Method for minimizing electrical runout of a rotary shaft

Abstract

Method for minimizing electrical runout of a machinery having a rotary shaft and two or more bearings, the method comprising the steps of making (100) a groove at at least one portion of an external surface of the rotary shaft near at least one bearing, applying (200) a coating layer in the groove using a thermal spray deposition process and finishing the coating layer by turning or grinding. The coating layer comprises or consists of a Fe or Ni or Co based alloy or a cermet.

Description

TITLEMethod for minimizing electrical runout of a rotary shaftDESCRIPTIONTECHNICAL FIELD

[0001] The subject-matter disclosed herein relates to a method for minimizing electrical runout of a machinery having a rotary shaft and a machinery having a rotary shaft with electrical runout minimized.BACKGROUND ART

[0002] In rotary machines, shaft vibration measurements are used to monitor machine conditions and / or failures and / or the need of maintenance. Typically, eddy current proximity probes are used to monitor such vibrations. The signal from an eddy current proximity probe is a function of the gap between the probe tip and the target material, as well as the electrical conductivity and magnetic permeability of the target material. The eddy current proximity sensor provides a signal that comprehends both mechanical runout and electrical runout.

[0003] Mechanical runout is a measure of the shaft’s deviation from a perfectly uniform radius as its circumference is traversed. Electrical runout is a measure of a shaft’s electrical property variations as its circumference is traversed.

[0004] A proximity probe senses both types of runouts - therefore it is customary to speak of Total Indicated Runout (TIR), which is the sum of mechanical runout and electrical runout - but cannot distingue the amount of each of them. However, proximity probes are often used for radial vibration measurements where the “track” observed by the probe is constantly changing(repeating itself every 360 degrees) as the shaft rotates. This results in a proximity probe signal composed of both actual vibration and runout. Because the runout signal is not related to actual shaft vibration, it can lead to erroneous vibration readings and machinery diagnostic conclusions. To avoid this problem, the amount of TIR must be kept to allowable levels, generally 25% or less of expected vibration amplitudes.

[0005] Failure to meet runout specifications (i.e. the amount of allowable runout) can cause expensive delays and re-work, impacting both the customer and their machinery supplier. In addition, usually it can be reduced just mechanical runout and sometimes is not enough to target the requirements. For this reason, discovering and correcting electrical runout issues early in the manufacturing process can save a great deal of cost (avoiding even the scrap of expensive shaft).

[0006] Therefore, it would be desirable to have a rotary shaft in which the electrical runout is minimized. More in particular, it is desirable to have a method for minimizing the electrical runout of the rotary shaft of a machinery.SUMMARY

[0007] According to an aspect, the subject-matter disclosed herein relates to a method for minimizing electrical runout of a machinery having a rotary shaft and two or more bearing. The method comprises the steps of making a groove (20) at at least one portion of an external surface of the rotary shaft near at least one bearing, applying a coating layer in the groove using a thermal spray deposition process and finishing the coating layer by turning or grinding, the coating layer comprising or consisting of a Fe or Ni or Co based alloy or a cermet.

[0008] According to another aspect, the subject-matter disclosed herein relates to a machinery comprising a rotary shaft and two or more bearings where therotary shaft comprises a coating layer applied in a groove made at at least on a portion of an external surface of the rotary shaft near at least one bearing. The coating layer comprises or consists of a Fe or Ni or Co based alloy or a cermet and is applied using a thermal spray deposition process and finished by turning or grinding.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] A more complete appreciation of the disclosed embodiments of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:Fig. 1 shows a flowchart of an embodiment of an innovative method for minimizing electrical runout of a machinery having a rotary shaft, andFig. 2 shows a partial longitudinal section of a rotary shaft of a machine having electrical runout minimized according to the embodiment of Fig. 1.DETAILED DESCRIPTION OF EMBODIMENTS

[0010] According to an aspect, the subject-matter disclosed herein relates to an innovative method for minimizing electrical runout of a rotating shaft machine sensed by a probe, in particular a Bently Nevada probe, close to at least one bearing of the rotating shaft machine. It has been studied that the use of a high thickness thermal spray coating on an external surface of the rotary shaft is able to minimize the affection of electrical runout of rotary shaft by surface inhomogeneity due to microstructure or machining operations. It has also been studied that the best coatings consist or comprise a Fe or Ni or Co based alloy or a cermet.

[0011] According to another aspect, the subject-matter disclosed hereinrelates to a machinery comprising a rotary shaft having a high thickness thermal spray coating at least on a portion of an external surface of the rotary shaft near at least one bearing of the shaft.

[0012] Reference now will be made in detail to embodiments of the disclosure, examples of which are illustrated in the drawings. The examples and drawing figures are provided by way of explanation of the disclosure and should not be construed as a limitation of the disclosure. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure without departing from the scope or spirit of the disclosure. In the following description, similar reference numerals are used for the illustration of figures of the embodiments to indicate elements performing the same or similar functions. Moreover, for clarity of illustration, some references may be not repeated in all the figures.

[0013] Referring now to the drawings, Fig. l is a flowchart of an embodiment of the innovative method for minimizing electrical runout 1000 of a machinery having a rotary shaft and Fig. 2 is a partial longitudinal section of a rotary shaft of a machine having electrical runout minimized according to the embodiment of Fig. 1.

[0014] Typically, in order to reduce the electrical runout sensed by the eddy current proximity probe, on one side of the rotary shaft near the bearing, where the eddy current proximity probe sense its measurements, is placed a sleeve, in particular an Inconel sleeve, for example made of Inconel-625 or Inconel- 718. However, it often happens that on the other side of the rotary shaft it is not possible to use a sleeve for geometric reasons and therefore it is difficult to reduce and preferably minimize the electrical runout sensed by the eddy current proximity probe.

[0015] The innovative method herein disclosed essentially allows to effectively reduce the electrical runout sensed by the eddy current proximityprobe(s) of a machinery having a rotary shaft and two or more bearings by applying a high thickness thermal spray coating on an external surface of the rotary shaft near at least one bearing, as it will be better disclosed in the following.

[0016] The method 1000 comprises the steps of:A. making 100 a groove 20 at at least one portion of an external surface of the rotary shaft 10 near at least one bearing,B. applying 200 a coating layer 25 in the groove using a thermal spray deposition process, andC. finishing 300 the coating layer 25 by turning or grinding.

[0017] As already stated above, in step B the coating layer 25 is applied near at least one bearing, in particular on the portion of the external surface of the rotary shaft 10 where a probe, in particular an eddy current proximity probe (e.g. a Bently Nevada probe), senses its measurements.

[0018] Preferably, the coating layer 25 is applied at a maximum distance of 10 cm from the at least one bearing. Preferably, the coating layer 25 has a thickness of at least 0.5, even more preferably a thickness of 0.8-1.2 mm. Advantageously, the coating layer 25 is applied using High Velocity Oxigen Fuel.

[0019] The coating layer 25 comprises or consists of a Fe or Ni or Co based alloy or a cermet. According to a first preferred embodiment, the coating layer 25 is a nickel -based superalloy such as Inconel-625 or Inconel-718. According to a second preferred embodiment, the coating layer 25 is a cermet as tungsten carbide-based coating, in particular WC-Co 88-12 or WC-Co-Cr 86-10-4.

[0020] As already stated, the coating layer 25 is applied 200 in the groove 20 (see e.g. Fig. 2). Advantageously, the groove 20 is an annular groove whichextends around the axial axis of the rotating shaft 10 on its external surface.Preferably, the groove 20 has a depth of 2 mm or less.

[0021] According to another aspect, the subject-matter disclosed herein refers to a machinery processed according to the method herein disclosed and comprising a rotary shaft 10 and two or more bearings with electrical runout minimized. The rotary shaft 10 comprises a coating layer 25 applied in a groove made at at least on a portion of an external surface of the rotary shaft 10 near at least one bearing and it is applied using a thermal spray deposition process and finished by turning or grinding, and wherein the coating layer 25 comprises or consist of a Fe or Ni or Co based alloy or a cermet.

Claims

CLAIMS1. Method (1000) for minimizing electrical runout of a machinery having a rotary shaft (10) and two or more bearings, the method comprising the steps of:A. making (100) a groove (20) at at least one portion of an external surface of the rotary shaft (10) near at least one bearing,B. applying (200) a coating layer (25) in the groove (20) using a thermal spray deposition process, andC. finishing (300) the coating layer (25) by turning or grinding, wherein the coating layer (25) comprises or consists of a Fe or Ni or Co based alloy or a cermet.

2. Method (1000) of claim 1, wherein the groove (20) is an annular groove.

3. Method (1000) of claim 1, wherein the groove (20) has a depth of 2 mm or less.

4. Method (1000) of claim 1, wherein the coating layer (25) is a nickel- based superalloy such as Inconel-625 or Inconel-718.

5. Method (1000) of claim 1, wherein the coating layer (25) is a cermet as tungsten carbide-based coating, in particular WC-Co 88-12 or WC- Co-Cr 86-10-4.

6. Method (1000) of claim 1, wherein the coating layer (25) is applied using High Velocity Oxigen Fuel.

7. Method (1000) of claim 1, wherein the coating layer (25) has a thickness of at least 0.5, preferably of 0.8-1.2 mm.

8. Method (1000) of claim 1, wherein the coating layer (25) is applied at a maximum distance of 10 cm from the one or more bearings.

9. Machinery processed according to the method of claim 1, the machinery comprising a rotary shaft (10) and two or more bearings, wherein the rotary shaft (10) comprises a coating layer (25) applied in a groove made at at least on a portion of an external surface of the rotary shaft(10) near at least one bearing, wherein the coating layer (25) is applied using a thermal spray deposition process and finished by turning or grinding, and wherein the coating layer (25) comprises or consist of a Fe or Ni or Co based alloy or a cermet.

Images