1、12FTM14AGMA Technical PaperLarge Pinions for OpenGears: The Increase ofSingle Mesh Load - ANew Challenge forManufacturing andQuality InspectionBy M. Pasquier, CMD, andF. Wavelet, Ferry CapitainLarge Pinions for Open Gears: The Increase of Single MeshLoad - A New Challenge for Manufacturing and Quali
2、tyInspectionMichel Pasquier, CMD, and Fabrice Wavelet, Ferry CapitainThe statements and opinions contained herein are those of the author and should not be construed as anofficial action or opinion of the American Gear Manufacturers Association.AbstractMost of the large open gear sets for mining ind
3、ustry are designed according to ANSI/AGMA 6014-A06 andANSI/AGMA 2001-D04.Basically, customer specifications and AGMA service factor ratings both depend on design of the pinion(including material selection and heat treatment), as well as the finishing process of the teeth (to achieve thedesigned geom
4、etry).Today, with the increase of mesh load, design and manufacture of gearing to meet specifications and ratingsbecomes even more challenging.In complement to the traditional mechanical properties (such as hardness or yield strength), elastic andthermalbehaviorsandtheirinfluenceontransmissionaccura
5、cyhavetobetakenintoaccountfromthedesignstage, especially for large open gears (over 5 m in diameter).That implies a rise of cutting quality selected at the design stage, and of course and consequently,improvements in manufacturing and quality control, as normal processes that were used successfully
6、foryears are nowadays reaching their limits.This paper, using detailed examples, introduces these mandatory improvements in design, manufacturingandinspections,startingfrommaterialelaborationtofinalmachining,andfocusontodayslargeandpowerfulgearing.Copyright 2012American Gear Manufacturers Associatio
7、n1001 N. Fairfax Street, Suite 500Alexandria, Virginia 22314October 2012ISBN: 978-1-61481-045-23 12FTM14Large Pinions for Open Gears: The Increase of Single Mesh Load - A NewChallenge for Manufacturing and Quality InspectionMichel Pasquier, CMD, and Fabrice Wavelet, Ferry CapitainIntroductionThis pa
8、per is based on the fact that mining mills are becoming more and more powerful (up to 8500 kW perpinion). Then the pinions have to grow to meet the single mesh power increase, and consequentlyconventional manufacturing and inspections reach their limits. The methods that have been used success-fully
9、 for years must improve. Most customers have already taken into account this situation, in therequirements of their technical specifications.Starting from the rough material and ending with final inspections, the intent of this paper is to introduce theneeded technical improvements in manufacturing
10、and inspection of large pinions to achieve the requiredtransmitted power and the related service factors, defined by the worldwide agreed standard ANSI/AGMA6014-A06.Gear rating according ANSI/AGMA 6014-A06TheratingprincipleofalargepinioninanopengearsetaccordingtoANSI/AGMA6014-A06,isdefinedbyitspossi
11、bility totransmitacertainpower consideringacertainsafety factor,bothinterms ofbendingstrengthaswell as for pitting resistance:ANSI/AGMA 6014-A06, equation 14Pa= the lesser ofPacmCSFandPatmKSFwherePais transmissible power;CSFis safety factor for pitting resistance;KSFis safety factor for bending stre
12、ngth.Considering now ANSI/AGMA 6014-A06 formulas to determine Pacmand Patm:Pacm= npF396 000IKvmKmdsacZNCHCp2(1)(3)Patm= npd396 000 KvmFPdJsatYNKmKBmCircled above, are the parameters having the most influence on the final results:- Kvm(dynamic factor) and Km(load distribution) are directly related to
13、 tooth accuracy.- Sac(pitting fatigue limit) and Sat(bending fatigue limit) are purely depending on material.Their definition and actual results condition the service life, no less. In other words, the control of themanufacturing and inspection of the parameters that make these criteria, is of the m
14、ost importance.MaterialMaterial is of great importance to the service life, but is also of great importance in terms of design. Letsconsider an open gear set designed to transmit a power of 7000 kW (9387 hp) using a steel pinion, casehardened:- Grade M1 (low quality): KSF= 2.77; CSF= 2.21.- Grade M2
15、 (best quality): KSF= 3.10; CSF= 3.02.4 12FTM14Inthecaseoflargepinions,achievingtherequiredmechanicalpropertiesallthroughthepartisachallenge. Aperfectcontrolofthemanufacturingprocessandqualitycontrolfromtheingotcastingtothefinal heattreatedforging (including case hardening) is mandatory. Thats what
16、the selection of a M2 material is bringing.Rough materialThe pinions are manufactured from forged parts, themselves coming from an ingot. The ingot castingrequires high technical skill to achieve both the metallurgical requirements (mechanical properties,homogeneity, etc.) as well as some other para
17、meters known for their influence on the behavior of the part inservice (cleanliness, compactness. etc.).Ingot castingSomeof thekey parameters inrespect tofatiguebehavior of theparts, areobtainedfrom thecastingandwillnot change afterward:- Soundness is the absence of macro-defects like porosities or
18、cracks;- Cleanliness is the absence of endogen non-metallic inclusions and segregation;- Homogeneity of microstructure through the entire thickness;- Uniformity of secondary structure (grain, etc.);- Chemical composition is an adequate and controlled quantity of alloy elements such as manganese,chro
19、mium, nickel, copper, molybdenum, vanadium.The following is a review of the parameters:SegregationEven though it is not a standard requirement, the first point relevant to the solidification process is thesegregation. Segregations arealocal over-concentrationof alloyingelements, implyingafall of mec
20、hanicaland fatigue properties and may lead to shrinkages. As heat treatment cannot erase such segregations, itmust be avoided. With technology development and solidification knowledge, solidification can be moreaccurately computer simulated. Some ingots have very low levels of segregations, even for
21、 large castings.An example of computer simulation and comparison with the actual ingot is given in Figure 1 and Figure 2.CleanlinessCleanlinessisonthetopofmetallurgicalstandardrequirementsforobviousreasons. Cleanlinessisrelatedtonon-metallic inclusions, even though they are needed to initiate solidi
22、fication and to obtain a thin andhomogeneousstructure. Alocalconcentrationoftheseelementswillleadtoburieddefects. Adefinitionoftheacceptance criteria is then needed, but the problem is that cleanliness can be stated according to severaldifferent standards for different results. InANSI/AGMA 6014-A06,
23、 the cleanliness requirement is accordingtoASTM866orAMS2301. ISO6336referstoISO4967. Sometimes,steelmanufacturersratecleanlinessin accordance with DIN 50 602, method K. Should we consider only ANSI/AGMA 6014-A06 cleanlinessrequirements for steel pinions which are meant for the teeth area (table 5, n
24、ote 2), while case carburizedpinions have different requirements (table 7, item 4).Figure 1. Computer simulation of segregation5 12FTM14Figure 2. Actual segregation in ingotThemultiplicityofstandards,andofcoursetheirrespectiveacceptancecriteria,makesitalmostimpossibletodetermine an appropriate conte
25、nt for the different kinds of non-metallic inclusions (sulphides, aluminas,silicates and oxides). For the large parts we are talking about, cleanliness shall be achieved throughout thecomplete thickness.H2 contentEven though it has been made evident for many years that free hydrogen content is of th
26、e greatestimportance, none of the existing rating standards defines a maximum content. Free hydrogen may have adramatic effect on the part, whether at the manufacturing stage or during service. As the hydrogen contentincreases,theinternalgas pressureincreases inanexponentialrate. Combinedwithinheren
27、t materialdislo-cations and atomic diffusion (embrittlement is a very complicated process), hydrogen may lead to severedamages. Awellknoweffectofthat,andprobablythemosttypical,isasuddenbreakwhileeffortsundergoneby the part are very low. See Figure 3 and Figure 4. Another effect can occur during ingo
28、t casting or at theforgingstage. Figure 5showsacrackthatoccurredduringforging,generatedbyhydrogenembrittlementinabainitic structure.Figure 3. Sudden breakage due to hydrogen embrittlement6 12FTM14Figure 4. Magnification of hydrogen burst in the broken surfaceFigure 5. Free hydrogen influence - micro
29、crack formed during forgingThe origin can be summarized as follows:Steel IngotDendrites Segregations + FreeH2Embrittlement CrackingA solution to avoid such embrittlement is to maintain a low level of free hydrogen. This can be achieved byrequiring vacuum de-gas process. By todays standards, 2 ppm of
30、 H2is a limit commonly reached andguarantees aminimum risk of embrittlement. But, naturally, thencomes thequestionof themeasurement offreehydrogeninsuchsmall amount. Whatever theequipment used, thehydrogencontent is better testedinthe hot top (ingot casting) rather than via ladle analyses.ForgingThe
31、secondimportant step concerningrough material is forging. Theingot is cut head and foot, as showninFigure 6.Figure 6. Ingot location of head and foot cuts7 12FTM14The key point is the location where the initial piece is taken from the ingot. Figure 7 explains the coolingprocessoftheingotandthefinall
32、ocationofporosities(inthetop). Iftheinitialpieceistakenclosetotheheadof the ingot, it shouldbecarefully checkedthat theheadcut is enough toremove all porosities, seeFigure 8.An example of defect found in a large pinion forging is shown in Figure 9. Small cracks or very small crackswereobservedinthec
33、oreoftheforgedpart. Theoriginofthedefectcanbeexplained,thatduetothelocationoftheinitialpiececlosetothetopoftheingot(lastsolidificationarea),importantareasofporosityarepresent,as shown in Figure 10.Underconstraints(thermal,mechanical),porositiesturnintocracks. Byavoidingthisareaoflastsolidificationwh
34、en cut, the ingot is absolutely needed to obtain a quality product. For forgings, it is expectedto achieveacertainreductionratio(commonly3:1). Whatdoesthismeanforpinions,andspecificallyforlargepartsintheteeth area? Reduction ratio means the difference in terms of diameters between the ingot and the
35、wroughtpiece. Forgingreductioninducesacompactnessimprovement andastructureorientationthatarebothgoodfor mechanical properties.Figure 7. Computer simulation of coolingFigure 8. Location of the porosities in the ingotFigure 9. Crack in a forged part formed from a porosity8 12FTM14Figure 10. Example of
36、 initial part location of a failed forgedConsidering the volume represented by a large pinion, and the increased influence of segregations,porosities, hydrogen, etc., and due to its size, the use of wrought product with a high reduction ratio isobviously of more importance than for small pinions.Ins
37、pectionANSI/AGMA 6014-A06 , as well as the customers technical specifications often give some inspectionrequirementsandacceptancecriteriafortheabovementionedkeyparameters. Whatevertheyare, themostdifficult inspection regards internal material soundness through ultrasonic, UT, inspection and its rela
38、tedacceptance criteria.ANSI/AGMA 6014-A06table5andtable7givebothtest conditions (“For pinions, above UT applies inradialdirection, 360 degrees around, and axially from both ends”) as well as acceptance criteria. The concerncomes with the ultrasonic inspection that is to be repeated after carburizati
39、on (for case carburized pinion) -anything different from the initial test is to be recorded. That is quite imprecise and difficult in practice.For this reason, some specific requirements for through hardened and case carburized pinions have beendevelopedinrecentyears. Thisincludesbothtestmethodsandh
40、ighlystringentacceptancecriteria,basedonthefactthatwithproductsbeingbiggerandmorepowerful, anysingleproblemcouldleadtodramaticeffects.Concerning through hardened pinions, only one test is carried out at the rough machining stage. For casecarburized pinions, two inspections are carried out: the first
41、 at the rough machining stage; and the secondafter case carburizing and final grinding.Ultrasonic inspection is done on machined surfaces with a surface finish equals to Ra 6.3 mm (160 micro-inches) or less, which is better than required in ANSI/AGMA 6014-A06. Inspection is performed by eitherusing
42、reflection on calibration blocs (AVG method), or DGS/CAD method (automatic calibration). Straightbeam probes of 2 MHz or less are used. 100% of the pinions volume is tested in the radial direction on themajor diameters. In addition, the pinion is inspected lengthwise from each shaft end. This last t
43、est gives agood idea of the material quality, even if this not part of theacceptance criteria. Usinga 2MHz probe, shootfrom one shaft end:- should you obtain a backwall echo with a loss less than 30% - thats what you can expect;- obtain two backwall echoes in the same conditions - forging is a good
44、one;- get three backwall echoes - this forging is an excellent product.Even though more restrictive acceptance criteria have been defined, the available feedback does notconclude whether these requirements are correct or too conservative.A well-known method in the medical field is now currently unde
45、r development for industrial applications -phased array ultrasonics, PAUT. This new technology, applied to steel forgings, may bring a new level ofinterpretation for expertise purposes, as shown in Figure 11 and Figure 12.9 12FTM14Figure 11. UT inspection basic principleFigure 12. Phased array inspe
46、ction basic principlesPhased array probes typically consist of a transducer assembly containing from 16 to as many as 256 smallelementsthatcaneachbepulsedseparately. Inthemostbasicsense,aphasedarrayultrasonicsystemusesthe wave physics principle of phasing. A certain volume of the part is swept indiv
47、idually by each ultrasonicelement,withaverytinydelaybetweeneach. Electronicinterpretationofthesignalgivesa2Dmappingofthesection tested.As far as soundness of forgings is concerned, the phased array method provides new levels of informationand visualization compared to common ultrasonic inspection. I
48、t remains an ultrasonic technology, meaningphasedarrayultrasonicswillstillimplydifferentdirectionofshootingtodeterminetheexactvolumeofaburiedindication. The accuracy and the visualization introduced by this continuously improving technology, and ofcourse the possibilities and limits given by todays
49、electronics, make PAUT a significant gain over traditionalUT for expertise.MicrostructureThrough hardened steelsThrough hardening is the most common treatment for such heavy parts. Hardness requirements are 340 400HB. Nevertheless,quenchinginanadequatebathandtemperinghavetobecarriedouttoensurethatthe10 12FTM14requiredmicrostructureis achievedinthecoreof thepart. Evenif bainitic structureis required,for verylargeparts, agivenamount of martensiteandor residual austenitecanbeacceptedinthecorewherethestressinserviceisverylow.Case h
