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SUPER-SIZED Quality ControlA Guide to Improving Big GearsMatthew Jaster, Senior Editor

Its not easy being big. Maybe thats not exactly how the phrasegoes, but its applicable, particular-ly when discussing the quality require-ments of large gears. The size alonepromises unique engineering challenges.Those involved in producing large gearscontinually strive to meet higher qual-ity requirements, adapt to new testingmethods and seek out ways to top theirown manufacturing capabilities. Seemsan awful lot needs to go right in order to

achieve the quality requirements neces-sary to survive in the big gear business.In-shop inspections are mandatory,

says Fabrice Wavelet, product line man-ager, Ferry Capitain. No customer canafford to put a gear into service that is

not 100 percent sure/sound. A miningcompany, for example, can do nothingwithout a functional driving system onits mill, as 100 percent of the ore is goingthrough it. Failure is not acceptable.

The quality of large gears takes tech-nical expertise, years of experience andproper equipment, says William Quinn,business development lead, mill prod-ucts at Rexnord. Improvements inmaterials, lubrication and gear qualitylevels have made positive impacts in the

life of todays large gears. Modern gearcutting and grinding machines need tobe met with equally advanced geometricinspection equipment.

With higher accuracies of the gearingwe can extend the lifetime of the equip-

ment, says Holger Fritz, product manag-er mill gearing, Hofmann Engineering.To be able to determine higher quali-ties, the measuring equipment has to bea minimum of one accuracy level high-er than the item that is being inspect-ed. This is a challenge for the futureand were working hard to improve theinspection methods and one day mighthave a minimum big gear (above eightmeters) quality level of AGMA 12.

While its always good to improve the

quality of large gears, the current require-ments are already impressive thanks toASTM A609 and ASTM E709 or E1444,adds Wavelet. The same requirementsfor a 3 m gear and for a 10 m gear makesthe 10 m gear of a comparatively higher

Photo courtesy of Rexnord

For the equipment manufacturers' perspective on large gearinspection, see our online-exclusive article, "Big or Small: Inspection

is Key to Success," at www.geartechnology.com/big_gears.htm

gear inspection

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at www.geartechnology.com

22 GEAR TECHNOLOGY | January/February 2014 [www.geartechnology.com]

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quality, simply because casting such aheavy part (more than 20 tons a segment,finished weight) has nothing to do withcasting a 3-ton segment.

Tools of the TradeWhats the best way to inspect theselarge gears? According to our big gear

experts, its a combination of many dif-ferent tools.Hofmann Engineering is using laser

trackers for the dimensional inspectionon big mill gears and portable CMMarms to determine the form on the invo-lute and the lead line, Fritz says. For thepitch we use a special D&P pitch tester.But the ultimate test is still the mesh testof a precision ground mill pinion that ismeasured on a CMM together with themill gear. Mill pinions are always mea-

sured on a gear CMM machine.He adds that before they even startmachining at Hofmann they use ultra-sonic units and magnetic particle unitsto determine the quality of the materialor of the welds.

Varying challenges exist depending onthe inspection required; in-process non-destructive inspections can be done withrelative ease in the manufacturing envi-ronment. Once the gear is in operation,the same type of nondestructive testing

can take a significant amount of timefrom a couple hours to multiple days.Usually this involves shut down, remov-ing guarding, and cleaning the area to beinspected of lubricant, Quinn says.

Other operational inspections can becompleted continuously or with ease,such as vibration monitoring, lubrica-tion testing, and infrared temperaturemonitoring, says Quinn. In-processnon-destructive testing is done primar-ily with magnetic particle inspection and

ultrasonic inspection. Complex geom-etry in large gears can present challengesto ultrasonic inspection, but with skilledtechnicians and control processes we canovercome these.

For field inspections, infrared ther-mometers and cameras, and multi-axis vibration monitoring equipment withread out capability make continu-ous monitoring relatively straightfor-ward. More in depth field inspectionsof the gear may involve using a MAAG

TMA gear checker to check pitch, mag-netic particle inspection with a hand

yoke, and standard ultrasonic inspection

equipment, Quinn adds.The development of UT Phased Arrayand of Eddy Current (classical or PhasedArray) is of the highest interest for us.These techniques have been successfullyused on site, allowing an interesting timesaving compared to the classical meth-ods, but they are not economical on largesurfaces and in-process inspections for the moment, Wavelet says.

The question regarding the most use-ful inspection cant really be answered as

all the above mentioned inspections arenecessary to prove that we manufactureda top quality gear, Fritz adds.

Why are so many different inspectionrequirements necessary for big gears?

The size of the items in question,Fritz says. Temperatures for examplehave a big impact on the final sizes anda temperature controlled environment isnecessary.

Also, large gears today imply largemodule and consequently, large rim

thickness, particularly when talkingabout foundry. I suppose it is the samething with forgings or plate; the mainchallenge is to maintain the high qual-ity level required into such parts. For agear module 36 in cast steel (somethingthat was exceptional 10 years ago andusual today), the as-cast gear rim is eas-ily wider than 220 mm, considering boththe machining stock and the riser defor-mations. Avoiding internal indicationsas small as 5 cm in this outer rim is the

highest challenge a foundry is confront-ed with today, says Wavelet.

Such defects have to be avoided or the

foundry undertakes the risk of havingthe part rejected.This is where the experience and

the knowledge come into the equation,whether the gear is in steel or in ductileiron. The number of foundries capableof doing small gears (i.e. 3 m) in cast steelor ductile iron is high throughout theworld. The number of foundries capableof producing the largest and most power-ful gears today can be counted on the fin-gers of one hand, Wavelet says.

Although size matters, the inspectiontechniques (ultrasonic or magnetic par-ticle) are identical for small and largegears as well as the quality require-ments.

These techniques are reliable andrepeatable when used by qualified per-sonnel. The type of products being madefor narrow markets use in-house inspec-tion people. This is what we do in FerryCapitain. All our inspection personnelare qualified ISO 9712 / Cofrend level 2

(at least equivalent to ASNT level 2) forUT, MPI, dye penetrant test and radiog-raphy, although these two last techniquesare not commonly used on gears. Use ofclassical techniques, rather than the UTPhased Array, for example, is still jus-tified as this saves time in production,while the equipment is economical. Webelieve at Ferry Capitain that the newtechniques, including UT Phased array,are of the most interest, but for expertise,not production control, Wavelet says.

Magnetic particle inspection is stillthe industry standard for checking sur-

Photo courtesy of Hofmann Engineering

23January/February 2014 | GEAR TECHNOLOGY

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UT Phased Array, the only question thatinspection equipment manufacturershave to solve is the question of probes:they have to be reliable, economical andadaptable to all kinds of materials, sur-face finish and size, Wavelet says.

Improvements in continuous moni-toring system analysis will offer faster

indication of distress, helping plant per-sonnel to make necessary adjustmentsand avoid costly downtime. Conditionmonitoring/analysis systems allow theuser to identify a problem in one areabefore it has an adverse effect on equip-ment in another. Eddy current inspec-tion is likely to gain ground as a quickand thorough way to check for surfacediscontinuities in ring gears, allow-ing the user to log a permanent record(map) for future reference. Phased

array will gain wider acceptance as animproved method for inspecting sub-surface defects as acceptance criteria areestablished and validated in the largegearing industry, Quinn says.

The technology is changing whenit comes to inspecting large gears.Manufacturers of these components will

be the first to tell you there are no short-cuts. Good news for those looking forthe highest quality components for amassive application.

For more information:Ferry CapitainPhone: +(33) 3 2594 0424ferryby@ferrycapitain.fr www.ferrycapitain.com

Hofmann EngineeringPhone: +(61) 8 9279 5522Mail.hofmann@hofmannengineering.com www.hofmannengineering.com

Rexnord CorporationPhone: (414) 643-3000www.rexnord.com

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25January/February 2014 | GEAR TECHNOLOGY

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