1. Field of the Invention
This invention relates to the pipe machining art, and, more particularly, to an improved mandrel arrangement useful in mounting a pipe machining tool for rotation relative to at least one end of a pipe bend to be machined and, in particular, to such a mandrel having application to comparatively small pipe bend internal diameters.
2. Description of the Prior Art
Many pipe machining tools are designed to be rotated about the center line of a pipe to accomplish a machining operation on the pipe. Two examples thereof are described in U.S. Pat. No. 3,875,832, issued Apr. 8, 1975, entitled MANUAL PIPE BEVELLING TOOL and U.S. Pat. No. 3,927,584, issued Dec. 23, 1975, entitled PIPE END FACING AND GROOVING MACHINE. U.S. Pat. No. 3,875,832 discloses a manual tool to be rotated about the axis of a pipe adjacent its end for the purpose of cutting a bevel thereon. U.S. Pat. No. 3,927,584 discloses a tool, the cutting assembly of which is adapted to rotate about the axis of a pipe to machine a square face and an external annular groove on the end of the pipe for the reception of a pipe coupling element.
In tools of this type, a mandrel is required to mount the tools for rotation. Since the mandrel shaft must be coaxial with the pipe being machined, it is easiest to mount the mandrel arrangement directly to the pipe. Such mandrels must be extremely rigid to provide an accurate cut and to withstand the substantial forces placed thereon, but should also be able to be installed and removed easily relative to a particular length of pipe. The ease of installation and removal is particularly important for use in the field, where pipes are machined with a minimum of sophisticated tools and alignment mechanisms. A mandrel must also be relatively inexpensive to justify extensive field use.
Mandrels exist for use with straight sections of pipe. U.S. Pat. Nos. 3,875,832 and 3,927,584 illustrate mandrels for use with straight sections of pipe comprising a plurality of longitudinally directed radial fins which may be expanded by tightening an axial draw bar, drawing those fins over a set of radially inclined camming surfaces. The radially outer edges of the fins may thus be caused to engage the inner surface of the pipe in a clamping relationship to rigidly fix the draw bar along the axis thereof. Either the draw bar itself or a hollow bar fitted thereover serves as a mandrel for rotation of the pipe machining tool.
The above described mandrels are unsatisfactory for use in machining the ends of pipe elbows and other pipe bends, because pipe bends generally do not possess the length of straight pipe necessary to engage and retain an expanding fin arrangement. The curved inner surfaces of pipe bends present unique and previously unsolved problems in securing a mandrel. Mandrels for such use must be accurately and rigidly mountable within a pipe bend, and must also be of a simple design allowing quick and easy installation.
Other structures are shown in U.S. Pat. Nos. 3,478,318 and 4,050,836, and in Great Britain Pat. No. 198,621.
In the above mentioned copending patent application Ser. No. 883,178, filed Mar. 3, 1978, now U.S. Pat. No. 4,169,396, issued Oct. 2, 1979, and assigned to the same assignee as this patent application, there is described an elbow mandrel for overcoming the above mentioned deficiencies and useful in a wide variety of pipe bends. However, it has been found that in certain applications involving pipe bends having a comparatively small internal diameter, the structure of the above described mandrel does not lend itself to all such applications, since the mandrel must be sufficiently strong to withstand the forces associated with its use and yet small enough to be removably insertable in a pipe bend. Therefore, while certain basic dimensions of the pipe mandrel may be scaled down when adapted for utilization in smaller pipe bends, the amount of decrease in physical size to allow insertion into smaller diameter pipe bends is limited by the strength required in the structure to withstand the above mentioned forces.