Microstructure and properties of laser cladding of 316L stainless steel on hydraulic support tube

In consideration of the special environmental conditions of coal equipment in mining, the seamless steel tube of hy-draulic prop made of 20^# carbon steel was taken as the substrate, and 316L stainless steel powder was used to clad the sub-strate by a fiber-coupled semiconductor laser. The microstructure of the cladding layer was determined by metalloscope. The hardness, wear resistance and corrosion resistance of the cladding layer were measured. The results show that metallurgy bind-ing interface between the cladding layer and the substrate is obtained without defects such as cracks and pores. The hardness of the cladding layer is much higher than that of the matrix, and the wear resistance and corrosion resistance are simultaneously better. According to the analysis, it is summarized that the improvement in performance of the cladding layer is closely related to the change of microstructure and the thermal effect in the cladding process. The maximum hardness occurs in the equiaxed zone, and with the grain coarsening, the hardness reduces simultaneously. In addition, the precipitated phase, hard particles and trace elements also have a great influence on the properties of the cladding layer, and they will prevent the surface from ab-rasion and reduce the plastic deformation of the matrix. It is verified that the 316L stainless steel is suitable for the 20^# steel in laser cladding repairing process. Since this study focused on coal machine equipment parts, it has certain practical significance for the repair of hydraulic equipment.

Dynamic impact experiment and response characteristics analysis for 1:2 reduced-scale model of hydraulic support

It is significant to research the impact resistance properties of hydraulic support due to its key support role in the fully mechanized mining face.However,it is difficult for the entire hydraulic support to implement the impact experiment underground and analyze the response characteristic.Therefore,a dynamic impact experiment for the entire hydraulic support was proposed in this paper,where a 1:2 reducedscale model of hydraulic support was designed and its response characteristics under dynamic impact load were analyzed.Firstly,a comprehensive monitoring scheme was proposed to achieve an effective monitoring for dynamic response of hydraulic support.Secondly,a multi-scale impact experiment was carried out for the entire hydraulic support and dynamic behaviors of hydraulic support under the multi-scale impact load were revealed by experimental data.Then a dynamic impact experiment of the entire hydraulic support was simulated in ADAMS with the same experiment conditions,and the experimental and simulation data were verified mutually.Finally,the characteristics of energy conversion and dissipation of the entire experiment system after impact were analyzed.The experiment results showed that the impact resistance properties of hydraulic support largely depended on the initial support conditions and different vertical rigidities affected energy distribution proportion of the entire support system.

Horizontal roof gap of backfill hydraulic support

For the backfill hydraulic support as the key equipment for achieving integration of backfilling and coal mining simultaneously in the practical process, its characteristics will directly influence the backfill body's compression ratio. Horizontal roof gap, as a key parameter of backfilling characteristics, may impact the backfilling effect from the aspects of control of roof subsidence in advance, support stress, backfilling process and the support design. Firstly, the reason why horizontal roof gap exists was analyzed and its definition, causes and connotation were introduced, then adopting the Pro/E 3D simulation software, three typical 3D entity models of backfill hydraulic supports were built, based on the influence of horizontal roof gap on backfilling effect, and influence rules of four factors, i.e. support height, suspension height, suspension angle and tamping angle, were emphatically analyzed on horizontal roof gap. The results indicate that, the four factors all have significant impacts on horizontal roof gap, but show differences in influence trend and degree, showing negative linear correlation, positive linear correlation, positive semi-parabolic correlation and negative semi-parabolic correlation, respectively. Four legs type is the most adaptive to the four factors, while six legs(II) type has the poorest adaptability, and the horizontal roof gap is small under large support height, small suspension height, small suspension angle and large tamping angle situation. By means of optimizing structure components and their positional relation and suspension height of backfill scrape conveyor in the process of support design and through controlling working face deployment, roof subsidence in advance, mining height and backfilling during engineering application, the horizontal roof gap is optimized. The research results can be served as theoretical basis for support design and guidance for backfill support to have better performance in backfilling.

Nonlinear Static and Dynamic Stiffness Characteristics of Support Hydraulic System of TBM

Full-face hard rock tunnel boring machines(TBM)are essential equipment in highway and railway tunnel engineering construction.During the tunneling process,TBM have serious vibrations,which can damage some of its key components.The support system,an important part of TBM,is one path through which vibrational energy from the cutter head is transmitted.To reduce the vibration of support systems of TBM during the excavation process,based on the structural features of the support hydraulic system,a nonlinear dynamical model of support hydraulic systems of TBM is established.The influences of the component structure parameters and operating conditions parameters on the stiffness characteristics of the support hydraulic system are analyzed.The analysis results indicate that the static stiffness of the support hydraulic system consists of an increase stage,stable stage and decrease stage.The static stiffness value increases with an increase in the clearances.The pre-compression length of the spring in the relief valve a ects the range of the stable stage of the static stiffness,and it does not a ect the static stiffness value.The dynamic stiffness of the support hydraulic system consists of a U-shape and reverse U-shape.The bottom value of the U-shape increases with the amplitude and frequency of the external force acting on the cylinder body,however,the top value of the reverse U-shape remains constant.This study instructs how to design the support hydraulic system of TBM.

VIRTUAL DESIGN OF A NEW TYPE OF HYDRAULIC SUPPORT

Using virtual reality to design a new type of hydraulic support is discussed.That is how to make use of the virtual design to develop coal mining machine in practice. Theadvantages of virtual design are studied and the simple virtual reality system is built. The 3Dparts and elements of hydraulic support are modeled with parametric design in CAD software, thenexported to VR environment, in which the virtual hydraulic support is assembled, operated andtested. With the method, the errors and faults of design can be fined easily, many improvements aremade and the new hydraulic support is developed successfully.

Mechanisms and Kinematics of Hydraulic Support for Top-Coal Caving

The structure and characteristic of new type of hydraulic support for top coal caving were discussed. The mechanism and kinematics of the hydraulic support were analyzed. The formulas were deduced to calculate the velocity and acceleration of top beam, shield beam, front and back legs, which give the solution to the design and research for hydraulic support.

Anchoring mechanism and application of hydraulic expansion bolts used in soft rock roadway floor heave control

Comparing with the resin bolt, the hydraulic expansion bolt has different anchoring mechanism and application advantage. According to the working mechanism of the hydraulic expansion bolt, its anchoring force is expressed in four forms including support anchoring force, tension anchoring force, expansion anchoring force and tangent anchoring force, and their values can be obtained on the basis of each calculation formula. Among them, the expansion anchoring force, which is the unique anchoring force of the hydraulic expansion bolt, can provide confining pressure to increase the strength of rock. Aiming at solving the problem of stability control in the soft rock roadway in Jinbaotun Coal Mine which has a double layer of 40 U-type sheds and cannot provide enough resistance support to control floor heave, the study reveals the mechanism of floor heave in the soft rock roadway, and designs the reasonable support parameters of the hydraulic expansion bolts. The observed results of floor convergence indicate that the hydraulic expansion bolts can prevent the development and flow of the plastic zone in the floor rock to control floor heave. Research results enrich the control technology in the soft rock roadway.

Optimization of Molten Salt Cleaning Process for Surface Roughness of Remanufactured 27SiMn Hydraulic Support Column

During molten salt cleaning of remanufactured 27SiMn hydraulic support column,oxidation occurs on the surface of metal substrate.This results in a change of the surface roughness of metal substrate after cleaning,which affects subsequent remanufacturing process.To decrease the effect is very important.This paper analyzed the oxidation mechanism of molten salt cleaning,explored the oxidation reaction that occurred during cleaning,and determined the key process parameters of cleaning that affecting oxidation reaction.By using central composite experimental design method and taking surface roughness variation of 27SiMn steel samples before and after molten salt cleaning as response variable to optimize the key process parameters,the optimal parameters of molten salt for cleaning remanufactured 27SiMn hydraulic support column could be obtained.The results show that the oxidation reaction of cleaning paint dirt can protect metal substrate from oxidation to a certain extent,and cleaning temperature and placement depth of metal substrate have a direct impact on the degree of oxidation reaction.When the cleaning temperature is 300℃and the distance between paint dirt and free surface of molten salt is 0.5 times the height of the parts,the surface roughness variation is minimal.Therefore,the cleaning quality will be improved under such parameters.

STUDY OF A FAULT DIAGNOSIS EXPERT SYSTEM FOR SYNTHETIC MINING SYSTEM HYDRAULIC SUPPORT

Fault diagnosis expert system for hydraulic support is studied.The system is achieved by Turbo prolong Language, it summaries the experience of the domain expert and sets up a fault tree, knowledge base is developed by a productive rule.According to the feature of diagnosis, the system selects forward non determination inferring and limited depth first search strategy.It can accomplish expert diagnosis of more than 50 kinds faults in hydraulic support.

Surrounding rock control theory and longwall mining technology innovation

To accommodate surrounding rock structure stability control problem in underground mining, we study the coupling effect principle between hydraulic support and surrounding rock, and develop a series of longwall mining technology and equipment, which solves four common technical problems that significantly undermine coal mining safety, efficiency, and high recovery and extraction rates. Based on the coupling characteristic between mining-induced stress field and supporting stress field of hydraulic support, we identify six controllable factors in the application of hydraulic support to surrounding rock, and further reveal the relationship between hydraulic support and surrounding rock in terms of the strength, the stiffness, and the stability coupling. Our findings provide a plausible solution to the longwall mining technical problem with 6-8 m mining height. By analyzing the dynamic disequilibrium characteristics between hydraulic support and surrounding rock, we propose the intelligent top coal caving control method and the high-coal-recovery-rate tech- nology for fully mechanized caving faces. With the invention of this technology, China is likely to lead the world in terms of the fully mechanized top coal caving mining technology. We are also the first to employ the intelligent coupling technology between hydraulic support and surrounding rock, and automated mining mode, and supporting system coop- erative control with automatic organization. We develop the comprehensive multi-index intelligence adjusting height decision-making mechanism and three-dimensional navigation automatic adjusting straightness technology based on shearer cutting height memory association, cutting power parameters, vibration, and video information, leading to the first set of intelligent longwall mining technology and equipment for thin seam. Our innovation makes a solid contribution to the revolution of intelligence mining technology. With the innovative use of three-dimensional coupling control principle for surrounding rock, we successfully resolve the technological difficulties of longwall mining equipment and surrounding rock control for steep dipping seam, making a breakthrough of longwall mining technology with steep dipping seam.

New development of sets equipment technologies for coal mine longwall face in China

Background of the development and achievement on sets equipment technologies for coal mine longwall face in China was reviewed initially. On the theoretical side, a coupling model of hydraulic support and surrounding rock, support pa- rameters optimization and threedimensional （3D） dynamic design method were presented. On the practical side, this paper out lined some of practical issues and discussed some relative methods and technologies. In thin seam coal longwall mining, how to lower equipment height is the first problem that should be solved. Roof pressure regularity, control of rooffall and collapse, and hydraulic support stability were investigated preferentially in 5-7 m coal seam longwall mining. The application of equip- ment for longwall mining with 5-7 m cutting height in China was concluded. The characteristics of full-mechanized top coal caving for extra thick seam coal were presented. The automation of top-caving hydraulic support and relevant equipment have achieved important breakthrough. At the end of this paper, further development of China＇s coal industry and longwall mining technologies and equipment were prospected in brief. This paper gives readers a comprehensive understanding of China＇s coal mine longwall face equipment technologies. It will give help to other countries on its coal mining development.

Control strategy for multi-pump emulsion power station in coal mine face

Shearer and hydraulic support are matching equipments. To increase the operating speed of the shearer, the following speed of hydraulic support must be increased. This means increasing the volume of flow from emulsion power station. Analyzing the operating characteristics of hydraulic supports, the number of simultaneously operating supports is obtained by means of pressure parameter and time history at a certain time, which is a theory base for development of control system to multi-pump emulsion power station.

Virtual straightening of scraper conveyor based on the position and attitude solution of industrial robot model

The movement of the floating connecting mechanism between a hydraulic support and scraper conveyor is space movement;thus,when the hydraulic support pushes the scraper conveyor,there is an error between the actual distance of the scraper conveyor and the theoretical moving distance.As a result,the scraper conveyor cannot obtain the straightness requirement.Therefore,the movement law of the floating connecting mechanism between the hydraulic support and scraper conveyor is analyzed and programmed into the Unity3D to realize accurate pushing of the scraper conveyor via hydraulic support.The Coal Seam?Equipment Joint Virtual Straightening System is established,and a straightening method based on the motion law of a floating connection is proposed as the default method of the system.In addition,a straightening simulation of the scraper conveyor was performed on a complex coal seam floor,the results demonstrate that the average straightening error of the scraper conveyor is within 2-8 mm,and is in direct proportion to the fluctuation of the coal seam floor in the strike of the seam with high accuracy,the straightness of scraper conveyor is more affected by the subsidence terrain during straightening than by the bulge terrain.And some conclusions are verified by experiment.Based on the verification of the relevant conclusions,a comparison and analysis of Longwall Automation Steering Committee(LASC)straightening technology and default straightening method in the simulation system shows that the straightness accuracy of LASC straightening technology under complex floor conditions is slightly less than that of the default straightening method in the proposed system.

Development of 30Cr06A,a high strength cast steel and its welding ability

High performance hydraulic supports have a high requirement in strength,toughness and welding ability of socket mate- rial.Targeting this problem,we analyzed the properties of the high strength socket material 30Cr06,used in high performance hy- draulic supports both at home and abroad and developed a new kind of high strength cast steel 30Cr06A,by making use of an or- thogonal experiment,which provided the design conditions for its optimal composition.The result shows that the strength and toughness of the newly developed high strength cast steel 30Cr06A is much better than that of 30Cr06.Theoretical calculations,mechanical property tests and hardness distribution tests of welded joints were carried out for a study of the welding ability of the new material,which is proved to be very good.Therefore,this 30Cr06A material has been successfully used in the socket of high performance hydraulic support.

Longwall face roof disaster prediction algorithm based on data model driving

Hydraulic support is the primary equipment used for surrounding rock control at fully mechanized mining faces.The load,location,and attitude of the hydraulic support are important sets of basis data to predict roof disasters.This paper summarized and analyzed the status of coal mine safety accidents and the primary influencing factors of roof disasters.This work also proposed monitoring characteristic parameters of roof disasters based on support posture-load changes,such as the support location and support posture.The data feature decomposition method of the additive model was used with the monitoring load data of the hydraulic support in the Yanghuopan coal mine to effectively extract the trend,cycle period,and residuals,which provided the period weighting characteristics of the longwall face.The autoregressive,long-short term memory,and support vector regression algorithms were used to model and analyze the monitoring data to realize single-point predictions.The seasonal autoregressive integrated moving average(SARIMA)and autoregressive integrated moving average(ARIMA)models were adopted to predict the support cycle load of the hydraulic support.The SARIMA model is shown to be better than the ARIMA model for load predictions in one support cycle,but the prediction effect of these two algorithms over a fracture cycle is poor.Therefore,we proposed a hydraulic support load prediction method based on multiple data cutting and a hydraulic support load template library.The constructed technical framework of the roof disaster intelligent prediction platform is based on this method to perform predictions and early warnings of roof disasters based on the load and posture monitoring information from the hydraulic support.

TANDEM and GMAW Twin Wire Welding of Q690 Steel Used in Hydraulic Support

Compared with using semi-automatic gas shielded arc welding, using automatic TANDEM twin wire welding and twin wire gas metal arc welding （GMAW） to weld Q690 steel, a low-alloy high-strength structural steel used in the hydraulic support in the fully-mechanized mining face, the welding speed, deposition rate, production environment and welding quality can be obviously improved. Compared with GMAW twin wire welding, a refined micro- structure in the weld and heat-affected zone （HAZ）, narrow HAZ and improved joint strength were achieved with TANDEM on Q690. Also, due to the push-pull pulsed way in TANDEM welding, the droplet transfer, distribution on heat flow and interaction between two arcs were completely different from those in GMAW twin wire system. The heat input of TANDEM is only about 76.6% of GMAW, and correspondingly, the welding speed and welding seam can be obviously improved. The complete oscillation caused by TANDEM pulsed current occurred in the welding pool, which refined the grains in the microstructure. The results show that TANDEM twin wire welding is very suitable in the welding of Q690 used in the hydraulic support.