameters and of characteristics of coating, interface and metallurgical bonds. It may be referred herein that, these may include as many as overlay material, current, gas (plasma, protection, powder) flow and pressure, powder feed and interation time between plasma gun and component, and control of cracking of deposited metal, evenness of coating, uniform coating of entire surface, expected mechanical properties, corrosion and wear resistance properties etc. The list of aspects to be controlled as stated above is not exhaustive but may include many other aspects required to be control1ed.
The major disadvantage of requirement of control of such aspects as stated herein above is that innumerable experimental conditions are required to be tried by permutation and combinations of various process parameters and by making use o-f various coating materials with various worn-out machinery component. 5.
This disadvantage o-f requirement o-f control of several process parameters, as stated herein above, results in increase in cost of process of reclamation of worn-out machinery components. Such increase in cost of process, sometimes increases cost to such an extent that it is more than the cost of the component required to be reclaimed. OBJECTS OF THE. INVENTION
The primary and main abject of this invention is to propose a process for reclamation of machinery components which are worn-put after being in use over a period of time.
Another object of the present invention is to propose a process for the reclamation of worn-out machinery components which is economical.
Still another object of the present invention is to propose a process for reclamation of machinery components which eliminates exhaustive trials that are required in known process for the control of process parameters and the proposed process can also be used for correcting the dimensions of critical components for their reuse.
Further object of the present invention is to propose a process for reclamation of machinery components, which results in strong metallurgical bonding between deposit and substrate.
A still further object of this invention is to propose a process for reclamation of machinery components which results in coating in two layers.
Further object of this invention to propose a process which results in a defect-free coating over a surface of worn-out machinery component.
Still further object of this invention is to propose a process, which results in grain coarsening at the interface.
Yet another object of this invention is to propose a process, which does not result in formation of martinsite.
Still another object of this invention is to propose, a process, which provides corrosion and wear resistant coating over the surface of the substrate.
STATEMENT OF THE INVENTION
This invention discloses a process for reclamation of machinery components comprising of plasma weld Surfacing Technique wherein the coating material such as described herein in the form of powder or wire is melted by pilot arc, current 60 to 250 amp maintained between nozzle and electrode of Plasma Weld Surfacing Technique and the substrate (worn-out machinery component) is heated using transferred arc maintained between electrode and substrate, followed by plasma spraying of melted filler material on to the heated surface of the substrate.
In accordance with the present invention, the pilot arc is maintained between nozzle and electrode, and transferred arc is maintained between elctrode and component throughout the welding cylce, in semi-transferred mode at specific process parameters.
The process gives precise control of penetration into base metal. The penetration is restricted to 0.1mm. The deposit obtained is flatter, smoother with exceptional shining surfaces. Therefore no machining or minimal machining of deposit is required after reclamation to meet the dimensional requirements. The weld deposit is made on the surface without carrying out any special surface preparation. The process is completely automated from 'start' to 'stop' event of weld cycle.
Using this process technology, a wide variety of high cost and critical worn-out undersized machining components like rotors, crankshafts, axles, pumps shafts, implellers, valve bodies, propellers shafts can be salvaged for reuse. The process can also impart any special properties like corrosion, heat, wear and abrasion resistance on a baser substrate for specific applications.
DESCRIPTION OF- INVENTION WITH REFERENCE TO ACCOMPANYING DRAWINGS
Figure-1, shows the microhardness profile below the weld bead.
Figure—2, shows the microhardness profile away from weld bead.
Figure-3, shows microstructure of the substrate before reclamat ion.
Figure-4, shows microstructure of the coated substrate after reclamation
Figure-5, shows the line scan plot across the interface.
In accordance with present invention, the process for
reclamation of machinery components is economic and has overcome the
disadvantages of the known such processes of prior art and particularly
the disadvantage of exhaustive experimental work for process
The process comprises of melting of coating filler material
by pilot, arc, which is maintained between nozzle and electrode of PWST.
In the second step, the substrate, i.e worn-out component is heated by transferred arc, which is maintained between electrode and component throughout the welding cycle.
The coating material in accordance to the present process is taken in the form D+ powder wire.
In third step, the melted coating material (filler material) is plasma sprayed onto the heated surface of the substrate.
The coating material, in accordance to preferred embodiment of this invention is selected among the group of nickel, cobalt and iron base filler materials, which has, high tolerance level towards dilution, compatible thermal expansion co-efficient, structural stability over working temperature and generates no crack sensitive constituent at the interface of deposit and substrate.
In accordance to the most preferred embodiment of this invention the coating material is nickel base filler metal alloy having chemical composition with preferable weight percent of 10% Cr, 2.0% B, 2.25% Fe, 0.45% of C, 2.0% of S1, balance Ni.
The specific process parameters, in accordance to the most
preferred embodiment of this invention are primarily Operating mode
Current Gas flow and pressure Powder feed, Interaction
time between plasma gun and component. These
process parameters in general, are as given table-I:
General Process Parameters
The presently disclosed process was performed on brake disc of islander aircraft, which was required to be reclaimed for the reuse after correct dimensions. The brake disc comes in contact with frictional lining during operation and in process of use, thus the surface of the brake disc gets frequently worn-out. For reuse, the disc should be dimensionally stable within very close tolerances.
The brake disc was reclamed by coating with nickel base coating material, in accordance with the preferred embodiments of the presently disclosed process, as described here in above.
ThP steel plate/disc after reclamation in accordance with the process, as described herein above, is subjected to nan-destructive evaluation, chemcial analysis, metallaqraphic studies, microhardness analysis and electron probe micro-analysis (EPMA).
The chemical analysis proves absence of any appreciable dilution in the coated layer and defects at the interface of coating/deposit and substrate.
The microhardness analysis indicates the heat affected to 2.5 mm below the weld bead and 197 to 294 VPN hardness,
suggesting absence of hard constituents and as well of any softer constituent in the top layer and hence better wear resistance.
The total deposit thickness of O.981mm is achieved in two layers when the disc/plate is reclaimed in accordance to this process.
The process, as disclosed above permits to have weldment having a smooth transition in hardness values from 328 to 427 VPN from steel side to deposit/coating side by introducing a softer zone of about 0.2mm width adjacent to interface on the deposit side.
The microhardness profiles below the weld side bead and
away from weld bead are shown in figure 1 and 2
respectively. These profiles indicate the variation in
hardness values across the interface.
The microstructural analysis of the coated surface reveals the dense weldments having no porosity, crack or any other defect or martensites. The grain coarsening is introduced at interface.
The microstructure, as stated above can be understood from comparison of microphotographs A and B as shown in figure 3 and 4 respectively. The microphotograph A shows the microcstructure of the substrate before reclamation and microphotograph-B shows the microstructure of the coated substrate after reclamation in accordance to the presently disclosed process of this invention.
The microphotograph-A shows the pearlite and ferrite and grain coarsing effect.
The microphotograph-B shows the dendritic structure.
The quantitative microprobe analysis was carried out across the interface between coating/deposit and substrate/component. The data is shown in table-Ill and the line scan plot across the interface is shown in figure-5.
The process of the present invention is susceptible to adaptation and modification by those skilled in the art. Such adaptations, modifications are intended to be covered within the scope of the present invention which is set forth by the following
1. A process for reclamation of machinery components comprising of plasma weld surfacing technique wherein the coating material such as herein described is in the form of powder or wire melted by pilot arc current 60 to 250 amp maintained between nozzle and electrode of plasma weld surfacing technique and the substrate (worn-out machinery component) is heated using transferred arc current 50 to 400 amp maintained between electrode and substrate, followed by plasma spraying of melted filler material on to the heated surface of the substrate.
2. A process as claimed in claim 1 wherein the coating material is selected from the group of nickel, cobalt and iron base filler material.
3. A process as claimed in claims 1 and 2 wherein the coating material preferably used is Nickel based filler metal alloy with preferable chemical composition in weight percent of 10% Cr, 2.0% B, 2.25% Fe, 0.45% C, 2.0% Si and balance Ni.
4. A process as claimed in claim 1 wherein the pilot arc and transferred arc are varied independently to obtain control over the heat input to avoid warpage of a component.
5. A process as claimed in claim 4 wherein the plasma arc current is preferably between 80 amp to 120 amp.
6. A process as claimed in claim 4 wherein transferred arc current is
preferably 80 amp. 7. A process for the reclamation of machinery components substantially
as herein described and illustrated.
|Indian Patent Application Number||1887/DEL/1998|
|PG Journal Number||20/2010|
|Date of Filing||03-Jul-1998|
|Name of Patentee||RESEARCH AND DEVELOPMENT|
|Applicant Address||TECHNICAL COORDINATION DTE.,B-341 SENA BHAWAN, DHQ P.O.NEW DELHI-110011|
|PCT International Classification Number||F16D 65/853|
|PCT International Application Number||N/A|
|PCT International Filing date|