Types of Synthetic Oils Complete guide

Synthetic oils

1. Polyalpha-olefin (PAO)
2. Synthetic esters
3. Polyalkylene glycols (PAG)
4. Phosphate esters
5. Alkylated naphthalenes (AN)
6. Silicate esters
7. Ionic fluids

Solid lubricants

PTFE: polytetrafluoroethylene (PTFE) is typically used as a coating layer on, for example, cooking utensils to provide a non-stick surface. Its usable temperature range up to 350 °C and chemical inertness make it a useful additive in special greases. Under extreme pressures, PTFE powder or solids is of little value as it is soft and flows away from the area of contact. Ceramic or metal or alloy lubricants must be used then. "Teflon®" is a brand of PTFE owned by DuPont Co.

Inorganic solids: Graphite, hexagonal boron nitride, molybdenum disulfide and tungsten disulfide are examples of materials that can be used as solid lubricants, often to very high temperature. The use of some such materials is sometimes restricted by their poor resistance to oxidation (e.g., molybdenum disulfide can only be used up to 350°C in air, but 1100°C in reducing environments).

Metal/alloy: Metal alloys, composites and pure metals can be used as grease additives or the sole constituents of sliding surfaces and bearings. Cadmium and Gold are used for plating surfaces which gives them good corrosion resistance and sliding properties, Lead, Tin, Zinc alloys and various Bronze alloys are used as sliding bearings, or their powder can be used to lubricate sliding surfaces alone, or as additives to

Aqueous lubrication

Aqueous lubrication is of interest in a number of technological applications. Strongly hydrated brush polymers such as PEG can act as lubricants at liquid solid interfaces. By continuous rapid exchange of bound water with other free water molecules, these polymer films keep the surfaces separated while maintaining a high fluidity at the brush–brush interface at high compressions, thus leading to a very low coefficient of friction.

Other relevant phenomena

'Glaze' formation (high temperature wear)

A further phenomenon that has undergone investigation in relation to high temperature wear prevention and lubrication, is that of a compacted oxide layer glaze formation. This is the generation of a compacted oxide layer which sinters together to form a crystalline 'glaze' (not the amorphous layer seen in pottery) generally at high temperatures, from metallic surfaces sliding against each other (or a metallic surface against a ceramic surface). Due to the elimination of metallic contact and adhesion by the generation of oxide, friction and wear is reduced. Effectively, such a surface is self-lubricating.

As the 'glaze' is already an oxide, it can survive to very high temperatures in air or oxidising environments. However, it is disadvantaged by it being necessary for the base metal (or ceramic) having to undergo some wear first to generate sufficient oxide debris.

 Additives

A large number of additives are used to impart performance characteristics to the lubricants. The main families of additives are:

• Antioxidants
• Detergents
• Anti-wear
• Metal deactivators
• Corrosion inhibitors, Rust inhibitors
• Friction modifiers
• Extreme Pressure
• Anti-foaming agents
• Viscosity index improvers
• Demulsifying/Emulsifying
• Stickiness improver, provide adhesive property towards tool surface (in metalworking)
• Complexing agent (in case of greases)

Note that many of the basic chemical compounds used as detergents (example: calcium sulfonate) serve the purpose of the first seven items in the list as well. Usually it is not economically or technically feasible to use a single do-it-all additive compound. Oils for hypoid gear lubrication will contain high content of EP additives. Grease lubricants may contain large amount of solid particle friction modifiers, such as graphite, molybdenum sulfide.

Application by fluid types

1. Automotive
1. Engine oils
1. Petrol (Gasoline) engine oils
2. Diesel engine oils
2. Automatic transmission fluid
3. Gearbox fluids
4. Brake fluids
5. Hydraulic fluids
2. Tractor (one lubricant for all systems)
1. Universal Tractor Transmission Oil – UTTO
2. Super Tractor Oil Universal – STOU – includes engine
3. Other motors
1. 2-stroke engine oils
4. Industrial
1. Hydraulic oils
2. Air compressor oils
3. Gas Compressor oils
4. Gear oils
5. Bearing and circulating system oils
6. Refrigerator compressor oils
7. Steam and gas turbine oils
5. Aviation
1. Gas turbine engine oils
2. Piston engine oils
6. Marine
1. Crosshead cylinder oils
2. Crosshead Crankcase oils
3. Trunk piston engine oils
4. Stern tube lubricants

Complete Description of Lubricants

Types of lubricants

The Complete Description of Lubricants

In 1999, an estimated 37,300,000 tons of lubricants were consumed worldwide.Automotive applications dominate, but other industrial, marine, and metal working applications are also big consumers of lubricants. Although air and other gas-based lubricants are known, e.g., in fluid bearings), liquid and solid lubricants dominate the market, especially the former.

Lubricants are generally composed of a majority of base oil plus a variety of additives to impart desirable characteristics. Although generally lubricants are based on one type of base oil, mixtures of the base oils also are used to meet performance requirements.

Base oil groups

Mineral oil term is used to encompass lubricating base oil derived from crude oil. The American Petroleum Institute (API) designates several types of lubricant base oil

• Group I – Saturates <90% and/or sulfur >0.03%, and Society of Automotive Engineers (SAE) viscosity index (VI) of 80 to 120

Manufactured by solvent extraction, solvent or catalytic dewaxing, and hydro-finishing processes. Common Group I base oil are 150SN (solvent neutral), 500SN, and 150BS (brightstock)

• Group II – Saturates over 90% and sulfur under 0.03%, and SAE viscosity index of 80 to 120

Manufactured by hydrocracking and solvent or catalytic dewaxing processes. Group II base oil has superior anti-oxidation properties since virtually all hydrocarbon molecules are saturated. It has water-white color.

• Group III – Saturates > 90%, sulfur <0.03%, and SAE viscosity index over 120

Manufactured by special processes such as isohydromerization. Can be manufactured from base oil or slax wax from dewaxing process.

• Group IV – Polyalphaolefins (PAO)
• Group V – All others not included above such as naphthenics, PAG, esters.

In North America, Groups III, IV and V are now described as synthetic lubricants, with group III frequently described as synthesised hydrocarbons, or SHCs. In Europe, only Groups IV and V may be classed as synthetics.

The lubricant industry commonly extends this group terminology to include:

• Group I+ with a Viscosity Index of 103–108 
• Group II+ with a Viscosity Index of 113–119 
• Group III+ with a Viscosity Index of at least 140

Can also be classified into three categories depending on the prevailing compositions:

• Paraffinic 
• Naphthenic 
• Aromatic

Lubricants for internal combustion engines contain additives to reduce oxidation and improve lubrication. The main constituent of such lubricant product is called the base oil, base stock. While it is advantageous to have a high-grade base oil in a lubricant, proper selection of the lubricant additives is equally as important. Thus some poorly selected formulation of PAO lubricant may not last as long as more expensive formulation of Group III+ lubricant.

Biolubricants made from vegetable oils and other renewable sources

These are primarily triglyceride esters derived from plants and animals. For lubricant base oil use the vegetable derived materials are preferred. Common ones include high oleic canola oil, castor oil, palm oil, sunflower seed oil and rapeseed oil from vegetable, and Tall oil from tree sources. Many vegetable oils are often hydrolyzed to yield the acids which are subsequently combined selectively to form specialist synthetic esters. Other naturally derived lubricants include lanolin (wool grease, a natural water repellent).

Whale oil was a historically important lubricant, with some uses up to the latter part of the 20th century as a friction modifier additive for automatic transmission fluid.

In 2008, the bio lubricant market was around 1% of UK lubricant sales in a total lubricant market of 840,000 tonnes/year.

Lanolin is a natural water repellent, derived from sheep wool grease, and is an alternative to the more common petro-chemical based lubricants. This lubricant is also a corrosion inhibitor, protecting against rust, salts, and acids.

Water can also be used on its own, or as a major component in combination with one of the other base oils. Commonly used in engineering processes, such as milling and lathe turning.

Dispensing of adhesives by robotics, or Painting by Robotics

Dispensing

Dispensing of adhesives at home can be a challenging job when one is trying to seal a window or door leak with a tube of silicone rubber. The silicone always seems to be too thick to start the flow, and then does not seem to stop soon enough to prevent it from continuing to ooze out and deposit where it is not really desired.

The automated dispensing is an art in itself. Some automation firms will place their dispensing end effectors on a series of available robots, while other firms will make their own specific dispensing machine, usually a gantry system.

Most car owners will agree that the original windshield of a car is always installed with better quality compared to a replacement windshield. This is because the replacement is installed by hand application of the adhesive, and the car frame surface it is applied to is never perfectly cleaned of the original adhesive, no matter how hard one tries.

How to select a robotic arm for particular application

SELECTING A ROBOT ARM

When exploring robot arms as the core device of an automation machine, several questions will arise:

1.  What kinds or types of robots are there?
2.  What are their speeds?
3.  What are their cycle times?
4.  What are their payloads?
5.  What are their costs?
6.  How intelligent are they?
7.  How are they different from automation?

We will explore the first question in the next section. The next four questions can be related to the consumer comparing automobiles and asking the car salesperson for information, but there are hidden issues, just as with cars.

 The payload question seems simple enough. Either a robot can lift X pounds or it cannot, but one will find that the robot manufacturer will list a maximum payload that corresponds to the robot being able to operate under effective control of its electronics, 24 hours a day for 7 days a week. A robot listed for 10 lbs sounds like a weakling compared to the average human.

One might compare it to a child. However, this rating is for continuous operation. If one misused the robot, it might lift 50 or 100 lbs before something broke.

This is why for safety reasons, a novice thinking a robot is only as strong is as a child draws a false sense of security.

In an uncontrollable motion, the robot night be able to swing a 50 lb weight at a tremendous speed and either knock one out cold or perhaps even kill.

The payload question is also coupled to the lack of a gripper out of the shipping crate. If one decides upon a robot with a 10 lbs payload, and the required gripper is 5 lbs, one only has 5 lbs of capacity to lift something! So it is important to scope out the tasks, and the probable robot gripper, before selecting the right robot.

As robots evolved over the 1970s, 1980s, and 1990s, their speed and cycle times were advertised similar to a car going from 0 to 60 mph. Faster speeds and quicker cycle times seemed an obvious goal, and in many operations this is basically true.

 It assumes a cycle where the object is grabbed and lifted 1 in., moved 12 in., and placed 1 in. below. The robot and gripper must also return to the starting grabbing location to complete the cycle. The cycle time for many years hovered around 1 sec. Then some SCARA manufacturers and others were able to
reach 0.5 sec and less.

Now if this were a reduction of time for 0–60 mph, race car enthusiasts would be drooling. It has its merits for automation also, but there are other issues to consider. If one uses high school physics, one will determine that the 0.5 sec time and given displacement conditions produce accelerations of close to 10 times gravity.

Other issues are:

•  Can the gripper close and open almost instantaneously?
•  If it does close instantaneously, will the reaction forces on the gripped part be OK?
•  Would the part be misaligned if the gripper closes this fast?
•  If a suction cup is used, will a vacuum be achieved in time?
• Will the part slip during the 12 in. motion and become a projectile?

Many of these issues cannot be answered without some experimental testing

on the specific parts one has to assemble. Many robot vendors have customers

testing robots at various locations around the country just for these purposes. One

may not get all of the answers to 100% satisfaction, but many of the risk factors

can be removed.

The next two questions on robot costs and intelligence are somewhat linked. Usually robots right out of the shipping crate are not well outfitted as mentioned before, but one needs to explore if the candidate robot has the appropriate controller processing capabilities if one does add sensors and external devices.

Most robot controllers today have these features, but they range from limited to powerful. One needs to discuss the details of a pending automation project with robot vendors, well beyond payload and cycle time. Nothing is more frustrating than someone giving a project team a 15-year-old robot that seems to be able to perform all of the required motions without trouble, yet the controller does not have the capacity to handle the types and flows of sensory information. As for how a robot differs from automation, one needs to look at the components found in most robots:

• Structural members and bearings;
• Electrical motors;
• Optional gearboxes (depending on motor type);
• Position encoders;
• Wire cabling for motor power and feedback from sensors;
• A computer/controller;
• Amplifiers to boost computer level output signals to high amperage power signals.

All of these components are most likely to be found in automation. It is just that as an automation designer, one would be selecting these individually from catalogs, not simply selecting the assembled robot as one item. And the robot’s software is usually far more versatile than what one uses in automation. So this is where robots get their advantage in reprogrammability and ready availability.

Disadvantages of Magnetic Bearings

Disadvantages of Magnetic Bearings

Although significant improvement has been achieved, there are still several disadvantages in comparison with other, conventional bearings. The most important limitations follow.

•  Electromagnetic bearings are relatively much more expensive than other non contact bearings, such as the hydro static bearing. In most cases, this fact makes the electromagnetic bearing an uneconomical alternative.

•  Electromagnetic bearings have less damping of journal vibrations in comparison to hydro static oil bearings.

•  In machine tools and other manufacturing environments, the magnetic force attracts steel or iron chips.

• Magnetic bearings must be quite large in comparison to conventional non contact bearings in order to generate equivalent load capacity. 
• An acceptable-size magnetic bearing has a limited static and dynamic load capacity. 
• The magnetic force that supports static loads is limited by the saturation properties of the electromagnet core material.
•  The maximum magnetic field is reduced with temperature. In addition, the dynamic load capacity of the bearing is limited by the available electrical power  supply from the amplifier.

•  Finally, electromagnetic bearings involve complex design problems to ensure that the heavy spindle, with its high inertia, does not fall and damage the magnetic bearing when power is shut off or momentarily discontinued. Therefore, a non interrupted power supply is required to operate the magnetic bearing, even at no load or at shutdown conditions of the system.
• In order to secure safe operation in case of accidental power failure or support of the rotor during shutdown of the machine, an auxiliary bearing is required. Rolling-element bearings with large clearance are commonly used. During the use of such auxiliary bearings, severe impact can result in premature rolling element failure.

Disadvantages of Hydrodynamic Bearings or journal bearings

Disadvantages of Hydrodynamic Bearings

• One major disadvantage of hydrodynamic bearings is that a certain minimum speed is required to generate a full fluid film that completely separates the sliding surfaces. Below that speed, there is mixed or boundary lubrication, with direct contact between the asperities of the rubbing surfaces. 

• For this reason, even if the bearing is well designed and successfully operating at the high rated speed of the machine, it can be subjected to excessive friction and wear at low speed, such as during starting and stopping of journal rotation.

• In particular, hydrodynamic bearings undergo severe wear during start-up, when they accelerate from zero speed, because static friction is higher than dynamic friction.

• A second important disadvantage is that hydrodynamic bearings are completely dependent on a continuous supply of lubricant. If the oil supply is interrupted, even for a short time for some unexpected reason, it can cause overheating and sudden bearing failure. 

• It is well known that motor vehicle engines do not last a long time if run without oil. In that case, the hydrodynamic bearings fail first due to the melting of the white metal lining on the bearing.

• This risk of failure is the reason why hydrodynamic bearings are never used in critical applications where there are safety concerns, such as in aircraft engines. 

• Failure of a motor vehicle engine, although it is highly undesirable, does not involve risk of loss of life; therefore, hydrodynamic bearings are commonly used in motor vehicle engines for their superior performance and particularly for their relatively long operation life.

• A third important disadvantage is that the hydrodynamic journal bearing has a low stiffness to radial displacement of the journal (low resistance to radial run-out), particularly when the eccentricity is low.

•  This characteristic rules out the application of hydrodynamic bearings in precision machines, e.g., machine tools. 

• Under dynamic loads, the low stiffness of the bearings can result in dynamic instability, particularly with lightly loaded high-speed journals.

• The low stiffness causes an additional serious problem of bearing whirl at high journal speeds. 

• The bearing whirl phenomenon results from instability in the oil film, which often results in bearing failure.

Further discussions of the disadvantages of journal bearing and methods to overcome these drawbacks are included in the following POSTS.

DRY AND BOUNDARY LUBRICATION BEARINGS

DRY AND BOUNDARY LUBRICATION
BEARINGS

Whenever the load on the bearing is light and the shaft speed is low, wear is not a critical problem and a sleeve bearing or plane-slider lubricated by a very thin layer of oil (boundary lubrication) can be adequate.

Sintered bronzes with additives of other elements are widely used as bearing materials. Liquid or
solid lubricants are often inserted into the porosity of the material and make it self-lubricated. However, in heavy-duty machinery—namely, bearings operating for long periods of time under heavy load relative to the contact area and at high speeds—better bearing types should be selected to prevent excessive wear rates and to achieve acceptable bearing life.

In most applications, the sliding surfaces of the bearing are lubricated.

However, bearings with dry surfaces are used in unique situations where lubrication is not desirable. Examples are in the food and pharmaceutical industries, where the risk of contamination by the lubricant forbids its application. The sliding speed, V, and the average pressure in the bearing, P, limit the use of dry or boundary lubrication. For plastic and sintered bearing materials, a widely
accepted limit criterion is the product PV for each bearing material and lubrication condition. This product is proportional to the amount of frictionenergy loss that is dissipated in the bearing as heat. This is in addition to limits on the maximum sliding velocity and average pressure.

 For example, a self lubricated sintered bronze bearing has the following limits:

Surface velocity limit, V, is 6m=s, or 1180 ft=min

Average surface-pressure limit, P, is 14 MPa, or 2000 psi

PV limit is 110,000 psi-ft=min, or 3:85 106 Pa-m=s

In comparison, bearings made of plastics have much lower PV limit. This is
because the plastics have a low melting point; in addition, the plastics are not
good conductors of heat, in comparison to metals. For these reasons, the PV limit
is kept at relatively low values, in order to prevent bearing failure by overheating.

For example, Nylon 6, which is widely used as a bearing material, has the following limits as a bearing material:

Surface velocity limit, V, is 5m=s

Average surface-pressure limit, P, is 6.9 MPa

PV limit is 105 103 Pa-m=s

Remark.

 In hydrodynamic lubrication, the symbol for surface velocity of a rotating shaft is U, but for the PV product, sliding velocity V is traditionally used.

Conversion to SI Units.

1 lbf=in:2 ðpsiÞ ¼ 6895 N=m2 ðPaÞ

1 ft=min ¼ 0:0051 m=s

1 psi-ft=min ¼ 6895 0:0051 ¼ 35 Pa-m=s ¼ 35 10 6 MPa-m=s

An example for calculation of the PV value in various cases is included at the end of this chapter. The PV limit is much lower than that obtained by multiplying the maximum speed and maximum average pressure due to the load capacity.

The reason is that the maximum PV is determined from considerations of heat dissipation in the bearing, while the average pressure and maximum speed can be individually of higher value, as long as the product is not too high. If the maximum PV is exceeded, it would usually result in a faster-than-acceptable wear rate.