GAS AND OIL POWER DISTRIBUTION RATIO OF A NEW HYDRAULIC BREAKER

CHINESE JOURNAL OF MECHANICAL ENGINEERINGGAS AND OIL POWER DISTRIBUTIONZHAO HongqiangRATIO OF A NEW HYDRAULICLI MeixiangBREAKERGAO BinHE QinghuaAbstract: The working principle of aoperated jointly by gas and hydrauliollege of Mechanical and Electricalflow which has a reasonable structure, highlife-span, is analyzed, and theoptimal power distribution ratio of the sealChangsha 410083, Chinalation, it is determined that the impact system has optimal mechanical performance and highest eciency when the distribution ratio is between 0. and 0.5. The theoretical result is also verified byrepeated testsKey words: Hydraulic breaker Power Distribution ratio Efficiency0 INTRODUCTIONcan maintain a constant high pressure and the back chamberalternates between high pressure and low pressure during the imA hydraulic breaker breaks rocks by means of kinetic energyAs shown in Fig. la, the piston has just finished impactingof an impact piston which is driven by hydraulic pressure. Com- the pickaxe and the distribution valve has already changed itstechniques, hydraulic breaking provides both economical and At this time, chamber 14 of the distribution valve connects oilking condi-tions and relieves working intensity. therefore, it has undergonerts l andⅢ,rapid development. Ever since the first hydraulic breaker in the pressure oil all the time through the oil circulation. As a result, theworld was borm, which was invented by krupp company in spool 13 is pushed to the left position, and the pressure oil entersGermany in the late 1950, and was first used in constructionengineering. In the 1970s, it began to be used in mining industry chamber 5 connects the oil through port IV, chamber ll andne secondary breaking. Compared with the traditional chamber 10. Therefore, impact piston I starts its retun strokeof bareness demolition and drilling demolition, thebreaker gives incomparable advantages. At the same time, chamber(Fig 1b), and the nitrogen chamber 6 is compressed. Thebecause of its characteristics, such as low energy consumption, oil accumulator 15 begins to store oil. Along with the returnngand operational convenience, whicity of nitrothe existing pneumatic breaker can not even match, it is highly continuously, which means the pressure in nitrogen chamber 6evaluated by the mining industries. Hence it is applied broadly in increases, alongside system pressure p also increases accordinglymetallurgy, coal, traffic and construction operations dWhen the pressure reaches a value that pressure control valve 16with the rapid development of modem industry, the old hy. can be opened( Fig. Ic), the high pressure oil enters pushing valvedraulic breaker is considered to be too complicated to be sufficient chamber 14 through control valve 16. Because the action area ofand efficient, In order to get over these problems, we aim to de- chamber 14 is larger than that of chamber 8, the spool 13 movesvelop a new hydraulic breaker, which is not only of simple struc- more quicker towards to the right under the action of the differen-ture but also of high efficiencytial pressure, which leads to connection of chamber 11 and cham-ber 12. As a result, both the front and back chambers of the piston1 PRINCIPLE OF NEW HYDRAULIC BREAKER connecting the high-pressure oil forms a differential connection.Then the impact piston stops accelerating and the system enters tothough there are many types of hydraulic breakers of dif. the stroke state( Fig. ld). Due to the influence of the differentialferent designs, all of them have a commonforce of the pressure oil and the influence of the expansion ofruns into the front chamber to drive the piston. While the accu- the final period of acceleration, more oil is needed as the pistonamong those hydraulic breakers are the methods of accomplishing (Fig. le), the high-pressure accumulator discharges pressure oil tohe stroke and the way of distributing5.The newthe back chamber. When end surface B of the impact pistonbreaker discards the traditional principle of stroke feedback con- crosses feedback signal hole I (Fig. 1f), which has the ability totrol and adopts a new concept of pressure feedback control. By change the direction of the stroke, pushing valve chamber 14this, impact energy and oil flow can be controlled independently connecting oil tank through ports I and Ill. At the same time,with stepless adjustment. It also means the performance parame- control pressure cone valve 16 is closed. The spool rapidly movesters of the hydraulic breaker can be controlled accordinglyto the left under the action of high pressure. The stroke finishesyhen piston I strikes pickaxe 17. Then, the breaker returns to the1. Operation principleongThe operation principle is shown in Fig. 1. The distribu凵中国煤化工mcmbtion valve is a cone valve which adopts the optimal technique found thof unequal opening size of the valve port. The front chamber pressureCNMH GIs the impact systemof the control pressure P, will cause the control pressure of thecone valve to change accordingly. Therefore, the impact energy ofation of China the hydraulic breaker can also be changed. The impact energyJuly 5, 2007; accepted July 17, 2007becomes high when the pressure is high, and vice versaCHINESE JOURNAL OF MECHANICAL ENGINEERINGf甲齒谜(a)Beginning state of a retum stroke)Acceleration of a returm stroke直(c)Control pressure cone valve opens(d)Beginning state of a stroke(e) Acceleration of a stroke(f Control pressure(Operation principle of the new hydraulic bre1. Impact piston 2 Front chamber of the impact piston 3. Middle chamber of the impact piston 4 Cylinder5. Back chamber of the impact piston 6. Nitrogen chamber 7. Return oil accumulator8. Back chamber of the distribution valve 9. Valve body 10. Low pressure ch11. Variety pressure chamber of the distribution valve 12. High pressure chamber of the distribution valve13. Control pressure cone valve 14. Push valve chamber of the di中国煤化工emulator16 Control pressure cone valve 17. Pickaxe PrCO--Retum oil A, B, C-Surfaces of the impactCNMHGThe flow rate of the pump governs the impact frequency when the flow rate is low, it decreases. So both impact energy andwhich can also be adjusted steplessly. That is to say, when the frequency can be adjusted either simultaneously or separateflow rate is higb, the impact frequency increases, On the contrary, Therefore the impact frequency can be adjusted to be very lowZHAO Hongqiang, et al: Gas and oil power distribution ratio of a new hydraulic breakerlevel and the impact energy to be very high. In this way, we can nitrogen can be considered as an insulation process. According tomake full use of the engine load capacity to adapt it to various the equation of the gas state, we obtainworking conditionsOn the other hand, if Pr is adjusted too high, the systempressure can not reach the value to open pressure control conePNvalve 16. The piston will continue its retum stroke until end surface A crosses signal hole l. On this occasion, the pressure oil where n is the polytropic index,n=1.4will flow into pushing valve chamber 14 through front chamber 2Then Eq. 4)can beand ports I and I. Then, the spool immediately moves right tochange the direction of the return stroke. When the high-pressured(A,y)oil enters the back chamber, the return stroke of the piston decel-erates until the stroke movement begins. By this, the breakerwould not be damaged because the maximum system pressure is1 rhlimited, and the impact stroke and the impact energy are kept atsuitable values by effective controlSupposing the ratio of nitrogen work Wx to oil work W1.2 Distribution valveA new oil distribution cone valve that characterizes conesurface seal and cylindrical surface seal is adopted in the breaker.When the spool moves to limited positions and keeps static, theSupposing the resistance coefficient of piston movement is Kvalve port is sealed by the combination of the cone surface and the and the movement energy of the piston isE, WN can be expressedcylindrical surface. When the spool is in a moving state, the valveport is sealed only by the cylindrical surface. Because the spool isusually in the limited position and keeps in a static state, the valveport leakage is nearly zero. Because the flow coefficient of theool port is very large, the presoil passes through the valve port. Accordingly, the energy loss isAccording to Eqs.(1)and (2), the volume of the nitrogensmall. Furthermore, the new oil distribution valve adopts the tech-lber at impact time isnique of the optimal and unequal open area of the valve port.When the hydraulic breaker requires more flow during the pistonlarger open area. When the hydraulic breaker requires less flow From Eqs. (D),(2)and(8), the charging pressure in the niduring the piston returning period, the spool moves left where the trogen chamber isvalve port has a smaller open area. Therefore, the moving stroke(n-DX-IkpEof the spool is shortened compared with the ordinary distribution4S(-λ(+中)valve which leads to the decline of energy consumption of thespool direction changingFrom the equation of the gas state, the maximum pressure in2 GAS AND OIL WORK DISTRIBUTION RATIO2(m-1)4-DkE(11)As we know,the maximum volume of the nitrogen chamber isAS(-)(1+中)(1)In addition, in order to make the piston undergo the returnstroke successfully, the system pressure must satisfywhere V and V are the maximum and minimum actionvolumes of the nitrogen chamber cylinder(m) S is the piston(12)roke(m); and Ag is the effective action area of the nitrogenwhere A, is the effective action area of the front high-pressure oilThe ratio of the working volume of the nitrogen chamber is chamberpressureP,, the impa2) can not work. During the working process, the systemmust fulfill the following condition in order for theConsidering from the point of gas sealing, the ratbreaker to gain the required impactoperation volume of then chamber can not bewhen the gas volume is frequently changed. Generally,P2=-PNmaxs(13)able range of this ratio is A =1.3-1.5Supposing the piston displacement is y, the volume of the It means that if the system pressure is lower than Pa, the impactogen chamber at the time isFN=Nmin +Ay(3) 3 DETERMINATION OF GAS AND OIL POWERThe variation of volume is dy= A, dy. The power applied byDISTRIBUTION RATIOnitrogen on the piston isIf the gas and oil work distribution ratio is low, the charg-will be low and thePPN中国煤化工APn is the pressCNMHGstroke, the peak oilAs the hydraulic breaker works in a hightransmission between the nitrogen chamber and the surroundcrease of action area of back chamber 4, which leads tocan be neglected in a given time. Therefore, the compression of loss and system inefficiency. So the gas and oil power distributionCHINESE JOURNAL OF MECHANICAL ENGINEERINGratio f can not be too lowresult is shown in Figs. 5 and 6On the other band, if the gas and oil power distribution ratioPis too high, the charging pressure P in the nitrogen chamberwill be high and the power Wn applied by nitrogen will be largeHence the action area of the piston back chamber 4, becomessmall. With less oil flow being needed, the stored energy increasesTo determine the optimal distribution ratio a lot of simula-tion calculations and experiment tests are carried out.Giving the pump flow rate 2=120 Lmin, the control presure P=14.0 MPa, and changing the original charging pressurePNmi of the nitrogen chamber continually, the result of simulationPressure PNa/MPFig 5 Results of the impact energy E andcalculation is shown in Figs. 2, 3 and 4the impact frequency fof experiment2.5Fig 2 Results of the impact energy e ofIts of the distribution ratio g andthe efficiency nThrough the analysis of the results of simulation calculationand expcriment tests, we can obtain the following conchusions,) On the condition that the pump flow rate e and the feedback control pressure of direction alteration P are fixed, the pres-sure in the nitrogen chamber P is low when the value of issmall. In this case, the piston stroke S will be quite long. As thestroke feedback controls the direction alteration of the returnstroke, the impact system pressure can not rise to the requirvalue. In short words, the smaller the value of f, the lower the2pressure of the impact system. Consequently, the lower the impactPressure PNn MPaE(2)With the increase of the value of s, the charging pressureFig 3 Results of the impact frequency fandthe piston stroke S of simulation calculationin the nitrogen chamber increases. The system pressure also in-creases until the pressure feedback is established. As the piston07stroke S decreases, the impact frequency f becomes higher andhigher. Hence the impact system efficiency n also improves.(3)The charging pressure in the nitrogen chamber becomes◆05higher as f increases. However, the feedback controlfixed. So when the bydraulic pressure reaches the feedback con-trol pressure, it can rise no longer. without sufficient hydraulicpressure, the piston can not be driven to return. For this reason,(4)In order to achieve good breaker performance, d must bemaintained within a certain range. The pressure P in the nitrogenchamber also has an optimal range. If p is too small, it is easy toestablish stroke feedback because the system pressure is low, but theimpactbe high either. As a result, the impact en-Fig. 4 Results of the distribution ratio and中国煤化工 too large., the pressurethe efficiency n of simulation calculationin thecase, the impact systemC N MH Gthe hydraulic breaker.IfGiving the pump flow rate @=120 L/min, the control prtme maximum pressure limit of thesure P-=14.0 MPa, and changing the original charging pres- system. Therefore the adjustment range would be narrow. From theure P of the nitrogen chamber continually, the experiment analysis of the simulation and experiment results, we can draw the58·ZHAO Hongqiang, et al: Gas and oil power distribution ratio of a new hydraulic biconclusion thatt吨mthe optimal value of y is between 0.3 and 0.5, [7 ZHAO Hongqiang, YANG Xiangbi, WU Wanrong, et aL. Study on a newas the greatest impact energy e, the widestflow valve of hydraulic breaker[]. Journal of Central South Universityjustment range and highest efficiency ndraulic system of new hock breaker[J]. Rock Drilling Ma-4 CONCLUSIONShines and Pneumatic Tools, 2000, 1: 41-45.(in Chinese)[9] ZHAO Hongqiang, ZHU Jianxin, ZHOU Hongbing, et al. The test ofThe new hydraulic breaker powered jointly by gas and oimachines and Pneumatic Tools, 2000, 4: 25-29.(inoptimally designed and has the characteristics of long piston life [10] ZHAo Hongqiang. The research of aand high system efficiency. It discards the traditional principle ofwith independent and stepless adjustmentarameters[D]. Changshstroke feedback control and adopts a new principle of pressureCentral South University of Technology, 1998. ( in Chinesecontrolled independently with stepless adjustment. This means the Bograiang is curently an associate professor in College of Mechanicalto meet the needs of various working conditions. Through theo- and electnical engineering, Central Soutretical analysis, simulation calculation and experiment tests, it is degree from college of Mechanica and eCentral Southfound that the hydraulic breaker has best mechanical performance University, China, in 1998. His researcdrive and con-and highest system efficiency when is between 0.3 and 0.5cl:+86-731-4020638;E-mail:zhaohq9922@sina.comReferencesElectrical Engi ening c a nl south univent Chin gher feMecrch intend[I] GEOFF P. Hydraulic impact hammers( ). Mining Magazine, 1990, 12: include fluid drive and control, etc33-35Tel:+86-13467514053;E-mail:Lmx620620@yahoo.com.cn[2]wooF P. Hydraulic breakers[). Would Mining Equipment, 1990, 6:GAo Bin is currently a graduate candidate in College of Mechanical and Elec-B] MIKE W Breaking new ground[]. Would Mining Equipment, 1996,trical Engineering, Central South University, China. His research interestsinclude fluid drive and control etcGEOFF P Secondary breaking[]. Mining& Quarry, 1988, 7: 11-13Tel:+86-13007426782;E-mail:gboyy@163.comI WOOF P. How to analyze and compare hydraulic hammers(. MiningEquipment InternationaL, 1983, 5: 45-47chanical and electric[6] ZHAO Hongqiang, HE Qinghua, ZHU Jianxin, et al. New bydraulicCentral South University, Chinent Machinery Co, Ltd, China.caker with independently and stepless adjustment of its parameters []Construction Machinery and Equipment, 1999, 30( 8): 35-38(in Chinese) electrical engineering, etc.essure engineering mechanism, special robot, mechanical and中国煤化工CNMHG