JJ615 MECH COMPONENT & MAINTAINENCE: CHAPTER 2: LUBRICATION

INTRODUCTION

Lubrication is the process or technique employed to reduce friction between, and wear of one or both, surfaces in close proximity and moving relative to each other, by interposing a substance called a lubricant between them. The lubricant can be a solid, (e.g. Molybdenum disulphide) a solid/liquid dispersion, a liquid such as oil or water, a liquid-liquid dispersion (a grease) or a gas. With fluid lubricants the applied load is either carried by pressure generated within the liquid the due to the frictional viscous resistance to motion of the lubricating fluid between the surfaces, or by the liquid being pumped under pressure between the surfaces. Lubrication can also describe the phenomenon where reduction of friction occurs unintentionally, which can be hazardous such as hydroplaning on a road. The science of friction, lubrication and wear is called tribology. Adequate lubrication allows smooth continuous operation of equipment, reduces the rate of wear, and prevents excessive stresses or seizures at bearings. When lubrication breaks down, components can rub destructively against each other, causing heat, local welding, destructive damage and failure.

1.0 PRINCIPLE OF LUBRICATION

Viscosity is probably the single most important characteristic of oil that affects the engine. By definition, viscosity is a measure of oil’s resistance to flow, and it is measured at one or more standardized temperatures so that we can define viscosity grades of engine oils. It’s important to understand that the viscosity of engine oil changes continuously as the temperature of the oil changes. A properly formulated engine oil of the proper viscosity grade will provide a lubricant film in-between moving parts in the engine and protect them from wear. Viscosity characteristics of the oil will also affect things like oil consumption rates, low-temperature oil flow to the engine, and the speed at which the engine will crank — especially if the ambient temperatures are cold.

1.0.1 Viscosity requirements

Factors such as application speed, load, and operating temperature are all important factors influencing the choice of the correct oil to apply in any application. Generally, low viscosity oils are preferred for applications where either high speeds or low temperatures and pressures are present. When application speeds are reduced or operating temperatures are increased, the viscosity of the oil required to provide lubrication also increases.

Choosing an oil with the correct viscosity for any given application requires consideration of all the operating and environmental factors that the lubricated surfaces will be subject to in use. Basically, the oil must be thick enough to provide an adequate separation of the lubricated surfaces. That is heavily influenced by the speed, load, and surface temperatures that the surfaces will be exposed to in operation. The ideal oil for a given application will be viscous enough to ensure a proper fluid film under all operating conditions, yet fluid enough to avoid power losses resulting from excessive fluid friction.

Generally, we use the lowest viscosity oil in an application that will support the required loads. Sometimes, all of these criteria can result in a scenario where almost any oil will do, although it may not be optimal. Other times, it can be difficult to identify a single oil that will function adequately in the entire range of operating or environmental conditions that an engine may be subject to. For instance, an aircraft piston engine generally requires a fairly heavy oil to provide good lubrication due to design, cooling, and normal engine operating parameters. But high viscosity oils are usually limited in their ability to provide adequate flow characteristics at very low winter-time ambient temperatures. Therefore, aircraft piston engine designers must resort to the use of supplemental crankcase heaters for aircraft that must start under those cold conditions because using an oil with low enough flow characteristics at those low temperatures that would allow an engine to start when it is cold would not provide adequate protection when the engine gets to normal operating temperatures.

1.0.2 Viscosity measurement systems

Two common viscosity measurement systems are the Saybolt and Kinematic systems. These systems differ in the design used to make the measurement and the way it is calibrated, but the principle is the same. Oil to be measured is contained in a vessel which is immersed in a bath at a constant temperature. Remember viscosity of oil changes as temperature changes. So, if we are going to understand the viscosity of an oil, we need to understand the temperature at which the measurement was taken.

Once the temperature of the sample is allowed to stabilize, the sample is allowed to flow through a calibrated restriction (basically this is a fancy funnel). The time for a measured volume to pass through the restriction is measured. The higher the viscosity of an oil, the longer it will take to flow through the funnel.

1.0.3 Multi-grade oil

Remember that the viscosity of an oil changes constantly as temperature rises and falls. A viscosity index is a way to measure the rate at which that viscosity change occurs. Engine oil viscosity is measured and standardized in a document managed by the Society of Automotive Engineers (SAE) called SAE J300, and it defines the requirements of each SAE viscosity grade.

Single-grade oils are by definition oils that meet the requirements of only one grade defined in SAE J300. Multi-grade oils will meet the requirements of two grades as SAE J300 defines them. Multi-grade oils will meet the requirements of one W-grade on the SAE grading scale, and one non-W-grade. An SAE 10W and an SAE 30 are examples of single-grade oils that would meet the requirements of only one of the defined SAE grades. It’s entirely possible to formulate an oil that would meet the viscosity requirements of both of these grades, in which case the oil would be defined as a multi-grade SAE 10W-30.

The viscosity of multi-grade oils changes with temperature at a slower rate than it does with an equivalent single-grade oil. And when calculated, they will have a higher viscosity index number than similar single-grade products.

In order to formulate a multi-grade oil, an additive is used that alters the rate at which the viscosity of the oil changes with temperature change. These additives are chemical polymers that are commonly referred to as viscosity index improvers. Each W grade in the SAE grading system looks at low temperature viscosity at a different temperature due to the wide variability of the viscosities of different oils at the low end of the scale, where the oil may be nearing its pour point, or that temperature where it effectively begins to transform from a liquid to a semi-solid state.

Multi-grade oils feature several performance advantages over single-grade oils, particularly in ambient conditions that are less than ideal. They offer their greatest advantages when an engine must operate at the extremes of ambient conditions, either hot or cold. They tend to be cleaner burning because they allow the formulator to cut back on the use of a lubricant base blending oil called bright stock that tends to contribute more heavily to the formation of engine deposits as the oil is burned. When engine oil sump temperatures are high, a multi-grade oil will actually maintain a higher viscosity than its single-grade counterpart. SAE 15W-50, 20W-50 and 25W-60 are all common grades of aviation piston engine oil.

1.0.4 Types of friction

Friction is the force that provides resistance when two surfaces attempt to move relevant to each other. Reduction, and ideally the elimination, of friction is the primary function of a lubricant. There are three types of friction we will discuss: sliding friction, rolling friction, and fluid friction.

Engines experience both sliding and rolling friction at various points depending on engine design. Friction also results from the flow of a lubricant. This type of friction is called fluid friction. Although much less of a factor than solid friction, it also factors into the amount of energy that is required to turn the engine, particularly during start-up when the lubricant is the most viscous. Proper balance of fluid friction with solid (either sliding or rolling) friction is the key to a properly functioning engine

1.0.5 Sliding friction

When two surfaces move relative to each other, coming into contact with each other, the resulting sliding friction provides resistance against that motion occurring. The amount of friction is dependent on such factors as the weight of the two surfaces, the speed at which they are moving, surface finish of those surfaces, and any external pressures applied. The amount of friction will directly influence the rate at which the surfaces will wear as friction occurs.

1.0.6 Rolling friction

Rolling friction requires much less force to overcome, and produces less heat since the actual contact surface providing resistance is much smaller than with sliding friction. This principle illustrates the desirability of ball and roller type bearings where their design is compatible with the equipment design, rather than the use of plain sleeve type bearings where there is much more contact area and sliding friction is the type of friction we have to overcome.

1.0.7 Fluid friction

Fluid friction provides the least amount of resistance to overcome when two surfaces are moving relative to each other. It occurs as fluid molecules slide past each other. Since they are pliable and elastic in nature, fluid friction produces the least amount of heat resulting from friction and takes the least amount of energy to overcome. In general, lubrication is the substitution of fluid friction for solid friction.

2.0 LUBRICATION MANAGEMENT

All process industries use lubricants as part of an effective preventative maintenance strategy. Increasing control and technology, reducing complexity and cost through a plant review can:

Ø Improve plant productivity through lubricant technology

Ø Reduce risk

Ø Rationalise usage

Ø Control re-lubrication intervals

Ø Minimise down time

Ø Assist with audit compliance

Ø Minimise admin and maintenance tasks.

Each survey can include:

Ø A review of all the plant lubrication requirements,

Ø A detailed photographic/ visual survey of the full manufacturing facility

Ø A customised information folder

Ø Colour coded identification of all lubrication points

Chemical Process Management (CPM)

v Intimately understanding the customer’s requirements and needs

v Providing a personalised site plan

v Implementing cost saving initiatives.

v Ensure adequate stock levels are held

v Providing advice and support on lubricant machinery requirements and modifications

v Carry out condition monitoring and lubricant assessments

v Schedule regular meetings to discuss progress and future opportunities

3.0 LUBRICATION PROTECTION

The typical function of a lubrication is to protect against friction and wear. Lubrication are also used to protect against corrosion by displacing moisture and leaving a continuous coating on the part.

When choosing a lubricant, it is important to consider the intended application as well as the environment conditions to which the assembly will be exposed. Environment conditions are critical successful selection of the right lubrication product. Factors including high temperature, harsh chemicals and contaminants may have an adverse effect on the expected lubricant performance.

4.0 LUBRICATING SYSTEM

INTRODUCTION

Lubricating system is mechanical system of lubricating internal combustion engines in which a pump forces oil into the engine bearings lubricating system. Mechanical system of lubricating internal combustion engines in which a pump forces oil into the engine bearings force feed, force-feed lubricating system, pressure-feed, pressure-feed lubricating system. Internal combustion engine, ICE is a heat engine in which combustion occurs inside the engine rather than in a separate furnace heat expands a gas that either moves a piston or turns a gas turbine.

Type of lubricant system:

- Mechanical system (a system of elements that interact on mechanical principles).

Part of lubricant system:

- Oil filter (a filter that remove impurities from the oil used to lubricate an Internal- combustion engine).

- Oil pump (a pump that keeps a supply of oil on moving parts).

Lubricant device:

Lubricators and lubrication systems automatically provide bearings with the correct quantity of lubricant. This prevents the most frequent cause of rolling bearing failure: inadequate or incorrect lubrication. Approximately 90% of bearings are lubricated with grease. Re-lubrication with the correct quantity of grease at the appropriate intervals gives a significant increase in the life of bearings. For manual re-lubrication, grease guns are suitable.

Lubrication system:

- A single-point or multi-point lubrication system can supply lubrication points precisely and irrespective of temperature. The dispensing times can be set individually.

Lubricators

Automatic lubricators convey fresh grease in the defined quantity at the correct time to the contact points of the rolling bearing. The devices adhere to the lubrication and maintenance intervals and prevent under-supply or oversupply of grease. Plant downtime and maintenance costs are reduced as a result. The lubricators are matched to the bearing position. They have a wide range of applications, for example on pumps, compressors and fans, in conveying equipment, machinery etc.

Lubricators have following advantages:

- Individually configured, precise supply to each bearing position.

- Fully automatic and maintenance-free operation.

- Reduced personnel costs compared to manual re-lubrication.

- Different dispensing times can be selected.

- Pressure build-up to max. 50 bar, thereby overcoming any obstructions.

5.0 Application of Lubricating Program plan and Implementing

The typical industrial environment contains silica dust, oxides, metal ﬁlings, and other abrasive materials. When these materials are mixed with some lubricants, they create a lapping compound that greatly accelerates wear. Unless proper lubricants and lubricating systems are utilized and proper procedures are followed to prevent contamination, premature equipment failure results. A well-planned and properly implemented lubrication program, designed to place the right amount of the right material in the right place at the right time, will more than pay for itself in reduced downtime, lower maintenance costs in both parts and labor, and reduced energy costs.

5.0.1 SELLING MANAGEMENT

Because plant management often balks at what it perceives to be an increase in indirect costs for maintenance, it may be necessary to sell management on the cost savings possible through an eﬀective lubrication program. In order to sell management on such a system, it will usually require collecting historical data on the cost of equipment malfunctions, including parts, labor, and downtime. If such records do not exist, this information will need to be collected. If equipment maintenance records have been kept on a computer, it may be necessary to add a few ﬁles to collect the data needed to justify the additional expenditure to implement an eﬀective lubrication program. In addition to historical data, recording of amp meter readings may be used to show the energy savings possible when superior lubricants replace inferior products for given applications. This approach has proved particularly eﬀective in chain and conveyor applications. Some plants are also using vibration analysis equipment with recorded vibration patterns to indicate bearing conditions and to predict failures and lubricant eﬀectiveness.

5.0.2 SELECTING LUBRICANTS

The multitude of lubricants recommended by equipment manufacturers can be simpliﬁed by selecting good multipurpose lubricants to reduce inventory requirements and the possibility of misapplication. Thin-ﬁlm/dry-ﬁlm molybdenum sulfide lubricants and synthetic lubricants can play an important role in reducing contamination and energy consumption. Dollar savings from longer lubricant life, reduced equipment maintenance, lower power consumption, and less downtime can be several times greater than the higher cost of these lubricants. On the other hand, premium-grade lubricants will not improve or correct lubrication problems if mechanical factors such as misalignment or severe environments (high levels of dirt and water contaminants) are involved. These products should be purchased on the basis of in-service results rather than on the price per pound or gallon. It is also necessary to determine the compatibility of the selected lubricants with seals and hose linings before putting them into service.

5.0.3 LUBRICATION TRAINING

Increasingly, pressure is being placed on maintenance management to hold down or even reduce the number of people performing maintenance functions. During times of personnel cutbacks, the oilers are often the ﬁrst to go, usually replaced by untrained personnel. Depending on plant size and contractual obligations, the employee responsible for lubrication should be a machine operator, skilled tradesman, or trained designated oiler. Selecting an employee who knows the equipment will greatly improve the results of any lubrication program. Some plants are using highly skilled preventative maintenance inspectors who also lubricate. These people see every piece of equipment in the operation on a scheduled basis. In any case, it is important to provide the individual with proper instruction in application methods, types of lubricants, handling methods, and safety procedures. Engineering personnel should be trained on proper design procedures of lubrication systems and be up-to-date on the latest technological advances in the lubrication industry. They also need to be aware of the problems in the plant that maintenance personnel have in troubleshooting lubrication system malfunctions. Lubrication system speciﬁcations should be written to ensure that every piece of equipment entering the plant has a properly designed lubrication system. The lubrication equipment speciﬁcations should inform the equipment supplier exactly what is expected of the lubrication system. This would include such items as low-level switches, high/low-pressure sensors, ﬂow switches, or metering devices. All sensors should inform the operator of lubrication system malfunction and, in some cases, provide for machine shutdown if a fault occurs. Nearly all poor lubrication practices are traced to a lack of training. The level of performance of equipment in an operation is directly proportional to the quality of the lubrication program in that operation and the support provided to the program by management and engineering personnel.

CONCLUSION

The lubricant play an importance role in un-lubricated sliding part creates tremendous friction that needs great amount of power to move, slide or separate them. If friction reached the critical level, the heat will fuse the parts and will cause seizure that will ultimately bond the parts or burn them beyond use. Proper lubrication eliminates the friction that totally contributes to this failure phenomenon. The lubricant stays in between the sliding matter and serves like roller bearings. It continuously reduces the coefficient of friction, thereby reducing the force to move and heat that leads to seizure, bonding and fire. The general purpose of lubrication is to separate the two sliding bodies to reduce friction. Lubricant in machineries has to stay and maintain the lubricating ability to serve its purpose. This is indicated in the lubricant as drop point for grease and viscosity for oil. Load and working temperature condition are also a major consideration is lubricant selection. Oil and grease comes in basic forms as produced. The additives make the difference as to what lubrication compounds are added to satisfy the end use. The main purpose of lubrication is to reduce friction and wear in bearings or sliding components to prevent premature failure. Direct metallic contact between the bearing rings, rolling elements and cage, which are the basic components of a bearing, is prevented by an oil film that reduces the friction and wear in the contact areas. It prevents inter metallic contacts between slides by allowing film of lubricants preventing friction. The sliding or rolling fatigue life of bearings depends greatly upon the viscosity and film thickness between the rolling contact surfaces. A heavy film thickness prolongs fatigue life, while insufficient film thickness shortens it. Circulating lubrication may be used to carry away frictional heat or heat transferred from the outside to prevent the bearing from overheating and the oil from deteriorating.

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