FR2479784A1 - METAL CONVEYOR BELT AND PROCESS FOR PRODUCING THE SAME - Google Patents

Abstract

THE INVENTION RELATES TO AN ENDLESS STAINLESS STEEL BELT FOR CONVEYOR WITH A WELDED SEAL. ACCORDING TO THE INVENTION, THE STEEL CONTAINS, IN PERCENTAGE BY WEIGHT, C 0.07, N 0.03, 0.5 SI 2.5, MN 4.0, 5.0 NI 9.0, 12.0 CR 17 , 0, 0.5 CU 2.5, 0.2 TI 1.0, AL 1.0, THE REMAINDER BEING FE, THE VALUE OF A DEFINED BY A 17 CTI 0.70 MN 1 NI 0.60 CR 0, 76 CU - 0.63 AL 20.871 REPRESENTING LESS THAN 41.0, AS WELL THE WELDED ZONE 10 AS THE PARENT METAL 12 OF THE BAND HAVING A SENSITIVELY MARTENSITIC PHASE STRUCTURE WITH PRECIPITATED INTERMETAL COMPOUNDS. THE WELDED ZONE AND THE PARENT METAL OF THE BAND HAVE A TENSILE STRENGTH OF AT LEAST 1373.4 10 PA, A HARDNESS OF AT LEAST 430HV AND A FATIGUE LIMIT OF 490.5 10 PA. THE INVENTION APPLIES IN PARTICULAR TO CONVEYORS FOR THE FOOD, MECHANICAL, AUTOMOTIVE AND OTHERS INDUSTRY.

Description

The present invention relates to an endless conveyor belt.

  More particularly, it relates to a stainless steel conveyor belt with an improved welded joint having high strength, very good hardness and fatigue resistance that could not be achieved with steel conveyor belts. traditional stainless. Due to their corrosion resistance, heat resistance, oil resistance, abrasion resistance and other desirable properties, stainless steel conveyor belts are widely used in the general food, chemical, mechanical, electrical and other fields, not only for the general purpose of the transport of goods but also as conveyor belts, accompanying heat treatment or other treatment of goods,

  furnace conveyors, refrigeration conveyors,

  operators, press conveyors, conveyors of

calenders and the like.

  In any case, the stainless steel conveyor belt is stretched under high tension between two rollers, such as the driven and tensioned head and tail drum. It is therefore necessary that the ends or ends of a sheet or strip of stainless steel of predetermined dimensions are securely joined, to form the endless band. We know a junction by riveting and a junction by welding. If possible, the joint or welded joint is preferred, because a riveting joint damages the surface flatness of the strip and poses a problem of stress concentration.

  occurring as a result of repeated effort.

  Typical and known stainless steel conveyor belts are based on either stainless steel

  of the hardened type at work, prepared by dipping a steel -

  austenitic stainless steel such as SUS 301 or SUS 304 steel,

  by cold rolling or on a martensi stainless steel

  as described in the patent publication

Japanese Ne 51-31085.

  With a band based on the stainless steel of.

  In the above-mentioned hardening type, a very strong welded joint can not be formed because the weld zone is softened by the heat of welding, resulting in a lower resistance than that of the material.

  original. Moreover, such a band undergoes deforma-

  when used in a conveyor, for example as in an oven conveyor, which is subjected to a cycle of hot and cold. These disadvantages can be attributed to the fact that the steel of the strip has a two-phase structure comprising a stress-induced martensite phase and austenite phase. This in turn makes it difficult for the band to be subjected to a known treatment, where a rubber band is applied to the back of the band under heat and pressure to prevent winding movements of the band. This is due to the fact that during this treatment, the band deforms with heat and waves. When joined by riveting, the strip has a tensile strength of at most 1079.1 x 106 Pa and a hardness of the order of 350 Hv, and thus the design and application of conveyors using

such a band are limited.

  The tape based on the martensitic stainless steel of Japanese Patent Publication No. 51-31085 does not pose the above-mentioned problems because even if a seal is formed by welding, the weld zone of the strip may have a resistance. which is not substantially reduced compared to that of the original material, and the band withstands deformation due to heating and cooling. It is indicated that the steel of the strip contains 0.03 to 0.06% by weight of C, not more than 0.03% by weight of N, 0.5 to 1.0% by weight of Si, 3 to 10% by weight of Ni, 10 to 18% by weight of Cr and preferably of (C,% by weight + N,% by weight) x 5 to (C,% by weight + N,% by weight) x 16 of Ti. However, the web has a tensile strength that is at most 1079.1 x 106 Pa and a hardness of the order of 380 Hv. As a result, this band is again applicable to conveyors where the properties

  mentioned above are acceptable.

  The present invention aims to expand the limited applications described above of

  conveyor. in traditional stainless steel.

  Another object of the present invention is an endless conveyor belt made of stainless steel having a welded joint, where the strength and hardness of the weld zone are not substantially reduced compared with those of the parent metal, and o both the weld zone than the parent metal have higher strength and toughness than those of conventional stainless steel conveyor belts and also have excellent fatigue strength and other properties

  inherent benefits of stainless steel.

  Another subject of the present invention is a process

  the production of a conveyor belt allowing to reach

the objective above.

  A conveyor belt according to the invention is formed of a sheet or strip of stainless steel having predetermined dimensions, by welding the ends or ends of this sheet or strip to form an endless band, this stainless steel containing no more from 0.07% by weight of C, not more than 0.03% by weight of N, 0.5 to 2.5% by weight of Si, not more than 4.0% by weight of Mn, 0 to 9.0% by weight of Ni, 12.0 to 17.091 by weight of Cr, 0.5 to 2.5% by weight of Cu, 0.2 to 1.0% by weight of Ti, not more than 1, 0% by weight of Al, the value of A defined by the equation A = 17 x (C, wt% / Ti, wt%) + 0.70 x (Mn, wt%) + 1 x (Ni ,% by weight) + 0.60 x (Cr,% by weight) + 0.76 x (Cu,% by weight) - 0.63 x (Al,% by weight) + 20.871 representing less than 41.0 and the rest being iron and impurities inevitably coming into the stainless steel

-479784

  during its manufacture, both the weld zone and the parent metal of this strip having a structure of a martensitic sensitive phase with at least one intermetallic compound of the alloy elements precipitated the weld zone and the parent metal of this band having a tensile strength of at least 1373.4 x 106Pa hardness of not less than 430 Hv and a fatigue limit of not less than

490.5 X 106 Pa.

  Preferably, the tensile strength of the parent metal is at least 1569.6 × 10 6 Fe, while that of the solder zone is at least 90% that of the parent metal, the hardness of the parent metal is at least 480 Hv while that of the weld zone is at least 90% of that of the parent metal, and the fatigue limit of the parent metal is at least 559.2 x 106 Pa while the limit at the weld zone fatigue is at least 90% that of the parent metal. Note that the steel conveyor belts

  according to the invention have considerable properties.

  have been improved, in comparison with the above-described conveyor belts described above, which have a tensile strength of at most of the order of 1079.1 × 10 6 Pa and a hardness of at most about 380 Hv. It should also be noted that the best properties of the conveyor belts according to the invention can be achieved by a welded joint rather than a riveted joint. Moreover, as will be shown by the examples given below, the conveyor belts according to the invention are sufficiently satisfactory with respect to other properties, such as an elastic limit of 0.2%, which are generally desirable in the

belts of conveyors.

  The invention will be better understood, and other purposes, features, details and advantages thereof

  will become clearer during the description

  explanatory text which will follow with reference to the accompanying schematic drawings given solely by way of example illustrating several embodiments of the invention and in which: - Figures 1 to 6 are schematic cross-sectional views of conveyors, where are used the

  conveyor belts according to the invention, respectively showing

  a conveyor with an extended and strongly tensioned reach (FIG. 1), a calender conveyor (FIG. 2), a conveyor for transporting articles, which are heavy in weight or have sharp surfaces (FIG. 3), a conveyor for heat treatment (Fig. 4), a conveyor for treatment with a liquid (Fig. 5) and a conveyor for treatment with hot air (Fig. 6); FIG. 7 is a schematic cross-sectional view of the welded zone of a conveyor belt according to the invention;

  - Figure 8 is a graph showing the changes

  hardness along the welded zone and the parent metal on several conveyor belts; and FIGS. 9 to 12 are graphs showing the indicated mechanical properties of the welded or welded zone and the parent metal of certain bands according to the invention, in comparison with those of controls, relating respectively to the yield strength at 0.2% (FIG. 9), the tensile strength (FIG. 10), the elastic limit value (FIG. 11) and the limit of

fatigue (Figure 12).

  Conveyor belts. according to the invention may preferably be used in various conveyors and apparatus for transporting, processing or shaping articles. Some of these conveyors and apparatuses are illustrated in FIGS. 1 to 6. In each of the illustrated examples, a conveyor belt 1 according to the invention is kept very tight around a driving pulley 2 and a tension pulley 3. and the tension exerted on the web is controlled by varying the relative distance between the driving pulley 2 and the tension pulley 3 by adjusting a tensioning device, such as a spring loaded tensioning device, a weighted device nd sed% ueauypem enbsn% uo, u Tnb a. 'uoFuaeAu, uoeas sinaeoAuoo ap sapueq seal quapssod anb' sael9oQuemalq-agpTsuoo 9% aanp aeun aoPe. eIl B aouesTspe au ammoo sanbTreueq sg949Tdoid sae ue.apTsuoo ua aJTea etl ua suaeqpdmoo quos Tnb xneao B saueaedde 4uoies UOTUeAuTiUles iNoUoAuoo ep sepueq sap suoTeoTtd of saznesp siegsTI.n ae.Z eou, 9 $ jd epfneeded uorqUeAUT, I uoles ineXoAuoo ep sepueq salt to xneo ep saldmexe sap% uos O0 seoloje, p eaeuuoSe; el no juemejej:% el '% aodstue. el inod s9al4snllt sIteaedde% e sjneúoAuoo salt enb sTpuel 9, TeJ. npl9ez el oeAe @ oexTp% ojBeUOo a anod suoTe.aojied sas aed jassed assznd pneqo Tesl anb uTje eag ied ae.g eoueaJgpad ep Ined I epueq el '9 eangT; gz el ep ena oAuoo np seo el suse * pneqo Fesl ep.eueme nod 6 uaeou unp nAinod aneaoAuoo a e9% snT 9 ean2T; eq 'quemesspTo; eai ap neeI ap no epTnbTI enbTmrto 4.eBe a ei.z% ned 9 uFeq el suep nueauoo epTnb-T el Àaaesed q eaojo; % Is. epueq el o jed 8 apTnbTI ep uTeq Oz unp wnod xneXoauoo a sn e5anrE2 I - * essed q e9ao; % sa 1 eld of the no oed L anoZ unp n..nod fneloBuoo a aesnIIT a en2; e '* g senfflte9W' saoeTd seuaeaeo emmoo 'sanS2e seoes; ns sep duo no spTod ue spinol; uos Tnb' saeloyaep% .odsuez. etl inod ineaoAuoo un azi.9snlT 51

  ú eanS2; e si.znos; pa senbuld ap no selTnI. ap uojq.

  -Teleqqqqqqqqqqqqqqqqqqqqqqq. ejTsem aunp eamzo; it is the world and seagelltnae; no seaguTmel seqouetd ap -4a sgnbeld-ailuoo op uoqeoTaqes; el inod aiti Ise taiesdds jeq. a oe2; u; neqo ep 4a uoTssa.d op 5 ue.Lom a.nod 01 i sanealod xneetnoi ep ni.znod% sa t [Te.zeddEe 'ee opeg ue eo op sguel.tnmTs eSessTlod el 9e emazo ue asTm el mnod (ón q q ss ss ss ss ss ss ss Bl Bl Bl un un un un un un un un un un un un un un un un '' '' '' '' '' '' '' '' '' '' '' e A nn ute ullllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllll

  taldoxe an eesnTTT e1znj; e '- * eTnnod etl xTj' enbTI.

  -eBmneud no enbTlTne.pXpq uoTsue. In addition to desirable properties such as high heat resistance, high corrosion resistance, and beautiful surfaces inherently possessed by conventional stainless steel conveyor belts, it is also possible to achieve these properties in known stainless steel conveyor belts. stainless steel. An example of these other applications is a vibration device for a test run of automobiles, a

moving sidewalk and the like.

  As described above, the stainless steel conveyor belt according to the invention is characterized in that the stainless steel has a specified chemical composition of the component elements and that the weld zone and the parent metal have substantially the same specified structure. With respect to the specified chemical composition of the stainless steel, it is partially similar to that of the stainless steel suitable for springs, proposed by some of the inventors of the present invention in Japanese Patent Publication No. 51-131610 and Japanese Patent Publication No. NI 51-131611. However, in these publications is envisaged a material suitable for springs and is revealed a new stainless steel having a combination

  properties required and desired for springs.

  For stainless steel of these applications, it is stated that the carbon content should not exceed 0.03% by weight and that the ratio of Cr equivalent to Ni equivalent and the value of H, not referring to the present The invention must be controlled in certain specified ranges, respectively. In addition, the welding of spring materials is outside the ordinary knowledge of a competent person. In other words, no spring piece has heretofore been used or manufactured after fixing or welding. As a result, the above publications are completely silent

  concerning the weldability of the material.

  Unlike the spring, the conveyor belt according to the invention has a welded joint. It is necessary that the welded zone and the parent metal have substantially the same structure. In addition, the best mechanical properties, which can not be achieved by

  known stainless steel conveyor, are obtained.

  To meet these needs, the chemical composition of

  stainless steel has been specified as indicated above.

  ously. The criticality or technical importance of the

  Specified composition will now be described.

  0.07% by weight An excessive amount of carbon tends to give a strong martensite phase, requiring increased energy consumption in the cold rolling stages at the time of manufacture of the sheet or steel strip stainless. On the other hand, if the carbon content is too high, an increased amount of austenite is retained in the welded zone due to the resolution of C at the time of welding. It is not easy to form a desired martensite phase in such a post-treatment welded zone, and thus a welded joint strong enough for a conveyor belt can not be formed. For these reasons, C must be controlled to a level not exceeding 0.07% by weight. In addition, while the C content increases, the amount of TiA ajawerpour

  hardening or quenching by precipitation must be increased.

  The increased amount of Ti affects not only the surface quality of the stainless steel but also the fluidity of the molten metals at the time of welding. Moreover, the titanium oxides formed at the time of the

  welding adversely affect weld seams.

  This is an additional reason to control the quantity

  from C to the level specified above.

  N d. 0.03% by weight N has a high affinity for the precipitation quenching element, Ti. If the N content is too high, relatively large inclusions of TiN are formed in the material, leading to an appreciable reduction in web tenacity. Furthermore, such an inclusion of TiN may represent nuclei o a fatigue fracture of the strip begins when it is subjected to a repeated bending force. For these reasons, N is

  controlled at a level not exceeding 0.03% by weight.

  0.5% by weight Z Si <2.5% by weight According to one aspect, Si is one of the precipitation quenching elements. If the Si content is less than 0.5% by weight, it becomes necessary to increase the amount of Ti to obtain a sufficiently strong band. Too much Ti increases various disadvantages as described above. According to another point of view, Si is an element added in order to improve the fluidity of the molten metals formed at the time of welding. With Si below 0.5%, the desired fluidity is not obtained, and as a result, the cords tend to form a gutter at the time of welding, leading to a reduction in the strength of the welded joint. For these reasons, the lower limit of Si is set to at least 0.5% by weight. On the other hand, the upper limit of Si has been established at most at 2.5% by weight. This is due to the fact that no appreciable additional beneficial effect on the increase in resistance is observed even if Si

  is added in excess of 2.5% by weight. On the contrary, the addi-

  An excessive amount of Si promotes the formation of a ci-ferrite phase. The presence of such a phase shortens the fatigue life of the strip when examined by subjecting it to repeated bending stress. Moreover, an increase in the amount of ferrite in the welded zone leads to a reduction of

the resistance of the joint.

  12.0 wt% Cr <17.0 wt% At least 12.0 wt% Cr is required to obtain

  the corrosion resistance inherent in stainless steel.

  On the other hand, if an excessive amount of Cr is added, 5-ferrite and retained austenite are formed, thus the formation of the desired martensite structure is prevented, and as a result it becomes difficult to obtain a conveyor belt having the desired properties. The fact that the amount of β-ferrite formed in the welded zone is considerably increased is particularly serious, and thus the strength of the welded zone is reduced as the objectives of the invention can not be achieved. For these reasons, Cr is used

  in an amount of not more than 17.0% by weight.

  0% by weight d. Neither due 9.0% by weight While it is generally necessary to increase the amount of Ni, while the amount of Cr increases, in order to suppress the formation of -ferrite, an increase in Ni results in a reduction of the Ma point of the stainless steel and therefore a low Ni content must be used as long as the formation of S-ferrite can be avoided. However, if the Ni content is too low, it adversely affects quenching by precipitation, and therefore the desired band strength can not be obtained. For this reason, it is necessary to use at least 0.5% by weight of Ni. On the other hand, an excessive amount of Ni results in the formation of appreciable amounts of retained austenite, which interferes with the formation of the desired martensite structure and reduces the strength, and consequently the objectives of the invention can not be overcome. achieved. On the other hand, if the Ni content is unduly high, it requires intensive cold rolling and the steel has a two-phase structure containing austenite phase and a stress-induced martensite phase. If a strip of steel having such a two-phase structure is used in a conveyor, which is subjected to a repeated cycle of hot and cold, it undergoes deformation. For these reasons, the upper limit of Ni has been established at most

to 9.0% by weight.

  0.2% by weight; Ti <1.0% by weight Ti is a primary element which develops quenching by precipitation. For efficient precipitation quenching, at least 0.2% by weight of Ti is required. On the other hand, an excessive amount of Ti adversely affects the surface quality of the stainless steel, the fluidity of the molten metals and the performance of the weld seam.

  moment of welding, as well as the tenacity of the steel.

  The reduction in toughness, in particular the resistance of the notch toughness, poses a problem concerning the fracture after cracking, for example in the case where the strip is used for a prolonged period of time in a fast conveyor, such as 'a

  conveyor used in the testing of motor vehicles.

  Due to the reduced toughness with notch, the band breaks as soon as cracks occur. For the reasons described above, the upper limit of Ti has been established

  as being at most 1.0% by weight.

Al <1.0% by weight.

  Al can be used as a precipitation quenching element, and Ti can be partially replaced by Al. For toughness, the upper limit of Al has been

  established to be not more than 1.0% by weight.

  0.5% by weight A Cu 4 2.5% by weight Cu is one of the elements that can develop quenching by precipitation. The amount of Cu added can be determined according to the amounts of Si and Ti. With Cu in an amount of less than 0.5% by weight, no appreciable effect of the addition is observed. Even if an additional amount of Cu is added in more than 2.5% by weight, the effect of the addition is not appreciably increased in proportion to the additional amount. On the other hand, the hot workability of the steel is frequently hindered by the addition of an excessive amount of Cu. For these reasons, the upper limit of Cu has been

  established to be not more than 2.5% by weight.

  Mn <4.0% by weight As does Ni, Mn contributes to the suppression of Sferrite and therefore Mn can replace a portion of Ni. Up to 4.0% by weight of Mn can be used in view of its S-ferrite suppression effect as well as the rest of the components relating to the formation.

of a retained austenite phase.

  Value of A 4 41.0 Components C, Ti, Mn, Ni, Cr, Cu and Al should be adjusted so that the amount of each component is within each range specified above. They must also be adjusted so that the value of A, calculated according to the equation defined above, is less than 41.0. It has been found experimentally, as will be demonstrated in the examples below, that if the value of A exceeds 41.0, an appreciable amount of daistCnite phase is retained in the parent metal as treated in solution and the weld zone of the gang. While an austenite phase retained in the solution-treated stainless steel can easily be converted to a martensite phase by a mild cold rolling, the austenite phase retained in the welded zone is refractory, and It is difficult, although not impossible, to industrially convert the latter to the desired martensity phase. The band having the austenite retained in the weld zone can not be sufficiently reinforced, even if it is subjected to the subsequent aging and hardening treatment, and therefore, the band breaks up frequently at the welded zone during its use. In addition, a value of A too high requires intensive cold rolling, resulting in a two-phase structure of austenite and stress-induced martensite. As already indicated, a web having such a two-phase structure tends to deform when subjected to a repeated cycle of hot and cold during use, or to a processing or forming Rubber is applied to the back of the band under heat and pressure to prevent winding movements of the band. For the reasons described above, the value of A must be

controlled below 41.0.

  aeuTUe8I ep sade9 salt sqzde enoa; eje.Tnoae ep% uemaelTea

  a.zpuazdmoo qned uoTq.nTos ue luemaeslTae. at-

  There is no doubt that this is not the case, but it is not so easy to use, because it is so important that it can be used in a variety of ways. epnos bucketTmue.lappJd suoTS -uemTp op epueq aun eue apueq no ellTnej el. adnoo o uoTq.eoTqe es op sanoo ne elqepAxouT.zeToeaT suep% uamaeq: .T.auT; ueuse, sqa.ZlendmT sap a Jae; np: ue: the q.uel.sesa eT. '0'1 SU SUTOM I. uei.uescda' I..Lg'OZ + (spTod ue% 'IV) x g9'o - z (spTod ue%' no) x 9L'0 + (spTod ue% 'O ) x 09'O + (spTod ue% 'TN) x I + (spTod ua% uN) x o04o + (spTod ue%' T, / spTod ue% 'I) x /. = V UOTqenb, l.zeTd TUTjP y el op inleA 41'v ap spTod ue% 0'I ep Snid sed T ep spTod OZ ue% 0'1 Z1 'O' nD ep SPTOd ue% 'q Z 5'o '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • Bp N spTod ue% u0'0 op Snid south 'g ue op sPTod% iO'O op snTd south u.ueueuoo to esqep xouT.eToe qpeT' epueq No. eTllTnej alle. amunp uoT.eoT.que; op snsseooozd el suep uoTInlos uemeus9.Te eu ..: a ê eaqepXxouT aeToep apueq No. eTTinej aun ez.aemnos p sadela set pueadmoo qpnos% UTO [a: .ueXe xneXoâuoo ep uT; sues enbTlîe: L.m apueq eunp uoTonpoTd op ppeooid a 'uOTueAuT, 5 uoleS 01 À.Tns Tnb peood î IBd e aeTnpo.zd e.xl luemesneSelueAe lnedd enbTmTqo uOTI.Tsodmoo ella. aun% e aen.onzls alle. aun EUEU znasXoauoo Sp apueq A'I 'seTdTo.ezd aseTlle4p squemeTa September senbTlieq.eme.luT S.uesodmoo sap oaie e: .TsueaJl.m Sp q.uemalqTsuas asetd op ean% .on.ls aun ç xnep sno..uo epueq el ep I.uesed ieg.m al.e e9pnos auoz and 'snTd ea' seeTjTogds s.ae; Tuenb twelfth scTSTo9ds sueamlp Hi: ueueleuoo elqep.xouT.zeToe unp esodmoo as 'uoTua.uT T uoles' apnos a Luto oeae ine.oAuoo Sp apueq Ba

ú1-6Z3

  Cold.; The solution treatment is preferably carried out by heating the sheet or strip at a temperature of 900 to 1050 C and cooling the sheet or strip

  heated to room temperature, by means of air or water.

  In the case where the solution-treated sheet or strip contains any retained austenite phase, it must be conditioned by cold rolling with a rolling reduction of up to 50% to convert the austenite phase to a martensite phase induced by stress, and the sheet or strip having a substantially martensite structure must be cut to the predetermined dimensions. In the case where the sheet or strip treated in

  solution has a substantially phase structure of marten-

  site, it can be cut directly into a predetermined size band. However, even in such a case, the solution-treated web or sheet should preferably be cold rolled with a reduction of up to 50% before it is cut into a predetermined size strip to obtain

  Conveyor belt with considerable properties

have been improved.

  If the sheet or strip treated in solution is packaged, a reduction by rolling greater than 50% should be avoided, or otherwise the toughness of the product

  final may be adversely affected.

  Preferably, the aging cure treatment can be carried out by maintaining the endless belt at a temperature of 425 to 550 ° C, preferably 450 to 525 ° C for 10 to 300 minutes, and more preferably 10 minutes. Advantageously, the welded zone of the endless belt can be hammered before curing treatment with aging. In place of or in addition to pounding, the welded zone of the endless belt may be subjected to a treatment below zero prior to aging cure treatment. The treatment below zero can be performed by cooling the welded zone of the endless belt to temperatures of -20 ° C or less for about 30 minutes. The treatment below

  zero can be followed by another pounding.

  Any known butt weld technique may be used to weld the ends or ends of the

  band to form an endless band.

  According to the present invention, there is provided a stainless steel conveyor belt having a welded seam stronger than in any such band. The conveyor belt according to the invention has a sufficiently reliable fatigue strength when subjected to repeated and prolonged bending stress. Its metal structure is stable and undergoes no significant change even if it is subjected to a repeated cycle of hot and cold. Consequently, the conveyor belt according to the invention is substantially free of problems due to a deterioration of the performance during its lifetime, such as a deterioration of its surface flatness and a reduction

  tenacity or rigidity.

  The improved properties that the band of

  conveyor according to the invention will now be more particularly

  described with reference to examples and witnesses

that follow.

  Table 1 shows the chemical composition (in weight percent) and the A value of each steel species tested. Of the steel species tested or examined, N-1 to N-6 represent examples according to the invention, N-7 and N-8 represent controls outside the scope of the invention, M-1 is a control according to Japanese Patent Publication No. 31085 and SUS 301 and SUS 304 are

  steel strips that are marketed.

  From each of these steel species N-1 to N-8, a steel strip was prepared by a conventional method, and at the last stage of the process, the strip was annealed (solution treated) by heating it. at a temperature of 10501C and letting the heated band cool

  to room temperature. The band as annealed

24797-84

  was then conditioned by cold rolling with a reduction of the order of 20%. The strip thus packaged had a thickness of the order of 1.0 mm. The annealed strip and the packaged strip were subjected to an aging cure treatment by heating them at 480 ° C. for 1 hour. The tensile strength, hardness and fatigue limit of the strips were examined before and after aging cure treatment. Also, a steel strip was prepared from the M-1 steel species, and the annealed strip was aged by heating at 450 ° C for 1 hour. The band made of M-1 was also examined before and after aging. The commercially available SUS 301 and SUS 304 steel strips obtained were also examined before and after aging (heating at 400C for 1 hour). The results are

shown in Table 2.

  The strips prepared from N-1 to N-8, having been annealed and conditioned, were welded (TIG weld) at their ends or ends to form endless belts and after pounding the welded zone they were hardened by aging at a temperature of 480 ° C. for 1 hour. The welded zone was cut from each strip and its 0.2% yield strength, tensile strength and yield strength kb were examined. The limit value of elasticity was measured according to the standard test prescribed in the Japanese standard

  JIS H 3702 6.4. The results are shown in Table 3.

  Table 2 reveals that the bands according to the invention (N-1 to N-6) have, after aging-hardening, remarkably improved mechanical properties, compared to the known stainless steel strips (M-1, SUS 301 and SUS 304). For example,

  known bands have a tensile strength which does not

  of about 1128.1 X 106 Pa while those according to the invention have a tensile strength of at least about 1451.5 X 106 Pa (with those annealed and cured on aging) and can reach at least about 1716. , 7 X 106 Pa (with those annealed, packaged and

hardened to aging).

  Tapes, such as annealed, prepared from N-7 and N-8, having a value of A outside the range specified above, do not have mechanical properties

  satisfactory even after age hardening.

  Annealed and packaged strips, prepared from

  N-7 and N-8, have good mechanical properties compared

  bands according to the invention, both before and after

  aging cure treatment. However, with control strips prepared from N-7 and N-s, a strong weld joint can not be formed as shown by the results in Table 3. This is because appreciable amounts of austenite are retained in the

welded zone.

  The steel species M-1 has a value of λ which falls within a prescribed range here. However, this M-1 steel is not of a precipitation quench type and therefore

  it does not have satisfactory strength and toughness

  even after aging, as revealed

by the results in Table 2.

  09mbn - [eo uou 9ZO'O 1T V f IT 'T 8'81 66'8 06'0 ú0' 1 OLO'O iyoç sns JeTou ua puepI * - - a0Tno _ __ 0ú sns -ieo5zo'o - - - GL'99lOk'LO'l 6'0 01'O JaTou ua uou or apueg 09'Sú 1in0'0g10'0 8Z'0- 6'k1 IZ'i06'009'0 çw0'0 1 Oz '110'0 5Z0' 09Z'0 09'0u'G1 0'9 00'1 I 'I890'0 9 - N,' Zi

Z1.0'O

9ZO'O ilz 'O' 0 00'91 'L. z8'0

ú5 '1I

  O 'OO L - N CD% o I- iiC 16'8uZ1,0'0sO'O 65'0 9''1 ú'if. 9O9'Z58'0 ZO'9 g _ N L6'8u 010'0o Z'oLú'o 05'1.0y'I úú'LIZ 'O50'LOZO'O - N _ - 4 ti o 0S'6úi10' 0 Z0'0 Zú'0 69 '18' IL W1Lúú'0o55lOl'O - N mzl It 017wllO'úZO'0970 00'1 OL'àw51'L6z'O990 9çgo'o9 - Na /. 6 '' 170'0'ZO '1O 0' "O 6'9'0lZ91'LO 'O95'1. 90 Il Z - N w o -collo zolo çc" O go, col1c 917 1 LK "O Lg -ço 4 O -, N 'l 996u 0'? 0 'ú 7'O O0'0 09'IuO'59'L 0ú'0L9'1 8G70'0 - N naisAi; _ xD TNFS saoqds Vap eTToua p WTUA.N TV the nO TN N T9 0 ood Co N. 0% N. w W -IIVH'iI TABLE 2 (Parent metal) State before

aging

Annealing Before aging

resistant

to.

  Traction (1O Pa 990.8 Hardness (HV) 'Limit

of

  ti ue (10i Pa) 416.9 After aging

resistant

tance to trace (10ie

1529.4

Hardness (Hv) Limit

of

  (1 Pa> i3 'f 1030 306 416.9 1589.2 500 f3.7 i.

976.1 299 402.2 1511.7 480 569

  955.5 293 397.3 1522.5 490 564.1 l 956.5 295 392, 4 1623.5 515 5b, G 946, 7 407.1

1536.2

y t t I t t 4 4 Annealing and

condi-

tioned

1167.4

524.8 6, f

1157.6 335 519.9 1785.4 525 686, ',

1187 352 534.6 1818.8 533 686.7

1074.2 327 515 1769.7 530 66 /,

  1084 325 510.1 1819.7 536 676C e 1 i_

1068.3

500.3

1730.5

I, J i ,, i,

N - 7,892.7 240,323.7 979,305,343.3

  Y N - 8 Annealing 868.1 235 299.2 918.2 252 318.8

  E 4 M - 1,1069.3 330 510.1 1098.7 349 5

  . / ... -JO -'IJ Co Steel species N - 1 N - 2 N - 3 N - 4 N - 4 N - 5 N - 6 NG N - 1 N - 2 N - 3 N - 4 N - 5 N - 6 r. Where C H C vM [y -, T I. I a

9'9817

Z'7LO

+ i t 1 1--

6'Z'I 6

ú II, 81

e9 TIaTO eub e- [OI [li I I II I 0 7

I I I -

17 '198 1

  6'615 06 9uuoTI.Tpu0D 1.TnoBeI snS IeTO, ap epuu 'oç snsa JaeTou p epUBefG 8 - mi

L. -N

  (e 01 O (lac 01) (12d 01) (a 01) ## EQU1 ## where: (AH) -OBZD (- p) -IBAHB ut.ueu eD; TmTI 9alnp e where STSUU 0 e uTmT 9e.0ajzr oo TE96 -esBTIITaTA JGeTou1p uemeBs FITeTOA sqaIdy luemesTIITTT.A. IU 'BAe Fs wr_r,% C o cm q'G 6 CDs o I-'. (El.Tns) (lueaBd him .9x) z nynavi TABLE 3 (Welded area) Species Llmite Reslstance Steel limit value 0 to 0, a2q tensile elasticity kb (106 Pa) (106 Pa) (106 Pa)

N - I 1535.3 1569.6 1795.2

N - 2 1569.6 1618.6 1868.8

o

N - 3 1520.5 1584.3 1785.4

i ,. i ,. - i i

N - 4 1500.9 1544.1 1667.7

N - 5 1510.7 1546.1 1672.6

o

N - 6 1545.1 1564.7 1746.2

N - 7,833.8 1230.2 691.6

  FIG. 7 shows a schematic cross-sectional view of the welded zone of a conveyor belt according to US Pat. No. 5,784,812,416,4657,3. invention, where the reference numeral 10 designates the welded metal zone of the strip, the reference numeral 11 designates the zone affected by the heat and the reference numeral 12 designates the parent metal;

  which was not influenced by the heat of welding.

  Fig. 8 is a graph showing changes in hardness along the weld zone and the parent metal on several conveyor belts, where the ordinate axis denotes the hardness (Hv = 10 kg) and the abscissa means a longitudinal distance, in ma, from one of the ends of the weld. Curve A refers to steel species N-2. The strip examined was prepared by welding (TIG weld) the ends of an N-2 strip 1.0 mm thick, 1000 mm wide and 25 m long, which had was annealed and conditioned with a rolling reduction of 20%, hammering the welded zone and aging the strip at 480C for about 1 hour. Curve B also refers to the N-2 steel species. The examined strip was prepared in the manner described above with the exception that the welded zone was immersed in a liquid bath of alcohol and dry ice at a temperature of -25 ° C for 30 minutes instead of being hammered. . Curve C refers to the N-5 steel species. The strip examined was prepared by welding (TIG weld) the ends of an N-5 annealed strip having the same dimensions as those indicated above with respect to curve A, and by aging the strip as welded in Same conditions as above for curve A. Curve D refers to steel species M-1. The test strip was prepared as described with respect to curve C but with aging carried out by heating the welded strip at 450 ° C. for 1 hour. Curve E refers to SUS 304 steel. The examined strip was prepared by welding (TIG weld) the ends of a commercially available SUS 304 strip, hammering the welded zone and aging the strip at a temperature of 400C.

for 1 hour.

  Comparing with the results represented by curves D and E, which relate to the known stainless steel bands, the result shown by the curves A, B and C, relating to the bands according to the invention, reveals that one can get a considerably improved hardness

  both in the welded zone and the parent metal of the

  hardened to aging according to the invention. In the case where the value of A is less than about 39.0, as in the case of the steel species N-5, the improvement can be obtained even if the band as welded is directly cured on aging. In the case where the value of A is of the order of 40.0 or more but less than 41.0, as in the case of steel species N-2, it is preferable to subject the welded zone to a simple treatment, such as a pounding or a treatment below zero (for example at a temperature of -25C or less for about

  minutes) before curing treatment at aging

is lying.

  Figures 9 to 12 are bar graphs showing the mechanical properties of the welded zone (hatched bars) and the parent metal (white bars) of the

  bands indicated. The band indicated by N-2 20% condition-

  (b) was used in the above-described test with respect to curve A of FIG. 8. The bands indicated by annealed N-5, annealed annealed (R) and SUS 304 were those used in FIG. The test described above with respect to FIG. 8. The annealed N-2 band was prepared by welding the ends of an annealed 1.0 mm thick N-2 band, width of 1.000 mm and a length of 25 mm, hammering the welded zone and aging hardening the strip at a temperature of 480C for 1 hour. Test samples were cut from the welded zone and parent metal strips examined, and then examined by standard tests. FIGS. 9, 10, 11 and 12, respectively, relate to the 0.2% yield strength, the tensile strength and the yield strength (measured according to the Japanese standard JIS H 3702 6.4) and at the limit of

tired. -

  As can be seen from the results of FIGS. 9 to 12, the mechanical properties, including the 0.2% yield strength, the tensile strength, the limit value of elasticity and the fatigue limit that the belts possess Conveyor according to the invention both in the welded zone and in the parent metal are surprising. Of course, the invention is not limited to the embodiments described and shown which have been given by way of example. In particular, it includes all the means constituting technical equivalents of the means described and their combinations if they are executed according to its spirit and implemented.

  in the context of protection as claimed.

Claims (12)

R E V E N D I C A T I ONS   1.- metal conveyor belt formed of a sheet or strip of a metallic material having predetermined dimensions, by welding the ends of said sheet or strip to form an endless band, characterized in that said metallic material is of stainless steel containing not more than 0.07% by weight of C, not more than 0.03% by weight of N, 0.5 to 2.5% by weight of Si, not more than 4, 0% by weight of Mn, 5.0 to 9.0% by weight of Ni, 12.0 to 17.0% by weight of Cr, 0.5 to 2.5% by weight of Cu, 0.2 to 1.0% by weight of Ti, not more than 1.0% by weight of Al, the value of A defined by the equation A = 17 x (C, wt% / Ti,% by weight) + 0, 70 x (Mn,% by weight) + 1 x (Ni,% by weight) + 0.60 x (Cr,% by weight) + 0.66 x (Cu,% by weight) - 0.63 x (Al ,% by weight) + 20,871 representing less than 41.0, and the remainder being iron and impurities inevitably coming into the stainless steel during its manufacture, both the weld zone (10) and the parent metal (12) of said band having a substantially martensitic phase structure with compounds intermetallic precipitates.   2. Strip according to claim 1, characterized in that the welded zone and the parent metal have a tensile strength of at least 1373.4 x 106 Pa, a hardness of at least 430 Hv and a fatigue limit at minus 490.5 X 106 Pa.   3. Band according to claim 1, characterized in that the tensile strength of the parent metal is at least 1569.6 X 106 Pa, while the tensile strength of the welded zone is at least 90 % that of the parent metal, the hardness of the parent metal is at least 480 Hv while that of the weld zone is at least 90% of that of the parent metal and the fatigue limit of the parent metal is at least 559.2 X 106 Pa while that   of the welded zone is at least 90% that of the parent metal.   4. A process for producing an endless conveyor belt of metal with a welded joint, characterized in that it comprises the steps of: subjecting a sheet or strip of stainless steel to a solution treatment during the producing such a sheet foande, said stainless steel containing not more than 0.07% by weight of C, not more than 0.03% by weight of N, 0.5 to 2.5% by weight of Si, not more than 4.0% by weight of Mn, 5.0 to 9.0% by weight of Ni, 12.0 to 17.0% by weight of Cr, 0.5 to 2.5% by weight of Cu 0.2 to 1.0 wt.% Of Ti, not more than 1.0 wt.% Of Al, the value of A defined by the equation A = 17 x (C, wt% / Ti,%) by weight) + 0.70 x (Mn,% by weight) + 1 x (Ni,% by weight) + 0.60 x (Cr,% by weight) + 0.76 x (Cu,% by weight) - 0.63 x (Al,% by weight) + 20.871 representing less than 41.0, and the remainder being iron and impurities inevitably coming into the stainless steel during its manufacture, cut the sheet or strip into a strip from di predetermined lengths, weld the ends of the strip to form an endless band, and subject the endless band to aging hardening.   5. A process according to claim 4, characterized in that the sheet or strip treated in solution is packaged by rolling with a reduction of up to 50% before it is cut to the predetermined dimensions.   6. Process according to any one of the claims   4 or 5, characterized in that the solution treatment comprises an annealing treatment carried out after the steps cold rolling. Z479784   7. Process according to any one of   4 or 5, characterized in that the treatment   in solution is carried out by heating the sheet or strip to a temperature of 900 to 1050C and by rolling the sheet to the strip heated to room temperature with air or water.   8. Process according to any one of the claims   4 or 5, characterized in that the aging hardening treatment is carried out by maintaining the endless belt at a temperature of 425.degree. at 300 minutes.   9. A process according to claim 8, characterized in that the aging hardening treatment is carried out by maintaining the endless band at a   temperature of 450 to 525 C for 10 to 60 minutes.   10. Process according to any one of   Claims 4 or 5, characterized in that the welded zone   of the endless band is hammered before the treatment of aging hardening.   11.- Process according to any one of   4 or 5, characterized in that the area   welded endless belt is cooled to a temperature of -20 C or less before aging cure treatment. 12. Process according to any one of   claims 10 or 11, characterized in that the area   welded and cooled to -20C or less of the endless belt is hammered before aging cure treatment.