Lubrication and Oil Analysis

Lubrication and Oil Analysis

Most lubricants used in industry are mineral based and obtained from petroleum by refining processes and further purification and blending.

Function of a Lubricant

Lubricants have three major functions: limit friction, minimize wear and dissipate heat.

Limit Friction

Friction is defined as the resistance to motion of contracting surfaces. Even smooth metal surfaces have microscopic rough spots called asperities. Friction is increased by the presense of asperities on surfaces. Attempts to overcome the force of friction will increase the localized heat generated by the contracting surfaces. This heat can actually create temperatures high enough to weld two surfaces together.

Lubrication prevents peaks of asperities from touching each other through what is called film strength. Molecules of lubricants are naturally bonded together, often in chains. Any attempt to break the chain creates an opposite tension that prevents separation.

Minimize Wear

Wear is the removal of material from one or more moving surfaces in contact with each other. The material removed becomes the source of additional friction and increased wear on the surfaces involved.

A quality lubricant will fill the valleys of the asperities and provide an additional film over the peaks of the asperities. The asperities of the two surfaces are prevented from contracting each other and wear will be minimized.

Dissipate Heat

Even well-lubricated parts will heat up as a result of friction and external heat. One advantage of liquid lubricants is their ability to absorb and dissipate point sources of heat.

Wire Ropes

Wire Ropes

Wire Rope Construction

Essentially, it is made of a number of strands laid helically about a metallic or non-metallic core. Each strand composed of a number of wires also laid helically . Various types of wire rope have been developed to meet a wide range of uses and operating conditions. These types classified by the kind of core; number of strands; the number, sizes and wire arrangement in each strand.

Wire Rope Materials

Materials used in the manufacture of wire ropes are, in the order of increasing strength: iron, phosphor bronze, traction steel, plow steel, improved plow steel and bridge rope steel. Iron wire rope is largely used low strength applications such as elevator ropes not used for hoisting and for stationary guy ropes.

Phosphor bronze wire rope is used occasionally for elevator governor-cable rope and marine applications as life lines, clearing lines, wheel ropes and rigging.

Traction steel wire rope is primarily used as hoist rope for passenger and freight elevators of the traction drive type, an application for which it was specifically designed.

Galvanized wire or coated with zinc by the electrode position process are used in certain applications where additional protection against rusting is required.

Galvanized carbon steel, tinned carbon steel and stainless steel are used for small cords and strands ranging in diameter from 1/64” to 3/8” and larger.

Bearings

Bearings

Bearing types and styles are classified into: plain and anti-friction bearings. Plain bearing operates in sliding motion principle and the anti-friction bearing operates in rolling motion principle.

Plain Bearing

There is a relative sliding movement between shaft and bearing surfaces. A lubricant is used to keep the surfaces separated and minimized friction. A film of lubricant should be maintained to prevent from making contact and to have long service life. The common practice is to use a steel shaft and to make a plain bearings made of bronze, babbitt or some other materials soften than steel. A bearing material that is softer than steel will wear before the shaft and usually can be replaced more easily, quickly and cheaply.

Another factor that has a major influence on plain bearing operation is the surface finish of both journal and the bearing. Simply stated, the rougher the surface, the thicker the film required to separate them. Oil film thickness, even in very large bearings, does not exceed a couple of thousands and in small bearings may be a few ten-thousands. This gives some indication of the importance of fine surface finishes to satisfactory bearing performance.

Anti-friction Bearing

It has series of rollers or balls interposed between the moving and stationary members. These rollers or balls are usually mounted in a cage or separator and enclosed between rings or races. In theory, the rolling elements in anti-friction bearings perform the function that the lubricant film performs in the plain bearing. In practice however, anti-friction bearings require lubrication as some sliding action occurs between rolling elements and races.

Gaskets, Packings and Seals

Gaskets, Packings and Seals

A gasket is a material that is used to seal two faces of a machine. Gaskets can be made of a soft materials, such as asbestos or elastomers, or they can be made of harder materials, such as metal ring gaskets made of iron, steel and other materials. Combinations of materials such as spiral-wound metal/asbestos-filled gaskets are also common.

Gaskets are designed for compressibility and sealability. Compressibility is a measure of the gasket's ability to deflect and conform to the faces being sealed. Gaskets compressibility compensates for surface irregularities, such as minor nicks, non-parallelism, corrosion and variations in groove depth. Sealability is the measure of fluid leakage through and across both faces of a gasket. Most of the leakage for a properly installed face to face connections will occur through the gasket.

Types of Gaskets

Gaskets are classified usually either by the material from which they are made and the type of construction or design or in some cases both.

Flat Gasket

Flat gaskets are cut from flat stock of gasket material. The material can be elastomer, either natural ( rubber ) or synthetic ( hypalon, viton, SBR ). Fiber material is often formed with a binder into flat stock gasket material. Flat stock comes in standard thickness ranging from 1/64” to 1/4”. Flat stock gaskets are often cut into full face gaskets, in which the gasket design incorporates the appropriate bolt-hold pattern and the flange bolts are used to center the gasket in place. The full face design is most often used with the flat face flange design. Ring face gaskets are cut so that the outer diameter of the gasket rest inside the bolt pattern and the gasket is centered by resting it on the flange bolts.

Envelope Gasket

Envelope gaskets consist of an elastomeric material protected by another material as a gasket. TFE is common envelope material because of its resistance to many chemicals. Envelope gaskets are usually ring face sized so that the gasket is centered by resting on the flange bolts. Different metals can be used as the envelope material.

Pumps

Pumps

A mechanical device or machine that lift liquids against the force of gravity or remove exhaust gases from closed vessels. It is used to lift liquid from a source below the pump to a higher elevation, to move liquid from one location to another, to move liquid from a low pressure area to a higher pressure area. The machine used to withdraw air or any gases from a closed vessel is also classified as a pump.

Pumps are classified with respect to their construction or the service for which they are designed. The three groups of pumps are centrifugal, reciprocating and rotary.

Centrifugal Pumps

This pump derived its name from the type of force that this design of pump utilizes. Centrifugal force acts on a body moving in a circular path, tending to force it farther from the center of the circle. Inside the body of a centrifugal pump, the liquid is force to revolve and so generates the force that enable this style of pump to develop pressure and move liquids. It compose of blades or vanes called the impeller and the surrounding case called housing or volute.

Centrifugal pumps are made in a great variety of types, styles and sizes to suit application requirements and operating conditions. A basic design difference between pumps is the number of stages. Pumps with one impeller are classified as single-stage pumps and those with two or more are called multistage pumps.

Air Compressors

Air Compressors

Compressed air is air forced to pass through a smaller space, thus the pressure increases. The power available from compressed air is used in many applications as a substitute for steam, in operating rock drills, shop tools and engines.

A compressor is an equipment driven by any prime mover that compresses air into a receiver to be used at a greater or lesser distance. The system is not subject to loss by condensation in the pipes, as is the case were carrying the steam in pipes for long distances.

Heat of Air Compression

This subject has probably received more considerations in air compressor design than any other. The principal losses in the earlier compressors were traceable to this source.

It should be noted that the heat of compression, as already explained, represents work done upon the air for which there is usually no equivalent obtained, given that the heat is all lost by radiation before the air is used. The selection of any air cylinder lubricant is, of course, governed to a considerable extent by knowledge of the cylinder temperature it must withstand.

When the air pressures are known, the corresponding temperatures are ascertained fairly accurately.