CA1307681C

CA1307681C - Seamless tube production

Info

Publication number: CA1307681C
Application number: CA000540444A
Authority: CA
Inventors: Karlhans Staat; Hermann Moltner
Original assignee: Kocks Technik GmbH and Co KG
Current assignee: Kocks Technik GmbH and Co KG
Priority date: 1986-06-25
Filing date: 1987-06-24
Publication date: 1992-09-22
Anticipated expiration: 2009-09-22
Also published as: GB2191966A; FR2600562A1; IT8721000A0; IT1205176B; GB2191966B; DE3717698A1; DE3717698C2; GB8714770D0

Abstract

ABSTRACT OF THE DISCLOSURE
A method and apparatus is disclosed for the production of seamless tubes. An ingot heated to the rolling temperature is pierced in a skew-rolling mill to form a hollow ingot which is then stretched into a tube bloom and rolled out into a finished tube. According to the invention, the stretching takes place immediately after piercing during the same heat, wherein the rolled goods is stretched in the same skew-rolling stand, but in a direction opposite to the direction of the piercing. The operation is simpler, technically better and more economical when compared with prior art. The process can be carried out with relatively low investment costs.

Description

Thl~s inventlon -~elates ~o seamless tube product~on an~
~nor~ prop~rly conc~rs~s a proc~ or the produ~tion of ~Q~aml~s~
~ub~1 ln whieh l3r, ln~oe heate~ to the ~olllng temper~ture is pi~rced ~n a skew rolling ~tand to ~ m a h~lto~ lngot, then ~tret~hed into ~ tube bloom and rolled ou~ into iElnishe~ tub~.
In the vast ma~orlty o~ ca~s the ~bove ~h~ee pro~eaur~l ~teps ar~ carried out during s~amless tu~e E~ro~ ction~ w~h th~ ald of three different app~ratuseB~ Th~ ~iet~ng fr~quen~ly take~
e in a ~kcw-rolling starld be~au~e the latter ~ rs a h~llow ingot wlth a low wall ~hlckne~s toler~nce and a rol~tlv~ly g~ea~ l~ngt~. The ~tr~tching frequen~ly occur~ in a æ~c~nd ~kew-r~lling st~nd~ ~hich i~ d~$gned as an Assel or her rol'~ stana. q~he ~ubQ ~loom thzl~ thus reBul~s during st~e~chlng i5 rolled ou~ ~nto fln~be~ tuba ~ter interr~edia~e h~a~in~ ln ~ ~u~s~qu~nt ~ r~du~ing or ~e'cch-~edll~ ion ~oll rcr~in~

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~ ~ ~ .. ' ' " '' 1 3076~1 The pleroln~ o ingo~s ~o hollo~ lngots and the stret~hing of hollow ingo'cs into tube blooms ~lth the sarne ske~-rolling 8tand 15 already known (the ~ournal ~ander, leche, Rohre, Vol. 14, No. 4, pp. 150-lSl (lg73~ . With this f2sDlliar pro~e~s, ho~ever, a number o~ hollow ~ngots were ~ir5t~ produced by pie~cing, ~he ;kew-rc)llln~ ~tand w~ then conver~ed from pie~oing to st~et~hing ~nd then a numh~r o hollow ingo'cs ~ere Purther prç~ce~sad b~ stret~hing into tube bloo~Ps.
Because the plercln~ o sev~ral c:on~eCu~i~te lngot~
r~quire~ a longer period o~ time ~nd ~h~ conver~ion of the ske~-rolling ~tand ~rom p~ercin~ to str~tehln~ aleo require-~ solne time, it is no~ poss;~le to carr~ out the p~ercing and stretching 1n one hea~1ng ln l:hl~ familiar proce~. Th-ls, ~he hollow ingots have to be heated ~ain prior to ~tre~ching, whioh i5 uneaonomical ~nd time~Consuming ~ ~nd which also r*quire~ the inst~ tion and oper~tion o~ ~ 6ui~bl~ furn~ce.
In addit1On, during both pl~rclng And ~retching th~
rolled good~ a~ move~ f rom tha lngot guide channel looat~d on thR antrance ~id~ through ehe roll ~t4n~ to the exi~ si~e, where it i~ disch~ed ~om the ~i~e. A 'cran~Fo~ arrangemene is thus ~equir~d to conv~y the hollow ingots :E~om ~h~ exlt to the entrAnce side of ~be skew-roll~ng ~and, whi~h call~ ~or ~he corr~ponding investmen~ ~osts.
Furthermore, a mandrel rod 1~ lnserte~ lnto ~he hollow ngot ~n the en~rance ~lde at the ~eginning of the s~re~ching ' 1 307~8 1 proces~ until 1~B frc~nt end strik~ the ~ottom of the pierced h~l~ow ingot. The mandrel rod ~chen pushes, ln ~he manner of a pu~h bench, the hollow ingot into the re~ i~n o~ the rolls of the ~kew-~olling s~an~, where the 6tretching proces~ is carried ou~. Consequently, a ~ollow ingot th~t is not ~ie~ced a11 the way through, b~l~ r2ther ~as a bot~otn that a~ts as a St~opper ~or 'Gh~ manarel ~od i~ required ~n th~s ~amil~ar proce~s. AB a result, thQ pieraing proces~ in ~he ~kew-rolling ~tand must be ~top~?ed prematurely in order to obtain a bottQm ~e~tlon, or ~he hollow Ingo~ m~s~ be pro~luced wit~ a pun~hing pre~s. ~oth have ~he disadvantage that the ~ubstan~ial proportion of mate~ ial mu~t be scrapped bec~use thl~ bottom section mu~t b2 ~ut of 3nd d1scar~ea a~te~ 3tretchlng. For the a~ove rea~ons, the familiar pro~es~ was ~um~ersome, tlme-consuming ~nd uneconomi~al ~nd çould be us~ onl~ fo~ ~ small produc~iQn Outp~t7 there~ore, this p~o~e~ has not been wi~ely us~d in praati~e.
~ h~ invention p~opo~s to organi~e the abo~te proces~
ln ~ ~lmpl~r, te~hni~ally better and more e~onomic~l manner and ~o offer an arrangement ~h~ akes ~t ~ossib'le ~o c~rry Ol~t the p~oce~s according to the lnv~ntlon wi~h relativ~ly low lnv~tment ~ost~.
Thi~ p~blem i~ ~ol~ed accor.ding to the inventlon in that the ~re~ching takes place lmmedia~ely after piercin~ in the ~me heat, where ~h~ ~olled ~ood~ ls ~retch~d ~n the ~ame 3~

, , skew-rolllng s~an~, but wi~h a pass~ge direction opposite that of piercin~.
This invan~ion proce~ thu~ differ~ fr~m the familiar proce3s in that the 5kew-rolling stands operates for p;erclng and st~e~hing in ~eve~ng roll operation and both pas~Age~
gulckly ~ollow e~ch o~her. l~he lngot is pierced d~ring the ~irst pa~aqe, wh~le in th~ second passa~e and ~n the opposlte dlrectiorl t:he ~ame ingo~ is shor~ly ther~af~er 6tre~ched in the ~ame ~kes~-rolling mill ~o form a ~ube bloom. ~s a result, no ~ppreciable cooling o~cur~ be~ween ~?îer~in~ and stre~ching and an intermedi~e heatln~ ~ not needed. There iB a~ l no need 1~or a tran~po~l: mechanlsm for con~reyin~ th~ rolled ~oods from ~he exit ~lde to ~he entranc~ e around the ~kew-rollln~
stand. qlhe mandrel rod gl~idance i~ ~implified al~o becau~e a mandrel rod ~na ~ support bearlng ar~ re~uired only on ~he exi~
side o the ~kew-rolling ~st~nd~ Its ~trok~ i~ v~ry sho~ here b~cau~ the m~ndrel ~od does not have ~o b~ withdrawn from ~he hollow ingC:t~ rAther~ th~ la~te~ is ~olled down during the secon~ pa~ag~ o th~ m~ndr~l ~oc~ Furthermoee, the ax~t guldAnce for ~he hollo~ ingot dueing piercing al~o constitut~s a good 2ntrance ~uld~no~ ~uring ~tretching, in whiah ~he holl~w lngot oan ~sily rol:ate ~nd i~ not turn~d by loadlng ~7ith a high ~o~ue .
~ no~her ~va~ltage C01'11~ 3 in the ~a~t ~hat a~ the beginning ~ plercin~ anD 6tretching the maxlm~lm stress that . . .

arise8 ~hen on ~he roll ~tand and rolled good~ iS r~duced in t~at ~he~e 1B a gradual ac~eleratlon from the ~o~ped ~tate of the rolls or fro~ ~ low roll r~p.m. to the normal opera~ing r.p,m. S~oppage of the rolls and/or a low roil r~p.m. re~ult ~tho~t additlonal re~ulation from t.he rever3ing-roll operatlon accor~ing to ~he lnven~ion~ ln which th~ rolls ~ust be ac~le~tea ~ro~ ~he stationary ~ta~e at the beginning of p~ercing an~ of ~tre~hlng d~e to ~he reversal ~n the di~ec~lon o$ ~otatlon or ~he rolls.
~ uring piersln~ and 6tret~hing th~ mandr~l ~od re~ain~
inslde of ~he hoilo~ ingo~ and~or tube bloom, ~h~ch prevents a~r, especially the oxygen o~ ~he air from ~en~tratlng into the hollow ~ngot an~or tube bloom and produoin~ ~cal~ on the inner wall th~re. Furthermore, it i~ p~s~ibl~ wlth ~he in~ention process to keep the ~pace between tha mandrel r~d and ~he inner wall of the hollow ~ngot and/or th~ tube ~loom p~rtic~larly small b~cau~ the m~narel rod do~s not hav~ to ~e newly in~er~ed. ~he ~m~ iz~ o~ thi~ g2p al50 keep~ the re~idual ul~ount o~ a~r ~n~ oxyg~n ~ch~ ean ~till ~ne~ratQ h~re very lo~
80 th~t n~ ~ppreoiable ~al~ng o~ ~he inn~r wall oCcur~.
~onsequen~ly~ th~ rolling o~ scElla particles in~o ~he inner wall 19 ~lxo avoided d~ring ~tr~tchin~s the lnner w~ll ia thu~
con~erably smootherO
Although the hollo~ ing~t ~ generally stretched after piercin~ ov~r an innel mandxel rod ~o for~ 8 tu~e bloom, ln 1 3076~1 order to o~taln a ~hinner wall with ~rea~er stretching of the rolled goods, it ls ~uite expedient in ~ number of ca~es if ~he hollow in~o~c iS stret~he~ ~f ter piercing ln a hollow p~lS8 , i . e ., w~ o~ an inne~ tool. A ~u~e bloom w1th a thi~ke~ wall iS then indeed obt~ined ~ ~u~ thi~ wall ~hicknes~ i~ withln par~icularly narrow to~eranae limits, whlch definitely impro~7es the ~aua~ ity of ~che firlished tube.
It iR particularly recommen~ed to ~nl~h-roll ~he tube bloo~ in a size-reduGing OX ~t~ch~r~ductic)n roll 'craln af'cer piercing and ~re~ch~ng with~ut intet~edlate he~tlng. Th~ is also rende~ed po~sible by ~he prC~ce~ ~c~or~ g to 'che ~nventionO because with it pler~ing ~nd ~tretohlng follow e~ch other very r~pldly and one ~ork~ wi~h only a ~lngle lnner tool, ~Yhlch removeS heat from th~ rolted goods only once.
Cons~quently, Ithe initisl rolling h~at i8 suf~iclent not only for plercing an~ s~retchin~ bu~ ~al~o ~o~ ~h~ sizin~ and ~'cre~h-redu~iorl rolllng.
On th~ othex hand~ lt i~ also possible ~o ~u~ther ~tretch ~he tube bloom after pie~Cing and ~t~et~:hin~ in thc r~sve~sing-roll stand in one or mor~ subsequen~ pro~edural ~teps. A re~ rin~ of the loa~ ~n ~he e,ubseguent streSch~ng units And par'~icularly ~hin ~al~ed ~ube bl~om~ S s ~chie~ed in thi~ manner~ Plug mill or pilqer rc~ tan~s, ~or ex~rnple, can be u~ed for the subsequent pfocedu~ tep~ fo~ ~tre~ ::hin~.

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-` 1 307681 The inven~lon also concern~ an arrangsment for c~rrylng out the inven~ion prc)cess. Thls h~s a ~kew-rolling ~and, whic~ ;s e~uipped on the el~tran~e side wi~h an ingot guide channel and a pu~her and on the exit side w1th a rolllng mand~el on a m~ndrel rod that l~ ro~atable, axially displaceable and ~upportea in a bear~ng, ln which case a s1zirl9 ~oll train or stretch-reduc~1On roll traln is located beyond ~he skew-rolling stand. Accordin~ ~o the invention, thi~ arrangement is ~harac~er~zed in that the drlve as w~ll as the position o~ the rolls ar~d po~ibly the po~itlon of the yuides o~ he skew-rolling s~and can b~ adjusted ~t w1ll af~er ea~h p~ssage ~o piercin~ or ~tre~hing and the oth~r air~c~lon of pass~ge o~ the rolle~ goods and that a mech2nlsm for ~arrylng of ~ the ~tretched tube blooln ls located in the 2~ne of the in~ot g~id~ ~hannel.
tt~r;ous embodilnent ~orms ~an be used a~ skew-rolllng 6tands, but primarily A~sel and Diescher roll 6tands. S~it~ the latter the speed o the Die~Qh~r d1s~: ls abou~ 4-20 timeq greater during ~tr~qhing than during pier~in~ w~ found ~ha~ lt is ~uite possible itl such ~ke~-~olling ~tan~s to de~lgn the adjustment ~evices ~or the pos1tlon~ o~ the ~olls And po~1bly also the guldes, such a8 th~ ~le~cher d1sk~, so th~S ~hey can be adjusted rom str~'cchlng to pier~ing or from pierc1ng to stret~hing w i ~h in a f ew se~ond g . ~he r ~d i a l pos i t ion ar~d.~or the a~ le aa~ustment of the axe5 o~ r~ta~ion o~ the roll~ mu~t ~e prlmarily Inodi~i~d in order to ~e~ 'che ~kew rollin~ stand ~o the -`` 1 307681 other shaping p~Qce~s. The driYe speedB and the di~e~tion of ~otation o~ the drive can, if necessary~ ~lso be modified within a few second~. A few s~ructural changes are ~e~ired for this as aompared with the familiar ~kew-rolling stand~, but they can be done. I~ ~he a~sting devices ~or setting the rolls ~re desiyned so ~hat they can also work ~alnst the rolling force, i.e~, wi~h ln~erted rolled goodR, the rolls are ~hen also in the position withqut p~shln~ equipment eo dr;~w the rolled goods into the p~ss opening a~ the beginning o~ the next ro~l ~a~age~
In a pre~e~red e~bodimen~ of the ;nvention the acu~e an~le~ o~ at~a~k o~ the rollx enclosed by ~he longi~udinal axls of the rolled goods ~nd an axi~ o~ ro~ation of the rolls during piercing And s~re~chin~ ha~e a vertex that i3 loc~ted on the ent~ance sidq of the ~kew~rolling st~nd eq~ipped wit~ the ingot gulde channel. The ~einition of ~ntrance and exit sides alway~
re~ers only to the plercing process ln thi~ text. The re~ult h~re 1~ that the rolled good~ dur1ng piercing pas$es thro~gh a roll pa5g with roll rotation axe~ with a dive~gent exten~ion -wlth rc~e~ence to th~ dir~t1on o pa~age - while durlng ~tret~hing i~ i~ passed ~hrough a roll pass wl~h Convergent axes o~ rotation of P-he rolls. This ~educe~ an undesirable turning of ~h~ ~olle~ ~oods during pier¢ing and favors its expansion, Dur~ng stretching the then convergent roll rotation axix ~et~in~
effeat~ a restric~ion in the exp~n~ion and t~us advantageously ~180 prevents the development o aornered ~ube bloom ends in the ~:
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case o~ thln ~olled goods walls, In orde~ to ~chieve these ~dvant~ges, no o~her direction o$ in~llna~ion need be imparted to ~he roll rota~ion axes in ~he reversing rolls ac~ording to the lnven~ion ~ecause ~he ch~ng@ ~rom dlvergent ~o convergen~
arr~ngem~nt o~curs only through ~he ~e~ersal of the direction o passage o~ th~ ~olled ~ood~.. Thl~, all ~h~t 1~ re~uired afte~ a pAS~:~I9~ 0~ the rolle~ good~ ~s to ~han~e the size of the angle of a~tack o the ~0115. It is reoommende~ that ~he angle of a~aek be between one and ca. t~enty degree~, where the hlqher degree number~ are se~ during l?ier~lng. It 1~ al~ exp~dient to install ~he arive motor~ for rolllng on the ~1de of t~e mandr~l ¦
rod supporl: bearing.
dvantageous ~f a guide ~ube tha~ is rotatable ~o~lnd it~ longitudlnal axis is installed b~yond~ ~oaxlal t:o t~e axi~ o~ rolled goods pa~sag~ as a d~vl~e fo~ ~arrying of the ~tre~che~ tube bloom oi~ tha lngot guide ~hannel ~n the side fa~ing ~way from the ~k~w~roll~ng s~and~ Su~h ~ gulde tu~e 1~ al~eady ~he ob~ect o~ an older West German published patent apPlicati-n .
~DE~OS 3~ 33 11~ ~ the u~e o~ which is al~o proposed ~er~
It 1~ r~eommended her~ that t~e mdndrel ro~ be pa~sed through ~he ~411 pa~ a~c a controlled ~peed a~ th~ b~ginlling of ~trotching and exten~ into ~he entranaR zone o~ ~he ~uide tube, where it is held with the aid o~ the ~upport bea~ln~ at le~st urltil the tube bl~oln entQrs lnto the gu~de tube. Thi~ mean~
tha~ the mandrel rod i5 run into the guide tube ~ the ~eginning 9.

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1 3076~

of the ~tre~ching proce~ ~y ~ control~ed displacement of the ~uppor~ beAring 'chrough the re~ion c~f the roll~ an~ ls not retaLn~d unt~l in ~chi~ posi~lon~ ~:he beginning o~ ~he s~r~tched tube bloo~n is ~hus also fla~ ly brou~h~ in the zone of the ln~ot ~uide channe~ ~nd ls ~elia~ly en~e~ed in'co the en~ranoe opening of the gulde ~ube. ~s ~oon a~ ~he l~tter occurq, th~
~andrel ro~ can be gradually withdrawn during the stre~chin~
proces~ to the exit ~lde; but ~hich ~an also oc~r a~te~ ~he ~tre~oh1ng prw ess ~s complete~
~ n an adv~ntagQous embodiment o~ the invention a shaft rod that ~rives th~ man~rel rod, 1~ ~oaxially coupled with the la~ter and is ~upported In ~he bearlng i~ ~rovld~d with a larger outslda diamete~ than th~ hollow in~ots a~ a pu~her for the latter ~t the beglnning o st~e~hing. Pushing of the hollow in~ota in~o tbe re~ion o tbe rPll~ thu~ t~ke~ place du~lng ~tr~tchlng witho~lt a~itional ~ructural expenditure through the ~haf~ ro~ thRt 1~ pr~6Bnt and thus r~lieve~ ~he ~trongly stre~ed zone ~n thi~ ~ide o~ ~hb ~kew-rollin~ ~tand, Pue to th~ large outc~ide diameter o~ ~he ~hA~t r4~, a radial bu~tr~s~ln~ again~t buakling i~ al~o unne~es~ary.
In ~n~t~er ~mbodimen~ of th1s inventlon ~he roll component that e~e~ts th~ oxl?~nslon durir.g ~ier~ing i~ utilized du~ing ~r~tchin~ or smoothing ~he rolled good~. ~his central roll oompsnent r~mains rel~tively spar~d durin~ pierc$ng ~ such t ~t ig a~so ~sseabl~ a~ter a pr :?longed ope~tlng t~me for ., 10.

1 3û76~1 stretching in which higher ~e~u;rements ~e lmposed on the precision and ~urf~c~ ~uality of the rolled good~. In addition, the roll component that ~ffects the reductlon duri~g ~erc;ng i~
provided during stretching for rounding the tube bloom, and vice versa.
~ here i~ also the posslbil~ty of changing the dir~ction of pas~a~e of the rolled ~oods by modiying tbe feed angle o~ ~he rolls. In thi~ manner~ a rever~al o~ the d1re tion of rotation of the roll driv~ c~n b~ ~voided, during whi~h eubstan~ial m~ments of inertla ~ris~ whereby ~ bra~;ng and ~e8tar~ing o~ ehe drive in the opposlte dir~ctlon o~ r~ea~lon bocomes ~ostly and time-aonsuming. A chAnge in the ~eed angle of the roll~ m~ke~ it po~sible ~ wo~ ln ~h~ re~r8~-rolling operaSlon accor~ing to the inv~ntion wi~ho~t ~h~n~ng the dirQction o roll rot~tion.
It is expeaient to have a lo~er pas~age ~peed of the rolled goo~s duxing plerain~ th~n du~ing ~tretching~ ~he greater ~orque required dur~ng p1er~ing leads in the case of ~n app~opriAtely lowe~ pA~sage sp~d to appro~lm~tely the same power raquirem~nt o~ the dri~ a~ str~tch~ns th~t re~uire~ ~
le~ser torgu~ ~ith ~ correspondingly bigher p~age ~peed. In the i~eAl ~a~e the s~me in3~alled d~ e power can ~e ~ully utl î i zsd in bo'ch pi erc ing an~ ~tre ~h ln~ .
ally~ i~ i8 ~d~tisable to ~oYide ~ sep~ratln~
~e~ia~ ~4r cr~ppln~ ~he end ~ecti :>n~ of ~he tube bloom~ in rorlt 11~

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, f the ~izing or s~re~ch-reducti~n roll train. ~hls i~
re~Q~enaed because the tube bloom end sectiOn~ are uneven after pie~cing ~na ~retc~ing, whlch can lead to disturb~nces durlng fini~h-~olllng.
The lnven~ion i~ illustrat~d in ~he drawings on the basis o~ one pre~erred ~xample.
Figure 1 ~how~ an arr~ngem~nt accordin~ to ~he invention in top view, ~ g~re 2 6hows an inclined roll ~uring piercing~ ~nd Flgu~e 3 ~hows an inclined roll durlng ~tre~chiny.
In F~gur~ 1 ~n ingot heated to the rolling ~emperature pa~s~s ro~ a ~urnace, not ~hown~ over ~ roller bed 1 ~nd a transver~e conveyor 2 into ~n în~ot gui~e channel 3. A pusher 4 there move~ ~he lngot in the axial ~irection out of the in~ot guide ~h~nn~l 3 between the rnll~ S ~ a sk~w-r~llin~ stand 6A
From ~he dl~charga ~ide a ~andrel rod 7 with ~llin~ m~ndrel 7a p~ect~ lnto thfl ~one o~ the ~ 5, ~h~re the ~nd~ed rod 7 l~ guided an~ h~l~ ln the radial dir~ction by a mandr~l roa ~nd hollo~ lngot guiae 8 and ~n ~ ial dieection by ~ ~h~f~ rod 1~ Ana by ~ ~upport ~rin~ 9. The ~h~t rod 1~ has an o~t~ide diame~er ~ha~ ~9 greater than that of ~h~ hollow ingots 15~ It ~160 serve~ as a pu~her for the h~llo~ ingot~ 15 ~k ~he beginn~ ng of str e tch i ng .
Durln$ pi~r~ing the ingot iB ~oll~d on~o ~ m~ndrel ~o~ 7, ~here a lubricant and/~ a ~oxl~i~ing ~gent 1 12.

`-` 1 3076gl expediently introd1lced through the mandrel rod 7 and po~ibly also through th~ roll mand~el 7a in~o ~he inn~r hole 16 of the rolling ingot 15a - see ~igure 2.
~ g ~oon a~ the ~tre~chin~ o ~he re~ulting hollow ln~ot enclos~ng the mandrel rod 7 i5 oomp:Le~ed, ~he hollow ?ngot ~ B stretched by the ~ame rolls 5 to orm ~ tube bloom and in ~o doing is ~onveyed ba~k ln the oppo l~e direc~lon to ~he ingo'c guid~ charlnel 3. The mandrel rod 7, with or without its roll maodrel 7~ ~hich is ~omewhat g~e~eE in d;~met~r and m~y have been removed~ i9 mc>ved herg ~o the ingot gui~ channel ~ in the axial dlrectlon by ~r~ appropriate.Ly re~ul~l:e~ ~vance of ~he ~uppo~ bearing g~ Thls occur6 l~ntll the ~oll mandre~ 7a ls lo~ed in the enl:rance zone ~f th~ ~ir~ ctlon 10~ of the quide tub~ 10. The roll ~andrel 7a r~main~ in th~ ent~anee ~one o~ th~ gulde tube ~e~tlon lOa aS laa~ un~il the ~ront p~rt o~
the t~ loom ha-~ run in the~. Then th~ mandrel eod 7 with the rol~ mancl~l 72 can be ~lo~ly withd~a~dn with ~he ald of the ~upport ~aring 9 ana ~he 6ha~t rod 18. ~hi~ is pos~ible ev~n dur~ng ~t~e~ohing, but not the extent ~h~t the roll mandrel 7a 5till r~malns on th~ ~ide Oe the roll~ 5 ~aoing the ing~t guide channel 3. Only aft~r oomE~letion o th~ ~tretchin~ process ~n the ~And~el ~od 7 and 6haft rod 1~ l~e ~ithdrawn into the po~itlon ~hown ln Figure 1~ in whi~h th~ plercing process ~or the nex~ ingot 13 begun.

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~ he stxetched tube bloom is moved through the g~lde ~ube ~ection~ lOa, lOb, lOc, with the aid of drivlng roller3 ll to ~ sizing or ~tre~ch-red~ction roll ~rain 12. ~he tube bloom is rolled o~t there into a ~inish~d tube. A ~eparating device ~ provid~d in f~on~ o~ the sizing or ~retch-reduç~ion roll traln 12; 1~ ls possi~le wit~ it to ~rop a p~r~ion o~ the tube bloom end ~e¢tions if ~his should be r~eces~a~y due tO B~ze de~iation6 or ir~egula~itie~ in shape at the end~.
~ he roll3 of ~he ~kew-rolling 6~and ~re dri~ten by the moto~s in a ~miliar manne~ through long dri~?e ~h~ft~. ~hey an~
the motors 14 can also be loca~e~ on ~he o~he.r ~ide o~ th~ skew-roll~ng ~tand ~ ~acing the support bea~ng 9, ~o that the apices o~ the angle o~ a~ta~k formed by the ~oll ~otation axes are on the ~ntrance 3ide~ approximately in the re~ion o the ingot ~uide ch~nnel 3. The roll~ 5 ar~ then also set in th~ oppo~lte manner, as show~ ln Figure 1, in~llnea with regar~ ~o the longituain~l axis o~ ~he ~oll~d good~, In orde~ to ~h~n~e the direation o~ pas~age~ ~h~r~ i9 first the pos~ibl1ty o~ charlgin~
tbo ~irection o~ rot~ion o~ the motors 14. ~her~ is also the pOs~ibillty of mo~ifying only the f~ed ansl~ o~ the rolls 5.
Thi~ f~ed an~le i~ not deteatabl~ ~' n the ~a~n~ drawings . I~ ~8 th~ ~n~le b~tween the paper pl~ne and the ~ot~tlon ~xis o~ the ~oll~ 5. Th~ Dxa~ o~ rota~on o the roll~ 5 in ~kew rollin~ :
3tands a~e not parallel tu ~h~ ~hop 1OOL U~ to the paper plan~
o~ Figu~e 1, bu~ are inclined to th,~m by a ~e~ degree.q~ If ~hi~

i .
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:

-"` 1 307681ln~l~nation is changed in~o the oppc)~l~e dir~c~lon, the feed ~irection o the rolls 5 and thus ~e dir~ction of rolled good~
pas~age aee ~l~o changed .
~ igure 2 3hows a roll S ~n l~rger s~ale and repre~en~ed with ~ di~ferent d~rec~cion o~ ~nclina~ion tha~n in Figu.re 1 d~ring pier~lng. Here the roll mandrel 7a o th~
~nandrel rod 7 penetr~te~ in'eo the ~ ngot 15 and producQ~ an lnner hole 16. It ~an be ~le~tly seen that only a narrow annular space ~ s pres~nt ~etween ~he mandrel ~od 7 an~ the in~id~ wall 17 o~ the lnn~r hole 16, ln which the~e ~ only very little air and pr~ctlcally no oxygen. T~e roll has a ron~ ~ec'cion 5a that ~erves to dra-Y th~ ~n~t 1~ into the p~sq. ~ aonnec~ed more conical ~e~tlon 54 ~aus~s a reduc~cion in the ingot cro~ se~tion ~nd a xoll ahouldee 5c: and ~he c~yl;ndrical se~tion 5d, which s~rv~ to pler~ and exE~and t~e ~olled goc~d~, then follow. The l~t ~c~lon se o~ t~e roll S indu~e~ a xounding of the r~sultlng hollo~ in~ot lSa.
Th~ Isam~ roll 5 1~ shown ~n ~lgu~e 3 du~ing the s~,;retchlng o~ the hollow lllgot lSa tO fo~ tube bloom 15b.
~h~ roll mandrel 7~ is ~dvallced th~ou~h ~h~ pAS~ eninq fo~ed by the roll~ 5, in whl~h ~ase the cylindrlcal ~ection ~d of ~he Loll8 5, whi~h sar~re~ ~o ind~lce exp2nsion d~lr1n~ plerc~n~
u~ed during th~ ~tre~hln~ showrl in Fi~ure 3 for ~moothing and calibratin~ he w~ hickn~ 8 c)f th~ tube bloomt lI;ogether with the m~ndr~l rod 7. The ~oll sec~on 5e~ which was u~ed durln~

15, '''' ' '' p~er~ing only for ~ounding, is used durin~ ~retchin~ ~ccording to Figure 3 for reduclng the wall thicknes~ and ~t th~ ~ame ti~e for drawlng the hollow ln~o~ ~5a into the pa99. ~he laSter task ls tak~n over during piercing by ~he roll ~ection 5a, ~hlc~
we~s relatively r~pldly due to the usu~l unevenRss o~ the ingot 15, the rotatlon acceleration to be applied~ rolling work a~d ~he vari3ble ~peed~. As i~ cle~rly ~vident in ~lgu~e 3, this roll ~e~ion 5~ no longer comes ~n contac~ w~th thR fini~hed tube bloom 15~ 50 tha~ the un~venes~ caused ~y thi~ roll 6ectlon 5a that may exhibit wear p~enomena need no lon~er be f~ared.
~he roll po~ition ln Figure 3 has been su~stantially modifl~d ln ~omparison to that in ~igure 2 du~ ~o t~e fac~ tha~ the angle of a~t~ck C~ ha~ become almost 7.~r~ flnd ~ corrasp~nding radial inciaenc~ re~ul~R~, whl~h e~sentlslly de~ermines ~he w~ll ~h~cknes~ of the tube bloom 15b~
H~wever, ~t ~hould be lndl~ted that other ~oll po~tion~ ~r~ ~plic~ durin~ both plerclng ~nd ~tretching and othe~ ~oll ~ha~es CAn al~o be used.
~ n eh~ ~oregolng speciic~tion ~e hsv~ ~t out c~rtain pre~R~re~ praotlce~ and embodiment~ o our inven~ion, however~
lt w~ll he unde~ood th~ thi~ invention ~y be otherwi~e embodie~ within ~h~ ~cop~ of the ~ollow~ng cla~m~.

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Claims

1. Process for seamless tube production comprising (a) heating an ingot to rolling temperature;
(b) piercing said ingot to form a hollow tube in a pass opening having an axis defined by a mandrel and rolls in a skew rolling mill;
(c) reversing the direction of rotation of said rolls and stretching said hollow tube by passing said hollow tube in reverse direction through said same rolling mill and along said same axis to form a tube bloom;
(d) said stretching taking place immediately after piercing; said steps (b)-(a) being carried out in one heating.

2. The process of claim 1 employing a mandrel in said stretching step.

3. The process of claim 1 without employing a man-drel in said stretching step.

4. The process of claim 1 including a first cross rolling step to feed said ingot to said rolling mill and a second cross rolling step to remove said tube bloom from said rolling mill.

5. Process according to claim 1 wherein said tube bloom is finish-rolled after piercing and stretching with-out intermediate heating in a sizing and stretching re-duction roll mill train.

6. Process according to claim 1 wherein the tube bloom is further stretched after piercing and stretching in one or more subsequent steps.

7. An apparatus for seamless tube production com-prising a skew-rolling stand, an ingot guide channel and a pusher on the inlet side of said skew rolling stand, a roll mandrel on a mandrel rod that can be rotated and/or axially displaced, said mandrel rod supported in a bearing on the exit side of said skewed-rolling stand, skewed rolls having attached drive means operatively positioned with respect to said mandrel, the direction of rotation of the rolls and said drive means being reversible so that an ingot passed in one direction through said apparatus becomes pierced to form a hollow tube and so that said hollow tube passed in reverse direction through said apparatus upon a reversal of rotation direction becomes stretched to form a tube bloom.

8. Apparatus according to claim 7 wherein the posi-tion of the rolls and the drive means is adjustable.

9. Apparatus according to claim 7 wherein the posi-tion of the rolls and the drive means is fixed.

10. Apparatus according to claim 7 wherein the acute angles of attack enclosed by the longitudinal axis of the rolled goods and an axis of roll rotation of the rolls have a vertex during piercing and stretching that is located on the entrance side of the skew-rolling stand that is equipped with the ingot guide channel.

11. Apparatus according to claim 10 wherein the angle of attack is between one and about twenty degrees, and a larger angle is set during piercing than during stretching.

12. Apparatus according to claim 10 or 11 wherein drive motors for the rolls are located on the side of the mandrel rod support bearing.

13. Apparatus according to claim 7 or 10 or 11 wherein a guide tube that is rotatable around its longitu-dinal central axis is located coaxially subsequent to the axis of rolled goods passage as a device for carrying off the stretched tube bloom of the ingot guide channel on the side facing away from the skew-rolling stand.

14. Apparatus according to claim 13 wherein at the beginning stretching, the mandrel rod is moved through the roll pass in a speed-controlled manner and penetrates into the entrance zone of the guide tube, where it is held with the aid of the support bearing at least until the tube bloom enters into the guide tube.

15. Apparatus according to claim 7 or 10 or 11 wherein a shaft rod that drives the mandrel rod is coaxi-ally coupled with the mandrel rod and is supported in the bearing is provided with a larger outside diameter than the hollow ingots as a pusher for the hollow ingots at the beginning of the stretching.

16. Apparatus according to claim 7 or 10 or 11 wherein the roll component that effects the expansion during piercing is provided during stretching for smoothing the rolled goods.

17. Apparatus according to claim 7 or 10 or 11 wherein the roll component that effects the reduction during piercing is provided during stretching for rounding the tube bloom and vice versa.

18. Apparatus according to claim 7 or lo or 11 wherein the direction of passages of the rolled goods can be changed by modifying the feed angle of the rolls.

19. Apparatus according to claim 7 or 10 or 11 wherein the speed of passage of the rolled goods is lower during piercing than during stretching.

20. Apparatus according to claim 7 or 10 or 11 wherein a separating device for cropping the end sections of the tube bloom is located in front of the sizing or stretching reduction rolling train.