This chapter discusses lubrication as it applies to specific equipment generally encountered at Dams, Hydroelectric Power Plants, Pumping Plants, and related Water Conveyance Facilities.
Auxiliary equipment, such as small Pumps, Air Compressors, and Tools are discussed throughout this manual.
The following discussions emphasize major equipment such as Turbines, Pumps, Governors, Gates, Hoists, and Gear Drives. This equipment is often custom designed and constructed according to specifications, at significantly greater cost than off-The-Shelf commercial equipment.
12.2 Environmental Regulations
Environmental concerns are having a growing impact on the development and use of lubricants for Turbines, Governors, and Gear Drives. Although some lubricants are identified as food grade and have been FDA-approved and are subject to ASTM standard testing procedures, there is no worldwide standard definition or specification for environmental lubricants intended to replace standard lubricants.
U.S. regulations are becoming more restrictive with regard to the Contents, Use, and Disposal of lubricants. Four regulations are of particular interest at the Federal level:
- Comprehensive Environmental Response Compensation and Liability Act (CERCLA) - Imposes liability for cleaning up contamination caused by hazardous substances.
- Resource Conservation and Recovery Act (RCRA) - Regulates hazardous waste and solid waste.
- Superfund Amendments and Reauthorization Act (SARA) - Amended and extends CERCLA to include toxicological profiles of hazardous substances.
- Toxic Substance Control Act (TSCA) - Governs the manufacturing, importing, distribution, and processing of all toxic chemicals. All such chemicals must be inspected and approved by the Environmental Protection Agency (EPA) before entering the market.
As environmental regulations become more restrictive, finding environmentally acceptable lubricants that comply with Turbine, Pump, and Gear Drive manufacturer's specifications is becoming increasingly difficult. Operators should exercise caution when evaluating and accepting alternative lubricants to ensure that the product selected complies with the manufacturer's requirements.
12.3 Turbines, Generators, and Governors
Thrust and Journal Bearings
Hydro Turbines, whether Francis, Pelton, or Kaplan designs, Vertical Shaft or Horizontal Shaft, generally have a minimum of two Journal Bearings and one Thrust Bearing. These bearings consist of some form of babbitt surface bonded to a steel backing. The rotating element of the bearing is usually polished steel, either an integral part of the turbine shaft or else attached mechanically to the shaft. The thrust bearing is usually the most highly loaded bearing in the machine. The thrust bearing resists hydraulic thrust developed by the axial component of the force of the water on the turbine wheel.
In the case of Vertical Shafts, the Thrust Bearing also supports the weight of the rotating parts of the Hydro Generator. The shaft bearings in the case of horizontal shaft machines support the weight of the rotating parts; in the case of Pelton wheels, they also support the component of the hydraulic thrust that is perpendicular to the shaft. In the case of both horizontal and vertical shaft hydro generators, the shaft bearings support and stabilize the shaft while resisting unbalanced forces.
Requirements For Selecting Turbine Oils
As part of the operation and maintenance information, Hydro Generator manufacturers provide a chart of viscosities acceptable for various operating conditions. The oil recommendation will also include whether Anti-Wear (AW) additives are necessary.
Traditionally, petroleum based Turbine R&O Oils have been the type of lubricating oil selected for use in Hydro Turbines. Today, United Bio Lube offers Bio Turbine R&O Fluids that outperform petroleum based mineral oils and synthetic esters in terms of superior tribological qualities, properties, and features.
Note: Most Hydro Turbines are connected to a Plant Oil System that has a centrally located Oil Filtration and Moisture Removal System. The Governor System often uses oil from the same system, so in addition to lubricating the Journal and Thrust bearings, the oil must function satisfactorily in the Governor.
The following discussion identifies the requirements for selecting Bio Turbine R&O Oils:
Viscosity is perhaps turbine oil's most important quality as it is directly related to Film Strength. The manufacturer's operation and maintenance instructions usually contain suggested viscosities for specific operating conditions. These suggestions should be followed.
In absence of such suggestions, or if the operating conditions have changed materially, or if there is compelling evidence of excessive wear that could be linked to breakdown of the oil film between stationary and moving parts, it may become necessary to revisit the viscosity selection process.
United Bio Lube's in-house technical staff of Chemical Engineers should be consulted about this decision. To recommend the proper oil, they will require information on dimensions of all the bearings, including area of the thrust bearing, rotational speed of the shaft, load supported by the bearings, and normal operating temperatures.
Note: When substituting or ordering Bio Turbine R&O Fluids, it is very important to use the correct units for the viscosity. For example, many of the hydro generators in use today were built several years ago, when the most common unit of viscosity was the Saybolt Universal Seconds (SUS).
Thus, a generic turbine oil called out in the Operations & Maintenance manual might be Turbine Oil #44 (SUS). When the differing viscosity units are taken into account, the correct equivalent in terms of modern viscosity units would be Turbine Oil ISO 32 (cSt).
Turbine Oil ISO 32 (cSt) is the most common viscosity in use in Hydro Turbine bearings.
(2) Rust and Corrosion Inhibitors
The next requirement, which determines the corrosion protection provided by the oil additive package, is often denoted by the letter 'R' in the lubricant's trade name, i.e. Bio Turbine R&O Fluids.
A primary function of Hydro Turbine Oil is to protect against rust on steel bearing surfaces and corrosion in close tolarance oils passage ways, since Hydro Turbine Oils are naturally susceptible to water contamination.
Bio Turbine R&O Fluids are fortified with Bio Corrosion Inhibitors (BCI™) chemistry to protect bearing surfaces against rust and corrosion. When using Bio Turbine R&O Fluids, there is no risk of the additive package reacting with the metal in the bearings.
Applicable standards that must be passed by the oil are:
- ASTM D 665 B, Rust Test using synthetic Salt Water (must be noted "Pass").
- ASTM D 130 1B, Copper Strip Corrosion Test, 3 hours at 100 °C (212 °F).
(3) Oxidation Inhibitors
It is common for the lubricating oil in a hydraulic power unit to be kept in service for 20 years or more. One of the ways that the oil degrades is Oxidation, which causes Gums and Varnishes to form. These contaminants may accumulate in narrow passages or oil system valves and damage the machine.
Even though the operating temperatures are moderate, the oil is exposed to the air continuously and the extreme length of time the oil is kept in service makes it necessary to have a high performance antioxidation package, often denoted by a letter 'O' in the trade name.
The oil must pass ASTM D 943, "Turbine Oil Oxidation Test", and should be over 3500 hours to reach an acid Neutralization Number = 2.0.
(4) Anti-Foam Additives
In the bearing tubs, turbine oil splashes and entrains air. It is important that the lubricating oil release entrained air quickly. Additives that increase the air release rate are called Anti-Foam additives.
Bio Turbine R&O Fluids with Anti-Foam additives meet and exceed the ASTM D 892 ,"Foam Test", Sequences III, II, & I.
(5) Water Release (Demulsibility)
The oil in Hydro Turbines often becomes contaminated with water. It is important that the oil and water not remain in emulsion as this affects the oil's film strength and causes increased oxidation and corrosion rates.
Bio Turbine R&O Fluids have excellent Demulsibility properties that meet and exceed the ASTM D 1401, "Emulsion Test" at 54 °C (130 °F).
In Hydro Turbines, there is usually a large amount of oil in the bearing oil system. Therefore is more pertinent to discuss maintenance rather than change intervals. Usually, the facility has a testing laboratory run periodic tests on the oil. Regular sampling and testing can indicate the timing and effectiveness of filtration, can help pinpoint problem areas, and can indicate when the current oil will need to be changed out with Bio Turbine R&O Oils.
The lubricant has four different areas of possible degradation: Viscosity Breakdown, Particulate Contamination, Additive Breakdown, and Water Contamination.
(1) Viscosity Breakdown
Turbine oil's ability to maintain separation between the surfaces in the bearing depends on its film strength, which is related closely to viscosity. A loss in viscosity is usually due to shearing stresses in the bearing that reduce the length of the oil molecules. An increase in viscosity usually indicates that the oil temperature is high enough that the lighter molecules are being boiled off. While this may not negatively affect the film strength, the increased viscosity can increase the bearing operating temperature.
(2) Particulate Contamination
Unless the bearing surfaces are actually touching, the major cause of wear is through contamination by particles. The sources of particle contamination may be either internal or external. Internal sources may be loose particles created during run-in or oxide particles created by water in the oil. An increase in iron or other metallic oxide particles also may indicate additive breakdown. Particles may also be present in new equipment due to inadequate flushing after system run-in.
External contamination may be due to dust and dirt introduced through vents, or poor filters. Contaminants may also be introduced through unclean oil-handling practices, used Make-Up oil, or contaminated new oil. For this reason, new oil should be tested before it is added to the system.
(3) Additive Breakdown
As additives perform their intended functions they are used up. This depletion of additives may increase wear by allowing corrosion to create particles of different oxides that can damage bearings. Over filtration may actually remove components of the additive system. As stated above, maintaining the additive package is the best reason to use a lubricant maintenance program offered by the manufacturer of the oil.
(4) Water Contamination
This is the one form of degradation that can sometimes be observed visually, usually by the oil taking on a whitish, cloudy, or milky cast. This is in some ways a disadvantage. By the time enough water is mixed in the oil to be visible, the oil's film strength has been severely decreased. Thus testing for water should be performed with the other tests even if the oil does not appear to be contaminated with water.
Wicket Gates have two or three Journal bearings and one Thrust bearing or Collar per Gate. The journal bearings resist the hydrostatic and hydrodynamic loads involved in regulating the flow of water into the turbine. They also resist bending in the shaft that results from the thrust of the actuating linkage. The thrust bearing or collar positions the wicket gate vertically between the upper and lower surfaces of the speed ring in the distributor. The thrust collar has to support the weight of the wicket gates but under some conditions must resist an upward thrust as well.
Wicket Gate bearings are subject to high loads and the shafts do not make complete revolutions, but instead move over an arc, with usually about 90 degrees of motion from completely closed to completely open. This quarter-turn usually takes 5 seconds or more.
Traditionally, wicket gate bearings have been lubricated with a Lithium-based, EP NLGI-2 grease. Auto-lubrication can be used to provide fresh grease every day. Generally the bearings in the Wicket Gate Linkages are lubricated with the same grease and by the same system.
Even when shaft seals are provided, the grease can come into contact with water. In the worst cases, water can wash the lubricant out of the bearings. Environmental concerns have led to attempts to use environmentally acceptable greases. There are no standards for environmental acceptability, but two areas generally acknowledged to be important are biodegradability and toxicity.
Note: It is important to note that greases meeting Food Grade standards do not necessarily meet any of the standards for biodegradability or toxicity.
Bio EP Greases offer a smart way to eliminate the harmful effects from the release of greases to the environment.
A Governor consists of a high-pressure Pump, an Accumulator Tank, an unpressurized Reservoir, Control Valves, Hydraulic Lines, Filters, and Actuators called Servomotors. Servomotors develop the force that is used by the wicket gates to regulate the flow of water through the turbine, and thus the amount of power generation it generates.
Governors generally utilize the same oil that is used in the Hydro Generator Guide and Thrust Bearing System. Governors that operate at over 68.9 bar (1000 psi) may require Anti-Wear protection.
Bio Turbine R&O Fluids operate successfully in the governor system because the requirements for the oils are very similar. Anti-Foam characteristics prevent compressible foam from being introduced into the high pressure lines. Anti-Rust and Anti-Oxidation characteristics are needed because the high pressure pumps and the Pilot Valve assembly have very small clearances. Rust or other oxidation products could be transported into those clearances and cause the pump to wear or the Pilot Valve to stick or be sluggish, resulting in a degradation or loss of governor function.
Auxiliary filters are sometimes used to keep the governor oil supply free of particulates.
12.4 Main Pumps and Motors
Main pumps and motors come in various shapes and sizes, but can be divided into categories. The first dividing criterion is the orientation of the shaft. Pumps are available in Vertical Shaft and Horizontal Shaft configurations. The second criterion is the size of the unit. Large units are similar in layout and component size to hydro generators. Some parts are embedded, and the pump appears to be built into the pumping plant. Small units have a wide range of size, but generally have an identifiable pump and motor and often are mounted on skids or plates.
Lubricating Large Units
Large units with Vertical Shafts typically use journal bearings and a sliding contact thrust bearing. These units sometimes are dual-purpose, being used both as pumping units and turbine generators. There may be a plant oil system that has oil storage and filtering capabilities.
Large units with Horizontal Shafts utilize journal bearings Each bearing has its own oil reservoir. Oil rings that rotate with the shaft pick up oil from the reservoir, and it runs or drips down into holes in the top of the bearing. Very large units may have an oil pump to provide an oil film before start-up.
For lubricating large main pumps and motors, Bio Turbine R&O Oil - ISO 32 is the ideal lubricant.
Lubricating Small Units
Smaller vertical-shaft machines may have a variety of pumps attached to the motor, such as propeller, vertical turbine, or mixed flow. These pumps normally have a grease-lubricated suction bushing, and the rest of the bearings in the pump itself are sleeve-type, either lubricated by the fluid being pumped (product-lubricated) or else by oil dripped into a tube enclosing the shaft bearings (oil-lubricated). There are also vertical-pumps with bronze bearings or bushings that are grease-lubricated by individual grease lines connected to grease points at floor level.
Motors for the smaller vertical units generally utilize rolling-contact bearings. The upper bearing is a combination of radial and thrust bearing -- many times a single-row spherical bearing. Because of the large heat loads associated with these bearing types and conditions, they are usually oil-lubricated. The lower bearing is either a ball or roller bearing and is lubricated by grease. This bearing provides radial support and is configured in the motor to float vertically so it is not affected by axial thrust.
Smaller horizontal units often have rolling-contact bearings in both pump and motor, and can be lubricated by either grease or oil. Oil-lubricated bearings will have an individual oil reservoir for each bearing that is fed by an oil-level cup that maintains the level of the oil.
Turbine Oil Maintenance
Oil changes sometimes do little good if the oil is cold and particulate matter has been allowed to settle out. This problem is resolved by changing the oil after the pump has been running at normal operating temperature. Running the pump helps mix particles into the oil before it is drained.
Another method that may work is to drain the oil, then flush the oil reservoir with warmed oil, discard the oil, then fill the bearing. This can help to dislodge foreign matter that has settled to the bottom.
Another problem is condensation caused by thermal cycling of the motor as it starts and stops. A desiccant air breather on the bearing equalizing air intake will prevent extra moisture from being taken into the reservoir. Proper flushing of the oil reservoir can help carry out water that has collected in the low spots.
Grease Lubricated Bearings
For the greased bearings, Bio Multi-Purpose High Temp EP Grease - NLGI 2 is the prefferable choice. Maintenance problems with these machines center around oil changes and grease changes.
Grease lubricated bearings can have grease cups that provide a reservoir with a threaded top that allows new grease to be injected into the bearing by turning the top a prescribed amount at set intervals of time. In some cases, grease nipples are provided. These receive a prescribed number of strokes from a manual grease gun at specified time intervals.
Having adequate grease in rolling element bearings is important, but too much grease can cause overheating and bearing failure. Maintenance procedures must be followed to avoid over greasing.
Bearing housings need to be disassembled and all the old grease cleaned out and replaced at intervals.
12.5 Gears, Gear Drives, and Speed Reducers
Lubrication requirements for gear sets are prescribed by the equipment manufacturers, based on the operating characteristics and ambient conditions under which the equipment will operate. often the nameplate data on the equipment will indicate the type of lubricant required.
If no lubricant is specified on the nameplate, recommendations should be obtained from the equipment manufacturer. If the manufacturer is unknown or no longer in business, a United Bio Lube's staff of Chemical Engineers should be consulted for recommendations in selecting Bio EP Gear Oils.
In general, gear lubricants are formulated to comply with ANSI/AGA 9005-D94, "Industrial Gear Lubrication Standard." Gear lubricants complying with AGA are also suitable for drive unit bearings in contact with the gear lubricant.
The AGA standard is intended for use by gear designers and equipment manufacturers because it requires knowing the Pitch Line Velocity of the gear set to select a lubricant. Because this information is rarely known, except by the gear manufacturer, the standard provides little assistance for equipment operators trying to select a gear lubricant. The superseded standards, AGA 250.01 and AGA 250.02, require that the operators know the Centerline Distance for the gear sets.
The Centerline Distance can be calculated or approximated by measuring the distance between the centerline of the driver and driven gear. Although updated standards have been in use for several years, many gear unit manufacturers and lubricant producers continue to publish selection criteria based on the old standard. Therefore, equipment operators may want to save the old standard for reference until manufacturers and producers update all their publications. When the Pitch Line Velocity is unknown or cannot be obtained in a timely manner, an educated guess may be necessary. A lubricant can be selected by referring to the old standard and subsequently verified for compliance with the latest standard.
Reference to manufacturer's data indicates that an AGA 3 or AGA 4 grade lubricant will cover most winter applications, and an AGA 5 or AGA 6 will cover most summer applications. Extreme Pressure (EP) oil should be used for heavily loaded, low-speed equipment.
Note: AGA provides recommended gear lubricants for continuous and intermittent operation. The intermittent lubricant recommendations are especially important for these applications where water flow regulation requires that the gates remain in a fixed position for prolonged periods. Gear lubricants formulated for continuous operation are too thin and may run off during the standing periods, resulting in inadequate lubrication and possible gear tooth damage when the gate moves to a new position.
Bio EP Gear Oils should be selected for the highest viscosity consistent with the operating conditions. When very low ambient temperatures are encountered, the oil viscosity should not be lowered. A reduced oil viscosity may be too low when the gears reach their normal operating temperature. If possible, oil heaters should be used to warm the oil in cold environments. The heater should be carefully sized to prevent hot spots that may scorch the oil.
The ideal alternative is to select United Bio Lube's Bio Turbine R&O Oil - ISO 32 or Bio EP Gear Oils since they are both fully compatible with gear materials and seals.
Couplings requiring lubrication are usually spring, chain, gear, or fluid drive type.
Table 12-1 provides lubricant recommendations for couplings. Additional recommendations are provided below.
Lubrication should follow the manufacturer's recommendations. When no suitable recommendations are available, NLGI No 1 to 3 grease may be used for grid couplings. Gear and chain couplings may be lubricated with NLGI No. 0 to 3 grease.
Grease Lubricated Couplings
(1) Normal Applications
This condition is descriptive of applications where the centrifugal force does not exceed 200 g (0.44 lb), motor speed does not exceed 3600 rpm, hub misalignment does not exceed three-fourths of 1 degree, and peak torque is less than 2.5 times the continuous torque. For these conditions, Bio Multi-Purpose High Temp EP Grease - NLGI 2 with a high viscosity vegetable base oil (higher than 198 cSt at 40 °C (104 °F) should be used.
(2) Low Speed Applications
This application includes operating conditions where the centrifugal force does not exceed 10 g (0.2 lb). If the pitch diameter "d" is known, the coupling speed "n" can be estimated from the following equation (Mancuso and South 1994):
Misalignment and torque are as described for normal conditions in (1) above. For these conditions an NGLI No. 0 or No. 1 grease with a high-viscosity base oil (higher than 198 cSt at 40 °C (104 °F)) should be used.
(3) High Speed Applications
This condition is characterized by centrifugal forces exceeding 200 g (0.44 lb), misalignment less than 0.5 degrees, with uniform torque. The lubricant must have good resistance to centrifugal separation. Consult a manufacturer for recommendations.
(4) High Torque, High Misalignment Applications
This condition is characterized by centrifugal forces less than 200 g (0.44 lb), misalignment greater than 0.75 degrees, and shock loads exceeding 2.5 times the continuous torque. Many of these applications also include high temperatures (100 °C (212 °F), which limits the number of effective greases with adequate performance capability. In addition to the require- ments for normal operation, the grease must have antifriction and antiwear additives (polydisulfide), extreme pressure additives, a Timken load greater than 20.4 kg (40 lb), and a minimum dropping point of 150 °C (302 °F).
Oil Lubricated Couplings
Most oil-filled couplings are the gear type. Use a high-viscosity grade oil not less than 150 SUS at 36.1 °C (100 °F). For high speed applications, a viscosity of 2100 to 3600 SUS at 36.1 °C (100 °F) should be used.
12.7 Hoists and Cranes
Various types of hoisting equipment are used in hydroelectric power plants and pumping plants, including gantry cranes, overhead traveling cranes, jib cranes, monorail hoists, and radial gate hoists.
The primary components requiring lubrication are Gear Sets, Bearings, Wire Ropes, and Chains.
The lubrication requirements for gear sets should comply with the same AGA requirements for gears discussed above.
Lubrication of wire ropes and chains used in hoists and cranes is discussed later in this chapter.
12.8 Wire Rope Lubrication
Lubricant Related Wear and Failure
Wear in wire ropes may be internal or external. The primary wear mode is internal and is attributed to friction between individual strands during flexing and bending around drums and sheaves. This condition is aggravated by failure of the lubricant to penetrate the rope.
Corrosion damage is more serious than abrasive damage and is usually caused by lack of lubrication. Corrosion often occurs internally where it is also more difficult to detect. Corrosion of wire ropes occurs when the unprotected rope is exposed to weather, to corrosive environments such as submergence in water (especially salt water), or to chemicals. Corrosion results in decreased tensile strength, decreased shock or impact-load resistance, and loss of flexibility. Unprotected wire ropes that are used infrequently have a greater potential for rust damage due to moisture penetration. Rust may prevent relative sliding between wires, creating increased stresses when the rope is subsequently placed in service.
A common misconception among facility operators is that stainless steel ropes do not require lubrication. This misconception is probably due to corrosive operating conditions.
This misconception is easily corrected by considering a wire rope as a machine with many moving parts. The typical wire rope consists of many wires and strands wrapped around a core. A typical 6 x 47 Independent Wire Rope Core (IWRC) rope, is composed of 343 individual wires that move relative to each other as the rope is placed under load or wrapped around a drum. During service these wires are subject to torsion, bending, tension, and compression stresses. Like all machine parts, ropes also wear as a result of abrasion and friction at points of moving contact. Therefore proper lubrication is essential to reduce friction and wear between the individual wires and to ensure maximum performance.
During operation, tension in the rope and pressure resulting from wrapping around drums forces the internal lubricant to the rope surface where it can be wiped or washed off. Tests conducted on dry and lubricated rope operating under similar conditions provide ample evidence of the beneficial effects of lubrication. The fatigue life of a wire rope can be extended significantly (200 to 300 percent) through the application of the correct lubricant for the operating conditions. However, under certain operating conditions lubrication may be detrimental. Unless recommended by the rope manufacturer, wire rope operating in extremely dirty or dusty environment should not be lubricated.
Abrasives may combine with the lubricant to form a grinding compound that will cause accelerated wear. In applications where ropes undergo frequent and significant flexing and winding around a drum, the rope should be lubricated regardless of whether the wire rope is constructed from stainless steel.
Note: Industry experience has shown that wire ropes used in fairly static applications, where flexing and winding are minimal, should not be lubricated. Tests have shown that lubricated ropes may actually experience more severe corrosion than unlubricated ropes because the lubricant tends to tap and seal moisture in the voids between the wires.
Wire Rope Lubricant Qualities
To be effective, a wire rope lubricant should:
- Have a viscosity suitable to penetrate to the rope core for thorough lubrication of individual wires and strands.
- Lubricate the external surfaces to reduce friction between the rope and sheaves or drum.
- Form a seal to prevent loss of internal lubricant and moisture penetration.
- Protect the rope against external corrosion.
- Be free from acids and alkalis.
- Have enough adhesive strength to resist washout.
- Have high film strength.
- Not be soluble in the medium surrounding it under actual operating conditions.
- Not interfere with the visual inspection of the rope for broken wires or other damage.
New wire rope is usually lubricated by the manufacturer. Periodic lubrication is required to protect against corrosion and abrasion and to ensure long service life. Wire rope lubricants may require special formulations for the intended operating conditions (for example, submerged, wet, dusty, or gritty environments). The rope manufacturer's recommendations should always be obtained to ensure proper protection and penetration. When the manufacturer's preferred lubricant cannot be obtained, an adhesive- type lubricant similar to that used for open gearing may be acceptable.
Two types of lubricants are generally used: Oils and Adhesives. often mineral oil, such as an SAE 10 or 30 motor oil, is used to lubricate wire rope. The advantage of a light oil is that it can be applied cold with good penetration. However, the light oil may not contain adequate corrosion inhibitors for rope applications. Also, it tends to work out of the rope just as easily as it works in, necessitating frequent applications.
Heavy, Adhesive lubricants or dressings provide longer lasting protection. To ensure good penetra- tion, these lubricants usually require thinning before applying. Thinning can be accomplished by heating the lubricant to a temperature of 71.1 to 93.3 °C (160 to 200 °F), or by diluting with a solvent. A properly applied heavy lubricant will provide both internal lubrication and a durable external coating to prevent cor- rosion and penetration of dust and abrasives.
In addition to the qualities noted above, good adhesive lubricants or rope dressings:
- Must not cake, gum, or ball up when contaminated with dust and dirt.
- Must not thin and drip at the highest operating temperature.
- Must not become brittle or chip at the lowest operating temperature.
- Should have inherently high viscosity without adding thickeners or fillers.
When damp conditions prevail, or when severe flexing under heavy loads is encountered, a two- stage lubricant application may be the most effective. Application of a lighter adhesive followed by a very heavy adhesive lubricant to seal in the oil provides the best protection.
In certain ropes subjected to highly corrosive environments such as acids, alkalis, or salt water, providing a heavy impervious exterior lubricant coating to guard against corrosion may be more important than ensuring adequate penetration.
Wire rope lubricants can be applied by brush, spray, drip, or preferably, by passing the rope through a heated reservoir filled with the lubricant. Before application the rope must be cleaned of any accumulated dirt, dust, or rust to ensure good penetration. The lubricant should be applied to the entire circumference of the rope and the rope slowly wound on and off the drum several times to work the lubricant into the rope. If the lubricant is being applied by hand it may be helpful to apply the lubricant as it passes over a sheave where the rope's strands are spread by bending and the lubricant can penetrate more easily.
Rope Applications and Lubricant Requirements
There are five general rope application categories based on operating conditions:
- Industrial or Outdoor
- Low Abrasive Wear and Corrosion
- Heavy Wear
- Standing Rope
Each of these conditions has its own lubrication requirements. These conditions are summarized in Table 12-2.
(1) Industrial or Outdoor Applications
This category includes mobile, tower, and container cranes. Internal and external corrosion are possible, but external corrosion is the more serious and deserves primary consideration. Desirable lubricant qualities include good penetration into the wires and core, moisture displacement, corrosion protection, resistance to washout and emulsification, and freedom from buildup due to repeated applications. The best lubricants for these applications are solvent-based that leave a thick, semidry film after evaporation of the solvent. A tenacious semidry film will minimize adhesion of abrasive particles that cause wear. Thin-film lubricants such as MoS and graphite are not recommended because they tend to dry, causing surface film breakdown and subsequent exposure of the wires.
This category includes elevators, friction hoists, and capstan winches. Fatigue and corrosion are the primary considerations. Desirable lubricant qualities include corrosion protection, internal lubrication, moisture displacement, lubricant buildup prevention, and minimizing loss of friction grip. Note that unlike other lubrication applications, where efforts are made to reduce friction, in this instance a desirable quality includes increasing the coefficient of friction. A solvent-based dressing that deposits a thin slip-resistant semidry film offers the best protection.
(3) Low Abrasive Wear and Corrosion
This category includes electric overhead cranes, wire rope hoists, indoor cranes, and small excavators.
Internal wear leading to fatigue is the primary consideration. Maximum internal and external lubrication are essential. Mineral-oil-base lubricants such as SAE 30 are commonly accepted as the best alternative, but these oils provide minimal corrosion protection and tend to run off. The best alternative is to use a lubricant specifically designed for wire rope applications. These lubricants contain corrosion inhibitors and tackiness agents. Thin-film dry lubricants such as MoS and graphite are also commonly used, but claims of increased fatigue life attributed to these lubricants have been questioned by at least one wire rope manufacturer.
This category includes ropes used in excavators, winches, haulage applications, and offshore mooring systems and dredgers. Protection against abrasion is the primary consideration. Desirable lubricant qualities include good adhesion, crack and flake resistance, antiwear properties, resistance to moisture, emulsification, and ultraviolet degradation, and corrosion-resistance -- especially in offshore applications. The best lubricants are those with thixotropic, (resistance to softening or flow under shear) characteristics to ensure good lubricity under shearing action. These lubricants offer good penetration, and they resist cracking and ultraviolet degradation. Viscous oils or soft grease containing MoS or graphite are commonly used. Tackiness additives are also beneficial.
(5) Standing Rope
This category includes guy and pendant ropes for onshore use, and towing cables, cranes, derricks, and trawl warps for offshore applications. Corrosion due to prolonged contact in a corrosive environment is the primary consideration. Desirable lubricant qualities include high corrosion protection, long-term stability over time and temperature, good adhesion, and resistance to wash- off, emulsification, and mechanical removal. The best lubricants are thixotropic oils similar to those required for heavy-wear applications, except that a higher degree corrosion-resistance additive should be provided.
12.8 Chain Lubrication
Drive chains combine the flexibility of a belt drive with the positive action of a gear drive. Various designs are available. The simplest consist of links that are rough cast, forged, or stamped. These chains are seldom enclosed and therefore exposed to various environmental conditions. They are generally limited to low-speed applications and are seldom lubricated.
Roller chains have several moving parts and, except for the self-lubricating type, require periodic lubrication. Lubricants should be applied between the roller and links to ensure good penetration into the pins and inner bushing surfaces.
Lubricant Related Wear and Failure
Like wire ropes, chains experience both internal and external wear. Internal wear generally occurs on the pins and adjacent bearing surface of the roller bushing, and at the link surfaces. Wear is attributed to friction between metal contacting surfaces. Use of improper lubricant, inadequate lubricant penetration into the pin and bushing clearances, poor lubricant retention, and inadequate or infrequent lubrication are the primary causes of premature wear. Poor chain designs, such as those that provide no grease fittings or other lubricating schemes, also contribute to premature wear.
Corrosion damage is a serious problem and often occurs internally where it is difficult to detect after the chain is assembled and placed in service. Corrosion occurs when the unprotected chain is exposed to weather or corrosive environments such as prolonged submergence in water. Corrosion results in decreased tensile strength, decreased shock or impact-load resistance, and loss of flexibility.
Chain Lubricant Characteristics
The most important considerations in chain lubrication are boundary lubrication and corrosion. Chain life can be extended through the proper selection and application of lubricant for the operating conditions.
An effective chain lubricant should possess the following characteristics:
- Have a viscosity that will enable it to penetrate into the link pins and bearings.
- Lubricate the external surfaces to reduce friction between the sliding link surfaces and chain sprockets.
- Form a seal to prevent moisture penetration.
- Protect the chain against corrosion.
- Be free of acids and alkalis.
- Resist washout.
- Have high film strength.
- Not be soluble in the medium surrounding it under actual operating conditions.
- Displace water.
- Not cake, gum, or ball up when contaminated with dust and dirt.
- Not thin and drip at the highest operating temperature.
- Not become brittle, peel, or chip at the lowest operating temperature.
Most chains, such as those used on conveyors, transporters, and hoists, are accessible and easily lubricated while in service. Lubrication of these chains is generally accomplished through oil baths, brushing, or spray applications.
Lubrication of tainter (radial) gate chains poses an especially difficult challenge. Chain design, construction, application, and installation often render them inaccessible. The operating constraints imposed on these gates include water flow regulation, changing water surface elevations, poor accessibility, and infrequent and minimal movement. These gates may remain in fixed positions for prolonged periods. The submerged portions of chains have a significantly greater potential for rust damage due to exposure to corrosive water, lubricant washout, and moisture penetration into the link pins and bearings. Infrequent movement and inaccessibility adversely affect the frequency of lubrication.
Typical chain lubricants include:
- Light General Purpose Oils
- Turbine Oils
- Gear Oils
- Penetrating Fluids
Light oils may be adequate for continuous chains exposed to oil baths.
Sprays employing solid lubricants such as graphite and MoS are also common.
When the potential for environmental contamination or pollution is a major concern, a Food-Grade lubricant may be required to prevent contamination of ground, water, and air.
For heavily loaded chains, the Extreme Pressure (EP) grades should be used.
Low Speed -- 0 to 3 m/s (0 to 10 ft/s):
- Below 38 °C (100 °F) ISO 100 (AGMA 3)
- Above 38 °C (100 °F) ISO 150 (AGMA 4)
Medium Speed -- 3 to 9 m/s (10 to 30 ft/s):
- Below 38 °C (100 °F) ISO 150 (AGMA 4)
- Above 38 °C (100 °F) ISO 220 (AGMA 5)
Chain lubricants may require special formulation or incorporation of multiple lubricants to cope with severe operating conditions including submerged, wet, dusty, and gritty environments.
When necessary, an Adhesive type lubricant similar to that used for open gearing may be acceptable.
Heavy roller chains such as those used in radial gate applications require heavier lubricants to ensure adequate protection over prolonged periods of submergence without benefit of periodic lubrication. Chain lubricants used in this application must be especially resistant against washout.
New or rebuilt gate chains are usually lubricated during assembly, but periodic lubrication is required to protect against corrosion and abrasion and to ensure long service life.
A properly applied lubricant will provide both internal lubrication and a durable external coating to prevent corrosion and penetration of dust and abrasives.
Application of Chain Lubricants
The need for lubrication will be evident by discoloration appearing as reddish-brown deposits. often bluish metal discoloration can be detected.
Chains can be lubricated by various methods including:
- Oil Can
- Oil Mist
The method of application depends on operating conditions such as load, speed, and size and whether the components are exposed or enclosed.
Lubricant should be applied to the lower strand of the chain immediately before engaging the gear or sprocket. Centrifugal action will force the lubricant to the outer areas.