Sunday, September 20, 2020

What is plain bearing

Sleeve bearings

Sleeve bearings are one of the most common and efficient types of bearings.We will show you the basic types of sleeve bearings and try to point out the differences between them and other types of bearing. There are two basic categories of bearings which are widely used in industry today: sliding contact bearings and rolling contact bearings.

The rolling contact bearings, also referred to as anti-friction bearings, rolling contact bearings utilize balls or rollers to reduce friction. Which rolls between the two races thereby cutting down on friction. The other category is made up of sliding contact bearings like this also referred to as sleeve or plane bearings A sleeve bearing is a non-moving or rotating surface on which a moving part such as a shaft slides or rolls. It has no balls or rollers and usually depends on some type of lubrication to help reduce wear and friction. You will often hear sleeve bearings referred to as journal bearings - well this is only partially true. We say it's only partially true because all of these bearings, the rolling contact and the sleeve bearings, may be referred to as journal bearings. The term journal is the name for the part of the shaft which fits inside the bearings therefore both rolling contact and sleeve bearings can be considered journal bearings.

Sleeve bearing clearance

Plain bearing


Types of plain bearing

However, the sleeve bearing there are two basic types of sleeve bearings now in common use they are the single piece type and the split type of course.

a properly installed and lubricated sleeve bearing will often last as long as the equipment. It's mounted in another variation in sleeve bearing and has to do with the thickness of the bearing.

The wall thickness can vary considerably depending on the application and the requirements of the equipment.

The advantages and disadvantages Sleeve bearing

Advantage Sleeve bearing

  1.  Sleeve bearings can support very heavy loads at high speeds.
  2. They usually require less radial space for installation, which is a very important consideration in some machines and equipment.
  3. Sleeve bearings are also normally quieter in operation than most rolling contact bearings since they have no moving parts because of their solid construction.
  4. They are much more resistant to unexpected overload and shock condition contamination, such as dirt dust and other foreign particles, and are less likely to damage sleeve bearings than precision rolling contact bearings.
  5. This is true because the smaller particles will embed themselves in the soft-bearing material, resulting in less damage to the bearing of another.
  6. Advantages they do not require as much care in storage sleeve bearings may be stored just about anywhere.
  7. Indefinitely with a minimal amount of deterioration, this is not true of rolling contact bearings.

Disadvantaged of Sleeve bearing

  1. The disadvantage of sleeve bearings is that they require more axial or linear space than a comparable rolling contact bearing.
  2. They generally require considerably more lubricant than comparable rolling contact bearings.
  3. Sleeve bearings also create a greater load on the driver during start-up.
  4. Since the shaft is riding directly on the bearing at which time there is a greater chance of damage to the shaft journal and would be the case where rolling contact bearings are used.
  5. However, once it reaches operating speed, the friction decreases since the shaft is riding on an oil film and not directly on the bearing itself.

Metrology

Metals used in plain bearing manufacturing

The bearings themselves may be manufactured from several different metals depending on their application.

It is usually made of cast iron, bronze or aluminium sleeve bearings with a shell of aluminium or bronze that may have a lining or they may not however sleeve bearings with a shell of cast iron will normally have a lining such as the Babbitt lining being pointed out. Here the lining or coating which is used in sleeve bearings may be made of a variety of materials such as aluminium, copper lead cadmium base / plated silver and Babbitt of all the different metals a tin or lead based Babbitt is the most commonly used Babbitt is an alloy made of several metals. Which is applied as a thin coating over the shell enlarger sleeve bearings for heavy-duty equipment a thicker layer of Babbitt is used to line a rigid backing of steel-bronze or cast iron you are not expected to select bearings for use in equipment the manufacturer of the equipment will specify exactly what type of bearing is to be used. This is true because sleeve bearings are often designed specifically for a certain application.

Working principle of plain bearing

 A film of lubricant between the shaft and the bearing separates the two parts during the operation, reducing friction and also helping to dissipate any heat. This is generated by the lubricant and may be introduced into the bearings by a variety of methods force feeding lubrication systems. here are used frequently to pump oil through the bearings of various machines if grease is used as a lubricant it may be introduced through one of several methods and this would include grease fittings or a grease pocket as shown in this illustration another common method of lubricating sleeve bearings with oil is the use of oil rings which pick the lubricant up out of a sump below the bearings and carry it up to the bearings as the rings rotate on the shaft?

 Since there is such a variety of Lube systems in use, we won't go into detailed explanations of how they work in this course. You should already be familiar with the basic systems now in use once the lubricant reaches the bearing itself, the bearing design takes care of the distribution of the lubricant along the shaft journal, for instance, this bearing is lubricated by grease, the grease is forced downward by gravity through a slot at the top of the bearing until it comes into contact with the shaft. You won't encounter this type often since most sleeve bearings are lubricated with oil and not greased oil lubricated bearings are a different story, a force-fed Lube system in which the oil reaches the bearings and is distributed along the shaft through oil grooves. Which is machined into the surface of the bearing itself the workman is now pointing to one type of groove known as an axial groove?

Since it is parallel to the axis of the shaft note that the groove stops short of the end of the bearing. This is to prevent the lubricant from running out of the end of the bearing during operation of the machine this is called a circumferential oil groove. It channels the flow of lubricant around the circumference of the shaft, and bearing circumferential oil grooves are also used as collector grooves. The bearing of the oil flows along the length of the bearing then collects in this oil come channeled back to the oil sump. Through these drain passages from the groove, this arrangement helps to prevent leakage of the lubricant out of the end of the bearings of his bearing is pressure lubricated.

 The two basic types of sleeve bearings,  the split sleeve and the solid sleeve, were designed to restrict the radial movement of the shaft during operation of the machine. These sleeve bearings with a thrust shoulder are designed to restrict both the radial and axial movements of the shaft. There is a split sleeve bearing with thrust shoulders being pointed out as you can see the thrust faces are also coated with the same Babbitt lining.

Which is used on the inside of the bearing sleeve bearings with thrust faces will normally have oil grooves which run all the way to the ends as shown here this is necessary since lubricant must be supplied to the thrust faces of the bearings. Oil grooves in the thrust face like these then distribute the oil across the face of the bearing during operation, as with the basic sleeve bearing, there is a film of lubricant between the shoulder on the bearing and the bearing surface of the rotating assembly, this type of sleeve bearing then controls both the radial and axial movement of the shaft.

Thursday, September 10, 2020

What is balance drum and disk

What is the balance drum?

Balance drum in centrifugal pump

It is a device which is used to balance the axial thrust build-up by impeller. it is also used with thrust bearing which is transfer very less residual thrust load to thrust bearing.

This is the main benefit of drums. The balance drum is a circular device installed on pump rotor generally drum is installed on the discharge end side.

What is the balance disk?

Balance disk in centrifugal pump

The balance disk is use for compensate axial thrust and capable to compensate fully generated thrust load. The balance dick is used to manage axial clearance between casing and rotor disk. The balance dick is used immediately just after the last stage so it has full discharge pressure on one side of the disk.

What is balance piston?

Balance piston

The balance piston is also called the balance drum.

What is axial thrust bearing?

Thrust bearing

The residual axial thrust is always present in the system to compensate for this thrust using axial thrust bearing.

What is flange drum?

Flange drum is used in the combination of balance drum and balance disk. But principally depending on hub leeway.

What is stepped drum?

It is also used in the combination of balance drum and balance disk. But principally depending on hub leeway.

What is the difference between a balance disk and a balance drum?

Balance drum vs Balance disc

Both are used for compensate thrust load. Drum is use for managed high axial thrust and generally use in discharge end. The pressure acted on drums on both sides (left and right) and cancelled out to each other.

Balance line

The balance line is system use to compensate for generated thrust load by discharging fluids. the balance line is provided from the pump suction side to discharge side. To nullify the axial thrust generated by impeller discharge use a balance line also. Because of this back force the internal part will be damaged so a taping is given from discharge to balance drum.

Learn centrifugal pump 


Thrust load

Two types of thrust load are applied to bear axial thrust and radial thrust. Below is an example of the axial thrust mentioned. 

We will discuss boiler feed water pumps. It is also a multistage centrifugal pump. Suppose that in this pump suction pressure is 7 kg per centimetre square and discharge pressure is approx 130 kg Per centimetre Square at final outlet in 6 stage pumps.

According to this condition, in the first stage, impeller suction pressure will be around 8 kg per centimetre square due to the increase in velocity with the help of diffuser. 

The first stage of centrifugal multistage pump circulating Liquid on the periphery of casing around the Imperial Outlet. Suppose that at the impeller First stage discharge pressure is increased to around 20 kg per centimetre square. 

Due to this 20 kg Per centimetre Square in Outlet it will generate back pressure approx 20 kg/centimetre square and that force pushes the impeller assembly in backside according (Newton's third law of motion: 'Every action has the same and opposite reaction.). 

In the next 2nd stage, the suction pressure at inlet around 20 kg per centimetre square and discharge Pressure will be around 40 kg per centimetre square. 

Due to the same phenomena that occurred with the Second stage impeller also and the second stage discharge liquids also pushed the rotor assembly in back side after that liquid goes forward to the stage. This process is continued till the last stage. 

To balance this type of generated back Force, use three parts with pump casing, rotor assembly balance disc, balance drum, Balance line. And in the place of bearing or with the bearing to bear thrust load Thrust bearing is also provided. 

But the thrust bearing is not sufficient only for compensate hundred percent thrust load So Balance disc, balance line or balance drums used to reduce  net thrust use impeller in opposite to each other.