Claims:WE CLAIM:
1. A salvaging method for a workpiece comprising the steps of:
a) preparing a salvaging mixture by mixing a predetermined amount of sulphuric acid and nitric acid in water;
b) pouring the prepared salvaging mixture at a predetermined location of the workpiece;
c) retaining the poured salvaging mixture for a first predetermined amount of time;
d) cleaning the treated workpiece with water; and
e) tempering the cleaned workpiece at predetermined temperature for a second predetermined amount of time.
2. The salvaging method as claimed in claim 1, wherein the workpiece is a gear having spline errors therein.

3. The salvaging method as claimed in claim 2, wherein the gear is a bull gear having spline errors therein.

4. The salvaging method as claimed in claim 1, wherein the salvaging mixture includes Sulphuric acid in a range of 10% to 20% Vol. /Vol.

5. The salvaging method as claimed in claim 1, wherein the salvaging mixture includes Nitric acid in a range of 2% to 4% Vol. /Vol.

6. The salvaging method as claimed in claim 1, wherein the salvaging mixture includes water in a range of 76% to 88% Vol. /Vol.

7. The salvaging method as claimed in claim 1, wherein the predetermined temperature is in a range of 150° to 200°C.

8. The salvaging method as claimed in claim 1, wherein the first predetermined amount of time is at least 8 hours.

9. The salvaging method as claimed in claim 1, wherein the second predetermined amount of time is at least 2 hours.
Dated this 27th day of December 2019

For MAHINDRA & MAHINDRA LIMITED
By their Agent

GIRISH VIJAYANAND SHETH IN/PA- 1022
KRISHNA & SAURASTRI ASSOCIATES LLP

, Description:FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003

COMPLETE SPECIFICATION
[See Section 10, Rule 13]

A SALVAGING METHOD FOR A WORKPIECE

MAHINDRA & MAHINDRA LIMITED, HAVING ADDRESS MAHINDRA & MAHINDRA LIMITED, MAHINDRA RESEARCH VALLEY, MAHINDRA WORLD CITY, PLOT NO: 41/1, ANJUR P.O., CHENGALPATTU, TAMILNADU – 603004, INDIA

THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED

FIELD OF THE INVENTION
The present invention relates to methods of salvaging a workpiece and more particularly to a salvaging method for rejected gears having spline errors therein.
BACKGROUND OF THE INVENTION
Large driving gears, such as a bull gear are used in final drives or in gear transmission systems. Each bull gear has a spline configured to be engaged with mating part of adjacent gear in order to facilitate transmission of the torque. These gears are generally made of alloy steel having high strength and hardness prevent wear resistance. However, these gears still undergo wear or deformation over the period of time thereby having errors in the spline. On the other hand, the newly manufactured bull gears also get rejected during testing due to gear spline errors therein. Hence, these newly manufactured gears cannot be utilized due to errors in the size of gear spline. Also, the Go/ No-Go spline gauges used for measurement of splines have structural limitations to be inserted in the defective internal spline due to heat treatment shrinkage problem.
Accordingly, various methods of repair and salvage are known in the art to revitalize a worn or rejected gear spline. One method which has been widely used is Electrical discharge machining (EDM, hereinafter) that removes a material from the work piece. EDM, also known as a spark machining, is a manufacturing process whereby a desired shape is obtained by using electrical discharges/ sparks. In EDM, the material is removed from the work piece by a series of rapidly recurring current discharges between two electrodes, separated by a dielectric liquid and subject to an electric voltage. One of the electrodes is called the tool-electrode, while the other is called the workpiece-electrode. The process depends upon the tool and work piece not making actual contact. When the voltage between the two electrodes is increased, the intensity of the electric field in the volume between the electrodes becomes greater than the strength of the dielectric (at least in some places), which breaks down, allowing current to flow between the two electrodes. This phenomenon is the same as the breakdown of a capacitor (condenser). As a result, material is removed from the electrodes. Once the current stops (or is stopped, depending on the type of generator), new liquid dielectric is usually conveyed into the inter-electrode volume, enabling the solid particles (debris) to be carried away and the insulating properties of the dielectric to be restored. Adding new liquid dielectric in the inter-electrode volume is commonly referred to as "flushing." Also, after a current flow, the difference of potential between the electrodes is restored to what it was before the breakdown, so that a new liquid dielectric breakdown can occur.
However, the aforementioned EDM method has various disadvantages or limitations. For example, the EDM method needs expert machinists to handle the operation. Moreover, the EDM method has a very slow rate of material removal and may result to a fire hazard due to use of combustible oil-based dielectrics. Further, the EDM method involves additional time and cost for creating electrodes for ram/sinker EDM. Further, EDM has serious limitations in reproducing sharp corners on the workpiece due to electrode wear which may occur during the machining process. Moreover, the EDM method consumes very high power and an excessive tool wear may occur during machining. In addition, the EDM process involves electrically non-conductive materials that can be machined only with specific set-up of the process.
Therefore, there is felt a need of an improved salvaging method for rejected gears having spline errors contained therein.
SUMMARY OF THE INVENTION
The present disclosure provides a salvaging method for a workpiece comprises an initial step of preparing a salvaging mixture from a predefined amount of sulphuric acid, a predetermined amount of nitric acid and a predetermined amount of water. In next step, the salvaging mixture is poured at a predetermined location of the workpiece and retained for a first predetermined amount of time. In next step, the treated workpiece is cleaned with water and tempered at predetermined temperature for a second predetermined amount of time followed by checking and machining progress at regular intervals thereby repeating the salvaging method of the present invention until desired machining of the workpiece is ensured. In the context of the present invention, the workpiece is a rejected gear spline having spline errors therein. In the context of the present invention, the salvaging mixture includes Sulphuric acid, Nitric acid and water wherein Sulphuric acid is having concentration in a range of 10% to 20 % Vol./Vol., Nitric acid is having concentration in a range of 2% to 4% Vol./Vol. and the water is in a range of 76% to 88% Vol./Vol.. In the context of the present invention, the first predetermined amount of time is at least 8 hours and the second predetermined amount of time is at least 2 hours.
BRIEF DESCRIPTION OF THE DRAWINGS
A method of the present disclosure has been described with reference to accompanying drawing, in which:
Figure 1 illustrates a graphical representation of material removal in mm Vs Time in hrs with salvaging mixture having 10% Sulphuric acid, 2% Nitric acid and 88% water; and
Figure 2 illustrates a graphical representation of material removal in mm Vs Time in hrs with salvaging mixture having 20% Sulphuric acid, 4% Nitric acid and 76% water.
DETAILED DESCRIPTION OF THE INVENTION
The foregoing objects of the present invention are accomplished and the problems and shortcomings associated with the prior art, techniques and approaches are overcome by the present invention as described below in the preferred embodiments.
Although specific terms are used in the following description for sake of clarity, these terms are intended to refer only to particular structure of the invention selected for illustration in the drawings and are not intended to define or limit the scope of the invention. References in the specification to “preferred embodiment” means that a particular feature, structure, characteristic, or function described in detail thereby omitting known constructions and functions for clear description of the present invention.
The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope of the invention.
In general aspect, the present invention relates to a method for salvaging gear internal spline thereby removing metal from internal and external gear teeth to obtain desired size in terms of Diameter over pin (DOP), Diameter inside pin (DIP) and Span Size (SS). In the context of present invention, the method of salvaging is an acid machining process that removes alloy steel material in a controlled manner to obtain desired size of gears after heat treatment.
In a preferred embodiment, the present invention provides a salvaging method for a workpiece, said method comprising the steps of:
a) preparing a salvaging mixture by mixing a predetermined amount of sulphuric acid, a predetermined amount of nitric acid and a predetermined amount of water;
b) pouring the prepared salvaging mixture at a predetermined location of the workpiece;
c) retaining the poured salvaging mixture for a first predetermined amount of time;
d) cleaning treated workpiece with water; and
e) tempering the cleaned workpiece at predetermined temperature for a second predetermined amount of time.
In an embodiment, the Sulphuric acid of the salvaging mixture has a concentration in a range of 10% to 20 % Vol. / Vol. in water. In an embodiment, the Nitric acid of the salvaging mixture has a concentration in a range of 2% to 4% Vol. /Vol. in water. In an embodiment, the salvaging mixture includes water in a range of 76% to 88% Vol. /Vol. The Sulphuric acid and Nitric acid are preferably mixed in an equal volumetric proportion thereof. However, it is understood that the concentration and volumetric proportion of Sulphuric acid, Nitric acid and water may vary as per intended salvaging requirement of the workpiece.
In an embodiment, the workpiece is a rejected bull gear spline having spline errors contained therein. However, it is understood that the shape, size and type of workpiece may vary in other alternative embodiments of the present invention.
In an embodiment, the first predetermined amount of time is at least 8 hours. However, it is understood however that the first predetermined time may vary in other alternative embodiments of the present invention as per shape, size and type of the workpiece undergoing salvaging treatment.
In an embodiment, the second predetermined amount of time is at least 2 hours. However, it is understood however that the second predetermined time may vary in other alternative embodiments of the present invention as per shape, size and type of the workpiece undergoing salvaging treatment.
EXAMPLE
EXAMPLE-1
Salvaging of the rejected bull gear work piece with salvaging mixture containing 10% Sulphuric acid, 2% Nitric acid and 88% water-
In an initial step, a salvaging mixture is prepared by adding an equal proportion of the 10% Sulphuric acid and 2% Nitric acid. In next step, the salvaging mixture prepared in earlier step is poured into the spline of the rejected bull gear work piece followed by keeping said rejected bull gear work piece for the first predetermined time of 8 hours. Thereafter, the rejected bull gear work piece is subjected to clean with normal water followed by tempering in the range of 150-200ºC thereof for the second predetermined time of 2 hours. In next step, the treated bull gear is checked for spline entry thereby repeating aforementioned steps until spline entry was ensured. The material removal rate in this context was plotted in a graphical format as illustrated in FIG. 1. It was observed that for the first predetermined time is 8 hours there was an increase of 0.020 mm in DIP of the rejected bull gear spline after being treated for 8 hours by the salvaging method of the present invention.
EXAMPLE-2
Salvaging of the rejected bull gear work piece with salvaging mixture containing 20% Sulphuric acid, 4% Nitric acid and 76% water -
In an initial step, a salvaging mixture is prepared by adding an equal proportion of the 20% Sulphuric acid and 4% Nitric acid. In next step, the salvaging mixture prepared in earlier step is poured into the spline of the rejected bull gear work piece followed by keeping said rejected bull gear work piece for the first predetermined time of 8 hours. Thereafter, the rejected bull gear work piece is subjected to clean with normal water followed by tempering in the range of 150-200ºC thereof for the second predetermined time of 2 hours. In next step, the treated bull gear is checked for spline entry thereby repeating aforementioned steps until spline entry was ensured. The material removal rate in this context was plotted in a graphical format as illustrated in FIG. 2. It was observed that for the first predetermined time is 8 hours there was an increase of 0.044 mm in DIP of the rejected bull gear spline after being treated for 8 hours by the salvaging method of the present invention.
The salvaging method of the present invention can be advantageously utilized to provide localized machining to remove internal and external material of any ferrous part from the workpiece. The salvaging method of the present invention has a controlled metal removing rate which is predictable. The salvaging method of the present invention is suitable for metal removing operations demanding small but uniform metal removal such as for example metal removal in a range of 0.010 mm to 0.050 mm which is otherwise not possible with conventional gear machining processes. The salvaging method of the present invention requires less amount of acid as compared to acid bath treatments known in the art.
The foregoing description of specific embodiments of the present invention has been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching.
The embodiments were chosen and described in order to best explain the principles of the present invention and its practical application, to thereby enable others, skilled in the art to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated.
It is understood that various omission and substitutions of equivalents are contemplated as circumstance may suggest or render expedient, but such are intended to cover the application or implementation without departing from the spirit or scope of the present invention.
Figures are merely representational and are not drawn to scale. Certain portions thereof may be exaggerated, while others may be minimized. Figures illustrate various embodiments of the invention that can be understood and appropriately carried out by those of ordinary skill in the art.