Gear cutting – milling – or planing – Milling – Process
Reexamination Certificate
2000-01-25
2003-04-01
Howell, Daniel W. (Department: 3722)
Gear cutting, milling, or planing
Milling
Process
C409S179000, C409S175000
Reexamination Certificate
active
06540455
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a circumferential milling machine for milling along an arcuate portion of a cylindrical work piece having a cylindrical outer surface and, more specifically, to such a milling machine which is capable of milling a series of circumferentially space holes or slots, axially expanded holes or slots and/or tapered holes or slots in the arcuate portion of the cylindrical work piece.
2. Brief Description of the Prior Art
In the power industry, a number of steam power plants have been in existence for a number of years. These steam power plants include countless components, machines, equipment and systems which tend to degrade or malfunction with age and must be repaired or replaced with time. Further, in order to determine the status of such components, machines, equipment and systems with time, it is not uncommon for the operators of such power systems to rely on various testing and maintenance programs to detect and evaluate the condition and reliability of various components, machines, equipment and systems of the power plant.
One such area of the steam power plant includes the steam piping and distribution systems that are essential for the effective and safe operation of the of the plant. For example, many steam power plants utilize large cylindrical header pipes which include a plurality of smaller distribution pipes mounted on and extending from the headers. In such a header configuration, there would be a plurality of sets of pipes which would be generally mounted at one side of the header. Each set includes all the pipes thereof which are circumferentially separated and aligned with in a common arcuate sector of the cylindrical header. Each set of pipes is axially separated from adjacent sets of pipes. The terminal end of each pipe in each set extends perpendicularly from the outer cylindrical from the header. As each pipe of the set extends outwardly from the cylindrical header, it is bent or curved to be generally aligned with the other pipes of the set and with the pipes of the other sets axially separated therefrom so that all the pipes will be directed in the same direction generally away from the header.
The joining of each of the pipes in each set to the header is a critical and is subject to significant wear and deterioration with time. Accordingly, it has been found through elaborate nondestructive testing that weakened areas due to stress may develop in the regions of the header between the adjacent pipes of various sets of pipes. Such area affected by the stress tend to significantly weaken the header and have not been found to be correctable by simple welding or patching.
Accordingly, it has been found that the best and most reliable way to repair such a weakened header is to remove all of the pipes of a set, to completely remove all of the affected metal in the radial area and to replace it with weld material. However, the removal of the affected metal on the radial area has not been found to be a simple matter. In fact, it has been found to be extremely difficult. The headers are cylindrical in shape with thick walls that are typically made of high tensile steel. While there are numerous machining tools that are capable of removing such steel, there are significant problems with bringing and directing such tools to the cylindrical walls in a controllable manner in order to effectively and accurately remove the desired material. Additionally, any manner of removing the material must also be able to physically shape and form the hole that results in a proper condition for the receipt and retention of the new welding material.
When a portion of the header is found to have weakened stress areas that reduce its strength or reliability, the best way to reform the affected area first includes removing all of the pipes in the particular set of pipes in that area. If only one set of pipes are involved, the results would be a narrow arcuate area or portion the is physically located in the middle of the remaining array of sets of pipes. Clearly, accessibility to the affected area could be quite limited. Since it would be pointless and counter-productive to remove any pipes in unaffected areas simply to gain access to the affected areas, the problems of access and space limitations in a narrow arcuate area surrounded by a plurality of pipes is most significant.
Generally, if space were not an issue, there are any number machines or devices that could be used, at least to some extent, to remove material from at least a portion of a cylindrical surface. U.S. Pat. No. 4,459,883, discloses a portable machine tool for preparing pipe joints for welding but is installed within the interior of the large, hollow header. The tool components are small enough to be supported at the interior of the relatively thin walled header after they are passed through access holes. Such a system assumes that cutting or milling is only needed in the area of the pipes and that the header is of a type in which access openings are appropriate and, in fact, exist. U.S. Pat. No. 4,761,104 discloses a tube milling machine that appears to be mounted within a hole and able to mill a circular region around that hole but would not appear to be able to mill areas between adjacent hole or pipe ends such as could occur with the header problems discussed above. Similarly, U.S. Pat. No. 4,743,149 discloses a header tube tool that is specifically configure to prepare the cylindrical surface for the attachment of the ends of the pipes thereto. The tool is basically attached to the hole in the header and is configured to cut a circular area around the hole to generally provide a recess or socket into which the end of the pipe can be positioned for welding to the header.
There are various types of axial cutters for forming slots or key ways. U.S. Pat. No. 3,354,784 discloses a portable milling machine that can be mounted by a large bracketing framework to direct the cutting tool thereof to a limited axial region along the surface of the cylindrical surface of the work piece. U.S. Pat. No. 5,123,790 discloses an apparatus for milling grooves which is basically mounted on a work piece by a magnetic base. Such an apparatus would only be capable of effectively being mounted on a cylinder if it extends axially along the surface and it would then only be able to have the cutting tools to be advance axially along the surface of the cylinder to form a groove or key way that extends in the axial direction. Similar milling machines that move in the axial direction have been mounted to a cylinder by a self-centering device that is banded or strapped to the cylinder.
U.S. Pat. No. 5,161,291 discloses an adjustable machining apparatus for machining a cylindrical work piece to initially form the rotor teeth of a rotor core by the formation of a plurality of axial grooves therebetween. The milling tool is mounted on a device which is magnetically attached to the cylindrical outer surface of the rotor core. The milling tool can be primarily adjusted in three directions—the first direction would be tangential to the outer surface, the second direction would be parallel to the axis of the core, and the third direction would be perpendicular to the tangential direction. The combined movement of in the first and second directions would generally allow the milling tool to be inserted into the cylindrical surface to form the groove cross-section and movement in the third axial direction would form the grooves to establish teeth therebetween. The tool can also be adjusted about an axis that is parallel with the axis of the rotor core to allow fine, controlled adjustment of the tool head within the grooves to be able to generally shape the cross-section of the grooves which can be continued along the lengths thereof by moving the entire tool relative to the mounting in the third axial direction.
Generally, while the devices and apparatus discussed above would be capable of milling some portions of a cylindrical surface, there is nothing taught therein that wou
Howell Daniel W.
Sherman James L.
Speranza Specialty Machining
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