CA1112031A - Method of making a helically corrugated tube - Google Patents

Abstract

METHOD OF MAKING A HELICALLY CORRUGATED TUBE

ABSTRACT OF THE DISCLOSURE
A helically corrugated tube with improved heat transfer characteristics is made by twisting a deformable tube of circular cross section and at the same time moving the ends of the tube axially relative to one another. First the tube is twisted while the axial ends of the tube are moved relatively toward each other to cause helical corrugations to develop progressively along the tube. When the corrugations have been formed, the twisting and moving of the ends of the tube are terminated and then the tube is reverse twisted and axially stretched to a length greater than the length of the original tube. The resulting tube is corrugated and longer than the original tube, and has improved heat transfer and fluid flow characteristics.

Description

BACKGROUND OF T~E INVENTION
The present lnvention relates to a method of making helically corrugated tublng with improved heat trans~er and ~luid ~low characteristics.
U.~. Patent 3,53~,267 issued to T. R. Bunnell dlscloses ~O a method and apparatus for ~ormlng helically or spirally corru-gated tube~ by ap?lylng twisting and axial movements or ~orces to the tube aod ~iShout direct application of tools to the tube wall The method includes the basic ste~s~of twistlng one end of an unde~ormed tube relative to the opposite end while the ends of the tube are moved axially relative to one another at a ~' ll~Z~31 contro-led rate. Hellcal corrugations develop as the tube wall deforms progres~ivelr ln the a~ial dlrectlon. The relationshlp o~ the rates oi twl~tlng and axlal movement o~ the tube end~
controls the pitch o~ the corrugatlon~ ior~ed ~n the tube.
A maodrel 18 ln~erted lnto the tube prior to step~ oi twlsting and aovlng the tube ends, and durlng the~e ~teps the mandrel ll~it~ the lnward deiormatlon oi the tube ~all and thu~
the depth oi the ~lutes between the corrugatlon~. The number oi ilutes and corre~pondlng corrugatlon~ can be determlned by lnltlal lndentntions or, conver~ely plmples, iormed ln the tube wall prlor to the step6 oi t~istln~ and movlng. Alternatlvely, the tube wall mny be locall~ stre~sed nt a plurallty oi points clrcumierentlally spaced about the tube a~ de~crlbed ln U.S. patent 4,059,004 lssued to R. w. Perklns.
One apparatu~ ~or carrylng out the corrugation iormlng process 18 lllustrated 1~ the clted Bunnell patent and comprlses a t~lstlng machlne havlng a rotatable headsto-ck and a talLstock-~hlch 18 translated a~lally relatlve to the hesds~ock~- by a po~er actuator such a~ a hydraulic cyllnder. A sectlon oi tublng to be

2~ corrugated i~ mounted at ltfi opposlte ends wlthln the ~achlne, and a per~on or an auto~atlc control devlce re~ulate~ the relative rate~ o~ hend rotatlon and tallstock~ translntlon to establlsh the pltch o~ the resultlng corrugation~ formed ln the tube wall.
In the prlor art process, the mandrel utillzed to llmlt the depth oi the corrugatlons 18 sometl~e~ held securely by the ~llZ~3~

derormed tube a~ter the twl~tlng operatlon, and to allcvlate thl~
condltion and release the mandrel, the tubc ls untwisted to a limited degree to rcllcve the restraining forces between the mandrel and deformcd tube ~all. In addltion to rélea~lng the tube ~rom the mandrel, the unt~lsting o~ the tube aiter the t~lstlng operatlon tcnds to correct for posslble ~rregular~tles ln the spaclng between the corrugation~ and to otherwlse ~a~e more unliorm and improve the appearance o~ the ~lnlshed tube as lndlcated by Bunnell.

SUNMARY OF TBE INVENTION
The pre~ent lnvention reside~ ln a method oi hellcally corrugating a sectlon o~ de~ormable tube. In the method a de-formsble tube ls provlded wlth at least one 6ectlon of predeter-mlned axlal length wlthout hellcal corrugatlons. ~re~erably the tube i6 made ~rom n metal ~uch as copper or alumlnum and has a ~all o~ a clrcular or other unl~orm cro~s sectlon. The one end o~ the tube sectlon 18 then t~lsted relatlve to the opposlte end, and at the same time the ends are moved a~lally clo~e~ to each other at a rate controlled ln relatlon to ehe rate o~ twl~tlng.
Stre~s de~eloped ln the tube walls by ~uch t~lstlng and ~ovement cause~ helical corrugatlons to be generated progresslvely along the axlal length o~ the tube sectlon untll such t~lstlng and move-ment 18 terninated.
A~ter the hellcal corrugatlons are ior~ed along a deslred length o~ the tube sectlon, the sectlon 18 reverse t~lsted

-3-illZ~3~

and ~tre*ched axlally at the sa~e ti~e ~o that the resulting length oi the sectlon bet~een the oppo6ite ends iB greater than the orlginal length o~ the section.
The method oi the present lnventlon produces a helically corrugated tube o~ greater length and lncreased lnternal dlameter, ; When a serles or bundle o~ such tubes 18 used, ~or e~ample, in a heat excbanger, an overall reductlon lo pressure losse~ ~or the heat excha~ge ~luld 1~ achleved, Furthermore,. the proces6 pro-duce6 corrugations that have a longer or lower pltch, whlch 1~
desirable ~or certain heat cxchange instnllatlons and lmproves the he~t transier characterlstlcs through the ~all o~ the tube.
The ~lutes between such hellcal corrugatlons are al90 more open ~hlch allo~s ~luld~ on the e~ternal ~lde of the tube to ilow more easlly along the ~lute~, aod mlsl corrugatlon~ developcd wlthln the ~lutes l~prove the heat tranR~r characterisics.

BRIEF DE~CRIPTION OF T~E DRA~INGS
Fl~. 1 18 a ~lde elevatlon vle~ oi a t~lsting ~achlne ~or hellcally corrugatlng tube lo accordance wlth the present ln~entlon.
Flg. 2 19 a partially sectloned vlew o~ the headstock aDd tailstock o~ the t~l~tlng ~achlne ln Flg. 1 and lllustrates ln detall the ba~lc elements for ~or~lng hellcal corrugatlon~.
Flg. 3 18 R sectlonal ~le~ o~ the tube as seen along the ~ectlon llne 3-3 ln Flg. 2 prior to t~lstlng, and illustrates the ele~ents of the tallstock . ~ Fig. 4 18 a partially ~ectloned view o~ the tube and tailstock durlng a twi~tlng operation.
~ lg. 5 illu~trates tube conilguratlons at three dli$er-ent staees o~ development ln accordance wlth the pre~ent lnventlon for comparatlve nnslysls.
Flg. 6 18 an end vlew oi a t~lsted tube prlor to the step~ o~ reverse twl~tlng and stretchlng.
Flg. 7 18 an end vieu o~ the tw~ted tube a~ter the steps o~ rever~e twlstin~ and stretchlng.

DESCRIPTION OF T~E PREFERRED D BODIMENTS
The method o$ hellcally corrugatlng a tube havlng a deiormable ~all 1~ carrled out oo a twl~tlng machlne 10 such as 6ho~n ln Flg. 1. The machl~e 10 generally resemble~ a lathe ln that lt ~nclude~ a headstOck~ 12 ~hlch 1B il~edly attached to the machlne ~rame 14 at one end and a tallstock 16 wblch i8 movably mounted on the ~rame by ~ean~ oi ~ay~ 18 80 that the tallstock can be ehiited toward and away irom the headstock along the tu~n-lng axls oi the ~achlne. ~ovement oi the tall~tock 16 18 produced b~ an actuator 20 iormed by a plstoD and cyllnder a~sembly whlch 2~ 18 $1xed to the ~rame 14 and ha~ a movable pl~ton rod 22 connected to the tallstock 16. A control valve 24 regulates the $10w o$
hydraullc or pneumatlc fluld to the actuator cyllnder, and the valve and ilow rates may be manuall~ controlled by mean~ o~ a handle 26 or, alternatlvely, a more sophlstlcated automatlc con-trol may be provlded as shoRn, ior example, ln the Bunnell patent ~L~12~3~.

referenced above. For ~urther descrlptlon oi the pre6eDt inven-tion, it will su~1ce to under~tand that move~ent o~ the handle 26 to the phantom posit10n lllustrated at the le~t ln Flg. 1 causes the plRton rod 22 to extend and move the tall~tock 16 at a glven rate along the ~ays 18 toward the headstock 12 at the oppos1te end o~ the bed 14. ~o~e~ent o~ the operatlng handle 26 to the phantom po~ltlon at the right ln Fig. 1 re~er~es the opera-t10D o~ the pi~ton rod 22 and cau~e~ the tall6tock to be pulled at a selected rate toward the actuator 20 and away ~rom the head-0 6 tock 12.
The head~tock 12 ha6 a rotatable chuck 30 bearlng a plurallty o~ clamplng ~aw~ 32 whlch engage and t~l~t the tube T
about the turnlng axis of the mac~ine to develop the de~lred corrugations ln the twl~tlng operatlon descrlbed belo~. The tall-~5 stock 16 ha~ a nonrotatable chuc~ 34 ln a~lal allgnment ~lth tSe - rotatable chuck 30 and carrles a plurallty of clamplng ~a~s 36 ~or engaglng aod holdlng the end o~ the tube T oppos1te that eDgaged ln the ~aws 32. Pre~erably the head~tock 12 or the tall-stock 16 or both deilne an open bore 80 that the tube T may be ln~talled through one or the otSer oi the stock~ at the beglnnlng o~ a t~l~tlng operatlon and may be removed at the end.
~ hen a cyllndrlcal tube T 1~ ln~talled ln the machine, a cyllndrlcal maDdrel 40 18 placed ~lthln the tube as ~hown ln Figs. 2 and 3. In one ~orm, the mandrel 40 has a s~aller dlameter thaD the 1nslde dlnmeter o~ the tuhe T slong Rubstantlally the ~llZel31 entire length o~ the mandr~ cept ~or an enlsrged end portion 42 whlch ha~ a dlameter appro~i~ately equal to th~ ~n~lde diameter o~ the tube. The enlarged end portlon 42 19 placed ~lthln the ~-tube end enga~ed by the oonrotntlng Ja~ 36 oi the tail~tock 16 and prevent~ tube de~ormatlon and corrugatlons from developlng ln the stres~ed portlon o~ the tube wall wlthln tAe tube sectlon oc-cupled b~ the enlarged portlon 42. The remalnlng portlon o~ the mandrel havlng the ~maller dlameter ll~lt~ the lnward de~ormatlon or radlal depth o~ the corrugatlons developed durlng the t~lotlng proces~ ln the long ~ldsectlon o~ the tube.
The end o~ the mandrel 40 oppo~lte the enlarged portlon 42 18 held coa~ially wlthln the tube by means o~ a bu~hing 44.
The bu6hlng permlts the mandrel to fillde relatlve to the headstock 12 as the tall~tock move~ n21ally toward or a~ay ~rom the head-stock, and also allows the part o~ the tube engaged by the ~aws 32 to rotate relatlve to the mandrel clamped wlthln the opposlte end o~ the tube by the ~a~s 36. The bushlng 44, howeYer, 18 not essential in all ca~es ~lnce the corrugatlons whlch are ~ormed ln the tube durlng a t~i~tlng operatlon tend to deveLop in cO~xlal relatlonshlp ~lth one another.
Prlor to the ln~tallatlon o~ the tube T ln the machlne 10 or at least prlor to lnitlation o~ the t~lstlng ~tep lt 1 necessary to ~tress the tube ~all locally at a plurallty o~
polnt6 about the tube ~rom ~hlch ~lutes or corrugatlon~ ~pread durlng t~l~tlng. For thl~ purpose a speclal tool ~ay be used to 3~

produce lndentatlons at, for example, four equnlly spaced polnt~
about the tube a~ taught in the above-referenced Bunnell pntent.
Alternntively, the ~aw~ 36 of the tallstock 16 m~y be p~ovlded ~lth protruslons 50 spaced trom clamplng ~hoe portlons 52 to develop loca~ly pre~surlzed or ~tressed areas ln the tube wall when the ~n~ 36 are clo~ed and grasp the tube. It wlll be noted that the enlarged portlon ~2 ot the mandrel 40 18 po~itloned ~lth-in the tube ~o that the tube ~all 1~ ~upported dlrectly under the shoe portlon~ 52, but the ~nll 19 un~upported uDder the protru-~lons 50. Under these circumstnnce~ and wlth approprlate dlmen-slonlng or the protru~ions, local stre~ing Or the tube wall l~
developed at the iour ditferent and equally ~paced locatlons oi the protrusions shown ln Flg. 3. ~hen torque 18 appl1ed at the be-glnning ot a t~isting operation, four ~eparate ~lutes and corru-gatlons emanate troa the streesed locAtlons at the end ot the tubegrasped by the tailstoc~ and spread axlally along the tube as the tall~tock translates.
Accordingly, ~lth a detormable tube lnstalled in the machlne a~ shown ln Flg. 1, the tvl~tlng operatlon ls lnltlated by rotating the chuck 30 aDd causln~ the o~e end ot the tube en-gaged by the ~aw~ 32 to be torqued and rotated about the tube or turnlng axls relative to the oppo~lte end held ln the nonrotatlng Jaws 36 ot the tallstock 16. At the same time, the end o~ the tube held iD the tallstock l~ ~oved at a controlled rate to~ard the hesdstock by mean~ ot the actuator 20. The ~all oi the tube ~Z~3~

de~orm6 flr~t at the stre~ed localitles under the plmples 50 and ~orm~ corrugation~ ~hlch ~pread a~ially along the tube in helical paths. The rate nt ~hlch the ends o~ the tube move relatlvely clo~er to each other ls controlled ln proportlon to the rate o~
5 rotatlon o~ twlst1ng o~ the tube ln the chuck 30, snd the~e rate~
establ1sh the pltch o~ the hellcal corrugatlons ~hlch are gener-ated in the tube ~all. The depth o~ the corrugatlons 19 llmlted by the ~andrel 40 as shown in Flg. 4.
~R long a~ the step~ oi t~l~tlng and movlng contlnue, the hellcal corrugatlon~ contlnue to be generated. ~hen the cor-rugatlon~ have spread along a predetermlned sectlon o~ the tube or to a partlcular statlon o~ the tube, tbe twl~ting and movement oi the tube ls ter~lnated and the generatlon or the corrugatlon~
stops.
In accordance ~lth the present lnventlon, the tube 18 - no~ rever~e twi~ted and at the same ti~e the tube 1~ stretched axlally to a le~gth bet~een lts opposlte end~ greater than the orlglnal length o~ the tube when the tube ~a~ ~lrst lnstalled ln tbe turnlng machlne. The reverse t~lstlng 18 acco~pll~hed by reveralng the dlrectlon o~ rotatlon o~ the chuck 30 60 that one end o~ the tube ~eld by the ~a~s 32 16 rotated ln a dlrectlon about the tube axls oppo~lte to the lnltlal directlon o~ t~lstlng ~hlch developed the corrugatlons.
The stretchlng o~ the tube 1~ accompll~hed by retractlng the plston rod 22 lnto the cyllnder o~ the actuator 20 by means o~
the handle 26 on the control valve 24. Thus, the tall~tock 16 is ~i3~

dra~n toward the actuator 20, and wlth the tube T still engaged ln the machlne, the end o~ the tube gra~ped by the ~aws 36 18 pulled a~ially a~ay ~rom the end grasped b~ the rotatlng Ja~ 32.
Agaln, the rates o~ reverse rotatlon or twlsting and a~lal move-ment are controlled at a predetermlned ratlo ~hich ~ay be the sameor dl~erent ~ro~ that employed to lnltlally de~orm the cylindrl-cal tube and generate the hellcal corrugations ln the tube walls.
~hen the tube has been stretched to a predetermlned length, tho reverse twlstiog aod stretchlng are termlnated sl~ultaneou~ly.
The ~inlshed tube 18 then removed ~ro~ the machloe.
The reverse t~l~tlng and stretching o~ the tube produces ~everal ad~aotageous result~.
Flrst o~ all, lt should be understood that the rever~e twlstlng aod ~tretchlng operatloo does not remove the hellcal corrugatlons ~ro~ the tube wall. In other words, the lnltlal cor-rugatlon ~ormlng proce~s is not reverfilble, and the reverse twlst-lng and stretchlng adds new dlmenslon~ to the ~orm and shape oi the lnitlally ~ormed corrugatlon~.
~econdly, lt should be recognlzed that the ~lnal product i~ a corrugated tube tbat 18 longer than the orlglnal tube ln-stalled ln the t~lstlng machine. For comparatlve purposes, Flg.
5 lllustrates a tube T1 a~ ln~iall~ lnstalled ln the machlne wlth-out corrugatlons 1D tube ~alls o~ clrcular cross ~ection. The tube T2 18 the same tube a~ter the lnltlal steps o~ twlstlng and mo~log whlch develop the hellcal corrugatlons ln the clrcular tube ~all~. Note that the overall length oi the tube has been '3~

shortened in the twlstlng proces~. The tube T3 1~ the ~ame tube aiter the steps oi reverse twlfitlng and stretching ln accordance wlth the pre~ent lnventlon. Note that the corrugatlons ~tlll appear ln the ~all oi the tube but the overall length o~ the tube 18 greater than the inltlal tube by the dlmenslon a and greater than the corrugated tube T2 by the dimen~lon b.
~ ~urther ieature o~ the tube T3 1~ the relatlvely lo~
or long pltch o~ the corrugatlons. The lovention, lncludlng the stretchlng step, permlts the formatloD o~ corrugntlons havlng a lo~er pltch than those lnltlally developed ln the tube, and such low pltch corrugRtlon~ are advantageoue ln a nu~ber of heat tran~-ier app~lcatloDs. For e~mple, where the heat exchange fluld pa66e~ e~ther through or over the tube ln the axlal dlrectlon, the lo~ pltcb corrugatlons permlt the fluld to more ea~lly follo~
the tube ~urfaces at lncreased veloclty levels. Addltlonally, the dlstance between ad~acent corrugatlons 18 greater due to a~lal stretchlng of the tube and ~luld can more readlly reach the depths o~ the ~lute~ between adJacent corrugatlon~. Overall, therefore, more erfectlve heat transier characterlstics can be obtalned.
Addltlonal advantages are apparent irom t~e comparlson of the tube~ T2 and T3 ~lewed ~ro~ one end ln Flgs. 6 and 7 respec-tlvely. The lnslde diameter c of the tube T2 18 smaller than the inside dlameter d oi the tube T3. The increase 1D dlameter takes place when the tube 18 rever~e twl~ted, and provlde6 a lar~er overall cro~s sectlon ~lthln the tube. ~'lth lncreased cros6 sectlon, a heat exchange ~luld flo~lng ~lthln the tubes encounter~
less ~lo~ resistance and the resulting pres~ure drop 18 there~ore smaller.
A stlll ~urther but uoexplalned advantage noted ln tub~s ~ub~ected to the steps o~ rever~e twl~tlng and axlal ~tretchlng 1 the development oi a mlnor corrugatlon ln the troughM o~ the ilute~
bet~een the ma~or corrugatlono iormed during the lnltial twl~tlng operatlon whlch dlmlnlshed the length o~ the tube. These ~lnor corrugatlon~ add to the overa~l sur~ace area both lnternally and e~ternally o~ the tube and produce a concomltant lmprove~ent ln the heat tran~er characterlstlcs oi the tube.
Con~equently, the tube corrugating proceo6 o~ the pre-~ent inventlon produces slgnliicant l~provement~ over the prlor art tube~ ~hlch enhance the utllltg oi the tubes especlally ln heat tran~fer appllcatlons.
~ h~le the pre~ent lnventlon has been descrlbed ln a pre-ierred embodiment, lt should be under~tood that numerou~ ~odl~lca-tlons and substltutlon~ can be had wlthout departing iro~ the splrlt oi the lnventlon. For e~ample, the re~erse t~lstlng step oi the lDYentlOn 18 generally preiormed by rotatlog one end o~
the tube reLatlve to the OppoHite end bv an amouat less than the lnltlal or ~orward rotatlon, ~hlch ~or~s the corrugatlons, oo that the ~lnlshed tube 18 partlally untwlsted. Howé~er, the re~erse t~lotlng step ls not llmlted in thlo respect, aad ~lgnl~icantly hlgher a~ounts oi t~lstlng are clearly contemplated. At the same ~.~lZ~3~

tlme, the ratlo o~ the twlstlng and ~tretchlng parameter~ ~ay be sultAbly adJusted to achleve a ~lnal tube length and ~lute or corrugatlon ~hape that are most sultable ~or tbe partlcular ~unc-tlon to whlch the tube wlll eveutually be rele~nted. The machlne ~or iormlng the corrugatlons rotates only one end o~ the tube ~hlle the opposlte end 18 held rotatably ~l~ed. Correspondlngly, the oppo~lte end 16 moved toward the rotated end. Other twlstlDg machlne~ ~ay move or rotate the same, opposlte or both ends o~ a tube sectlon to control the resultlng corrugatlon~. Tubes havlng clrcular and other cro~ sectloD~ can be employed in developlng the corrugatlon~. Accordlnglg, the present lnventlon has been de~crlbed iD a pre~erred embodlment by ~ay o~ lllu~tration rather than ll~ltatlon.

Claims (10)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of helically corrugating a section of de-formable tube comprising the steps of:
providing a deformable tube having one section of pre-determined axial length without helical corrugations in the tube wall between the opposite ends of the tube section; then twisting the one end of the tube section relative to the opposite end and at the same time causing the one end of the tube section to move axially relatively closer to the opposite end at a rate controlled in relation to the rate of twisting to generate helical corrugations in the tube wall along the axial length of the section; and after the helical corrugations are formed along the length of the tube section, reverse twisting the tube section and at the same time stretching the tube section axially to a length between the opposite ends greater than the original predetermined axial length.

2. A method of helically corrugating a section of de-formable tube as defined in claim 1 wherein:
the step of twisting comprises applying a torque to the tube section in one direction about the tube axis; and the step of reverse twisting comprises applying a torque to the tube section in a direction about the tube axis opposite the direction used during the step of twisting.

3. A method of helically corrugating a section of de-formable tube as defined in claim 1 wherein the step of reverse twisting comprises reverse twisting the corrugated tube section by a predetermined amount.

4. A method of helically corrugating a section of tube as defined in claim 3 wherein the step of reverse twisting com-prises untwisting the tube section by an amount less than the twist imposed upon the tube section during the generation of the helical corrugations in the step of twisting.

5. A method of helically corrugating a section of de-formable tube as defined in claim 1 wherein the step of reverse twisting comprises partially untwisting the helically corrugated section of tube while the tube section is stretched to a length greater than the original predetermined length.

6. A method of helically corrugating a section of de-formable tube as defined in claim 1 including the additional step of inserting a mandrel within the tube section prior to the step of twisting to limit the inward deformation of the tube wall as the helical corrugations are generated.

7. A method of making a helically corrugated tube comprising:
providing a given length of tube having a deformable tube wall with a generally circular cross section along the given length in the undeformed condition;
twisting the one end of the tube in one direction about the tube axis relative to the opposite end;
moving the one end of the tube relatively toward the opposite end at a controlled rate during the step of twisting to cause the tube wall to deform and develop helical corrugations progressively along the tube in the axial direction;
terminating the steps of twisting and moving when the helical corrugations have developed along a selected portion of the deformable tube; and then twisting the one end of the tube in the opposite direc-tion about the tube axis relative to the opposite end;
moving the one end of the tube relatively away from the opposite end at a controlled rate during the step of twisting in the opposite direction to extend the tube; and terminating the steps of twisting in the opposite direc-tion and moving the end away when the tube with the helical corrugations has been extended to a selected length greater than the given length of tube in the undeformed condition.

8. A method of making a helically corrugated tube as defined in claim 7 further including the step of limiting the inward deformation of the tube wall as the helical corrugations develop progressively along the tube in the axial direction.

9. A method of making a helically corrugated tube as defined in claim 7 wherein the step of twisting comprises twisting the one end of the tube about the tube axis while holding the oppo-site end of the tube rotatably fixed.

10. The method of making a corrugated tube as defined in claim 9 also wherein the step of moving comprises holding said one end of the tube axially fixed while moving said opposite end axially relative to said one end.