Note: Descriptions are shown in the official language in which they were submitted.
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
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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
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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
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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
31
. ~ 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
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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
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~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
--10--
'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
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31
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
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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.
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