Performance of a Nozzle to Control Bath Level Oscillations and Turbulence of the Metal-Flux Interface in Slab Molds

The characterization of the turbulent flow of liquid steel in a slab mold using a commercial nozzle was carried out through physical experiments and mathematical models. Six ultrasonic sensors were located at each side of the nozzle to obtain real-time plotting of the bath levels during the experimental time. An ultrasonic transducer located in the mold, 20 mm below the meniscus, determines the velocities and the turbulent variables along with the distance from the narrow face to the position of the nozzle’s outer wall. These data, together with the mathematical simulations, demonstrated a high correlation of bath level oscillations and the time-dependent behavior of the discharging jets. The flow inside the mold shows low-frequency non-symmetric patterns without a severe turbulent in the meniscus. The source of this instability is the partial opening of the slide valve gate used to control the mass flow of liquid.

Design of Refrigeration Control System for Parallel Refrigerator Unit Based on PLC

In order to improve the refrigeration control efficiency and reduce the temperature fluctuation in the cold storage. In this paper, the refrigeration control system of the parallel unit of the cold storage is designed based on the upper and lower computers. The lower computer uses PLC to monitor the field parameters and control the execution of the field equipment. The upper computer uses HMI to realize the real-time monitoring, parameter display and alarm function during the operation of the cold storage, and uses the slide valve to adjust the energy of the compressor. The results show that the control system runs reliably and meets the control requirements of large cold storage.

Simulation Study on the Influence of Injector Coupling Leakage on Fuel Injection

In order to study the effect of fuel leakage of an ultra-high pressure common rail injector control valve coupling on fuel injection performance, a simulation model was established by AMESim and the accuracy was verified by fuel injection test data. The leakage law of couples with different clearances was analyzed by using numerical simulation method and then the influence of control valve coupling on fuel injection performance was analyzed. The results demonstrate that the increase of the matching clearance of the slide valve coupling makes the start time of needle valve advanced and delay its end time. The injection rate and injection duration increase with the increase of the matching clearance of slide valve coupling. The increase of the matching clearance of the control plunger coupling keeps the start time of the needle valve unchanged at first, and then delay slightly, while the end time remains unchanged at first, and then show the trend of advance. The injection rate and injection duration decrease with the increase of the matching clearance of plunger coupling.

Optimization of the critical overlap length of hudraulic distributors regarding cavitation inception

The present paper is focused on the optimization of the overlap length in various types of distributors in hydraulic systems. It has been shown that this length has a strong influence on cavitation in rotating distributors, so its optimization would be beneficial to reduce the detrimental effects of cavitation, such as noise, vibrations, and instabilities. The objective of the present study is to generalize the modelling of the overlap length to different types of distributors and to determine the critical length at cavitation inception. The results show that the pressure losses in rotating distributors and in other types of distributors are similar, including the slide-valves that are the vast majority of distributors in hydraulic systems. It is confirmed that the overlap length has a stronger influence on the cavitation development than the distributor rotation speed. A critical overlap length of 0.071 mm is obtained, below which no significant development of cavitation is obtained, at all rotation speeds. Article Highlights The pressure losses in a rotating distributor and in a slide-valve can be expressed similarly. The overlap length has a large influence on the cavitation development, much larger than the rotation speed. A critical overlap length of 0.071 mm was obtained, below which there is almost no cavitation, for any rotation speed.

INVESTIGATION OF TRANSITIONAL PROCESSES IN THE ADAPTIVE SYSTEM OF HYDRAULIC DRIVES OF THE MECHANISM FOR CUTTING AND UNLOADING STALK FODDER

The problem of creating an energy-efficient and competitive mechanism for cutting and unloading stalk fodder from trench storage, by developing and justifying the parameters and modes of operation of the adaptive system of hydraulic drives of the mechanism is researched. The principal implementation of the adaptive system of hydraulic drive of the mechanism for cutting and unloading is proposed, in which a spool flow divider is placed between two executive hydraulic motors, which allows to regulate the supply of a U–shaped frame according to the load change which affects the cutting mechanism. The adaptive system of the hydraulic drive of the mechanism allows to stabilize energy consumption for separation of a portion of a stalk fodder under the condition of change and fluctuation of parameters which essentially influence the process of separation and unloading of a stalk fodder from the monolith. The transients in the adaptive systems of hydraulic drives of the mechanism for cutting and unloading of stalk fodder are received and analyzed. As a result of the study, it was found that by changing the operating widths of the slide valve of the separator in the direction of reduction, a significant increase in the responsiveness of the hydraulic drive system of the mechanism for cutting and unloading to the changes in the loading on the cutting apparatus. As a result, the range of the adjustment of the feeding of the hydraulic cylinder of the U–shaped frame, which increases the efficiency of stabilizing the separation process from the monolith of block-portion of stalk fodder with a minimum power of the hydraulic drive system, is substantially expanded. It is noted that the dynamic characteristics of the hydraulic drive of the mechanism for cutting and unloading stalk fodder adaptive to the load are influenced by the design parameters of the spool flow divider which implements feedback. On the basis of the conducted experimental research recommendations on the choice of constructive parameters of the spool flow divider are given.

Model Construction and Performance Degradation Characteristics of a Deflector Jet Pressure Servo Valve under the Condition of Oil Contamination

The deflector jet pressure servo valve is a kind of high-precision hydraulic component that can be widely used in the antiskid braking system of an aircraft. In actual service, it will be faced with extreme working conditions of gradual oil contamination, which will cause performance degradation and function maladjustment of the whole valve. To this end, the paper proposes a performance degradation characteristic analysis method. In which, firstly, the structural characteristics and working principle of the deflector jet pressure valve are analyzed; then, the entire dynamics model of the pressure valve is built using the braking cavity as the load blind cavity. Secondly, the two main failure modes induced by oil contamination such as erosion wear of pilot stage and stuck of slide valve stage’s valve core are determined based on the engineering experience, aimed at which the failure mechanism is analyzed; then, the sensitivity simulation model of the servo valve’s output pressure with respect to key degradation parameters is established and the sensitivity analysis is performed. Finally, combining the theoretical analysis with multiphysics simulation correction methods, the performance degradation model of the typical failure modes are established, and then, the performance degradation characteristics under dynamic contamination conditions are analyzed, which is combined with the failure threshold determined by the dynamics simulation to finish the service life prediction of the deflector jet servo valve.

Process Diagnosis of Liquid Steel Flow in a Slab Mold Operated with a Slide Valve

Slab molds receive liquid steel from the tundish through bifurcated submerged entry nozzles (SEN) using a slide valve as throughput control. Due to the off-centering position of the three plates’ orifices that conform to the valve to control the steel passage, the flow inside the nozzle and mold is inherently biased toward the valve opening side. In the practical casting, a biased flow induces inhomogeneous heat fluxes through the mold copper plates. The nozzle design itself is also a challenge, and has direct consequences on the quality of the product. A diagnosis of the casting process regarding the internal and external flows, performed through experimental and mathematical simulation tools, made it possible to reach concrete results. The mathematical simulations predicted the flow dynamics, and the topography and levels variations of the meniscus characterized through a full-scale water model. The flows are biased, and the meniscus level fluctuations indicated that the current nozzle is not reliable to cast at the two extremes of the casting speeds of 0.9 m/min and 1.65 m/min, due to the danger of mold flux entrainment. A redesign of the nozzle is recommended, based on the experimental and mathematical results presented here.

A 4/3-Way Flat Slide Valve With a Metallic Main Stage

Most proportional directional control valves currently in practical use are piston spool valves. A disadvantage of this type of design is the occurring leakage between spool and sleeve or housing. A second disadvantage is that the service life is limited by wear on the control edges. The ceramic flat slide valve is a promising concept, which allows to reduce the mentioned leakage and to increase service life. In contrast to piston spool valves, the main stage of the flat slide valve consists of three plates. Two control plates and a movable slide plate, which is located in between. An external force is applied to the plates by the so-called pressure compensation, which presses the plates together and thus counteracts a gap expansion and thereby an effective reduction of occurring leakage is accomplished. The plate-by-plate design of the main stage allows the use of technical ceramics, which are more resistance to abrasive wear and can thereby extend the service life of valves. A challenge in the realization of the flat slide valve is the design of the pressure compensation. If the force applied by the pressure compensation is not sufficient to prevent a gap formation between the plates, an increased leakage will occur, which results in a reduction of efficiency. In case the applied force is too high due to the pressure compensation, high frictional forces between the plates occur and an adjustment of the slide plate position through an actuator is no longer possible. Therefore, the design of the pressure compensation is essential for the success of the concept. This contribution presents the results of testing a main stage, which consists out of two metallic control plates and a slide plate made of special brass. The main stage is designed in such a way that a 4/3-way directional control valve with a proportional characteristic can be realized, as it is also achieved by valves currently available on the market. Therefore, in addition to the pressure forces, further influences on the resulting force of the pressure compensation were determined and their influence was estimated based on test bench results. With a program written in MATLAB, the forces prevailing in the valve can be calculated time-efficiently for different geometries and are validated with test bench trials.