Description: FIELD OF INVENTION AND USE OF INVENTION [001] This present invention, in general, relates to a rotor attachment to restore non-driving thrust end for rotor repair, more particularly, to a special attachment for the centrifugally expandable rotor end portion with the provision of thrust collar and journal in it. The proposed rotor end attachment facilitates faster and easier repair of shaft end. BACKGROUND OF THE INVENTION [002] The rotor is a moving component of turbo machinery equipment viz. turbine, compressor, generator etc.. There are many causes for broken or damaged rotors near end. The most common causes are mal-operation which subjects the rotor to high dynamic loads other than intended such as misalignment, altered balance condition etc and natural degradation material with time especially for rotor with hot operating condition. [003] Another reason for rotor damage or breakage near ned is subjecting a machine for higher loads than intended design condition such as higher thrust load due to high fluid flow or flow path blockade occurring due to poor operation and maintenance practices. Further, thermal overload and cracks due to high temperatures are additional causes. [004] In many occasions, high speed turbomachinery rotors are provided with shrunk-on thrust collar or keyed thrust collar locked by locking screws and sometimes low thrust requirement of turbomachinery application leads to slender rotor before thrust collar. [005] With the above situations, rotors are liable to fail at front thrust collar end during operation due to misaligned condition, poor collar runout condition, high vibrations, high axial thrust, oil starvation or oil contamination in thrust bearing or thrust bearing babbitt failure etc. Sometimes rotor journal also suffers irreparable damages due to oil starvation or oil contamination or bearing babbitt failure. [006] Prior attempts to satisfy the stub shaft attachment are disclosed in U.S.Pat.No.3191976. This invention relates to driving connections and more particularly to an attachment for connecting a stub shaft to a drive shaft applicable for power driven units, such as electric motors, gasoline engines with a projecting shaft accommodating pulleys and overhung units, such as pump propellers etc. with shorter overhang without thrust collar on it. However, the arrangement is not reliable for higher span rotor with a requirement of radial supporting bearings and thrust bearing in it. Another disadvantage associated with this arrangement is, stub shaft radial fit condition in the threaded joint is liable to get disturbed with centrifugal dilation effect at high speed under high dynamic radial forces. [007] Referring to Figure 2, (Prior Art Ref. 3191976 United States Patent Office) illustrates an attachment for connecting a stub shaft to a drive shaft. The stub shaft 12 is connected to drive shaft, 10, which has a key slot, 22 for key, 32. Sleeve nut, 30 having a keyway, 28 is engaged over drive shaft, position along the split rings,34 at annular groove, 24. With the stub shaft, 12 in such a position the setscrew, 50 is placed in the screw hole 52 and is then tight ended. The stub shaft connecting means or unit is then in condition for accommodation of whatever driven apparatus the stub shaft 12 is to receive. [008] There is another assembly arrangement and method of attaching stub to drum of axial compressor as disclosed in Canadian patent application Ref. 2823409 A1 20123/01.24 where a flanged joint configuration is used for attaching stub shaft which has thrust as well as journal bearing provision. However, as the entire thrust and radial load need to be borne by the flange joint itself, the design integrity requirement demands the joint to be established on higher drum diameter as visible in the relevant art depiction. In steam turbine, or gas turbine, such joint tends to fall in hot gas portion where hot creeping environment makes such joint highly unreliable as flange bolts are normally pre-stressed to high value in such joint. [009] Referring to Figure 3, (Prior Art Ref. 2823409 A1 20123/01.24 Canadian Patent Office) illustrates an assembly and method for an axial compressor includes an axial shaft extending between an inlet casing and a discharge casing along the longitudinal length of ac compressor housing. The axial shaft assembly includes a first stub shaft, a second stub shaft, and a hollow shaft drum having a longitudinal axis. The first stub shaft and the second stub shaft are coupled to opposing ends of the shaft drum along its longitudinal axis. A plurality of pins engage the plurality of keys, whereby the pins prevent the shaft drum from rotating axially relative to the first shaft and the second stub shaft and prevent the shaft drum from axially and radially separating from the stub shafts. [0010] Another method for repairing a steam turbine or generator rotor by means of special welding arrangement is depicted in ref. EP0212921 B1 ref. application 86306129.7 European patent specification. This system is also susceptible in the tendency of the rotor material cracking at weld deposit location, especially with high Chromium steel rotors unless the welding process is conducted under highly controlled environment and precise welding process parameters. In addition, after material deposition, stress relieving heat treatment is needed which could have further complex implications on rotor shape and further machining corrections and uncertainty of rotor performance in operation. For carrying such controlled welding process with vertical set up, special facility is needed which make this alternative costly. [0011] Referring to Figure 4, (Prior Art Ref. EP0212921 B1 (86306129.7) European Patent Office) illustrates a method for repairing low alloy steel large machinery rotors wherein: mating attachments on a replacement end and a remaining portion of the original rotor are fittingly machined. Replacement end and original rotor are mated, characterized in that, replacement end is welded to said original rotor by narrow-gap arc welding up to a depth of 1.27-5.1 cm from the rotor surface. The remaining 1.27-5.1 cm of the mating attachment are welded by gas tungsten arc welding, and at least the 10 inner 63 mm of the weld are bored out and said weld is inspected through said bore. OBJECT OF THE INVENTION [0012] It is therefore an object of the present invention, to solve the aforementioned and other drawbacks existing in the conventional methods and attachments for rotor repair. [0013] Another primary object of the present invention is to provide a special attachment for the centrifugally expandable rotor end portion with the provision of thrust collar and journal in it for the absorption of mechanical thrust of turbo-machines and supporting of radial load of the shaft respectively. [0014] Yet another primary object of the present invention is to provide rotor attachment with machining and fixation for damages including a rotor end sealing portion (Alternative-1). [0015] Yet another objective of the present invention is to provide rotor attachment with machining and fixation for damages not extending up to a rotor end sealing portion (Alternative-2). SUMMARY OF INVENTION [0016] Considering the limitations of prior art work, for reliable restoration of damaged rotor end portions with provision for thrust collar and journal support, a special attachment is improvised to enable rotor repair and assembly simple, 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 a part of the claimed disclosure. [0017] The present subject matter relates to an attachment for centrifugal expansion of a rotor end portion. The attachment comprises a machined end portion, a plurality of joint bolts and a plurality anti-rotation pins. Further, the machined end portion comprises a plurality of radial locating steps, a male threaded portion, a plurality of drilled holes for the plurality of joint bolts and a plurality of drilled holes for the plurality of anti-rotation pins. The plurality of radial locating steps is machined in different arrangements of L - shape, inverted - U shape and U shapes. The male threaded portion is located at a centre of the machined end portion and surrounded with the plurality radial locating steps, the plurality of drilled holes for the plurality of joint bolts and the plurality of drilled holes for the plurality of anti-rotation pins. The attachment is coupled to the rotor end portion by means of the plurality of the joint bolts, the plurality of anti-rotation pins and threaded portion of the male threaded portion. The attachment is coupled to the rotor end portion by means of the plurality of the joint bolts, the plurality of anti-rotation pins and threaded portion of the male threaded portion. the rotor end portion is machined complementarily to the machined end portion and drilled for threaded holes corresponding to the plurality of drilled holes for the plurality of joint bolts and the plurality of drilled holes for the plurality of anti-rotation pins [0018] In an aspect, the attachment has a plurality of axial clearance at leading and trailing ends of the plurality of radial locating steps and the male threaded portion. [0019] In an aspect, the attachment has a provision for a thrust collar on one end other than the machined end portion of existing rotor. [0020] In an aspect, the attachment has a provision for a journal support on one end other than the machined end portion of existing rotor [0021] In an aspect, the dimensions of machined end potion are optimized using finite element analysis or analytical criteria and operating conditions. [0022] In an aspect, the operating conditions comprise one or more minimum stress parameter in the radial locating steps and the male threaded portion [0023] In an aspect, the plurality of drilled holes for the joint bolts are positioned diametrically, outer to the male threaded portion. [0024] In an aspect, the operating conditions comprise conformal contact pressure established at coupling faces by opting bolts count and bolts size. [0025] In an aspect, the operating conditions comprise conformal contact pressure established at coupling faces by opting proper thread size of the male threaded portion. [0026] In an aspect, the plurality of anti-rotation pins is position diametrically, outer to the plurality of joint bolts placement. [0027] In an aspect, the plurality of anti-rotation pins is secured in position by caulked grub screws. [0028] In an aspect, the plurality of drilled holes for the plurality of anti-rotation pins are positioned at certain angle (0