CMMS AND PREVENTIVE MAINTENANCE - 2

Summary from part I: The company has decided to replace the bearings once a year during the annual shut down. They had always done that but had still had three break downs of the bearings during the last ten years.

The manufacturer’s handbook said “Once a year, open top of screen, idle screen and listen to the bearings with a stethoscope or similar device. If the bearings sound bad, replace bearings”

To install transducers for vibration analysis of bearings is an obvious alternative. To do that will cost Euro 1500. The financial decision maker said no to the maintenance manager’s request to install the transducers because she thought it was too expensive and the maintenance manager had not provided a financial justification to install transducers. Besides that, she referred to the instructions in the manufacturer’s handbook and claimed that must be right.

This example is a true case from many plants with an almost identical manufacturing process. To help the maintenance manager optimize maintenance of the bearings in the screen, we made a short consequence of failure analysis of different scenarios that might occur and then put a financial value to each of them.

If we accept the failure developing principles described in the May/June issue of this magazine we can use this as a methodology to bridge the gap between a technical solution and financial language. It is obvious that the manufacturer’s recommendations are wrong and you do not need to be an expert on their equipment to prove this fact. Attaching a vibration transducer in each bearing housing and pull wires to a point outside of screen is of course a better and more financial viable solution.

As a case study I like to use a discussion I have had in many plants with groups of experienced maintenance professionals.



Picture 1. The picture shows a rotating screen where incoming media is separated in good product, and reject. The inside rotary assembly rotates with 350 rpm inside a stainless steel basket with drilled holes. The diameter of stainless steel basket is one meter. The inside bearings are lubricated through two pipes. The rotary assembly is driven by an electric motor and V-belts. If the function of the screen ceases, it will shut down a process at a cost of Euro 20000 per hour in lost production. A break down of the bearings might cause the rotary assembly and the stainless steel basket to be destroyed at a cost of Euro 100000.

There are three options we can choose from to maintain the bearings:

O.T.B = Operate To Break Down
F.T.M = Fixed Time Maintenance
C.B.M = Condition Based Maintenance
If we chose O.T.B. the job to change bearings and very possibly also V-Belt drive and other damaged components can be planned, but not scheduled. We can make sure we keep spare parts in store, our people know how to do the job, what special tools are needed etc. This often leads to that we keep some very expensive parts in store to prepare for the worst case scenario. It is likely to occupy at least six people to correct the break down. They will not all work, but because scope of work was unknown when the symptoms of the broken down screen function was noticed, all available resources would migrate to the broken down screen and it is likely we would call more people than necessary for overtime. In most plants the unscheduled break down is 76.2 % likely to happen when the maintenance crew is not there. So they have to be called in on overtime or you fall into the bad habit of having maintenance people on shift. This is of course not only because of this equipment but because most maintenance is reactive in nature.

If we choose F.T.M. we can both plan and schedule the job. In this case the process line has scheduled clean up and process material shut downs every four weeks during eight or alternating twelve hours. It will be easy to plan and schedule this job during one of these shut downs thus avoiding any lost production due to screen maintenance. We would still have to keep a very expensive exchange part in store because without it, it would take longer time to replace bearings than allowed by the scheduled shut downs. The disadvantage of F.T.M. is that we will over maintain the screen, work has to be done more frequent than necessary. It is always the risk that we will induce failures to components when they are disassembled and assembled. The fact is that the estimated life of new bearings is 1 – 15 or even 1- 25 years so it is obvious that we will never know if we replaced good bearings with good once.

If we chose C.B.M. we optimize maintenance of the bearings in the screen. The assumed break down frequency used to calculate cost for O.T.B. will be the same. You can not detect more failures than you assumed would occur. The failure frequency might not be right, but the comparison between costs for O.T.B. and C.B.M. is right.

In the table (click here to see the table pfd) a break down frequency of one failure per year will occur. On an annual cost basis that is 1/5 or 0.2 failures per year. In the O.T.B. case the failure will develop to a break down. Repair time for break down is 12 hours with six people. Cost for crafts people is 40 Euro per hour (Plus extra cost for very likely overtime and management/supervision time). The material cost is the cost for bearings and V belt drive. If it is estimated to take 12 hours to repair, it will cause 15 hours of lost production @ 20000 Euro per hour before process is up running making quality product. The worst case scenario is that the rotary assembly will destroy the stainless steel basket which will cost 100000 Euro to replace, in the best case scenario this will not occur. In the example above we have assumed a 50% likelihood that worst case scenario will occur.

In this example cost to carry spare parts is not included. In the O.T.B. alternative a full set of the rotary assembly and screen will be stocked at a carrying cost of 30000 Euro per year. In the other cases this cost will be much lower or even 0.

To do C.B.M transducers at a cost of 1500 Euro must be installed and it is apparent that it will pay off. If this had been specified when the screen was purchased the cost would have been 700 Euro and two break downs would have been prevented.

With the above example we have shown the financial impact of Optimized Preventive Maintenance. The difference in cost can be 1 – 100 as in the example above.

It must be made clear that in most cases an analysis like the one described here is not necessary to do. Only about 5% of all components require an analysis to decide the most cost effective maintenance method, for most other components the best maintenance procedure can be decided in a much less time consuming way.

CMMS AND PREVENTIVE MAINTENANCE

A very important part of a cost-effective preventive maintenance program is what I call the route-based activity. These are activities that are easiest to do, and to administer, if they are presented in a list. This list can be presented in electronic format or in a paper format and includes such activities as lubrication and inspections by maintenance craftspeople and equipment operators.

There are two major things that surprise me regarding these basic preventive maintenance activities:

1. With the very good return on investment (ROI) you get from these programs, I am surprised at how many plants lack these programs or perform them very poorly.

2. All major computerized maintenance management systems (CMMS) lack the capability to administer these routes in an efficient manner.

RETURN ON INVESTMENT. We use cost avoidance analysis as a tool to measure the return on investment (ROI) from route-based activity programs (exclusive of lubrication). In the last year we have verified the ROI to be between five to 10 times the initial investment and, after that, 10 to 30 times the cost to run the program. Even if such a good ROI can be verified, the inspection program is very poor in most plants and, if one exists, it is not executed with the highest priority.

Computerized Maintenance Management Systems (CMMS) SHORTCOMINGS. All CMMS providers we talk with say their systems can produce inspection lists to support inspection and lubrication routes. We must understand that, in the computer world, the answer is always, "Yes, our system can do that.” It is never “no.”

The dilemma is that the CMMS provider does not think in terms of route-based activities at all. Their systems are driven by work orders. If each inspection is given a work order number, you can do the inspections in a route documented with more than 250 work orders. First of all, this is impractical for the person doing the inspections, and, secondly, it will require a lot of time for someone to close all the work orders.

Another way route-based activities are performed in a work order driven CMMS is to give each route a work order number and describe each inspection in a sub work order. This still creates complications and administrative time. A third example of how some plants try to document and administer route-based activities is to give each route a work order number and have the route documented in a spread sheet. Again, the dilemma is that this method will not support effective routes and will make it more cumbersome than necessary to change the content of inspections, transfer tasks to operators, change frequencies, merge mechanical and electrical inspections, and so forth. All of these activities are frequently done if you have a good system implemented.

To date, we have only found small CMMS packages that have good inspection programs. The solution is, therefore, to have a standalone system for route-based activities. Even in a time when it seems like all activities must be integrated into one company-wide system that covers everything, the best solutions can still be standalone systems. There are very few things—if any at all—in a route-based system that need to be tied with other activities. Therefore, you can very well buy a standalone system for this activity. A single-user system that can do this well is not expensive. The minimum requirements for a good route-based system must allow you to:

See all programmed preventive maintenance activities per equipment identification in one document.

-Change an activity from one craft to another in seconds. (For example, moving a mechanical inspection to an operator inspection).

-Change a frequency in seconds.

-Change a standard activity in minutes. (For example changing the standard inspection of gears to a new inspection method, or changing three types of lubricants to a single new type.)

-Add or delete equipment in minutes.

GOOD INSPECTION PROGRAMS. If you do have a good inspection program implemented, you should recognize the following indicators:

-All hours for lubrication, mechanical, and electrical and instrumentation preventive maintenance activities are 6% to 12% of total maintenance hours.

-Most work in shut down and weekly and daily schedules is the result of early problem detection from preventive maintenance inspections.

-There are no unnecessary duplications of preventive maintenance activities between mechanical, electrical, lubrication, operators, and so forth.

-The content of the preventive maintenance program is right and you actually perform 100% of programmed preventive maintenance activities.

-Average vibration level continuously decreases

PLANTS SHUTDOWN OR TURNAROUND MAINTENANCE TIPS

In best practices, a closeout review or critique meeting gathers all the information from the last event and uses it to prepare for the next event. It is the ammunition your organization can use to either support the current Shutdown/Turnaround/Outage process as cost and safety effective or to challenge how the process is currently performed.

Unfortunately, many organizations either don’t do the review or have the meeting and do not use the information to impact the next shutdown cycle.

Capturing the Right Information

The effectiveness of the closeout review is directly related to the information captured during the execution of the shutdown/turnaround. During the execution you should be capturing information including:

Was it on time?

Was it on budget?

Was all priority work completed?

Was any work delayed or had a scope change?

Were work delay codes entered into properly into the CMMS?

Did the handover and hand back go as planned?

What was the condition of the equipment?

Did all resources work as planned? (Contractors, shifts, maintenance, operations)

Were all infrastructure and logistics needs accomplished?

Were all materials staged?

Were Work order feedback forms logged?

Was progress communicated daily?

Were KPI’s met or adjusted?

Did the overall plan perform as expected?

What work is left for the next shutdown cycle?

Was a lessons learned process flow followed?

Who’s Responsible for the Closeout Review?

Ultimately, the plant management team is responsible for ensuring that the closeout review is completed and effective. They are accountable for ensuring that all the Shutdown Group Stakeholders attend the closeout review. Prior to the meeting, they should have an agenda with clear objectives and during the meeting maintain a constructive meeting (no finger pointing, everyone’s input is valuable).

Each stakeholder group (management, maintenance, engineering, stores/purchasing, contractors, operations) is responsible for reviewing their metrics and performance. A good way to do this is to have each group complete self-evaluations. These evaluations are a good reflection of how each believed the shutdown was performed and should be compiled versus actual KPIs to help improve the next shutdown/cycle.

A best practice is to hold the meeting within a month of the complete shutdown. This allows each group to review their metrics, compile results and reports and make a list of suggestions to be brought to the meeting to improve the next shutdown and to list work items to be added to the next shutdown or added to maintenance’s schedule if they work can be done as non-shutdown tasks.

Shutdown Turnaround Optimization Program includes 6 reviews of the Shutdown/Turnaround Process:

Strategic Review

Work Scope Review

Plan Review

Schedule Review

Execution Review

Closeout Review

These six reviews are designed to uncover and design the most effective shutdown process for your organization that focuses on how to bridge the

gap between your current Shutdown Process and best practices. By applying these 6 reviews, your organization can improve preparation, which

impacts execution efficiency, cost, and usage of resources.

PLANTS MAINTENANCE MANAGEMENT

INTRODUCTION

The objectives of a plant maintenance program should be to the improve the over-all plant reliability and safety by preventing equipment breakdown, and to maintain the equipment in a satisfactory condition for normal operation or emergency use; all at the lowest possible maintenance cost.

SCOPE

The program encompasses the practical and technical approaches to provide a complete and well rounded program to cover every aspect of good Preventive / Predictive and Equipment Condition Monitoring Maintenance. The scope of this procedure will cover program development, personnel requirements and responsibilities and equipment requirements.

MAINTENANCE STRATEGIES

Maintenance is the combination of all those technical and administrative actions, including supervisory actions, with the purpose of maintaining or restoring an item to a status allowing it to execute the required function.

Maintenance has the following main objectives:

 Productive Objective – Guarantee the availability of Plants and Equipment to Production, so that they can perform their services under the best conditions, in terms of efficiency, reliability and safety.

 Economic Objectives – Ensure that the services rendered is at minimum costs with the maximum of efficiency.

Opportunity Maintenance – Work carried where the timing is determined by other events that can either be predictable or not predictable, e.g key equipment failure or production shutdown.

Predictive Maintenance – Is the preventive maintenance carried out whenever the trend of one, or more operating parameters of an item of equipment shows an incipient failure. The Predictive Maintenance uses measuring or monitoring devices in order to identify conditions that require correction before a functional failure occurs. Typical condition monitoring techniques are vibration analysis, crack detection, thermography, pressure and temperature monitoring, oil analysis, etc.

 Using the inspection data gathered to accurately predict the allowable lapse time and point of expected equipment failure for initiation of corrective action prior to catastrophic failure.

                                                 Fig. 1: Bearing Conditions Monitoring

Fig.2. Stationary condition diagnostics and monitoring system typically consists of a personal computer or a diagnostic station connected to signal commutation and conditioning blocks and then vibration and rotation speed sensors. The number of channels and measurement points in such a system may be from a few ones up to several hundreds.

Technical Inspection

Technical inspections are those performed by highly skilled technical personnel using sophisticated monitoring equipment to gather, store and analyze equipment condition data for accurate predictions of lapse time before failure. This type of ECM is usually performed on an established frequency basis, except when special technical field analyses are requested by field maintenance or the daily practical ECM inspection group.

Fig 3: Plant Technical Inspector using monitoring equipment

Practical Inspections

Practical inspections are those performed by maintenance personnel with many years of field   experience using less technical monitoring equipment. Primarily, they apply their skills of looking at, listing to and feeling of equipment on established daily routes to spot potential problems and correct them. The practical ECM inspectors fill a very important void between the technical inspection frequencies by monitoring   every piece of equipment daily and provide a constant flow of equipment daily and provide flow of equipment conditions data.

                                      Fig 4: Experience equipment inspectors at work

                                                                                                                                                                    Plant Maintenance Program Development

Lubrication Program

The first and most important step in a successful PM/ECM program is lubrication. Plant lubrication program will prevent or solve approximately 60% of rotating equipment problems. Therefore, the lubrication program must be initiated and implemented as designed by the Lubrication Engineer.

Equipment Lists

Equipment lists are prepared from plant Material Station Reports (MSRs). Preparation of the equipment list for the PM/ECM program can vary depending upon the plant being a new facility, less than one year old, or an older plant having operated more than one year. Extreme care must be exercised to overloading the program with none PM/ECM items such as statutory  or pre-turnaround inspections. To ensure optimum program effectiveness, equipment list should be prepared using the following guidelines.

Equipment Lists for New Plants

v Select the top 20 pieces of equipment most critical to the continuity of plant operations.

v Select the top 20 pieces of equipment that experiences has dictated will require the most maintenance.

v Select the top 20 pieces of equipment that would result in the highest monetary loss should they fail.

v Then progress down the MSR list selecting equipment, again as outlined above, for the progress, considering frequencies, manpower a walked and remembering that every piece of equipment will be walked by everyday by the practical inspectors.

Equipment Lists for Old Plants

v Select the top 10 pieces of equipment most critical to continuity of plant operation.

v Select the top 10 pieces of equipment causing the most plant downtime or production loss.

v Then progress down the MSR list selecting equipment, as outlined above, for the next group of 10’s.

Equipment Classification

v Each piece of equipment is categorized or classified (pumps, motor, blowers, compressors), and is assigned a service number, which indicates the type equipment and its in-line process position.

v Finalized Equipment List should be reviewed and approved by the Maintenance Manager.

Inspection Frequencies

Using the finalized PM/ECM equipment lists, frequencies for both the technical and practical inspections are established. If equipment historical data is available, it is used to establish the frequencies (how often individual pieces of equipment are looked at). If historical data is not available (i.e., new plant) the frequencies are established maintenance and maintenance engineering personnel with experience and knowledge of similar plants and equipment. Frequencies will be set at either daily, weekly, bi-weekly or monthly, depending upon the criticality of the equipment. Care must be exercised to avoid overloading available manpower, yet a full day’s activity should be planned for each inspection discipline. Also, consideration must be given to the equipment cost, spares inventory, installed spares and criticality to continuity of plant operation. Frequencies should be reviewed annually.

Inspection Routes

Inspection routes are established by actually walking through each unit, with the prepared equipment list and established frequencies, formulating the routes to avoid excessive travel by the Practical PM Inspectors, yet ensuring that all equipment is covered and walked by each day. The routes must be plotted on equipment layout drawing in order to train the inspectors. Inspection routes are not normally needed for the Technical Inspections since these activities are usually confined to certain pieces of critical equipment or dictated by request from the PM Maintenance Supervisor.

                                            Fig 5: Plants Inspection Routes 

Inspection Schedules

Workable area PM schedule / check sheets are prepared by calendar days based upon the number of pieces of equipment on each route and their inspection frequencies. Schedules are prepared as a balanced system to where the daily work load will be fairly consistent. The number of schedules per area / unit can vary from one to as many as fifteen with each schedule averaging four equipment list sheets.

Fig 6: Plant Maintenance Schedule

Inspection Calendar

PM calendars are designed into number of periods with an open block under each day of the week. The schedule numbers are entered in these blocks. The PM Inspector simply checks the day of the week and the schedule numbers therein, pulls the appropriate schedule from the file cabinet, providing that particular day’s inspection assignment. A calendar is prepared for each process unit, depending upon the size of the plant.

                                     Fig. 7: Equipment Maintenance Calendar

                                                                                                                                                                                         

                                 

INDUSTRIAL LUBRICATION OF ROTATING EQUIPMENT

                              

                         

Introduction

Correct and efficient lubrication is essential for the satisfactory function of rolling element bearings and to attain maximum service life. It is advisable for both design engineers and maintenance technicians thoroughly understand the basics of tribology and its effects on the proper function of rolling element bearings.

            

      

Each rolling element bearing represents a “tribological system” consisting of the bearing and an adequate lubricant. In the system – namely, in a rolling element bearing – the lubricant primarily separates the metallic surfaces and thereby reduces friction, as well as preserving the steel parts and preventing or neutralizing the effects of contamination.

In many cases, the bearing life is determined by the service life of the lubricant: the failure of the lubricant will definitely terminate the life of the bearing. In the case of oil lubrication, the lubricant may also act as a coolant, actively taking part in the heat dissipation and thereby supporting the thermal equilibrium in bearings operating at high speeds.

Lubrication types

Generally, three types of lubrication are used in rolling element bearings – grease, oil and solid or dry lubricants. The selection of a suitable lubrication method should be made in the early stages of design. The operating conditions – such as operating speeds, temperature and environment – have to be carefully evaluated.

The latest state-of-the-art lubricants feature special agents – additives – to enhance specific lubricant properties, i.e high pressure characteristics, temperature stabilization, etc.

Grease lubrication

Grease is by the most common form of lubricants, in fact, about 90% of all rolling element bearings are grease lubricated. Simple application, minimal maintenance, easy sealing, a wide spectrum of lubricants and the availability of pre-greased and greased-for-life bearings are some of the main advantages of grease lubrication.

Grease consists of a soap structure, which in most cases is a metal soap based on lithium soap with a base oil and additives.

Oil lubrication

Oil is usually used for bearing lubrication, if an oil supply system is already incorporated into the design of a machine for other purposes (e.g gearbox lubrication, etc.)

Oil lubrication is also used for special conditions that require effective heat dissipation. In certain high-speed applications, the use of oil allows for a highly accurate and easily dosed application, for example via oil jet or oil mist.

Solid and dry lubrication

Where application do not allow the use of oil or grease, for example, due to heat, several other materials can be used, such as graphite powder or pressed graphite cages, polytetrafluomethylene (PFTE) powder, metallic coverings, sliding varnish and various other surface treatments.

Speed ability

Different lubricants and lubrication methods have different abilities for operating under given speeds. The most important factor for evaluating the “speed ability” of a certain lubrication method is the speed characteristics (n.dm); where n is the bearing operating speed (rpm) and dm the bearing pitch diameter (mm):

 dm = (d + D)/2

where, d = bearing bore diameter and D = outer diameter.

Table 1. Typical n.dm values of different lubricant types
S/N	Lubrication method	n.dm
1	Grease lubrication:
	(a)  Standard bearing greases	500,000
	(b) Special greases	1,000,000
2	Oil lubrication:
	(a)  Oil bath lubrication	500,000
	(b) Circulating oil lubrication	750,000
	(c)  Splash oil lubrication	800,000
	(d) Oil mist lubrication	1,500,000
	(e)  Minimum quantity lubrication	3,000,000

Note: For n.dm values of ˃1,000,000 practical experience is of major importance as special appliances such as oil coolers, additional pumps or a separate compressed air system for oil and air lubrication, may become necessary.

Table 1 shows some typical n.dm values of various lubricating methods. All values are for guidance only. The lubricant supplier should be contacted for detailed and accurate values for a specific lubricant.

Characteristic parameters

Viscosity

This is one of the most important features for selecting an oil or grease. The term viscosity describes the ability of oil to flow under given conditions and temperatures. A low figure indicates thin oil; higher figure denote thicker oils. In the case of grease, the viscosity of the respective base oil is indicated.

Since the viscosity of a lubricant depends considerably on its temperature, the nominal viscosity of a lubricant is typically indicated with a defined reference temperature, usually 40˚C.

                                                                                                                           

Consistency

The consistency indicates the "stiffness" of a grease. It is classified by the NLGI (National Lubrication Grease Institute) scale according to DIN 51818 where the penetration depth of a standard test cone into a grease specimen at a standard test temperature and after a standard time is measured. The deeper the test cone penetrates, the softer the grease is and hence the lower the NLGI grade. (see Table 2)

Table 2. NGLI consistency grades of greases
S/N	NGLI consistency grades (DIN51818)	Worked penetration (0.1mm)
1	000	445 to 475
2	00	400 to 430
3	0	355 to 385
4	1	310 to 340
5	2	265 to 295
6	3	220 to 250
7	4	175 to 205
8	5	130 to 160
9	6	85 to 115

                                                                                                                                                            

Stiffer lubricants have higher consistency and therefore higher NLGI grades. For lubricating rolling bearings, grease lubricants of NLGI grades 2 and 3 are widely used. For certain high-speed applications, for example spindle bearings, grade 0 and grade 1 greases may be used. 

Soft greases are optimal for small and miniature bearings, low temperatures, high-speeds or when central lubrication system is installed. Stiffer greases are suitable for large bearings running at low speeds or for high-temperature applications. Stiffer greases also provide a better sealing effect.    

Grease volume

The lubricating grease fill volume in bearing housings is determined mainly by the bearing design and its actual operating speed. The free space within the bearing itself has to be fully filled with grease in all cases. The grease fill volume for bearing housing cavities should be chosen according to Table 3.

Table 3. Relationship between speed ratios and grease filling volumes
S/N	Speed ratio (%) ͦ		Grease filling (%) ͦ ͦ
	˃	≤
1	-	20	80 to 90
2	20	75	30 to 50
3	75		25
˚ In % of the speed ratings with grease lubrication given in the bearings product tables ˚˚ In % of bearing housing cavity volume

Grease volume

The lubricating grease fill volume in bearing housings is determined mainly by the bearing design and its actual operating speed. The free space within the bearing itself has to be fully filled with grease in all cases. The grease fill volume for bearing housing cavities should be chosen according to Table 3.

Table 3. Relationship between speed ratios and grease filling volumes
S/N	Speed ratio (%) ͦ		Grease filling (%) ͦ ͦ
	˃	≤
1	-	20	80 to 90
2	20	75	30 to 50
3	75		25
˚ In % of the speed ratings with grease lubrication given in the bearings product    tables ˚˚ In % of bearing housing cavity volume

Grease service life

Bearing lubricants undergo permanent mechanical stress as they are over-rolled continuously by the rolling elements. Additional lubricants change their characteristics, particularly when opening at high temperatures, in the presence of humidity, pollution and chemical agents. The service life of lubricants is therefore limited; its length depends on the individual operating conditions, particularly the operating temperatures and the speed.

In the case of grease-for-life bearings, mainly with shields or seals on both sides, the service life of the lubricant is expected to be longer than the required bearing life rating. When considering the maintenance of bearings, it is essential to estimate the service life of the lubricant realistically and schedule regular re-lubrication.

Re-lubrication intervals

Re-lubrication intervals are very much related to the actual operating conditions and the individual characteristics of the lubricants in question. Modern high-performance lubricants allow for much longer service life due to the progress in lubricants research, development and manufacturing. For accurate figures on specific lubricants  the grease vendor should be consulted; for standard lubricants the realistic service life in hours, tn, can be roughly estimated with the following equation:

t_n = (a.10⁶/n.√d) – b.d

where, a and b = bearing type and series coefficient (see Table 4 below), n = bearing operating speed (in rpm); d = bearing bore diameter (mm)

Table 4. Bearing type and series coefficients for calculating lubricants service life
S/N	Bearing types and series	Coefficient
		a	b
A	Deep groove ball bearings
1	160, 60, 62	75	18
2	63	65	18
3	64	55	18
B	Angular contact ball bearings
1	72 B	65	18
2	73 B	55	18
3	32	55	18
4	33	55	18
C	Four-point contact bearings
1	QJ 2	65	18
2	QJ 3	55	18
D	Self-aligning ball bearings
1	12, 22	75	18
2	13, 23	65	18
E	Cylindrical roller bearings
1	N. 10, N. 2, N. 2..E	75	18
2	N. 3, N. 3..E	65	18
3	N. 4	55	18
F	Taper roller bearings
1	302..,320..,322..,	20	7
2	303..,313	18	7
3	323..,	15	7
G	Spherical roller bearings
1	222..	20	7
2	223..,	15	7

For safety reasons, the re-lubrication intervals of new machines or plants where no practical experience exists should not exceed 50-60% of the initial calculated service life of the lubricant.

Additional and more precise information on specific characteristics of lubricants, their chemical reactions with some elements and the anticipated service life of the lubricant under certain operating conditions are available from the lubricant manufacturers.