換刀機(jī)械手設(shè)計(jì)帶CAD圖

換刀機(jī)械手設(shè)計(jì)帶CAD圖,機(jī)械手,設(shè)計(jì),CAD ISSN 0967?0912, Steel in Translation, 2011, Vol. 41, No. 1, pp. 4147. Allerton Press, Inc., 2011.Original Russian Text G.N. Elanskii, I.F. Goncharevich, 2011, published in “Stal,” 2011, No. 1, pp. 1421.41The mold in a continuous?casting machine is acomplex multifunctional system. This system includesthe mold itself, which is primarily a thermal unit, con?trolling the heat transfer from the steel melt that willform the continuous?cast billet; a suspension system,which ensures specified billet trajectory and, if it iselastic (usually a spring system), also somewhat com?pensates the dynamic loads; a drive ensuring specifiedvibration of the mold; and a supply system for the slag?forming mixture. On melting in the gaps between thecasing of the continuous?cast billet and the moldwalls, the slag?forming mixture performs a series offunctions, such as control of the thermal processes;lubrication with reduced drag on the billet as it movesthrough the mold; and removal of nonmetallic inclu?sions from the melt. Note the important role of thelubricant in transforming frictional forces that do notdepend on the speed (dry friction) into viscous fric?tion. Viscous friction between the mold and the billetis essential for effective asymmetric vibration. Effec?tive operation of the mold system depends on smoothinteraction of all the subsystems, which must performtheir assigned functions.When continuous casting was first introduced, themold was motionless. However, it was quickly estab?lished that this process is problematic. Then recipro?cating motion (rocking) of the mold along the cast bil?let was induced, with significant improvement in theprocess. The benefits of reciprocating motion arelargely due to the replacement of static frictionbetween the casing of the continuous?cast billet andthe mold walls by dynamic friction, which is less pro?nounced and more stable.When using large rocking speeds (higher than thebillets extrusion rate), the interaction between thecasing of the continuous?cast billet and the mold wallsis fundamentally changed. In some stages of motion,the mold walls outpace the billet, which was not previ?ously the case. The exclusively tensile force on the cas?ing of the continuous?cast billet in the stationary moldis replaced by compressive force in some stages ofmold motion. It is also found that the damage to thebillet casing that sometimes appears when the moldoutpaces the billet (when its speed exceeds the billetsextrusion rate) will be partially or completely elimi?nated. This is a fundamental benefit of a rocking moldover a stationary mold.Detailed study of defect amelioration permits thedevelopment of special rocking conditions to maxi?mize this effect. To this end, very complex suspensionmechanisms and drives are required. In practice, how?ever, many of these systems are unwieldy and difficultto maintain; in other words, their operational effi?ciency is poor. Special rocking conditions withunsmooth motion and dramatic changes in moldspeed create considerable dynamic loads in the drivemechanisms, on account of the associated accelera?tion. Therefore, in industry, molds with balllever sus?pension operate predominantly in smooth slow har?monic processes characterized by low frequency andlarge amplitude, which are more stable and lessdynamic.When steel plants began to increase the billetsextrusion rate so as to improve productivity, it was nec?essary to increase the molds rocking speed. Thisrequired increasing the rocking frequency (to whichthe rocking speed is proportional), because the rock?ing amplitude could not be increased without impair?ing the billet surface. As a result, the accelerationsharply increased (in proportion to the square of therocking frequency) and hence the dynamic loadincreased. In many hinges with fixed technologicalgaps, impact loads arose, breaking the suspension 1.In those conditions, hinged?lever suspension systemsproved impracticable and were replaced by deformableelastic suspensions (specifically, spring suspensions),which had long been used in vibrational engineering.Thanks to the lack of free play, such suspensions per?mit the mold to precisely track the specified billet con?figuration (linear or curvilinear). Elastic spring sus?pensions proved extremely effective in practice, bothin technological terms and in terms of simplifying thedesign of the continuous?casting machine and reduc?ing its cost.Improving Mold Operation in Continuous?Casting MachinesG. N. Elanskiia and I. F. GoncharevichbaMoscow State Evening Metallurgical Institute, Moscow, RussiabRussian Engineering Academy, Moscow, RussianAbstractMold operation with spring suspension and a programmable hydraulic drive is considered. Com?puter methods of investigating the moldbillet interaction are developed. A new mold with longitudinaltransverse vibration and dynamic stabilization has been developed for continuous?casting machines.DOI: 10.3103/S096709121101004942STEEL IN TRANSLATION Vol. 41 No. 1 2011ELANSKII, GONCHAREVICHTo improve the billet produced by traditional con?tinuous?casting machines, we need to investigate thefactors responsible for unsatisfactory product quality.Industrial experience indicates that, in outdated con?tinuous?casting machines, the main factor reducingbillet quality is imperfection of the molds hinged?lever suspension. However, analysis shows that suchsuspensions cannot be replaced by spring suspensionswithout changing many auxiliary systems. In particu?lar, old and new continuous?casting machines differfundamentally in design. Therefore, replacing any sin?gle component of an old system by new mechanismsunavoidably entails the installation of appropriateauxiliary equipment, at great cost.Accordingly, a low?cost option is not to replace theentire suspension but to use elastic hinges, which havebeen satisfactorily employed in cyclic systems 1.As well as the equipment, continuous?casting tech?nology has been radically changed. In new molds withelastic suspension that are switched to high?frequencyoperation with low amplitude, asymmetric vibrationproves more effective in technological terms. Toensure reliable maintenance of complex nonharmonicmold oscillation, programmable electrohydraulicdrives are employed.Thus, there is a qualitative shift from traditionalmolds with rigid kinematic elements and undeform?able eccentric drives to machines with deformablelinks and nonrigid hydraulic drives and from harmonicvibration to spectrally more complex nonharmonicvibration. Whereas the rocking conditions are rigidlyspecified in molds with eccentric drives (providedthere are no gaps in the hinges), the presence of elasticlinks in the new molds means that their motion isdetermined not only by the drive but also, to someextent, by the dynamic properties of the whole systemconsisting of the billet, the mold, and the continuous?casting machines drive mechanisms.In developing new casting processes, designersmust take full account of these design changes and thenew scope for the operation of continuous?castingmachines. Special research is required to make senseof the wide range of parameters for the new molds, toclarify the diverse criteria for the assessment of castingefficiency, and to reconcile the sometimes contradic?tory technological and dynamic requirements. Thus,new approaches are required in view of the radicalchanges in design principles for the new molds and thepowerful and continuous dynamic relation betweenthe process and the operating conditions of the equip?ment.The further development of continuous?castingtechnology requires the consideration of the wholecomplex machineload system. Note that the con?tinuing increase in casting speed entails appropriateincrease in amplitude of the rocking speed in any con?ditions (including harmonic conditions, which stillpredominate). On account of technological consider?ations, this entails increasing the carrier frequency ofthe vibrations, with considerable increase in dynamicloads in all the components of the system and in themold drive.If we use special asymmetric nonharmonic vibra?tions (containing higher harmonics), which are techno?logically more effective, the mold acceleration and thecorresponding inertial forces increase considerably.This increase in inertial forces is even greater than inharmonic conditions, since it is proportional to thesquare of the oscillation frequencies in the nonhar?monic motion (including the higher harmonics).Accordingly, methods of reducing the dynamic load onthe continuous?casting machines must be developed.The dynamic loads may be reduced if the inertialforces of the rocking masses are compensated by theelastic forces of the spring suspension. The inertialforces are completely balanced when the eigenfre?quency of the mold (determined by the rigidity/massratio of the spring suspension) matches the drive fre?quency (in resonant conditions).Reduction in the dynamic load of drives in contin?uous?casting machines by ensuring resonant condi?tions with asymmetric rocking is complicated that thesystem only has only operating frequency, whereasasymmetric rocking of the mold is a polyfrequencyprocess. Another difficulty is that the eigenfrequenciesof existing molds are constant, specified in the designprocess (by the mold mass and the rigidity of the springsuspension), and cannot be adjusted during moldoperation, whereas the oscillation frequency is deter?mined by the selected technological conditions andvaries widely in the course of operation Therefore, theeigenfrequency of the mold must be established byoptimal design with inconsistent quality criteria 2, 3.Partial dynamic balancing of the mechanisms of con?tinuous?casting machines that operate in asymmetricpolyharmonic conditions has been developed. Meth?ods that permit maximum possible reduction indynamic load by selecting optimal parameters of thespring suspension have also been formulated. It hasbeen shown that continuous variation in oscillationfrequency of the drive within each cycle imposes fun?damental constraints that prevent the complete bal?ancing of dynamic loads within the vibrating parts ofthe continuous?casting machine.Thus, in switching new?generation molds of con?tinuous?casting machines to effective nonharmonicoperation, it is important to develop an optimal?design method for continuous casting such that thedynamic complications may be reconciled. At present,progress is being made in that areain particular,thanks to introduction of special biharmonic moldvibrations. We will now focus attention on the optimalcombination of effective operation and dynamic bal?ancing of the continuous?casting machine.STEEL IN TRANSLATION Vol. 41 No. 1 2011IMPROVING MOLD OPERATION IN CONTINUOUS?CASTING MACHINES43The measures considered next facilitate the use ofhighly efficient nonharmonic vibration and simultaneousreduction in dynamic loads within the molds drive.INTERACTION OF THE CONTINUOUS?CAST BILLET WITH THE MOLDS WALLSThe interaction of the continuous?cast billet withthe molds walls is affected not only by the conditionsof mold vibration but also by the supply of slag?form?ing mixture and its properties. According to currentconcepts, the slag?forming mixture dissolves in themelt within the mold and mixes with the solid particlesto form a coating with lubricant properties. Close tothe meniscus, it acts as a viscous lubricant, and mea?surements show that viscous?friction forces predomi?nate in this region. These forces are proportional to therelative velocity of the frictional pair (the billet and themold wall).On moving away from the meniscus, viscoplasticfriction (viscousdry friction) is observed; this forcedepends less on the relative speed of the billet and moldand begins to depend on the pressure of the billet casingat the wall. As the billet moves toward the mold exit, theproportion of viscous?friction forces declines, and theproportion of dry?friction forces increases. Specialistsassert that dry friction largely acts when the billet leavesthe mold; its magnitude depends on the force pressingthe continuous?cast billet against the mold wall. Wemay also assume that this effect is due to the maximumferrostatic pressure on the billet casing at its exit fromthe mold. Thus, in model research, these experimentallaws should be reproduced.Note that these processes are also accompanied byincrease in thickness of the billet casing. Accordingly,the stress in the casing declines on moving toward themolds exit, despite the increase in frictional forces.The casing usually breaks down in the meniscusregion, especially on account of the increase in stressdue to the unfavorable balance of the forces acting andthe strength of the casing.Study of the formation of drag on the billet in themold is important not only to develop preventive mea?sures, but also so as to reduce the extrusion forces ofthe blank and reduce the load in the tractional mech?anism. This requires appropriate selection of the com?position of the slag?forming mixture, its delivery con?ditions, and the rocking parameters of the mold. Inaddition, it is important to formulate rocking condi?tions corresponding to sufficient lubricant supply,specified billet motion, and reduced frictional forces.The interaction of the billet with the mold wallsdepends primarily on their relative speed, which deter?mines the viscousdry frictional forces. When theirrelative speed is reversed, the direction of action of thefrictional forces changes. The efficiency of mold oper?ation is characterized by the ratio of the times of moldoperation in the same direction as the billet and theopposite direction. For mold motion in the samedirection at a speed exceeding the extrusion rate, themold walls outpace the billet, and the frictional forcebetween them becomes a motive force, with corre?sponding decrease in mean drag forces over the cycle.According to the available data, the compressive stressin the casing is associated with 2030% decrease inthe defects arising at the billet surface in the case ofopposite motion of the mold and billet, when tensileforces act in the billet casing. With increase in the ratiobetween the times of mold operation in the samedirection as the billet (positive motion) and the oppo?site direction (negative motion), mold rockingbecomes more effective, in technological terms. Anal?ysis shows the high efficiency of asymmetric rocking innew?generation molds, especially when viscous dragpredominates. Thus, with sufficiently asymmetricvibration, the speed may be significantly higher in thepositive part of the cycle than in the negative part. Themean drag over the cycle also changes on account ofmold rocking. The available data indicate relatively effi?cient mold operation in asymmetric conditions, interms of reduced mean drag (predominantly viscousdrag, with a modest dry?friction component) on the bil?let as it travels through the mold. Because of the greaterefficiency with viscous drag, it is expedient to organizereliable lubrication in asymmetric vibration. Note thatasymmetric conditions tend to increase the lubricantsupply. In correctly selected conditions, the new?gener?ation molds more effectively reduce the mean drag onthe billet in comparison with traditional molds.To assess the effectiveness of the rocking condi?tionsin particular, to determine the stress in the bil?let casing and the lubricant supplyphenomenologi?cal inertial elastoviscoplastic models and correspond?ing systems of nonlinear differential equations havebeen developed. The methods used in developing themodels were outlined in 412. These models may beused to select optimal rocking conditionsin terms ofminimal internal stress of the billet casingwithoutimpairment of the systems dynamic properties. Onthat basis, there is a real possibility of selecting non?harmonic rocking conditions while reducing thedynamic loads on the drives of the continuous?castingmachine.Note that it is impossible to eliminate dynamicloads in the drives of the continuous?casting machinewith asymmetric polyharmonic operation, becausethere is only a single operating frequency, whereas theasymmetric rocking of the mold is polyharmonic;within a single cycle, the drive frequency varies con?tinuously, while the eigenfrequency of the existingmold systems is constant.At present, a possible approach to efficient rockingof the mold and reduction in the dynamic loads on thedrive is to develop special biharmonic mold vibrations.As shown by computer experiments, this approach isrelatively effective, both in technological terms and in44STEEL IN TRANSLATION Vol. 41 No. 1 2011ELANSKII, GONCHAREVICHreducing the dynamic loads in the continuous?castingmachine. In Figs. 1 and 2, we compare some charac?teristics of continuous casting for the proposed andtraditional methods. In Fig. 1, we show the stress inthe billet casing: (a) force due to dry friction; (b) forcedue to viscous friction; (c) total viscoplastic forces onthe billet casing. In Fig. 2, we show the uncompen?sated dynamic loads in the drive due to mold rockingwith a hinged?lever suspension and the load compen?sated by the recovery forces of the elastic spring sus?pension in biharmonic oscillation.NONTRADITIONAL ROCKING OF THE MOLDTo ensure high billet quality in continuous casting,two basic methods are employed: casting through arocking mold; and mild billet reduction on leaving themold. In these processes, a reduction cell is usedtogether with the mold. In the present section, we con?sider the possibility of initial billet reduction within themold. In other words, we analyze the feasibility andexpediency of combining the initial stage of reductionwith casting. We briefly review the necessary precondi?tions for such an approach.The operational efficiency of the mold is primarilydetermined by its rocking conditions along the billetaxis. The reduction cell is pressed against the mold bytransverse forces. Since rocking occurs along the billetaxis, the frictional forces between the mold walls andthe billet produce tensioncompression stress in thebillet casing. This will considerably affect the billetquality and the overall stability of the process.In longitudinal rocking, the frictional force at themoldbillet casing may only be regulated when theforces between them depend on their relative speed(that is, viscous?friction forces). In the presence ofsuch forces, only the rocking speed or the extrusionrate of the billet need be adjusted. In the sections ofbilletwall contact characterized predominantly bydry friction, which is unaffected by the relative speed,the frictional forces may vary only in direction; theirmagnitude is constant.In practice, as already noted, different combina?tions of viscous and dry forces act on the billet at dif?ferent points of the mold. This must be taken intoaccount in formulating the rocking conditions.Noting that viscous friction predominates within alimited zone (mainly around the meniscus), we mayconclude that the rocking conditions developed pri?marily for viscous friction (in particular, highly effi?cient asymmetric rocking, which is widely promoted)are of very limited value over the whole contact zone.At the same time, we know that the frictional forcemay be very effectively regulated by oscillations per?pendicular to the relative velocity of the frictional sur?faces. (Modern molds operate in conditions of high?frequency vibration.)250255075012345PReduced force50P40200204060012345PsPReduced forcePs(a)(b)(c)100500246810Reduced energy consumptionQPhase angle of driveQFig. 1. Forces transmitted from the mold to the billet inbiharmonic vibration: (a) viscous force P and plastic forcePs; (b) total viscoplastic force; (c) energy consumption ofmodel in overcoming the frictional forces on the continu?ous?cast billet.5056420Phase angle of driveDGReduced loadFig. 2. Uncompensated dynamic load G from the rockingload that acts on the continuous?casting machines drivewhen using hinged?lever suspension and load D compen?sated by the restori