Patent Application
20180243879
The present disclosure relates generally to a device to aid a lapping process of two components, and more particularly, to a device to aid in lapping a spherical washer to another steam turbine component.
A conventional steam turbine includes a higher pressure turbine and at least one lower pressure turbine coupled to a single shaft. Steam enters the turbine at the high pressure turbine through a stop valve and a control valve. The thermal energy of the steam is converted to mechanical energy in the higher pressure turbine, and the steam is exhausted to reheaters. In each reheater, the steam is dried, reheated, and superheated prior to its entry into the lower pressure turbine. The superheated steam is routed through the stop valve as it travels from the reheater to the lower pressure turbine. Energy conversion occurs again in the lower pressure turbine as the steam expands into the vacuum of the main condenser.
A spherical washer is part of the stop valve assembly that seals off the steam and helps to align the steam turbine shaft. In the stop valve assembly, the spherical washer seats against the shaft shoulder on the flat side and against a casing bushing on the spherical side, the casing bushing disposed concentrically with and surrounding the shaft. Each time the stop valve is inspected during periodic maintenance, the stop valve is removed from the steam turbine, and the spherical washer is replaced with a new one. In order to ensure that the spherical washer will seal properly, the new washer is lapped against its mating counterpart, the casing bushing, in the valve casing and the shaft shoulder. Lapping two components is a machining process which involves rubbing the two mating surfaces of the two components together with an abrasive, or lapping compound, between them.
Holding the spherical washer from the inside in order to lap its spherical seat to the spherical mating surface of the casing bushing has proven to be difficult. For example, the spherical washer, in its assembled location within the stop valve, is in a fairly confined area. A field technician working within the valve to lap the spherical washer will find the working space cramped and difficult to maneuver. A variety of methods have been used by field technicians to lap the spherical washer. As an example, a block of wood has been used to hold the spherical washer by its inner diameter and rotated by hand as the technician manually applies the lapping compound onto the outer diameter surface of the spherical washer. The drawback to this approach is that it very labor intensive.
Consequently, a tool that allows a technician to firmly hold the spherical washer while the washer is being lapped to the casing bushing within the reheat valve assembly is desired.
Briefly described, aspects of the present disclosure relates to a device to aid in lapping a spherical washer to a steam turbine component and a method to lap a first turbine component to a second turbine component.
A device to aid in lapping a spherical washer to a steam turbine component is provided. The device includes a drive head, the drive head made up of a drive cap and a hollow cylindrical portion projecting from the drive cap. The drive cap is configured to abut a surface of the spherical washer. The cylindrical portion fits within and is concentric to an inner diameter of the spherical washer. The device also includes an expanding gasket, the expanding gasket including an outer diameter having a contour configured to fit a contour of an inner diameter of the spherical washer and an inner diameter slides onto the cylindrical portion such that the gasket and cylindrical portion are concentric. The drive head is configured to attach to a drive unit which may impart a torque sufficient to lap the spherical washer with respect to a steam turbine component. The expanding gasket expands and holds the spherical washer during the lapping.
A method to lap a first turbine component to a second turbine component is provided. A lapping compound is applied to an outer surface of the first turbine component. The device as described above is prepared for the lapping of the first component to the second component by positioning the device including the first component against the second turbine component such that the outer surface of the first turbine component abuts an inner surface of the second turbine component. A drive unit may then be attached to the drive head. A torque is imparted by the drive unit to the device sufficient to lap the first turbine component to the second turbine component.
To facilitate an understanding of embodiments, principles, and features of the present disclosure, they are explained hereinafter with reference to implementation in illustrative embodiments. Embodiments of the present disclosure, however, are not limited to use in the described systems or methods.
The components and materials described hereinafter as making up the various embodiments are intended to be illustrative and not restrictive. Many suitable components and materials that would perform the same or a similar function as the materials described herein are intended to be embraced within the scope of embodiments of the present disclosure.
Referring now to the figures, where the showings are for purposes of illustrating embodiments of the subject matter herein only and not for limiting the same,
As discussed above, a device 10 to aid in lapping a spherical washer 40 to another steam turbine component is desired. The proposed device 10, shown in
A spherical washer 40 secured to the device 10 is illustrated in
In the embodiment described below, the steam turbine component is a stop valve casing bushing 210. A cross section of the casing bushing 210 within a steam turbine stop valve casing 240 may be seen in
Referring back to
The two plates 80, a first plate and a second plate, one each disposed on opposite sides of the gasket 70 may be used to expand the gasket 70 when the two plates 80 are axially compressed towards one another into the inner diameter of the gasket 70. Each of the two plates 80 may be tapered internally on an outer diameter such that the contour of each taper conforms to the inner diameter taper of the gasket 70. When compressed together the tapers of the two plates 80 may abut and conform to the inner diameter taper of the gasket 70. In this way, the compression of the two plates 80 may be used to expand the gasket 70 and grip the spherical washer 40 without deforming the spherical washer 40. A deformed spherical washer could not be correctly lapped to its mating counterpart necessitating a replacement for the part and resulting in lost time and perhaps a longer shutdown time for the steam turbine.
A first alignment device 50, illustrated in
Referring now to
The tension bar assembly 100 includes a tension shaft 110, which may be embodied as a cylindrical shaft. A first end of the tension shaft 110 fits within the cylindrical portion 30 of the drive head 20 and extends into the drive cap 22 where it is secured. The tension bar assembly 100 may also include a stop plate 120. The stop plate 120 is configured to abut a surface of a further steam turbine component so that a constant and consistent tension may be provided to the spherical washer 40 and the end surface 220, as seen in
The tension bar assembly 100 may also include a compression knob 130 disposed at a second end of the tension shaft 110 opposite the first end. Both the compression knob 130 and the stop plate 120 may include a central hole such that an inner diameter of the compression knob 130 and stop plate 120 may be disposed onto the tension shaft 110 and positioned concentric to the tension shaft 110. The stop plate 120 and the compression knob 130 may be connected by a spring 140 so that the stop plate 120 may easily move relative to the tension shaft 110 and position the stop plate 120 so that it abuts the surface of the further steam turbine component. A tightening adjustment of the compression knob 130 compresses the spring 140 against the stop plate 120 which then induces a constant axial tension along the device 10 pulling the drive head 20 including the spherical washer 40 against the end surface 220 of the casing bushing 210. In this way, controlling the compression knob 130 enacts a constant controllable force between the spherical washer 40 against its mating component 220.
The tension bar assembly 100 may also include a second alignment device 150 having an inner diameter disposed onto the outer diameter of tension shaft 110 and an outer diameter abutting the inner diameter of the casing bushing 210. The second alignment device 150 allows the spherical washer 40 to be reliably lapped concentric to the end surface 220 of casing bushing 210. In the shown embodiment of
Referring back to
In the embodiment shown in
The latching mechanism 230 comprises a catch piece as shown in
In the illustrated embodiment of
The tension shaft bushing 150 may be locked into the tension shaft 110 of the tension bar assembly 100 using a locking mechanism. The locking mechanism may be embodied as a spring plunger. A spring plunger 260 may be used within each tension shaft bushing 150 to lock the tension shaft bushing 150 to the tension shaft 110. The spring plunger 260 may include a conical tip which fits a matching groove in the tension shaft 110 locking the tension shaft bushing 150 into the tension shaft 110. A break away force may be controlled by how much the spring plunger 260 is threaded into the tension shaft bushing 150. The spring plungers 260 may be radially threaded into the tension shaft 110. Thus, to install the tension bushings 150 onto the tension shaft 110, one may slide a tension shaft bushing 150 onto the tension shaft 110 and locate it onto a designated position using the locking mechanism. Multiple spring plungers 260 may be used and evenly spaced around the circumference of the bushing 150 in order to more securely lock the tension bushing 150 onto the tension shaft 110. For example, three spring plungers 260 may be spaced 120 degrees apart around the circumference of the tension bushing 150.
Referring now to
For illustrative purposes,
Referring to
The lapping procedure commences when the drive unit 300 imparts a torque to the device 10 sufficient to lap the first turbine component 40 to the second turbine component 210. During the lapping procedure, the first turbine component 40 rotates with respect to a stationary second component 210 lapping the first component 40 to the second component 210. The lapping procedure may be accomplished in less than 4 hours, a significant improvement from the 4 to 12 hours that the conventional procedures have taken.
In an embodiment, preparing the device 10 includes attaching a tension bar assembly 100, as described above, to the drive head 20. The tension bar assembly 100 applies a constant and consistent axial force during the lapping procedure of the first turbine component 40 to the second turbine component 210 by thrusting the first turbine component 40 against the second turbine component 210. The tension bar 110 is attached to the drive head 20 by inserting a first end of the tension shaft 110 into the hollow cylindrical portion 30 of the drive head 20. The device 10 is secured within the drive cap 22 by latching the first end with a latching mechanism 230 within the interior of the drive cap 22.
As described above, in order for the lapping procedure to be successful such that a proper seal may be formed between the two components 40, 210, the method may include aligning the first turbine component 40 to be concentric with the second turbine component 210. The aligning may be accomplished by positioning a tension bushing 50 over the outer diameter of the cylindrical portion 30 of the drive head 20. An inner diameter of the tension bushing 50 slides over the outer diameter of the cylindrical portion 30. The tension bushing 50 may align the device 10 and the first component 40 to be concentric with the second component 210.
In the described embodiment of the method, the first component is a spherical washer 40 and the second component is a casing bushing 210 of a stop valve assembly 240 in a steam turbine engine, however, one skilled in the art of turbomachinery would understand that other industrial components may be lapped to one another using the proposed device and method.
The disclosed device and method to lap a first turbine component to a second turbine component accomplishes the objective of firmly holding the spherical washer in order to lap it to the casing bushing within the stop valve assembly. By providing an alignment device, the tool may also align the device including the spherical washer with the casing bushing so that the lapping procedure produces good results. Additionally, using the provided tool reduces the time to lap the spherical washer to casing bushing at least by half and makes the lapping procedure less physically challenging for the technicians performing the procedure.
While embodiments of the present disclosure have been disclosed in exemplary forms, it will be apparent to those skilled in the art that many modifications, additions, and deletions can be made therein without departing from the spirit and scope of the invention and its equivalents, as set forth in the following claims.
