FLEXIBLE POWER-TRANSMITTINGELEMENTS

USEFUL INFORMATION

❑ Flexible connectors are machine elements used when the distance between the driving shaft and driven shaft is too great to be connected by gears. These elements are in the form belts, ropes and power chains. These are the important members of the class of links that are termed as non-rigid and flexible.

TYPES OF FLEXIBLE CONNECTORS

1. a. Flat Belts Belts – flexible connectors which are usually made of leather, rubber, or woven fabrics; flat and thin; and run on pulleys nearly cylindrical with smooth surfaces. o Used to connect shafts as much as 9 m (30 ft) apart; Run economically at speeds as high as 23 m/s (4500 fpm); Made of leather, rubber, or woven fabrics; and Run on pulley nearly cylindrical with smooth surfaces. b. V-belts – made with V-shaped cross section to be used on grooved pulleys o Used for connecting shafts which are less than 5 m (15 ft) apart; Speed ratios up to 7 to 1; Speed is up to 25.5 m/s (5000 fpm); An endless type constructed of canvas, cotton cords, and rubber; Run in grooved pulleys, the angle of groove being about 36o in the smaller-diameter pulleys and 38o to 40o in the larger pulleys; The sides of the belt are slightly concave, and the included angle is usually 42o; Belt may be operated very satisfactorily with a short center-to-center distance. Center distance need not be greater than the diameter of the larger pulley; and require little adjustment to compensate for wear or stretch owing to the wedging action in the groove c. Timing belts or Synchronous belts – are basically flat belts with series of evenly spaced teeth on the inside circumference, thereby combining the advantages of flat belts with excellent traction of gears and chains. 2. Ropes – flexible connectors that are nearly circular in cross section and made up of manila, hemp, cotton, or wire. These are used instead of flat belts or V-belts when power must be transmitted over long center distances as in hoists, elevators, and ski lifts o Run on either grooved pulleys or drums with flanges; Used for connecting shafts up 30.5 m (100 ft) apart; and Operate at a speed of less than 3 m/s (600 fpm) 3. Chains – flexible connector composed of metallic links jointed together, and run on either sprockets or drums either grooved, notched, or toothed, to fit the links of the chain. • Used for connecting shafts less than 5 m (15 ft) apart; Speed depends on the type of chain; and Roller and silent chains may operate at speeds up to 13 m/s (2500 fpm). o Roller Chains – are used to transmit power through sprockets rotating in the same plane.

ELTS CONNECTING PARALLEL SHAFTS (FLAT BELT)

1. Open Belt Connection

Characteristics:

Pulleys are of the same sense or direction of rotation; No slipping between the belt and pulley surfaces; Angle of contact for bigger pulley is greater than the angle of contact for smaller pulley; Surface speeds of smaller pulley is the same as the bigger pulley; Belt speed is the as the pulleys surface speeds; and Used for connecting parallel shafts

2. Crossed Belt Connection

Characteristics:

Pulleys are in opposite directions of rotation Belt is moving without slipping on the pulley surface

Angles of contact for both pulleys are the same Surface speeds of smaller pulley is the same as the bigger pulley

Belt speed is the same as the pulleys surface speeds. Used for connecting parallel shafts

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V-BELTS

❑ USEFUL INFORMATION

❑ V-belts are used with electric motors to drive a great number of components such blowers, compressors, machine tools, etc. ❑ Used to drive accessories on automotive and other internal combustion engines. ❑ V-belts are made to standard lengths and with standard cross-sectional sizes.

❑ V-belts run on grooved pulleys, called sheaves. ❑ V-belts are used on short center distances ❑ Sheaves are usually made up of cast iron, pressed steel or die-cast iron. ❑ V-belts have a fiber glass-reinforced neoprene core and fabric-impregnated neoprene jacket that protects the interior and provide a wear resistant surface for the belt. ❑ V-belt cross-sections are trapezoidal and are classified into A, B, C, D, and E.

Advantages of V-Belt

• Wedging action permits a smaller arc of contact • Shorter center distances that economize space • Lower belt tension due to its gripping action • Absorbs higher shock than flat belts • Do not require frequent adjustment of initial tension

POWER-TRANSMISSION CHAINS

USEFUL INFORMATION

❑ Chains are made of a series of jointed metal links in a variety of forms in accordance with their uses as a) hoisting and hauling, b) elevator and conveyor chains, and c) power-transmission chains. ❑ The roller chain is used mainly as a power-transmission chain. The construction at the joints is as shown in the figure below.

Types of Chains

1) Detachable Chains 2) Cast Roller Chains 3) Pintle Chains

Roller Chains

• 1. • These roller chains are manufactured to the specifications in the American National Standard for precision power transmission roller chains, attachments, and sprockets; and These roller chains and sprockets are commonly used for the transmission of power in industrial machinery, machine tools, motor trucks, motorcycles, tractors, and similar applications. Standard roller chains 2. • These roller chains are similar in form and construction to standard roller chains but do not conform dimensionally to standard chains; Some sizes of these chains are still available from the originating manufacturers for replacement on existing equipment; and These are not recommended for new installations. Nonstandard roller chains 3. • These roller chains are like standard roller chains, except that their link plates have twice the pitch of the corresponding standard-pitch chain; and These are especially useful for low speeds, moderate loads, or long center distances. Standard double-pitch roller chains A roller chain is made up of two kinds of links: roller links and pin links alternately spaced throughout the length of the chain as shown in Figure 9.11 below; Roller chains are manufactured in several types, each designed for the particular service required; All roller chains are so constructed that the rollers are evenly spaced throughout the chain; The outstanding advantage of this type of chain is the ability of the rollers to rotate when contacting the teeth of the sprocket; Two arrangements of roller chains are in common use: the single-strand type and the multiple-strand type; In the multiple-strand type roller chains, two or more chains are joined side by side by means of common pins that maintain the alignment of the rollers in the different strands.

Types of Roller Chains

b)

WIRE ROPES

c)

USEFUL INFORMATION

❑ Individual wires are twisted into strands, and then the strands are twisted around a hemp or steel center to form the rope. ❑ The central element is an independent wire rope core (IWRC). ❑ Wire rope is made with two types of winding, the regular lang lay and the lang lay rope. ❑ Regular lang lay rope – is the accepted standard, has the wire twisted in one direction to form a strands and the strands twisted in opposite direction to form a rope.

❑ Lang lay ropes have the wires in the strand and the strands in the rope twisted in the same direction, the outer wires run diagonally across the axis of the rope.

Uses of Wire Ropes

• Wire ropes could be used in elevators, cranes, hoists, drilling, conveyors, tramways, haulage devices, suspension cables, guy wires, etc.

Materials for Wire ropes

• The common materials for wire ropes are: plow steel (PS), Mild Plow Steel (MPS), Improved Plow Steel (IPS), wrought iron, cast steel, alloy steel, stainless steel, copper, or bronze.

Designation of Wire Ropes

• First number is the number of strands, second number is the number of wires per strand. • Nominal diameter of wire rope, Dr, is the diameter of the circle that just enclosed the rope.

Example: 6 x 7 IPS, 1.25”, a wire rope with 6 strands, 7 wires per strands, made of improved plow steel, and having a nominal diameter of 1.25 inches

SLIDING CONTACT BEARINGS

DEFINITIONS AND USEFUL INFORMATION

❑ Bearing – is a machine member that supports another part that rotates, slides, or oscillates in or on it. ❑ Sliding contact bearing – is a bearing that permits constrained relative motion of rigid parts; lubricant is generally inserted or supplied between the mating surfaces to reduce friction and wear, and to carry away the heat generated. ❑ Rolling-element bearing – a bearing where surfaces are non-conformed and motion is primarily rolling; it composed of rolling elements interposed between outer and inner rings. ❑ Non-conformal surfaces – are surfaces that do not conform to each other very well as in the rolling-element bearings. ❑ Tribology – is the study of lubrication, friction, and wear of moving or stationary parts. ❑ Lubrication – is the process of separating relatively moving parts or elements for the purpose of reducing the friction, wear, and heating of parts. ❑ Lubricant – is any substance, when inserted between moving surfaces, reduces friction, wear, and heating of the surfaces; and provides smooth running and satisfactory life for machine elements. ❑ Viscosity – is the measure of the resistance to flow of the fluid or the property that resists shearing of the fluid or lubricant. ❑ Absolute viscosity or dynamic viscosity – is the ratio of the fluid layer shearing stress to that of its shear strain rate. ❑ Kinematic Viscosity – is the ratio of absolute viscosity and the density of the fluid or lubricant. ❑ Shear strain rate of a particular fluid layer is the ratio of velocity to that of its perpendicular distance from the stationary surfaces. ❑ Babbit – is a tin or lead base alloy that is used as bearing material.

TYPES OF BEARING ELEMANTS

1. Sliding-element bearings 2. a) Ball bearing element – rolling element bearing that uses spherical balls as rolling elements b) Roller bearing element – rolling element bearing that uses cylindrical rollers as rolling elements. Rolling-element bearings

CLASSIFICATIONS OF SLIDING BEARINGS

1. Radial bearing or Journal bearing – a bearing that supports radial loads and furnishes lateral support to rotating shaft. 2. Guide bearing – a bearing that primarily guides the motion of a machine member without specific regard to the direction of load application. 3. Thrust bearing – a bearing that carries a load collinear to the axis or a bearing designed to support axial load of the rotating element. 4. Slipper or slider bearing – a bearing in which two surfaces are flat and nearly parallel and the relative motion is translation.

JOURNAL BEARINGS

❑ Journal bearing is the one that supports radial loads and furnishes lateral support to rotating shaft. ❑ Journal bearing is composed of two principal parts: the Journal which is the inside cylindrical part, usually a rotating or an oscillating member; and the Bearing which is the surrounding shell or the bushing, may be stationary as on the line shaft bearing or moving as on a crankpin.

Classifications of Journal Bearing Based on the Angle of Contact of the Bushing

1. Full journal bearing – is a bearing with the angle of contact of the bushing or bearing with the journal is 360o . 2. Partial Journal Bearing – a bearing with angle of contact of the bushing or bearing with the journal is 180o or less, 120o the common value.

Classifications of Journal Bearings Based on the Radii of Journal and Bushing

1. Clearance bearing – a journal bearing where the radius of the journal is less than the radius of the bushing or bearing. ▪ Clearance refers to the thickness of the space allowed for the lubricant that separates the parts having relative motion. 2. Fitted journal bearing – is the one where the radii of the journal and the bushing are equal; it must be a partial bearing and the journal must run eccentric with the bushing in order to provide space for the lubricant.

Types of Partial Journal Bearing

1. Centrally loaded bearing – is a partial journal bearing where the line of action of the load or bearing reaction is bisecting the arc of the partial bearing. 2. Eccentrically loaded bearing or Offset bearing – is the one where the line of action of the load is passing to one side of the center.

ROLLING ELEMENT BEARINGS

DEFINTIONS AND USEFUL INFORMATION

❑ Bearing – is a machine member that supports another part that rotates, slides, or oscillates in or on it. ❑ Rolling Element Bearing – is a bearing where surfaces are non-conformed and motion is primarily rolling; it is composed of rolling elements interposed between outer and inner rings. ❑ Non-conformal surfaces – are surfaces that do not conform to each other very well as in the rolling element bearings. ❑ Ball bearing element – is a rolling element bearing that uses spherical balls as rolling elements. ❑ Roller bearing element – is a rolling element bearing that uses cylindrical rollers as rolling elements.

ROLLING-CONTACT BEARINGS

❑ Rolling-contact bearings or rolling-element bearings are ball or roller bearings used as substitute for a hydrodynamic or hydrostatic fluid film to carry an impressed load without wear and with reduced friction. ❑ Rolling-contact bearing or rolling-element bearings are also called as “Anti-friction Bearing” because of greatly reduced starting friction. ❑ Deep-groove Ball Bearing is a rolling contact bearing, which is the most common anti-friction bearing application, with ribbon-type separator and sealed-grease lubrication used to support a shaft with radial and thrust loads in rotating equipment. ❑ These bearings are made to high standards of accuracy and with close metallurgical control. ❑ Balls and rollers are normally held to diametral tolerances of 0.0001 inch or less within one bearing and are often used as “gage” blocks in routine tool-room operations.

Advantages of Rolling-Element Bearings

o The following characteristics make rolling-element bearings more desirable than hydrodynamic bearings. 1. Low starting and good operating friction 2. The ability to support combined radial and thrust loads 3. Loads can be inclined at any angle in the transverse plane 4. Thrust components can be carried 5. Maintenance costs are low 6. Less axial space is required than for journal bearings, shafts are shorter, and may even be smaller in diameter. 7. Less sensitivity to interruption in lubrication 8. No self-excited instabilities

9. Good low-temperature starting

Disadvantages of Rolling-Element Bearings

o The following Characteristics Make rolling-element bearings less desirable than hydrodynamic bearings 1. Finite fatigue life subject to wide fluctuations 2. Larger space required in the radial direction 3. Low damping capacity 4. Higher noise level 5. More severe alignment requirements 6. Higher cost

Types of Rolling-Element Bearings

1. o Balls are placed in the grooves between the inner ring and outer ring. o Balls are kept in position by a separator or retainer or cage. Deep-groove ball bearing, also known as Condrad-type ball bearing, is a bearing in which the balls are assembled by the eccentric displacement of the inner ring. 2. Filling-slot type of ball bearing is a bearing that has slots or notches that permit the assembly of more balls, giving a bearing of larger radial load capacity. This bearing is used where the load is principally radial. 3. Self-aligning ball bearing is a ball bearing that compensates for angular misalignments that arise from shaft or foundation deflection or errors in mounting. o Recommended for radial loads and moderate thrust in either deflection. o Since the outer race has a spherical shape, the shaft may pass through the bearings at a small angle without causing bending. 4. Angular contact bearing is the one that is intended to take heavy thrust loads. 5. Double-row ball bearing is the one that is similar to single-row ball bearing, except that each ring has two grooves. The two rows of balls give the bearing a capacity somewhat less than twice that of a single-row. 6. Cylindrical roller bearing is the one in which the contact is a line instead of a point as in ball bearing, which results in a greater area carrying the load and in a larger radial capacity. 7. Self-alignment roller bearing is the one with spherical rollers running in a double-grooved inner ring, has curved outer ring that looks much like the outer ring of a self-aligning ball bearing. 8. Needle bearing is a cylindrical roller bearing that has no retainer to hold the rollers in alignment. An application of this is a universal joint with needle bearing. 9. Tapered roller bearing is the one in which the rolling elements are frustums of cones, so mounted in the races that all of the surface elements and the axes intersect at a point on the axis of the shaft. It is capable of carrying sustainable radial and thrust loads. 10. Hyatt spherangular roller bearing is an angular contact bearing with rollers instead of balls. It is a self-aligning bearing and has a high load capacity.

BALL BEARINGS

❑ Ball Bearings – are rolling element bearings that use spherical balls as rolling elements.

Parts of Ball Bearing

o The main parts of ball bearing are the following:

1. The inner ring 2. An outer ring 3. The balls 4. The cage or separator

Types of Ball Bearings

o Most types of ball bearings originate from three basic designs: the single-row radial, the single-row angular contact, and the double-row angular contact. 1. ▪ This ball bearing is also known as the “Conrad” type or “Deep-groove” type. ▪ It is probably the most widely used ball bearing and is employed in many modified forms. ▪ A symmetrical unit capable of taking combined radial and thrust loads in which the thrust component is relatively high, but is not intended for pure thrust loads. ▪ This type is not self-aligning; that accurate alignment between shaft and housing bore is a requirement. Single-row Radial, Non-filling Slot 2. ▪ This ball bearing type is designed primarily to carry radial loads. ▪ Bearings of this type are assembled with as many balls as can be introduced by eccentric displacement of the rings, as in the non-filling slot type, and then several more balls are inserted through the loading slot, aided by a slight spreading of the rings and heat expansion of the outer ring, if necessary.Single-row Radial, Filling Slot

▪ This bearing takes a certain degree of thrust when in combination with a radial load but not recommended where thrust loads exceed 60 % of the radial load. ▪ This bearing is designed for combined radial and thrust loads where the thrust component may be large and axial deflection must be confined within very close limits. A high shoulder on one side of the outer ring is provided to take the thrust, while the shoulder on the other side is only high enough to make the bearing non-separable. ▪ This type is applied either in pairs (duplex) or one at each end of the shaft, opposed, provided that it is not used for a pure thrust load in one direction. ▪ These are two single-row angular-contact bearings built as a unit with the internal fit between balls and raceway fixed at the time of bearing assembly. The fit is not dependent upon mounting methods for internal rigidity. ▪ These bearings usually have a known amount of internal preload built in for maximum resistance to deflection under combined loads with thrust from either direction. ▪ These bearings are very effective for radial loads where bearing deflection must be minimized. ▪ This bearing can be used to compensate for an appreciable degree of misalignment between shaft and housing due to shaft deflections, mounting inaccuracies, or other causes commonly encountered. ▪ Alignment is provided by a spherical outer surface on the outer ring for a bearing with single row of balls ▪ Alignment is provided by a spherical raceway on the outer ring for a bearing with double row of balls. 3. Single-row Angular-contact 4. Double-row Bearings 5. Self-aligning ball bearing

LIFE OF BALL BEARING

❑ Life of an individual bearing is defined as the number of revolutions (or hours at any given constant speed) which the bearing runs before the first evidence of fatigue develops in the material or either ring or any of the rolling elements. ❑ Million revolutions, mr, is the unit of life of bearing in terms of revolution.