Application of external gear pump in water-hydraulic system

Joumnal of Harbin Institute of Technology (New Series), Vol 17, No.1, 2010Application of external gear pump in water-hydraulic systemBAI Hua白桦(School of Mechatronics Engineering, Harin Insitute of Technology . Habin 150001 ,China, baihua@ hit. edu. en)Abstract: The ceramic coating technology of microare oxidation ( MAO) was utilized to modify surface proper-ties of the movable endplate of a high pressure gear pump used in water-hydraulic system, which is made of alu-minium alloy. A coMPact ceramic layer of more than 130 μm was developed on the movable endplate with thehardness up to HV1000 by means of microare oxidation. A trial of tests conducted in a water power transmissionsystem show that the maximum outlet pressure of the gear pump with the movable endplate treated by microareoxidation, can reach 16 MPa. It is pointed out that the ceramic coating developed by microarc oxidation tech-nology on the surface of aluminium alay , is economical and feasible.Key words: microarc oxidation; ceramic coating; high-pressure gear pump; waler-hydraulic systemCLC number: TG174. 45Document code: AArticle ID: 1005-9113(2010)01 _0085-04With the increasing demand for an environmental-cal characteristics.ly-friendly fluid medium in the fluid power industries ，Since ceramics have good mechanical performancerecent advances in water hydraulics technology havewith high intensity and hardness，wear -resistance, cal-sparked renewed interest in the application of water,orific performance of anti-thermal shock and dynamicinstead of oil, as the energy -transmission medium. Wa- creep， and chemical performance of corrosion-resist-ter hydraulics technology, after being tucked away forance, anti-oxidation, they are becoming more and morealmost half a century, has been taken seriously". Wa-attractive and have been increasingly finding numerouster hydraulics is a technology which uses the tap-water applications in today ' s industry. The major advantagesas working pressure medium in hydraulic systems in-of using ceramics as friction pairs of water hydraulicsstead of mineral oil with the advantage of no pollution,components are among: (1 ) good performance of hard-hygienic，nonflammable, nontoxic, readily available ，ness , intensity and wear-resistance; (2) good tribolog-and cost-effective. At present, more and more reical performance of anti-adhesion， i. e. tribologicalsearchers are interested in modem water-hydraulics.pairs made of either ceramics/ ceramics, or ceramics/However, since the basic physicochemical charac-polymers, or ceramics/ metal，they exhibit excellentteristics of pure waler is quite different from the mineralperformance under abrasion and sliding wear modes;oil, water hydraulics system has the disadvantage ol(3) good performance of anti-cavitation, the ceramicssever errosion, high leakage, high friction and wealwith high hardness can resist cavitation formed by waterrate, cavitation, water hammer and heavy contamina-vapour and dissolved gases such as oxygen, chlorinetion on the water hydraulic components and system,and the others, and erosion formed by acoustic stream-etc, it is very difficult to develop the water hydraulicsing; (4) good performance of stability. Ceramic is ofcomponentsIn recent years, with the developmentssteady-state, it hardly has any measure transmutationof materials and machining technology, it is possible tounder the condition of high temperature. High assemblyproduce water hydraulics components which are madeprecision, closer tolerance on fit, and better surfaceof lubrication-free , anticorrosive materials to reduce in-performance of ceramic component can effectively re-temal leakage due to the low viscosity of water. To aduce leakage，improve the eficiency and prolong serv-void the pure water' s features of low viscousity, highice life.leakage, poor lubrication and erosion, components inHowever, the application of ceramic to water hy-water hydraulics should be made of corrosion-resistantdraulic components was limited by the ceramic manu-materials such as stainless steel, special bronze, sur- facturing process. The main influencing factor is thatface treated aluminum, polymers, and ceramics. Athe ceramic' s shaping and machining quality are poor.present, the typical approach is to select the new mate-中国煤化工luced by makingrials for water bydraulic components with good tribologi- mould_high temperature,YHCNMHGReceived 2008 -05 - 23.Sponsored by the National Natural Science Foundation of China( Grant No. 60772077).●85●Journal of Harbin Institute of Technology (New Series)， Vol. 17, No. 1, 2010and then followed by mechanical machinings, so it isFig.1. The basic parameters of the pump include:hard to produce components with complex shape. Duemodule of gear (m) is 3; tooth number (Z) is 11;to ceramic' s hard and brittle feature, it is hard tonormal rated pressure is 16 MPa; pump output floe ratemanufacture such components by the usual mechanicalis 16 mL/r. Toothed gear and shaft are made ofprocessing equipment, and thus increases the manufac-20CrMnTi，clearance fit of H7/g6 betweenshaftture cost, its application is limited 21 .and bearing is chosen. Central distance of two toothedOn the basis of analyzing the tribological charac-gearisL = 33 +0.015 mm.teristics of ceramics in water surroundings, and sum-ming叩the special requirements for water hydraulicshousincomponents，a new ceramic coating technologyMAO ( Microarc oxidation) was chosen to modify thetoothedsurface properties of the movable endplate of high pres-gear. pumpsure gear pump which is made of aluminium( AI) al-casingloy. And the performance of the treated gear pump hasbeen tested.Movableendplate1 Experimental Details1.1 MAO TechnologyFig. 1 Configuration of the tested high-pressure gear pumpMicroare oxidation commonly called“plasma elec-trolytic oxidation ( PEO)”，“ microplasma oxidationADCI2 Al alloy with a nominal composition of( MPO)”and “anodic spark deposition ( ASD)”in9.6%一12% Si，1.5% 一3.5% Cu, 0.3% Mgmodern scientific literatures, is a relatively new surface0.5% Mn,0.5% Ni, 1.3%Fe, 1%Zn was used as themodification technique, and is attracting increasing in-substrate for the coatings.terests in fabricating ceramics--like coating on Al al-A MAO coating processing unit consists of a spe-loys, with the purpose of providing corrosion- andcially designed electrical controller， which is sub-wear- -resistance or various functional properties. Thismerged in the electrolyte of alkal-silicate solution. Intechnique is characterized as economy and efficiency,order to obtain coatings with optimum surface morphol-friendly ecology and high productivity.ogy, a step-by-step increment of adjustment regime inMAO is based on the conventional anodic oxida-positive pulse current is applied. The electrolyte istion of metals and alloys in aqueous electrolyte solu-cooled by a cooling system to keep its temperature be-tions under the conditions of plasma discharge at thelow 50 9C.exceeding critical values of the polarization potential ,The thickness of the coating is measured using anand the fact that discharge leading to localized higheddy-current coating-thicknessmeasurement gauge ,temperature and high pressure, which allows formingsurface roughness is measured by a Surtronic surfacecoatings composed of not only predominant substrateroughness tester ( RANK Taylor Hobson , England ).oxides but also the more complex oxides containingSEM( Scanning Electron Microscopy) is employed tocompounds which involve the components presented inanalyse the coating surface microstructure characteris-the electrolyte. So this technique can produce hard,tics. On the coated sample surfaces , the coating thick-thick ceramic oxide coatings on different style of Al al-ness and surface roughness are measured at 10 differentloysl3].randomly selected locations and the average value isAt present, Al aloys have become a kind of im-calculated.portant engineering structure materials due to their highspecifec strengthl4) ，and almost all component parts of2 Analyses and Resultshigh pressure gear pump， such as pump housing,pump cover, are made up of Al alloys, except their2.1 Characteristics of Coatingsshafts and bearings. So we can utilize MAO techniqueThe average roughness of MAO coatings was 4. 8to modify the surface performance of component part of+0.4 μm and the average coating thickness measurednormal gear pump, and carry out the performance testwas 130 μm. The structure rough increase with coatingin a water hydraulics system.thickness. The microhardness gradient exists along the1.2 MAO Coating Procedurecoati中国煤化工hardness was 1790In this study, a high-pressure gear pump made upbelow the sutfaceof ADC12 Al alloy was chosen. The construction of theandYHCN M H Gf the coaing. Thetested gear pump ( model CBT-E316， Shanghaisalt spray test result shows that the corrosion-resistantDazhong Hydraulics Component Co. ) is shown inproperty of MAO coating increases with its thickness ,，86●Joumal of Harbin Instiute of Technology (New Series)，Vol. 17, No. 1, 2010and the erosion resisting level could reach 10° whenefficiency is minimum when system pressure at 17 MPathe coating thickness is more than 80 μm.and then exhibits a trend to increase with the decreaseSEM micrographs of MAO coatings exhibit a uni-of system pressure. The variation range is from 56% toform coating thickness with a clean wavy interface, and83%.the coating appears to be well bonded with the sub-strate. However, two distinct regions, the inner densi-fied region with defect-free microstructure and the outerthrotlevalvegranular region were exhibited. Consequently, undererosion conditions, abrasive and sliding wear volumeon inner area was limited.Only the movable endplate was treated by MAO, A.C motortechnology. Fig. 2 is the photo of movable endplatetreated by MAO procedure.gear pumpceramiePoatinecoatingADC12.substrateFig.3 Setup and result of hydraulic pressure testFig.2 The photo of movable endplate treated by MAOtechnology迟802.2 Performance Test喜60The performance of the gear pump with ceramiccomposite coating formed by MAO technology was test-40十ed in a water hydraulics system. Fig. 3 shows the setup言2of the hydraulic pressure test rig. It includes a holdingtank, a gear pump, and control valves ( a throttle valve101520and a overlow valve). The control valves are providedTest pressure P/MPato control the system pressure. When shut off the throt-tle valve, and gradually open the overflow valve ( mod-Fig.4 Variation of volume eficiecy with the system pres-el YF-B10H, Shanghai)，the system pressure increa-sureses, and gradually reaches to the maximum value with3 Conclusionsthe overflow valve completely open. The pressure valuewas read from a pressure gauge ( Red sun, Tianjin).1) At present, Al alloys have become one of im-The range of pressure gauge ( Red sun, Tianjin)is 25portant materials for high pressure gear pumps due toMPa. The energy-transmission medium is raw water,their high specific strength, and almost all componentand its temperature is 12. 5 C. The volume efficiencyparts, such as pump housing, cover, movable end-of the gear pump was tested by a volumetric method.plate, are all made of Al alloys. MAO is a practicalThe setup and the result of hydraulic pressure test aremethod to modify the component parts surface performn-shown in Fig. 3.From the pressure gauge, the maximum systemance of normal gear pump as well as high-pressurepressure is 17 MPa when overflow valve was openedpum中国煤化工1-1. It has the advan-tages suitable for batchcompletely. , and the high-pressure water-hydraulic sys-tatem was working stable. Fig. 4 illustrates the variationprocYHC N M H Gasible manufactureof the volume eficiency of the gear pump with the in-process to make normal gear pump suitable for water-crease of system pressure. It is evident that the volumehydraulic component with better accuracy and mechani-●87.Joumal of Harbin Instiute of Technology (New Series), Vol. 17. No. 1, 2010cal performance, under the situation that the currentlateral clearance could be eliminated by using dis-components made of complete ceramics are not maturecharge pressure to hold movable endplates against thein water power transmission. This technology has re-gear faces while the pump is running, more effortceived a patent( ZL 2004 2006 3533. 6).should be taken to get higher volume efficiency, such2) The test results showed that volume fficencyas reducing the fit clearance in radial between the mov-of the tested gear pump is relatively low with contrast toable endplate and the pump housing by means of im-the condition of using oil as working medium. Theproving machining precision and fit quality of workingmain reason is that slip varies strongly with differentialpairs.pressure and viscosity. Slip is the difference between3) Test showed that DU bearing can be adapted tohe theoretical flow and actual flow, assuming thatwater mediumn, but it is easier to be worn out contrastthere is no cavitation. Three paths are common to allto the condition of working in oil medium. Test data in-gear pumps: between the ends of the gears and thdicate that the adaption of DU bearing to pure waterendplates ( known as lateral clearance), between themedium is unsuitable because the inner sprayed poly-tips of the gear teeth and the inside of the casingflon coating began to spall and copper substrate( known as radial clearance) , and between the proflesposed after working for 30 hours. So it is a key prob-of the meshing teeth. Slip is directly proportional tolem to be solved in the future.differential pressure, and it varies inversely, but notReferences:proportional, with viscosity. Slip varies asymptoticallywith viscosity, approaching zero slip at high viscosi-[1] Lim G H, Chua P S K, He Y B. Modem water hydrau-ties. This means that at low viscosities, small changesics-- the new energy transnission technology in nuidcan mean large differences in slip. There is also apower. Applied Energy , 2003, 76 :239 - 246.strong relationship between clearances and slip. Slip,[2] Tang Qunguo, Li Zhuangyun, Zhang Tichua. Applicationand invinvestigation of engineering ceramics in water powerthrough a particular clearance, varies directly with thecomponents. China Mechanical Engineering, 2003, 8: 717cube of that clearance. This means that if you double- 720.the lateral clearance, you will get eight times as much[3] Rama K L, Sornaraju K R C, Sundararaj G. The tribologi-slip through that clearance. Usually, Water viscosity is:al performance of ultra-hard ceramic composite coatingsonly 1/20 - 1/30 that of hydraulic mineral oil. Thatoblained through microarc oxidation. Surface and Coatingsmeans at the same clearance , much slip is caused con-[4] Wu Min, Sun Yong. Development of surface treatment forTechnology, 2003, 163 - 164 :484 - 490.trast to using oil as power transmission medium. So inaluminum and it' s alloys. Surface Technology, 2003, 32order to increase volume efficiency, more attention(3):13-15.should be paid to reduce the length of gap. Although中国煤化工MYHCNMHG.88●