BACKGROUND OF THE INVENTION
This invention relates to a device for uniformly peening and finishing the inside of a tube.
It has long been customary to shot peen to increase fatigue strength, to relieve tensile stresses that contribute to stress-corrosion cracking, to form and straighten metal parts, etc. A detailed description of this process and the materials used therein is found in the ASM Committee "Metals Handbook", Volume 2, Eighth Division, 1964, pages 398-405, and incorporated herein by reference. Prior art shot peening processes are also described in numerous U.S. patents, e.g., U.S. Pat. No. 2,542,955 and 2,982,007. In conventional shot peening, spheroidal particles of cast steel, cast iron, glass, etc. are blown or mechanically impelled in a high velocity stream against the surface to be treated. The individual shot particles produce shallow, rounded overlapping dimples in the surface, stretching it radially from each point of impact and causing cold working and plastic flow. The resultant compressive stress tends to counteract tensile stresses imparted to the substrate by the preceding rolling, bending, abrading, and similar processes.
The degree of peening, which is generally expresses as "peening intensity," is a function of the weight, size, hardness and velocity of the peening particles, exposure time, type of substrate, angle of impingement, and various other factors. It is conventional to express peening intensity in terms of Almen arc height, according to SAE Test J 442, described in some detail in U.S. Military Specification MIL-S-13165B. In this test, a thin flat piece of steel is clamped or otherwise secured to a solid block and exposed to a blast of shot, which, as previously indicated, tends to stretch the surface, so that the strip will be curved when removed from the block. Test strips are SAE 1070 cold rolled spring steel uniformly hardened and tempered to a hardness of 44-50 Rockwell C, 3± 0.015 inches long and 0.745-0.750 inch wide. The strips are one of three thicknesses: A, 0.051 inch ± 0.001; C, 0.0938 inch ± 0.001; and N, 0.031 inch ± 0.001 inch. The height of arc of the resultant chord in inches is referred to as the Almen arc height, greater heights indicating greater peening intensity for a given test strip thickness.
Conventional shot peening has been effective for many purposes but there are certain applications where this process has been extremely difficult or impossible to perform. For example, heretofore there has been no simple and convenient way to peen the inside of a tube without the use of expensive, specialized equipment.
Although a unitary, portable peening wheel is described in copending U.S. application Ser. No. 746,366, filed Mar. 20, 1968, such structure is not well adapted for the peening of a tube for several reasons. For example, when the wheel is mounted on a shaft and inserted inside a tube, especially a long tube, it is extremely difficult, if not impossible, to control the position of the wheel. Because the peening wheel cannot be pressed against the wall of the tube with uniform manual force, it is essentially impossible to achieve uniformity of peening. Furthermore, if the peening wheel is allowed to bounce about the inside of the tube, it is likely to scrape metal from the walls.
For the most part, the prior art has been limited to the use of various abrading and swabbing materials for cleaning and polishing the inside of a tube. For example, shafts having radially extending sandpaper or emery cloth flaps are common and are used for abrading the inside of tubes. It is also old to employ a shaft having an eccentrically mounted head for removing deposits from boiler tubes.
SUMMARY OF THE INVENTION
This invention provides a light-weight mechanical device for peening and finishing the inside of tubes, conduits, cylinders, pipes, etc. The device is portable, simple, inexpensive and convenient to operate and yet provides a peening action which is very uniform. Because even a relatively unskilled operator can easily control the device, there is no danger of scraping metal from the inside of a tube during peening. One embodiment of the invention can be used to peen tubes which have bends or curves in them.
The simplest form of the invention comprises a rotatable shaft having at least one peening flap affixed to and extending radially from a portion of the shaft. Each such flap comprises a flexible, tough, tear-resistant support member having mounted at the radially outer portion thereof particles consisting at least predominantly of relatively smooth hard inorganic impact-resistant peening particles. At least one support means is rotatably mounted or journaled on the shaft so as to hold the portion of the shaft having peening flaps affixed thereto in close proximity to and at a fixed distance from the wall of the tube to be peened.
The device is operated, and the consequent peening action obtained, by driving the shaft with, e.g., an air-operated motor, an electric motor, or the like. As the shaft rotates, a whipping action is imparted to the flaps, whereby the peening particles at the radially outer portion of the flaps impinge upon the inner wall of the tube and effect the peening thereof. The shaft support means holds the rotatable shaft, and thus the peening flaps, at a fixed distance from the wall of the tube so that each peening particle impinges upon the wall at nearly the same angle. The shaft may be rotated at any desired speed, although speeds of 3,000-10,000 r.p.m. are preferred.
In another embodiment the shaft extends through and beyond an elongate tubular sheath. At least one sheath support means is fixedly mounted on the sheath near one end thereof for holding that end of the sheath in close proximity to and at a fixed distance from the wall of a tube to be peened. At least one peening flap is affixed to and extends radially from a portion of the rotatable shaft which extends beyond the sheath. The device of this embodiment may also be provided with a shaft support means rotatably mounted or journaled on the rotatable shaft so as to hold the portion of the shaft having peening flaps affixed thereto in close proximity to and at a fixed distance from the wall of the tube to be peened. Generally, the shaft support means is not required in this embodiment unless the portion of the rotatable shaft having peening flaps thereon is of such length that the sheath support means cannot, by itself, hold the peening flaps in close proximity to the wall of the tube to be peened. To obtain uniform peening action about the inside of the tube, the sheath may be slowly rotated independently of the shaft, thereby causing both the sheath and the shaft to travel around the inside of the tube at a fixed distance from the wall thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be described in more detail hereinafter with reference to the accompanying drawings, wherein like reference characters refer to the same part throughout the several views and in which:
FIG. 1 is a simple form of a device made in accordance with the invention;
FIG. 2 is a longitudinal cross-sectional view of a tube having positioned in the interior thereof a peening device made in accordance with the invention;
FIG. 3 is a transverse cross-sectional view of the tube and peening device of FIG. 2, taken along section line 3--3; and
FIG. 4 is a transverse cross-sectional view of the tube and peening device of FIG. 2, as taken along section line 4--4.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In FIG. 1 there is shown a simple embodiment of a peening device 10 of the invention. A plurality of peening flaps 18 are affixed to a portion of flexible shaft 16 and each flap 18 comprises a flexible, tough, self-supporting, tear-resistant support member 19 having particles 20 mounted thereon at its radially outer end. It is preferred that particles 20 be located only on the outer half of support member 19 for most efficient peening. Preferred support members 19 are comprised of the open mesh woven web material shown and described in copending U.S. application Ser. No. 746,366, filed Mar. 20, 1968.
Particles 20, as shown, consist at least predominantly of substantially spheroidal inorganic impact-resistant peening particles. Common particles which are useful are formed of cast steel, cast iron, tungsten carbide, and other such materials. Sintered aluminum oxide and zirconium oxide particles are very useful, and tungsten carbide particles are especially preferred, as peening particles. Generally, the particles should have a hardness of at least 10 Rockwell C and preferably the particles should be as hard as possible to increase their useful life. Preferably, the particles should be harder than the wall of the tube to be peened. Friable particles are not desired because they may break during use. Preferably, the particles have an average diameter in the range of 0.1-2.5 mm., although smaller or larger particles be fairly uniform in size. Particles having a surface configuration other than spherical are also useful when the portion of the particle surface which impinges upon the wall of a tube has a radius of curvature in the range of 0.1-2.5 mm.
At least one shaft support means 22 is provided along shaft 16, whereby when device 10 is mounted in the interior of a tube support means 22 holds the portion of shaft 16 having flaps 18 affixed thereto in close proximity to and at a fixed distance from the wall of the tube. Since shaft support means 22 is rotatably mounted on shaft 16, it does not interfere with the rotation of shaft 16 or flaps 18.
In FIGS. 2, 3, and 4, peening device 11, which is another embodiment of the invention, is disposed in the interior of cylindrical tube 50. Elongate tubular sheath 12, one end of which is being held in close proximity to, and at a fixed distance from, the inner wall of the tube 50 by sheath support means 14, has rotatable shaft 16a extending therethrough. Although it is not necessary to provide support means along the entire length of the sheath, it is desirable to provide such means near the end of the sheath which is closest to the peening flaps, especially when peening long tubes. Each support means 14 is fixedly mounted or fastened to sheath 12 and may be simply a disc-shaped member having a transversely bored hole adjacent a peripheral edge thereof for sheath 12 to pass through; alternatively, support means 14 may be an elongated member which is designed to hold at least the end of sheath 12 in close proximity to the wall of the tube. Generally, it is preferred to make the support means out of nylon, polyoxymethylene or fluorinated polymers because such materials are self-lubricating, wear-resistant, non-scratching, and strong. It is desirable that support means 14 have dimensions slightly smaller than the inside diameter of the tube to be peened (i.e., a circle circumscribing support means 14 is of a smaller diameter than the inside diameter of the tube), so that the support means will not bind in the tube when the sheath is rotated.
As in the embodiment of FIG. 1, the embodiment of FIGS. 2, 3, and 4 has at least one peening flap 18 affixed to shaft 16, although it is preferred to have a plurality of such flaps affixed at several locations along shaft 16. Preferably the peening flaps 18 are provided very close together along shaft 16 for most efficient and uniform peening of the tube.
Shaft support means 22 are provided at various points along shaft 16 so as to maintain said shaft and peening flaps 18 in close proximity to and at a fixed distance from the wall of the tube. Support means 22 comprise mounting portion 35 which is rotatably mounted or journaled on shaft 16, an adjustable length rod 31 connected at one end to mounting portion 35, a shank 26 mounted on the opposite end of rod 31, and wheels 24 mounted on an axle 37 which extends parallel to shaft 16 and at right angles through shank 26. By means of set screw 32 and rod 31 it is possible to shorten or lengthen the long dimension of support means 22. Another construction of the shaft support means is shown as 22a, where a single wheel 24 is mounted on axle 37 disposed in a fork-shaped shank 28. Because the mounting portion 35 of each type of support means is rotatably mounted or journaled on shaft 16, said shaft may rotate independently of support means 22 and 22a.
To prevent binding when peening device 11 travels around the inside of tube 50, a circle circumscribing support means 22 and 22a should have a slightly smaller diameter then the inside diameter of tube 50. Thus, rod 31 is desirably extensible to permit adjustment of support means 22 and 22a to the appropriate size, set screw 32 holding the thus-established dimensions. Rod 31 may also be spring loaded so that slightly elliptical tubes may be peened with the device of the invention.
Support means 22 and 22a may be of any of several designs, e.g., disc-shaped or elongated, and may be constructed of the same materials as support means 14. It is important only that support means 22 and 22a be rotatably mounted on or journaled about shaft 16 and be capable of holding shaft 16 and peening flaps 18 in close proximity to and at a fixed distance from the wall of tube 50 in such a manner that the travel of shaft 16 around the inside of tube 50 is not impeded.
In order to peen tube 50 with divide 11, one may connect an electric motor to shaft 16 to drive it at any desired speed, preferably between 3,000-10,000 r.p.m., whereby peening particles 20 on the end of peening flaps 18 strike against the wall of the tube. As sheath 12 is rotated slowly, support means 14, being fixedly and eccentrically mounted thereon, causes sheath 12 to travel in a path about the inside of tube 50 and at a fixed distance from the wall thereof, shaft 16 also travelling in a similar path. Support means 22 on shaft 16 keep the shaft, and also the peening flaps 18, in close proximity to and at a fixed distance from the wall of the tube. Thus, the peening is much more uniform than that which might be obtained with manual control of a simple rotating peening wheel or the like, where the rate of movement of the shaft around the wall of the tube, as well as the distance between the wall and the shaft is erratic.
In order to peen tubes having curves or bends therein, shaft 16 may be provided with a flexible joint 34. It has also been found desirable for shaft 16 and sheath 12 to be flexible so that long tubes may be peened easily when using a minimum of support means 14 for sheath 12. Thus, it is possible for one portion of the shaft to be flexible, e.g., portion 16a which is located within sheath 12, and another portion of the shaft to be rigid, e.g., portion 16 to which the peening flaps are attached. When peening straight tubes, it has been found possible to inter-connect support means 22 and support means 14, e.g., by replacing axle 37 with an elongate rod of sufficient length to inter-connect support means 14 and 22.
Peening flaps 18 are securely affixed on shaft 16, as shown in the drawings, Peening particles 20 are firmly bonded or mounted to flaps 18 at the radially outer end thereof so that when shaft 16 is rotated in the direction shown, a whipping action is obtained whereby peening particles 20 on the radially outer end of flaps 18 strike against the wall of the tube. It has been found that the most efficient peening is obtained when the peening particles impinge on the wall of the tube at an angle that is as close to normal as possible. For this reason it is desirable that peening particles 20 be located only on the outer half of flaps 18. It has also been found that the distance between shaft 16 and the wall of the tube is important because the peening flaps 18 and the peening particles 20 must pass therethrough without scraping the wall of the tube. Thus, the length of the flap 18, the flexibility of the flap, the location of peening particles 20 on the flap, and the distance between the flap and the wall of the tube are parameters which may be varied so as to obtain optimum peening efficiency.
Generally each peening flap 18 should not be so long as to interfere with other peening flaps mounted on a common length of shaft 16. As is shown in FIG. 3, particularly where two peening flaps are mounted on a common length of shaft 16 but at opposite sides thereof, the exposed length of each peening flap is shorter than the circumference of shaft 16. One flap will thus not interfere with the whipping action of the other flap. Preferably the length of each flap 18 is about one-half the circumference of shaft 16, although it is possible to use much longer flaps if the shaft is not positioned as close to the wall of tube 50 as it is shown in FIG. 3. It is also possible to mount more than two peening flaps 18 on a common length of shaft 16 if they are of such length that they do not interfere with each other's peening action. However, the peening flaps should not be so short that the peening intensity is drastically reduced. For example, the peening intensity will be reduced if the flap is so short that the peening particles do not impinge upon the wall at an angle nearly normal thereto.