US2337490A

US2337490A - Method of manufacturing integral finned tubing

Info

Publication number: US2337490A
Application number: US329819A
Authority: US
Inventors: Penner Edward
Original assignee: CALUMET AND HECLA CONS COPPER
Current assignee: CALUMET AND HECLA CONS COPPER
Priority date: 1940-04-15
Filing date: 1940-04-15
Publication date: 1943-12-21
Anticipated expiration: 1960-12-21

Description

Dec. 21, 1943. PENNER 2,337,490

METHOD OF MANUFACTURING INTEGRAL FINNED TUBING F iled April 15, 1940 INVENTOR.

EDWARD PENNER ATTORNEYS Patented Dec. 21,1943

UNlTED STATES PATENT OFFICE METHOD OF MANUFACTURING INTEGRAL FINNED TUBING corporation of Michigan Application April 15, 1940, Serial No. 329,819

5 Claims.

The invention relates to integral finned tubing of that type in which the metal forming the fins is displaced axially and radially from the outer portion of the tube blank. This operation is usually performed by placing the tube blank on a mandrel and feeding it axially with respect to the fin-forming means, such for instance as longitudinal series of rolls circumferentially spaced about the blank. Thus, the fins will be formed "".,l5hl'0llgh0llt the entire length of the blank and 1 because of the displacement of the metal, the wall thickness intermediate the fins is necessarily reduced. Such tubing may be used in the manufacture of heat exchange units where the ends of the fin tubes are connected into headers o as form a sealed joint. This necessitates stripping the fins from the end portions of the tube, leaving a wall thickness which is reduced from that of the original blank. It has been found that the wall thickness required for making a proper joint with the header is greater than that which is sufiicient for the finned portion of the tube, but where the fins are formed as above described, the wall thickness must necessarily be the same throughout the length of the tube. Thus, the weight of metal in the tubes must be considerably increased if the end portions are to be made of greater thickness.

It is the object of the instant invention to obtain a method of forming integral finned tubes which will have greater wall thickness in certain portions of their length than in other portions. More particularly, it is an object toincrease the wall thickness of the unfinned portions of the Figure 5 is a diagrammatic cross section illustrating the manner of finishing the outer surface of the tube ends;

Figure 6 is a view similar to Figure 2, showing a modified construction;

Figure 7 is an elevation, illustrating one construction of finned tube unit having an unfinned return-bent portion. v

In manufacturing the finned tubes by my improved method the tube blanks A, preferably formed of seamless drawn tubing of copper or similar material, are first placed upon a mandrel B which has one or moreportions thereof reduced in diameter. Thus, as shown in Figure 1, the central portion 3' of the mandrel fits the internal diameter of the tube A, while the end portions B and B -are somewhat smaller in diameter. C are the rolls between which the tube is axially fed, said rolls being suitably fashioned to progressively displace the metal in the outer portion of the cross section of the tube, so as to form radially projecting helical fins A. The radial inward pressure of the rolls upon the outer surface of the tube is resisted by the portion B of the mandrel, so as to preclude any contraction in diameter of this portion. On the other hand, the portions of the tube which extend over the portions B and B? of the mandrel are not so sup-, ported, and as a consequence these portions will be contracted in diameter by the pressure of the rolls, instead of having fins formed thereon. If desired, the tube may be contracted over the small diameter portions of the mandrel in advance of the feeding of the same into engagement with the rolls, and thi is preferably done on the forward end of the tube which first comes in contact with the rolls. Thus, as shown in Figure 1, the forward portion A has been contracted by means of dies (not shown) to fit the mandrel portion B A tapering. pilot D is then engaged with the forward end of the mandrel, preferably by means of a threaded shank D' engaging a correspondingly threaded aperture. This pilot is of a diameter to just clear the rolls, the portion A of the tube being slightly larger. Thus, when the tube is fed between the rolls the latter will merely slightly indent the outer surface of the portion A but the following portion A which is over the mandrel portion B will have the fins A formed thereon. The rear end portion A of the tube which is over the mandrel portion B, will be contracted by the pressure of the rolls to conform to the mandrel with only a slight indenting of its outer surface. Thus, as shown in Figure 2, the central portion of the tube is finned while the opposite end portions are portion A by the mandrel portion B, as shown in Figure 3. The mandrel may then be completely removed, after which the end portionsof the tube may, if desired, be further expanded by a suitable tool, such as F shown in Figure 4. Finally, these end portions are externally finished toremove the indentations therefrom, this operation being performed by any suitable tool, such as diagrammatically shown in Figure 5, having a pilot G fitting within the tube and one or more external cutters H. This will not only smooth the outer surface but will also remove any slight eccentricity between the outer and inner surfaces, so as to form an annular wall of uniform thickness.

For certain uses it may be desirableto form a tube having one or more unfinned portions intermediate finned portions thereof. This may be accomplished by the use of amandrel, as shown in Figure 6, in which portions I fitting the internal diameter of the tube are connected by a portion J which is of smaller diameter. Thetube and mandrel are then fed between the fin-forming rolls, as previously described-which will merely f, veiopment, removing the mandrel from the tube,

expanding the unfinned end portion thereof, and externally finishing said end portion concentric with theinner surface thereof.

3. Ina method of forming integral finned tubing having one or more finned portions of exactly contract the portion K which is over the mandrel portion J, while forming fins on the portions K and K at opposite ends of the portion K. The portion K will'thus be of greater wall thickness than the portions K and K with only a slightly indented outer surface. When the mandrel is driven out of the tube, this portion K will be enlarged to its original diameter and its outer surface may then be finished to remove the indentations. Such a construction is useful in the forming of return-bent finned tubes, as illustrated at L in Figure '7.

A finned tube of the construction above described when formed from seamless drawn copper tubing, will'have a high rate of heat exchange,

due to the thermal conductivity of the material and the integral fins. At the same time, the unfinned portions may be of any desired wall thickness without the necessity of increasing the we] thickness of the finned portions. When, as shown in Fig. 4, the unfinned portion of the tube is finally expanded to a diameter greater than that of the original tubular blank, the thickness of the walls will becorrespondingly reduced. However, this thickness may be maintained to be at least as great as that of the finned portion, thereby avoiding any weakened portion. What I claim as my invention is: 1. The method of forming integral finned tubing having one :or more unflnned portions of greater'wall thickness comprising, placing atubular blank upon a mandrel having portions thereof fitting and supporting the wall of the tube, and one or more otherportions of smaller diameter spaced from the tube wall, feeding the blank and mandrel as a unit axially and throughout their length in intersecting relation to external fin-developing means which exerts radially inward pressure in excess of the resistance of said tubing, whereby fins will be developed and the wall thickness intermediate the same reduced in the portion of the tube supported by the mandrel'while the portions unsupported by the mandrel will be radially contracted to avoid substantial fin development, removing the mandrel from the tube, and expanding the contracted portions thereof.

2. The method of forming integral finned tubing having an unfinned end portion'oi' greater wall thickness comprising, placing a tubular blank upon a mandrel for fitting and supporting the wall oi the tube but having an end portion of smaller diameter,feeding said tube and mandrel together as a unit axially throughout their length in intersecting relation to external fin-developing means which exerts radially inward pressure predetermined length intermediate unfin'ned portions, the steps of placing the tubular blank on a mandrel having a portion corresponding in length to each portion of the tube to be finned, said portion being of a diameter to fit within and support the wall of the tubular blank, said mandrel also having portions of smaller diameter forming shoulders at opposite ends of each larger portion, and feeding the blank and mandrel as a unit axially in intersecting relation to extemai fin developing means which exerts radially inward pressure in excess of the resistance of said tubular blank, whereby said blank will be radially contracted about said shoulders in the unsupported portions thereof and appreciable fins will be developed only on the supported portion between said shoulders.

.4. In a method of forming integral finned tubing having one or more finned portions of exactly predetermined length intermediate unfinned portions, the steps of placing the tubular blank on a mandrel having a portion corresponding in length to each portion of the tube to be finned, said portion being of a diameter to fit within and support v the wall of the tubular blank, said mandrel also having P rtions of smaller diameter forming shoulders at opposite ends of each larger portion, contracting the leading end of the blank over the smaller diameter of the corresponding end of the mandrel, and feeding the blank and mandrel as a unit axially in intersecting relation toexternal fin developing means which exerts radially inward pressure in excess of the resistance of said tubular blank, whereby said blank will be radially contracted about said shoulders in the unsupported portions thereof and fins of appreciable height will be developed only on the supported portion between said shoulders.

5. In a method of forming integral finned tubing having one or more finned portions of exactly predetermined length intermediate unfinned portions, the steps of placing the tubular blank on a mandrel having a portion corresponding in length to each portion of the tube to be finned, said portion being of a diameter to fit within and support the wall of the tubular blank, said mandrel also having portions of smaller diameter forming shoulders at opposite ends of each larger portion, contracting the leading end of the blank over the smaller diameter of the corresponding end of the mandrel, securing said blank on said mandrel by means abutting the leading end of the blank, and feeding the blank and mandrel as a unit axially in intersecting relation to extemai fin developing means which exerts radially inward pressure in excess of the resistance of said tubular blank, whereby said blank will be radially contracted about said shoulders in the unsupported portions thereof and fins of appreciable height will be developed only on the supported portion between said shoulders.

' nnwxan PENNER.