裝配圖換刀機械手設計

裝配圖換刀機械手設計,裝配,圖換刀,機械手,設計 ISSN 0967hyphenminus0912, Steel in Translation, 2011, Vol. 41, No. 1, pp. 41–47. ? Allerton Press, Inc., 2011. Original Russian Text ? G.N. Elanskii, I.F. Goncharevich, 2011, published in “Stal’,” 2011, No. 1, pp. 14–21. 41 The mold in a continuoushyphenminuscasting machine is a complex multifunctional system. This system includes the mold itself, which is primarily a thermal unit, conhyphenminus trolling the heat transfer from the steel melt that will form the continuoushyphenminuscast billet; a suspension system, which ensures specified billet trajectory and, if it is elastic (usually a spring system), also somewhat comhyphenminus pensates the dynamic loads; a drive ensuring specified vibration of the mold; and a supply system for the slaghyphenminus forming mixture. On melting in the gaps between the casing of the continuoushyphenminuscast billet and the mold walls, the slaghyphenminusforming mixture performs a series of functions, such as control of the thermal processes; lubrication with reduced drag on the billet as it moves through the mold; and removal of nonmetallic incluhyphenminus sions from the melt. Note the important role of the lubricant in transforming frictional forces that do not depend on the speed (dry friction) into viscous frichyphenminus tion. Viscous friction between the mold and the billet is essential for effective asymmetric vibration. Effechyphenminus tive operation of the mold system depends on smooth interaction of all the subsystems, which must perform their assigned functions. When continuous casting was first introduced, the mold was motionless. However, it was quickly estabhyphenminus lished that this process is problematic. Then reciprohyphenminus cating motion (rocking) of the mold along the cast bilhyphenminus let was induced, with significant improvement in the process. The benefits of reciprocating motion are largely due to the replacement of static friction between the casing of the continuoushyphenminuscast billet and the mold walls by dynamic friction, which is less prohyphenminus nounced and more stable. When using large rocking speeds (higher than the billet’s extrusion rate), the interaction between the casing of the continuoushyphenminuscast billet and the mold walls is fundamentally changed. In some stages of motion, the mold walls outpace the billet, which was not previhyphenminus ously the case. The exclusively tensile force on the cashyphenminus ing of the continuoushyphenminuscast billet in the stationary mold is replaced by compressive force in some stages of mold motion. It is also found that the damage to the billet casing that sometimes appears when the mold outpaces the billet (when its speed exceeds the billet’s extrusion rate) will be partially or completely elimihyphenminus nated. This is a fundamental benefit of a rocking mold over a stationary mold. Detailed study of defect amelioration permits the development of special rocking conditions to maxihyphenminus mize this effect. To this end, very complex suspension mechanisms and drives are required. In practice, howhyphenminus ever, many of these systems are unwieldy and difficult to maintain; in other words, their operational effihyphenminus ciency is poor. Special rocking conditions with unsmooth motion and dramatic changes in mold speed create considerable dynamic loads in the drive mechanisms, on account of the associated accelerahyphenminus tion. Therefore, in industry, molds with ball–lever sushyphenminus pension operate predominantly in smooth slow harhyphenminus monic processes characterized by low frequency and large amplitude, which are more stable and less dynamic. When steel plants began to increase the billet’s extrusion rate so as to improve productivity, it was nechyphenminus essary to increase the mold’s rocking speed. This required increasing the rocking frequency (to which the rocking speed is proportional), because the rockhyphenminus ing amplitude could not be increased without impairhyphenminus ing the billet surface. As a result, the acceleration sharply increased (in proportion to the square of the rocking frequency) and hence the dynamic load increased. In many hinges with fixed technological gaps, impact loads arose, breaking the suspension [1]. In those conditions, hingedhyphenminuslever suspension systems proved impracticable and were replaced by deformable elastic suspensions (specifically, spring suspensions), which had long been used in vibrational engineering. Thanks to the lack of free play, such suspensions perhyphenminus mit the mold to precisely track the specified billet conhyphenminus figuration (linear or curvilinear). Elastic spring sushyphenminus pensions proved extremely effective in practice, both in technological terms and in terms of simplifying the design of the continuoushyphenminuscasting machine and reduchyphenminus ing its cost. Improving Mold Operation in ContinuoushyphenminusCasting Machines G. N. Elanskii a and I. F. Goncharevich b a Moscow State Evening Metallurgical Institute, Moscow, Russia b Russian Engineering Academy, Moscow, Russian Abstract—Mold operation with spring suspension and a programmable hydraulic drive is considered. Comhyphenminus puter methods of investigating the mold–billet interaction are developed. A new mold with longitudinal– transverse vibration and dynamic stabilization has been developed for continuoushyphenminuscasting machines. DOI: 10.3103/S0967091211010049 42 STEEL IN TRANSLATION Vol. 41 No. 1 2011 ELANSKII, GONCHAREVICH To improve the billet produced by traditional conhyphenminus tinuoushyphenminuscasting machines, we need to investigate the factors responsible for unsatisfactory product quality. Industrial experience indicates that, in outdated conhyphenminus tinuoushyphenminuscasting machines, the main factor reducing billet quality is imperfection of the mold’s hingedhyphenminus lever suspension. However, analysis shows that such suspensions cannot be replaced by spring suspensions without changing many auxiliary systems. In particuhyphenminus lar, old and new continuoushyphenminuscasting machines differ fundamentally in design. Therefore, replacing any sinhyphenminus gle component of an old system by new mechanisms unavoidably entails the installation of appropriate auxiliary equipment, at great cost. Accordingly, a lowhyphenminuscost option is not to replace the entire suspension but to use elastic hinges, which have been satisfactorily employed in cyclic systems [1]. As well as the equipment, continuoushyphenminuscasting techhyphenminus nology has been radically changed. In new molds with elastic suspension that are switched to highhyphenminusfrequency operation with low amplitude, asymmetric vibration proves more effective in technological terms. To ensure reliable maintenance of complex nonharmonic mold oscillation, programmable electrohydraulic drives are employed. Thus, there is a qualitative shift from traditional molds with rigid kinematic elements and undeformhyphenminus able eccentric drives to machines with deformable links and nonrigid hydraulic drives and from harmonic vibration to spectrally more complex nonharmonic vibration. Whereas the rocking conditions are rigidly specified in molds with eccentric drives (provided there are no gaps in the hinges), the presence of elastic links in the new molds means that their motion is determined not only by the drive but also, to some extent, by the dynamic properties of the whole system consisting of the billet, the mold, and the continuoushyphenminus casting machine’s drive mechanisms. In developing new casting processes, designers must take full account of these design changes and the new scope for the operation of continuoushyphenminuscasting machines. Special research is required to make sense of the wide range of parameters for the new molds, to clarify the diverse criteria for the assessment of casting efficiency, and to reconcile the sometimes contradichyphenminus tory technological and dynamic requirements. Thus, new approaches are required in view of the radical changes in design principles for the new molds and the powerful and continuous dynamic relation between the process and the operating conditions of the equiphyphenminus ment. The further development of continuoushyphenminuscasting technology requires the consideration of the whole complex machine–load system. Note that the conhyphenminus tinuing increase in casting speed entails appropriate increase in amplitude of the rocking speed in any conhyphenminus ditions (including harmonic conditions, which still predominate). On account of technological considerhyphenminus ations, this entails increasing the carrier frequency of the vibrations, with considerable increase in dynamic loads in all the components of the system and in the mold drive. If we use special asymmetric nonharmonic vibrahyphenminus tions (containing higher harmonics), which are technohyphenminus logically more effective, the mold acceleration and the corresponding inertial forces increase considerably. This increase in inertial forces is even greater than in harmonic conditions, since it is proportional to the square of the oscillation frequencies in the nonharhyphenminus monic motion (including the higher harmonics). Accordingly, methods of reducing the dynamic load on the continuoushyphenminuscasting machines must be developed. The dynamic loads may be reduced if the inertial forces of the rocking masses are compensated by the elastic forces of the spring suspension. The inertial forces are completely balanced when the eigenfrehyphenminus quency of the mold (determined by the rigidity/mass ratio of the spring suspension) matches the drive frehyphenminus quency (in resonant conditions). Reduction in the dynamic load of drives in continhyphenminus uoushyphenminuscasting machines by ensuring resonant condihyphenminus tions with asymmetric rocking is complicated that the system only has only operating frequency, whereas asymmetric rocking of the mold is a polyfrequency process. Another difficulty is that the eigenfrequencies of existing molds are constant, specified in the design process (by the mold mass and the rigidity of the spring suspension), and cannot be adjusted during mold operation, whereas the oscillation frequency is deterhyphenminus mined by the selected technological conditions and varies widely in the course of operation Therefore, the eigenfrequency of the mold must be established by optimal design with inconsistent quality criteria [2, 3]. Partial dynamic balancing of the mechanisms of conhyphenminus tinuoushyphenminuscasting machines that operate in asymmetric polyharmonic conditions has been developed. Methhyphenminus ods that permit maximum possible reduction in dynamic load by selecting optimal parameters of the spring suspension have also been formulated. It has been shown that continuous variation in oscillation frequency of the drive within each cycle imposes funhyphenminus damental constraints that prevent the complete balhyphenminus ancing of dynamic loads within the vibrating parts of the continuoushyphenminuscasting machine. Thus, in switching newhyphenminusgeneration molds of conhyphenminus tinuoushyphenminuscasting machines to effective nonharmonic operation, it is important to develop an optimalhyphenminus design method for continuous casting such that the dynamic complications may be reconciled. At present, progress is being made in that area—in particular, thanks to introduction of special biharmonic mold vibrations. We will now focus attention on the optimal combination of effective operation and dynamic balhyphenminus ancing of the continuoushyphenminuscasting machine. STEEL IN TRANSLATION Vol. 41 No. 1 2011 IMPROVING MOLD OPERATION IN CONTINUOUShyphenminusCASTING MACHINES 43 The measures considered next facilitate the use of highly efficient nonharmonic vibration and simultaneous reduction in dynamic loads within the mold’s drive. INTERACTION OF THE CONTINUOUShyphenminusCAST BILLET WITH THE MOLD’S WALLS The interaction of the continuoushyphenminuscast billet with the mold’s walls is affected not only by the conditions of mold vibration but also by the supply of slaghyphenminusformhyphenminus ing mixture and its properties. According to current concepts, the slaghyphenminusforming mixture dissolves in the melt within the mold and mixes with the solid particles to form a coating with lubricant properties. Close to the meniscus, it acts as a viscous lubricant, and meahyphenminus surements show that viscoushyphenminusfriction forces predomihyphenminus nate in this region. These forces are proportional to the relative velocity of the frictional pair (the billet and the mold wall). On moving away from the meniscus, viscoplastic friction (viscous–dry friction) is observed; this force depends less on the relative speed of the billet and mold and begins to depend on the pressure of the billet casing at the wall. As the billet moves toward the mold exit, the proportion of viscoushyphenminusfriction forces declines, and the proportion of dryhyphenminusfriction forces increases. Specialists assert that dry friction largely acts when the billet leaves the mold; its magnitude depends on the force pressing the continuoushyphenminuscast billet against the mold wall. We may also assume that this effect is due to the maximum ferrostatic pressure on the billet casing at its exit from the mold. Thus, in model research, these experimental laws should be reproduced. Note that these processes are also accompanied by increase in thickness of the billet casing. Accordingly, the stress in the casing declines on moving toward the mold’s exit, despite the increase in frictional forces. The casing usually breaks down in the meniscus region, especially on account of the increase in stress due to the unfavorable balance of the forces acting and the strength of the casing. Study of the formation of drag on the billet in the mold is important not only to develop preventive meahyphenminus sures, but also so as to reduce the extrusion forces of the blank and reduce the load in the tractional mechhyphenminus anism. This requires appropriate selection of the comhyphenminus position of the slaghyphenminusforming mixture, its delivery conhyphenminus ditions, and the rocking parameters of the mold. In addition, it is important to formulate rocking condihyphenminus tions corresponding to sufficient lubricant supply, specified billet motion, and reduced frictional forces. The interaction of the billet with the mold walls depends primarily on their relative speed, which deterhyphenminus mines the viscous–dry frictional forces. When their relative speed is reversed, the direction of action of the frictional forces changes. The efficiency of mold operhyphenminus ation is characterized by the ratio of the times of mold operation in the same direction as the billet and the opposite direction. For mold motion in the same direction at a speed exceeding the extrusion rate, the mold walls outpace the billet, and the frictional force between them becomes a motive force, with correhyphenminus sponding decrease in mean drag forces over the cycle. According to the available data, the compressive stress in the casing is associated with 20–30% decrease in the defects arising at the billet surface in the case of opposite motion of the mold and billet, when tensile forces act in the billet casing. With increase in the ratio between the times of mold operation in the same direction as the billet (positive motion) and the oppohyphenminus site direction (negative motion), mold rocking becomes more effective, in technological terms. Analhyphenminus ysis shows the high efficiency of asymmetric rocking in newhyphenminusgeneration molds, especially when viscous drag predominates. Thus, with sufficiently asymmetric vibration, the speed may be significantly higher in the positive part of the cycle than in the negative part. The mean drag over the cycle also changes on account of mold rocking. The available data indicate relatively effihyphenminus cient mold operation in asymmetric conditions, in terms of reduced mean drag (predominantly viscous drag, with a modest dryhyphenminusfriction component) on the bilhyphenminus let as it travels through the mold. Because of the greater efficiency with viscous drag, it is expedient to organize reliable lubrication in asymmetric vibration. Note that asymmetric conditions tend to increase the lubricant supply. In correctly selected conditions, the newhyphenminusgenerhyphenminus ation molds more effectively reduce the mean drag on the billet in comparison with traditional molds. To assess the effectiveness of the rocking condihyphenminus tions—in particular, to determine the stress in the bilhyphenminus let casing and the lubricant supply—phenomenologihyphenminus cal inertial elastoviscoplastic models and correspondhyphenminus ing systems of nonlinear differential equations have been developed. The methods used in developing the models were outlined in [4–12]. These models may be used to select optimal rocking conditions—in terms of minimal internal stress of the billet casing—without impairment of the system’s dynamic properties. On that basis, there is a real possibility of selecting nonhyphenminus harmonic rocking conditions while reducing the dynamic loads on the drives of the continuoushyphenminuscasting machine. Note that it is impossible to eliminate dynamic loads in the drives of the continuoushyphenminuscasting machine with asymmetric polyharmonic operation, because there is only a single operating frequency, whereas the asymmetric rocking of the mold is polyharmonic; within a single cycle, the drive frequency varies conhyphenminus tinuously, while the eigenfrequency of the existing mold systems is constant. At present, a possible approach to efficient rocking of the mold and reduction in the dynamic loads on the drive is to develop special biharmonic mold vibrations. As shown by computer experiments, this approach is relatively effective, both in technological terms and in 44 STEEL IN TRANSLATION Vol. 41 No. 1 2011 ELANSKII, GONCHAREVICH reducing the dynamic loads in the continuoushyphenminuscasting machine. In Figs. 1 and 2, we compare some charachyphenminus teristics of continuous casting for the proposed and traditional methods. In Fig. 1, we show the stress in the billet casing: (a) force due to dry friction; (b) force due to viscous friction; (c) total viscoplastic forces on the billet casing. In Fig. 2, we show the uncompenhyphenminus sated dynamic loads in the drive due to mold rocking with a hingedhyphenminuslever suspension and the load compenhyphenminus sated by the recovery forces of the elastic spring sushyphenminus pension in biharmonic oscillation. NONTRADITIONAL ROCKING OF THE MOLD To ensure high billet quality in continuous casting, two basic methods are employed: casting through a rocking mold; and mild billet reduction on leaving the mold. In these processes, a reduction cell is used together with the mold. In the present section, we conhyphenminus sider the possibility of initial billet reduction within the mold. In other words, we analyze the feasibility and expediency of combining the initial stage of reduction with casting. We briefly review the necessary precondihyphenminus tions for such an approach. The operational efficiency of the mold is primarily determined by its rocking conditions along the billet axis. The reduction cell is pressed against the mold by transverse forces. Since rocking occurs along the billet axis, the frictional forces between the mold walls and the billet produce tension–compression stress in the billet casing. This will considerably affect the billet quality and the overall stability of the process. In longitudinal rocking, the frictional force at the mold–billet casing may only be regulated when the forces between them depend on their relative speed (that is, viscous