Cast construction elements for heat treatment furnaces

Transcription

1 ARCHIVES of FOUNDRY ENGINEERING Published qurterly s the orgn of the Foundry Commission of the Polish Acdemy of Sciences ISSN ( ) Volume Specil Issue 3/ /3 Cst construction elements for het tretment furnces B. Piekrski*, A. Drotlew West Pomernin University of Technology, Al. Pistów 7, Szczecin *Corresponding uthor. E-mil ddress: bogdn.piekrski@zut.edu.pl Received ; ccepted in revised form Abstrct The study presents sketches nd photos of the cst creep-resistnt components used in vrious types of het tretment furnces. The shpe of the elements results from the type of the opertion crried out in the furnce, while dimensions re djusted to the size of the furnce working chmber. The cstings re minly mde from the high-lloyed, ustenitic chromium-nickel or nickel-chromium steel, selecting the grde in ccordnce with the furnce operting conditions described by the rted temperture, the type nd prmeters of the pplied operting tmosphere, nd the chrge weight. Typicl exmples in this fmily of construction elements re: crucibles, roller trcks, rdint tubes nd guides. The mjority of cstings re produced in snd moulds. Keywords: Innovtive foundry technologies nd mterils, Cstings for het tretment plnts. Introduction The het- nd creep-resistnt metl prts forming ccessories of the het tretment furnces include [ 3]:. Functionl ccessories (e.g. pllets or bskets) on or in which the het treted prts re plced. The tsk of this equipment is to ensure similr het tretment conditions to ll prts nd to mke their loding into nd unloding from the furnce esier. The operting conditions of the equipment result from the het tretment regime pplied to the chrge, which in prctice comes down to: cyclic heting nd cooling, nd periodic effect of the furnce tmosphere.. Construction elements tht llow the het tretment to be crried out in the furnce. These elements re usully permnently fixed in the furnce. Depending on function they re supposed to perform in the furnce, the conditions under which they operte re: reltively stble when these elements re subjected to continuous influence of the furnce tmosphere only, with rther insignificnt chnges in temperture (e.g. rdint tubes, crucibles, or rotors), or vrible, when the elements re subjected to complex thermomechnicl lods rising from direct contct with the chrge (e.g. bottom pltes, roller trcks nd guides), combined with simultneous constnt effect of the furnce tmosphere. The mjority of creep-resistnt metl prts re cst in snd moulds s monolithic elements or prts of lrger ssemblies []. Cstings operting in furnces in which the rted temperture does not exceed the vlue of 000 C re mde from high-lloyed steels (Cr, Cr-Ni nd Ni-Cr type). The selection of lloy chemicl composition is lso determined by the type nd prmeters of the furnce tmosphere nd by the thermo-mechnicl lods to which the cstings will be subjected during opertion. In the cse of high-temperture furnces, which nevertheless operte t temperture below 50 o C, cstings mde from nickel or coblt lloys re lso used [ 4]. ARCHIVES of FOUNDRY ENGINEERING Volume, Specil Issue 3/0,

2 The cst functionl ccessories were presented in [3]. This rticle discusses the most commonly used cst construction elements for het tretment furnces. φ 403. Cst construction elements In the mjority of het tretment furnces, regrdless of their mnufcturer, the shpe of construction elements tht perform the sme or similr tsks is similr. Using this similrity, clssifiction of this fmily of cstings bsed on the most importnt tsks they perform hs been proposed:. Air-tight seprtion of the furnce working chmber nd/or heting elements or exhust gs from the rest of the furnce instlltion operting t high tempertures insulting elements.. Chrge trnsfer inside the furnce - elements of the internl chrge hndling system. 3. Protection of cermic furnce lining from dmge during chrge loding nd unloding - shielding elements. 4. Temperture field equlistion nd/or forcing uniform flow of tmosphere in the working chmber - rotting elements (fns)... Insulting elements Typicl products included in this group of elements mking furnce equipment re designed to perform the following tsks: provide n ir-tight working chmber in the furnce (crucibles, muffles, nd retorts), nd protect heting elements from the effect of furnce tmosphere (one- nd multi-segment rdint tubes). Crucibles, muffles, nd retorts of smll size (Fig. ) nd weight (up to bout 00 kg) re produced by csting. Elements lrger re shped from the steel sheet. Rdint tubes re usully cst. Metl crucibles operte in bth furnces heted by electricity or gs (mx. operting temperture 000 C). They re filled with molten slt or liquid metl (usully led). Crucibles re cylindricl (Fig. ), rectngulr or formed like polygon cube. In cst version, their cpcity is up to 00 litres. Cstings re chrcterised by uniform wll thickness on the entire crosssection nd collr formed in the top prt (Fig. ), used for fixing the crucible in the furnce housing/ lining. The crucibles, whose operting temperture does not exceed 500 C, cn be mde from crbon steel or corrosion-resistnt steel. At higher tempertures, the recommended lloys re GX40CrSi4 or GX40CrNiSi5-0 cst steel (PN-EN 095: 00). Muffles nd retorts in the het tretment furnces perform simultneously severl functions: prevent contct between the gseous tmosphere kept in their interior nd the surrounding tmospheric ir, fcilitte the circultion of working tmosphere, nd provide uniform temperture distribution in the working chmber. 50 Fig.. Crucible operting in PET-/45 slt bth furnce with lugs fstened by screws for esy trnsport [5]. Wll thickness 5 mm, mteril: GX40CrSi4 or GX40CrNiSi7-4, ccording to the drwing provided by ELTERMA (present SECO/WARWICK ThermAL SA) Fig.. Box-shped muffle [5]; see the text for explntion of symbols used in the drwing Muffles consist of one or more segments (Fig. ). By welding the successive segments, muffles of length reching even severl metres re mde. In continuous furnces, muffles re usully closed with pltes on both sides (Fig. -); the pltes help in fixing the muffle to the furnce lining. In btch furnces, one side is closed with welded plte (Figs. -3). The wlls of muffle re often designed s folded elements to enlrge the het trnsfer surfce re nd compenste for dimensionl chnges resulting from chnges in the operting temperture. In the cse of furnces designed for lot or mss het tretment, the working cross-section of muffle is dpted to the shpe of the het treted prt (see Figs. - nd -4). Metl muffles re used in low- nd medium-temperture furnces, nd therefore, similr to crucibles, they re produced from vrious grdes of the crbon cst steels nd low- nd high-lloyed cst steels. An exmple of the muffle of different design is muffle operting in drum furnce (Fig. 3). The muffle-drum of circulr section or section in the form of polygon cube is the design used for het tretment of smll prts, like screws for steel plte, nuts or bolts. Drum furnces re designed for continuous (Fig. 3) or periodic opertion. The difference in the design of muffles for these furnces minly consists in the presence of dischrge door (Figs. 3-3) ARCHIVES of FOUNDRY ENGINEERING Volume, Specil Issue 3/0,

3 Cst muffles re designed s one monolithic item (Fig. 3), or they re mde in segments. The drum hs dimeter of 400 to 600 mm nd is from 500 to 3000 mm long [6, 7]. In furnces for continuous opertion, the drum rottions mke the chrge move long heliclly-shped bffle from the chrging to the dischrging door (Fig. 3-). 3 Fig. 3. Cst monolithic muffle for continuous drum furnce [5]: - loding of chrge, - internl helicl bffle, 3 - dischrge door, mteril: GX40CrNiSi5-0, GX40NiCrSi35-7 or GX40NiCrSiNb38-9 Retorts re cylindricl in shpe nd hve uniform thickness (bout 5-0 mm) on the entire cross-section. They re used in the furnces of: pit-type het tretment instlltions (Fig. 4-) (operting temperture C), nd endothermic/exothermic-endothermic genertors (operting temperture C), nd mmoni dissocitors (operting temperture C). Retorts re heted electriclly or by gs. closed with cst cnopy of properly selected dimeter (Fig. 5). As with the retorts operting in pit furnces, the retorts re more durble when they re cst [6, 7]. Φ Fig. 4. Pit furnce retort () nd bse for its instlltion t the bottom of the furnce chmber () [5]; mteril: GX40CrNiSi5-0, GX40NiCrSi35-7 or GX40NiCrSiNb38-9 or steel of similr chemicl composition Retorts in pit furnces re designed in lrge vriety of sizes from the dimensions of the working spce φ mm to φ mm [6, 7] nd lrger. The retort is either supported by collr or cn rest on cst bse plced on the bottom of the furnce (Fig. 4-). By the technology of csting, only the smllest retorts re mde. Using welded steel sheet, the wll thickness is -3 times thinner, which hs positive effect, reducing the energy consumption level nd totl weight of the retort. In spite of these fcts, it ws found tht cst retorts re more durble thn retorts mde from rolled tubes. As regrds cst retorts, those mde by grvity technique hve life shorter thn the retorts centrifuglly cst [6, 7]. The retorts operting in genertor furnces re mde from 0 to 400 mm tubes rolled or cst [6]. The bottom of the retort is Fig. 5. Cnopies with wlls from to 0 mm thick used in the genertors mnufctured by SECO/WARWICK ThermAL SA [5]; mteril: G-NiCr8W In mny design embodiments of the furnces, rdint tube heters re used (Fig. 6). Stright rdint tubes (Fig. 6) cn operte in horizontl or verticl position. Multi-segment structures (Fig. 6b-c) re mounted in horizontl position. The stright section of pipe with length of up to severl metres nd dimeter of bout 60 mm my consist of more thn one segment. The construction of rditors is completed with the following ccessories: elements enbling fixing the rditor to the furnce body (Fig. 6-), supports to prevent distortion (hnging down) of tubes during opertion (Figs. 6- nd 7-), elements closing the spce inside the tube (Fig. 6-3), elbows connecting the stright tube sections (Figs. 6-4 nd 7-4). Another exmple of elbows/ bends connecting rdint tubes is TermIn type connector (Fig. 8) of low-voltge heting elements developed by SECO/WARWICK from Świebodzin. The operting temperture of the tube surfce (heted electriclly or by gs) is o C. The life of tubes increses when rolled tubes re replced by tubes grvity cst. Further life increse is obtined by ppliction of the centrifuglly cst tubes [,, 6]. ARCHIVES of FOUNDRY ENGINEERING Volume, Specil Issue 3/0,

4 c b 3 4 Fig. 6. Rdint tubes: ) single-segment type, b nd c) two nd four-segment type [5]: - element used to ttch the tube to the housing of the working chmber, tube support, 3 element closing the tube, 4 - elbows linking individul tube members; mteril: GX40NiCrSi35-7 or GX40NiCrSiNb mm Fig. 7. Cst rdint tube support () nd tube-connecting elbow (4) (designtion of components s in Fig. 6) [5]; mteril: GX40NiCrSiNb35-7 b mm Fig. 8. Connector of heting elements used by SECO/WARWICK ThermAL SA [5]; mteril: GX50NiCrCoW Elements of the internl chrge hndling system Roller trcks re the oldest nd most widely used design solution enbling smooth trvelling of chrge inside the furnce chmber (Fig. 9). A roller trck consists of two sections (Fig. 9) mounted on the furnce bottom, symmetriclly long its longitudinl xis. Ech section cn consist of severl segments (Fig. 9b), depending on the length of furnce chmber. Fig. 9. Roller trcks [5]: ) drft scheme ccording to IMP Compny folder, b) for opertion in PeKt or type furnces mde by SECO/WARWICK ThermAL SA: trck members, - chin guide mounted between the trcks; mteril: GX40NiCrSiNb35-8 Besides multi-roller members, lso single-roller members re used (Fig. 0); in n pproprite number they re mounted in two rows on the furnce bogie, symmetriclly long its longitudinl xis. Rollers of this type re used in muffle furnces in which the chrge is hndled by: shker pltes /chutes (Fig. ), or wire woven belts. 66 ARCHIVES of FOUNDRY ENGINEERING Volume, Specil Issue 3/0,

5 70 50 Fig. 0. Roller moving in clmping ring [5] The shker plte (Fig. ) resting on rollers performs reciprocting movements. Adjusting properly the plte "bck nd forth" feed rte, the het treted prts trvel successively throughout the entire length of the furnce chmber. The shkegenerting system llows the shke frequency to be very flexibly djusted to the object's shpe [6, 7]. A typicl plte is chrcterised by: corrugted surfce to fcilitte even chrge distribution nd movement (Fig. ), nd multi-segment welded structure of totl length typiclly exceeding few metres. Fig.. Shker plte operting in muffle furnce [5] Conveyor pltes nd belts working in muffle furnces re used in the het tretment of smll nd fine prts, e.g. screws or engine vlves [6]. Generlly, for the hndling equipment operting in mediumnd high-temperture furnces (operting temperture of o C), two types of metl belts re used: woven from Cr-Ni or Ni-Cr steel wire [6, 7], or composed of the cst segments (Fig. ). Cst segments re of similr shpes; the construction of those tht form the belt edge is dditionlly provided with sfety side bord protecting the het-treted prts from flling out (Fig. c). The belt is driven by drum (Fig. b) mounted on the dischrge side of the furnce. The conveyor length cn rech 30 metres, while its width is between 300 to 000 mm [6, 7]. Structurlly less complex, compred to the belt conveyors, designs of the in-furnce chrge hndling system re shown in Fig. 3: ) guide nd push rod system operting in verstile chmber furnce with quenching bth, nd b) wlking herth operting in chmber furnce. A guide (Fig. 3-) nd mting push rod (Fig. 3-) re mounted on the bottom of the crburising furnce between the cermic sliding rils, which ber the try nd/or bsket with the het-treted items. When the prt of the het tretment process which is crried out in the furnce chmber is completed, the rod pushes the try nd/or bsket from the chmber to the quenching vestibule nd returns next to the strting position. The operting temperture of the het-treted items does not exceed 050 o C. The wlking herth (Fig. 3b) opertes in heting furnce in the tmosphere of ir t temperture of bout 000 C. The chrge is moving stepwise in the furnce chmber long the furnce herth from the chrging to the dischrging side. The chmber herth consists of four rows of supports: two permnently fixed nd two movble. The supports re moving long trjectory forming closed circuit, which mens tht they rise the whole btch of items nd move it forwrd by distnce equl to the pitch ( notch ) on cstings; they lower the btch (below the level of the fixed supports), let it rest on these supports nd move bck. An exmple of the tsk tht furnce of this type performs is heting to predetermined temperture the steel rods before they re rolled up in springs. b Fig.. Belt conveyor composed of cst segments [5]; schemtic representtion ccording to folder published by COURTH Compny - designtions re explined in the text; mteril: GX40NiCrSi35-7 or GX40NiCrSiNb c ARCHIVES of FOUNDRY ENGINEERING Volume, Specil Issue 3/0,

6 b 500 Fig. 3. Sketches of cst ccessories for trnsport of chrge in the furnce chmber designed nd mde by SECO/WARWICK from Świebodzin [5]: ) trys nd/or bskets pulled out from the chmber; mteril: GX40CrNiSi5-0, b) het-treted steel rods trvelling stepwise in the chmber; mteril: GX40CrNiSi5-0 Guides nd wlking trcks re cst s monolithic items, or in the cse of furnces with very long working chmbers, they consist of two or more segments. The exmples of cst prts fcilitting the trnsport of chrge do not cover ll designs used in the furnces for het tretment. Other widely used systems re rollers for the trnsport of: tubes nd rods (Fig. 4, b), metl sheets or pltes (Fig. 5), or different types of truck wheels (Fig. 6). 40 φ 00 Fig. 4. Sketches of trnsport rollers mounted individully or in ssemblies [5]: ) ccording to folder of FAI-FTC Compny, b) ccording to drwing supplied by SECO/WARWICK from Świebodzin; mteril: GX40CrNiSi Fig. 5. Sketch of roller to fcilitte trnsport of sheets /pltes in the chmber of btch furnce ccording to folder supplied by POSE-Mrre Compny [5] b φ 386 Fig. 6. Sketch of wheel for trnsport truck designed by SECO/WARWICK SA from Świebodzin [5]; mteril: GX40CrSi3.3. Shielding elements Some elements of the furnce interior ccessories require shielding but with no dditionl requirement for the shield to be ir-tight, s in the cse of elements discussed under section.. If this is the cse, then the min tsk of the shield is to protect the enclosed element from mechnicl dmge. The first two exmples of such solutions re shown in Figs. 7 nd 8. When the furnce bogie herth is equipped with n electric heting system (Fig. 8) plced on cermic substrte, the tsk of the shield is not only to keep the hevy chrge in stble position bove the heting elements, but lso to slightly reduce the het flow in this re. To stisfy these requirements, shield composed of openwork pllets nd 54 rcks ws designed (Fig. 8b-d). When the herth is not heted, the tsk of the shield is to protect from dmge the cermic lining, especilly during loding nd unloding of the chrge. This tsk is sufficiently well performed by one- or multi-segment bottom plte (Fig. 9) with trnsverse ribs, which fcilitte the bove mentioned opertion. Metl bottom pltes re lso commonly used in mediumtemperture chmber furnces operting in the temperture rnge from 700 to 000 o C. They shield the cermic herth of furnce, usully provided with system of electric heters. Pltes re designed s monolithic or multi-segment cstings (Fig. 9) of dimensions vrying in the rnge of mm up to mm, nd the weight from 0 up to even 600 kg. The chrge is either put directly on the pltes or is plced in the continers. 68 ARCHIVES of FOUNDRY ENGINEERING Volume, Specil Issue 3/0,

7 Fig. 7. A view of VWC 036 vcuum furnce with bogie herth mde by SECO/WARWICK Świebodzin: ) generl view, construction of welded steel rods plced on the herth indictes the spce occupied by chrge, b nd c) bse for the chrge-holding continers plced on the furnce herth nd composed of pllets nd rcks cst from G-NiCr8W lloy, d) rck with mounted hed whose pins hold pllets together Fig. 8. Multi-segment bottom plte of bogie herth furnce cst from G-X40CrNiSi7-4 or G-X40CrNiSi5-0 lloys [5] nd ) nd re mde s single-pieces or s segments connected together into one whole. The weight of single cstings rnges from 0 to 50 kg [5]..4. Rotting elements (fns) Fig. 9. Sketches of single- nd multi-segment bottom pltes operting in chmber furnces mde by SECO/WARWICK ThermAL SA [5]: mterils: GX40CrSi4, GX40CrNiSi7-4 or GX40CrNiSi5-0 In the heting chmber of most of the het tretment furnces, ir gittion devices re instlled. Their tsk is to intensify the circultion of the tmosphere, which ccelertes the homogenistion of its chemicl composition within the entire chmber volume, mking lso the temperture distribution more uniform. Depending on the tsk tht the furnce is expected to perform nd the size of its chmber, ir gittors of different shpes nd sizes mde from different lloys re used (Fig. ). Selected frgments of the cermic lining re lso protected by cstings other thn the bottom pltes. They vry in shpe (Figs. 0 ARCHIVES of FOUNDRY ENGINEERING Volume, Specil Issue 3/0,

8 3. Conclusion Fig. 0. Elements protecting the cermic lining; sketches ccording to the documenttion supplied by SECO/WARWICK SA Therml nd SECO/WARWICK Świebodzin [5]; mteril: GX40CrSi7 nd GX40CrNiSi5-0 Fig.. Frme protecting the chrging-dischrging door [5]; mteril: GX40CrSi7 00 mm Fig.. Cst ir gittors (fns) mde by POLCAST Foundry for the following customers: SECO/WARWICK ThermAL SA, SECO/WARWICK from Świebodzin, RIVA from Międzyrzecz, nd REMIX from Świebodzin [5]; mteril: GX40CrNiSi5-0, GX40NiCrSi35-7 nd GX40NiCrSiNb38-9 Cst components re used in ll types of the industril het tretment furnces. The min types of lloys used for cstings operting in the temperture rnge of o C re specified in the PN EN 095: 00 Stndrd Het resistnt steel cstings. At lower tempertures lso cst corrosion-resistnt steel nd crbon steel re used. The rules for the selection of chemicl composition of the cst steel used for these elements, depending on the operting conditions, re widely described in the source studies [8, 9]. The principles of designing cstings of this type re presented in [, 0, ]. References [] Steinkusch W.: Hitzebeständiger Sthlguß für Wärmebehnd-lungsnlgen. Gs Wärme Inter., 6(987)340. [] G. Y. Li: Het-Resistnt Mterils for Furnce Prts, Trys, nd Fixtures. ASM Hndbook, 4(99)50. [3] Piekrski B., Drotlew A: Cst functionl ccessories for het tretment furnces. Archives of Foundry Engineering, 4(00)83. [4] Piekrski B.: The therml ftigue behvior of creep-resistnt Ni-Cr cst steel. Archives of Foundry Engineering, 4(007) 55. [5] Drotlew A., Piekrski B., Het-resistnt furnce prts, trys, nd fixtures. Szczecin (unpublished) (in Polish). [6] Grzyb J., Trzciłkowski J., Urządzeni do obróbki cieplnej w tmosferch regulownych. WNT, W-w 975. [7] Pordnik inżynier. Obróbk ciepln stopów żelz. WNT, W-w 977. [8] Het Resistnt Mterils, Edited by JR Dvis Dvis & Assocites, ASM Specility Hndbook, ASM Interntionl 997. [9] Li GY., High-Temperture Corrosion nd Mterils Applictions, ASM Inter-ntionl, 007. [0] Piekrski B., Drotlew A.: Designing of cstings working in conditions of temperture cyclic chnges. ATMiA, Poznń 3(008)95 (in Polish). [] Steinkusch W.: Verbesserte Werkstoff und Konstruktionen verringern Betriebskosten bei der Wärmebehndlung. Fchberichte Hütten. Metll., 9(985) ARCHIVES of FOUNDRY ENGINEERING Volume, Specil Issue 3/0,