1 - Gear Seminar Manual [PDF]

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TABLE OF CONTENTS

•

CONTACTS

•

History of Company

•

Section 1 ............................. GEAR BASICS

•

Section 2 ............................. BEARINGS AND SEALS

•

Section 3 ............................. LUBRICATION

•

Section 4 ............................. GEAR METALLURGY AND FAILURE MODES

•

Section 5 ............................. START - UP & PREVENTATIVE MAINTENANCE

•

Section 6 ............................. VIBRATION NOISE & TEMPERATURE

•

Section 7 ............................. SHORT & LONG TERM REPAIRS

Lufkin Industries, Inc. | P.O. Box 849 | 711 Industrial BLVD| Lufkin, TX 75904 | t: 936-637-5224 | www.lufkin.com

CONTACTS

LISA FORD. .................................. PT DIRECTOR OF ENGINEERING 936.637.5275 [email protected] Engineering Design for All Gear Products ED MARTIN ................................... CHIEF ENGINEER [email protected] 936.637.5169 Engineering Design of High Speed Gears SCOTT FRANKS .......................... CHIEF ENGINEER 936.637.5493 [email protected] Gear Repair Engineering ROSS PINNER .............................. CHIEF ENGINEER 936.637.5476 [email protected] Design of Low Speed Gears and Marine RORY CULL......... ........................ GENERAL MANAGER GEAR REPAIR 936.631.2771 [email protected]

BEN JORDAN .............................. OPERATIONS MANAGER 936.631.2719

[email protected]

MARCH LI, PhD ............................ LEAD METALLURGIST 936.637.5115 [email protected] Materials, Heat Treatment, Welding and Failure Analysis NICHOLAS TERRY....................... FIELD SERVICE MANAGER [email protected] 936.637.5158

ART NELSON................................MECHANICAL ENGINEER [email protected] 936.637.5423

DUSTIN BECKMAN ......................DESIGN ENGINEER 936.676.4392

[email protected]

MIKE MAY..... ............................... SALES COORDINATOR 936.637.5145 [email protected] DARREN SMITH........................... SALES COORDINATOR 936.631.2731 [email protected]

Lufkin Industries, Inc. | P.O. Box 849 | 711 Industrial BLVD| Lufkin, TX 75904 | t: 936-637-5224 | www.lufkin.com

CONTACTS

RABI JABBOUR........................... SALES COORDINATOR 936.631.2797

GILBERT SY.................................. SALES CORDINATOR 936.631.2709

[email protected]

[email protected]

JAY BURNS .................................. SALES COORDINATOR 936.631.2716 [email protected]

SONIA JACOBO ............................ ADMINISTRATIVE ASSISTANT - GEAR REPAIR 936.637.5413 [email protected]

Lufkin Industries, Inc. | P.O. Box 849 | 711 Industrial BLVD| Lufkin, TX 75904 | t: 936-637-5224 | www.lufkin.com

HISTORY OF LUFKIN INDUSTRIES AND POWER TRANSMISSION

Lufkin Industries is composed of three divisions: Power Transmission, Oil Field, and Foundry. In 1902, Lufkin Industries (then known as Lufkin Foundry and Machine Company) was founded as a small repair shop for sawmill equipment and locomotive boilers. The company steadily expanded its facilities and began to market its own line of sawmill equipment. In 1917, Lufkin shifted its manufacturing emphasis toward the oil industry, building steam engines for rotary drilling rigs, heavy-duty hoists, large refinery castings, and central power units for multiple oil well pumping operations. Power Transmission: Lufkin began manufacturing enclosed gear drives in 1924, in conjunction with the manufacture of oilfield pumping units, and began specializing in industrial gearing applications in 1939. During World War II, Lufkin built marine gears for destroyers, cargo ships, and LTS landing crafts. As a result of this experience, Lufkin developed a line of marine propulsion drives, and since 1956, has been a major supplier of propulsion gearing for many types of marine applications. Lufkin’s line of industrial gears may be found in various applications, ranging from sugar mills, steel mills, conveyors, rubber mills, and paper manufacture of all gearing, including industrial, marine, and high speed, and small product lines, such as winches. All gear producing facilities are located at the main plant, in Lufkin, Texas. Gear Sales: The Lufkin gear sales force is strategically located to provide application expertise both domestically and internationally. Domestic sales offices are located in the following metropolitan areas: Pittsburgh, New York, Baltimore, Chicago, Cleveland, Atlanta, New Orleans, Houston, and Los Angeles. We have another manufacturing facility, Lufkin-France S.A., located in Fougerolles, France. All Lufkin sales offices—domestic and international—are staffed by Lufkin employees, not representatives who may serve other companies. In addition to the field sales offices, a Customer Service Group is located in Lufkin, Texas, and is responsible for processing incoming orders and providing order status information. Gear Sales provides a direct link from customer to Design Engineering and are responsible for conveying to Engineering the scope of each order. Before order shipment, Sales is the focal point for information concerning the progress of the order. Design Engineering: Design Engineering interprets the requirements of a gear application, as provided by Gear Sales and the customer. The requirements are used to determine the suitability of the gear selection, the optimum manufacturing methods, design of the gear, and to provide Manufacturing and Quality Assurance with the information needed to perform their functions.

©2012 Lufkin Industries, Inc.

Design Engineering provides support throughout the gear order to Sales, Manufacturing, Quality Assurance, and the customer. The Application Engineering group provides gear selection, technical assistance, and pricing to Sales for special or unusual gear requirements. Lufkin’s technical expertise in all types of parallel shaft gearing is recognized throughout the industry and is evident by its leadership and representation in the American Gear Manufacturers Association (AGMA) and the American Petroleum Institute (API). Now, as in the past, Lufkin engineers participate on and chair several AGMA committees on subjects such as marine gear materials and rating practices, gear lubrication, high speed enclosed drives standards, and low speed enclosed drive standards. Two Lufkin engineers have served as AGMA President. Lufkin technical capabilities extend not only to the design, manufacturing, and testing of gearing for new installations, but also to the redesign and manufacturing of drop-in replacement units of other manufacturers. Lufkin’s technical experience also encompasses field diagnosis and repair of LUFKIN and other manufacturer’s gear units. Quality Process: Although Lufkin Industries has long been recognized by customers and competitors alike as a producer of outstanding quality products, to further our leadership role, the need for a companywide awareness of quality concerns was recognized. A comprehensive, continuous improvement quality process, based on the Crosby Quality Education System, formally began at Lufkin industries in 1991. All employees receive training in problem-solving, teamwork, error recognition and removal, and the goal of “zero defects.” As the backbone of the quality awareness effort an Error Cause Removal (ECR) process was implemented. Through this process, any employee is encouraged to bring to light any breaches in quality or ideas to make work processes more efficient. The procedure for resolving errors begins with the employee attempting to solve the problem himself or with the aid of his supervisor. If the informal approach is unsuccessful, the individual turns in an ECR form, which describes the problem and who the person thinks will be able to solve it. The ECR is then logged by the department ECR coordinator and assigned to an individual or group for resolution. When necessary, a Corrective Action Team is formed interdepartmentally or across functional lines for resolution. The ECR process is governed by the Lufkin Quality Manual which details the resolution process and the record keeping requirements. In addition, each department maintains a log of corrective action for future reference. To better accommodate the world-wide market Lufkin serves, Lufkin management set an ambitious goal in June 1992, to obtain ISO 9001 certification by July 1993. This goal was undertaken enthusiastically with personnel dedicated to producing the documentation, procedures, and training necessary by the deadline. The ISO 9001 (International Organization of Standards) standard covers the Design, Manufacturing, and Testing functions. The company was audited by Det Norske Veritas, an independent certification agency, and Lufkin received Certification Number QSC-3449, dated July 23, 1993, certifying conformance to the ISO 9001:1987 Quality System Standard For The Design And Manufacture Of Industrial Gear And Oilfield Equipment. ISO certification, required by many customers, provides a guarantee that

©2012 Lufkin Industries, Inc.

Lufkin is dedicated to the quality process and maintains design, manufacturing, testing and installation procedures and controls, and is dedicated to continuous improvement. Lufkin currently holds ISO 9001:2008 certification. Gear Testing: A no-load mechanical run-in test is performed on each gear unit shipped. Lufkin utilizes two test stands for gear testing. One test stand is primarily used for low speed applications which require a standard run-in test with a minimum of instrumentation. The second test stand is a very sophisticated operation, designed to provide API 613 test data, locked torque capability, and instrumentation monitoring. The majority of testing on this stand is partial load with sound and vibration reporting. The test stands are staffed by test stand operators trained to set-up the required testing, monitor the outputs of the testing instrumentation, and provide an interface with Design Engineering and Quality Assurance for interpretation of test data. The test stand operation is supported by Gear Engineering and coordination meetings are hosted by the Project Engineer before witnessed testing, to familiarize all involved with the testing requirements and procedures. Gear testing is supervised through Power Transmission Manufacturing. Scheduling of both test stands is coordinated by the operators and Customer Support. A major renovation had recently enhanced Lufkin’s gear testing capability. A new 2500 HP motor has been installed and may be used in tandem with a 1000 HP motor. This will provide a total capability of 3500 HP. An existing 1000 HP motor has been installed in the Lufkin Gear Repair facility to provide additional gear testing capacity for repaired units. A 2000 HP dynamometer has been installed to allow testing at loads up to 2000 HP, depending on unit speed. Lufkin has locked torque testing experience at up to 70,000 HP, 35,000 ft./min. pitch line velocity, and 22,000 RPM pinion speed. A new test stand lubrication system with over 3000 gallon capacity has been installed. This provides up to 1000 gallon per minute flow. Also, the system is designed to provide flow at a different pressure and temperatures for testing two or more units simultaneously. A complete data acquisition system will be used to gather bearing, inlet, and drain temperature monitoring points. The temperature monitoring system will accommodate types T, K, J, and E thermocouples and platinum and nickel RTD’s. Also, a Bently Nevada Adre dynamic acquisition system, with windows, has been installed to meet our customer’s data needs. This system is used for vibration and temperature data acquisition and may be used to continually gather data and display it in many output formats. All of the points may be monitored simultaneously for comparison. New slave gears, used for dynamometer testing, allow loading of units, with the 2000 HP dynamometer, with pinion speeds up to 30,000 RPM. The Lufkin test stand and its improvements demonstrate Lufkin’s concern for quality. Gear testing can be conducted to meet the most stringent customer specifications with a specially designed test program, if required. A total of seven test positions are now available. The purpose of the test facility is to demonstrate the proper performance of each gear unit; thereby

©2012 Lufkin Industries, Inc.

assuring the user of a smooth initial start-up and years of service. Manufacturing: Table 1 details the maximum turning, boring, milling, and cylindrical grinding capabilities at Lufkin. However, specific applications may require fit analysis due to crane capacity or parts configuration limitations. Table 1. Turning, Boring, Milling, and Cylindrical Grinding Capacity

Operation

Max. Width (Inches)

Max Height (Inches)

Max. Length (Inches)

Crane Capacity (Tons)

117

96

348

30

Using Index Table

84

140

144

60

Using Index Table

84

159

276

60

Line Boring

48

120

144

Operation

Max. Diameter (Inches)

Max. Length (Inches)

Crane Capacity (Tons)

60

127

30

Shaft Turning

37

240

30

Gear Turning

128

72

30

Shaft Grinding

72

123

30

Shaft Grinding

19.5

168

30

Milling Boring

Shaft Turning

Lufkin gear cutting capability is constantly updated through acquisition of new and more accurate equipment. In addition to hobbing capacity, Lufkin maintains a large holding of herringbone tooth shaping machines. Following in Table 2 are the maximum sizes of gearing Lufkin are capable of producing, by hobbing and shaping. In addition, Lufkin produces internal and external splines and sprockets. In the early 1980’s, Lufkin recognized an industry trend toward more accurate gearing, usually accomplished by gear grinding. Also, tooth case hardening became a common requirement to increase load carrying ability for given size gear. Lufkin uses Pfauter/Kapp form finishing machines and Hofler gear grinders. The form grinders use a wheel with the exact form of the required space between the gear teeth. The wheel is formed to the correct shape, then coated with cubic boron nitride (CBN). The process is often referred to as “CBN grinding”. The CBN cutting closely resembles a milling process, with each crystal acting as a milling cutter. This cutting action produces less heat than conventional generating-type grinding, reducing the possibility of grinding burns. Other advantages Lufkin

©2012 Lufkin Industries, Inc.

has found are the teeth are completely finished including the root, thereby eliminating any steps or excessive undercut, or inadequate depth of profile, and, also, the processing time for the finishing operation is greatly reduced. In Lufkin’s experience, the finish and accuracy produced by the form finishing equipment have surpassed the generating grinding process. To date, we have finished up to 80,000 HP gears on these machines with remarkable accuracy. Following in Table 3 are the gear grinding capacities at Lufkin. In addition to Lufkin’s grinding capacity and expertise, the lapping process may be used to finish gearing. Years of using the lapping process to finish gears have proven value of this operation. Table 2. Maximum Hobbing and Shaping Capacity

Type

Accuracy

Max. Face

Outside Diameter

Width

Min.

Max.

(Inches)

(Inches)

(Inches)

Diameter Pitch Finest

Coarsest

Max.

AGMA

Weight

Quality (lbs.)

Hobbing

Spur

General

76

0

197

32

0.75

90000

10-11

Spur

Special

52

0

120

16

1

66000

11-12

Helical

General

70

0

197

2

0.75

90000

10-11

Helical

Special

48

0

120

16

1

66000

11-12

Double Helical

General

70

0

197

32

0.75

90000

10-11

Double Helical

Special

48

0

120

16

1

66000

11-12

Splines

76

0

any

any

Sprockets

76

0

197

Herringbone

24

1

120

16

1.5

35000

8

Internal

6

1

36

60

3

2000

9

90000 4" CP

Shaping

©2012 Lufkin Industries, Inc.

Table 3. Gear Grinding Capacity

Type

Generating Form

Min. Diameter

Max. Diameter

Max. Axial Travel

Coarsest

Max. Weight

(inches)

(inches)

(inches)

DP

(lbs.)

1.5

78

29

1

17600

0

70

39

1

33000

Lufkin checks all ground gearing, and occasionally other gearing on request, on its state-of-theart gear measuring machines. These machines are used to determine lead, involute, tooth spacing, and runout variation from the desired geometry. Undulations of the tooth surface may also be evaluated using a specially developed program. Dedication to the evolution of gear technology led Lufkin, in 1991-92, to install a complete carburizing facility. The company spent approximately one million dollars on equipment and start-up costs to completely outfit the facility. Integral quench tanks and accurately controlled atmosphere furnaces help reduce the distortion inherent in carburized parts. The carburizing facility is used almost exclusively for gearing. A fully equipped lab is included in the carburizing facility so that results of the cycle may be analyzed as soon as possible. Complete through-hardening facilities also exist within Lufkin. For decades, before its involvement with carburizing, Lufkin dealt almost exclusively in through-hardened gearing. Most of the through-hardened of hot roller bar stock and forged round is performed at Lufkin. Some gear and pinion forgings are purchased through-hardened by the vendor. With these facilities, Lufkin is not only able to through-harden rotating elements, but also to provide stress relief cycles for extremely large gear casings and bases, when necessary. Foundry: Lufkin’s Foundry produces ASTM Class 20 through Class 40 gray iron and all grades of ductile iron. The foundry is equipped to produce castings ranging in size from 1,000 pounds to 40,000 pounds. Three molding areas are used: the Small Casting Facility (SCF), the Main Bay, and the Ductile Iron Facility (DIF). The SCF produces up to 20 molds per hour. Casting average weight in the SCF is 70 pounds, in both gray and ductile iron. The Main Bay is used to pour large gray and ductile iron castings. The average weight of a Main Bay gray iron casting is 4000-5000 pounds, with the largest poured to date being 35,000 pounds. The largest ductile iron casting pour weight is 40,000 pounds.

©2012 Lufkin Industries, Inc.

The Ductile Iron Facility (DIF) is primarily used to produce ductile iron gear blanks for pumping unit gear boxes. The DIF is largely automated and computer controlled. Combined production is currently approximately 250 tons per day, 10-15% of which is ductile iron, and the rest is gray iron. Capability is in place to produce up to 400 tons per day, with up to 25% being ductile iron. With downturn in oilfield business in the 80’s, Lufkin began searching for ways to utilize excess Foundry capacity. A group was formed to solicit gray and ductile iron casting business. At this time, approximately 60 to 70% of the Foundry capacity is employed in servicing commercial accounts. Currently, the construction, mining machinery, pump, valve, compressor, and power transmission product industries are the main recipients of Lufkin castings. The commercial castings business complements the gear business by keeping Foundry operational and efficient. Fabrication: Lufkin’s structural fabrication shop allows the manufacture of gear housings and welded gearing in-house; thus providing timely delivery of needed fabrications. The fabrication equipment available is continually upgraded and represents some of the fabrication industry’s latest technology. Several DNC plasma arc shape-burning machines are used for cutting sheet steel. These allow “nesting” of the cut parts to reduce steel waste. Also, the plant includes a submerged arc welder, capable of welding with two wires at once, for welding large gears. The Fabrication Department has produced welded gears up to 120 inches in diameter, weighing 48,000 pounds. Capability exists to fabricate gears in the 60,000 to 70,000 pound range. All gearing is welded to Lufkin Design Engineering specifications. Welded gear housings have been produced in many different configurations. Some of the most outstanding were casings for an integrally geared compressor, approximately 20 feet long and five feet wide, with large welded flanges for mounting the volutes, and a housing for a 6000 HP twin screw extruder drive. Service: The Service Manager maintains a force of full-time servicemen. All servicemen are available on a seven-day-per-week, 24-hours-per-day basis. Requirements for service are usually routed through the Service Manager. Additional field service is provided by Design Engineering personnel, when needed. Gear Repair: Lufkin has long recognized the need in industry for competent, quick, and efficient gear repair of all types of gear units. For years, Lufkin has repaired gears manufactured by other gear makers. Lufkin has become very adept at determining tooth geometry and reproducing it. The goal for repairs is to provide the most economical and expeditious return to service of the gear unit. Lufkin will search for ways to salvage whatever parts may be of use, thus keeping repair cost low.

©2012 Lufkin Industries, Inc.

Within the last few years, the gear repair business has been seen as a growth industry; so to take advantage of the opportunity, Lufkin has invested considerable capital in developing a repair facility in Lufkin, Texas, separate from the main plant. In this way, the repair work does not compete with new unit orders, since the repair facility contains a complete gear shop, with the exception of tooth grinding equipment. The Power Transmission Repair facility boasts an 80,000 square foot building, with engineering, machining, inspection, testing, and paint capabilities. An additional advantage, with the close proximity to the main plant, Gear Repair has access to all the grinding, manufacturing, and inspection equipment in the main shop. This enables Lufkin to repair an extremely wide variety of gearing. Lufkin Power Transmission Repair specializes in reworking existing gear sets, building matching parts, and design of drop-in replacement gear boxes. Although Lufkin is primarily a manufacturer of parallel shaft gearing, the Repair group will analyze and quote, if possible, any type of power transmission equipment repair that we have the capability of renewing. Lufkin Gear Repair is available to provide failure analysis, non-destructive testing, and alignment services, in addition to reworking gears and housings. The aim of the operation is to provide a single source for complete restoration of gear units. Lufkin has authorized repair service center representatives in Indiana, Alabama, and Nisku, Alberta, Canada.

Lufkin Industries Acquires French Gear Manufacturer COMELOR

In November 1998, Lufkin Industries acquired Comelor, a diversified gear manufacturer located in Fougerolles, France. Comelor, now known as Lufkin-France, was founded in 1941 and has an established reputation in several power transmission markets. Lufkin-France specialized in engineered products for a wide range of industrial applications: • • • • •

Turbo gearing for industrial refrigeration, petrochemical, power generation, nuclear, and high speed test bench applications Speed increasers for micro-hydroelectric (low head) power generation Reducers for a wide range of steel and aluminum mill applications Flexible gear type couplings Power swivels for oil and gas production platforms

Lufkin-France employs approximately 200 people and is strategically located in northeast France near the juncture of France, Germany, and Switzerland. The plant has a total floor area of approximately 377,000 square feet with offices occupying an additional 21,500 square feet. ISO 9001 certification was achieved in June 1995, and the plant, its Quality Assurance processes, and its products have been approved by the French nuclear industry. If fact, Comelor was the first French gear company to provide equipment to the industry.

©2012 Lufkin Industries, Inc.

Design processes are computer-based and the CAD system incorporates 3-D modeling technology. Their units feature carburized and ground gears, and the product lines are based on high precision, cost-effective, high torque density designs. In-house capabilities include ISO, DIN, and AGMA gear rating programs; finite element analysis; bearing analysis; and a full range of gear tooth geometry analytic programs. Lufkin Industries has achieved significant synergies with its new French operation. The European markets served by Comelor are largely incremental to Lufkin, so new sales opportunities were created. Further, Lufkin Industries has successfully grown European sales of turbo gearing products for the petrochemical, oil and gas transmission, and power generation markets, and the Lufkin-France factory is a key strategic factor in extending the global presence of Lufkin throughout Europe, Western Asia, North Africa, and the Mideast. Lufkin has committed significant capital resource to insure that its Lufkin-France operations are a fully capable facility for the design, manufacture, testing, and aftermarket support of turbo gearing. An API-caliber test facility was created in Fougerolles and the new test bed has been operational as of March 2000. This upgraded capability is beneficial for our European clients, who routinely elect to witness various Quality procedures and the mechanical performance test. Further, Lufkin has the flexibility to manufacture its world-class turbo gearing in the facility best suited to the point of delivery and the needs of its customers. The Fougerolles facility is also a strategic base for Lufkin’s Aftermarket Gear Services. Trained field service technicians are based in France, dramatically improving our response time to Easter Hemisphere user locations. Services available will include installation and commissioning assistance, field diagnostic services, preventive maintenance services, retrofit and field repair. Further, Lufkin-France has become a base of expansion for our successful Gear Repair Operations, which focuses on rapid repair and rebuild of gear units of all types, both Lufkin and non-Lufkin. This fast-growing facet of Lufkin’s Power Transmission Division will experience even more rapid growth now that dedicated facilities and services are available in Central Europe.

©2012 Lufkin Industries, Inc.

GEAR BASICS Gears Go Back in History Many Centuries

Early Chinese Gear Application

1

Grist mill gear

Primitive Parallel Shaft Gearing

2

Primitive Right Angle Gearing

Gear Built in Early 20th Century

3

21st Century Gearing

• Speeds in excess of 70,000 RPM • Velocity of teeth over 300 MPH • Some units designed and built to run 7-10 years continuously • Output torque over 25 million in-lbs • Transmit over 100,000 HP

The Involute Curve

• Webster defines an “involute” as ‘a curve traced by a pint on a string kept taut as it its un-wound from a cylinder.’ • The profile of most gear teeth manufactured in the US are an “involute”

4

Involute

• It doesn’t matter where on the involute you operate, you will have conjugate motion between the rotors.

5

6

Relative Sliding & Rolling Motion

Used with permission from Dr. Douglas Wright University of Western Australia

7

8

9

Gear Tooth Loading Patterns

10

Gear Nomenclature

11

Large Spur Gear

Forces from Spur Gears

• Tangential Force • Separating Force

12

Bluing Contact Shows Multiple Teeth in Contact

13

Forces from Helical Gears

• Tangential Force • Separating Force • Axial or Thrust Force

Single Helical Gears Generate Thrust

14

Single Helical Gears with Rider Rings

Double Helical Gear

15

Destructive Pitting

Tooth Breakage

16

Gear Set Rating

Gear Rating 120 High 100 Torque Capacity

Strength 80 Pitting Wear Scoring 60 40 20 0

0

Pitch2000 Line Velocity 4000

6000 Very High

PLV

Rating Factors

 Pitch diameter of pinion & gear  Material properties of pinion and gear  Chemistry  Hardness  Face width  Torsional & bending deflection  Tooth accuracy  Speed  Tooth shape & size

17

Effect of Geometry on Load Distribution

LUFKIN

L

TORQUE

- - - --4:7·-

F y

BENDING

TORSION

Cot-JIBINED D E FL E C T I O N

·----------.I.U.!-

THEORETICA L ..----------·-·LONG!TUDINAL.--·-- ·-- CORRECTION

FIG . 9

F'INION IONS

,

Jd

-+_.1 !J

- - ;_-......,+ I- - -

'"'L- - _ J I

DEFLECTIONS

AND

LONGITUDINAL

CORR E CT

Typical Tooth Alignment Chart

DESIREDTOOTHALIGNMENT -

APEX

WING

-TOLERANCE BAND 1/ I

t ENDEASEOFF

t

lf) lf)

v v

'I

r-,...

:1

O-r

r;

P2

t

P/;

TOOTHALIGNMENTCORRECTION

N ---- 4500 rpm  PLV > 7000 fpm (35 mps) • Gearboxes sized on rated HP of Driver • Reasonable repeatability between manufacturers

The Evolution of API 613 & 677 Engineering in Reliability

25

API 613, 1st Edition

 1st Edition released in 1968  AGMA 421.06 Rating  4 Hour Mechanical Test

API 613, 2nd Edition

• • • • • • •

2nd Edition Additions (1977) Conservative “K-Factor” Rating Tilt-pad Thrust Bearing Provisions for Vibration Probes Axial Stability Check Lateral Critical Speed Analysis 15 minute testing at 110 % over speed Include Service Factor of Driver in Rating

26

API Gear Rating Method Equation for De ter mining Tooth Pitting Index “K” K = Wt / (Fw)(d) x (R+1) / R where, K = Tooth Pitting Index (lbs/in2) Wt = Transmitted tangential load (lbs)=126,000 (Pg) / (Np) (d) Fw = Net Face Width (in) d= Pinion Pitch Diameter (in) R = Ratio (Number of Teeth in Gear / Number of Teeth in Pinion) Pg = Gear Unit Rated Power (hp) Np = Pinion Speed (rpm)

API 613, 3rd Edition

 3rd Edition Additions (1988) • “Observed” vs. “Witnessed” Inspection

27

API 613, 4th Edition (1995) • Gear Tooth Charts > 30,000 fpm (150 mps) • Minimum Instrumentation Requirements ・ 4 Radial Vibration Probes ・ 2 Axial Vibration Probes ・ 2 Accelerometers ・ 12 Temperature Sensors

API 613, 5th Edition  Integrally flanged shaft ends are standard  1.0 mil maximum vibration  High quality material grade per ISO 6336 specified  Taper land thrust bearings are allowed with customer approval below 2000 RPM

28

API 677, 2nd Edition (1997)

 Basic Requirements & Features  Conservative “K-Factor” Rating  Anti-Friction or Hydrodynamic Bearings  1-hr. Full Speed, No Load Mechanical Run Test

Size Comparison of API vs. AGMA 6011

The API unit will be about 50% larger than an AGMA rated gear for the same application

29

Cost of Specifications

1800 rpm Electric Motor to 4000 rpm Compressor, 1800 HP AGMA 6013 Center Distance Net Face Width AGMA 6011 S.F. Cost

10 6 1.20 100%

AGMA 6011 10 7 1.38 110%

API 677 API 613 14 7 2.70 180%

14 7 2.70 290%

Benefit: Reliability

ISO 6336 Ratings  Durability Ratings:  Carburized Gears may be comparable to AGMA  ISO 6336 derates through hardened gears  ISO 6336 Strength ratings are more liberal than AGMA  ISO 6336 favors use of smaller teeth

30

Gear Manufacturing

31

32

Hobbing Process

33

Herringbone Gear Generation

34

Sykes Cutters

Sykes Generating System

LUFKIN

35

Typical Sykes Cut Tooth Surface Finish

LUFKIN

36

Lapping

37

Gear Tooth Lapping

38

39

Gear Grinding

40

Quality Assurance

41

Part Data •Part Geometry •Quality Requirements •Left & Right Flank •Measured Values Profile •Variation from true involute •Tip relief Lead variation •Variation from helix angle •Lead modification •End ease-off

42

Spacing Measurement •Pitch •Accumulated Pitch •Runout

Gear Tooth Quality Numbers  New ISO 1328-1 Quality numbers range from 0 to 12, with the 0 being the best  Sykes cut teeth 9  Hobbed teeth 7-8  Ground Teeth 2-6

 Old AGMA 2000 Quality numbers ranged from 3 to 15, with the Q 15 being the best  Sykes cut teeth Q8  Hobbed teeth Q9-Q10  Ground Teeth Q11-Q15

43

Magnetic Particle Inspection

Ultrasonic Inspection

44

UT Angle Beam

Electrical & Mechanical Runout Check

45

Residual Magnetism Check

Apex Runout Inspection

46

Gear Tooth Alignment

47

Tooth Contact Check

Double Helical Contact A. Perfect contact no modification needed B. Acceptable contact - · Gear with end ease-off modification - · slight crowning . C. Acceptable contact-· Gear with crowning modification D. Acceptable contact-· Gear shafts slightly off parallel E. NOT Acceptable contact -· Gear shafts out of parallel F. NOT Acceptable contact -· Gear shafts out of parallel

G. NOT Acceptable contact-· (if no lead modification present) gear and/or pinion miscut - correct parts H. NOT Acceptable contact-· (if no lead modification present) gear and/or pinion miscut - correct parts

48

Offset Carrier

49

Offset Carrier 3 f.a. :-.1o!t lhll

I LL -hf:U. . . 'f P 4 EO'JALL 0

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SECTION 4: GEAR METALLURGY AND FAILURE MODES

Part 1 Metallurgy and Heat Treatment of Gear Steels Part 2 Common Wear and Failure Modes of Gears

Wood gears

Plastics gears

1

Sugar mill gear

Gas compressor gear

Part 1 Metallurgy and Heat Treatment of Gear Steels

Gear Tooth Loading Patterns

2

Material Consideration Strong?

•Tensile/ultimate strength, yield strength, elongation, area reduction Hard? •Hardness Tough? •Fracture toughness, impact strength Fatigue resistant? Fatigue strength Corrosion resistant? Easy to machine? Cost?

Material Options Woods, polymers (plastics/rubber), ceramics, metals and alloys steels (carbon steels, alloy steels)

Typical Steel Options • Through Hardening: AISI-SAE 4140 AISI-SAE 4145 AISI-SAE 4340 (AISI: American Iron and Steel Institute; SAE: Society of Automotive Engineers)

• Surface Enhancement – Flame/Induction Hardening – Carburizing: AISI-SAE 4320 AISI-SAE 9310 – Nitriding

3

Iron Carbon Equilibrium Diagram

Heat-treatment Changes Iron from Body Centered Cubic to Face Centered Cubic

High temperature: Austenite/f.c.c.

Low temperature: Ferrite/b.c.c.

4

Carbon Solubility • Face Centered Cubic Iron (Austenite) can dissolve up to 2 wt.% carbon • Body Centered Cubic Iron (Ferrite) can only dissolve 0.02 wt.% carbon

Typical Heat Treatments • Anneal - heat to austenite region and cool in furnace. • Normalize - heat to austenite region and cool in air. • Quench - heat to austenite region and cool rapidly in oil, water, etc.

5

Anneal • Carbon is dissolved at high temperature and on cooling comes out of solution and forms iron-carbide by a diffusion controlled process. • Structure of iron and iron-carbide is known as pearlite.

Normalize • Same process as anneal but because cooling is faster there is less time for the formation of iron-carbide and the pearlite structure is much finer.

6

Pearlite

Effect of Cooling Rate on Pearlite Spacing 6

Pearlite Spacing

4 2 0

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2

3

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Cooling Rate

7

Quench On rapid cooling insufficient time is allowed for iron-carbide formation and a supersaturated solid solution of carbon in iron is formed which transforms by a shear mechanism to form a body centered tetragonal crystal structure called martensite.

Martensite

8

The martensite transformation produces a volume increase in the material of over 4%. Martensite hardness is proportional to the carbon content.

Effect of Carbon

• As quenched martensite hardness. • Maximum of around 900 HV - 64 HRC. • Flattens off at about 0.8% carbon.

9

Tempering of Martensite

Tempered Martensite

10

Tempered Steels

Engineering Steels • Steels which have been quenched to form martensite and then tempered to restore a level of ductility offer the best combination of properties attainable from a given alloy.

11

Alloy Selection The size of piece which can be successfully quenched to produce martensite depends on the alloy. Addition of alloys such as chromium, nickel, and molybdenum increases the size of part which can be successfully quenched.

Transformation Diagram

12

Transformation Diagrams • Adding elements such as Nickel, Chromium and Molybdenum move the “nose’ of the TTT curve to the right. This gives more time for the quench to be performed or permits larger pieces to be quenched.

AISI-SAE System • • • • • • •

10xx: Carbon steel 15xx: Manganese 1.00 - 1.35% 33xx: Ni 3.5%, Cr 1.5% 41xx: Cr 1%, Mo .25% 43xx: Ni 1.75%,Cr .75%,Mo .25% 86xx: Ni .5%, Cr .5%, Mo .2% 93xx: Ni 3.25%, Cr 1.25, Mo .12%

13

Heat Treatment Response Through Hardened Material (285 - 415 HB) • • • •

5 inch 4140 10 inch 4145 24 inch 4340 4340 (mod) 36 inch

Surface Hardening • Induction/Flame - produces quenched layer on the surface of a quenched and tempered part with higher hardness. • Carburizing - produces a composite material with high carbon high hardness surface layer, strong, ductile, low carbon core.

14

Induction Hardening

Flame Hardening

15

Carburizing The hardness of the carburized surface after quench is proportional to the carbon content usually around 62 - 64 HRC. Tempered at approx. 350 °F and the final hardness is in the range 58 – 62 HRC.

Why low carbon core? • Since carburized parts are tempered at a relatively low temperature in order to retain maximum surface hardness it is necessary to have a relatively soft martensite in the core in order to avoid material which is too brittle.

16

Heat Treatment Response Carburizing Grades • 4320 – Core hardness ~ 255 HB – Small section size – Yield strength 75,000 psi – Fracture toughness 100 ksi in

• 9310 – Core hardness ~302 HB – Large section size – Yield strength 95,000 psi – Fracture toughness 125 ksi in

Carburizing

17

Nitriding Hardening by the growth of fine particles in the surface layer. Low temperature diffusion process typically in the range 900 – 975 °F.

Nitrogen produced by cracking ammonia diffuses into the surface and forms hard nitride particles.

Aluminum containing alloys are particularly good for nitriding since they readily form aluminum nitride needles.

18

Case depth is limited since diffusion at the temperature used for nitriding is slow and maximum case depths are typically 0.025 0.030-inch. However the low temperature gives much lower part distortion and the case has high hardness of up to 83 HR15N (~ 45 HRC) for regular through hardening steels and 93 HR15N ( ~ 64 HRC) for special nitriding grades.

AGMA 2001 • • • • • • •

Allowable Bending Stress Numbers Sat, psi Cast Iron 8500 Ductile Iron 33500 Through Hardened 50000 Induction Hardened 55000 Nitrided 52000 Carburized 70000

19

AGMA 2001 • • • • • • •

Allowable Contact Stress Number Sac, psi Cast Iron 65000 Ductile Iron 128000 Through Hardened 150000 Induction Hardened 190000 Nitrided 163000 Carburized 225000

Part 2 Common Wear and Failure Modes of Gears

20

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Gear Tooth Meshing • Gear teeth slide into mesh, then roll, then slide out of mesh. • Need to lubricate to prevent metal to metal contact. • Need to provide hardness to resist alternating stresses applied during load transfer. • Need to provide strength to resist bending.

21

Class

General mode

Wear

Adhesion, abrasion, corrosion, fretting, electric discharge, etc.

Scuffing

Scuffing

Plastic deformation

Plastic deformation, e.g., indentation

Contact fatigue

Pitting (macropitting), micropitting, subcase fatigue

Bending fatigue

Low‐cycle fatigue, high‐cycle fatigue

Cracking

Hardening cracks, grinding cracks, rim and web cracks, case/core separation, fatigue cracks

Fracture

Brittle fracture, ductile fracture, mixed  mode fracture, etc.

Some of the photographs of gear wear and damage are taken from ANSI/AGMA 110: Nomenclature of Gear Tooth Failure Modes and ANSI/AGMA 1010: Appearance of Gear Teeth-Terminology of Wear and Failure with permission of the publisher The American Gear Manufacturers Association 500 Montgomery Street Alexandria, Virginia 22314

22

Wear • Is a term describing change to a gear tooth surface involving the removal or displacement of material, due to mechanical, chemical, or electrical action. • Can be categorized as mild, moderate or severe. • Mild wear is considered normal in many applications. Moderate and sometimes even severe wear may be acceptable in some applications.

Mild wear

23

Abrasion • Is the removal or displacement of material due to the presence of hard particles: metallic debris, scale, rust, sand or abrasive powder, suspended in the lubricant or embedded in the flanks of the mating teeth. • Can be categorized as mild, moderate or severe. • Abrasion causes scratches or gouges on the • tooth surface that are oriented in the direction of sliding. It normally appears at the addendum and dedendum where sliding is present.

Severe abrasion

24

Corrosion is the chemical or electrochemical reaction between the surface of a gear and its environment.

Electric Discharge • An electric discharge across the oil film between mating gear teeth produces temperatures that may be high enough to locally melt the gear tooth surface. • Microscopically, the damage appears as small hemispherical craters. The edges of the craters are smooth and they may be surrounded by burned or fuse metal in the form of rounded particles that were once molten.

25

Severe electric discharge damage

Scuffing • Is severe adhesion that causes transfer of metal from one tooth surface to another due to welding and tearing. • The damage typically occurs in the addendum, dedendum, or both, away from the operating pitchline, in narrow or broad bands that are oriented in the direction of sliding.

26

Contact Fatigue • Repeated contact stresses may cause surface or subsurface fatigue cracks and the detachment of material fragments from the gear tooth surface. • General modes are macropitting, micropitting and subcase fatigue.

Initial pitting

27

Progressive pitting

FlgureFiake pitting

28

Micropitting

Subcase Fatigue • A crack initiates close to the case-core interface usually as a result of the combined effect of high stresses and slightly soft core and the presence of sharp non metallic inclusions. • The crack grows slowly back toward the load flank due to the compressive residual stresses and more quickly through the tooth due to small tensile residual stress. • The resulting crack is smooth through the core of the tooth and very rough as it grows back towards the surface. Often the load face shows no evidence of wear or damage .

29

Subcase fatigue

Bending Fatigue

Root bending fatigue of two spur teeth

30

Grinding Crack •

• •

•

Abusive grinding during finishing operations can reheat the surface of a case hardened part sufficiently to soften, re-harden or crack parts. The cracks are usually shallow and appear either as a series of parallel cracks or in a crazed, mesh pattern. Tempered areas appear brown or black on a light brown or gray background. Areas where untempered martensite has formed appear as white areas surrounded by black, tempered areas. Can be detected by magnetic particle or dye penetrant inspection.

Grinding cracks Cracks

Magnetic particle (Magnaglo) inspection

31

Fatigue crack

Fatigue cracks propagate under repeated alternating or cyclic stresses which are below the tensile strength of the material.

Fracture • When a gear tooth is overloaded it may fail by plastic deformation or fracturing. • Depending on the deformation/crack propagation processing, fractures are classified as brittle, ductile or mixed modes. • Ductile fracture is preceded by appreciable plastic deformation. It has a gray, fibrous appearance. • Brittle fracture is with little prior plastic deformation or rapid crack propagation. It has a bright, granular appearance.

32

Ductile fracture

Brittle fracture

33

Ordinary Tooth Damage Mechanisms

34

SECTION 5: START-UP & PREVENTATIVE MAINTENAN Pre-Installation Open inspection cover and inspect for internal corrosion. Carefully remove black coating from exposed machined surfaces  Use solvent on a soft rag to remove  Keep solvent away from rubber seals Install couplings insuring there is an interference fit between couplings and shafts  For keyed fits use 0.0005”/inch of shaft diameter interference Install keys Keyless fits: The desired interference is generally job specific. Consult Lufkin service or engineering for recommendations.

Installation  Verify foundation is “flat”  Pick up gear unit using lifting lugs or eyes.  Do not lift unit by placing slings under shaft extensions

 Clean foundation and mounting surface of gear foot.  Set gear box on foundation  Establish rough alignment  Make certain unit is “sitting down”  If gap is greater than 0.002” place shim between gear unit and foundation

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Installation  Tighten bolts  Check for “soft foot”  Remove inspection cover and review contact pattern in layout blueing from previous operation  Check soft blue contact  Determine desired soft blue contact  Soft blue recorded at Lufkin  Generally speaking 80% contact is acceptable  This may not be acceptable if lead correction is present

 Clean two or three teeth on low speed gear and spray layout blue on cleaned teeth.  Replace inspection cover

Gear boxes are not “plug and play” machines

Alignment Determine thermal movement of all components to be aligned Determine mechanical movement of components to be aligned Align components using optical or mechanical (dial indicator) methods For units with dual output shafts, align one shaft and then determine the misalignment of the second shaft. Split the difference. ・Torque foundation bolts ・Align prime mover to gear unit

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Misalignment limits Shaft Surface

Outside Diameter

Face TIR

Velocity 5000 FPM & up

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3000‐5000 FPM

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0.0005"

1500‐3000 FPM

0.006

0.0006"

500‐1500 FPM

0.008"

0.0008"

500 FPM and less

0.010"

0.001"

Note: for close coupled couplings.

Start-up • Fill gear with desired oil to full level on dipstick or level gauge. Filter the oil as it is pumped into the gear unit. • Prime and operate auxiliary lube oil pump if unit is so equipped. Stop auxiliary pump after 10 minutes and refill sump with oil. • Prime main oil pump. • Start machine.

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Start-up If unit has shaft driven oil pump, make certain oil pump If it doesn’t, “picks up” after 30 seconds operation. stop unit and check for loose piping connections. Re-prime pump and re-start system. If unit has a lube system but limited sump capacity, operate system for 2-3 minutes and shut down. Refill unit with oil. Restart system. Immediately observe the oil pressure. Adjust pressure to desired pressure. If no pressure is specified or the requirement is unknown, set pressure to 25-30 PSIG as close to the inlet to the gear box as possible.

First Hour • Monitor vibration and temperature until temperatures stabilize. • Adjust cooling water so that oil temperature maintains at approximately 120-130°F. • Monitor the housing temperature surrounding the bearings. – The temperature of roller bearings should be about 30°F hotter than the oil temperature. The housing temperature should be somewhat less than the bearings. – The temperature limit for hydrodynamic bearings should be 220°F

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First Hour • Monitor housing vibration. – Expected vibration level: 0.10 – 0.30 in/sec RMS depending on foundation  Operate unit under modest load for 2 hours. Stop unit and remove inspection cover. Inspect hard bluing.  The tooth contact should be evenly distributed across the face of the teeth.

Daily Maintenance • Check oil level •Check level with unit stationary. •Check oil temperature and pressure against previously established norms. •Check for oil leaks •Check for unusual vibration and noise

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Monthly Maintenance • Check operation of auxiliary equipment and alarms • Clean breather • Check tightness of foundation bolts • Clean/replace oil filter

Semi-Annual Maintenance • Remove inspection cover and inspect gear teeth for wear. • Check shaft alignments. • Inspect heat exchanger zinc anodes. • Extract oil sample for spectrographic and ISO 4406 cleanliness examination. – A semi-annual oil analysis is a good starting point. – The interval between sampling may need to be shortened if problems are suspected

• Filter oil or replace oil as suggested by oil analysis

6

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Annual Maintenance • Perform vibration analysis – Tooth related vibration – Bearing related vibration

• Check heat exchanger for erosion, corrosion and foreign material • Check bearing clearance and end play. • Check tooth contact pattern – Look for area previously coated with layout blue. – Make certain contact is evenly distributed. • Compare to previous contact • A contact change suggests other issues • Maintenance may be required

– Clean teeth and recoat with new layout blue

7

SECTION 6: VIBRATION NOISE & TEMPERATURE Design for Low Vibration, Noise, & Temperature • Rotor Dynamics • Bearing stability • Gear tooth geometry • Lubrication Method

What are Rotor Dynamics? The study of how a rotor-bearing system responds when forces are applied to it.

1

10/13/2014

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Gear Vibration Causes • Unbalance • Coupling misalignment

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2x Rotor Speed (misalignment)4th)

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5

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Gear Vibration Causes • Unbalance • Coupling misalignment •Inadequate foundation or loose bolts •Lateral and torsional critical speed response

6

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Gear Vibration Causes • • • •

Unbalance Coupling misalignment Inadequate foundation or loose bolts Lateral and torsional critical speed response

•Bearings - design, manuf., assembly, wear

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7

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Gear Vibration Causes • • • • •

Unbalance Coupling misalignment Inadequate foundation or loose bolts Lateral and torsional critical speed response Bearings - design, manuf., assembly, wear

•Couplings - lockup, wear, no lubricant, not as designed •Gear tooth errors - design, manufacturing, assembly, wear

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Vibration Frequencies Unique to Gearing • • • •

Tooth Mesh Frequency Tooth Repeat Frequency Assembly Phase Frequency Ghost Frequency

Tooth Mesh Frequency • How many teeth come into mesh every second. – Same for hunting or non-hunting tooth gear set – TMF = Pinion speed x number teeth in pinion » Or

– TMF = Gear wheel speed x number teeth in gear wheel

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Tooth Repeat Frequency • A certain tooth on the pinion hitting a certain tooth on the gear wheel. Typically heard as an audible beat. – Hunting tooth gear set - TRF = gear speed/number teeth in pinion – Non-Hunting tooth gear set - TRF = gear speed x product of the prime numbers common to pinion and gear wheel/ number of teeth in pinion

Assembly Frequency • A vibration caused by non-hunting tooth gear sets. – Assembly frequency = Tooth mesh frequency / product of the prime numbers common to pinion and gear wheel teeth

11

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Ghost Frequency • Similar to tooth mesh, but related to the gear tooth cutting/grinding machine . – GF = # teeth in worm wheel x rotor speed

Acceleration data • Tooth mesh frequency – Number of teeth times shaft speed • Smooth meshing of gears • Not smooth - causes high multiples • Level measured in: 1g=acceleration due to gravity (32.2 ft/sec/sec) • Typical values – good under 4 g – elevated 4 to 8 g – concern over 10 g

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Gear Noise Causes • Tooth errors from manufacturing – Spacing, profile (involute), lead (tooth alignment), surface finish, gear cutting machine error, etc.

• Degradation of tooth profile during operation – Wear, pitting or tooth breakage

• Improper design – Tip or root relief – Resonance in gear unit

13

10/13/2014

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• Degradation of tooth profile during operation – Wear, pitting or tooth breakage

• Improper design – Tip or root relief – Resonance in gear unit

•Rolling element bearings •Clutches and couplings •Lube oil pump and piping •Natural frequency response of supports

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High Bearing Temp. Causes • Poor design - Shallow groove, Clearance, etc... • Restricted or orificed oil passages

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High Bearing Temp. Causes

• Poor design - Shallow groove, Clearance, etc... • Restricted or orificed oil passages •Misalignment

•High spot

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High Casing Temp. Causes • Misdirected oil flow

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High Casing Temp. Causes •Misdirected oil flow • Too little oil flow • Too much oil flow • Inadequate clearance

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High Casing Temp. Causes • • • •

Misdirected oil flow Too little oil flow Too much oil flow Inadequate clearance •Inadequate drain •Rubs

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High Oil Outlet Temp. Causes • Too little oil flow • Too much oil flow • Casing coated with foreign material

20

SECTION 7: SHORT & LONG TERM REPAIRS Gear Repair • Repair Procedure • Repair Options – Design Upgrades – Rush – Standard

• Common Failures – Gears – Shafts – Bearings

100 year old gear built to be repaired

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Receiving Inspection • Photograph customer furnished equipment as received and verify against the bill of lading • Mark all equipment and parts with identification numbers • Wait for customer communication before teardown and further evaluation

Communication • What is the scope of the repair? • What caused the failure? • Is the failure reoccurring? • How long has the unit been in operation? • What are the operating conditions?

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Disassemble Unit

3