1、92 FTM 4The Design, Development and Manufacture ofAdvanced Technology Gearing for Hot StripRolling Mill Applicationsby: Raymond J. Drago, PE, Drive Systems Technology,Inc.andLaurence E. Scott, Jr., PE, United States Steel CorporationiI IAmerican Gear Manufacturers AssociationTECHNICAL PAPERThe Desig
2、n, Development, and Manufacture of AdvancedTechnology Gearing for Hot Strip Rolling Mill ApplicationsRaymond J. Drago, PE, Drive Systems Technology, Inc.Laurence E. Scott, Jr., PE, United States Steel CorporationeThestatementsandopinionscontainedhereinarethoseof theanther andshouldnotbe construedasa
3、nofficial actionoropinion of the AmericanGearManufacturersAssociation.ABSTRACT:Gear drives areone of the most criticalmec,hanicalsystemsin the overall operationof,a steel hot striprolling mill.Typically, these systems use large throughhardenedgears, often of east construction,meshing with solid on s
4、haftpinionsof onlyslighfly greaterhardness.Whilethes_gearsperformedadequatelywhenthe typie_ fortyorfiftyyearoldmill was placedin service,increasingloadsand throughputhaveresultedin highmaintenanceactivityandunexpectedfailures. Since gear manufacturingis a relatively long lead time operation, and spa
5、re gear sets are not generallyavailable,improvingthe performanceof a gearsystemis key to improvingthe overall performanceof the mill itself.This paperdescribesthe initiationandprogressof a programwhichaddressesverylargegears(approaching200 inchesin diameter)and a numberof pinionconfigurationsranging
6、from long,integral,solid on shaftdesigns to multipleshellpinion designs, mostof whicharecarburizedand hardfinished, all of which meet or exceedAGMA Quality Class 10.The general design proceduresand overall implementationof the design and manufacturingprogram as well as adescriptionofthe resultsinter
7、msofimprovedmill gear systemexperiencearcalsopresented.WhilethisprogramwasinitiatedatUnitedStatesSteelGaryWorks,similargearshavebeeninstalledorarccurrentlybeingdesignedandmanufacturedforseveralothermillsandsimilarpplicationsbothforUnitedStatesSteelandotherDSTclients.Thispaperwilladdressthegenericapp
8、licationofAdvancedTechnologyGearingwithoutreferencetoaparticularsiteorinstallation.Examplesaredrawnfromtheanthersjointexperienceandapplicationandmayrepresentcompositepresentationsforthesakeofclarityandillustration.Copyright 1992AmericanGearManufacturersAssociation1500KingStreet,Suite201Alexandria,Vi
9、rginia,22314October,1992ISBN: 1-55589-584-0The Des_qn, Development, and Manufacture_ofAdvanced Technology Gearin,qforHot Strip Rolling Mifl ApplicationsRaymondJ. Drago, PE LaurenceE. Scott, Jr., PEChief Engineer ProcessManager - Sheet _-_-“ . _“ loads experienced by todays operational requirements a
10、lso_._: increase the possibility of basic fatigue failures, such as the- “:_i_ _ _ _ mill pinion shaft fracture shown in Figure 12, occurring muchmore frequently. Such major fatigue fractures carry with themthe possibility of extensive consequential damage which couldconceivably render an entire mil
11、l inoperative.Figure 7 Typical Surface Distress While, of course,the subject of much concern, the conditionof existinggears alsoprovidesa great deal of insight into thein the gear blanks, Figure 9, are common in the more highly design modifications which are required in order to obtainloadedmills. K
12、eepingthesegearsoperatingrequiresextensive, maximum capacityfromthe new AdvancedTechnologyGears.frequent maintenance actions. These range from hand grindingthe teeth to relieve badly deteriorated areas, Figure 10, to stop In addition, the condition of the existing gears also providesdrilling and rei
13、nforcing the gear blanks with plates either valuable insight into the improvements and changes which willwelded or bolted in place, Figure 11. These measures are be required to the existing gear boxes, particularly in thecostly and result in down time for the mill. alignment of their bores and modif
14、ications to their lubricationsystems, which must be made to allow the new AdvancedDespite these holding actions, catastrophic failures, such as the Technology Gears to reach their full potential.pinion shown in Figure 12, have occurred and, unless actionis taken to improve the capacity of the gear s
15、ystem, such A thorough survey of each mill gear system is, therefore thefailures will become more common and extensive. The higher first step in the application of Advanced Technology Gearing.-5-_ -i;:. Another major area of concern is lubrication. Most often, allof the gear drives in a given mill a
16、re lubricated by a commonsystem. Oil is fed to the gears through spray bars inside theindividual boxes which are themselves drained by gravity. Thedrain lines deliver the oil to a common sump or, in some casesto a common settling tank and then on to a common sump.From the sump, the oil may be passed
17、 through a common filter and then back to the spray bars in each box. Throughsimilar piping arrangements, the same oil system also feedsthe bearings which support the gears. While the overallefficacy of such systems varies substantially from mill to mill,their filtration efficiency is generally not
18、especially good.Since new Advanced Technology Gears are usually introducedinto a typical mill system in stages (i.e. not all gear drives areconverted at once, rather new sets are installed in each, but.- _=_ ma_m_Figure 9 Gear Web CracksSURVEY gear tooth Harizmgd “_inaccuracy, misalignment of the be
19、aring bores, and gear blankand shaft deflections.As noted above, before any Advanced Technology Gears areinstalled in an existing drive, it is essential that the bearingbores be checked for proper alignment and repaired if they are Figure 13 Pinion Shaft Lateral Deflectionsfound to be in error. Such
20、 improvements help to minimize theproblem of load distribution, however, further steps are profile modifications applied to the gears. By carefullyrequired to assure long life. The problem of gear box bearing modifying both lead and profile of the Advanced Technologybore accuracy is extremely import
21、ant and cannot be Gears, a further improvement in overall load capacity isoverstated. If the basic alignment of the gears in the box is not obtained, as compared the existing gears, since the load isvery good, then the best possible gears will still perform much more uniformly distributed across the
22、 face width andpoorly. The alignment factor must thus be addressed first, among the teeth in contact.Many existing gears are of relatively low quality in terms of Profile modifications applied to the Advanced Technologybasic tooth geometry, generally falling into the range of Gears takes the form of
23、 tip relief on both the pinion and gearAGMA Quality Class 7 or below, particularly as far as lead of sufficient magnitude and extent to virtually eliminate hardis concerned. Lead mismatch between the pinion and its contact during the entrance and exit phases to tooth meshing.mating gear is thus quit
24、e common. In addition, many older The magnitude of the tip relief is dependent on the actual toothgears started life as lead matched gear sets. That is, since it is deflections, however, this is a difficult parameter to analyzedifficult to control the lead on a large wide face width gear, accurately
25、. If the gear blanks are rigidly constructed such thatthe gear was frequently cut first and then the pinion was cut the rim supporting the teeth does not participate significantlywith a lead to match. This worked well enough initially, in the tooth deflections (i.e. the gears are “thick rimmed),howe
26、ver, it is con-anon practice in mill maintenance to mix then tooth deflections can be calculated by considering toothand match gears and pinions indiscriminately when a failure beam bending, tooth rotation in the rim, and Hertzianoccurs thus, over time, many of these initially “matched“ sets deflect
27、ions at the contact point. While FEM methodology canbecame mismatched, further exacerbating the problem. The be employed for this purpose, the model size, lead time forimproved accuracy of the Advanced Technology Gears allows model development, and cost of optimization can bethem to truly be used in
28、 an interchangeable manner thus this prohibitive for most mill gear designs. For these applications,mix and match problem is virtually eliminated, a more conventional approach is generally utilized.-10-=WBy far, the most significant modification which must be The definition of the lead (and profile)
29、 modifications is,developed, however, is in the lead direction. The lead must be however, greatly complicated by several factors. First,modified to account for both system (primarily shaft) although great pains are taken to improve the housingdeflections, and allowable alignment variations within th
30、e box. alignment before the Advanced Technology Gears areIn order to accommodate shaft deflections, they must be first installed, because of the very large size of the housings andcalculated. While torsion of the shaft is considered, as Figure the difficulty associated with modifying the housings on
31、 site,Figure 15 Gear Rim Lateral DeflectionFigure 14 Gear Rim Radial Deflectionit is impossible to align the gears “perfectly“ thus some13 shows, bending is generally more significant for most allowancefor basicgeometricmisaligument must be provided.pinions. The primary deflections occur in the pini
32、on shafting This is done by superimposing an appropriate crown on thesystem.For the Advanced Technology Gears, theconstruction lead modification required to accommodate the systemof the blanks is designed such that the deflectionsof the rim deflections.A secondvery important factor is the problem of
33、and web are insignificant when compared to the pinion shaft loading. During a typical rolling cycle, the load applied to thedeflections. For example, Figure 14 shows the maximum gear set varies tremendously - from virtually zero to severalradial deflection (between the arms of the web plate) of the
34、times the drive motor rating (TAF). This loading problem isrim of a typical triple web design while Figure 15 shows the further complicated by the fact that many different widths andlateral rim deflection of the same gear. In both cases, the grades of steel are rolled in a typical mill and each appl
35、ies adeflections for this gear (which is close to 100 inches in different load to the gear set. Yet another complication to theoverall diameter) are quite small. As a point of interest, in this problem of loading is the fact that a given pinion or gear maycase, the triple web design was selected to
36、optimize the rim be used in a number of locations in a particular mill. Forthickness and rim deflections so that a rim somewhat thinner example, the same pinion might be used in mesh with differentthat the usually specified three times the tooth whole depth gears in the first and second roughing sta
37、nds for a given millcould be used. drive. This commonality of parts greatly eases the spare partsburden for the mill but adds an enormous level of-11 -complication to the problem of selecting the correct Since the optimum modifications for any given gear set aremodifications (both lead and profile -
38、 though lead is the most unique to that set, it is impossible to provide specificsensitive) for a given gear set. numerical guidelines herein. For reference purposes, however,typical lead and profile modifications range from a fewIt is tempting, of course, to simply calculate the deflections thousan
39、dths to over 0.010 inch, depending on the size and theassociated with the worst possible combination of factors and pitch of the gear teeth and the system deflections.apply that as the basic modification, however, this will notusually yield satisfactory results in terms of overall systemperformance
40、and, especially, life. If the gears are modified for EDGE ROUNDINGthe worst case loads, then the contact pattern on the gear teethat lower loads will be significantly less than full face and the One of the most important factors in the success of thegears will be quite noisy in operation. Further, i
41、t is quite Advanced Technology Gears, simple as it may sound, ispossible that, even though the loads are below peak, the gears proper edge rounding. All of the edges of the gear teeth, bothmay be locally overloaded at part load conditions due to the at the tooth tips and at the ends of the face widt
42、h, must bereduced contact pattern and thus they may suffer a failure at adequately, uniformly, and generously rounded. This roundingpart load which might not have occurred at full load. Such accomplishes several important missions. When edges aredistress at part load, while not commonplace, is more
43、likely smoothly rounded, stress concentrations at the sectionto occur when the difference between the peak and nominal transitions are minimized. More importantly, however,loads is extreme (i.e. high TAF). The basic design and properly rounded edges allow the gears to be more highlyconstruction of t
44、he Advanced Technology (3ears, however, modified for lower load conditions since when they arereduces the TAF and thus tends to mitigate this problem subjected to higher loads than the modifications weresomewhat. In reality, for most applications, the most originally designed;for, the smooth rounded
45、 edges will notsignificant consequence of designing the modifications at too concentrate the load nearly as much if it tends to run off orhigh a load point will result in noisy operation at part load near the edges of the teeth. The importance of smooth roundedconditions, edge breaks is often (in fa
46、ct, almost universally) overlooked,however, such seemingly minor details can be the differenceConversely, if the modifications are calculated at the low load between a successful and an unsuccessful gear set.end of the spectrum, it is likely that the contact pattern, whichwill appear quite full at n
47、o or low load (i.e. at installation and One of the first Advanced Technology Gear sets to be installedinitial roll over), will run off the ends or tips of the teeth at in a large mill drive provides a good object lesson in thisthe peak load conditions and thus early failure may well occur regard. Wh
48、en it was subjected to mesh testing at the geardue the very high localized stresses which would be present at manufacturers plant, it was noted that the tooth tips on thethese highly concentrated contact points. In our experience, gears were not adequately rounded and instructions werespecifying too
49、 little modification is actually the more common defined for the proper rounding to be accomplished.problem (as compared to over modification) in large mill Unfortunately, the rounding operation was missed and the geargearing. In many cases, it is mistakenly believed that full face set was installed with relatively sharp corners. After severalcontact at installation (no load) is a desirable goal, weeks of operation, the gear set was visually evaluatedandaunfortunately, such full no load patterns, as noted above, often very fine line of extremely light micropitting was observe
