GB2183519A - Method of and apparatus for producing helically finned tubes - Google Patents

Abstract

A blank tube 30 is supported on a grooved mandrel 24 and relative rotation between the tube and disc rollers 54 causes a plurality of vertical helical fins to be formed in the outer wall of the tube, and a plurality of helical ribs 33 to be formed in the internal wall of the tube. Further engagement between the finned tube and disc rollers 56 causes the vertical fins to be bent over in incremental steps to form subsurface channels. The disc rollers 56 have spacers therebetween and each has an angled contact face which varies in inclination along the length of the disc roller cluster. <IMAGE>

Description

SPECIFICATION Method of and apparatus for producing externally enhanced tubes using multiple lead starts Background of the invention This invention relates generally to a method of and apparatusforforming integral helical external fins on lengths ofevaporatortubes and, more particularly, to such a method and apparatus wherein the fins are formed with multiple fin starts and the fins of each helix are rolled overto form subsurface channels having pores spaced around each helix.

Tubes manufactured in accordance with the present invention are used in a heat exchanger ofthe evaporatortypewherein a fluid to be cooled is passed through the tubing and a boiling liquid is in contact with the exterior ofthe tubing whereby heat istransferred from the fluid in the tubing to the boil- ing liquid. As disclosed in U.S. patent4,425,696an enhanced evaporatortube is manufactured according to a method whereby a grooved mandrel is placed inside an unformed tube and a tool arbor having a tool gang thereon is rolled over the external surface ofthe tube. The unformed tube is pressed againstthe mandrel to form at least one internal rib on the internal surface of the tube.Simultaneously, an external fin convolution is formed on the external surface of the tube by the tool arbor with the tool gang.

The external fin convolution has depressed sections above the internal rib wherethetube is forced into the grooves ofthe mandrel to form the rib. Asmooth roller-like disc own the tool arbor is rolled overthe external surface ofthetube after the external fin is formed. The smooth roller-like disc is designed to bend overthe tip portion ofthe external fin to touch the adjacent fin convolution only at those sections of the external fin which are not located above an internal rib. Thetip portion ofthe depressed sections ofthe external fin, which are located above the internal rib, are bent over but do not touch the adjacent convolutiontherebyforming a pore which provides fluid communication between the surroundings of the tube and the subsurface channels ofthetube.

Also, itis known that multi-startfinning orforming multiple sets of helices permits a more rapid finning operation. However, it has been found thatwhen the smooth roller-like disc of the above-identified patent is used in conjunction with multi-startfinning,that thefins are not rolled over properly bythesmooth roller-like disc but are squashed down thereby reducing the cross-sectional area ofthe subsurface channel and thus reducing the heat transfer perform- ance of the tube.

Summary of the invention It is an object ofthe present invention to overcome the foregoing difficulties and shortcomings experienced in the prior art and to improve the heat transfer performance of an enhanced evaporator tube manufactured by the multiple start method.

Another object ofthe present invention is to provide multiple lead tool gangs with roller discs that will roll overthe multiple sets of helices without squashing the fins down and reducing the crosssectional area ofthe subsurface channels.

These and other objects of the present invention are attained by a novel apparatus and method forfor ming pores and subsurface channels in enhanced tubes having multiple sets of helices. According to the present invention, a finned tube manufactured bya multiple lead process has its fins rolled overthe desired amount by a plurality of roller discs. The roller discs are mounted on a tool arbor, and adjacent discs are separated by spacers. The roller discs have generally angled faces. The point of contact between the face of adjacent roller discs and the fin to be rolled-over, and the chamfer angle ofthe face ofthe adjacent roller discs, progressively changeto pro- ducethedesired rollover.

The various features of novelty which characterize the invention are pointed out with particularly in the claims annexed to and forming part of this specification. For a better understanding ofthe invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there is illustrated and described a preferred embodimentofthe invention.

Briefdescription ofthe drawings Other objects and advantages of the present invention will be apparent from the following detailed description in conjunction with the accompanying drawings, forming a part ofthis specification, and in which reference numerals shown in the drawings de signatelikeorcorresponding partsthroughoutthe same, and in which: Figure lisa schematic representation of a multilead finning machineforthemanufactureofenhan- ced tubes in accordance with the present invention; Figure2 is a side elevation view ofonetool arbor ofthefinning machine shown in Figure 1 with a fragmentary sectional view of a tube on a mandrel; and Figure 3 is a fragmentary sectional view on an enlarged scale showing a typical finned tube being rolled over by the roller disc arrangement ofthe present invention.

Description ofa preferred embodiment The embodiment of the present invention described below is especially designed for use with enhanced evaporatortubes because these tubes have a critical dimension which must be precisely controlled to maintain good heat transfer performance. These enhanced tubes are designed for use in an evaporator of a refrigeration system having a fluid to be cooled passing through heattransfertubes and having refrigerant, which is vaporized, in contact with the ex ternal surfaces ofthe tubes. Typically, a plurality of heattransfertubes are mounted in parallel and connected so that several tubes form a fluid flow circuit and a plurality of such parallel circuits are provided to form a tube bundle.Usually, all thetubes ofthe various circuits are contained within a single shell wherein they are immersed in the refrigerant. The heat transfer capability ofthe evaporator is largely determined by the average heat transfer characteristic of the individual heat transfertube. The size ofthe subsurface channels and the pores on the surface of the tubes are particularly critical. Moreover, multi-lead manufacturing processes for making enhanced tubes are preferred, since it permits a more rapid operation.

Referring nowt the drawings, Figure lisa diagrammatic representation of a finning station for manufacturing enhanced tubes used in connection with the present invention. The finning station 10 includes an electronic control cabinet 12, a feed section 14, a multi-lead finning head section 16, an ejection section 32, and a quality control section 18. The elec- tronic control cabinet includes an operator console 22 having a programmable controller associated therewith, which performs logic execution, timing, sequencing, and calculationsforthefinning operation. The feed section 14 generally includes two axially parallel mandrels 24 (the rearward mandrel is in the same horizontal plane as the forward mandrel and isthus notshown in the Figure).Typically,the mandrels are supported by a plurality of support arms 26 and are moved by piston means 28. Accordingly,the operatorwill load a blank tube on the front and rearmandrels24andcyclethefeedcyclesection 14such that one mandrel, e.g.the front mandrel,will drop down and move along the longitudinal finning axis 29 into the finning head section 16. Thefinning head section includes a plurality offorming roll assemblies. Preferably, three forming roll assemblies are used and are mounted with their axis essentially parallel to each other but spaced 20 apart.The axis of the form ing roll assemblies are skewed at a slightangletothe longitudinal finning axis in a mannersothatasthetubeisadvancedthroughthe finning head section, the fins will be formed about the surface to define a multiple helical configuration.

Each forming roll assembly includes a tool arbor with tool gangs thereupon. Thetool gang includes at least one clusteroffinning discs and a cluster of rollers cooperating with the mandrel to produce the enhanced tube in accordance with the present inven tion.Thefirstfinning discon each tool gang contacts the blanktube in a planetransversetothelong- itudinalfinning axis 29.Thus, the start of each helical groove, although skewed to form a helix, will be in the same transverse plane but equidistantly spaced aboutthe circumference of thetube, e.g. for a finning machine having three tool arbors, three distinct finned helices may be formed and each fin will start in the same transverse plane but 120' apart. Accordingly, after each complete revolution ofthe tube, i.e.

360% there will have been formed three distinct finned helices and each revolution thereafterwill form three more finned helices. The tool arbors are simultaneously synchronously rotatable in the same angulardirection, and causethetubeto rotate and to advance due to the frictional engagement between the finning discs and the tu be. When the blanktube is completely enhanced over a desired length, the tube contacts a position switch (not shown), which causes the three forming roll assemblies to radially move away from the enhanced tube while ejection means 32, e.g. ejectwheels, will engage the enhanced tube and send it into the quality control section 18.Once the enhanced tube is positioned completely into the quality control section 18 the front mandrel will retract to its original position and the rear mandrel will now drop down and the process will repeat itself.

Referring now to Figure 2, the relationship between a tube being enhanced andtheforming roll assemblies spaced thereabout and the mandrel inserted therein can best be seen. Although the preferred embodiment contains a pluralityofforming roll assemblies, e.g., three spaced 120 apart, only one forming roll assembly is shownforclarity. The tube 30 is loaded on mandrel 24 and moves from leftto right. The mandrel 24 is of sufficient length that the interior surface ofthe tube 30 is supported beneath the disc clusters 54 and roller clusters 56. The disc clusters 54 on the tool arbor are brought into contact with the tube 30 art a small angle relative to the longitudinal finning axis 29.This small amount of skew provides the force necessary fortube 30 to be driven along its longitudinal axis astheforming roll assemblies are rotated. The finning disc54displacethe material on the wall of the tube 30 to form the ex ternal fin convolutions while at the sametimedep- ressing the tube 30 against the mandrel 24to displace the tube wall of the tube 30 into the grooves 31 ofthe mandrel 24to form the internal ribs 33.The displacement of the tube wall to form the internal ribs 33 results in forming depressed sections ofthe external fin convolution overlying the internal ribs 33 so thatwhen the rollers 56 are rolled overtheexternal surface ofthe tube 30, afterthe finning discs 54 have formed the external fin convolutions, the roller discs bend the tip portion of the fin over in incre- mental steps to touch the adjacent convolution only at those sections of the fin convolution which are not located above an internal rib 33 and therefore, which are not epressed. This results in the formation ofthe subsurface channel.The sections ofthe external fin convolution which are located over the internal ribs 33 are rolled over but do not touch the adjacent con volutiontherebyforming pores spaced along the subsurface channels.

Referring now to Figure 3, the general construction details ofthe roller cluster 56 are depicted. Accordingly, in operation of the preferred embodiment, e.g.

having three forming roll assemblies, the cluster of rollers 56 include a plurality of roller-like discs 58 having spacers 59therebetween. The rolling surface 57 of each roller-like disc 58 is angled ata pro gressivelylargeranglefromthevertical along the longitudinal axis ofthetube, in the direction of movement of the tube, to permitthefin tips 34to be rolled over in incremental steps, thus, preventing the fins from being squashed down and having the cross-sectional area ofthe subsurface channels 38 reduced. The spacers 59 prevent an already partially rolled over fin from hitting the back portion ofthe roller-like disc 58 on the subsequent tool arbor. In a typical finning head section having threeforming roll assemblies, afin will be first struck by an angled rolling surface 57 ofthefirst roller-like disc 58 and then proceed to rotate to the next forming roll assembly (positioned 120' from the first assembly) and pass along a plane of a spacer and not be struck by a roller-like disc, and then proceed to the third forming roll assembly (located 240 from the first assembly) where it will be struck by the angled rolling surface 57 ofthe second roller-like disc in the cluster. This procedure of having a fin struck by roller-like discs on alternating forming roll assemblies is continued until thefin tip 34 is rolled overto form a proper subsurface channel.Generally, the width ofthe spacers 59 are slightly less than the width of the roller 58, e.g.

the spacer may be 0.003 inches less than the roller, so that the point of contact 56 between the angled rolling surface 57 and the fin tip 34 will progressively move along the angled rolling surface 57 toward the backface ofthe roller on subsequent rollers 58. Thus, as the fins are rolled over in stepwise progression the rolled over fin will not contact the back face 55 of the previous adjacent roller 58, since the point of contact 56 of the subsequent roller has moved thus generally keeping the same distance between the point of contact 56 and the backface 55 ofthe prior roller.

Of course, the foregoing description of a method and apparatusforproducing externallyenhanced tubes using multiple lead starts is directed to a preferred embodiment, and various modifications and other embodiments of the present invention will be readilyapparentto one of ordinary skill in the artto which the present invention pertains. Therefore, while the present invention has been described in conjunction with a particular embodiment, it is to be understood that various modifications and other embodiments of the present invention may be made without departing from the scope ofthe invention as described herein and is claimed in the appended

Claims (4)

claims. CLAIMS

1. An apparatusforforming a multi-lead helically finned evaporatortubecomprising: meansforsupporting a length of blanktube; a multi-lead enhancement meansforforming multiple helical fins on the external surface ofthe evaporator tube, each enhancement means including a cluster offin forming means for rolling a plurality of extending straightfins onto the outer surface of said tube blank and a cluster of fin rolling means for rolling oversaid helically extending straightfinsto form a plurality of continuous subsurface channels, said subsurface channels having pores spaced along the top portion thereof.

2. An apparatus as setforth in claim 1 wherein said cluster of fin rolling means includes a plurality ofsmooth roller-like discs having a spacer means therebetween and an angled rolling surfacethereon for contacting said helically extending fins for rolling over said fins.

3. An apparatus assetforth in claim 2wherein said angled rolling surface of each adjacent rollerlike disc has a different angletothevertical than the previously adjacent roller-like disc whereby the angleto the vertical ofthe rolling surfaces increase in the direction oftravel ofthetube being enhanced so that said fins are progressively rolled over in increment from their initial vertical position to their desired position forming the subsurface channels with pores therein.

4. A method offorming a multi-lead helically finned evaporator tube comprising the steps of: supplying a length of blanktube; supporting the internal surface of said blanktube; engaging said blanktubewith a pluralityoffinfor- ming means and causing relative rotation therebetween, said fin forming means forming multi-lead helical straight fins; and rolling a plurality of roller disc means over said helical straight fins to form a plurality of continuous subsurface channels having pores spaced along the top portion thereof, each said roller disc means in cludingaclusterofsmooth roller-like discs having spacers between each disc and having progressively shallower angled rolling surface on each successive disc in the direction of travel of the tube so that the fins are rolled over in incremental steps in forming the subsurface channels.