Industrial Machinery Repair Part Episode 2 Part 4 doc

Figure 14.35 Normal wear patternFigure 14.36 Wear pattern caused by abrasives in lubricating oil Abnormal Wear Figures 14.36 through 14.39 illustrate common abnormal wear patternsfound i

TF= tangential force

STF= separating force

TTF= thrust force

hp= input horsepower to pinion or gear

Dp= pitch diameter of pinion or gear

rpm= speed of pinion or gear

φ = pinion or gear tooth pressure angle

λ = pinion or gear helix angle

Herringbone Gears

Commonly called “double helical” because they have teeth cut with right andleft helix angles, they are used for heavy loads at medium to high speeds.They do not have the inherent thrust forces that are present in helical gearsets Herringbone gears, by design, cancel the axial loads associated with asingle helical gear The typical loads associated with herringbone gear setsare the radial side-load created by gear mesh pressure and a tangential force

in the direction of rotation

“power” side

Note that it has become standard practice in some plants to reverse thepinion or bullgear in an effort to extend the gear set’s useful life While this

Table 14.1 Common failure modes of gearboxes and gear sets

Excessive or too little backlash • •

Excessive torsional loading • • • • • • •

Foreign object in gearbox • • • •

Gear set not suitable for

application

Gears mounted backward on shafts • • •

Incorrect center-to-center distance

between shafts

Incorrect direction of rotation • • •

Lack of or improper lubrication • • • • • • •

Misalignment of gears or gearbox • • • • • •

practice permits longer operation times, the torsional power generated by

a reversed gear set is not as uniform and consistent as when the gears areproperly installed

Gear overload is another leading cause of failure In some instances, theoverload is constant, which is an indication that the gearbox is not suitablefor the application In other cases, the overload is intermittent and onlyoccurs when the speed changes or when specific production demands cause

a momentary spike in the torsional load requirement of the gearbox.Misalignment, both real and induced, is also a primary root cause of gearfailure The only way to assure that gears are properly aligned is to “hardblue” the gears immediately following installation After the gears have runfor a short time, their wear pattern should be visually inspected If thepattern does not conform to vendor’s specifications, alignment should beadjusted

Poor maintenance practices are the primary source of real misalignmentproblems Proper alignment of gear sets, especially large ones, is not aneasy task Gearbox manufacturers do not provide an easy, positive means toassure that shafts are parallel and that the proper center-to-center distance

is maintained

Induced misalignment is also a common problem with gear drives Mostgearboxes are used to drive other system components, such as bridle orprocess rolls If misalignment is present in the driven members (either real

or process induced), it also will directly affect the gears The change inload zone caused by the misaligned driven component will induce mis-alignment in the gear set The effect is identical to real misalignment withinthe gearbox or between the gearbox and mated (i.e., driver and driven)components

Visual inspection of gears provides a positive means to isolate the potentialroot cause of gear damage or failures The wear pattern or deformation ofgear teeth provides clues as to the most likely forcing function or cause.The following sections discuss the clues that can be obtained from visualinspection

Normal Wear

Figure 14.35 illustrates a gear that has a normal wear pattern Note that theentire surface of each tooth is uniformly smooth above and below the pitchline

Figure 14.35 Normal wear pattern

Figure 14.36 Wear pattern caused by abrasives in lubricating oil

Abnormal Wear

Figures 14.36 through 14.39 illustrate common abnormal wear patternsfound in gear sets Each of these wear patterns suggests one or morepotential failure modes for the gearbox

Abrasion

Abrasion creates unique wear patterns on the teeth The pattern varies,depending on the type of abrasion and its specific forcing function.Figure 14.36 illustrates severe abrasive wear caused by particulates in thelubricating oil Note the score marks that run from the root to the tip of thegear teeth

Figure 14.37 Pattern caused by corrosive attack on gear teeth

Figure 14.38 Pitting caused by gear overloading

Chemical Attack or Corrosion

Water and other foreign substances in the lubricating oil supply also causegear degradation and premature failure Figure 14.37 illustrates a typicalwear pattern on gears caused by this failure mode

Overloading

The wear patterns generated by excessive gear loading vary, but all sharesimilar components Figure 14.38 illustrates pitting caused by excessive tor-sional loading The pits are created by the implosion of lubricating oil Otherwear patterns, such as spalling and burning, can also help to identify specificforcing functions or root causes of gear failure

“Only Permanent Repairs Made Here”

Hydraulic Knowledge

People say knowledge is power This is true in hydraulic maintenance Manymaintenance organizations do not know what their maintenance personnelshould know We believe in an industrial maintenance organization where

we should divide the hydraulic skill necessary into two groups One isthe hydraulic troubleshooter; they must be your experts in maintenance,and this should be as a rule of thumb 10% or less of your maintenanceworkforce The other 90% plus would be your general hydraulic main-tenance personnel They are the personnel that provide the preventivemaintenance expertise The percentages we give you are based on a com-pany developing a true preventive/proactive maintenance approach toits hydraulic systems Let’s talk about what the hydraulic troubleshooterknowledge and skills should be

Hydraulic Troubleshooter

Knowledge:

● Mechanical principles (force, work, rate, simple machines)

● Math (basic math, complex math equations)

● Hydraulic components (application and function of all hydraulic systemcomponents)

● Hydraulic schematic symbols (understanding all symbols and their tionship to a hydraulic system)

rela-● Calculating flow, pressure, and speed

● Calculating the system filtration necessary to achieve the system’s properISO particulate code

● Trace a hydraulic circuit to 100% proficiency

● Set the pressure on a pressure compensated pump

● Tune the voltage on an amplifier card

● Null a servo valve

● Troubleshoot a hydraulic system and utilize “Root Cause Failure Analysis”

● Replace any system component to manufacturer’s specification

● Develop a PM program for a hydraulic system

● Flush a hydraulic system after a major component failure

General Maintenance Person

Knowledge:

● Filters (function, application, installation techniques)

● Reservoirs (function, application)

● Basic hydraulic system operation

● Cleaning of hydraulic systems

● Hydraulic lubrication principles

● Proper PM techniques for hydraulics

Skill:

● Change a hydraulic filter and other system components

● Clean a hydraulic reservoir

● Perform PM on a hydraulic system

● Change a strainer on a hydraulic pump

● Add filtered fluid to a hydraulic system

● Identify potential problems on a hydraulic system

● Change a hydraulic hose, fitting, or tubing

Best Maintenance Hydraulic Repair Practices

In order to maintain your hydraulic systems, you must have preventivemaintenance procedures and you must have a good understanding andknowledge of “Best Maintenance Practices” for hydraulic systems We willconvey these practices to you See Table 15.1

Table 15.1 Best maintenance repair practices: hydraulics

Preferred: based

on historical trending of oil samples.

1 Pressure filter:

Pressure filters come in

collapsible and

noncollapsible types.

The preferred filter is

the noncollapsible type.

Remove the old filter with clean hands and install new filter into the filter housing or screw into place.

Least preferred: Based on equipment manufacture’s recommen- dations.

2 Return filter:

Typically has a bypass,

which will allow

contaminated oil to

bypass the filter before

indicating the filter

needs to be changed.

CAUTION: NEVER allow your hand

to touch a filter cartridge Open the plastic bag and insert the filter without touching the filter with your hand.

Reservoir air

breather

The typical screen

breather should not be

Dissipate heat from the

fluid Store a volume of

oil.

Clean the outside of the reservoir to include the area under and around the reservoir.

Remove the oil by a filter pump into a clean container, which has not had other types of fluid

in it before.

Clean the insides of the reservoir by opening the reservoir and cleaning the reservoir with a lint-free rag.

Afterward, spray clean hydraulic fluid into the reservoir and drain out of the system.

If any of the following conditions are met:

A hydraulic pump fails.

If the system has been opened for major work.

If an oil analysis reveals excessive contamination.

Hydraulic

pumps

A maintenance person

needs to know the type

of pump in the system

and determine how it

operates in the system.

Example: What is the

flow and pressure of

the pump during a

given operating cycle?

This information allows

Review graphs of pressure and flow.

Check for excessive fluctuation of the hydraulic system.

(Designate the fluctuation allowed.)

Pressure checks: Preferred: daily Least preferred: Weekly Flow & pressure checks:

Preferred: two weeks Least preferred: monthly

Root Cause Failure Analysis

As in any proactive maintenance organization you must perform Root CauseFailure Analysis in order to eliminate future component failures Mostmaintenance problems or failures will repeat themselves without someoneidentifying what caused the failure and proactively eliminating it A pre-ferred method is to inspect and analyze all component failures Identify thefollowing:

● Location of component at the time of failure

● Sequence or activity the system was operating at when the failure occurred

● What caused the failure?

● How will the failure be prevented from happening again?

Failures are not caused by an unknown factor like “bad luck,” or “itjust happened,” or “the manufacturer made a bad part.” We have foundmost failures can be analyzed and prevention taken to prevent their recur-rence Establishing teams to review each failure can pay off in majorways

Preventive Maintenance

Preventive maintenance (PM) of a hydraulic system is very basic and simpleand if followed properly can eliminate most hydraulic component failure.Preventive maintenance is a discipline and must be followed as such inorder to obtain results We must view PM programs as performance orientedand not activity oriented Many organizations have good PM proceduresbut do not require maintenance personnel to follow them or hold person-nel accountable for the proper execution of these procedures In order todevelop a preventive maintenance program for your system you must followthese steps:

First: Identify the system operating condition

● Does the system operate 24 hours a day, 7 days a week?

● Does the system operate at maximum flow and pressure 70% or betterduring operation?

● Is the system located in a dirty or hot environment?

Second: What requirements does the equipment manufacturer state forpreventive maintenance on the hydraulic system?

Third: What requirements and operating parameters does the componentmanufacturer state concerning the hydraulic fluid ISO particulate?

Fourth: What requirements and operating parameters does the filtercompany state concerning its filters’ ability to meet this requirement?Fifth: What equipment history is available to verify the above procedures forthe hydraulic system?

As in all preventive maintenance programs, we must write proceduresrequired for each PM task Steps or procedures must be written for eachtask, and they must be accurate and understandable by all maintenancepersonnel from entry level to master

Preventive maintenance procedures must be a part of the PM job plan, whichincludes (see Figure 15.1):

● Tools or special equipment required for performing the task;

● Parts or material required for performing the procedure with store roomnumber;

● Safety precautions for this procedure;

● Environmental concerns or potential hazards

A list of preventive maintenance tasks for a hydraulic system could be:

● Change the hydraulic filter (could be the return or pressure filter)

● Obtain a hydraulic fluid sample

● Filter hydraulic fluid

● Check hydraulic actuators

● Clean the inside of a hydraulic reservoir

● Clean the outside of a hydraulic reservoir

● Check and record hydraulic pressures

ABC COMPANY PREVENTIVE MAINTENANCE PROCEDURE

TASK DESCRIPTION: P.M – Inspect hydraulic oil reserve tank level

1 Inspect hydraulic oil reserve tank level as follows:

a) If equipped with sight glass, verify oil level at the full mark Add oil as required b) If not equipped with sight glass, remove fill plug/cap.

c) Using flashlight, verify that oil is at proper level in tank Add oil as required.

2 Record discrepancies or unacceptable conditions in comments.

PM Procedure Courtesy of Life Cycle Engineering, Inc.

Figure 15.1 Sample preventive maintenance procedure

● Check and record pump flow

● Check hydraulic hoses, tubing, and fittings

● Check and record voltage reading to proportional or servo valves

● Check and record vacuum on the suction side of the pump

● Check and record amperage on the main pump motor

● Check machine cycle time and record

Preventive maintenance is the core support that a hydraulic system musthave in order to maximize component life and reduce system failure.Preventive maintenance procedures that are properly written and followedproperly will allow equipment to operate to its full potential and life cycle.Preventive maintenance allows a maintenance department to control ahydraulic system rather than the system controlling the maintenance depart-ment We must control a hydraulic system by telling it when we will performmaintenance on it and how much money we will spend on the mainte-nance for the system Most companies allow hydraulic systems to controlthe maintenance on them at a much higher cost.

Measuring Success

In any program we must track success in order to have support from agement and maintenance personnel We must also understand that anyaction will have a reaction, negative or positive We know successful main-tenance programs will provide success, but we must have a checks andbalances system to ensure we are on track

man-In order to measure success of a hydraulic maintenance program we musthave a way of tracking success but first we need to establish a benchmark Abenchmark is method by which we will establish certain key measurementtools that will tell you the current status of your hydraulic system and thentell you if you are succeeding in your maintenance program

Before you begin the implementation of your new hydraulic maintenanceprogram it would be helpful to identify and track the following information

1 Track all downtime (in minutes) on the hydraulic system with thesequestions (tracked daily):

● What component failed?

● Cause of failure?

● Was the problem resolved?

● Could this failure have been prevented?

● Track all costs associated with the downtime (tracked daily)

● Parts and material cost?

● Labor cost?