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How Bearings Work:

 

A bearing is a device that is used to enable rotational or linear movement, while reducing friction and handling stress. Resembling wheels,bearings literally enable devices to roll, which reduces the friction between the surface of the bearing and the surface it’s rolling over. It’s significantly easier to move, both in a rotary or linear fashion, when friction is reduced, this also enhances speed and efficiency.

In order to serve all these functions, bearings make use of a relatively simple structure: a ball with internal and external smooth metal surfaces, to aid in rolling. The ball itself carries the weight of the load; the force of the load’s weight is what drives the bearing’s rotation. However, not all loads put force on a bearing in the same manner. There are two different kinds of loading: radial and thrust.

A radial load, as in a pulley, simply puts weight on the bearing in a manner that causes the bearing to roll or rotate as a result of tension. A thrust load is significantly different, and puts stress on the bearing in an entirely different way. If a bearing (think of a tire) is flipped on its side (think now of a tire swing) and subject to complete force at that angle (think of three children sitting on the tire swing), this is called thrust load. A bearing that is used to support a bar stool is an example of a bearing that is subject only to thrust load.

Many bearings are prone to experiencing both radial and thrust loads. Car tires, for example, carry a radial load when driving in a straight line: the tires roll forward in a rotational manner as a result of tension and the weight they are supporting. However, when a car goes around a corner, it is subject to thrust load because the tires are no longer moving solely in a radial fashion and cornering force weighs on the side of the bearing.

Types of Bearings:
There are numerous different kinds of bearings that are designed to handle radial load, thrust load, or some combination of the two. Because different applications require bearings that are designed to handle a specific kind of load and different amounts of weight, the differences between types of bearings concern load type and ability to handle weight.

Ball Bearings

These are extremely common because they can handle both radial and thrust loads, but can only handle a small amount of weight. They are found in a wide array of applications, such as roller blades and even hard drives, but are prone to deforming if they are overloaded.

The purpose of a ball bearing is to reduce rotational friction and support radial and axial loads. It achieves this by using at least two races to contain the balls and transmit the loads through the
balls. In most applications, one race is stationary and the other is attached to the rotating assembly (e.g., a hub or shaft). As one of the bearing races rotates it causes the balls to rotate as well. Because the balls are rolling they have a much lower coefficient of friction than if two flat surfaces were sliding against each other.

Ball bearings tend to have lower load capacity for their size than other kinds of rolling-element bearings due to the smaller contact area between the balls and races. However, they can tolerate some misalignment of the inner and outer races.

Roller Bearings

Roller bearings are designed to carry heavy loads—the primary roller is a cylinder, which means the load is distributed over a larger area, enabling the bearing to handle larger amounts of weight. This structure, however, means the bearing can handle primarily radial loads, but is not suited to thrust loads. For applications where space is an issue, a needle bearing can be used. Needle bearings work with small diameter cylinders, so they are easier to fit in smaller applications.

Ball Trust Bearings These kinds of bearings are designed to handle almost exclusively thrust loads in low-speed low-weight applications. Bar stools, for example, make use of ball thrust bearings to support the seat.

Roller thrust bearings,

Much like ball thrust bearings, handle thrust loads. The difference, however, lies in the amount of weight the bearing can handle: roller thrust bearings can support significantly larger amounts of thrust load, and are therefore found in car transmissions, where they are used to support helical gears. Gear support in general is a common application for roller thrust bearings.

• Tapered Roller Bearings This style of bearing is designed to handle large radial and thrust loads—as a result of their load versatility, they are found in car hubs due to the extreme amount of both radial and thrust loads that car wheels are expected to carry.

Specialized BearingsThere are, of course, several kinds of bearings that are manufactured for specific applications, such as magnetic bearings and giant roller bearings. Magnetic bearings are found in high-speed devices because it has no moving parts—this stability enables it to support devices that move unconscionably fast. Giant roller bearings are used to move extremely large and heavy loads, such as buildings and large structural components.

Introduction to Bearings
• Structure & Function
• History
• Types
• Amazing World of Bearings
• Future of Bearings

Bearing manufactures have made a vital contribution to the growth and advancement of the various industries that rely on machinery. As a comprehensive bearing retailer, Sealworld (Pvt) Ltd responds to needs in a wide variety of fields.

A surprisingly large number of bearings can be found all around us. Take automobiles, for example: there are 100 to 150 bearings in a typical car. Without bearings, the wheels would rattle, the transmission gear teeth wouldn't be able to mesh, and the car wouldn't run smoothly.

Bearings are not used only in cars, but in all kinds of machinery such as:

  • Trains
  • Aeroplanes
  • Washing machines
  • Refrigerators
  • Air conditioners
  • Vacuum cleaners
  • Photocopy machines
  • Computers
  • Satellites

Bearings enhance the functionality of machinery and help to save energy. Bearings do their work silently, in tough environments, hidden in machinery where we can't see them. Nevertheless, bearings are crucial for the stable operation of machinery and for ensuring its top performance.

The word "bearing" incorporates the meaning of "to bear," in the sense of "to support," and "to carry a burden." This refers to the fact that bearings support and carry the burden of revolving axles.

 

The two pictures below show the most basic bearings, known as rolling bearings.

• Rolling bearing    

• Rolling bearing   

Rolling bearings are made up of four elements and have an extremely simple basic structure.

• Outer ring        
The large ring of the outer race.

• Inner ring            
The small ring of the inner race.

• Rolling elements
Several balls or rollers that are contained in the space between the outer race and inner race.

• Cage                
Used to fix the position of the rolling elements.

 

 

 

The basic function of bearings is principally to reduce mechanical friction. Reducing friction means:

1. Machinery will run more efficiently
2. There will be less frictional wear, extending the operating life of the machinery
3. Preventing abrasion burn, avoiding mechanical breakdown

Bearings also contribute to lower energy consumption by reducing friction and allowing the efficient transmission of power. This is just one way in which bearings are environmentally friendly.

MECHANICAL SEALS IN CENTRIFUGAL PUMPS
The mechanical seal acts as a check valve and a slider bearing. The obvious function is that of a check valve to prevent liquid under pressure from leaking out of the pump, or from drawing air into the pump when under vacuum conditions.

Seal Life
Since the seal must function as a slider or friction bearing, the seal has an unpredictable life span. The seal of a centrifugal pump is usually replaced many times during the life of a pump. All bearings need lubricant and the seal lubricant is the liquid being pumped. Liquid infiltrates between the contact faces of the primary and mating rings. Some of this liquid does find its way through to the atmosphere but is so slight as to only be noticed as corrosion of 'build up' on the pump adapter. The condition of the pumped liquid will greatly affect seal life.

Abrasives
The number one enemy of a mechanical seal is abrasive particles in the liquid being pumped. Abrasives may be anything from dirt to dissolved impurities in the liquid precipitating out of solution. These abrasive particles infiltrate with the liquid between the seal faces and grind away the carbon primary ring. The normal shiny face of the primary ring and mating ring.

Heat Damage
Excessive heat can damage the seal in two areas - the primary ring and the elastomer parts. The primary ring is made primarily of carbon. Should the pump be operated without liquid - even for a very short period of time - the primary and mating ring faces are denied lubricant. This causes the faces to become very hot. The binder mixed with the carbon breaks down and the face of the primary ring turns to a dull black powder.
The O-ring, or cup, and flexible diaphragm of the seal are made of one of many types of rubber-like substance called an 'elastomer'. The type of elastomertic material is selected to match the temperature limit and types of material being pumped. Should the temperature limit be exceeded, the diaphragm and O-ring will become hard and sometimes crack. The seal will then start to leak.

 

Conclusion
The forgoing is a brief discussion of some of the most common reasons why seal life is shortened. Under normal conditions, seals wear out much faster than the other pump parts. Abrasives and excessive heat greatly shorten the seal's life span.

Shown above: Pump seal in a centrifugal pump from a Sentra mold temperature controller.

For more information on pump seals call the Sealworld Sales Department at +(263) 4 749040/ 749049/ 772766 / 780991 / 772 964 581 / 772 999 341-2 / 772 954 933 / 712 737 652 / 713 512 352 / 734 811 296 / 735 451 404-6 / 771 021 330 or E-Mail: This email address is being protected from spambots. You need JavaScript enabled to view it., This email address is being protected from spambots. You need JavaScript enabled to view it. or visit our website www.sealworld.co.zw. or contact them on their e mail address This email address is being protected from spambots. You need JavaScript enabled to view it. , This email address is being protected from spambots. You need JavaScript enabled to view it..

A mechanical seal is a device that helps join systems or mechanisms together by preventing leakage (e.g. in a plumbing system), containing pressure, or excluding contamination. The effectiveness of a seal is dependent on adhesion in the case of sealants and compression in the case of gaskets.[1]
A stationary seal may also be referred to as 'packing'.

Seal types:

• Induction sealing or cap sealing
• Adhesive, sealant
• Bodok seal, a specialized gas sealing washer for medical applications
• Bridgman seal, a piston sealing mechanism that creates a high pressure reservoir from a lower pressure source
• Bung
• Coating
• Compression seal fitting
• Diaphragm seal
• Ferrofluidic seal
• Gasket or Mechanical Packing
• Flange gasket
• O-ring
• O-ring boss seal
• Piston ring
• Glass-to-metal seal
• Glass-ceramic-to-metal seals
• Hose coupling, various types of hose couplings
• Hermetic seal
• Hydrostatic seal
• Hydrodynamic seal
• Labyrinth seal A seal which creates a tortuous path for the liquid to flow through
• Lid (container)
• Rotating face mechanical seal
• Face seal
• Plug
• Radial shaft seal

• Trap (plumbing) (siphon trap)
• Stuffing box, Gland Assembly (engineering) (mechanical packing)
• Split Mechanical Seal
• Wiper seal
• Dry gas seal
• Exitex seal

Mechanical seal fundamentals

A mechanical seal must contain four functional components, primary sealing surfaces, secondary sealing surfaces, a means of actuation, and a means of drive:

  1. The primary sealing surfaces are the heart of the device. A common combination consists of a hard material, such as silicon carbide, Ceramic or tungsten carbide, embedded in the pump casing and a softer material, such as carbon in the rotating seal assembly. Many other materials can be used depending on the liquid's chemical properties, pressure, and temperature. These two rings are in intimate contact, one ring rotates with the shaft, the other ring is stationary. These two rings are machined using a machining process called lapping in order to obtain the necessary degree of flatness.
  2. The secondary sealing surfaces (there may be a number of them) are those other points in the seal that require a fluid barrier but are not rotating relative to one another. Usually the secondary sealing elements are o-rings, PTFE wedges or rubber diaphragms.
  3. In order to keep the two primary sealing surfaces in intimate contact, an actuation force is required and is commonly provided by a spring. In conjunction with the spring, it may also be provided by the pressure of the sealed fluid.
  4. The primary sealing surfaces must be the only parts of the seal that are permitted to rotate relative to one another, they must not rotate relative to the parts of the seal that hold them in place. To maintain this non-rotation a method of drive must be provided.

Seal face technology

Mechanical seal face geometry is one of the most critical design elements within a mechanical seal. Seal face properties such as: balance diameter, centroid location, surface area, surface finish, drive mechanism, and face topography can be altered to achieve specific results in a variety of liquids. Seal face topography refers to the alteration of an otherwise flat seal face sealing surface to one with a three dimensional surface. Flowserve Corporation issued the first patent in 2007 for applying micro-topography to mechanical seal faces using an excimer laser.

Seal categories
All mechanical seals must contain the four elements described above but the way those functional elements are arranged may be quite varied. Several dimensional and functional standards exist which set precise configurations and sizes for mechanical seal used in Oil & Gas applications.
Mechanical seals are generally classified into two main categories: "Pusher" or "Non-Pusher". These distinctions refer to whether or not the secondary seal to the shaft/sleeve is dynamic or stationary. Pusher seals will employ a dynamic secondary seal (typically an o-ring) which moves axially with the primary seal face. Non-pusher seals will employ a static secondary seal (either an O-ring, high temperature graphite packing, elastomeric bellows or metal bellows). In this case, the face tracking is independent of the secondary seal which is always static against the shaft/sleeve.


A "cartridge seal" is a prepackaged seal that is common in more complex applications and were originally designed for installation in equipment where a component type seal was difficult due to the equipment design. Examples of this are horizontally split and vertical pumps. In 1975 the A W Chesterton Company designed the first cartridge seal that fit pumps with varying stuffing box bore sizes and gland bolt patterns. To accomplish this the seal utilized internal centering of the stationary parts and slotted bolt holes. This "generic" cartridge seal could be manufactured in higher production quantities resulting in a cartridge seal that could be used in all applications and pumps types. Cassette seals utilize a replaceable inner "cassette" mounted in the cartridge end plate or gland, while modular cartridge seal systems makes it possible to replace only the parts subject to wear, such as sliding faces, secondary seals and springs, while keeping the seal's hardware (gland, sleeve, bolts). Cartridge seals can suffer from clogging due to the bigger space occupied inside the stuffing box, leading to dense or charged fluids not moving enough to centrifugate the solid particles. Moreover, the sleeve which is necessary to keep the parts of the seal together is a rigid part in contact with the shaft and greatly decreases the seal's tolerance to radial misalignment. The sleeveless cartridge seal technology overcomes such issues and has been patented in 2006.


Gap seals are generally used in bearings and other constructions highly susceptible to wear, for example, in the form of an O-ring. A clearance seal is used to close or fill (and join) spacing between two parts, e.g. in machine housings, to allow for the vibration of those parts. An example of this type of seal is the so-called floating seal which can be easily replaced. These seals are mostly manufactured from rubber or other flexible but durable synthetic materials.

Seal piping plans
Since the rotating seal will create heat from friction, this heat will need to be removed from the seal chamber or else the seal will overheat and fail. Typically, a small tube connected to either the suction or the discharge of the pump will help circulate the liquid. Other features such as filters or coolers will be added to this tubing arrangement depending on the properties of the fluid, and its pressure and temperature.

Component seals
Usually these are considered to be disposable since refurbishing the metal parts and replacing the wearable items isn't economical.
Component seals are produced in high volumes so the end price is low in comparison to cartridge seals.
The majority of mechanical seal manufacturers offer seals that are dimensionally interchangeable with each other. The only difference being material quality and price. Also component seal is expensive to assemble as it will be assembled on the pump.

Tandem and double seals
Since almost all seals utilize the process liquid or gas to lubricate the seal faces, they are designed to leak. Process liquids and gases containing hazardous vapors, dangerous toxic chemicals or flammable petroleum must not be allowed to leak into the atmosphere or onto the ground. In these applications a second "containment" seal is placed after the primary seal along the pump shaft. The space in between these two seals is filled with a neutral or compatible liquid or gas (generally nitrogen) called a buffer seal (unpressurized) or barrier seal (pressurized).

In a tandem seal [face-to-back], the seal will leak into the buffer fluid contained in the unpressurized cavity commonly known as thermosiphon pot. If the cavity registers a dramatic increase in pressure or fluid level, the operator will know that the primary seal has failed. This can be achieved by using pressure/level switches or transmitters. If the cavity is drained of liquid, then the secondary seal has failed. In both instances, maintenance will need to be performed. This arrangement is commonly used when sealing fluids that would create a hazard or change state when contacting open air.

In a double seal [Generally Back to Back], the barrier liquid in the cavity between the two seals is pressurized. Thus if the primary seal fails, the neutral liquid will leak into the pump stream instead of the dangerous pumped fluid escaping into the atmosphere. This application is usually used in gas, unstable, highly toxic, abrasive, corrosive, and viscous fluids. Typically, nitrogen is used as its inert nature makes it advantageous due to mixing with the process stream being sealed.

Tandem and double seal nomenclature historically characterized seals based on orientation, i.e., tandem seals mounted face-to-back, double seals mounted back to back or face-to-face. The distinction between pressurized and unpressurized support systems for tandem and double seals has lent itself to a more descriptive notation of dual pressurized and dual unpressurized mechanical seal. This distinction must be made as traditional 'tandem seals' can also utilize a pressurized barrier fluid.

Origins
The mechanical seal was invented by George Cook and was originally called a "Cook Seal". He also founded the Cook Seal Company. Cook's seal (which actually did not have a means of drive) was first used in refrigeration compressors. The Cook Seal company was a sideline product for Cook and he sold the company to Muskegon Piston Ring Company where it was renamed as The Rotary Seal Division of Muskegon Piston Ring Co. Muskegon Piston Ring sold the Rotary Seal Division to EG&G Sealol who in turn was largely acquired by John Crane Industries of Morton Grove, IL.
In 1990, the world market for mechanical seals was estimated at $1 billion.[citation needed]

 

 



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